Tools of the Trade — Using Refractometers & Penetrometers

By Gary Digiuseppe

Forage producers can measure the percentage of sucrose and other soluble content of their grasses with the use of a refractometer, although the accuracy of the reading can be dependent on the cost of the instrument.

Martin Capewell, owner of Agriculture Solutions LLC in Strong, Maine, says an analog refractometer costs around $50-$200, while a digital model can run anywhere from $190- $10,000. A “simple, hand held, decent” digital refractometer, Capewell says, costs about $350 and will last a long time provided it’s properly cleaned and maintained and protected from extreme temperatures.

All refractometers work by passing light through sap or juice extracted from a crop, and then measuring the angle of the light as refracted by a prism. The readout, a percentage of soluble content, is called Brix, named for one of the originators of the method, Adolf Brix. The Brix reading is determined by where the line produced by the light refraction crosses the scale on the device. Technically, Brix is the percentage by weight of sucrose in a solution, but the refractometer can’t differentiate between sucrose and other dissolved solids.

The scale is calibrated relative to a temperature of 20°C, and Capewell says refractometers are either temperature compensated or non-temperature compensated. “The great thing about one with automatic temperature compensation is that it gives you the correct Brix reading, and you don’t have to do that formula yourself,” he says.

pentrometer in use in field

An analog refractometer has to be held up to a light source to be read; digital models use an internal light source. “When you click the ‘measure’ button, within about 3 seconds you can get an exact reading to one decimal place,” said Capewell. “It’s much more accurate, quicker and easier to use.”

In order to extract a sample for measurement by the refractometer, the farmer crushes several blades of grass in a vice grip or garlic press that should have a filter so the crusher will not push the solid material through the holes.

Cheryl Pike of Pike Agri-Lab Supplies in Jay, Maine, says there are devices specially designed to squeeze juices out of plants or fruit for sampling purposes. If a garlic press is used, it should be sturdy and made from stainless steel. “Most of the cheaper garlic presses won’t stand up to it, especially if you’re talking about pasture and trying to get the juice from grasses.”

Pike says most recommendations for an acceptable Brix reading are at 12 or higher. “The higher you have that number, it’s going to be a higher quality grass,” she said. “There have been studies showing the feed quality values matching the Brix reading. They are positively correlated — as one goes up, the other goes up.” Some studies indicate higher sucrose levels in pasture grass increase a ruminant animal’s conversion rate of feed to milk.

Temperature is just one of four variables that affect the reading. Concentration of dissolved solids, the atomic weight of the substances in the liquid and the number of covalent bonds, which are higher when components like amino acids and proteins are present also play a part. However, the farmer just needs to know if the meter is temperature compensated and to adjust for temperature if it’s not.

“If you have a very watery substance, it would read lower than something that has a lot of solids dissolved in the liquid,” said Pike.

In short, says Pike, “The more nutrition you have in your juice, the higher the reading will be … the more complex, and the more desirable things that are in our vegetables, fruits and grasses are the things that make the reading go higher.”

To ensure an accurate readout, Pike cautions that some inexpensive instruments they tested from overseas suppliers were not very accurate. “You get what you pay for.”


Another popular tool for farmers is the penetrometer, which measures resistance in soils. In addition to providing farmers with an idea of the tilth and oxygen content of soil, Capewell says it can also be used to determine the depth of the hardpan layer, so the producer can tell how much room a plant’s roots will have to grow.

He says in order to operate the penetrometer, push it into the soil at a constant rate while keeping an eye on the dial that shows how much resistance it is facing. “It might go up to 200 pounds per square inch (psi),” he said. “You’ll know that you’ve got oxygenation as you’re pushing it in, and you’ll certainly hear it go ‘thud’ as you’re hitting a harder layer. You can continue to push it past that point to see how hard it is to push through that, too, but when you hear it go ‘thud’ you can mark on the penetrometer where it met the harder layer, and you can see how deep your topsoil is and how good the tilth is.”

Penetrometers start at $250 with digital models being more expensive. They’re made of stainless steel and should last a number of years, but the tips may need replacing if they’re used very frequently. Capewell explains, “If you’re pushing into something all the time, you may hit rocks, and it may get blunted over time” which would affect the measurement. Luckily, the tips are inexpensive to replace.

Pike adds that plants do not perform well on ground where 300 psi or higher is required to push through the soil. The penetrometer produced by her company has marks along the length of the probe every 3 inches so the operator can record the depth at which the 200 psi, 300 psi mark, or hardpan is reached.

Finding the hardpan would be useful in a situation where the ground has been plowed. She says when that layer has been detected, “People are using different treatments, not necessarily just the plowing, that are supposed to either lighten up the soil or alleviate hardpans.” The penetrometer can be used before and after to gauge the efficacy of those treatments.

Editor’s Note: This article appears in the August 2014 issue of Acres U.S.A.

How To Select Your Soil Lab

By Susan Shaner

Soil lab selection: How does anyone choose the right laboratory? Aren’t they all the same? Should you send a sample to several different labs and average the results? How do you get the samples to a lab and what is the turnaround time? Some homework needs to be done here.

These are all questions that I hear on almost a daily basis. All labs are not the same. This does not mean that one laboratory is better than another. They all provide a different “menu” of services. It is important to find a lab that provides all of the services that you require. Are you just looking for a soil analysis, or do you also need an irrigation water test or tissue analysis?

Laboratories can also choose from a number of methods or “recipes” to obtain results. Which method would be best for your soil type or crop? “Presentation” of results can also vary greatly from one laboratory to another. It is important that you can read the report and make use of the information it provides. These are all questions that you should consider before choosing a laboratory.

Menu of Services

Packages with various soil parameters are usually available, plus some a la carte choices. This will vary greatly from one laboratory to another. I think we all agree now that there is a lot more to soil than pH. Therefore, look at what is included in the soil package you are requesting.

soil sample

Important parameters include pH, organic matter, exchange capacity and base saturation. Also important are the major elements calcium, magnesium, potassium, sodium and phosphorus.

Important minor elements include sulfur, boron, iron, manganese, copper, zinc and aluminum. A complete soil analysis including all of these parameters may cost a little more. More information will provide better insight into your fertility situation. If you base your decision on cost alone, you will probably get what you pay for. An inexpensive analysis may only include pH, phosphorus and potassium.


Methodology is the most confusing area when comparing laboratories. There are several different methods for almost every parameter on a soil analysis. Laboratories choose methods that are best suited for the geographical area that they service. Most labs will offer different methods upon request to accommodate most customers; you will have to know what to request first.

Sending the same sample to several labs for comparison will be quite confusing unless you do your homework to determine what methods are used. I have talked with several customers after they have submitted the same sample to different labs without understanding the differences.

They have been very unhappy and disappointed with the outcome. Let’s look at a good example of different methods — for example, phosphorus. There are nine phosphorus test methods that I am aware of. All of these methods were run on a specific soil sample and produced results anywhere from 10.5 to 656 ppm. If you know how to interpret the results for each of these tests, you should come up with the same recommendation. If you do not have the correct threshold levels for the method provided, you could make a big mistake in interpretation.

Presentation of Data

What units of measure do you feel comfortable with? Do you prefer graphic results, high and low distinctions or an actual value found?

Soil reports come in all shapes and sizes. Some reports are very colorful and show your results in a graphic form. Various reports show values as low, adequate, or high. A number of reports show actual values found for each parameter. Reporting styles also vary regarding the reporting of desired levels, sufficiency levels and base saturation percentages. What style are you most comfortable with? A combination of these styles may be most helpful.

Units of measure can vary from parts per million, pounds per acre, pounds per 1,000 square feet, or kilograms per hectare.

It is very important that the laboratory is aware of your sampling depth if you will be receiving your results in a pound per acre or pound per 1,000 square feet format. The sampling depth will affect the value reported. It is vital to be aware of units when comparing reports from different laboratories. You have to compare apples to apples. Looking at a phosphorus example again will explain this. A laboratory may report phosphorus at 50 ppm P and another may report it at 229 pounds per acre P2O5. These two results are the same; however the units are the difference.

Does the soil report offer a recommendation? Where did it come from? Some recommendations are generic computer recommendations that give a ballpark range for optimum levels of nutrients. These may or may not be for a specific geographical area. If you are growing a unique or exotic crop, then you may need some specific advice. Inquire about the services of an independent agronomist.


How do you get your sample to the lab? Most labs will provide a soil sample bag or suggest a suitable alternative. Soil laboratories receive hundreds of samples each day. Be sure to acquire the appropriate paperwork from the laboratory to submit with your sample. Incomplete information will only delay the processing of your samples. Packing your samples for shipment is very important. Be sure to pack the samples tightly in a box. Pack newspaper or other packing material around the samples to keep them from bouncing around in the box.

If samples can move around during shipment, they sometimes break open and can be destroyed. Resampling will add to your cost in time and money.

How long will this process take? Turnaround time in the whole soil testing process is imperative. Laboratories under stand that your test results can be time sensitive. Don’t hesitate to contact the lab if you have an emergency situation and need “rush” service. To determine your approximate turnaround time, consider the time it takes to get the sample to the lab (two-three days) and perform the analysis (three-four days).

Turnaround time varies from one lab to another and also varies by season. You may want to contact the lab to inquire about their current turnaround time. How do you get your report? You do not want the report held up somewhere after you have already waited through shipping and testing procedures. Reports are usually emailed or made available on the internet on the same day the testing is completed. Be sure your correct email address and/or a fax number is submitted with your samples to get your results as soon as possible.

This is just the tip of the iceberg when looking at differences in laboratories. Laboratory instrumentation is continually improving. More parameters can be detected in a short amount of time and detection limits keep getting smaller. More efficient and “green” procedures are always being investigated.

Embrace the advancements. Visionaries like Dr. Albrecht are still being cited in soil analysis circles. If he was continuing his research today, I believe he would embrace the latest technology and tools available.

So, the question still looms … which laboratory is best for you? Take the time to do your homework. It will be worth the investment and you will receive the value that you expect. Explore laboratory websites, call a lab and ask some questions, ask your friends about their experiences. Make sure you acquire the appropriate paperwork and instructions from the lab that you choose.

When you have selected a laboratory that meets your needs and you are comfortable, stick with it. Jumping from lab to lab will only discourage you on your quest to improving soil fertility.

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

Plant Stress & Proline

By Larry Zibilske, Ph.D. 

In his 1995 State of the Union speech, President Bill Clinton highlighted a USDA program addressing plant stress as an example of wasteful “pet project” government spending. We knew then, and know even more now, that plant stress is a very significant yield-and-quality-robbing factor in agricultural crops to which little attention has been paid.

We try to optimize fertility, irrigation, weed and pest management practices to achieve the best production under the constraints of environment and economics. However, it has become clear that plant stress comes from everything we try to control; it is additive and it can be cumulative — resulting in loss of yield and quality potential.

For the grower, visual detection of plant stress often comes too late to do anything more than damage control by preventing further loss of yields and quality for the season. One visually obvious “too late” example is dropped squares and bolls in cotton. Another is shed flowers and pods or a predominance of two and three-bean pods in soybeans if stress is present early on, or empty pods if stress occurs later.

In plant health, as in human health, there are signs, although they may not be obvious, that stress is present. The trick is in detecting and interpreting those signs – ideally, before they can be seen. This is evidenced by many of us having annual physical check-ups and blood (in the case of plants, sap) tests to detect “hidden” problems. Certain biological signals accumulate in the plant during periods of stress. They are produced in response to environmental stresses such as water, light, temperature and salinity. Their appearance signals that something is hindering normal plant growth and development with consequent loss of yields and quality.

Test tubes in a row of plant proline samples
Samples ready for instrument analysis. Even without precision and absolute instrument analysis, comparative differences in proline (plant stress) levels can be clearly seen.

One of the common stress molecules in plants is proline. Proline is an amino acid normally produced during protein production. In times of stress, plants over-produce this molecule which can be measured with whole leaf analysis. Elevated proline indicates stress responses have been initiated by the plant. The excess proline stimulates metabolic changes in the plant to cope with the stress.

However, proline is not only a signal but also directly helps maintain internal cell turgor, preventing electrolyte losses by supporting good osmotic balance. Proline also reduces the undesirable reactive oxygen species molecules (ROS) which, in times of stress, can overcome the natural ability of plants to dispose of these harmful molecules that are normally produced during metabolism.

Good crop nutrition is fundamental to warding off harmful effects of environmental stresses. Therefore, proline is both a plant stress response and a signal. Increased proline production allows a plant to marshal its physiology to accommodate the stress. But generally, the internal changes the plant makes to manage stress reduce its productivity in favor of survival advantage.

In short, high proline values are simply symptoms of larger problems in the plant. The primary use of the proline data is to formulate a plan to ameliorate or manage the stresses causing the proline response. With high proline, the plant is telling us that something is wrong.

stressed plants in the field
A dramatic field example of extreme plant stress resulting in unusually high proline levels, with the leaves on these sugar beets having collapsed. While this is a remarkable situation, the point of proline testing is to prevent unplanned crop performance-robbing stresses long before they happen.

We don’t want to eliminate stress, but control it so that the plant can continue to grow and produce well during the season. Elimination of stress is not a goal because the plant uses certain stresses as timing functions for several important metabolic processes.

While the overall concern is in reducing chronic or unanticipated stresses, there are certain conditions during crop development under which induced and carefully controlled plant stress can be of great financial benefit to the grower: Scheduled and managed stress can result in higher nutrient content of the crop (premium quality), greater yields, or both. This is demonstrated by field results.

healthy sugar beet leaves
For comparison, healthy sugar beet leaves.

Accordingly, the goal is not to minimize stress across the board throughout the season, but to carefully time the inducement, control and manage it.

Regardless, carefully managing overall stress responses during growth promotes better total plant performance. Your lab’s in-season recommendations will include steps to minimize destructive unplanned stresses and manage desired ones detected by increased proline production. As an example, for a low-moisture stress, the lab may recommend increasing potassium fertility to increase internal water use efficiency. Additionally, based on other plant tests, other nutrients may be recommended to maintain canopy structure and function and to reduce or eliminate disease and insect pressures.

The plant lab uses the proline test to monitor total stress in crop plants. If stress levels are high, the results, together with sap and tissue nutrient test results, guide the lab in prescribing changes to your management that will control those stresses. Remember, elevated proline levels indicate stresses that are most often caused by multiple factors. Your lab will consider those factors to formulate a complete remediation plan that addresses all stresses.

Proline may have other effects on plants as well. Collection of proline data has been ongoing for some time. Differences have been seen between reproductive tissues from stressed plants and those of low-stress plants. Therefore, if you hold seeds, tubers or bulbs over to plant yourself or sell them for planting, controlling stresses may influence future crops as well. These effects continue to be evaluated.

Editor’s Note: This article appeared in the December 2018 issue of Acres U.S.A. magazine.

Larry Zibilske, Ph.D., is vice president of research at TPS Lab in Edinburg, Texas. Zibilske holds degrees in microbiology and soil science from Texas A&M and a Ph.D. in soil microbiology from the University of Missouri-Columbia.

Acres U.S.A. magazine is the national journal of sustainable agriculture, standing virtually alone with a real track record — over 45 years of continuous publication. Each issue is packed full of information eco-consultants regularly charge top dollar for. You’ll be kept up-to-date on all of the news that affects agriculture — regulations, discoveries, research updates, organic certification issues, and more.

The Basics of Identifying Crop Quality

By Arden B. Andersen

Field trips in agriculture often are more like dog and pony shows than extended classroom experiences. Typically, the circulating tour group is paraded around at a distance, being shown various test plots, tillage systems, and management practices. One very important group experience that is rarely included in traditional field tours is the evaluation of crops, weeds, and soils in a hands-on manner in the field. Keen observation of field and crop details can tell the observer more than any soil or plant-tissue analysis. This is a key point because the farmer and consultant must take note of field observations to determine whether progress is being made and whether soil and plant-tissue tests are providing accurate pictures of the situation.

The Field Trip

Upon approaching any field, notice the overall appearance of the crop. Is it droopy? Rigid? Does it smell fresh? Are there any peculiar odors like methane gas, mold, ammonia, or pesticide? Is the overall color of the crop a deep blue-green? A mild-green or pale-green color? Do the leaves have a glossy sheen or a typical absorbent appearance? Are any birds nearby? Are they singing? How does the field feel to you? In other words, what sense do you get about the field?

As you move into the field, notice what types of weeds are growing and whether they or the crops are being eaten by insects. Ask whether a herbicide was used to control weeds and what type of weeds are most bothersome. Check the refractometer reading of both the weeds and the crop; write down the value of each. As the soil improves, the weeds will decline and the crop will increase in brix readings. Pull some weeds and slice open their stems lengthwise with a knife. Look at the pith of the weed. What color is it? Is the stem hollow? The healthier the weed, the higher the brix reading, the more solid the stem and the more pearly white its pith, and the less insect damage it will have. The same, of course, holds true for the crop. The healthier the weed, the more conducive your fertilization practices are to growing weeds rather than crops unless weeds (herbs) are your crop.

Notice what type of root structure the weed has. Grasses often have shallow, dense root systems that are attempting to loosen compact soil. Broadleaf plant generally have long taproots that are attempting to relieve hardpans and gain access to nutrient reserves at lower depths in the soil, as well as to extend the electrical circuit of the soil/plant complex to greater depths.


Dig up a corn plant. Notice the amount of root mass present and in which direction the roots grow. Are they pretty much growing out in the top two or three inches, or are they mostly growing down? Are there many or any live roots directly below the middle of the plant? Where does the soil structure change from a loose, crumbly structure to a platey, blocky one? Most soils in America have a crumbly structure for only the top one-half to two inches of the top soil and a platey structure from there on down. This means there is only a one-half to two-inch aerobic zone; the rest is predominately anaerobic, for all practical purposes.

In general, the roots will be concentrated primarily in the aerobic layer. You will notice that the greatest concentration of fine, fuzzy hair roots will be in the aerobic zone; this is because microbes and root hairs need oxygen. The microbes and root hairs make up the rhizosphere, which is the area of greatest nutrient exchange. Notice the color of the corn roots. Are they pearly white and soft, or are they brown and brittle? Pinch the roots slightly and pull to check whether the root bark sloughs off easily. If it does, there is a salt problem. Check for hardpan using a penetrometer, shovel, or brazing rod. This condition can be present in a sandy soil as well as in a clay soil. Notice that the roots pretty much stop at the hardpan.

Cut the corn stalk lengthwise and look at the plant’s plumbing system. Is the bottom of the stalk base, the pons, brown and hard? In general, we find that it is. This is congested or plugged tissue caused by toxins in the soil. These toxins might be pesticides, or they might be metabolic by-products from anaerobic breakdown of crop residue and manures. These could be products like formaldehyde and alcohol. Notice that the corn stalk has sprouted brace roots above this area. This is the back-up or by-pass plumbing system functioning to keep the plant alive. You may find that the node where these first brace roots sprouted is also brown and hard. In this case, a second layer of “by-pass” roots has sprouted. Brace roots are the plant’s rescue response when the plumbing system below gets plugged. If the plant did not sprout brace roots, it would die. In this case, as David Larson and others have reported, covering the brace roots, through cultivation, can increase corn yields by 5 to 15 bushels per acre. This allows the brace roots to contact the soil and, consequently, to interact with nutrients. In some areas the soil conditions are so toxic that the brace roots curl or burn off upon touching the soil surface. Compare the conditions of the plumbing systems of corn stalks between fields and note the differences in corn quality and refractometer readings.

Cut the corn stalk horizontally. The stalk should be round, not oblong or teardrop shaped. Out-of-roundness is an indication of a calcium deficiency. Look at the veins. Ideally, they should be pearly white and packed so tightly that it is difficult to count them. The pith should also be pearly white. Pull off the leaves from the stalk and notice that at each node, on opposite sides as you progress up the stalk, there is a baby or embryonic ear. This represents the plant’s true potential, which will be realized only when the soil is regenerated to the point that the plant’s plumbing system remains clear throughout, and the roots have an aerobic zone of 10 to 12 inches in which to grow.

About the Author

Arden B. Andersen

Dr. Arden B. Andersen apprenticed with Dr. Carey Reams, worked as a research assistant with Dan Skow, D.V.M., and as a field researcher with Philip Callahan, Ph.D. In addition to his B.S. in agricultural education, he holds a Ph.D. in biophysics and a D.O. in medicine. He currently works in general preventative and nutritional medicine while still consulting to some of the largest farming operations around the world.

Corn Plant Potential: Average Yields

By Dr. Harold Willis

The very most basic thing for growing really good crops is good soil. Soil that is not only high in fertility, but is alive with beneficial organisms.

The ideal soil for growing corn is deep (six or more feet), medium-textured and loose, well-drained, high in water-holding capacity and organic matter, and able to supply all the nutrients the plant needs.

Of course, not everyone has the per­fect soil, and corn isn’t so fussy that it can’t do well on less than ideal soil.

grow corn
High yields start with good seed and a good soil management system.

Average Corn Yields

from USDA Statistics


1931-35 22.8

1941-45 32.8

1951-55 39.1

1957 47.1

1960 54.7

1966 73.1

1969 85.9

1973 91.3

1979 109.7

1985 118.0

1990 118.5

2000 136.9

2010 137.1

Source: How to Grow Top Quality Corn

Magnesium: Essential for Soil, Plant & Animal Health

By Paul Reed Hepperly, Ph.D. 

Although nitrogen, phosphorus, potassium and even calcium are often discussed, magnesium is mostly unheralded and misunderstood. In this article I will examine the nature of magnesium deficiency and show how ignoring soil magnesium can lead to dire consequences in human, plant and animal health.

Like the other aforementioned macrominerals, magnesium is essential for plant and animal health and productivity. In man, beasts and plants it is found in substantial amounts and can wreak havoc when it is deficient.

Our health is rooted in our soils both as vegetables we consume and as animal products, which are nourished from the soil. Since the vast majority of what we eat comes from the soil, our health partly depends on earthworm activity, but the overuse of modern chemical fertilizers and pesticides has left many soils deficient in earthworms. This in turn impoverishes the soil.

As soils lose their vibrant microbial activity they become depleted in critical nutrients even as fertilizers are applied in larger amounts. Synthetic fertilizers are not a solution and often aggravate soil issues they supposedly cure. Remedying this downward spiral is more critical than ever because a growing population needs not only more food but better food quality for present and future generations to thrive.

One cannot escape the reality that our health is a result of our farming systems, and the state of our health attests to that truth. We are a product of the food we eat, the quality of soil it is grown in and the practices we employ in its production.

corn field needs magnesium
Unlike nitrogen, phosphorus and potassium, magnesium is often overlooked in conventional fertility.

Grass Tetany: A Telling Saga

In early spring when animals first come off supplementation and onto pasture they can suffer a condition called grass tetany. In this condition animals suffer severe muscular tremors, and worse, from magnesium deficiency.

This condition is particularly frequent in pure grass nitrogen-fertilized pastures. Farmers who both selectively eliminate broadleaves and fertilize with ammoniated nitrogen alone are almost ensuring magnesium deficiency. When clovers and broadleaves are selected out in pasture management, as farmers we end up eliminating the magnesium champions; they are the first victims of selective herbicides used to control “weeds” in the pasture.

However, these plants are the solution because they contain several times the amount of magnesium of a typical high-yield grass that was favored. Concentrating on an unbalanced diet leads to an artificial magnesium deficiency.

Modern agricultural practices selectively eliminate forage diversity and selectively fertilize, deteriorating the quality of our forage and the environment. When we eliminate magnesium-rich clovers and broadleaves and concentrate solely on a single grass, we do not allow the grazing animals to have a diverse diet to satisfy their health as they do instinctively under more natural conditions. In this scenario, the farmer and the farm animals lose.

Early grass growth can be notably deficient in magnesium while legumes are several times higher in critical magnesium. Rather than count on nitrogen from the air via leguminous plants, we instead choose nitrogen from fertilizer and its unintended consequences of soil acidity and key nutrient depletion.

Magnesium deficiency of grasses such as corn and sorghum expresses as yellowing or chlorosis, particularly between the veins of plant leaves. This is most common in acid, older soils such as those predominating in the wet tropical regions such as in northern Puerto Rico. Maintaining the diversity of our pastures is essential to providing a balanced ration for grazing animals, and this is rooted in the balance of our soil resource.

In alkaline pH 7.3 or higher soil, many plants will be unable to absorb iron, leading to plant yellowing and poor performance. In the case of chlorophyll, it shares an almost identical heme structure with the substitution of magnesium for iron. Magnesium deficiency mostly occurs when soils are old, sandy in texture and acid in pH. Acidity is a key factor for nutrition and health of both plants and animals. Although plants and animals are considered separate, on the core biochemical level they are more alike than one might guess.

Soil Considerations

Know your soil pH

The acidity of soil has a major impact on optimizing essential and micronutrients. Best overall mineral availability is in a very weakly acidic or neutral soil pH (6.3 to 7.0). To optimize crop and animal nutrition, the fertility program needs to start with getting the soil pH correct.

In humid, weathered acid soil this means liming. In semi-arid and arid conditions high alkaline (pH 7.3 or higher) can cause micronutrients to become a major obstacle, and this may need acidification with sulfur. In mineralizing your farming system, start with a soil test and proceed with acidity adjustment.

Know your soil organic level

In all conditions productive natural soils are generally over 5 percent soil organic matter. Many cropped tillable soils have plummeted to 1 percent or less SOM. Farmers who want to optimize their farming systems need to be aware that the ability of their soil to provide water, air and minerals is a function of SOM, which governs soil biology and metabolism.

All farmers with less than 5 percent SOM need to consider and then develop effective practices to increase soil organic matter to optimize their results. While 100 pounds of dry soil at 1 percent SOM can absorb less than 30 pounds of water, the same soil with over 5 percent soil organic matter can absorb over 200 pounds of water. Since minerals can only be absorbed through water, not only is the state of organic matter critical for moisture levels, but also for mineral nutrition. The leading cause of crop loss is drought, but without SOM optimization our crops are unnecessarily jeopardized and demineralized.

  1. Total testing — Take a comprehensive soil test that includes both macro and micronutrients, and make the necessary adjustments to achieve balance.
  2. Make amends — Develop a remediation of toxicities and deficiencies found in soil and/or plant tissue assays.
  3. In the case of magnesium, when the soil test is under 100 ppm for magnesium any liming should be done with dolomitic limestone (CaMg(CO3)2 ) rather than calcitic limestone which has little or no magnesium. A dolomitic limestone should contain at least 2 percent magnesium, and the effect of lime will be best when finely ground.

Take care to lime only to pH 7 as over-liming will result in severe micronutrient deficiency. In acid soils pH 5.7 will be sufficient to eliminate aluminum and manganese toxicity.

  1. Trace elements — Such as iron, zinc, manganese, boron, molybdenum and others have enormous impacts on plant and animal health. As someone who has worked on thousands of soil and plant analyses it is seldom that no insufficiency or excess is found. These can be overcome but only through diagnosis and directed action including consulting experienced and knowledgeable professionals.

Widespread Deficiency

In a 2012 USDA nutritional report, it was found over 57 percent of males and females do not get the recommended minimum daily amount of magnesium in their diet. Scientists have also argued that the magnesium minimum dosage has been set too low. They suggest that just about everyone would benefit from upping their magnesium level by about three times the current estimate. It is important we get this right. Magnesium can lead to devastating health results such as: excitability, muscle cramps, headaches, apathy, confusion, insomnia, heart irregularity and thyroid disruption.

Magnesium governs over 300 biochemical reactions by playing important roles within enzymes. Researchers point to the tandem of low dietary intake and high refined sugar as the deadly duo driving deficiency of this critical element in humans.

Modern use of potassium as a key fertilizer, when not coupled with adequate magnesium, contributes to unbalanced nutrition from the food we eat. Additional causes of rampant magnesium deficiency may include stress and pharmaceutical drugs such as hypertension drugs which lower magnesium dramatically.

Magnesium Revelation

Unlike nitrogen, phosphorus, potassium and even calcium, magnesium is seldom considered in conventional fertilization programs. Just because we choose not to focus on it does not mean that our lives do not depend upon it, whether we know it or not. How we farm and the status of our food system, which is soil-based, can make the difference between health and disease; yet we are sometimes uninformed about these choices.

Synthetic chemical fertilization, often touted as a solution to our agriculture and food woes, represents a dangerous double-edged sword. Instead of boosting nutrients they can play anti-nutrient roles. After synthetic ammoniated nitrogen, potassium salts — muriate of potash or potassium sulfates — are the leaders in global fertilizer use. Unfortunately, although potassium can raise yield and sugar content, it can also play an antagonistic role in reducing magnesium and calcium.

This artificially induced depletion reduces the accumulation of these critical minerals, contributing to deficiency and disease.

Iatrogenic is a Greek word conveying the idea that curative practices or treatments can sometimes cause harm. In simple terms, the treatment causes malady. Without proper knowledge and management, nutrient imbalance becomes the norm. When balancing nutritional needs, a broader view and diversity must be valued if we are to remedy some of our nutritional issues rooted in unbalanced diets. For example, heavy application of ammoniated nitrogen is a key promoter of blossom end rot, a problem of calcium deficiency.

To improve our present situation we need to change our values. Our health will improve with soil health improvement. We need to address nutrition from the ground up and should not ignore the environment and health costs of the food system itself.

Plants & Animals Reflect the Soil

At my old experiment station the research plantings of sorghum would completely fail in some spots. The soil was an old weathered soil (Oxisol) notable for good physical condition, but it had a low mineral salt nutrient level. Very notable in this soil was an inability to detect measurable amounts of magnesium, and this was particularly acute in the spots where sorghum would not grow. This is not a coincidence. The issues were resolved by adjusting pH and amending with magnesium.

I was assigned to diagnose the same problem I ended up having in my own body. Magnesium deficiency, not tachycardia in my case, was the core root in both instances. All in all, this was a difficult but effective way to learn that soil and health are interrelated.

When we optimize one factor in isolation we often cause artificial imbalance and disruption of other critical factors. Through our so-called treatment we can induce unnecessary chronic mineral havoc. This is in fact what we have done in our industrialized, centralized agricultural food system. Our nutritional status is literally grounded in balanced nutrition from soil, and we can consciously improve this as farmers, gardeners and consumers by becoming good Earth stewards and making better management choices.

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

About the Author

Paul Reed Hepperly, scientist, consultant, educator and advisor, previously served as the research director for Rodale Institute (2002-09). His son, Reed Paul Hepperly, is CEO of Hepperly Enterprises, a premium compost supplier and developer of tropical root crops in Mayaguez, Puerto Rico. Paul currently resides in Maryville, Tennessee. Contact him at


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Plant Nutrition – Corn in Focus

By Gary Zimmer & Charles Walters

The following tables give an idea of corn’s nutrient requirements. It is not practical to have companion plants in most field situations, but it is possible to read deficiencies and surpluses of plant nutrients even without the certainty of a petiole test, a refractometer readout, or a laboratory’s final audit.

black and white corn stalk
Evaluation your corn stalk color, look and feel can give you clues on its nutrition.

This is just a guide to help you determine the nutrients you have too much/little of, and how to tell.

Nutrient Deficiencies Guide

Nitrogen—lower leaves yellow at tip and center, later dying; rest of plant pale yellowish green; slow growth; stalks slender; ears small, not filled at tip.

Phosphorus—leaves dark green, turning reddish-purple be­ginning at tips of upper leaves (in young plant; purple leaves in older plant usually from other causes [drought, barren stalk]); slow growth; stalk size small; ears small, misshaped, often twisted from missing rows of kernels, not filled at tip.

Potassium—lower leaves yellow at tip and edges, later dying; stalk weak; ears small, poorly filled at tip, kernels loose.

Magnesium—lower leaves streaked by yellow between the veins, sometimes with rows of dead spots; upper leaves may be­come reddish-purple at tip and edges.

Calcium—in young plant, leaf tips stick together (do not un­fold), giving a ladder-like appearance.

Sulfur—yellow streaks between veins and stunted growth, es­pecially in young plant.

Iron—upper leaves pale green to nearly white between veins (along entire leaf).

Copper—young leaves yellow as they emerge, becoming pale streaked between veins, edges may later die; youngest leaves twisted and dried; stalk soft and limp.

Boron—leaves brittle with small dead spots or streaks; top of growing plant with bushy appearance because stalk does not lengthen; tassels and ears reduced or do not emerge.

Manganese—leaves olive green, may become streaked; stalk may be thin and limber.

Zinc—leaves with wide whitish bands between edge and midrib (edges remain green or turn purplish) which may later die, young­est leaves may be white; plant short because of little stalk growth.

Corn Nutrient Use Guide

corn nutrient guide
From How to Grow Top Quality Corn.

Nitrate (NO³ in ppm) — Nitrates in the sap represent future growth. Their effect is visible in 10-14 days. Too many nitrates too soon reduces fruit set. Changes in nitrates take effect fast.

Phosphate (PO4 in ppm) — Phosphates are in the sap for future growth. They show present root activity. Phosphates can be increased with humus, plant growth regulators and microbes.

Potassium (K %) — Potassium affects water uptake and efficiency, sugar production, enzyme formation and plant health. There is a high potassium requirement to form sugars.

Sodium (Na %) — Low amounts of sodium are best; just a trace is essential.

Calcium (Ca %) — Calcium is needed for cell walls, nitrate utilization, roots, leaves, pollination, and development fruit set.

Magnesium (Mg %) — Magnesium is needed for chlorophyll, photosynthesis, phosphorus metabolism and respiration.

Zinc (Zn in ppm) — Zinc is a plant growth stimulator. It affects enzymes, and metabolic reaction.

Iron (Fe in ppm) — Iron is needed for respiration, chlorophyll formation and energy. It is an oxygen carrier.

Manganese (Mn in ppm) — Manganese is needed for enzyme activation, photosynthesis, and maturity. It is connected with P and Ca.

Copper (Cu in ppm) — Copper is needed for chlorophyll formation and energy. It also catalyzes plant functions.

Boron (B in ppm) — Boron is needed for nitrate uptake, calcium utilization, pollination and sugar transport.


Nutrient: Nitrogen

Growing pattern: Throughout season

Leaf Translocation: Yes, during grain

Peak time of availability: Tassel to silk through with two peaks development grain fill

Nutrient: Phosphorus

Growing pattern: Steady accumulation

Leaf Translocation: Yes, during grain fill

Peak time of availability: Early tassel and early until maturity (more than N) dent

Nutrient: Potassium

Growing pattern: 86 percent accumulated

Leaf Translocation: Very little

Peak Time of Availability: Early tassel by silking

Nutrient: Calcium

Growing pattern: Vegetative growth 86%

Leaf Translocation: No

Peak Time of Availability: Early tassel before blister stage

Nutrient: Magnesium

Growing Pattern: Throughout growing

Leaf Translocation: Very little

Peak Time of Availability: All season

Nutrient: Sulfur

Growing Pattern: Throughout growing

Leaf Translocation: Very little

Peak Time of Availability: Steady supply all season

Nutrient: Boron

Growing Pattern: Throughout season

Leaf Translocation: Very little

Peak Time of Availability: Steady supply all with two peaks season (tassel to early grain fill)

Nutrient: Copper

Growing Pattern: Steady accumulation

Leaf Translocation: No

Peak Time of Availability: Steady supply all throughout season

Nutrient: Iron

Growing Pattern: Two distinct times, (70%)

Leaf Translocation: Very little

Peak Time of Availability: Early through blister accumulation by blister stage

Nutrient         Grain  Stover

Nitrogen         150     116

P2O5              87       27

K20                 57       209

Magnesium    18       47

Calcium          4          38

Sulfur             15       18

Zinc                 0.18    0.37

Manganese    0.12    1.75

Iron                 0.17    1.10

Copper           0.07    0.06

Boron              0.15    0.06

SOURCES: Gary Zimmer/The Biological Farmer; Charles Walters/Ask the Plant

Learn in the field with Gary Zimmer!

The Acres U.S.A. On-Farm Intensive is held in partnership with experienced farm consultants Gary Zimmer and Leilani Zimmer-Durand at their famous Otter Creek Farm near Lone Rock, Wisconsin. This two-day educational experience will help farmers, growers and land owners maximize their land’s potential. Learn more here!

How Soil Helps Corn Survive

By Dr. Harold Willis

A big problem with growing corn is the weather, which seems to do just the opposite of what we want—rain when we want to plant or harvest and drought when the crop is trying to grow. Too high (over 90°F) or too low (under 50°F) temperatures are detrimental to growth and yield. Too much and too little soil moisture decrease the roots’ ability to absorb water and nutrients. Too little light (cloudy weather) decreases photosynthesis and growth. Wind and hailstorms can decimate a growing crop.

You may think that you have no control over such problems, since you can’t control the weather, but actually, the condition of your soil and the health of your crop determine how badly adverse weather affects the crop.

If the soil has plenty of humus and is loose and spongy, it will be well-drained but will soak up a tremendous amount of mois­ture and hold it for the plants during dry weather. You can drive around and see a lush green field next to one that is burned up by a drought; the difference is in the soil.

Also, healthy plants can withstand temperature extremes (in­cluding frost) and cloudy weather better than stressed ones. They also have stronger (but more elastic) stalks to withstand wind and can recover faster from all but the worst hail damage. Ammonium sulfate acts as a temperature moderator, warming soil in the spring and cooling it in the summer.

corn field flooded
Weather never does what we want it to, so ensuring your soil health system is focused on resilience is key.

Problems? Sure, we all have them. Do we let them get us down or are they a challenge to overcome?

Source: How to Grow Top Quality Corn

Corn Plant Biology

By Gary Zimmer & Dr. Harold Willis

Corn, commonly called “maize” in much of the world, is America’s most valuable agricultural crop, with the United States producing nearly half of the world’s corn. Corn is a member of the large plant family, the grasses, to which other important crops such as wheat, oats, barley and rice also belong.

A corn plant is a marvel of energy production and storage, capturing the sun’s energy during photosynthesis and converting it into food molecules. In only three or four months, a single kernel of corn grows into a plant 7- to 12-feet tall and produces 600 to 1,000 kernals similar to the one that was planted.

Corn grows best in warm, sunny weather (75°-86° F) with well-distributed moderate rains (or irrigation with 15 or more inches of water per season) and 130 or more frost-free days. For optimum growth and for top quality, the growing corn plant needs an adequate and balanced supply of all the essential nutrients, and it needs them throughout the growing. However, the peak time of nutrient need is in the middle of the growth cycle, when the greatest vegetative growth occurs, as well as during the reproductive and grain-filling period.

signs along a corn field
Understanding corn biology will help you increase your yields.

The great majority of U.S. corn is fed to livestock, both as grain and silage or fodder. Beef and dairy cattle, hogs, sheep, and poultry are the major consumers. Less than 10% is used for human consumption, but in recent years the production of corn-based ethanol has used up a sizeable proportion of corn production. Besides such familiar products as corn flakes, popcorn, corn meal, hominy, grits, corn starch, corn oil, corn syrup, and corncob pipes, other industrial uses include the production of chemicals (alcohols and liquors, acetone, furfural, antibiotics, enzymes, organic acids), plastics, paper, cardboard, insulation, grit for polishing, carrier for pesticides and fertilizers, animal litter, hand soaps, and cosmetics.

SOURCE: Gary Zimmer/From The Biological Farmer; Dr. Harold Willis/How to Grow Top Quality Corn

Learn in the field with Gary Zimmer!

The Acres U.S.A. On-Farm Intensive is held in partnership with experienced farm consultants Gary Zimmer and Leilani Zimmer-Durand at their famous Otter Creek Farm near Lone Rock, Wisconsin. This two-day educational experience will help farmers, growers and land owners maximize their land’s potential. Learn more here!