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Agronomy Rant - Reading Lab Reports

Editorial Note – This editorial is an overgeneralization of common terms that are often misused in soil fertility. It is not directed at any one entity. It is intended to be informative and mildly entertaining. Please keep in mind that the agronomists at ALGL spend a considerable amount of time with soil and are often isolated from human interaction with the outside world. Therefore, the phrase "mildly entertaining" is highly subjective.

We have all heard the phrase "reading a soil test report" or "reading a tissue test report." Although the apparent task may be readily inferred through superficial observation, such a characterization is wholly inconsistent with the actual procedural and operational semantics of the process. Or, to put it more simply, that may appear to be what is being done with laboratory results, but it is not how the process actually works.

We read text and interpret data. Read means to look at written words and understand their basic meaning. Interpret means to explain or determine what something means, often going beyond the literal words or data.

Like all agricultural laboratory reports, soil and tissue test reports contain data. The data itself has little, if any, meaning without additional interpretive information derived from university- or industry-based research. Once that interpretive information is applied, informed and prescriptive decisions can be made based on the data.

A good example of data interpretation can be found in our blog post, Lab Tests and Fuel Gauges. We can observe data values, but without interpretation we cannot make prescriptive decisions or take meaningful action to influence future outcomes. Without interpretive information, we can only track changes in the data and that is how researchers build the interpretative data.

One does not simply “read a soil test report”, one “interprets a soil test report!”

This concludes the Rant

The Push for Higher Soil Calcium Levels

Calcium, like most recognized soil nutrients, plays a large role in overall plant success. It is the foundation of cell walls, promotes root growth, acts as the plant’s defense, and helps manage stress. This macronutrient is readily available in most Midwest soils, however, there has been a movement to increase the soil calcium levels regardless of soil test levels. Have you ever experienced calcium deficiency?

Having adequate calcium levels is necessary for the most productive crop, but what happens when soil levels are excessive? The goal of increasing soil calcium levels is to remove magnesium from the soil colloid in hopes to maximize flocculation. Flocculation is when clay particles clump together forming aggregates, or larger clusters of soil particles. Calcium binds to the soil colloid stronger than magnesium and can form larger aggregates such as blocky formations. This is crucial for water drainage, root penetration and pore space but creating excessive soil calcium nutrient levels is unnecessary.

What is the correct calcium to magnesium ratios and levels? When discussing these two ranges of sufficiency levels, it is entirely dependent on soil type, parent material and region. The parent material, or the original base layer of the soil, is constantly being weathered and breaking down. This releases nutrients such as magnesium depending on the type of parent material. When examining soil test results, a 1:1 ratio of calcium to magnesium involves alternate management decisions. This is often switching from dolomitic limestone, which consists of about 11% magnesium and 21% calcium, to a high calcium lime like calcitic limestone, which contains about 40% calcium and .2% magnesium.

In The Great Lakes Region, higher magnesium to calcium ratios is not unheard of but exist in certain concentrated areas. These areas usually have a lighter CEC, or cation exchange capacity. This creates another challenge for applications and rates. If the CEC is low, there are fewer exchange sites on the soil colloid. Once a high calcium lime is spread, it can dramatically reduce the number of other cations on the colloid. Other cations, such as magnesium and potassium, are then leached away with calcium remaining on the exchange site. Magnesium is the center of chlorophyll. The main energy source for all living plants. Negative impacts of high application rates can reduce yields at a much greater rate than trying to achieve a better calcium to magnesium ratio.

Before making a management decision, there are some questions to answer with appropriate responses. Is the soil pH where it needs to be? Are calcium and magnesium in the sufficient range? What is the CEC? How many sampling events are providing this data, and are the levels consistent? It is recommended to not apply more than 2.5 tons of liming material in one application for most soil, and 2 tons for soils with lower CEC.

Tips for Summertime Lawn Care

The hot, dry, late summer months can be stressful on lawns. Lawns throughout the Midwest and Great Lakes regions are generally comprised of cool season grass varieties such as fescue, ryegrass, and bluegrass. While these varieties are adapted to surviving cold winters and thrive in cooler spring and fall conditions, they can struggle to maintain the desired appearance during the hottest times of the year. Here are a few tips to keep your lawn looking its best.

Fertility – A properly fertilized lawn is better able to withstand the stress of hot, dry weather even though it may still turn brown. The difference is that a nutrient deficient lawn is more likely to die under heat stress, where a healthy lawn may go dormant and quickly rebound when conditions improve. However, once a lawn has gone brown, fertilizer applications will not fix the problem if the weather is still not fit.

Nitrogen – Most lawn care programs will recommend nitrogen targeting about 4 pounds of nitrogen per 1000 square feet split into 3 or more applications throughout the growing season. Fertilizer products formulated for lawn use are generally treated to slow the release of nitrogen and may contain some potassium and traces of other nutrients such as sulfur and iron. This is a great start since grass responds well to nitrogen, but they generally do not address all the fertility needs of a healthy lawn.

Phosphorus and Potassium – P and K both play several important roles in plants. The most important roles for promoting a healthy lawn are that P stimulates root growth and transports energy and K regulates water movement within the plant. Residential lawns are often deficient in P and K since the soil used to construct the lawn is usually subsoil left from the construction of the house. A routine soil test will indicate if P and/or K fertilization is needed. Lawns should have a Bray P1 around 25 to 40 ppm and K around 150-200 ppm. If P and K are needed, the recommended amounts should be applied in the spring and/or fall when temperatures are cooler and soil moisture tends to be higher as these are generally fertilizer products with a high salt index that have the potential to cause damage to growing plants if they are stressed. Once desirable levels of P and K are reached, if the clippings are not removed from the lawn, little or no additional P and K are needed to maintain the levels.

pH – Management of the pH is critical for assuring nutrient availability. A routine soil test will indicate if the pH needs adjusted. Lawns perform well in a pH range of 6.3 to 7.3. If the pH is lower (acidic) it can be easily corrected with lime. Alkaline (high pH) soils are common due to the subsoils that make up many yards. High pH is much harder to correct but can be done through repeat applications of elemental sulfur in the spring and fall, but it may take 2 or more years before a noticeable change happens.

Aeration – One of the challenges with hot, dry conditions is that the soil is generally hard and crusted and what little precipitation there is often comes in short, intense events that quickly runoff or evaporate before the moisture can soak into the root zone. Having a will aerated lawn will help to improve water infiltration and utilization.

Irrigation – Irrigation certainly has the potential to minimize the effects of the stressful summer heat, but it is important to make sure that the water being used is not causing any additional problems. Most well and municipal sources of water will have a high pH. Continuous use of alkaline water can cause nutrient tie-up in the soil. Avoid using softened water. Softened water, from conventional treatment systems, will contain sodium which at high levels can be toxic to plants and destroy soil structure. Irrigation systems are generally plumbed separately from the interior plumbing to avoid this, but if using an outdoor spigot to run a sprinkler, this water may be softened. If so, bypass the softener while irrigating.

The key thing to remember to keep your yard looking its best is that most lawn care services do not address the P, K, or pH needs of your lawn. They generally apply only nitrogen fertilizer and insecticide and herbicides when needed. A lawn can look very good with frequent nitrogen applications but can quickly fail when stressed. Managing the other aspects of the lawn are generally up to the homeowner.

Sulfur Soil Testing and You

(For proper impact please read the title in a monotone voice with the crackle of a film projector audio)

A variety of questions have recently come into the lab regarding sulfur soil tests and how to interpret the results. Sulfur soil tests are often misunderstood and are frequently criticized for producing inconsistent or questionable results. Much of this perception stems from a lack of understanding that the soil test chemistry of sulfur differs from that of the other primary, secondary, and micronutrients. Analytically, sulfur behaves much like nitrate and should be managed more like nitrogen than phosphorus or potassium.

Unlike phosphorus or potassium soil tests, sulfur soil tests are not intended to measure a nutrient reserve that should be built or maintained. Instead, their primary purpose is to estimate the amount of sulfur currently being supplied from natural sources and determine whether additional sulfur fertilizer is needed for the crop. Understanding this distinction is essential for interpreting sulfur soil test results.

Of the various forms of sulfur, the two predominant soluble forms are sulfate (water- and acid-soluble) and sulfide (acid-soluble). Sulfide is not stable in most soil environments. During soil testing, an acid extractant such as Mehlich 3 is used to solubilize and extract sulfur. Only sulfate forms are extracted. If the primary sulfur source is sulfate fertilizer, it will be reflected in higher soil test values, provided the soil sample was collected before the sulfate leached below the sampling depth. Elemental sulfur, however, will not be detected until it has been oxidized to sulfate.

Sulfate leaches through the soil profile only slightly more slowly than nitrate. Like nitrate, sulfur soil test results can vary throughout the year, making it impractical to build and maintain elevated soil test sulfur levels. More than 50% of sulfate present in the soil profile during the fall may be lost through leaching before the following growing season. Consequently, sulfur soil test values represent the sulfur available at the time of sampling rather than a stable reservoir of plant-available sulfur.

The dynamics of sulfur soil testing and interpretation have changed considerably over the past 50 years. The time frame of an interpretation therefore has a major influence on its relevance. Before about 1990, atmospheric sulfur deposition on agricultural fields in the eastern half of the United States commonly exceeded 20 lb S/acre annually, primarily in the sulfate form. By the early 2000s, atmospheric deposition had declined to less than 5 lb S/acre annually and is currently less than 2 lb S/acre in many areas. Most publicly available sulfur soil test interpretations were developed before this dramatic decline in atmospheric sulfur deposition.

Although atmospheric sulfur deposition has changed dramatically, the purpose of the sulfur soil test has not. The sulfur soil test is intended to estimate the sulfur supplied from natural sources—not to establish a target soil test level to achieve or maintain. While atmospheric deposition has declined substantially, sulfur can still be supplied from soil organic matter, manure, sulfate fertilizers, soil minerals, and irrigation water. The sulfur soil test helps estimate the contribution of these sources and whether supplemental sulfur fertilizer is needed.

Modern interpretation of sulfur soil test results reflects these principles. An example of sulfur fertilizer recommendations based on Mehlich 3 sulfur soil test results is shown below.

• Over 30 ppm Mehlich 3 sulfur: No additional sulfur is recommended.
• 25–30 ppm Mehlich 3 sulfur: Apply sulfur to replace approximately 50% of annual crop sulfur removal.
• 20–25 ppm Mehlich 3 sulfur: Apply sulfur to replace approximately 100% of annual crop sulfur removal.
• 15–20 ppm Mehlich 3 sulfur: Apply sulfur to supply approximately 75% of annual crop sulfur uptake.
• Under 15 ppm Mehlich 3 sulfur: Apply sulfur to supply approximately 100% of annual crop sulfur uptake.

Learning from Plant Tissue Testing

Plant tissue testing can be an incredibly valuable tool in soil fertility management. However, plant tissue test results by themselves often lead to more questions than answers. While the results indicate which nutrients are normal, low, or high, it does not indicate why they are that way. To get the most information from plant tissue test results, they must be used in conjunction with crop scouting and knowledge of previous fertility practices and recent weather conditions.

Here is an example of utilizing tissue testing to evaluate a fertility trial graciously shared with the ALGL agronomy staff from a client in Northwest Indiana. The samples were collected to two areas where one had received ammonium thiosulfate in the starter program (Sample A) and one did not (Sample B). Upon visual inspection of the plants, the sample that received the sulfur treatment is obviously darker green. So, the conclusion here would be that the sulfur application was beneficial. However, comparison of the tissue test results shows that there may be more going on here than a simple sulfur response.

The first observation of the test results that seems unusual is that both samples fall in the normal range for sulfur levels. The sample not receiving no sulfur is obviously lighter in color, so a sulfur deficiency would be expected. Upon closer inspection of the normal ranges provided on the report though, you can see that the sulfur level in the untreated sample is only 0.01% above the lower limit of the normal range, so the plants may be experiencing a sulfur deficiency. It is important to look at the actual values of the test results and not just the bar graph ratings.

The unexpected result of this comparison is that the healthier looking plants are lower in both phosphorus and potassium. The darker colored plants are also showing some purpling in the older leaves which is common in the early growing season due to cooler nights or genetic differences, but the tissue test results show that the phosphorus is at the lower end of the normal range and the plants maybe experiencing a phosphorus deficiency even though they visually appear healthier. A closer look at the test results also shows that the untreated plants are marginally low in manganese which may be the cause of the lighter coloring.

What has likely happened in this scenario is that the sulfur application likely improved the formation of chlorophyl resulting in a darker colored plant that may actually be covering up the visual symptoms of other potential deficiencies that maybe occurring in the plants.

The takeaway from this is that visual comparison and tissue test results on their own do not always paint a complete picture of what may be going on in the field, but when used in conjunction with each other, a more complete conclusion can be made and future fertility plans can be adjusted accordingly.

Sample A

Sample B

The “Dilution Effect” in Plant Tissue Tests

Tissue testing is a great tool to use in a grower’s toolbox. However, just like any analysis it comes with specific interpretations, limitations and variables. A tissue test will reveal nutrient levels at the current time of sampling. This can help or hinder certain scenarios. Each test must be conducted with an end goal. Whether the goal is to constantly spoon feed a crop for maximum yield potential, use the results for diagnostic testing or just get a general idea how the plant is utilizing what the soil has to offer.

Agronomists are constantly trying to make patterns and accrued data to justify what they are seeing in the field. This will lead to tissue samples being taken for a “good” and “bad” situation. One section of corn, for example, is greener or has more biomass than its neighboring rows. It is always good practice to have a soil sample in the same tissue sampling area to complete the story. This will reveal what the soil has to offer and compare what the plant is taking up.

In a particular situation, “good and bad” samples are sent in for analysis. The bad samples show sufficient levels of nutrients. The good samples show sufficient levels as well except for potassium. When reviewing the soil samples, soil potassium was adequate too. The first place to start is verifying that the sample was taken correctly and handled in the right manner. This refers to sampling the correct part of the plant at the right growth stage. Then correctly staging the plant for interpretations of the data. It is important to correctly handle plant matter when analyzing potassium since it can be shed from the leaf surface as soon as it starts to wilt.

The dilution effect occurs when the plant’s total biomass, or growth, exceeds crop uptake. In situations where one section of plants seems larger than others, this can be the case. For example, the amount of potassium in the soil is the same, and the rate of plant potassium uptake has not changed either, but the plant is distributing the same amount over a larger volume of biomass. This would lead to lower potassium concentration in the tissue sample leaf taken.

This does not indicate a lower yield potential. As mentioned before, a tissue sample is a glimpse of the “now” when the sample is taken. As the root system grows, and higher nutrient uptake occurs, concentrations in the plant tend to find an equilibrium. When diagnosing the “bad” tissue sample, taking a closer look at the roots of the plant and the soil are key. Ensure that compaction, water drainage, fertilizer application and soil type are uniform before developing a recommendation. All variables influence the crop’s nutrient uptake and the efficiency of nutrient utilization.

Common Tissue Test Questions

Tissue testing season also brings questions about interpreting tissue test results. Here are five of the most common questions and answers.

“What yield goal is used for the sufficiency ranges on the report?”

In tissue analysis, there are “sufficiency” ranges and “target/optimal” ranges. Our sufficiency ranges are levels that should not result in a physiological deficiency; therefore, yield does not impact sufficiency values. Yield goals could impact target or optimal ranges, but that concept has yet to be fully vetted by the industry.

“I see visual deficiency symptoms, but everything is sufficient?”

Sometimes weather conditions can create situations that limit a plant’s ability to metabolize nutrients or process their effects. The best example is purple corn during the first few weeks of growth in a period of cool, wet weather. The corn is unable to utilize all of the photosynthates being produced during the day, leading to a buildup of the purple pigment anthocyanin. This is the same reaction plants have when they are phosphorus deficient and cannot transport photosynthates efficiently.

Secondly, don’t just look at the graphs on the report; look at the actual data. If the value for a given nutrient is at the very bottom of the sufficiency range, external or compounding factors could cause a visual deficiency to appear. Likewise favorable weather conditions or compounding factors can cover up visual deficiency symptoms. For examples excess nitrogen can reduce the visual appearance of sulfur deficiency.

“Why is my aluminum level so high? Do I have aluminum toxicity?”

This is a common question for very young plant samples, especially whole-plant samples. In most cases, this is the result of soil contamination, which is often paired with very high iron levels. True aluminum toxicity will kill plant roots before the plant is able to hyperaccumulate aluminum.

“Does ALGL wash tissue samples before analysis?”

While some labs wash tissue samples to remove contaminants, others do not, and both approaches have valid reasons behind them.

At ALGL, we do not wash plant tissue samples. If plant tissue is washed after the sample begins to wilt, potassium can be lost from the sample. Delaying washing until the sample arrives at the lab has limited success in removing foliar spray residues from plant tissue. We believe it is best to wash or rinse samples with de-ionized water at the time of collection if contamination is a concern.

“I took a sample of plants in really bad shape (AKA dead), and the results show multiple deficiencies and excessive levels. Which deficiency and/or excess should I focus on first?”

A wide range of physical processes that occur at plant death can confound deficiency data. Plants can lose a significant amount of biomass as they die and begin to decompose. This can lead to increased concentrations of structural and/or immobile nutrients. In addition, cell rupture can result in the loss of non-structural and mobile nutrients, decreasing their concentrations.

Dead plants tell no tales. Collect samples from the border of the affected area to capture usable tissue data.

If you have additional questions, please reach out to your ALGL regional sales agronomist.

CEMA 216 Basics

USDA's primary regenerative agriculture funding opportunity is the NRCS Regenerative Pilot Program, launched for FY2026. The program provides approximately $700 million to support the adoption of regenerative practices. As part of the application process, soil health testing is required at the beginning of the contract and throughout the contract period.

The challenge throughout the winter has been the list of required soil health tests outlined in the CEMA 216 document. Previous versions of the document not only specified the required tests but also required specific laboratory methods to perform them. These methods were not commonly offered by commercial laboratories, greatly limiting access to labs capable of completing the required testing.

In April, CEMA 216 was updated to the January 2026R version, which removed the laboratory method restrictions. The latest version of the CEMA documents can always be found here: https://www.nrcs.usda.gov/programs-initiatives/eqip-environmental-quality-incentives/cpas-dias-and-cemas.

While ALGL is not currently able to perform the entire suite of required tests in-house, we can subcontract the necessary soil health testing to help you and your customers participate in NRCS regenerative agriculture funding programs.

Contact your regional agronomist or the laboratory directly for more information.

Tips for Getting the Best Possible Results from Plant Tissue Analysis

Plant tissue testing continues to grow in popularity as growers and crop advisors work to fine-tune their fertility programs. With the ever-increasing costs of inputs, it is important to identify which ones are necessary and which ones work. Plant tissue analysis can help in several ways. It can potentially identify a nutrient deficiency prior to the development of visual symptoms. It can be used as a general monitoring of an overall fertility program. It can be used as a comparison between areas of a field that are obviously performing differently. Whatever the reason for collecting a plant tissue sample may be, it is critical to get a good quality sample to the laboratory. Here are some tips to help ensure that you receive reliable data back from the laboratory.

• Be sure to correctly identify the growth stage of the crop. There are numerous guides and diagrams available from university extension programs as well as commercial companies. Compile a small library for the crops that you routinely scout.
• Collect the proper plant part for the current growth stage. For the common row crops in our region, the proper plant part to sample changes throughout the growing season. Failure to submit the correct plant part will result in erroneous sufficiency ratings.
• Never send plants with the roots still attached. Early season plant samples often call for collecting the “whole plant”. This means the above ground portion. Plant should be cut off about ½ inch above the soil surface. Including the root material will result in contamination of the sample with soil primarily impacting the iron and aluminum levels in the results.
• Package your sample correctly. Always pack plant samples in paper bags. If you do not have the sample bags provided by the lab, brown paper lunch sized bags work as well. Do not use plastic bags for plant samples. Plastic bags seal in the moisture and speed up the decomposition of the plant material.
• When shipping multiple samples in a box make sure that the sample bags are secured so the samples do not dump out of the bag and do not over fill the shipping box. Stuffing too many plant samples into a box will also speed up the decomposition.
• Avoid shipping plant samples over the weekend, especially a holiday weekend. Packages shipped over the weekend are generally stored in trailers. During the heat of summer this could be detrimental to plant samples.
• Ideally plant samples are collected and shipped to the lab on the same day and only spend one or two days in transit. This is not always possible due to logistics and the weather. If necessary, let the plant material start to dry out. Spread the plant material out in a dry location and let it begin to airdry then repackage the sample and send it to the lab when it is convenient. All nutrient analysis is done on dried plant material. Starting the process will not impact your results.

If you have any questions or concerns about plant sample collection or shipping process, please do not hesitate to contact us. The customer service and agronomy staff will be more than happy to assist.

Hydroponic Systems and Nutrient Cycling

Hydroponic systems can be very elaborate, large scale and even automated from start to finish. They can also be simple, small and for home use but one thing they all have in common is nutrient cycling. The nutrient solution must be changed, or cycled, every two to four weeks depending on various factors.

It starts with the water source. After all, hydroponics is the production of plants in a water medium rather than soil. The water source should be tested before any additional nutrients or conditioners are added. Just like in soil, the pH must be addressed first. If the pH is too high, or too low, there may be nutrient availability issues. The solution should have a target pH of 5.5 to 6.0 for maximum required nutrient availability for most commercially grown crops. If the solution is too low, or acidic, there may be less available calcium and magnesium. If it is too high, or basic, many of the micronutrients and phosphorus are not available. Ammonia based nitrogen products tend to decrease pH and nitrate forms tend to increase pH in the nutrient solution.

The EC, or electrical conductivity, measures the water’s ability to conduct an electrical current. Salt concentration, minerals, metals and solids in the solution will increase the EC value. If the solution starts at a concentration higher than the desired threshold, it will only continue to increase as soluble nutrients are added to the solution. A starting EC of 1 mmhos/cm or less is desirable.

Not all nutrients are taken into the plant at the same rate, or speed. Phosphorus can accumulate over time in the solution due to slower uptake and is added back in most nutrient mixes at full strength. Other micronutrients and metals will accumulate over time at toxic levels if the solution is not cycled. Hydroponics is a balancing act, and once the EC gets too high from salt accumulation the roots will “burn” and decrease growth. Without a good root system, the plant will not have proper nutrient uptake.

The simple way to start with a consistent nutrient solution is to filter the water source using reverse osmosis. This ensures a clean starting point to add nutrients. Once the nutrient package is added, a water analysis can be used to know when it needs to be cycled out. Depending on the scale of the operation, this can be a very cost-effective way to manage nutrient levels and knowing when to cycle out the current solution.

Always sample the water source before adding nutrient packages. This will prevent costly mistakes like high EC levels, aid in the correction of hard water, management of pH and provide sufficient nutrients for the crops. Sampling the water source, in conjunction with sampling nutrient solutions, is the most effective way to manage a hydroponic system.

Fernandez, D. (2020, October 11). Factors limiting the life of a recirculating hydroponic nutrient solution. Science in Hydroponics. https://scienceinhydroponics.com/2020/10/factors-limiting-the-life-of-a-recirculating-hydroponic-nutrient-solution.html

Ronzoni, R., & Mattson, N. (2020). A guide to home hydroponics for leafy greens. Cornell University Controlled Environment Agriculture Program. https://bpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/8/8824/files/2020/05/Guide-To-Home-Hydroponics-For-Leafy-Greens.pdf