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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

Managing Apple Expectations with Nitrogen Regulation

For many cash crops, the more inputs and higher management practices lead to higher yields. A certain amount of nutrition is needed to produce the yield goal and still get a positive return on investment. With nitrogen, the higher the rate usually equates to higher yield. The same can be applied to apple production. There needs to be a calculation that leads to how much nitrogen can be applied to obtain a certain yield and receive a positive return on investment. To figure out what the best application rate will be, an end goal must be established.

Some growers prefer dessert apples, others culinary and sauce or cider. There are many different products produced using apples and this will be the leading variable to nitrogen rates. The cultivar can have a great influence on nutrient requirements. Seasonal changes and environmental factors, as well as soil test levels, play a key role in nutrient applications.

Nitrogen is one of the major drivers for vegetative growth in plants. Too much nitrogen uptake can lead to rapid vegetative growth and shoot elongation. This will lead to shading of fruiting areas, increased humidity in the canopy and a competitive fight for nutrients from the fruit. This is where apples can experience diseases, such as Bitter Pit, because the calcium is being used in cell construction of vegetative growth rather than fruit production. From a management perspective, it creates much more pruning to contain efficient harvest heights and open canopies.

For dessert apples, higher nitrogen rates can be used. The producer wants a large apple that is juicy. Using the term “juicy” does not necessarily mean better juice, perhaps just more of it. The higher the nitrogen, the higher the water content of the fruit juice. By pruning correctly, fruit size will increase but it is important to regulate nitrogen applications for higher sugar content. For cider and sauce uses, the amount of tannin, pectin and fruit size is mostly dictated by the cultivar. However, to have the highest sugar content, low nitrogen rates create smaller fruit. This leads to more fruit skin surface area resulting in much higher tannins and less water concentration creating a higher sugar content.

Precipitation amounts will play a large role in water content of an apple. A wet, rainy season during fruit growth stages will increase water uptake, carrying nitrogen with it, which will increase the fruit size and decrease sugar content. The type of soil, slope and location of trees can have a large impact as well. Soil with good drainage, will hold less water. Heavier soils with higher organic matter will mineralize more nitrogen and typically yield larger fruit with less sugar content.

Do Cover Crops Produce Nitrogen for Your Next Crop?

Cover crops provide many benefits to agricultural soil, increased organic matter, erosion reduction, weed suppression, moisture retention, improved soil structure, disrupting pest cycles, and the list goes on. However, a common question is, do they provide nitrogen to the next crop? The straightforward answer is yes, maybe, sometimes, and it depends…

The first thing to consider is the type of cover crop. Legumes such as clover and peas have the potential to provide nitrogen. Grass species such as rye and oats are not likely to provide any nitrogen to the next crop. It all comes down to the carbon to nitrogen ratio. The majority of nitrogen in plants is tied up in proteins. Legumes have more. The problem is that protein is not plant available and must be decomposed by soil microbes to be released as ammonium or nitrate for the plants to utilize. In order for the microbes to do their job, they need a C:N ratio of about 25:1. Grass species generally have a C:N around 30:1 to 50:1. This means that the microbes need to find another source of nitrogen to breakdown these cover crops leaving none to be released. On the other hand, legumes generally have C:N around 15:1 to 25:1. When there is more nitrogen in the cover crop than the microbes need, it can be released to the soil solution for the crop to utilize.

As with anything in agriculture, weather has the greatest impact on the potential for nitrogen release from cover crops. The microbes need warm soil temperatures and adequate moisture. Fortunately, when conditions are favorable for microbial activity, it is also favorable for plant growth which means there is a greater chance of utilizing the nitrogen.

So, how much nitrogen can you realistically expect from a legume cover crop? Some research has claimed that a clover cover crop can provide 70 to 90 pounds of nitrogen per acre. This is not entirely true. When testing the biomass of the cover crop, it is definitely possible for there to be that much nitrogen, but it does not, the crop will have access to all of it. Another misconception in some of the research is that all the yield gained following a legume cover crop is a result of a nitrogen contribution. As mentioned above, cover crops can provide many benefits that can improve yield. So, if you reduce a nitrogen application by all the nitrogen in the cover crop biomass, you may be under applying leaving missing out on potentially higher yields. A more realistic expectation following a well established legume cover crop is about 30 pounds of nitrogen per acre. Another thing to consider is tillage. A cover crop terminated through conventional tillage is more likely to decompose in a timely manner than one that is terminated with herbicide in a no-till situation due to the increased soil contact with the plant tissue.

Did the 2025 Drought Impact Soil Test Results?

In short, yes—for those areas that experienced a D3 drought. For much of the region, D3 drought conditions developed partway through the fall harvest of 2025 and extended through the spring of 2026. Over the past few years, areas impacted by D3 drought have shown consistent effects on soil samples. Observations suggest that late D2 into D3 droughts can significantly influence soil test results.

Below are previous blog posts with additional information on how drought impacts soil samples:

• algreatlakes.com/blogs/news/impacts-of-the-dry-2024-fall
• algreatlakes.com/blogs/news/soil-testing-after-a-drought-originally-posted-2012

How can you tell if your data is impacted?
The clearest indicator is areas within fields showing very high soil pH. While not ideal to manage, these locations are best suited to assess drought impact. These areas typically have a soil pH of 8.1 to 8.2 and are often associated with free calcium carbonate in the soil—meaning there are more carbonates (lime) present than can chemically react.

High soil pH is usually accompanied by very high calcium (ppm) levels and calcium cation saturation of 80% or greater in mineral soils with a CEC of 10–20, and over 90% in sandy soils.

This situation is unique because the acid-neutralization reaction stalls when soil pH reaches 8.1 to 8.2 and cannot increase further. At that point, unreacted carbonates (lime) remain in the soil, available to neutralize future acid inputs. This reserve capacity keeps soil pH elevated for the foreseeable future. These conditions can result from excessive lime applications or naturally occurring carbonates.

However, in areas with free or excessive carbonates that are severely impacted by drought, soil pH may drop below 8.0. In parts of northwest Indiana and northwest Ohio from fall 2025 through early spring 2026, soil pH values of 7.5 to 7.6 were observed in areas that historically tested between 8.0 and 8.2 - representing an approximate 0.5-unit decrease.

Soil test potassium (K) declines are less predictable but tend to occur under similar conditions. Reports indicate estimated declines of 15–30% in soil test K levels compared to recent historical values. While soil pH typically recovers quickly with increased rainfall, potassium levels may remain depressed for several months.

Some notable phosphorus (P) declines have also been reported. However, these may be influenced by reduced phosphorus application rates over the past few years.