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Soil Acidification

There are several variables influencing the outcome and production of any ornamental, cash crop or landscape. Weather and environment are the largest of variables, and unfortunately that is just the beginning of obstacles. One inevitable, and often overlooked, variable is soil acidity. Where most have been taught soil acidity is a product of using highly synthetic fertilizers or the result of acid rain there are several contributing factors beyond our control. What is acidity and where does it come from?

Acidity is considered one of the most important variables because it affects several biological and chemical soil properties. Soils with lower pH may even experience a higher fungi population. As a result, acidity can even change the physical properties of soil by promoting air and water movement throughout the soil and stabilize aggregate structures  “Acidity (or alkalinity) is usually quantified using the pH scale, which expresses the activity of concentration of H⁺ ions present in a solution.” (Brady and Weil et al. 2016) Where do hydrogen ions come from?

Carbonic acid is one of the most universal contributors to soil acidity  It is formed when carbon dioxide gas from soil air dissolves in water. This is caused by root respiration and the decomposition of soil organic matter by microorganisms. 

Organic acids are generated as microbes break down soil organic matter through biological metabolism.  These acids can range from citric and malic acids to much stronger types like carboxylic and phenolic groups in humic substances produced by litter breakdown. 

Accumulation of organic matter acidifies the soil for two reasons. During this process, cations are lost by leaching when organic matter forms soluble complexes with nonacid cations. The second is organic matter is a source of H⁺ because it contains many acid functional groups where ions can separate. 

The oxidation of nitrogen, or nitrification, is not solely a consequence of human overapplication.  Nitrogen can be oxidized from organic matter as well as fertilizers. The oxidation reaction produces hydrogen ions as a product which can be a result of bacterial and chemical processes. Two H⁺ ions are released for every NH⁺ ion oxidized.

Acids in precipitation is not always a result of pollution. It is a natural phenomenon and is a variety of acids that contribute hydrogen ions to the soil. As raindrops pass through the air, they dissolve CO² forming carbonic acid. This changes the pH of the water from approximately 7 to about 5.6. Pollution, lightning and natural disasters can contribute to a lower pH precipitation (acid rain). 

Plants must maintain a balance of positive and negative charges they take up from the soil. For every positive charge taken up by the plant it can either take up a negative charge or get rid of a positive charge. If the plant takes too many certain cations, it generally will release H⁺ ions into the soil to maintain balance. 

Soil acidification is inevitable. The good news is many growers can contradict these variables through liming practices. This is why it is always important to soil test and maintain a certain balance for crop/soil health and nutrient availability. 

Source: Brady, N. C., & Weil, R. R. (2016).  The Nature and Properties of Soils (13th ed.). Pearson.

Evaluating Nitrogen Management Late Season

As the 2024 corn crop is approaching maturity throughout the Great Lakes region, many producers and crop consultants are starting to question whether they have applied enough nitrogen to finish out the season. A corn stalk nitrate test (CSNT) can be a useful tool in assessing the effectiveness of a nitrogen program.  However, the test results often generate more questions than answers. Remember, when dealing with a natural system, the word always never applies. The general interpretation of a CSNT is that if the result is less than 700 ppm, nitrogen may have limited your yield, from 700 to 2,000 ppm, nitrogen use was optimal, and greater than 2,000 ppm indicates excess nitrogen. However, the CSNT data cannot be used on its own to make future management decisions. It must be utilized as a part of a more holistic approach including crop observations, soil test data, weather history, fertilizer application history, etc.

When a CSNT shows high levels, the most obvious explanation is that too much fertilizer was applied. No, this does not indicate that growers are carelessly over applying fertilizer. It simply means that for the current growing season, a lower amount of applied nitrogen would likely have generated the same yield for reasons that are impossible to predict at the time the nitrogen was applied. Drought stress is one of the leading causes of high CSNT results. Most growers are applying about 1 pound of nitrogen per bushel of projected yield. So, if 200 pounds of nitrogen is applied between a starter and sidedress application expecting to harvest 180-200 bushels, but a late summer drought cut that yield down to 100-120 bushels, the excess nitrogen will accumulate in the lower stalk since there is not enough grain to utilize the applied nitrogen. Another potential explanation is another nutrient deficiency. For example, if the crop was supplied with enough nitrogen to grow 200 bushels, but the plants are experiencing a severe sulfur or potassium deficiency reducing the yield, there will be excess nitrogen in the plants.

On the contrary, a low CSNT does not always mean that the nitrogen was lost or that more applied nitrogen would have resulted in additional yield. There are situations during unusually good growing seasons and the crop yield exceeds the early season expectations. The plants show no physiological deficiency symptoms and the CSNT shows less than 200 ppm. This indicates that the crop was able to efficiently utilize all the applied nitrogen and additional nitrogen would likely add little to no additional yield.

For more information about collecting CSNT samples and understanding the results, please visit our Cornstalk Nitrate Test Fact Sheet.

Corn Root Architecture and Nutrient Management

There have been many studies over the years documenting nutrient placement, rates, and several types of applications. It is not surprising that these must be conducted repeatedly because there has not been a definite answer to the “how, what and when” questions to nutrient management. In conjunction with nutrition, hybrid selection has also been vigorously evaluated. These studies usually compare offensive and defensive hybrids to certain applications. Is there a better way to portray which hybrid family does well to high fertility, drought conditions or sidedress applications etc.? Jim Schwartz, Beck’s Director of Research, Agronomy and PFR, has partnered with Dr. Fred Below, Professor at the University of Illinois, to understand how different root architectures and sizes affect nutrient management decisions.

The Root Reveal project is a new means of hybrid categorization. Its goal is to place each hybrid type into different root classes. A majority of the seed industry understands different root angles, but few have made the correlation between this and nutrient management on a per-farm basis. When selecting a nitrogen program, how often does the conversation happen discussing which hybrid will perform best with which fertilizer application? The common conversation is which hybrid efficiently uses higher rates of nitrogen or has little to no yield response to excessive amounts.  What Jim Schwartz and Dr. Fred Below are setting out to do is make the conversation, “This is the placement of the fertilizer that will most benefit this hybrid’s root architecture”.

To obtain the root architecture and root volume, each hybrid has been undergoing extensive observation. This has been conducted in several different ways. The first way is a more conventional method. The simple in-field root dig. After the root mass has surfaced, it is then photographed and documented. This, however, is not enough. So, it has been taken one step further by creating a photography chamber for each individual root. The chamber spins at high speeds, taking several pictures, giving a 3D makeup of each hybrid root. Researchers can collect the architecture and root volume of each hybrid root in the matter of a few minutes.

The third way to collect more data on each hybrid root type, is by utilizing Corn Root Boxes.  Beck’s Root Reveal Research is capable of growing an individual corn plant in an empty chemical tote.  “These empty chemical totes were shrink-wrapped, covered with boards, and filled with Turface Athletics™. They were then strung with line to help support and maintain the root architecture of the plant. Each cage contained an individual corn hybrid and was then watered and fed the same amount of nitrogen. Once the plants reached tassel, they were cur off form the water and nutrients and left to dry.” The results show how roots perform without restricting variables of different soil types, compaction, etc.

How will this impact nutrient management? Knowing a certain hybrid has a horizontal or vertical root development directs the grower to better management. Applications, such as nitrogen, are taken into the plant through a process called mass flow. Being an anion allows nitrogen to, mostly, move vertically in the soil profile. If we know where the roots will be, we know where to place the fertilizer. A vertical root system needs to be banded in or near the row. A horizontal root system does well with sidedress applications because it can reach below the application area. For more information visit: https://www.beckshybrids.com/about-us/media/becks-root-reveal-research-digs-deep-into-understanding-corn-root-architecture

Be Wise When Cutting Back on Broadcast Fertilizer

When working with a reduced fertilizer budget, some approaches are wiser than others. When evaluating the approach to take in reducing broadcast fertilizer rates this fall, be sure to ask some questions.

• How will this plan impact the higher yielding areas of the field?
• Is this field already have low fertility and will this reduction have a negative impact?
• How long will/can I follow this plan?
• Should the same approach be used with phosphorus and potassium?
• What is the producer’s tolerance to financial and yield risk?

Before answering these questions, let’s look at the basics of fertilizer recommendations. While there are a wide range of fertilizer recommendations structures, they all have some common fundamentals.

Soil Test Levels – Every fertilizer recommendation structure has a target soil test value that internally will lead to the following categories.

• Below this target value there is a strong probability that crop yield will increase with the application of fertilizer. In these areas, applying a minimum of crop removal of P and K is advisable. This means applying an equivalent amount of P and K to replace the nutrients removed from the field in grain, or forage. Without the financial restrictions, this is the area of the field would possibly receive more fertilizer than crop removal to increase soil test levels. The goal is to prevent soil test levels from declining further and gain any possible yield benefit from the application.
• Above the target soil test level, but below an optimum soil test level, the probability of yield increase from the application of fertilizer is diminished and not expected. If the nutrient is not applied the soil test level could decline below the target level over time. The long-term goal for this category is to apply enough fertilizer to keep the soil test level in this range such as crop removal or slightly less.
• Above the optimum soil test level, there is no benefit to increasing soil test levels any higher. This range of soil test levels receive a fertilizer rate less than crop removal, some fertilizer recommendation structures take this category to a zero application rate. The goal for this soil test range is to not build up or maintain, rather utilize the inventory of nutrients in the soil.
• There is a maximum soil test value where applications need to stop entirely. In most cases the soil reaches a point where it cannot retain all of the applied nutrients, and a notable portion of the nutrients will be subject to environmental loss. For financial and environmental benefit, do not apply nutrients to soils at these levels.

Secondly, we need to look at the behavior of yield in each field. One of two scenarios will develop. When fertility is the limiting factor to yield, soil test levels will correlate closely to yield. There will be low fertility in the low yielding area of the field. When fertility, or the soil nutrient in question, is not the limiting factor, soil test levels will have an inverse correlation to yield, it will result in higher soil test levels in the areas of low yield.

Finally, we need to look at the behavior of the nutrients themselves. While the values can vary, it is accepted on average that for every 18-22 pounds/acre of P₂0₅ applied to the soil above crop removal, phosphorus soil test (Bray or M3) should increase by 1 ppm. Research is beginning to show that it takes that amount, or more, P₂0₅ removal to lower the soil test 1 ppm. A very good yielding crop may reduce phosphorus soil test levels 1-3 ppm/year or less.  Conversely it requires an application of 6 to 10 pounds/ac of K₂0 (depending on CEC of the soil) to raise the soil test 1 ppm (ammonium acetate or M3). Recent research indicates that though crop removal, soil test potassium levels can reduce soil test levels by 1 ppm with less than 6 to 10 pounds of K₂0 removal per acre. A good yielding crop can reduce soil test potassium levels by as much as 20-30 ppm/year.

Knowing these factors and how they interact helps begin to prioritize ways to reduce fertilizer application rates and the associated risk from doing so. Some suggestions may include:

• Reduce/stop fertilizer application on soil testing above max and possibly those above optimum.
• For soils testing below the target, consider reducing or removing any fertilizer rates above crop removal.
• Phosphorus rates can be reduced or eliminated for a short period of time with little impact on phosphorus soil test levels. Once the levels do start to decline, it will take a significant application to build back up.
• Potassium levels can drop quickly in high yielding grain or forage fields, application rates below crop removal should be kept to a minimum. More frequent soil testing is advisable to monitor soil test potassium levels during aggressive potassium application rate reductions.
• When soil fertility is limiting yield, be sure to focus on applying at least crop removal on soils below the target level. Using a yield map to better define crop removal rates is advisable.
• When soil fertility is not a yield limiting factor, shift the fertilizer to the higher yielding areas of the field to maintain or increase yield in those areas.
• Consider applying a percentage of crop removal, maybe apply 70-80% of phosphorus above target level and full crop removal below the target.

Evaluating how a cut in fertilizer application rates may impact the situation will lead to wiser budget cutting. The worst thing you can do is simply reduce standard recommendations by a flat percentage across the board. This will usually place the greatest yield production risk on the highest yielding areas. Your ALGL regional agronomist can help evaluate the various options based on your situation.

The 2024 Growing Season and Late Season Tissue Testing

While things started off a little bumpy, the growing season of 2024 for much the Great Lakes region has been better than normal. Some areas have had excess rain and others would like a little more, but on average the rain has been fairly timely. As a result, crop performance is looking good to excellent. The plant tissue samples from row crops that we have seen support this. We are often asked by growers and advisors, “What are you seeing on other samples coming into the?” The answer is that most samples are reporting at normal to high ranges across all nutrients. The common patterns of deficiencies and excesses resulting from drought stresses or excess moisture are very rare this year. This has many questioning the nutrient status of their crops later into the growing season to see if there is enough fuel left in the tank to finish out these crops that right now look to have fantastic yield potential. However, as plant tissue samples are collected later in the growing season, the test results need to be evaluated with a cautious eye.

As plants transition from vegetative growth stages to reproductive stages, the nutrient content of the plant leaves will change, most noticeably nitrogen and potassium. These nutrients are mobile in plants, so as the plant starts transitioning to grain-fill, they may be translocated from the leaf to the grain resulting in low tissue test ratings that may not necessarily indicate a yield-reducing nutrient deficiency.

Another common trend in plant tissue nutrient levels is an increase in micronutrient concentrations as the plants approach physiological maturity. This is a result of carbohydrates and other carbon-based molecules being translocated from the leaf tissues to the grain effectively reducing the biomass of the leaf. The micronutrients (iron, manganese, zinc, and copper) are immobile in the plant tissue, so they remain in the leaf that has a lower mass and are now present at a higher concentration. The micronutrients may be rated as high or very high, however, this is not necessarily an indicator of excessive fertility or potential toxicity.

While plant tissue testing can be a very effective tool for fine-tuning a fertility program, be careful not to make drastic decisions based on late-season plant tissue test results alone. A continued favorable weather pattern and late-season disease control are going to be critical in finishing out this season.

Soil Types and Herbicide Rates

As for many growers across the Midwest, weed control and suppression has been a struggle for 2024.  Due to warm temperatures and high winds some may think twice about relying on their post-emergence application for the following year.  One of the best options, weather willing, is investing more in the pre-emergent rather than one or more post applications.  A crucial part of residual herbicide use is soil type.  Some of the herbicide applied is bound by soil.

Soil types can be categorized by sand, silt, loam and clay etc., but how do these affect herbicide applications?  Many of these categories are a combination of several different soil types.  These are generalized into different soil textures.  For pesticide application, they are separated into four different groups: Coarse, Medium, Fine and Organic.

Coarse soils include sands, loamy sands and sandy loams.  These have a general CEC of 1-5 for light colored soils and 5-10 for dark colored.  Medium soil include sandy clay loams, sandy clays, loams, silt loams and silts.  These have a CEC range of 11-15 for light colored and 15-20 for dark colored soils.  Fine soils include silty clay loams, silty clays, clay loams and clays.  Their CEC range is 20-25+.  Organic soils are most often referred to as peat or muck soils.  The CEC range can be 50-100. 

Textures are important to identify because each texture category corresponds to a different CEC range, or Cation Exchange Capacity.  CEC is the total capacity of a soil to hold exchangeable cations, which is usually included in soil test results.  Since soil is negatively charged, primarily due to clay and organic matter content, certain soils can hold onto more cations than others.  This too means that some soils will hold more herbicide than others.  Below is a chart showing herbicide rates in correspondence to organic matter and soil textures. 

Comparing the coarse, low organic matter soil to the fine, greater than 3% organic matter soil; it requires double the amount of herbicide applied to obtain proper weed control.  If over application occurs in a coarse soil type, too much herbicide is processed in the crop and can cause damage and/or death.  This can also cause movement through leaching, or runoff, to off-target locations.  Over application in a high clay or organic matter soil can potentially cause carryover to the following rotation. 

For more information on the different CEC ranges within textures and how this successful weed control, visit: https://www.canr.msu.edu/news/determining_soil_type_important_for_successful_preemergent_weed_control

“Good” Vs. “Bad” In Season Soil Tests

When diagnosing seasonal crop issues a soil test is often a key piece of information. When using a soil test in this manner it is best to collect a sample from the affected area and then another sample from just beyond the boundary of the affected area. If the issue appears to have various levels of severity, a sample from each of these areas is advisable.

Commonly when the cause of the issue is soil fertility related, the unaffected area, or “good” sample, is also being impacted to a lesser extent. Often in season crop issues related to soil fertility are not isolated and often more than one aspect of the soil test is impacting the plants. Without sampling the unaffected area, it may not be possible to isolate which aspect is ultimately leading to the issue at hand.

If the unaffected area has a low soil test value that is not affecting the crop performance that is equal to, or even lower than to the affected area, not having the “good” sample from the unaffected area could lead to a misdiagnosis. Mismanagement of a given soil test parameter is often not isolated to a small portion of a field and needs to be identified as part of the diagnosis process.

When both affected and unaffected paired samples they are often labeled as “Good” and “Bad”, upon review of the soil test data they would be better described as “Bad” and “Worse”. Understanding of how soil fertility is causing or impacting the crop issue can be missed without paired samples. For more help evaluating the impact of soil fertility from paired diagnostic soil samples, reach out to your Regional ALGL Sales Agronomist.

Selecting the Right Plant Tissue Test Package

All the routine plant analysis packages at A&L Great Lakes Laboratories include the elements, phosphorus, potassium, magnesium, calcium, sulfur, sodium, iron, aluminum, manganese, boron, copper, and zinc. The only difference between the packages is the type of nitrogen analysis that is included.

The P1 package does not include any nitrogen analysis. All the other nutrients are included because they are all collected with the same laboratory process. This package is generally used for research and field trials where nitrogen is not a variable.

The P2 package is the standard for all row crops and most specialty crops. This package includes total nitrogen. The nitrogen sufficiency status for nearly all crops is based on total nitrogen.

The P5 package includes nitrate analysis. Nitrate is the mobile form of nitrogen in most plants. So, when analyzing entire leaves, the concentration is generally very low. The nitrate analysis is only appropriate for very few crops and plant parts, primarily potato and tomato petioles. The concept is to capture the fraction of nitrogen that is moving between the leaves and stems so that fertilizer inputs can be adjusted in highly managed specialty crops. For most crops there are no sufficiency ratings for nitrate levels. For that reason, when routine row crop samples are submitted to the lab requesting the P5 analysis, the package will usually be changed to P2.

The P6 package includes both the total nitrogen and nitrate. Again, this package is intended to be used for the same crops as the P5 package. However, any plant submitted requesting the P6 package will receive it since it contains the total nitrogen that will provide sufficiency ratings.

For routine plant tissue testing, the nitrate levels really do not provide any useful information and are often below the minimum reporting limit. The P2 package is the appropriate package 99% of the time. If you are working with a new crop or have questions regarding plant tissue sampling, contact your ALGL agronomist.

Sampling Hay for Feed Analysis

Proper feed analysis is crucial for maintaining the health and productivity of livestock.  Accurate sampling of hay and forage is the first step in obtaining reliable feed analysis results.  This article outlines the best practices for sampling hay and forage to ensure that the samples accurately represent the feed being used.

Sampling hay and forage is essential for several reasons.  Knowing the nutritional content helps formulate balanced diets.  This ensures the animals receive all the essential vitamins and minerals required.  Feed analysis can prevent overfeeding or underfeeding, and in turn will optimize feed costs.  Sampling can also identify potential deficiencies or toxicities in the forage, preventing health issues in livestock.

According to the A&L Great Lakes Laboratories Agricultural Feed Analysis Sampling Guide 

Hay may be sampled as it is stored, if it is dry enough to keep without further curing. Different cuttings should be sampled and analyzed separately unless different cuttings are being fed at the same time, in which case they may be sampled in the same proportions as they are being fed.

 Hay samples should be taken with a core sampler, if possible.

1. Ensure that tips are sharp enough to cut through the hay to prevent selective sampling.
2. Core sampler should penetrate at least 12”‐18” into the bale.
3. If using an electric drill or a hand brace, run the drill at slow speeds. High speeds heat the probe and can damage supplies.
4. At least 12 cores of hay should be taken from random bales or locations if loose or chopped hay.

When sampling hay to be fed on your farm, avoid sampling decayed or moldy hay or other portions of hay that will be discarded or would likely be refused when fed to animals’ free choice. However, include deteriorated materials if the hay will be ground, sold, or purchased in order to best describe all the hay. Place the entire sample into a plastic bag and seal tightly.

 To sample square or round bales, collect one sample from each 15-20 bales (from a single lot).  The core sample must be pulled from the end of the bale with the core puller inserted in the center.  If these are round bales, take the sample from the wrapped circumference and not the open ends.  By doing this, on both types of bales, the sample will include the most layers and provide the best results.

For additional information about sampling pastures, loose or compressed hay and forage visit the Feed Analysis page on the A&L Great Lakes Laboratories website.  There the sample guide, pricing submittal form and a sample report will be located. 

Converting ppm to Percent

In fertilizer, compost, manure, and plant tissue samples both ppm and percent (%) data values are common. But how do they compare?

1% = 1 part/100 parts = 10,000 parts per 1,000,000 parts.

Both are units of concentration, just very different in magnitude. 10,000 ppm is the same as 1%. For larger concentrations % is commonly used to keep from reporting very large ppm numbers. With lower concentrations ppm is commonly used to avoid very small fractions of %. The reporting of nutrients in large ppm values is common on environmental reports for the analysis of biosolids.

The scale of the two units can be confusing. For example, a liquid fertilizer sample came to the lab for analysis and the results from total nitrogen was 0.14%. The customer called the lab concerned with such a small number. The customer had used test strips to do a rough estimation of the plant available nitrogen in the material. The material exceeded the maximum of test strips leading to a plant available nitrogen concentration of at least 500 ppm, how could the lab result be less than 1% total nitrogen? The 0.14% lab result was equal to 1,400 ppm total nitrogen.