How Nitrogen Works in Soil

By Jon Frank
This article first appeared in the July 2019 edition of Acres U.S.A. magazine.

Corn growers hold a special place in American agriculture. Corn is our largest crop, representing millions of acres under production. And farmers are the stewards of those acres. This is a serious responsibility and a massive opportunity to improve soil health on a significant proportion of American farmland.

As every corn grower knows, nitrogen is the most important nutrient for corn production. When it comes to corn yield, all other nutrients take a back seat. Field corn is a large plant — typically ranging from 6- to 8-feet tall and sown anywhere from 26,000 to 40,000 plants per acre. Yields today average from 150 to 300 bushels per acre. When you add up these three features — tall plants, high planting density and large yields — it’s no wonder corn requires a heavy dose of nitrogen.

High nitrogen rates enable excess nitrogen to run off into surface water and from there to aquifers. When nitrogen and phosphorous get into waterways, they stimulate the growth of algae. When this algae bloom dies and decomposes, it sucks up much of the oxygen out of the water, causing fish to die — especially game fish, which require higher oxygen levels.

It is here, at the intersection of agronomy and the environment, that every farmer walks a tightrope. Farmers have a fiduciary responsibility to make a profit, and profit requires a sizable yield. At the same time, farmers have a moral obligation to carefully steward the land they farm. Fortunately, most farmers are salt-of-the-earth folks who already feel this tension and want to do what is right.

In their defense, I do want to point out that nitrates are a natural form of water droplets pick up nitrates from the atmosphere and deposit free nitrogen into the soil. Because these nitrates come in small doses — 1-2 pounds per acre — plants pick them up quickly and virtually none escapes out of the root zone.

Nitrogen: It’s Complicated

Nitrogen is a peculiar element. Its home address is the atmosphere. Thus, its natural tendency is to find a way back home. It is in every breath of air we breathe and also in every single living cell. It is ubiquitous and rather mysterious. Nitrogen is a shape-shifter, easily changing from one form to another.

There are four main forms of nitrogen:

1. Nitrate (NO3) — Nitrate provides growth energy to corn, helping the plant build its infrastructure of stalks and leaves. Nitrates combine with many other elements, including a large number of trace minerals. This form of nitrogen is subject to leaching.

2. Ammonium (NH4) — This form of nitrogen, along with its close relative, urea, provides reproductive energy to corn. Reproductive energy promotes blossoms, flowers and pod set. Ammonial forms of nitrogen are subject to volatilization — the process in which nitrogen escapes the soil to return to the atmosphere. Combining nitrogen with growth energy and nitrogen with reproductive energy can suddenly release a lot of energy. This energy can be used both as an explosive and as a fertilizer for corn. Either way, it packs a lot of energy.

3. Amino Acid / Protein — This is the form of nitrogen made by biology. It can be produced in-house by soil microbes and growing plants, or by animals creating manure or fish harvested from the ocean. When nitrogen is in the amino acid or protein form, it will not leach or volatilize.

4. Humus — When soil biology combines an amino acid type of nitrogen with plant-available minerals in a carbon matrix, you get humus. Humus is reserve soil fertility — ready-to-use plant nutrients as soon as there is a need. Just like a well-stocked pantry.

Function in Soil

Nitrogen is the primary electrolyte in soil. This means that soluble nitrogen in soil increases electrical conductivity. In the human body we also have a certain balance of electrolytes in our blood and body fluids. These electrolytes carry weak electrical charges throughout our bodies.

In soils, electrolytes do the same thing. Having an adequate supply of electrolytes corresponds very closely with plant growth; or, to say it better, an adequate supply of electrolytes corresponds with nutrient availability, which drives plant growth. Nitrogen is not the only electrolyte. Other soluble nutrients or salts also conduct electrical charges.

By way of illustration, an electrical circuit has copper wires, which conduct electricity, and resistors, which moderate the flow of electricity. Soluble nutrients in soil conduct electrical charges just like a wire in a circuit. Humus and carbons moderate the electrical flow to make it suitable for plant uptake. Both functions are needed simultaneously.

As a point of clarification, any nutrient in soil, and many aspects of soil, can be looked at through various lenses. This is like having different kinds of glasses — each pair will illuminate objects differently. We can look at soil and nutrients through the lens of physics, chemistry or biology. It’s best to use all three to get a comprehensive view. Here is an example when looking at nitrogen:

• Physics — Nitrogen is an electrolyte that carries electrical charges that assist in nutrient delivery and plant growth

• Chemistry — Nitrogen is the center core of amino acids and proteins

• Biology — Soil biology builds amino acids through the microbial system

I will switch around between these various lenses. While nature works in all three realms simultaneously, I have to write in a linear fashion.

For corn growers there are two ways to apply nitrogen for its electrolyte function. Both methods work pretty well.

• Check soil EC (electrical conductivity) with a conductivity meter

• Guestimate based off experience from trial and error.

Most corn growers are not familiar with conductivity meters. But using one regularly throughout the season brings many revelations.

When soil has an adequate supply of available nutrients, and especially nitrogen, these nutrients carry an electrical charge. With a simple hand-held meter, farmers can measure the electrical conductivity of their soil. This reading is a de facto indicator of nutrient sufficiency.

The unit of measurement is micro Siemens per centimeter (µS/cm), or milli Siemens per centimeter (mS/cm). To convert between the two is simple; divide by 1,000 or multiply by 1,000. As an example, 0.36 mS/cm = 360 µS/cm. I prefer setting conductivity meters to auto range. This will default to readings of µS/cm. If the conductivity is above 2,000, it will then display as mS/cm.

I have found excellent corn growth when soil conductivity is around 700 µS/cm.

The more nutrients applied as fertilizer, the higher the conductivity reading. The more rainfall or crop uptake, the lower the conductivity. An over-application of fertilizer results in high or excessive conductivity.

A conductivity meter is an excellent diagnostic tool to help identify hidden nutrient deficiencies. When too little nitrogen is applied, yield suffers.

How to Take a Conductivity Reading

First make sure you have a meter with a direct soil probe. The old method of mixing half soil and half distilled water is accurate but way too cumbersome.

Neal Kinsey, Using Soil Analysis to Grow Crops, from the 2005 Eco-Ag Conference & Trade Show. (50 minutes, 12 seconds). Listen in as agronomist Neal Kinsey, the author of Hands-On Agronomy, teaches about how to test your soils, and use that data, to increase crop yield and decrease weed pressures.

I strongly recommend a meter with a 24-inch T-handle probe. This allows a quick check without having to squat to the ground. Next select a consistent location, such as 4 inches from the corn stalk. Be sure to have a regular depth. I normally suggest between 2 and 4 inches. Now take multiple readings across your field and average them together.

While the conductivity meter is incredibly valuable, there are a number of caveats to keep in mind.

• The higher the humus level, the more moderated conductivity readings become; i.e., less up and down swings. High humus generally lowers the base desired level.

• The healthier the soil, the more biology will provide the nutrition the crop needs in place of applied fertilizers. This lowers the desired conductivity level.

• A buildup of soluble non-nutrients such as sodium, chlorides and bicarbonates can impact the conductivity reading and raise the base desired level. The same applies to high conductivity irrigation water.

• The more the corn crop draws on nitrogen from humus and amino acid nitrogen, the lower the base level needs to be.

Consistently low conductivity indicates lost yield. A side dress or fertigation of liquid nitrogen or other soluble nutrients will immediately raise soil conductivity. In contrast, a foliar spray will not appreciably raise soil conductivity. Nutrients have to be in the soil, not on plant leaves, in order to raise conductivity.

Excessively high conductivity throughout the season indicates excess fertilizer application and the potential to leach nutrients out of the root zone into the subsoil. Very high conductivity levels are especially hard on germinating seeds and can burn roots if over 2,000 µS/cm.

If all of this seems too complex and overwhelming, now you know why most farmers and consultants use the tried-and-true method of calculating pounds of nitrogen applied throughout the growing cycle. It is so much easier — but there is a problem … no one agrees.

Ask a dozen crop consultants how much nitrogen a corn crop requires and you are likely to get at least a dozen answers and quite a few comments about desired yield. The answer to this question is every corn farmer’s dilemma: too much nitrogen is expensive for the farmer and expensive for the environment; too little nitrogen and you lose yield and thus profit.

Metrics are important in the economy, in business and on your farm. The most common metric everybody talks about is yield per acre. One of the most important metrics from a financial perspective is profit per acre. While this is a useful metric and should be tracked, it is a purely “Ebenezer Scrooge” kind of a number.

It is more inciteful to ask a deeper question: how many pounds of nitrogen are required for every bushel of corn I raise? The answer to this question gets to the heart of the corn farmer’s dilemma. Better soils and farming practices require less nitrogen per bushel.

Let’s say you broadcasted 100 pounds of monoammonium phosphate (MAP), 200 pounds of ammonium sulfate and 200 pounds of urea before planting. MAP is 11-52-0. The ammonium sulfate is 21-0-0, while urea is 46-0-0. All these numbers represent percentages. Thus, the “11” in 11-52-0 indicates 11 percent. This multiplied by the total amount of applied product gives the total pounds of nitrogen applied for that fertilizer. MAP (0.11 x 100) gives 11 pounds of nitrogen, the ammonium sulfate (0.21 x 200) provides 42 pounds and the urea (0.46 x 200) adds 92 pounds. Added up, this equals 145 pounds of actual nitrogen applied.

Let’s assume this farmer had read my earlier article on humus and had sprayed last year’s residue with 5 pounds of nitrogen as part of the residue spray for a nice even number of 150 pounds of total nitrogen applied. At harvest, this farmer averaged 200 bushels per acre.

Nitrogen Efficiency (NE) = pounds of N applied per acre divided by bushels of corn harvested per acre. Thus NE = 150/200 = 0.75. This farmer can say that for every bushel of corn, he applied ¾ of a pound of nitrogen. The inverse of this equation is also interesting. 200/150 = 1.33. This means that for every pound of nitrogen applied, the farmer harvested one and a third bushels of corn.


The Soil Works Podcast, by Glen Rabenberg, recommended for readers on this page. Listen in and learn how nitrogen can become available for your plants.


Nitrogen efficiency is at the very heart of the issue. It is actually the best metric to use when looking at overall efficiency of farming corn. Why? Because biological practices promote a healthy soil. A healthy soil supports a larger and broader diversity of microbial species in the rhizosphere that surround plant roots. This microbial system supports corn plants by predigesting soil amendments and rock minerals. As these additional nutrients and pre-made amino acids, derived from the dying off microbes, are taken up by corn plants, nitrogen efficiency increases. In other words, you get more corn with less nitrogen.

By pouring on excessive nitrogen, toxic agriculture can compete and win the bragging rights to yield per acre. But this comes at a very steep environmental cost. I also question this corn’s value as a feed ingredient. It is far better to focus on biological practices and use nitrogen efficiency as your main metric. And if we keep improving the health of the soil, the health of the microbes and nitrogen efficiency we should be able to compete on another metric: profit per acre.

Here is the place I must give a disclaimer. By improving the overall environment in your soil fertility program, you earn the right to use less nitrogen. Too many people have fallen for the half-truth that says, “Use this super-duper juice and cut your nitrogen in half.” Saves you a lot of money, right? And the scary thing is it might actually work for a couple of years. But eventually the Pied Piper has to be paid.

Super-duper juice products can work really well. And they may even be sold by very well-intentioned businesses. But without a zealous focus on the fundamentals — things like levels and ratios of available minerals, energy in the soil, full-spectrum nutrition, adequate NPK or sufficient calcium — things can crash and burn. Please don’t let that be you!

6 Ways to Increase Nitrogen Efficiency

Here are six ways to improve the health of your soil, the health of the microbial population and ultimately nitrogen efficiency.

1. Use Amino Acid / Protein Forms of Nitrogen

You don’t need all your nitrogen coming in this form. Just look for places they can be added. Products to use include legume green manure / cover crops, animal manure, liquid or dry fish, or compost. Unless produced on-farm, these products will be more expensive. In the chart for nitrogen efficiency it was listed that <0.15 was possible. This is not theoretical. It has been done numerous times, multiple years in a row. And if you are wondering about yield, it was consistently 200 bushels, all organic.

My longtime partner in International Ag Lab, Wendell Owens, made this profound discovery decades ago. Not only did he prove 200 bushels could be consistently harvested organically, he also demonstrated the greatest nitrogen efficiency I have seen to date. And it is so simple. Ready? Just side-dress 50 gallons of 5-1-1 liquid fish 6 inches over from the row of corn.

This fish is as thick as molasses but not so sticky. It will require a squeeze pump with all nozzles and filters removed. Use 3/8-inch to ½-inch tubing and dilute the fish 50:50 with water to make it flowable. That’s the complete nitrogen program.

So, let’s run the numbers and calculate the nitrogen efficiency. 5-1-1 fish weighs 9.5 pounds per gallon. 50 x 9.5 = 475 pounds. 475 x 5 percent = 23.75 pounds of actual N. NE = 23.75/200 = 0.12.

Wow – a nitrogen efficiency of 0.12!

With high-priced organic corn, this program penciled out. The nitrogen in the fish is 100 percent amino acid form. Low-nitrogen fish spiked with Chilean Nitrate to get t 5 percent N will not work this way because it is not an amino acid nitrogen.

Dr. Carey Reams taught that every living cell across all species of life has the same foundational formation. He called this the Primordial Cell. The center of every cell is life, but wrapped around that life are always these five elements: nitrogen, carbon, hydrogen, oxygen and calcium. Reams taught that every living cell has the same foundation, and from there various other elements and compounds are added according to its genetic instructions.

It is fascinating to note that amino acids have the exact same elemental components. Life may be absent, but the composition of elements is the same. It is also intriguing to consider that 0.12 lbs. of nitrogen is far less than the actual amount of nitrogen in a bushel of corn which is at least half a pound. Where did the remaining nitrogen come from? Here is my answer: Ask the trees of the forest where they got their nitrogen for their leaves and twigs.

2. Have a Reservoir of Nitrogen as Humus

Humus is fertility in a soil savings account with full liquidity. It can easily liquidate into its fertility components, including nitrogen. But if you look at most soil tests for corn, you find humus levels at the bottom of the barrel.

It is very useful to build up this “fertility bank account” during fall, winter and spring. During summer, withdrawals can be made to keep pace with corn’s rapid growth and intense nitrogen demand.

Having a reservoir of the humus form of nitrogen adds resiliency to your farming operation. And it allows for less overall nitrogen, thus increasing nitrogen efficiency. Check your soil reports. When you see 30 and above on humus, you are in great shape. If you are 10 or below, you do not have any appreciable reserve fertility in the humus form. Therefore, it must be fully supplied via applied nitrogen.

For ultimate success in building humus, avoid GMOs and especially Bt-traited corn. You also need to eliminate herbicides. Both practices hinder the humification process.

3. Fix the Cal:Mag Ratio to 7:1

One of the rules we follow at International Ag Labs is very simple: Create an optimum environment for roots and microbes. And nowhere is that more important than fixing your soil’s calcium-to-magnesium ratio.

On the soil test we promote, the original Morgan Test, the optimum calcium-to-magnesium ratio is 7:1. This ratio directly impacts soil physics, soil chemistry and soil biology. This ratio is easy to calculate: just divide the calcium by the magnesium. Because this number is so important, we put it on every soil test.

Gary Zimmer, Gaining a Working Knowledge of Calcium, from the 2002 Eco-Ag Conference & Trade Show. Listen to Gary Zimmer talk about how calcium drives the flow of other minerals and nutrients through the soil and plant, and how to measure and balance calcium levels in your fields.

When the Cal:Mag ratio is below 7:1, the magnesium pushes nitrogen out of the soil and back into the atmosphere as gaseous nitrogen. This represents a huge inefficiency! The lower the ratio, the more nitrogen is expelled from the soil, and the costlier it gets to raise corn in this field.

Have you ever farmed a sticky heavy soil with excess magnesium? If so, you will find corn always does poorly. Why? Because corn is a nitrogen-loving crop. However, soil physics are dissipating nitrogen back into the atmosphere. That means it will take more nitrogen just to get the same yield.

If you own a piece of ground like this with a calcium to magnesium ratio of 4:1 or less, you need to take two actions:

  1. Fix the Cal:Mag ratio to at least 6:1; and
  2. Quite growing corn on that field until the ratio is corrected.

A better crop would be one that produces nitrogen such as soybeans.

Make sure you use high-calcium limestone as your primary amendment to raise available calcium and correct the Cal:Mag ratio. Never use Dolomite on a soil with a low Cal:Mag ratio. Calcium nitrate, gypsum and soft rock phosphate can all contribute as supplemental calcium sources, but never as the primary source to raise available calcium.

4. Increase Soil Biology

Soil biology is an incredibly broad subject. Many books have been written on it. The bottom line for you as a corn grower is very simple. A large microbial population around corn roots is actually a biological fertilizer factory.

As microbes live, reproduce and die, they leave behind the protoplasm of their dead bodies. Along with many minerals, this also contributes a steady stream of pre-made amino acids. Plants pick up these amino acids. This saves the corn plant a tremendous amount of metabolic energy by not having to construct its own amino acids. By using biology to convert soil and atmospheric nitrogen into high-efficiency amino acid nitrogen, less overall nitrogen is required.

Please read the next sentence very carefully. The key focus is not soil biology … it is on creating the optimum environment for soil biology. And the optimum environment is always an automatic result derived from the level and ratio of available minerals.

If you follow the rule to create an optimum environment for roots and microbes, you will reap the reward of creating your own fertilizer factory right beneath your corn plants. To implement this really requires a change in mindset and budget allocation.

We all know budget is a limiting factor in corn production. The key is to move money away from high-priced GMO seeds and various toxic chemical applications and into fertility inputs that optimize the environment for soil biology. The key is to always start with the foundations: major minerals, secondary minerals, trace elements and even rare earth elements. Once these foundations are in place, things like microbial inoculants, biostimulants and foliar sprays really work well.

Gary Zimmer, Minerals for Healthy Soil, from the 2017 Eco-Ag Conference & Trade Show. (18 minutes, 56 seconds.) Listen in as agronomist Gary Zimmer, author of The Biological Farmer and Advanced Biological Farming, teaches why he puts these four minerals at the top of his priority list.

5. Spread Out Nitrogen Applications

A single large dose of commercial nitrogen is inefficient. By splitting up the nitrogen into several smaller doses, efficiency significantly increases. The exception to this rule is the use of amino acid/protein forms of nitrogen. They always maintain their efficiency.

In my opinion, the fiscal nitrogen budget for the next crop starts as soon as the current crop is harvested. This means that the fall residue program is the first small dose of nitrogen for the next crop. Additional applications can be made via:

  • Fall applications of manure or ammonium sulfate;
  • Incorporating N-producing legume crops;
  • Spring applied dry nitrogen as a broadcast;
  • Liquid or dry nitrogen in the starter, side-dress, or topdress;
  • Liquid nitrogen applied through pivot irrigation;

The key for increased nitrogen efficiency is to use multiple N applications over the growing season. This will allow you to safely reduce 5-10 percent of overall nitrogen use.

6. Modify All Liquid N Applications

Straight liquid nitrogen such as UAN 32 percent (Urea Ammonium Nitrate) is inefficient on two counts. It is a very useful tool in a farmer’s toolshed. And it is far superior to anhydrous ammonia — a toxic, but cheap, form of nitrogen that destroys humus and kills soil biology. It just needs a little tweaking to overcome its inefficiencies.

The first inefficiency is that nitrates are prone to leaching, while ammoniacal and urea forms can volatilize. The second inefficiency is more serious. Plants can pick up straight nitrogen like UAN, but to make amino acids and proteins they first have to add carbons to the nitrogen. To do this, plants cycle N up to plant leaves and then back down to the roots while they pick up additional carbons. This is repeated until the nitrogen has enough carbons to make amino acids and proteins. This is a terrible waste of metabolic energy in plants.

To help correct both inefficiencies in liquid nitrogen, simply add carbohydrates. The easiest way is to dissolve 2-3 pounds of dextrose per acre. I prefer dextrose because it is available, ships without water weight and dissolves much quicker than table sugar. You can also use molasses or various syrups at 1-2 gallons per acre.

I categorize all carbohydrates as energized carbons. This energy feeds soil microbes and improves plant metabolism. These carbohydrates also help reduce leaching and volatilization.

Look at liquid nitrogen as an opportunity to create an amino acid precursor. Do this by adding carbohydrates, sulfur and possibly calcium to the nitrogen base. Here is a typical application per acre:

  • 10-15 gallons liquid UAN
  • 2-3 pounds dextrose dissolved in water
  • 2-3 gallons ammonium thiosulfate or 2-3 gallons liquid Calcium Nitrate

For most soils use ammonium thiosulfate. For low calcium soils the ammonium thiosulfate can be replaced with liquid calcium nitrate. Don’t use both, since the mixture has issues with stability.

I want to leave you with 5 cultural practices and actions you can take to improve nitrogen efficiency on your farm:

  • Do the fall residue program on corn residue
  • Soil test and amend to fix the Cal:Mag ratio
  • Consider cover crops or manure applications
  • Always modify liquid nitrogen
  • Know your metrics

Every business has metrics and so should every acre of corn. Here are the top three metrics I suggest for corn production.

  • Profit per acre
  • Nitrogen efficiency
  • Reserve fertility = humus

Jon Frank is the owner of International Ag Labs (aglabs.com), based in southern Minnesota. He is a soil consultant with more than 20 years of experience and is the founder of Grow Your Own Nutrition (growyourownnutrition.com). This article first appeared in the July 2019 edition of Acres U.S.A..

Soil Carbon: Changing Dirt into Soil

Soil carbon’s role in creating healthy topsoil is becoming a global topic.

It’s a popular notion that humankind is contributing excessive amounts of carbon into the atmosphere in the form of greenhouse gas. There’s been debate on what can be done to correct this situation, going so far as to suggest methods of sequestering the carbon into places of long-term storage. Regardless of who’s right or wrong, it can’t be debated that the definition of a healthy topsoil is when the soil has a rich concentration of durable carbon compounds that change for the better the chemical, physical and biological nature of the soil.

I heard recently a Ph.D. horticulture specialist say that you cannot add too much compost to a soil and that compost was the key to building and preparing a soil. In fact, he published on his university’s letterhead a statement where he recommends adding as much as 6 cubic yards of compost to an area of 1,000 square feet while preparing the site for landscaping. I heard a similar statement was made at a Santa Fe nursery seminar by a guy who makes compost. Well, that statement may be true if the compost was still composed of extremely decay-resistant woody material that was also low in nutrients, but then it would not be compost.

The simple act of composting is where specialized fungi and bacteria called saprophytic microorganisms collaborate in the reduction (shrinkage) of organic matter by utilizing the calorie value of the fats, proteins and sugars contained in the organic matter. As the microbes eat, they are concentrating all the parts that cannot be eaten, such as the minerals and the humic substances (HS). If plentiful levels of oxygen are available, the microbes that need oxygen to function will do the composting. A bi-product of their work will be CO2 which the microbes liberated from the carbon that was part of the digestible (decomposable) organic matter — the proteins, the fats and the sugars (carbohydrates). We call this source of carbon “rapid cycling carbon,” as it simply will not persist in the soil as part of the long lasting carbon bank that defines a topsoil. The part of a topsoil that defines the very essence of the soil is the concentration of the carbon substance that is not rapid cycling, and which has a resonance time in the soil of thousands of years. These carbon molecules are powerful biologic chemicals of nature called humic acids (HA or HAs), which are contained within the whole material called humic substances. They are not food for microbes, fungi or bacteria, therefore, they are not decomposable and will persist for a long time. Compost is a poor source of these substances, which any commercial soil lab can verify by doing a humic acid extraction and assessment. Levels of 1 to 5 percent humic acid are typical of a high quality finished compost, which is insignificant and inadequate to expect compost to fulfill the objective of building soil carbon directly.

soil carbon

For this reason, you simply can’t add enough compost to make a difference without overdosing the soil with nutrients! This also makes the term humification in my opinion an obsolete term, since that term implies that composting (decomposition) of organic matter results in the formation and high concentration of humic substances, which it does not! If it did, we would see levels much higher than 5 or even 25 percent humic acid in commercial compost, which we rarely see unless the compost was salted (fortified) using humate/leonardite.

Soil Carbon and Compost

Carbon found within the molecular structures of proteins, fats and carbohydrates (sugars) is turned into CO2 when oxygen is plentiful and aerobic saprophytic microbes can do their work. If O2 is not plentiful, then only those microbes that can function anaerobically (without air) can do the decomposing. This is not good, because toxic chemical compounds are the byproduct of anaerobic organic matter decomposition.

Compounds such as lactic acid and alcohol are produced when oxygen is not available in adequate amounts and those chemicals are toxic to plants at even parts per million. Anaerobic metabolism can occur in our muscle tissue as well, when we are out of shape and have poor vascularity (blood flow) in the muscles. This causes poor gas exchange during exercise and the muscle cells will not have adequate levels of oxygen, resulting in the production and accumulation of lactic acid. The lactic acid is toxic and irritating to the cell walls of your muscles and nerve endings and you consequently will feel pain a day or two after you workout. So it doesn’t matter if we are talking about soil, or we are talking about our own bodies, we must have adequate amounts of oxygen at all times in order to have optimum health.

soil carbon field
Photo by the author.

Soil Carbon and Compost Limits

So we don’t want compost that is produced without oxygen, but here’s the other side of the problem when we look back at the original statement “that you can’t add too much compost.”

You can indeed add too much compost, and for many reasons, one of which is back to the problem of oxygen. Here’s how and why; the more decomposable organic material you have, the more microbes will want to get into the act therefore, the more oxygen will be needed to accommodate this feeding frenzy. We call this the “BOD” or the Biological Oxygen Demand. If you incorporate into the soil too much compost that still contains a lot of combustible organic matter, the resulting population explosion of saprophytic microorganisms will rapidly use up the oxygen and your soils will go anaerobic. This results in a whole slew of unhealthy conditions, including the production of lactic acid and alcohol, two chemicals that are toxic to plant roots.

The other problem with adding too much compost is that if it is really compost and if it is made from a source of nutrient-dense plant organic matter, it will contain a rich and concentrated source of plant nutrients. After all, who do you know that is intentionally looking for a poor nutrient source of organic matter in order to make their compost? That would be silly, plus you may not achieve the proper carbon to nitrogen ratio needed to actually instigate the composting process. If you made the compost using the proper carbon to nitrogen ratio, by default your finished product will contain a significant amount of nitrogen. The bulk density of compost can easily be 40 to 50 pounds per cubic foot, which is 1080 to 1350 pounds per cubic yard. If you add 6 cubic yards of compost, as suggested by the University Ph.D. for a total of 7,800 to 8,000 pounds of compost per 1,000 square feet, you have also added over 103 to 106 pounds of nitrogen, a toxic amount! On a per acre level, that’s approximately 4,600 pounds of nitrogen, an amount that no farmer on earth would dare apply. So yes indeed, you can add too much compost!

As I’ve already described, the carbon found in over 95 percent of the carbon-rich parts of a compost are easily and rapidly decomposed into CO2, which defends my claim that compost is the wrong tool in the tool box, needed to accumulate carbon into the soil. The purpose of this tool is that it could potentially be a source of plant available nutrients if the composter was actively utilizing nutrient dense sources of plant organic matter.

As a fertilizer, compost can nutritionally support vegetation and it is then that we see a more efficient and effective development of topsoil, only because the plant is better at photosynthesis! If the plant is better at photosynthesis it can convert more atmospheric carbon into biological carbon called glucose, which is then transported down into the roots and provided to the bacteria and the mycorrhizal fungus. “Root Exudates” are liquid glucose leaking into the soil from the roots of plants.

humus soil closeup

Soil Carbon and Humus

In the same article, May 2011 issue of Discover Magazine, my 30-year long opinion of where humus comes from is finally collaborated by another source. Humus does not come from humification of dead organic matter; rather, it’s a result of an efficient mutualism between plants and the terrestrial biosphere of soil microorganism, and most specifically the mycorrhizal fungi. The mycorrhizal plant fungi relationship is critical to the process of pedogenesis, because it’s the massive contribution this fungus makes to its host plant in the form of water and minerals that allows the plant to be healthier and to live longer. Science has demonstrated that when a plant is mycorrhizal, the uptake of minerals from the soil is dramatically better and the drought tolerance of the plant is also significantly better.

Once again, a healthier and longer living plant can contribute more carbon in the form of liquid glucose to the soils terrestrial biosphere and from there everybody gets fed. Be clear that almost without exception, farm soils worldwide are lacking a strong mycorrhizal component therefore, expecting humus to accumulate in those same farm soils is most likely not going to happen. Also, research has proven that plants must have the benefit of this amazing fungus in order to get those minerals out of the ground in a useful fashion and with the minerals comes water. This is how we grow a nutrient-dense crop and also grow soil. For farming, mine reclamation, landscaping, highway re-vegetation, and other venues where you hope to build soils, you must inoculate with a mycorrhizal product, if you expect to see these benefits.

In 1974 I described this relationship as the “Soil Food Web,” a process of soil formation and collaboration, where most terrestrial life benefits from the Bio-Geo-Chemical process of mineral nutrient sequestering and availability. The term humus is one used by the average person, but its technical description used in chemistry is humic substance! The term humic substance describes a whole bunch of carbon rich compounds that resist decay and which are products of soil chemistry. Within the whole substance is a chemical of nature called humic acid. While humic acids are powerful chemicals with many characteristics and benefits, it’s the whole substance of humic compounds that are the major bank of long lasting carbon in the soil, resulting in the formation and accumulation of a rich topsoil.

But What About Soil Compaction?

The large, air-filled spaces, or “macropores,” in untilled soil without compaction, often resemble the branching vessels of the human circulatory system. A team of Nordic researchers led combined computed tomography (CT) scanning with traditional measurements of air exchange to “diagnose” the long-term impacts of soil compaction on the hidden, but vital, soil pore network. When scientists examined cores of heavy clay subsoil suffering from compaction on a research site in Finland, they found the macropores were greatly affected compared with a non-compacted control soil. The compacted soil contained mostly long, vertical “arterial” pores, or pipes, with significantly fewer marginal pores branching from them.

Most troubling to the researchers was how lasting the impacts of compaction appear to be. In the study, the group examined soil cores taken from a depth of 0.9 to 1.2 feet in plots where 30 years earlier a heavy tractor-trailer drove over the ground four times to create compaction in an experimental treatment.

It’s where a lot of farmers end up at some point, with dirt. And turning it into soil starts with understanding carbon.

By Michael Martin Meléndrez. This report on soil compaction appears in the April 2014 issue of Acres U.S.A. magazine. This story originally published in October 2011 issue of Acres U.S.A. magazine. Michael Martin Meléndrez and his wife Kari, own Soil Secrets LLC, Soil Secrets Worldwide LLC, and the Trees That Please Nursery. Contact Soil Secrets and Michael by calling 505 550-3246, or email soilsecrets@aol.com.

Carbon Cycling, Carbon Building

By John Kempf

In this article I hope to provide some ideas concerning carbon cycling and how to effectively build soil carbonic organic matter. There seem to be three primary means by which we can increase a soil’s carbon content: carbon imports, carbon generation and carbon induction. Each of these possible methods can also offer other strengths to a soil-building program, compost can provide a biological inoculum, humates can provide a biological stimulant.

Adequate levels of functional organic matter and a robust soil digestive system are sorely lacking in most all agricultural soils. This lack of humic substances and biology significantly reduces a soil’s water-holding capacity and the ability to release nutrients, all of which leads to large losses in crop quality and yield.

Meanwhile, increasingly higher levels of atmospheric carbon or CO2 are being produced by the burning of fossil fuels and land desertification. Carbon sequestration — the term has been thrown around like a rubber ball. What does it really mean for agriculture? How can carbon be stabilized in soils most effectively?


Listen in to the Tractor Time podcast featuring guest John Kempf, and learn about his methods for farm and soil management. 45 minutes, 32 seconds.


Importing Carbon

There are three primary carbon imports: Humates or leonardite, and their derivatives such as fulvic and humic acids. The humic substances present in these materials generally provide very good nutrient exchange. Biochar is also a stable carbon import but not as active as leonardite seems to be. Compost can also be a viable carbon import with the added benefit of a strong biological component. Compost, however, tends to have a lower level of stable humic substances when compared with other materials. A fair proportion of compost can degrade over a period of a few years.

Carbon Generation

We have several opportunities to generate or capture carbon on the farm that would otherwise be lost. Managing crop residues, composting crop waste and animal manure, and cover cropping all provide us with a chance to capture more carbon and store it in our soils. Any of the practices will also help build a robust digestive system in the soil.

Andre Leu, Soil Carbon, from the 2007 Eco-Ag Conference & Trade Show. (53 minutes, 44 seconds). Listen in as Leu, the director of Regeneration International, teaches how to store and repurpose carbon in your soil.

Carbon Induction

Induction seems to best describe the possibility of generating higher levels of soil carbon by optimizing the carbon cycle and plant performance. Carbon induction has the greatest potential of any source to build large amounts of stable humic substances, stimulate biology, and improve soil and plant health. Carbon cycling — how does it really work? As plants are growing in the field they absorb carbon dioxide from the air.

Through the process of photosynthesis this carbon dioxide and water are used to form simple sugars, which are composed of carbon, hydrogen and oxygen. These sugar compounds are the foundational building blocks to build all the rest of the plant compounds, such as complex carbohydrates and polysaccharides, proteins and amino acids, and plant lipids.

All of these compounds contain an average of roughly 40 percent carbon. In exchange for nutrients supplied by the soil system, plants release large amounts of these substances into the soil to feed the soil biology. These root exudates contain a variety of organic and amino acids and lipids. The healthier a plant becomes, the greater the amount of root exudates and the higher the quality.

According to Horst Marschner, in his book Mineral Nutrition and Higher Plants, healthy plants can release as much as 60 to 70 percent of their total sugar production back into the soil as root exudates. This can only occur, however, if we have truly healthy and energy-positive plants, in other words, they have an energy surplus.

If we think about this for a moment we can realize the tremendous amount of carbon induction this can create. A healthy plant will have at least as much root biomass below ground as there is plant biomass above ground.

So if we have 100 pounds of plant biomass above ground, and an additional 100 pounds below ground, this still represents only 30 to 40 percent of this plant’s total energy production. This is the real secret to building soil carbon effectively and efficiently. We can readily see why forage-based livestock agriculture and perennial polycultures are the most efficient method of building soil organic matter and stable humic substances. Carbon induction is the answer.

The Importance of Fats

As plants become healthier and have greater photosynthetic efficiency and higher levels of sugars and energy, they will begin to form high levels of lipids (fats and oils). The lipids are energy storage compounds in the plant, just the same as fats are the energy storage in animals. Once a plant has surplus energy it is stored as fat.

All plants have a minimum baseline level of lipids needed to form the phospho-lipid soul membranes. As their energy increases, however, they will form higher levels of lipids, which will be stored inside the cells and utilized in building stronger cell membranes and stronger reproductive tissue. Many of these lipids will also be exuded from the roots into the rhizosphere, where they will be used as an energy source by soil microbes.

These lipids in the rhizosphere are an important piece of the puzzle in building stable humic substances, all of which have a fairly high content of both aliphatic and aromatic compounds, which are based on theses plant lipids.

The Importance of Soil Fungi

When these sugars, amino acids, and lipids are released as root exudates, they become a ready food source for the soil’s microbial system. How these compounds are digested will determine whether stable humic substances are formed or not.

There are several types of digestion in the rhizosphere. If we have a bacterially dominated digestive system, the bacteria will utilize these plant exudates as a food and energy source. The bacteria are then in turn used as a primary food source by other microbes such as nematodes and actinomycetes. These microbial metabolites are then quite stable and can be utilized by plants as an energy source.

This digestive cycle is termed mineralization, and is set in motion by bacterial dominance. If a soil has a fungal dominated digestive system, the fungi will be the primary digesters of the plant root exudates.

Fungi will absorb these compounds and digest them slowly over a period of time and combine them into complex long-chain compounds, which are referred to as humic substances. This digestive cycle is called humification, and is a critical piece of carbon sequestration.

As can be seen, carbon induction can be the best method of building soil organic matter. However, several important pieces need to be in place. Healthy plants with high levels of energy, coupled with soils that have a strong fungal dominated digestive system, will get the best results. A good example of such a system would be the perennial grasslands of the Great Plains.

This article appeared in the October 2011 issue of Acres U.S.A. magazine. Kempf is the owner of Advancing Eco-Agriculture, Middlefield, Ohio, an eco-agriculture consulting and solutions company. 

Learn more from John Kempf:

Increased Yield & Nitrogen Efficiency by John Kempf
Learn from John Kempf, founder of Advancing Eco-Agriculture, and his soil-building system; farmers who apply this program report increased nitrogen efficiency, decreased inputs, and increased yields.
Developing Regenerative Agriculture Ecosystems, part 1
John Kempf shares his vast knowledge about how to regenerate soil health, dramatically improve crop yields and quality, decrease pest pressure and grow crops more resilient to climate extremes at the SNC 2018 pre-conference.
Developing Regenerative Agriculture Ecosystems, part 2
John Kempf shares his vast knowledge about how to regenerate soil health, dramatically improve crop yields and quality, decrease pest pressure and grow crops more resilient to climate extremes at the SNC 2018 pre-conference.

Supplying Nitrogen: Tap into Nature

By Dr. Phil Wheeler.

Human activity is affecting planet Earth to such an extent that natural scientists are naming this time the beginning of a new geological age/epoch called Anthropocene (the recent age of man) and ending what was the Holocene epoch (about 17,000 years ago to present).

We are no longer observers of nature, but significant influencers of what is happening to nature. The sheer weight of humans and their livestock is now bigger than the Earth’s wild animal population. Our activities are rapidly increasing the amount of CO2 in the air. That is an established fact, the effect of which is the only thing in dispute, i.e. will it get warmer or cooler and will we be wetter or dryer?

The temporary warmth is obvious in the Arctic. Although growers usually help to absorb CO2 by growing crops, their improper handling of crop residue or improper feeding of livestock can add the CO2 back into the air. However, farming’s bigger polluting effect concerns nitrogen.

Plants have always used N from the air by a variety of natural methods. Now the rate we are taking N out of the air is 50 percent higher than what nature has done for millions of years. Most of this industrially created N is now used for fertilizer. This industrial process was originally used to make munitions prior to World War I.

Taking N out isn’t really the problem; it is the later consequences that matter. Chemical N leaches into the aquifer. We are all familiar with ocean “dead zones” where the oxidized N and P have fed algae blooms that starve aquatic life for oxygen and the concept of “blue babies” that occurs when excess nitrate in the water causes babies to turn blue from lack of oxygen in their blood. Even though people don’t turn blue, they may have, and not be aware of, a reduced amount of oxygen in their blood, which can affect their energy levels.

nitrogen cycle

As growers, we must do our part in mitigating our impact on natural systems by taking every opportunity to use naturally occurring N and cease the use of industrially created N. There are five main ways we can get the nitrogen we need to grow our crops without resorting to man-made N. The good news is that you will be raising healthier, more valuable crops in the process of using nature’s supply of N and can achieve comparable yields (or even greater yields).

Legumes

One of nature’s original methods of building available N is with N-fixing plants called legumes. Legumes range from small white clover to large shrubs and trees. They all have the ability to take N2 gas out of the air that is circulating in the soil and use a biological/chemical process to fix the N2 into ammonium ions and/or more complex amino acid molecules. There is a microorganism called rhizobia that establishes itself inside the root nodule to complete the process.

Since each legume may have need of a different rhizobium it is best to buy the inoculant that matches it the first time you use that particular legume. If you are not farming conventionally/chemically, the organisms will usually survive, and you will not have to keep buying new inoculum for the repeated crop. The amount of N fixed by a given legume varies widely, but 30-60 pounds per acre is common.

The legumes usually need the trace mineral molybdenum to make the process happen efficiently. Hopefully, you all remember to dig up your legume of choice, carefully cut open the visible nodule on the root and check its size and color. The larger the nodule, the more the fixation potential. The darker the pink, purple or maroon, the more molybdenum you have in your soils to make the process work. If you have dull grey nodules, you need to add some molybdenum. The easiest, least costly way is to use fish, seaweed and ocean liquid or dry products that contain traces of “Molly B” on a regular basis.

Azobacter

Nature’s second process of supplying N involves freestanding microorganisms called azobacter or azotobacter.

These organisms don’t have to use a root nodule to change the N2 gas to ammonias and other important compounds. They basically absorb the N2 gas and release ammonias and the other compounds. The other compounds are very significant, including amino acids (the building blocks of protein): glutamic, methionine, tryptophane, lysine, and arginine. This means your plants are receiving N in a form that they can use without expenditure of valuable internal energy that can be used for increased production.

Azobactor also produce vitamins B1, 2, 3, 5, 6 and 12 and vitamins C and E. In addition, the phytohormones indoleacetic acid, gibberellic acid and cytokines are produced. If you add up the cost of buying all the compounds separately, modern azobactor products are a real bargain. Conventional farming kills off these organisms and robs the grower of what amounts to free N and a whole slew of growth factors.

Thanks to a technology breakthrough, cyst forms of azobacter that can operate on a leaf surface to produce ammonias and all the other compounds for uptake by the plant are available in the marketplace. The amount of N produced in the soil and on the leaf is conservatively listed at 40-50 units per pound per acre per application. The azobacter can also deny surface space to disease pathogens. (Believe it or not, “good” nematodes are also great ammonia and amino acid factories.)

Manure

The next major natural source of N is from the waste products of livestock. Stable manure will also contain urine, so now you have ammonias, nitrates, urea and some protein N. Much of this can be wasted if manure is not handled properly.

Manure pits are the most common treatment/process that seeks to save/stabilize the N. However, without peroxide, biology and carbohydrates added to aerate and fix the N, much of it is lost, and odor is a problem.

Composting is the best way for sustainable growers to handle manure as the composting process, when done properly, kills pathogens, stabilizes the N and other nutrients, increases microbial activity, and creates other valuable enzymes, hormones and growth factors. Generally compost is used at 1-2 tons per acre providing 14-28 lb N (cow) and/or 60-120 lb N (poultry) the first year.

There are several ways to preserve more N from your manure when composting. Adding clay improves moisture retention and increases aggregation. Adding KS+, a natural mined acidic mineral, at the beginning of composting (or better yet, at the source of the manure) stops N volatilization, kills pathogens and reduces odors very quickly, and creates better amino acids for easier uptake by plants.

Protein By-Products

The fourth way to get N for your crops is to use a protein by-product: blood, feather meal, cottonseed meal or fish products. Protein nitrogen is composed of amino acids which are available for direct use by a plant without the use of internal plant energy to process them. Comparing protein N to industrially produced N is complex.

First, usually about 80 percent of the applied chemical N is lost either up (volatizing) or down (leaching). Second, research shows that the protein N in fish is equivalent to about five times the amount of remaining chemical N. Simply put, 100 units of chemical N winds up being 20 units used by the plant and that 20 units of chemical N has the equivalent effect of only 4 units of fish protein N. The added efficiency of protein N from fish comes from the additional microbial stimulation of “good guys” like azobactor. Five gallons of a 4-1-1 fish product can get you the same result or better than 400 pounds or 40 gallons of 28 percent.

Humus

The fifth natural source of N for your crops is from recycling previous years’ plants into humus. Humus is the product of plant residue broken down by microorganisms. You can build your humus levels through cover cropping and proper handling of crop residue. The humus-building process is greatly enhanced in biologically active soil.

Humus is produced as either active or passive factions from the plant residue. The active faction feeds your next crop, while the passive faction builds long-term humus levels. The usual figure for the amount of N released by humus is 40 pounds per percent of humus per year.

To be on the safe side, I use a figure of 30 pounds per percent of humus. Research shows that large amounts of chemical nitrogen stimulate microbes to eat plant residue, but the carbon volatizes instead of forming humus.

Another vital and positive side effect of microbial N versus chemical N is that mycorrhizae have a much better chance to do their job of producing glomalin (long lasting carbon compounds) which is the true soil “glue” that gives soil structure through flocculation and enables plants to increase the access of N from the air.

Keeping in mind the usual rule that says it takes a pound of N to produce a bushel of corn, let’s see how much N we can come up with using sustainable methods. We will assume you properly incorporated your crop residue in the fall with carbohydrates and bacteria and added protein N if the residue was brown. You have also planted a mixed legume, grain cover crop to take down next spring. Your current humus reading is only 2.5 percent.

Let’s delineate and calculate N sources and amounts for next year’s corn: Humus (30 lb x 2.5 = 75 lb N); Crop Residue (30-40 lb N); Legume plow down (30-60 lb N); 5 gal of a 4-1-1 fish product (22 lb equivalent N); 250 ml nitrogen-fixing azobacter in the row (40-50 lb N); sidedress fish and azobactor and/or foliar feed azobactor (20 lb N); “A few good nematodes” (10 lb N). And it all adds up to (75 + 30 + 40 + 22 + 40 + 20 + 10 = 236 lb N [low end] or 277 lb N [high end]). Add more to that number if you spread raw manure or compost this fall or next spring.

See? You have enough N to grow at least 200 bushels of corn without one pound of manufactured N! Meanwhile, you haven’t added nitrates to the groundwater, killed off any of your beneficial microbes or burned out your humus with artificial, costly processed N. Please break your high N addiction now! Make sure you handle this year’s crop residue correctly, plant a cover crop and get ready.

Editor’s Note: This article appeared in the December 2011 issue of Acres U.S.A.

Phil Wheeler, Ph.D., is well known in eco-farming circles, having served as a consultant to major growers in the Midwest and beyond for decades. He heads Crop Services International, a Grand Rapids, Michigan-based consulting and eco-inputs supply firm. He is co-author, with Ron Ward, of The Non-Toxic Farming Handbook available online from Acres U.S.A. at or by calling 800-355-5313.

Farming the CO2 Factor

By Will Brinton, Ph.D. 

In a rare moment in an early Rover reconnaissance mission to Mars, carbon dioxide (CO2) was released from a soil sample during a scientific test and was thought to indicate the presence of microbes. Excitement quickly faded to puzzlement, then dismay, as it was realized that a glitch in the expensive on-board lab had produced inorganic CO2. Chemicals used for the soil extract triggered release of inorganic CO2, perhaps from the ubiquitous magnesite (MgCO3) found in Martian soil.

On Earth, the release of carbon dioxide from moist soil due to microbial activity is so pervasive that it is difficult not to observe it. We don’t have the problem they do on Mars trying to distinguish biological CO2, in an atmosphere containing 96 percent CO2, from non-living sources. In science we call this dilemma “distinguishing small differences between large numbers.” Here on Earth, CO2 in the atmosphere is only 0.04 percent, and climbing just barely perceptibly, making it relatively easy to distinguish biological CO2. Curiously, almost nobody is doing it.

Will Brinton and soil
Will Brinton and Odette Menard (MAPAQ Quebec) speak at an on-farm event in Pennsylvania as part of the No-Till Alliance Field Days,

Borrowing From the Past

I learned about soil CO2 respiration working on a graduate program in Sweden investigating fertilizer and crop effects on soil biology. Agronomists in the 1950s set up farm plots and maintained them for decades, enabling later researchers such as myself to observe the long-term effects of differing soil management.

In the process, I discovered a trove of even earlier Swedish work on soil respiration.

The legacy of this soil biology work traces to soil scientist Henrik Lundegårdh (pronounced Lun-de-gourd) who, in the 1920s, established an essential framework for understanding the biology of crop productivity. Lundegårdh was concerned about the early rush into inorganic chemical farming based on the new discoveries of mineral plant nutrition. In his view, soil biological functioning should be part of routine soil fertility assessment.

He selected soil CO2 respiration since it reveals the all-inclusive metabolic activities of soil bacteria, fungi, arthropods and plant roots. He labeled this indicator “the CO2 factor.”

It’s possible that Lundegårdh built the first farm CO2-flux chambers. He set up as many as 42 in farm fields and nearby forests running year-round under differing soil and crop regimes. This kind of approach is only now coming into vogue to understand the potential of CO2-driven climate change. Lundegårdh already grasped the significance of the global carbon cycle at the time, but more importantly, saw an enormous upside to CO2 in the context of quantifying “healthy soils.”

Soil Biological Cycle
Figure 2. The Soil Biological Cycle. This shows the daily carbon and nutrient release rates in relation to the mass of microbes and soil organic matter.

From this effort Lundegårdh reached several astonishing conclusions. He was a systems researcher in the best sense, and to make a point about the relevancy of soil CO2, he adjusted soil profiles with microberich manure until steady CO2 rates were attained. Next, he grew wheat, oats and sugar beets and monitored their nutrient and carbohydrate assimilation.

From this he demonstrated a significant connection of soil respiration to plant photosynthesis. Considering the thoroughness of these studies and their dissemination in published literature of the time, it is hard to understand how such excellent work escaped further attention.

I have confirmed many of Lundegårdh’s measurements and calculations.

The essence of the discovery is that plants obtain the CO2 they need not from the atmosphere per se, but from soil respiration. Lundegårdh showed that if soil respiration fails to furnish a sufficient quantity of CO2, the supply from the atmosphere is furnished too slowly to prevent a CO2 deficit in the leaves, and thus a partial starving occurs. This can be intuitively grasped as a basis of truly biological-oriented farming.

Some very recent studies on forest canopies in ecological journals confirm that in highly functioning ecosystems the cycle of CO2 (and O2) between plants and the soil is nearly completely closed. In this regard Lundegårdh was a pioneer showing that we cannot separate living soil from high-yielding crops. This is a far cry from where we stand in the present, and this is unfortunate.

Lundegårdh outlined the biological pathways that directly contribute to crop productivity, including:

  1. Mineralization of organic nitrogen to nitrates (due to microbial activity);
  2. extraction and buffering of the soil solution (due to dissolved carbonic acid from microbial activity);
  3. soil aggregate formation (due to microbial activity) and;
  4. furnishing plants with CO2 for photosynthetic assimilation, also due to soil respiration.

The implications of Lundegårdh’s discoveries were largely ignored. Lundegårdh was aware of the conflict with prevailing mineral-theory views.

Writing a commentary in the journal Soil Science in April 1926 he voiced his concern: “The direct action of mineral fertilizers on increasing plant growth is the only one attention is being paid to in agriculture.”

Domination of the Mineral View

Lundegårdh’s remark in which he regrets the narrow focus on mineral nutrition of plants is certainly as true today as it was then — or even more so. Europeans in Lundegårdh’s time witnessed the explosive growth of the inorganic fertilizer industry and its integration into farming, sweeping away centuries of old customs. The founding of our Land Grant University system grew out of this turbulent era, a result of political fears that Europeans would gain an advantage over the United States with the new mineral theories applied in agriculture to attain stupendous crop yields.

Today, if you operate a soil lab as I do, virtually all the equipment and technology is tasked for testing inorganic minerals. The basics were laid down a century ago. Advances in technology have largely focused on making it easier to measure more minerals faster. Harsh soil extracts are designed to pull the nutrients from soil as rapidly as possible. We combine this with mathematical equations formulated in the late 19th century by German chemists Liebig and Mitscherlich to “calibrate” extracted minerals to crop response.

This chemistry-mathematical approach is also very convenient: it is directly tied to applying inorganic fertilizers keyed to soil analysis, a business model that catapulted the mineral industry into becoming the cornerstone of modern farming. As the damage from a century of one-sided practices comes more into focus, some are asking: was the compelling post-war business opportunity of industrialization, more than the science itself, the real impetus for these agricultural changes? Some caution that we are being too critical of these early advancements or not appreciating the extraordinary amount of early scientific work that went into the new protocols. The problem is, all that work was done before the field of soil biology was even recognized.

Lundegårdh could well have been an organic science pioneer, but the movement was yet to be born. He did something that was highly significant by drawing attention to the shortsightedness of the new chemistry discoveries, and he tied the best science to measurements in soil biology.

Lundegårdh was not opposed to inorganic nutrients. He pointed out that in some circumstances increasing inorganic fertilizers also increased soil biology and CO2 respiration due to greater root mass and more crop residues.

His approach clearly fits current concepts of soil health (the connection of soil-respiration to carbohydrate assimilation certainly belongs in the soil health arena). The point is that we have been trained for over a century to overlook soil biology with the best excuse being that it takes care of itself (which is partly true), and the somber threat that without inorganic fertilizers the world’s populations will starve.

A scientific survey from Richard Mulvaney (Univ. Illinois/Urbana) examining soil tests nationwide found that in spite of increased soil mineral applications, soils are steadily declining in organic nitrogen, the key indicator of soil vitality. I believe this proves that there is no connection between mineral fertilizers and soil improvement.

The inescapable conclusion is that soil degradation — despite our best efforts — is likely to continue unabated. Aside from erosion and salinization, the central crisis is depletion of soil biological capital, or Lundegårdh’s “CO2 factor.” In fact, it is possible that we are approaching, for the first time, a new low-water mark in soil fertility, for which Lundegårdh’s studies are a harbinger and warning.

But without new testing tools, no one will notice it.

Crisis to New Action

There is nothing like impending crisis to trigger new experimentation. Part of the exciting turning point is seen in efforts by progressive farmers who appear to be training the government and the Land Grant researchers.

Private soil labs have jumped into the fray to evolve new indexes for biological fertility. Underlying this is the age-old axiom that you can’t manage what you cannot measure. It explains our laboratory’s introduction of a new type of soil test called “Solvita,” making measuring soil CO2 factor respiration practical and cost-effective within the infrastructure of soil labs and crop consultants, who are starting to see the connections.

A transition era is upon us and is captured in Figure 1 below, showing the prevailing and new views.

soil fertility table
Figure 1

Putting Numbers to CO2

The basis for biological functioning related to soil CO2 starts with calculations anyone can perform. Take your entire dry matter crop yield and multiply by 50 percent to get your approximate carbon yield per acre.

Fertility comparison of two soils
Figure 3. Fertility Comparison of two soils. Left: Truck farm continuously tilled soil. Right: Virgin prairie soil.

Divide this into 60 (the most active carbon assimilation days) and you have the carbon factor per day, which multiplied by 3.7 gets you to the CO2 factor. This was Lundegårdh’s basis in comparing soil respiration to crop carbohydrate assimilation. These two sets of numbers — the plant uptake and the soil respiration of CO2 — can be found to be roughly comparable, in a healthy system.

Crop CO2 needs such as in corn can be as high as 450 pounds per day per acre during the active period (as pure carbon this is 125 pounds per day). It turns out that nature has designed redundant biological systems in soil to furnish adequate amounts of CO2 to keep plants in top shape, while the biology itself regulates the commensurate supply of nutrients and maintains soil structural integrity.

The cycle can be quantified, using an example of a soil moderate organic content as follows (Figure 2).

By more accurately quantifying the CO2 respiration rate we get closer to the mass of microbes and the potential nutrient supply to plants. Over time these measurements will be interpreted with greater precision. In the following example we show relative CO2 rates with the Solvita 24hr CO2-Burst test, used by Soil Health Tool labs (see note at end for a soil map showing labs offering this soil biology test).

In the example, given the “dead soil” on the left, a continuously cropped (truck farm) soil from North Carolina, had very low (12 ppm) daily CO2 rates. This is depletion farming (mineral test levels in the same soil were adequate and did not reveal the extent of the problem). For comparison we tested a virgin prairie soil from Nebraska, which showed almost seven times more biological activity. That system has accumulated biological capital. Associated with such a rich soil is a potentially high organic nutrient cycle. Modern mineral soil tests just do not show this.

Getting to the CO2 Factor

We need to alter the way we measure yield response in soil testing by paying attention to the capability of soil to produce the CO2, an integrated measure of all soil biota. In time, we will learn more about relationships of the biota to each other (fungi, bacteria, mycorrhizae) and to organic nitrogen fertility. It is well known that these have been factored out of calibration studies used in soil interpretation.

Correcting this omission is a challenge and is critical to assuring soil health and high-yielding crops and to fixing soil testing from being all about minerals to including biology.

Incidentally, we may rediscover mineral nutrition of soil from a new perspective: creating the optimal balance to foster microbial activity and diversity according to the edict: feed the soil. This work is only beginning today.

It is noteworthy that soil mineral theory is a self-fulfilling prophecy — not focusing on biology leads to emphasis on minerals, this in turn fosters management practices that ignore biology; this leads to increased dependency on inorganic fertilizers: the cycle repeats.

Including Soil Labs in the Biology Transition

We need to foster the independent relationship of grower to soil lab, with the new biology standing in for mineral theory. Growers interested in soil biology should contact their soil labs. A new open-source methodology integrating soil biology with common nutrient tests, called the Soil Health Tool, originated with support from USDA-ARS and is available to any lab. More than 30 labs around the world now offer the Solvita biology test.

The success of the transition depends not on a new era of “expertism” of the sort that brought us the chemical mineral revolution, but by on-farm efforts comparing yield stability and quality with soil biology. Therein may lie the key to breaking the 150-year-old N-P-K spell.

The author dedicates this article to the memory of Jerry Brunetti, a pioneer in soil, livestock and human health.

Editor’s Note: This article appeared in the April 2015 issue of Acres U.S.A.

Will Brinton, Ph.D., is founder and chief science officer at Woods End Soil Laboratories, Inc. in Maine. He runs his own 25-acre research farm and co-manages the family 1,000- acre tree farm in Pennsylvania.

Understanding Soil Carbon Dynamics

By Caitlin Youngquist, Ph.D. 

Carbon is an often overlooked, but very important com­ponent of the soil. We know how to manage nitrogen, phos­phorus and potassium for maximum production, and that micronutrients play a critical role in crop yield and disease resistance. Deficiencies can usually be corrected relatively quickly through the addition of soil or foliar fertilizer ap­plications. While soil nutrient status can change quickly, changes in soil carbon status are generally much slower and effects are less obvious in the short term.

Soil is a living system and has both inherent and dynam­ic properties — land managers work within the constraints of the inherent properties to change the dynamic proper­ties. Changes in type and amount of soil carbon is one of our biggest opportunities for soil improvement.

Soil health can be defined as the capacity of a soil to function in the areas of biological productivity (i.e. plant growth and decomposition), environmental quality (i.e. water filtration and erosion resistance) and plant and ani­mal health. It is also one of the best indicators of long-term sustainability in land management. The primary unifying factor in all of these areas is soil carbon, the major compo­nent of soil organic matter. It is what gives healthy soil its dark brown color and rich, earthy smell.

Soil organic matter encompasses all organic components of the soil system. This includes living and dead plant and animal tissue, as well as excretions and soil microbes. Soil organic matter is typically a small percentage of the soil but has a very important role to play in soil health, disease suppression, drought resistance, water quality and quantity and long-term agricultural viability.

Example of soil carbon difference between two samples
These two soils came from neighboring fields separated only by a fence. This Wyoming ranch recently converted half of the irrigated hay ground into pastures and implemented a rotational grazing system. The soil on the right is from the field that remained in hay production. The soil on the left is from the field that was converted to well managed pasture. Note the change in color (soil carbon) and rooting depth after only one year.

The terms soil organic matter and soil carbon are often used interchangeably, and while one is a component of the other, they are not the same thing. Carbon is the primary component of SOM, accounting for approximately half of the molecular weight. Nitrogen, phosphorus, calcium, magnesium, iron, zinc and other plant nutrients make up the rest. While plants do not take up any significant amount of carbon from the soil (instead they get it from the air), or­ganic matter is the food and energy source for soil bacteria, fungi, worms and the rest of the soil food web.

When it comes to managing for soil health, it is actually the organic soil carbon that is of interest. Soil organic car­bon was once a part of a living organism and will be again someday. In contrast, soil inorganic carbon includes things like charcoal and calcium carbonate (lime) and does not provide the same benefits to soil health.

Soil microorganisms (nematodes, bacteria, fungi, etc.) rely on organic matter as a food and energy source. These microbes break down complex carbon-based molecules in crop residues and manure like cellulose, lignin, fat and protein into smaller components. As a result, nutrients are made available to plants, and carbon dioxide is released as a byproduct.

The bacteria responsible for the most rapid organic mat­ter decomposition are aerobic (require oxygen). Tillage in­troduces oxygen into the soil, stimulating microbial activity. This burst of microbial activity leads to increased rates of organic matter metabolism in the soil and subsequent loss of soil carbon as carbon dioxide. This is why tillage is a pri­mary factor in loss of soil carbon and declining soil health.

Plants cannot use the nitrogen or many of the other nu­trients in organic matter until the microbes break it down. The process of releasing nitrogen from organic matter is “mineralization.”

soil layers
Grass and legume roots sequester carbon and help increase soil organic matter levels. Note the dark color that surrounds the large alfalfa root. This is caused by root secretions (polysaccharides) and resulting microbial activity.

Bacteria in the soil are also responsible for the conver­sion of ammonia to nitrate, the preferred form of nitrogen by most plants. Both processes require oxygen and warm temperatures. This is why plant-available nitrogen may be limited in saturated or cold soils.

Active, Slow & Passive Pools of Soil Carbon

Looking a little closer at carbon in the soil, there are several different pools that serve different purposes. The active pool (also called labile carbon) is composed primar­ily of living organisms, crop residues and manures. It turns over in seasons to years as soil microbes break it down and convert it into more stable forms. This pool plays an important role in structural stability (resisting erosion) and as a food source for soil microbes. Because it is made up of primarily “fresh” materials, nutrient release from this pool is relatively rapid. Levels of active soil carbon change rela­tively quickly with tillage practices and cropping systems.

The passive pool of soil carbon turns over in hundreds to thousands of years. It is very stable and physically pro­tected from the activity of soil microbes because it is bound up in organic-clay complexes. This pool of organic carbon is the major contributor to cation exchange capacity (the ability of the soil to hold nutrients), and water-holding capacity. It is very slow to change and primarily lost through wind and water erosion of topsoil. Humus is part of this pool, which has been shown to promote root development and plant growth.

The slow pool of soil carbon is an intermediate pool that turns over in decades. This pool also provides food for soil microbes and is especially valuable for its slow release of nitro­gen and micronutrients. It provides some benefits of both the active and passive pools as well. Changes in till­age and cropping systems will also impact this pool but effects may take longer to manifest than in the rapid pool.

Think of the active active, slow and passive pools of soil carbon as a checking account, savings account and retirement plan. You can add to these “accounts” with cover crops, manure and compost, and by in­cluding soil-building crops in your rotation. You can minimize losses by reducing tillage, leaving crop residues in the field and protecting the soil from erosion.

So, what does this mean for land managers and stewards? There are many soil functions that are directly or indirectly affected by soil carbon.

  • Soil microbial activity — plant nutrient availability, degradation of pollutants and disease suppression.
  • Soil structure — water infiltra­tion, rooting depth, resistance to ero­sion and compaction, and oxygen availability for roots and microbes.
  • Water-holding capacity — drought resistance and water storage.
  • Crop quality and yield — dis­ease resistance, seed germination, root development, and plant growth.

Changes in soil carbon can be measured in the lab or in the field. The simplest method requires only a shovel while more advanced methods involve laboratory analysis. By dig­ging a small hole and taking note of the color, smell and structure of the soil you can tell a lot about soil carbon status.

A soil with more carbon will be darker in color, have a stronger earthy smell (humus) and better tilth. You may also notice more earthworms and deeper roots. Compare soil from a cultivated field to soil from a pas­ture, fencerow, or garden. Observing changes in these three basic character­istics (color, smell and structure) over time can tell you a lot about the effects of your current management on soil health and carbon status.

Laboratory soil tests will typically include soil organic matter (as a per­cent of soil by weight) along with N, P, K and micronutrients. Watching how this number changes over time can be very informative, especially if you are making any changes to crop­ping or tillage systems.

There are also several lab and field tests available for soil microbial bio­mass and activity. As they say, “if you can’t measure it, you can’t manage it.” As you manage soil N, P and K for maximum crop production, consider ways to manage C too. The long-term benefits will be well worth the invest­ment.

By Caitlin Youngquist, Ph.D. This article appeared in the December 2017 issue of Acres U.S.A. magazine.

Caitlin Youngquist is a University of Wyoming Extension Educator in northwest Wyoming. While she tries to answer any question that comes through the door, her area of expertise is soil man­agement and composting. You can find some of her other articles in her blog: drcaitlin.us, or email her at cyoungqu@uwyo.edu.

Soil Organic Matter: Tips for Responsible Nitrogen Management

By André Leu
From the August 2012 issue of Acres U.S.A. magazine

For soil organic matter to work the way it should, it depends on a careful balance of nutrients and minerals, including one of the most important elements — nitrogen. One of the great paradoxes of farming is that lack of nitrogen is regarded as one of the great limitations on plant growth, and yet plants are bathed in it because the atmosphere is 78 percent nitrogen.

Most plants cannot use nitrogen in this form (N2) as it is regarded as inert. It has to be converted into other forms — nitrate, ammonia, ammonium and amino acids for plants to utilize it.

In conventional agriculture most of these plant-available forms of nitrogen are obtained through synthetic nitrogen fertilizers that have been produced by the Haber-Bosch process.

Many experts credit the Haber-Bosch process for producing the nitrogen needed for high-yielding agriculture. Others fur­ther state that without using this energy-intensive method to synthesize ammonia, we will not be able to feed the world. At the same time, the loss of soil fertil­ity is resulting in yield decline around the world. Farmers have to dramatically in­crease synthetic fertilizers and pesticides to maintain yields.

Soil organic matter creates healthy soils
Healthy, homegrown carrots in rich soil.

According to the United Nations Mil­lennium Assessment Report (MA Re­port) on the environment, there has been a dramatic increase in the amount of nitrogen fertilizers used and these are causing a range of problems.

Since 1960, flows of reactive nitrogen in terrestrial ecosystems have doubled, and flows of phosphorus have tripled. More than half of all the synthetic nitrogen fertilizer … ever used on the planet has been used since 1985.

Soluble nitrogen fertilizers from con­ventional farming systems are causing the eutrophication of freshwater and coastal marine ecosystems and acidification of freshwater and terrestrial ecosystems. These are regularly creating harmful algal blooms and leading to the formation of oxygen-depleted zones that kill animal and plant life. The dead zones in the Gulf of Mexico and parts of the Mediterranean are caused by this and other soluble nutri­ents from farming.

Biological Systems

The process of turning nitrogen in the air into plant-available forms occurs naturally in healthy soil systems through a multitude of microorganisms. This is called biological nitrogen fixation and is done by symbiotic organisms such as Rhizobium bacteria in legumes and free-living nitrogen-fixers: azobacters, cyano­bacters/blue green algae and countless thousands of other species of free-living nitrogen-fixers.

This process is strongly associated with the amount of soil organic matter (SOM). Stable soil organic matter will have carbon-to-nitrogen ratios between 11:1 to 9:1. Soil organic matter is the greatest store of soil nitrogen and most of this nitrogen is plant available.

Minute amounts of useable nitrogen can be fixed by electrical storms and be dissolved in the following rain. This is rarely enough for crop growth and in most areas with heavy or prolonged rain, if the soil has low levels of organic matter, most of these types of N will be leached out of the soil and into our river systems.

Biological fixation is the major source of plant-available nitrogen in natural soil systems.

The issue of soil organic matter and nitrogen continues to be largely ignored by most agronomists and this dates back to the 1840s when the father of synthetic fertilizers, Justus von Liebig, dismissed the roles of humus in plant nutrition.

Professor Albrecht’s Nitrogen Theory

Von Liebig was the first scientist to show that plant growth is dependent on adequate levels of nutrients in the form of ions — cations and anions and this formed the basis of modern agronomy with water-soluble synthetic fertilizers.

Emeritus Professor of Soils at the Uni­versity of Missouri Dr. William A. Al­brecht was the first soil scientist to show the importance of having all the soil minerals in a balanced ratio along with adequate levels of organic matter

Whereas Professor von Liebig felt that organic matter was not important and all necessary plant minerals could be sup­plied by soluble chemical fertilizers, Pro­fessor Albrecht wrote extensively on the importance of organic matter in acting as the primary source for plant nitrogen and as the buffer and storehouse of all the minerals that plants needed along with the importance of the correct soil biology to do this.

Albrecht strongly supported the con­cept of the soil as living body and the fundamental importance of organic mat­ter and soil biology in this process.

In the 1930s he wrote:

Decomposition by microorgan­isms within the soil is the reverse of the process represented by plant growth above the soil. Growing plants, using the energy of the sun, synthesize carbon, nitrogen, and all other elements into complex compounds. The energy stored up in these compounds is then used more or less completely by the mi­croorganisms whose activity within the soil makes nutrients available for a new generation of plants. Or­ganic matter thus supplies the “life of the soil” in the strictest sense. When measured in terms of carbon dioxide output, the soil is a live, ac­tive body. (Albrecht 1938)

Albrecht had science degrees in biol­ogy, agricultural science and botany. His life-long study was devoted to the roles of soil nutrients, soil organic matter and microbiology in producing high-yielding healthy crops. He was one of the first multidisciplinary scientists who took a whole systems approach to agriculture rather than a reductionist approach in the laboratory.

Albrecht also firmly established the link between plant health, particularly the role of soil mineral deficiencies, and the health of the animals and ultimately the humans who fed on the plants and ani­mals. He showed the direct link between poor-quality forage crops and the health of the stock that fed on it. For Albrecht soil health was the fundamental basis of crop health, good yields and animal and human health.

This clearly fits within the organic paradigm of building a healthy soil to grow a healthy plant, rather than the conventional farming paradigm of just adding the soluble nutrients for the plant to take up from the soil solution.

The two critical issues that Albrecht wrote about was to have soils that have adequate amounts of all the minerals that plants need and that these should be in the correct balance or ratios to achieve the highest yields.

While Albrecht wrote about calcium being the most important cation, his pa­pers on organic matter clearly state that nitrogen in the form of nitrate (an anion) is the nutrient that plants needed in the largest quantities, and insufficient nitro­gen was the one of the major limitations in yield.

In addition to carrying nitrogen, the nutrient demanded in largest amount by plants, soil organic mat­ter either supplies a major portion of the mineral elements from its own composition, or it functions to move them out of their insoluble, useless forms in the rock minerals into active forms within the col­loidal clay. Organic matter itself is predominantly of a colloidal form resembling that of clay, which is the main chemically active fraction of the soil. But it is about five times as effective as the clay in nutrient exchanges. Nitrogen, as the largest single item in plant growth, has been found to control crop-pro­duction levels, so that in the Corn Belt crop yields roughly parallel the content of organic matter in the soil. (Albrecht 1938)

Albrecht did his doctorate on soil ni­trogen and legumes and was an expert on the subject. In Albrecht’s writing the nitrate form of nitrogen is the most im­portant of all nutrients for plant growth.

Decades of research shows that nitrate anions, along with other anions, do not have many spaces in the soil where they can adsorb (stick) to be stored for later use by plants. Most of the electrostatic charges on the clay colloids are negatively charged. This means that that they will at­tract and store cations, however they will repel the negatively charged anions. This is one of the reasons why anions like ni­trate, sulfur and boron are readily leached from the soils with low levels of organic matter. The humus in organic matter has charged sites that will attract and store anions like nitrate. The majority of the nitrogen in the soil is stored on humus.

Albrecht’s research showed that soil organic matter is the most important source of nitrogen for plants. He wrote:

Soil organic matter is the source of nitrogen. In the later stages of decay of most kinds of organic mat­ter, nitrogen is liberated as ammonia and subsequently converted into the soluble or nitrate form. The level of crop production is often dependent on the capacity of the soil to pro­duce and accumulate this form of readily usable nitrogen. We can thus measure the activity that goes on in changing organic matter by mea­suring the nitrates. It is extremely desirable that this change be active and that high levels of nitrate be pro­vided in the soil during the growing season. (Albrecht 1938)

Albrecht was the first soil scientist to write widely on the relationship between nitrogen and soil organic matter and showing that the correct way to maintain sustainable fertility was to have farm­ing systems that recycled enough organic matter to have the quantities of nitrogen that are needed by the crop.

The other very important role for or­ganic matter that Albrecht wrote about was its buffering role. While Albrecht wrote widely about the need for the cor­rect percentages and ratio of available cations in soils, he also showed that ad­equate levels of organic matter would act as a buffer where the ratios were not exact and ensure that plants would receive the correct amounts of nutrients. The key was that there were no deficiencies and that there were adequate levels of all the nutrients that plants needed.

Equally important Albrecht showed that adequate levels of nitrogen, calci­um and other minerals were essential to building soil organic matter.

Bacterial activity does not oc­cur in the absence of the mineral elements, such as calcium, magne­sium, potassium, phosphorus, and others. These, as well as the nitro­gen, are important: Recent studies show that the rate of decomposi­tion is reduced when the soil is de­ficient in these elements. In virgin soils high in organic matter, these elements also are at a high level, and are reduced in available forms as the organic matter is exhausted. A decline in one is accompanied by a decline in the other.

It has recently been discov­ered that the fixation of nitrogen from the atmosphere by legumes is more effective where high levels of calcium are present in available form … Thus, if in calcium-laden soils, excellent legume growth re­sults and correspondingly large nitrogen additions are made, such soils may be expected to contain much organic matter. Liberal cal­cium supplies and liberal stocks of organic matter are inseparable. The restoration of the exhausted lime supply exerts an influence on building up the supply of organic matter in ways other than those commonly attributed to liming.

In the presence of lime (cal­cium) the legumes use other el­ements more effectively, such as phosphorus … and probably other nutrients. Thus heavier production results on soils rich in minerals, including more intensive and ex­tensive root development; the most effective means of introducing organic matter into the soil. The presence of large supplies of both organic matter and minerals points clearly to the fact that the soils were high in the latter when the former was produced. (Albrecht 1938)

Biology Fixes Nitrogen into the Soil

The most well-known form of biologi­cal fixation of N for plants is the Rhizo­bium bacteria that forms nodules in the roots of legumes and live symbiotically with them. The Rhizobium transform the N2 in the soil air into forms that plants can use. The legumes in exchange give the Rhizobium a home and glucose.

Researchers are continuing to find that there are an enormous number and types of symbiotic and free-living microorganism species that fix nitro­gen. Unfortunately most agronomy texts will only mention Rhizobium bacteria that live in symbiosis in the nodules of legumes. A few more will mention the free-living nitrogen-fixing organisms such as Azotobacter, Cyanobacteria, Ni­trosomas and Nitrobacter.

Many of these species live in the rhi­zosphere (the zone around plant roots) and help plants take up nitrogen from the soil. Very importantly they are finding that there are multiple species that work in symbiosis to achieve this.

Researchers are also finding new ni­trogen fixing species in the rhizospheres associated with most species including hostile environments like mangroves growing in seawater. Scientists from the Department of Microbiology, The Center for Biological Research in Mexico stated:

These findings indicate that (i) other species of rhizosphere bacte­ria, apart from the common diazo­trophic species, should be evalu­ated for their contribution to the nitrogen-fixation process in man­grove communities; and (ii) the nitrogen-fixing activity detected in the rhizosphere of mangrove plants is probably not the result of indi­vidual nitrogen-fixing strains, but the sum of interactions between members of the rhizosphere com­munity. (Holguin et al 1992)

The critical issue is that the majority of these species are associated with the or­ganic matter cycles of soils. Continuously building and maintaining soil organic matter is the key.

Amino Acids and Soil Nitrogen

A high percentage of the nitrogen in soil organic matter is in amino acid form. Amino acids are some of the most important building blocks of life because they are the basis of DNA, RNA, proteins, hormones and many of vital functions.

Plants generally synthesize the amino acids that they need by combining the nitrate form of nitrogen with the glucose sugar that they form through photosyn­thesis. This is why nitrate is so important.

Until recently scientists believed that plants rarely took up organic nitrogen in the form of amino acids. It was assumed these molecules were too big for roots to absorb. They believed that most of the amino acid nitrogen in the soil was not useful for plants unless it was trans­formed into nitrate.

An extensive body of published sci­ence is showing that amino acids are one of the most important forms of nitrogen, especially in natural systems such as for­ests where in some cases they can be the dominant form of nitrogen.

Scientists are challenging the tra­ditional view on organic nitrogen. Re­searchers from Griffith University in Aus­tralia wrote:

In recent years, there is increas­ing evidence that some plants are able to directly utilize and generally prefer amino acids over inorganic N (e.g. Schimel & Chapin 1996, Lipson & Monson 1998, Näsholm et al. 1998, Henry & Jefferies 2003, Weigelt et al. 2005). This challenges the traditional views of the ter­restrial N cycle that plants are not able to access the organic N directly without depending on microbial mineralization to produce inorgan­ic N and that plants cannot com­pete efficiently with soil microbes for uptake of nutrients from the soil. (Xu 2006)

Researchers are finding an increasing number of crops that readily take up large amounts of amino acids from the soil organic matter.

This emerging body of research is very important as it shows:

  • That the large pool of organic nitro­gen associated with organic matter is readily available to the crop.
  • That these forms of organic nitro­gen are very stable in the soil if or­ganic matter levels are maintained or increased.
  • And most importantly that the crop can access this organic nitrogen at the critical growth or seed produc­tion periods when they need large amounts of nitrogen.

Understanding the Ratios

It is important to get an understanding of the potential for how much nitrogen can be stored in the soil organic matter for the crop to use. Soil organic matter contains nitrogen expressed in a carbon-to-nitrogen ratio. This is usually between 11:1 to 9:1, however there can be further variations. The only way to firmly estab­lish the ratio for any soil is to do a soil test and measure the amounts.

For the sake of explaining the amount of organic nitrogen in the soil we will use a ratio of 10:1 to make the calculations easier.

The amount of carbon in soil organic matter is expressed as soil organic carbon (SOC) and is usually measured as the number of grams of carbon per kilogram of soil. Most texts will express this as a percentage of the soil to a certain depth.

There is an accepted approximation ratio for the amount of soil organic car­bon in soil organic matter. This is SOC × 1.72 = SOM.

The issue of working out the amount of SOC as a percentage of the soil by weight is quite complex as the specific density of the soil has to be factored in. This is because some types of soils are denser and therefore heavier than other soils. This will change the weight of car­bon as a percentage of the soil.

However for the sake of this article we will avoid the complex mathematics and to make these concepts readily under­standable we will use an average estima­tion developed by Dr. Christine Jones, one of Australia’s leading soil scientists and soil carbon specialists.

According to Dr. Jones:

… a 1% increase in organic car­bon in the top 20 cm [8 inches] of soil represents a 24 t/ha [24,000 kilograms] increase in soil OC…

Note that kilograms per hectare (kg/ha) is almost identical to pounds per acre. They are close enough so that people not familiar with the metric system can use the U.S. system and it is much the same.

This means that a soil with 1% SOC would contain 24,000 kilograms of car­bon per hectare. With a 10 to 1 carbon to nitrogen ratio this soil would contain 2,400 kilograms of organic nitrogen per hectare in the top 20 cm — which is around 2,400 pounds of organic nitrogen per acre in the top 8 inches of the soil.

Good management of soil organic matter means that the soil around the root layer of the crop will contain amounts of organic nitrogen. It con­tains tons and tons of nitrogen rather than the hundreds of pounds or kilo­grams that are recommended to be add­ed in most agronomy texts. This shows that there is no need for farmers to pay the huge cost to purchase the synthetic nitrogen produced by the Haber-Bosch process. Good farm management will mean that the farms can get considerably more crop-available nitrogen for free.

Building Up Total Soil Nitrogen

The key to increasing soil nitrogen is to increase soil carbon by increasing the SOM levels.

A typical soil is supposed to be 25 percent air, 25 percent water, 45 percent mineral and 5 percent soil organic matter.

The primary reason for good soil aeration is to get oxygen into the roots. Most plants acquire oxygen directly through their roots. What most experts forget is that air is 78 percent nitrogen in the form of the inert N2.

Biologically active soils continuously fix the N2 in the soil air into plant avail­able forms as well as build the total stores of organic N, provided that the systems are continuously fed with organic matter.

The key is the continuous supply of organic matter. How do you get it on to the farm? You grow it. Farm management should be about producing as much bio­mass as possible and avoiding bare earth.

Legumes should be incorporated as much as possible in all rotation systems in cropping and should be a permanent component in all perennial systems such as pastures and orchards.

The aim of the management systems should be to let cover crops get as tall as possible and as mature as possible. This not only produces more biomass on the surface, it ensures that the roots get deep into the soil depositing organic matter as they grow down.

The Importance of Mineral Balance

The efficient production and use of N requires the correct mineral balance. Some of the key nutrients to achieve this are calcium, phosphorus, sulfur, sele­nium, molybdenum and cobalt.

Molybdenum is essential for plants to turn the nitrate and glucose in the leaves into the amino acids — the basis of the proteins, hormones, DNA and other criti­cal components of life. It works as a cata­lyst and without it the plant can’t grow and reproduce (flower, fruit and seed).

Sulfur is critical as it is needed to form the key sulfur-based amino acids such as methionine and cysteine.

Selenium is also critical to forming the sulfur-based amino acids. An emerging body of research shows higher levels of these essential amino acids when soils have good levels of selenium.

Cobalt is needed to help the nitrogen-fixing micro-organisms make vitamin B12. Without it they cannot survive. Low levels of cobalt will significantly reduce the numbers of these organisms.

Calcium is critical to good legume growth and to healthy systems of soil microorganisms.

Phosphorus is very important as it is needed to power the activity of most cells — this includes the cells of the legumes, the cells of the Rhizobium bacteria that live in the root nodules of legumes and fix nitrogen as well the cells of the free-living nitrogen-fixing microorganisms.

Just adding organic matter may not al­ways be sufficient to achieve good results if it does not contain enough nutrients to correct deficiencies. Soil mineral balance is critical to optimizing the fixation of N in the soil and the use of that by the cash and cover crops.

Albrecht wrote about this in the 1930s:

It seems logical to ascribe caus­al significance to the minerals in the production of organic matter, whether or not they are effective in preserving it. If the soils that have lost their organic matter are to be restored, the loss of minerals, which has probably been fully as great, must be taken into account, and provision must be made to restore these mineral deficiencies before attempting to grow crops for the sake of adding organic matter. (Albrecht 1938)

Editor’s Note: André Leu first published this in the August 2012 issue of Acres U.S.A. magazine. Leu is the author of The Myths of Safe Pesticides.

The Eternal Search for Nitrogen

By Herwig Pommeresche
Excerpt from Humusphere

The biosphere contains a certain quantity of nitrogen in the form of organic (and generally living) compounds. According to Frederik Vester (1987), 200 billion tons of organic material are converted on and in the soil each year—as we shall see later, primarily through “eating and being eaten” processes in the form of the metabolism of living material.

This vast amount of organic material is the “waste” generated by the life processes that keep the biosphere running in all its variety. But it is also the nutrients for the following year’s life processes! In this “waste,” much of which is living (1–2 tons of living organisms per 1,000 square meters of uncontaminated agricultural soil), the much-coveted nitrogen is relatively firmly bound, by, for example, being built into the organic structures of protein molecules (among other substances).

This means that it cannot be washed out by the large quantities of water that are constantly flowing around it. Relevant to this issue are the findings of Virtanen, Schanderl, and Rusch, who showed that organic substances do not need to be reduced to inorganic ions in order to be absorbed by plants as nutrients once again.

Now let’s imagine an equal quantity of the synthetic, easily accessible nitrogen that we have put into circulation in the biosphere. For one thing, we have a very imprecise idea of what actually lives in the soil. Furthermore, we have essentially zero knowledge about which of the life-forms that aren’t known to us perish when we regularly apply large amounts of synthetically produced nitrogen salts.

On this subject, I will cite Gerhardt Preuschen from his Ackerbaulehre nach ökologischen Gesetzen—Das Handbuch für die neue Landwirtschaft (Agriculture According to Ecological Laws—The Handbook for the New Agriculture), written in 1991:

“For as long as people have believed that plants can subsist exclusively on water-soluble substances, they have understandably attempted to find these substances or compounds in the soil and to check the plants’ nutrient supply against an established amount, usually in a water-soluble state, and to classify them as signs of fertility. We know today that this theory was incorrect. Under very adverse conditions, plants can process water-soluble material, but they always need microbes to do so. This whole system of direct transfer of material into the plant’s body leads to diseases while at the same time damaging the life in the soil. To put it briefly—the entire mineral theory and the way that it has been applied was the wrong approach. We can also proceed on the assumption that the data used to determine actual fertility is unrelated and thus uninteresting, and in fact must sometimes be analyzed the opposite way (69).”

And he continues: “Free nitrates practically never appear in an undisturbed ecosystem. If this were not the case, rivers would have to have been carrying nitrates for centuries, and mountains of sediment would have formed in the seas and oceans, or they would contain some nitrate content. It is astonishing that scientists who want to be taken seriously continue to repeat the claim that nitrates are a natural component of the living soil and an important plant nutrient” (143).

Plants’ nitrogen supply is precisely regulated in nature. Because this aspect of plant nutrition is being ignored, we have an excess of easily soluble nitrogen compounds today.

Editor’s Note: This is an excerpt from the book Humusphere by Herwig Pommeresche. You can learn more or purchase this book at the Acres U.S.A. bookstore.
Front cover Humusphere book

About the Author

Herwig Pommeresche was born in Hamburg in 1938 and has lived in Norway since 1974. He received a degree in architecture from the University of Hanover. He has spent many years active as an architect and urban planner in Norway. After finishing his studies in architecture, he became a trained permaculture designer and teacher under the instruction of Professor Declan Kennedy.

Alongside other permaculture experts, he served as an organizer of the third International Permaculture Convergence in Scandinavia in 1993. He later served as a visiting lecturer at the University of Oslo. Today, Herwig Pommeresche is seen as a pillar of the Norwegian permaculture movement. He also serves as an author and a speaker.

Author Herwig Pommeresche
Herwig Pommeresche

Nitrogen: Organic vs. Synthetic

By John B. Marler

Organic nitrogen and inorganic nitrogen: what’s the difference?

Organic growers frequently attempt to quantify the amount of organic nitrogen they add to their soil ecosystems in the same manner that conventional growers use inorganic nitrogen units to calculate their nitrogen requirements. Logically, they reason that a ton of organic material with 4 percent nitrogen content as verified by a laboratory test will provide 80 pounds, or units by some determinations, of nitrogen.

The truth is that organic nitrogen sources vary in their efficiency of transformation into soil components over a much broader range of response than do inorganic synthetics, which offer precision measurement and a repeatable predictability of release. Use of inorganic nitrogen units to determine nitrogen needs for organic growers is therefore problematic. A popularly available and reliable conversion algorithm between tested inorganic nitrogen and untested organic nitrogen in organic soils does not exist, however. Without such an algorithm there can be no scientific basis of comparison.

plant organic humus fertilizer

Synthetic nitrogen

Synthetic, inorganic nitrogen sources are of a totally different nature than organic nitrogen. The term organic in this context should not be confused with its broader usage, as in “organic growing.”

Here, it refers to the carbon nature of its molecular structure. Inorganic nitrogen, found in nitrite, nitrate, and ammonium forms, does not have carbon in its molecule.

Synthetic, inorganic nitrogen is usually found dissolved or in a readily water soluble form. Due to the unstable nature of synthetic nitrogen, it easily volatilizes into the atmosphere or is lost in ground or surface water.

University and USDA studies have revealed that the nutrients from 50 to 82 percent of all inorganic synthetic nitrogen fertilizers are lost into the atmosphere or into surface or ground water. This alone would indicate that inorganic nitrogen unit rates are inflated to allow for the inefficiency of use.

If this is true, then out of 100 synthetic nitrogen units, only 50 — or perhaps as little as 18 — are actually used by plants. An organic farmer might reasonably calculate his nitrogen needs with the understanding that his plants need 50 percent less nitrogen than inorganic tables would indicate.

Organic Nitrogen

Organic nitrogen, on the other hand, is much more efficient in providing nitrogen nutrition than labile, inorganic sources. The efficiency of organic sources is illustrated by applications on turf on sand-based golf courses. The inorganic nitrogen nutrients, which may range from 8 to 16 percent inorganic nitrogen, must be applied every 30 to 45 days to maintain an acceptable level of dark-green color.

By contrast, only two applications of 4-4-4 organic fertilizers per year, in spring and fall, will maintain a deeper and healthier green. In our research at the University of Florida, 100 percent organic 4-4-4 fertilizer outperformed 8-5-5 fertilizer that contained both organic and inorganic nitrogen.

What are the levels of efficiency of organic nitrogen in plant growth when compared to inorganic nitrogen? We are not sure. However, we can again turn to the turf industry for comparisons. We do know that more intensively groomed golf courses typically use four to eight applications of inorganic nitrogen per year, compared to two applications a year for low-nitrogen-level organic nitrogen.

That would indicate a 200 to 400 percent greater level of effectiveness for high-efficiency organic fertilizers.

We are aware of one golf course that attempted to apply organic nitrogen sources at the same rate as inorganic fertilizer. The result was that the course developed such a thick turf that the grass could not be mowed.

We also have repeatedly seen, in hundreds of reported applications, acceleration of growth in field crops, orchards and vineyards that would indicate that efficient low-nitrogen-content organic fertilizers can deliver adequate nitrogen to grow a superior crop and still leave high levels of measurable inorganic nitrogen in the soil after the crop is harvested. This was illustrated by inorganic testing by a major California grower that indicated that even after a broccoli crop — known for its high nitrogen demands — was harvested, there was almost enough inorganic nitrogen in the soil to grow a second crop.

The Nitrogen Cycle theory

Compounding the problem of attempting to measure organic nitrogen in inorganic units is the fact that plants seem to be more inclined to use organic nitrogen than inorganic. In spite of “known facts,” researchers, after an intensive study in remote, pollution-free forests, have recently determined that the major source of nitrogen in a pristine area is actually organic nitrogen.

For soil science this was an earthshaking revelation. The “fact” that inorganic nitrogen is the only plant-usable form has been taught in our universities for at least a century.

Early soil scientists drew samples of what they thought was soil-leaked nitrogen from streams and lakes near urban areas. These sources were actually polluted by human consumption of hydrocarbon-based fuels, including coal and wood.

In North American polluted surface waters, only about 2 percent of leaked nitrogen was determined to be organic, while about 70 percent of the tested nitrogen was inorganic in nature. North American field testing supported European science that was seen to confirm the theory that plants can only use inorganic nitrogen. Slowly, that flawed field science developed into what we now know as the “Nitrogen Cycle.”

nitrogen cycle
The nitrogen cycle.

That longstanding theory was called into question, however, when very low levels of inorganic nitrogen, about 5 percent, were found in water sources in pristine areas. This new research suggests that plants have to efficiently use organic nitrogen — otherwise those pristine forests would not exist. Those of us who were taught the “Nitrogen Cycle” are now faced with learning new principles and revisiting our concepts of what forms of nutrition plants can use.

From our own research, and the research of others, we believe that the soil functions by building small sources of nitrogen, both inorganic and organic, using a wide range of mechanisms. Most of these mechanisms are microbiological factors that don’t seem to add up to much until measured together as a whole.

An example is the transformation of bacteria into nitrogen. Within a short time after the application of an organic food source that meets a bacterium’s needs, there is a massive explosion of the population of bacteria, followed shortly by an equally massive explosion of a population of beneficial nematodes that feed on the bacteria. Some microbiologists, such as Elaine and Russ Ingham, have suggested that a soil count of these nematodes offers a good means of determining the value of soil nutrition.

With a short life cycle — measured in days or maybe a week or two — beneficial nematodes will bloom within a soil in response to the increase in their food source. As they live, reproduce, and die, they leave behind elevated levels of nitrogen (most microbes have about 17 percent nitrogen content in their bodies). The result of these short life cycles is an increase in both organic and inorganic nitrogen.

This mechanism, along with many others that naturally add small incremental additions of nitrogen and other soil nutrients, occurs within organic soils only when the soils get the proper nutrition. Availability and application of soil minerals, including some aspects of the fixing of organic nitrogen in the soil, are often conditioned upon the presence of other soil minerals.

The Nitrogen Dilemma

An organic grower armed with this new information is faced with a dilemma. Some agronomists will no doubt continue to argue that the system of testing and application for synthetic, inorganic nitrogen is still applicable in conventional growing programs. That argument has real merit, given that their current science is based on the testing of inorganic nitrogen.

Arguing the validity of using synthetic inorganic testing and measurement programs for organic growing is another matter. If a grower is working to build up organic soils, which rely on organic nitrogen, then why test and measure inorganic nitrogen? There is no doubt that there is a correlation between inorganic levels and organic levels. Inorganic nitrogen transformations from organic nitrogen occur continually. Inorganic nitrogen is present in all organic soils. However, the primary standard toward which organic growers should work is the establishment of long-term, slow and steady organic nitrogen sources, not transient inorganic nitrogen.

Instead of focusing on short-term inorganic nitrogen sources like their conventional growing cousins, organic growers should concentrate on building up organic nitrogen sources in the form of soil acid gels in their soils. Any source of organic matter will, sooner or later, become a soil acid after it has deteriorated into the soil. As the soil acid absorbs moisture it becomes a soil acid gel. However, not all soil acids are equal in nature. Soil acids are widely varied as to the complexity of their molecular structure and their value to plants. The chelated (elements with carbon bonds, usually in the form of amino acids) nutrients that are available to the soil acid at the time of formation will become an immediate part of its molecular structure. For example, if chelated nitrogen and copper are available, then nitrogen and copper will become part of the soil acid molecular structure. The more complex molecular structures are the result of complex organic nutrition sources available at the time of molecule construction.

In the formation of organic nutrients, the old adage of “garbage in, garbage out” holds true. Higher-quality organic forms are much more efficient at transformation into soil acids with more complex nutrient structures. A ton of green leaves obviously has more overall organic nutritional value than a ton of dried, partially deteriorated leaves. A ton of “hot,” or nutritionally loaded, fresh chicken manure obviously has more nutrients than a ton of “cold” or aged chicken manure.

Neal Kinsey, Compost & Manure Analysis, from the 2005 Eco-Ag Conference & Trade Show. (50 minutes, 39 seconds.) Listen to Neal Kinsey’s helpful lecture on how to test compost and manure, to ensure those inputs are balancing your crops and soil.

That said, the hot manure may actually be a less efficient transformer than the cold manure due to its labile nature. While a snapshot, in the form of a laboratory test, of the inorganic nitrogen content is often possible, that test can quickly be rendered invalid by a hot drying wind or hindered by a cold snap that slows or stops nutrient transformation from the soil into soil acids. Bacteria content and the nature of the bacteria, pH, the chelated nature of the material, carbon content (such as animal bedding materials) presence of animal treatment materials (such as arsenic and antibiotics) size of the material, and internal temperature are all factors that can affect the amount of nutrients available for use by plants. Ambient temperature, sunlight, and wind are also large factors. Manure that is surface applied without soil cover can lose 25 percent of its nutrients in a single 24-hour period on a sunny, windy day.

The efficiency of transformation, which is a measurement of how efficient a decomposing organic is transformed into valued complex soil acid gels, is the single most important aspect involved in adding organic materials to a soil. Organic growers should focus on the efficiency of transformation of all organic nutrient supplements they add to their soils. Mineral and nutrient rich organic material that is slow release is of much greater value than that of a labile nutrient that volatilizes into the air and water around it. We have been in fields thick with the smell of releasing ammonia. Such a smell indicates a failure of the grower to capture the full nutrients from the organic material he has applied. Typically, the efficiency of transformation in a field that has the distinct smell of manure is low. High efficiency organic fertilizers have little or no smell after application.

While organic growers may benefit from knowing the levels of inorganic nitrogen in the soil, this measurement alone is almost insignificant when compared to the question of how much organic nitrogen is in the soil. The only reasonable means of measurement at this time is inference based on fulvic and humic acid levels in the soil. These tests are significant since they reflect the true nature of soil carbon and are reliable indicators of available soil nutrients.

Editor’s Note: This article was originally published in the July 2006 issue of Acres U.S.A.

Carbon-Nitrogen Ratio: Understanding Chemical Elements in Organic Matter

By Crow Miller

Carbon-nitrogen ratios are an important part of understanding soil.

There are two chemical elements in organic matter that are extremely important, especially in their relation or proportion to each other: they are carbon and nitrogen. This relationship is called the carbon-nitrogen ratio. To understand what this relationship is, suppose a certain batch of organic matter is made up of 40 percent carbon and 2 percent nitrogen. Dividing 40 by 2, one gets 20. The carbon-nitrogen ratio of this material is then 20 to 1, which means 20 times as much carbon as nitrogen. Suppose another specimen has 35 percent carbon and 5 percent nitrogen. The carbon-nitrogen ratio of this material then would be 7 to 1. Anyone who handles organic matter, who mulches, or who composts, regardless of which method is used, should have some idea about the significance of the carbon-nitrogen ratio.

Carbon is important because it is an energy-producing factor, and nitrogen, because it builds tissue. We are familiar with carbon in the form of charcoal. In that form it is practically pure carbon. A diamond is another form of pure carbon. In a plant it takes an entirely different form. Limestone is usually over 90 percent calcium carbonate (CaCo3), a compound made up of two partners — calcium and carbon. If you eat a radish or take bicarbonate of soda, you are consuming carbon.

So you can see how widely distributed carbon is. It can be a gas, an acid or other form of compound. I need not say much about nitrogen here; it is a term with which every grower is familiar with. A certain amount of is essential for plant health. Too much is undesirable. When organic matter decays, the carbon is dissipated more rapidly than the nitrogen, thus bringing down the carbon-nitrogen ratio.

Adding compost or other nutrients to soil can help you find the right carbon-nitrogen ratios.
Adding compost or other nutrients can help you find the right carbon-nitrogen ratios.
Andre Leu, Soil Carbon, from the 2007 Eco-Ag Conference & Trade Show. (53 minutes, 44 seconds). Listen in as Leu, the director of Regeneration International, teaches how to store and repurpose carbon in your soil.

Before I go further and cover the significance of this ratio, we should first look at some figures, examples of typical materials and their specific carbon-nitrogen ratios:

  • Alfalfa hay — 12:1
  • Composted Manure — 20:1
  • Cornstalks — 60:1
  • Straw — 80:1
  • Sawdust — 400:1

Note the high carbon-nitrogen ratio of sawdust. Such a material would be considered highly carbonaceous, and has a very low nitrogen content. If much of it is put into the soil, there would not be enough nitrogen, the food of bacteria and fungi, which aid in the function of decomposition. They would thus have to consume soil and create a deficiency of nitrogen, thereby depressing the crop yield. The eco-grower who applies organic matter must be conversant with the carbon-nitrogen ratio of the different materials they handle. Generally speaking, the legumes are highest in nitrogen and have a low carbon-nitrogen ratio, which is a highly desirable condition.

There is a difference between the carbon-nitrogen ratio of raw organic matter and that of humus. The nitrogen in a leaf may be only 1 percent, but by the time it turns to humus, the percentage of nitrogen of that more or less refined substance would be about 5 percent. The average nitrogen content of practically all humus is about 5 percent, but in organic matter it fluctuates considerably.

With carbon, however, a different condition exists. While decomposing organic matter loses large amounts of carbon as it turns to humus, the percentage of it to the total mass does not seem to go up or down considerably. If you begin with rotted manure that has a 40 percent carbon and 2 percent nitrogen content (which represents a carbon-nitrogen ratio of 20:1), you may wind up with a 10-to-1 ratio when it turns to humus — that is, a 50 percent carbon and a 5 percent nitrogen content. There is always a narrowing down of the carbon-nitrogen ratio when organic matter decomposes. The content of carbon in humus does not vary much. It averages about 50 to 53 percent.

Neal Kinsey, Using Soil Analysis to Grow Crops, from the 2005 Eco-Ag Conference & Trade Show. (50 minutes, 12 seconds). Listen in as agronomist Neal Kinsey, the author of Hands-On Agronomy, teaches about how to test your soils, and use that data, to increase crop yield and decrease weed pressures.

We have seen that raw organic matter has a higher carbon-nitrogen ratio than humus or of the average soil. Now, as we study the of the microorganisms of the soil, we find there a much lower level than in the organic matter humus or soil. The average carbon-nitrogen ratio of the bodies of bacteria and fungi falls between 4:1 to 10:1. Why is their carbon-nitrogen ratio always less than the humus in which they work? The answer is that they require more protein than carbohydrates. Protein is needed primarily for tissue building, while carbon of carbohydrates is for energy.

Humus is made up to a great extent of lignins and other high-carbon material. Or in other words, humus has more carbohydrates than the bodies of microbes, which are extremely high in protein. Since about 16 percent of protein is nitrogen, we can see that the microbes bodies will have a very high proportion of nitrogen to carbon. Usually the tissues of bacteria are richer in protein than fungi.

Carbon-Nitrogen Ratios Affected by Inputs

When a lot of raw organic matter is applied to a soil, the microorganisms will multiply rapidly, but in the process of working they have to consume nitrogen. That is an absolute necessity to their existence. If the material that is tilled under has a low carbon-nitrogen ratio (that is, it is low in nitrogen), the soil organisms decomposing it will have to look for their nitrogen in places other than in the decomposing substances. They will draw on the soil’s store of nitrogen, thus depleting it, with a depressing effect on the crop yield. But their bodies, now gorged with nitrogen, will die or be consumed by other predators and thus return the element to the soil. This shows that when tilling under highly carbonaceous organic matter, a sufficient period of time should elapse before the crop is planted. It will give the soil organisms time to pass on their nitrogen caches. Also, one should try to use organic materials with a low carbon-nitrogen ratio, which means a high nitrogen content.

We discovered that where the carbon-nitrogen ratio of added organic matter tilled under was 33:1 or more, a withdrawal of nitrogen occurred. Between 17-33 to one nitrogen, nothing was added or withdrawn; in other words, nitrification ceased. But if the ratio was under 17 to one, the nitrogen store of the soil was increased. This shows the value of adding compost to the soil, because its carbon-nitrogen ratio is usually quite low.

When tilling under organic matter with a high carbon-nitrogen ratio, the best practice is to apply with it a high-nitrogen fertilizer. The eco-organic grower can use for such purposes blood meal, bone meal, composted poultry manure, cottonseed meal, fish meal, feather meal and soybean meal, as well as a number of other organic materials having a high-nitrogen content. Such nitrogen-rich materials will speed decomposition and prevent the temporary nitrogen drain.

We found that earthworms feeding on oat straw composted with fish meal yielded a carbon-nitrogen ratio from 23 to 11 during a period of two years, while the soil microorganisms alone reduced it to about 18 during the same period. This means that the earthworm is an even more efficient user of nitrogen than microorganisms.

We’ve seen that the carbon-nitrogen ratio of tilled under organic matter is important to the conservation of the soil’s store of nitrogen. It is also important to the general operation of soils. Mainly, it is a matter of having enough nitrogen available. There is a difference in the way a low carbon-nitrogen ratio works, depending on whether it is raw organic matter or humus.

We’ve discussed the dynamic action of organic matter and showed that organic matter applied to the soil represents nitrogen on the move. In a finished compost, it is in a more static condition. Less is given off. In terms of the carbon-nitrogen ratio, we can express it in the following manner. In the application of raw organic matter, the extent of nitrogen movement depends on its carbon-nitrogen ratio. If it is high, as in sawdust, there will be no movement. But if it is a material like young sweet clover (12:1), there will be a very satisfactory rate of nitrification.

In humus, however, although the carbon-nitrogen ratio is low, let us say 10:1, there is a resistance to rapid decomposition. The movement is slower and will take place over a longer period of time. This is of some value as it means the nitrogen is stored for future use. In the case of fresh organic matter with a low carbon-nitrogen ratio, not only is there a fast movement, but much carbon is given off in the form of carbon dioxide. Many entomologists believe this may kill off some of the larvae of destructive insects.

As rainfall goes down, the carbon-nitrogen ratio also declines. The higher the rainfall, the lower the nitrogen. The carbon-nitrogen ratio of arid soils is always lower than those in regions of higher precipitation.

In a soil which had a rainfall of 15 inches per annum, the carbon-nitrogen ratio was 13:1. Where it was 10 inches or less of rain, the carbon-nitrogen ratio was about 11:1. It has also been found that the higher the temperature, the lower the carbon-nitrogen ratio. So in general, higher rainfall means a higher carbon-nitrogen ratio; higher temperature tends to lower the carbon-nitrogen ratios; and higher acidity raises the carbon-nitrogen ratio.

The carbon-nitrogen ratio of the soil humus remains almost unaffected by the addition of chemical nitrogen fertilizer. The application of organic matter that is high in nitrogen is necessary for the continuous accumulation of humus. Comparative studies of the carbon-nitrogen ratios of organic versus chemically managed soils is scant, though there is room here for future research.

Editor’s Note: This article was originally published in the April 2000 issue of Acres U.S.A. magazine.