Dealing With Herbicide Drift

By John Peragine

Nature can be unforgiving to farmers. Honest people trying in earnest to make a living growing crops regularly face storms, drought, hail and many other types of natural disasters. Today, unfortunately, these people’s neighbors sometimes add to the problem by introducing one more difficulty: herbicide drift.

All farmers face pressure from weeds. These pesky plants can consume resources — sunlight, water and nutrients — necessary for optimum plant growth. There are three primary ways to deal with the dilemma: pull, cut or use some other physical mechanism to kill the weeds; ignore them and take a loss of production; or use a substance to kill them.

Hand weeding is not typically cost-effective beyond a small acreage farm, forcing larger farms to either accept a decrease in yield or use a chemical to kill the plants. Some herbicides have little negative impact on the environment or the plants they are sprayed on. Unfortunately, though, most large-scale crops are sprayed with volatile chemicals.

Grape Vine damage caused by herbicide drift
Damage to grape vines caused by 2,4-D drift. Photos by Michael L. White, ISU Extension & Outreach Viticulture Specialist

Agricultural technology over the past century has allowed farmers to deal with weeds in a very direct and definitive manner with the use of chemical herbicides. A common herbicide is the phenoxy type (2,4-D and dicamba). This is sprayed over crops like corn around the periphery of fields and is quite effective in killing broad-leaf weeds; it is equally effective in killing similar plants such as grape vines, and dicamba is currently the topic of much discussion through-out the Midwest and beyond where it has been linked to non-target crop plant damage.

The Environmental Protection Agency defines drift as “The physical movement of pesticide droplets or particles through the air at the time of pesticide application or soon thereafter from the target site to any non- or off-target site. Spray drift shall not include movement of pesticides to non-or off-target sites caused by erosion, migration, volatility, or windblown soil particles that occurs after application or application of fumigants unless specifically addressed on the product label with respect to drift control requirements.”

There are two types of pesticide/ herbicide drift: particle and vapor. Particle drift occurs when small droplets of pesticides or herbicides travel via the wind from the field they were being applied to onto other crops.

Vapor drift occurs when temperatures in the upper 80s and 90s cause already-applied pesticides/herbicides to volatize into a vapor. These vapors then drift over great distances and destroy crops that are not immune to its destructive compounds.

The good news is that many states have laws to protect farmers from the damages caused by herbicide drift. In Iowa, laws were enacted around grape-producing regions in the western part of the state to stop the use of highly volatile herbicides in the late 1970s. The damage was done, though, and it took almost 30 years for the grape industry to bounce back. Spray drift causes a reduction in yield, poor fruit quality and even grapevine death. Problems can continue years after the drift exposure, reducing the life of a vineyard.

The degree to which crops are damaged from drift depends on the level of the susceptibility of the crop, its growth stage, environmental conditions, herbicide formulation, droplet size and the spray height above the target.

Emotions Run High

Because livelihoods are on the line, frustration and anger over herbicide drift often arises, and conflicts can ensue. Neighbors, farmers and companies will often apologize and promise they will not allow drift to occur again, but this is not always honored. Included on page 34 is a sample letter template that can be used to attempt to start a more positive conversation about drift.

If your neighbor does not respond in a positive way, you could seek assistance from your state department of agriculture.

Sample Letter

ABC Farm 123
Any Street
Anywhere, USA

XYZ Neighbor 124 Any Street Anywhere, USA

Re: Herbicide drift concerns
Dear Neighbor, I hope this finds you well and that you are having a good growing season.
I am writing to remind you that we have grape vines on two sides of the Old Grain Mill field in Hamlet township. We have registered on Driftwatch, which has a good map that shows where the vines are in case you have any questions. Here’s a link if you would like to see the online map:
I’ve also included a map that shows the location of the vineyards. Grape vines are especially sensitive to glyphosate, dicamba and 2,4-D.
We have appreciated the care you have taken over the years to avoid any problems. Unfortunately, we have had friends in the grape community who’ve had severe damage, so it seemed like a good idea to bring this up again.
Thanks for your attention to this. We’ve also spoken with your landlord about our concerns. If you have any questions, don’t hesitate to call.
Yours truly,
Friendly Farmer

Organic Solutions

There are a number of organic herbicides on the market, but they should be given the same attention as their synthetic counterparts. Organic herbicides do not offer a residual effect, which means they break down quickly after their application. This is good in that it reduces toxicity, but it also means that they have to be used more often.

Organic herbicides are not selective and can kill basil as easily as a weed, so application should be done carefully. They should be applied directly onto weeds on warm, sunny, non-windy days. They often contain fatty acids, vinegar or acetic acid, or essential oils like citrus, eugenol or clove.

Corn gluten meal can be used on larger farms, as it is a natural pre-emergence weed control for broad-leaf and grass weeds.


Sometimes the damage due to drift is so severe that compensation is necessary to replace lost crops. Michael White, Iowa State University Extension & Outreach Viticulture Specialist, says that over 95 percent of drift damage cases are settled out of court.

White suggests waiting before accepting payments from an insurance company. Some damage does not become evident until after the winter. Even though insurance companies do not like to carry claims over into another year, it is best to try to delay and not settle too soon. Once damage is suspected, White recommends taking pictures of healthy plants and damaged plants every week or two to demonstrate the progression of the damage.


Editor’s Note: This article appeared in the March 2019 issue of Acres U.S.A. magazine.

Increasing Soil Organic Matter Through Organic Agriculture

By André Leu

Numerous scientific studies show that soil organic matter provides many benefits for building soil health such as improv­ing the number and biodiversity of beneficial microorganisms that pro­vide nutrients for plants, including fixing nitrogen, as well as controlling soilborne plant diseases. The decom­position of plant and animal residues into SOM can provide all the nutri­ents needed by plants and negate the need for synthetic chemical fertilizers, especially nitrogen fertilizers that are responsible for numerous environ­mental problems.

The year 2015 was declared the International Year of Soils by the 68th UN General Assembly with the theme “Healthy Soils for a Healthy Life.” I was particularly pleased with the theme because this is a message that we in the organic sector have been spreading for more than 70 years, and at first we were ridiculed. Now there is a huge body of science showing that what we observed in our farming systems is indeed correct.

“Organic farming” became the dominant name in English-speaking countries for farming systems that eschew toxic, synthetic pesticides and fertilizers through J.I. Rodale’s global magazine Organic Farming and Gar­dening, first published in the United States in the 1940s. Rodale promot­ed this term based on building soil health by the recycling of organic matter through composts, green ma­nures, mulches and cover crops to increase the levels of soil organic matter as one of the primary management techniques.

organic field
Organic vs. Conventional. The higher levels of organic matter allow the soil in the organic field to resist erosion in heavy rain events and capture more water.
Water run-off

Soil organic matter improves soil structure so that it is more resistant to erosion and is easier to till, resulting in lower energy use and less greenhouse gas output. Soils with good SOM levels are more efficient at absorbing rain­water and storing it for plants to use in dry periods. Studies show that organic systems get around 30 percent higher yields in periods of drought than con­ventional systems due to the increase of SOM and its ability to capture and store water for crops.

SOM is composed largely of car­bon that is captured as CO2 from the air by plants through photosynthe­sis. Published, peer-reviewed meta-studies show that organic farming systems are superior to conventional systems in capturing CO2 from the atmosphere (the primary greenhouse gas responsible for climate change) and sequestering it into the ground as SOM.

Soil Organic Matter & Climate Change

Worldwide, agriculture is respon­sible for between 11 and 30 percent of greenhouse gas emissions, depending on the boundaries and methodolo­gies used to determine its emissions. According to the United Nations En­vironment Programme, the estimates of global greenhouse gas emissions in 2010 were 50.1 gigatons of carbon di­oxide equivalent (Gt CO2e) per year. To keep global mean temperature increases below 2°C compared to pre-industrial levels, GHG emissions will have to be reduced to a median level of 44 Gt CO2e in 2020.

This means that the world will have to reduce the current level of emissions by 6.1 Gt CO2e by 2020 and reduce it every subsequent year. According to the latest World Me­teorological Organization figures, the levels of GHG pollution in the atmosphere and the oceans are the highest in history and are still increasing.

Keeping the rise in temperature below 2°C will not only involve re­ducing emissions through energy effi­ciency, renewable energy and cleaner energy sources; sequestering GHGs already present in the atmosphere will also be necessary to reduce the current levels. Currently most seques­tration is based on growing biomass as carbon sinks and capturing it as wood-based products.

Soils are the greatest carbon sink after the oceans. According to Profes­sor Rattan Lal of Ohio State Univer­sity, there are over 2,700 Gt of carbon stored in soils worldwide. This is considerably more than the combined total of 780 Gt in the atmosphere and the 575 Gt in biomass.

The amount of CO2 in the oceans is already causing problems, particu­larly for species with calcium exo­skeletons such as coral. Scientists are concerned that the increase in acid­ity caused by higher levels of CO2 is damaging these species and threatens the future of marine ecosystems such as the Great Barrier Reef.

Mitigation Through Aboveground Biomass

Currently the major push for car­bon sequestration is through above-ground biomass, despite that fact that its potential as a carbon sink is signifi­cantly less than that of soil. The other issue is the need to take land out of food production to grow trees. There is some potential with agroforestry and trees as shade cover for some cash crops like coffee and cacao, however this will deliver considerably less than research has shown can be sequestered into soils with good agri­cultural practices.

Sequestration Through Agriculture 

The ability of soils to absorb enough CO2 in order to stabilize cur­rent atmospheric CO2 levels is a criti­cal issue, and there is a major debate over whether this can be achieved through farming practices. Reviews of conventional farming systems have found that most are losing soil car­bon and at best they can only slow the rate of loss. On the other hand, farming systems that recycle organic matter and use crop rotations can increase the levels of soil organic car­bon (SOC).

A preliminary study by the Re­search Institute of Organic Agricul­ture, Switzerland, published by FAO, collated 45 comparison trials between organic and conventional systems that included 280 data sets. These studies included data from grasslands, arable crops and permanent crops in several continents. A simple analysis of the data shows that on average the or­ganic systems had higher levels of soil carbon sequestration.

Dr. Andreas Gattinger and col­leagues wrote, “In soils under organic management, the SOC stocks aver­aged 37.4 tons C ha-1, in comparison to 26.7 tons C ha-1 under non-organic management.”

This means that the average differ­ence between the two management systems (organic and conventional) was 10.7 tons of C. Using the accepted formula that SOC x 3.67 = CO2, this means an average of more than 39.269 tons of CO2 was sequestered in the organic system than in the con­ventional system.

The average duration of manage­ment of all included studies was 16.7 years. This means that an average of 2,351 kg of CO2 was sequestered per hectare every year in the organic sys­tems compared to the conventional systems.

In a later peer-reviewed meta-anal­ysis, published in PNAS, that used 41 comparison trials and removed the outliers in the data sets in order not to overestimate the data and to obtain a conservative estimate, researchers reported that organic systems seques­tered 550 kg C per hectare per year. This equates to 2018.5 kg CO2 per hectare per year.

Based on these figures, the wide­spread adoption of current organic practices has the potential to sequester around 10 Gt of CO2, which is the range of the emissions gap in 2020 of 8-12 Gt CO2e per year.

The potential exists for higher lev­els of CO2 sequestration. All data sets that use averaging have outlying data. These are examples that are sig­nificantly higher or significantly lower than the average.

There are several examples of higher levels of carbon sequestra­tion than the averages quoted in the studies above. The Rodale Institute in Pennsylvania has been conducting long-running comparisons of organic and conventional cropping systems for more than 30 years that confirm organic methods are effective at re­moving CO2 from the atmosphere and fixing it as organic matter in the soil. Tim LaSalle and Paul Hepperly wrote, “In the FST [Rodale Institute farm systems trial] organic plots, car­bon was sequestered into the soil at the rate of 875 lbs/ac/year in a crop rotation utilizing raw manure, and at a rate of about 500 lbs/ac/year in a rota­tion using legume cover crops.

During the 1990s, results from the Compost Utilization Trial (CUT) at Rodale Institute — a 10-year study comparing the use of composts, ma­nures and synthetic chemical fertil­izer — show that the use of composted manure with crop rotations in organic systems can result in carbon seques­tration of up to 2,000 lbs/ac/year. By contrast, fields under standard tillage relying on chemical fertilizers lost almost 300 pounds of carbon per acre per year.”

Converting these figures into kilo­grams of CO2 sequestered per hectare using the accepted conversion rate of 1 pound per acre = 1.12085116 kg/ ha and SOC x 3.67= CO2, gives the following results: The FST legume-based organic plots showed that car­bon was sequestered into the soil at the rate of about 500 lbs/ac/year. This is equivalent to a sequestration rate of 2,055.2kg of CO2/ha/yr, which is close to the average found in the Gat­tinger meta-study.

However, other organic systems produced much higher rates of se­questration. The FST manured or­ganic plots showed that carbon was sequestered into the soil at the rate of 875 lbs/ac/year. This is equivalent to a sequestration rate of 3,596.6 kg of CO2/ha/year and if extrapolated globally would sequester 17.5 Gt of CO2.

The CUT showed that carbon was sequestered into the soil at the rate of 2,000 lbs/ac/year. This is equivalent to a sequestration rate of 8,220.8 kg of CO2/ha/year and if extrapolated globally, would sequester 40 Gt of CO2.

A meta-analysis by Eduardo Agu­ilera et al. published in the peer-re­viewed journal, Agriculture, Ecosystems and Environment, of 24 comparison trials in Mediterranean climates be­tween organic systems and non-or­ganic systems without organic supple­ments found that the organic systems sequestered 970 kg of C/ha/year more than the non-organic systems. This equates to 3559.9 kg of CO2/ha/year. The data came from comparison trials from Mediterranean climates in Eu­rope, the United States and Australia, and if extrapolated globally, would sequester 17.4 Gt of CO2.

The Louis Bolk Institute conducted a study to calculate soil carbon seques­tration at SEKEM, the oldest organic farm in Egypt. Their results show that on average SEKEM’s management practices resulted in 900 kg of carbon being stored in the soil per hectare per year in the fields that were 30 years old. Using the accepted formula of SOC x 3.67 = CO2, this means that SEKEM has sequestered 3,303 kg of CO2 per hectare per year for 30 years.

Based on these figures, the adop­tion of SEKEM’s practices globally has the potential to sequester 16 Gt of CO2, which is around 30 percent of the world’s current GHG emission into soils.

It is not the intention of this paper to use the above types of generic exercises of globally extrapolating data as scientific proof of what can be achieved by scaling up organic systems. These types of very simple analyses are useful for providing a conceptual idea of the considerable potential of organic farming to reduce GHG emissions on a landscape scale. The critical issue here is that urgent peer-reviewed research is needed to understand how and why — and for the skeptics, if — these systems seques­ter significant levels of CO2 and then look at how to apply the findings for scaling up on a global level in order to achieve GHG mitigation.

Greater Resilience in Adverse Conditions 

According to research by the UN­FCCC IPCC Fourth Assessment Re­port (IPCC 2007) and others, the world is seeing increases in the fre­quency of extreme weather events such as droughts and heavy rainfall. Even if the world stopped polluting the planet with greenhouse gases to­morrow, it would take many decades to reverse climate change. This means that farmers have to adapt to the increasing intensity and frequency of adverse and extreme weather events.

organic vs conventional fields
From The Rodale Institute: Organic vs. Conventional fields side by side.

Published studies show that organic farming systems are more resilient to predicted weather extremes and can produce higher yields than conven­tional farming systems in such con­ditions. For instance, the Wisconsin Integrated Cropping Systems Trials found that organic yields were higher in drought years and the same as con­ventional in normal weather years.

Improved Water Use Efficiency 

Research shows that organic sys­tems use water more efficiently due to better soil structure and higher levels of humus and other organic matter compounds. D.W. Lotter and col­leagues collected data over 10 years during the Rodale Farm Systems Trial. Their research showed that the organ­ic manure system and organic legume system (LEG) treatments improve the soils’ water-holding capacity, infiltra­tion rate and water capture efficiency. The LEG maize soils averaged 13 percent higher water content than conventional system (CNV) soils at the same crop stage and 7 percent higher than CNV soils in soybean plots. The more porous structure of organically treated soil allows rain­water to quickly penetrate the soil, resulting in less water loss from runoff and higher levels of water capture. This was particularly evident during the two days of torrential downpours from hurricane Floyd in September 1999, when the organic systems cap­tured around double the water as the conventional systems.

Long-term scientific trials con­ducted by the Research Institute of Organic Agriculture in Switzerland comparing organic, biodynamic and conventional systems had similar re­sults showing that organic systems were more resistant to erosion and better at capturing water.

“We compare the long-term effects (since 1948) of organic and conven­tional farming on selected properties of the same soil. The organically farmed soil had significantly higher organic matter content, thicker topsoil depth, higher polysaccharide content, lower modulus of rupture and less soil erosion than the conventionally-farmed soil. This study indicates that, in the long term, the organic farming system was more effective than the conventional farming system in re­ducing soil erosion and, therefore, in maintaining soil productivity (Regan­old et al. 1987).”

Humus, a key component of SOM, allows for the ability of organic soils to be more stable and to hold more water. This is due to its ability to hold up to 30 times its own weight in water, and being a ‘sticky’ polymer, glues the soil particles together, giving greater resistance to water and wind erosion.

There is a strong relationship be­tween SOM levels and the amount of water that can be stored in the root zone. The table below should be taken as a rule of thumb, rather than as a precise set of measurements. Different soil types will hold different volumes of water when they have the same levels of organic matter due to pore spaces, specific soil density and a range of other variables. Sandy soils generally hold less water than clay soils.

The table above gives an under­standing of the potential amount of water that can be captured from rain and stored at the root zone in relation to the percentage of SOM.

There is a large difference in the amount of rainfall that can be captured and stored between the current SOM level in most traditional farms in Asia and Africa and a good organic farm with reasonable SOM levels. This is one of the reasons why organic farms do better in times of low rainfall and drought.

The Rodale Farming Systems Trial showed that the organic systems produced more corn than the conventional system in drought years. The average corn yields during the drought years were 28 to 34 percent higher in the two organic systems. The yields were 6,938 and 7,235 kg per ha in the organic animal and organic legume systems, respectively, compared with 5,333 kg per ha in the conventional system. The researchers attributed the higher yields in the dry years to the ability of the soils on organic farms to better absorb rainfall. This is due to the higher levels of organic carbon in those soils, which makes them more friable and better able to capture and store rainwater which can then be used for crops.

This is very significant information as the majority of the world’s farming systems are rain-fed. The world does not have the resources to irrigate all of the agricultural lands, nor should such a project be undertaken. Improving the efficiency of rain-fed agricultural systems through organic practices is the most efficient, cost-effective, environmentally sustainable and practical solution to ensure reliable food production in the face of increasing weather extremes.

Synthetic Nitrogen Fertilizers 

One of the main reasons for the differences in soil carbon between organic and conventional systems is that synthetic nitrogen fertilizers de­grade soil carbon. Research shows a direct link between the application of synthetic nitrogenous fertilizers and decline in soil carbon.

Scientists from the University of Il­linois analyzed the results of a 50-year agricultural trial and found that syn­thetic nitrogen fertilizer resulted in all the carbon residues from the crop disappearing as well as an average loss of around 10,000 kg of carbon per hectare per year. This is around 36,700 kg of CO2 per hectare on top of the many thousands of kilograms of crop residue that is converted into CO2 every year.

Researchers found that the higher the application of synthetic nitrogen fertilizer the greater the amount of soil carbon lost as CO2. This is one of the major reasons why most conventional agricultural systems have a decline in soil carbon while most organic sys­tems increase soil carbon.

Plant-Available Nitrogen Levels

One of the main concerns about organic agriculture is how to get suf­ficient plant-available nitrogen with­out using synthetic nitrogen fertilizers such as urea.

SOM, particularly the humus frac­tions, tend to have a carbon nitrogen ratio of 9:1 to 11:1. As the carbon levels increase, the amount of soil ni­trogen increases in order to maintain the carbon-nitrogen ratios. Adding organic matter into the soil to increase carbon, results in the nitrogen levels increasing.

organic nitrogen in soil amounts
Table: amount of organic nitrogen held in soil.

Much of this soil nitrogen is fixed by free-living soil microorganisms such as azobacters and cyanobacte­rias. The use of DNA sequencing is revealing that cohorts of numerous thousands of species of free-living microorganisms are involved in fix­ing nitrogen from the air into plant available forms. There are many stud­ies that show that there is a strong relationship between higher levels of SOM and higher levels of soil biologi­cal activity.

This biological activity includes free-living nitrogen-fixers, and they turn the atmospheric nitrogen, the gas that makes up 78 percent of the air, into the forms that are needed by plants. They do this at no cost and are a major source of plant-available nitrogen that is continuously over­looked in most agronomy texts.

New research has found a new group of nitrogen-fixing organisms called endophytic microorganisms. These microbes can colonize the roots of numerous plant species including rice, grain crops and sugar cane.

Soil Carbon, Nitrogen Ratios 

It is important to get an understanding of the potential for how much nitrogen can be stored in SOM for the crop to use. SOM contains nitrogen expressed in a Carbon to Nitrogen Ratio. This is usually in ratios from 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 SOM is expressed as 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: SOC × 1.72 = SOM.

The issue of working out the amount of SOC as a percentage of the soil by weight is complex as the specific density of the soil has to be factored in 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.

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 percent increase in organic carbon in the top 20 cm of soil represents a 24 t/ha [24,000 kg] increase in SOC …”

This means that a soil with 1 percent SOC would contain 24,000 kg of carbon per hectare. With a 10:1 carbon to nitrogen ratio this soil would contain 2,400 kg of organic nitrogen per hectare in the top 20 centimeters, the primary root zone.

The conventional dogma around nitrogen is that it can only be used by plants if it is in the form of nitrate or ammonium and that organic nitrogen is mostly not available to the crop until it has been converted into these two forms of N.

There are hundreds of peer-reviewed scientific studies that show that this assumption is incorrect and that in natural systems plants take up nitrogen in numerous organic forms such as amino acids, amino acid precursors and DNA.

The fact is that the significant proportion of the organic nitrogen in the soil is readily available to the crop. The key to get an adequate level of N is to increase SOM levels rather than adding synthetic nitrogen fertilizers.

Given that synthetic nitrogen destroys organic matter, the use of these fertilizers should be avoided as they lock farmers into a perpetual dependence on these costly inputs once the organic matter levels have been run down and most of the organic nitrogen forms in the soil have been depleted. Farmers should be encouraged to obtain all their nitrogen from organic sources such as composts, manures, green manures and legumes and build up their organic matter levels.

By André Leu. This article appeared in the July 2015 issue of Acres U.S.A.

André Leu is the author of Poisoning our Children and The Myths of Safe Pesticides. He is the International Director of Regeneration International.

Understanding Solubility & Paste Testing

By William McKibben

Paste Testing

Low exchange capacity soils especially have a lot of issues when it comes to holding enough nutrients and maintaining colloidal balance. Sand with low organic matter is basically a soilless media. Since many of the nutri­ents required for crop production are not on the colloid, I find that the paste test is absolutely the best test for this situation. I also use the paste test along with the standard test on the higher exchange capacity soils. Since most of the nutrients taken up by plants are picked up by mass flow or diffusion at the air/water interface near the plant roots, the paste test better correlates to tissue analysis than the standard test.

The paste test is done primarily by taking a large sample, approxi­mately 200-400 grams of a composite soil mixture and saturating it with distilled water (or even better is to use clients’ irrigation water) until it becomes a pancake batter consistency.

Making Paste Analysis Recommendations

Making recommendations from a paste analysis incorporates both the SLAN approach and the BCSR approach. First, it is critical to meet the minimum strategic nutrient levels for growth and reproduc­tion (Figure 16). Secondly, the nutrients in solution should be kept in balance to minimize interference issues. Even if all the strategic levels have been met, if a nutrient such as potassium is two or three times higher than the desired level, other cations such as calcium and magne­sium should be elevated in order to maintain a balance. The type of crop and the level on the standard test would help make that determination. For crops such as corn or alfalfa that require a lot of potassium if the standard test does not show good levels of potassium, I would probably let the level stand and not elevate the calcium and magnesium. When raising levels to just balance out one nutrient, care must be taken not to create a salt issue. If the nutrient in excess is sodium and irrigation is available, flushing the soil may be the best solution. Most of the sodium issues that I see are created by irrigation practices. Irrigating with poor quality water or using poorly designed irrigation systems may result in the accumulation of sodium and/or bicarbonates.

Discussion of Paste Guidelines

The guidelines for the paste test shown on Figure 16 are just that —guidelines. I cannot emphasize enough that everyone needs to adjust these numbers based on their own crop tissue analysis and the subsequent crop response. There is one unknown factor that we face when using paste numbers and this is what I call the “flow rate into solution.

Paste level guidelines
Figure 1.0

Solubility Testing

Just what is a soil paste or solubility test and when should you consider running the analysis? Solubility analysis is an attempt to see what is in the soil solution, or that which can readily go into solution off the colloid.

The diagram below is a conceptual picture of a root hair in the soil solution in proximity to a clay particle or soil colloid.

The diagram 1.0 is a conceptual picture of a root hair in the soil solution in proximity to a clay particle or soil colloid. The standard soil analysis measures the dots (nutrients) floating in solution as well as the dots (nutrients) held on the surface of the clay mineral, but not those trapped between the clay layers. In a standard soil test, the minerals attached to the surface of the clay particle are removed for analysis by using an extracting solution. A solubility analysis primarily looks at only the blue dots (nutrients) floating in solution.

Soil test diagram

It makes perfect sense to look at a test that measures nutrients only in solution when you study the research work done by Barber and Olsen in 1968 and Dennis in 1971. That research showed the bulk of the soil nutrients taken up by plants was through mass flow and diffusion from the soil solution. Very little nutrition enters the plants by the roots directly intercepting nutrients from the colloid or soil particles. So when should you use a solubility analysis? Those soils with exchange capacities less than 10 should be the first targeted for solubility analysis. This includes all sandy soils even calcareous sands, which tend to get exaggerated TECs on the standard soil test. It is nearly impossible to balance and hold that balance on low exchange capacity soils.

It makes perfect sense to look at a test that measures nutrients only in solution when you study the research work done by Barber and Olsen in 1968 and Dennis in 1971. That research showed the bulk of the soil nutrients taken up by plants was through mass flow and diffusion from the soil solution. Very little nutrition enters the plants by the roots directly intercepting nutrients from the colloid or soil particles. So when should you use a solubility analysis? Those soils with exchange capacities less than 10 should be the first targeted for solubility analysis. This includes all sandy soils even calcareous sands, which tend to get exaggerated TECs on the standard soil test. It is nearly impossible to balance and hold that balance on low exchange capacity soils.

Since the holding capacity of low exchange soils is so small, plants grown on these soils primarily get their nutrition from applied nutrients with variable degrees of solubility. Solubility analysis will take you to a whole new level of understanding the relationship of soil and plant nutrition. When combined with the standard soil test and plant analysis you will get a much clearer picture of what soil nutrition means.

Source: The Art of Balancing Soil Nutrients

How to Read a Soil Test

By Charles Walters

The first step on the road to achieving healthy soils able to sustain productive plants is the soil or plant analysis test. For optimum results, the initial test relies heavily on proper sampling.

Quality samples submitted to the laboratory and excellent testing methods can produce the most accurate results possible but without an interpretation of the nutrient recommen­dations that speaks to the grower — all may be for naught.

Graphs and charts filled with color-coded lists of numbers speak volumes to those that know how to read them. But the uninitiated may glean just a fraction of the total message.

A soil or plant analysis test from a quality laboratory contains much more than just the raw data. Using an integration of field and cropping history with the test results, interpretations and recommen­dations are formulated to tell the grower the meaning behind the num­bers. It is these soil and plant test interpretations and recommendations that matter most and have the greatest benefit for many people.

Agronomist Esper K. Chandler, author of Ask the Plant and founder of TPS Lab, was asked to look at several plant and soil analysis tests from different crops and give his expert interpretation of the results. The results are below. For each example, Chandler’s com­ments offer new insight and enlightenment about what the results said to him. The soil and plant test samples presented in this chapter are actual real-life examples included here with Chandler’s dictated interpretation and recommendations — presented so others can gain a deeper insight into the important messages held within. For each example, the most important messages have been highlighted and explained by Chandler.

Above: A Guide from TPS Lab on Compost STA Test Reports. 

Source: Ask the Plant;

Water-Soluble Soil Tests for Crops

By Dr. Harold Willis

In order to get your soil into a proper balance of nutrients, you should have frequent soil tests made (at least once or twice a year, in spring and fall). The trouble with soil tests is that some are more reliable than others, and there are various ways of testing soil, some of which give accurate results but tell you little about what your crops really need. The type of soil test that gives the most useful information is a water-soluble test. This test tells how much nutrient is available to the plant at that time, rather than the total nutrients in the soil (but mostly unavailable). Most testing labs do not run water-soluble tests unless you request them.

Tests may vary slightly, but using one method (the LaMotte system), desirable water-soluble levels for major nutrients are:

  • 2000 pounds/acre calcium
  • 400 pounds/acre phosphate (P2O5)
  • 200 pounds/acre potassium
  • 40 pounds/acre nitrogen
Soil samples
Soil samples are prepared to run through analysis.

These figures do not translate to non-water-soluble tests and may be higher or lower than most experts recommend, but they do produce high quality crops. Generally, one should not worry about trace elements until the major elements are at proper levels.

Plant tissue testing, as done by most labs, is not as informative as water-soluble soil tests. Tissue tests only test the soluble contents of the cells. Some nutrients are part of the cell structure and are not soluble. Sometimes the soil may have plenty of nutrients, but they are not getting into the plant because of poor root functions or toxic soil conditions.

Source: How to Grow Super Soybeans

Using Lime to “Restock” the Soil

By William A. Albrecht

When limestone is put on the soil, it accepts acidity from the clay, just as other minerals do in the rock weathering processes. As a carbonate, it changes the active acid, or hydrogen, into water, of which compound the hydrogen is not such a highly active acid element. Therefore, the lime­stone corrects or neutralizes the soil acidity.

It has, however, been shown that this neutralizing effect from the liming operation is not so much the particular benefit derived by the crop, because compounds of calcium that do not neutralize the acidity, like calcium chloride, calcium sulfate or gypsum, and even ordinary cement for example, can improve the legume crop as well as calcium carbonate. Liming the soil puts calcium (or both calcium and magnesium if dolomitic limestone is used) on the clay, and thereby makes up this shortage on the list of nourishment of the crop.

It feeds the plant this one nutrient that the better forage legumes need so badly for their good growth and which is so readily removed from soils under higher rainfalls. It is the calcium put in, more than the acidity put out, that comes as the beneficial effect from liming the soil.

A farmer liming his fields after harvest.
A farmer liming his fields after harvest.

Source: Albrecht on Calcium

Nutrients & Minerals Needed for Soybeans to Grow

By Neal Kinsey

Soybean production factors out as fol­lows: a 50-bushel crop takes 280 pounds of nitrogen. Some texts tell you that a 60-bushel crop requires 295 to 300 pounds of nitrogen. The same general rule governs both soybeans and alfalfa. For ease of computation, I like to think in terms of 300 pounds of nitrogen and 60 bushels of beans.

In a normal growing season, you are going to get 50% effi­ciency from the nodulation on your beans. If it takes 300 pounds of nitrogen to grow a 60-bushel soybean crop, and you are get­ting 50% efficiency, this means another 150 pounds of nitrogen must be accounted for. What if you have 2.3% organic matter? That factors in another 66 pounds of nitrogen. Subtract 66 pounds from 150. This leaves another 84 pounds of nitrogen to be accounted for. Without that extra nitrogen, you will not grow 60 bushels of soybeans per acre.

The first clue for a decent production level is calcium in the 60% range. If the soil colloid does not have a proper calcium level, nitrogen will not deliver a top yield. Once you have your basics in place—60 to 70% calcium, 10 to 20% magnesium—then and only then do you start looking at nitrogen as a factor in growing high yield beans. There are very few farmers on my program who raise 60 bushels of beans without obtaining some extra nitrogen above the amount supplied by the soil and nodu­lation.

soybean nodules
Soybean nodules. Courtesy of How to Grow Super Soybeans.

A typical farmer question runs approximately as follows. If a grower wants to raise a 60-bushel bean crop and he is at a 60% calcium level, how many pounds of extra nitrogen would he have to add, the organic matter level being 2.5%? At 2.5% organ­ic matter, such a farmer will have 70 pounds of nitrogen sup­plied by the soil. He will need 150 pounds of additional nitrogen in a normal year, after accounting for the 50% supplied by nod­ules. Again, if you have 70% efficiency from your beans, that goes up. We are considering a 50% efficiency factor right now because it is easy—and expected in a normal year. In other words, 150 pounds of nitrogen generated by bacteria goes into production. We have another 150 pounds to go. Take that 70 pounds from 2.5% humus off the equation and we have to come up with another 80 pounds of nitrogen from some other source. All this assumes that we have a good fertile soil and that there is a proper phosphate and potassium level.


(from Modern Soybean Production, 1983, p. 171-73)

  • Nitrogen. Pale green or yellowish leaves. Seldom a problem if root nodule bacteria are present. Can be due to a molybdenum deficiency.
  • Phosphorus. Plants stunted; leaves blue-green and sometimes cupped.
  • Potassium. Irregular yellow border around leaves.
  • Calcium. Few nitrogen-fixing root nodules, causing nitrogen deficiency symptoms.
  • Magnesium. Leaves turning yellow or brown between veins; leaf tip curled down.
  • Sulfur. Slow growth; leaves becoming yellowish.
  • Iron. Slow growth; new leaves yellow or brown between veins.
  • Manganese. Leaves light green to white between veins.
  • Molybdenum. Reduced growth; leaves with nitrogen deficiency symptoms.
  • Zinc. Plants stunted; lower leaves turning yellow to brown to gray and dropping off; young plants with pale green leaves. Few flowers and pods; pods mature slowly.

It is not discussed generally, but there is a vicious nitrogen cycle that you can get into just by pushing nitrogen. And there are other things that can contribute to crop production for which nitrogen gets the credit. All things considered and all things in perspective should be a norm. We say legumes can get nitrogen out of the air, but we have to add that they don’t get it all from the air. At least 30% has to come from another source, and that 30% either has to be supplied by microbial activity in the soil or by applying some type of N source. The farmer must decide, but when the choice is made, he or she has to deal with the consequences.

Source: Hands-On Agronomy