Calcium Products - Applying Nitrogen to Enhance Corn Residue Decomposition: Does it Work?

Applying Nitrogen to Enhance Corn Residue Decomposition: Does it Work?



Applying nitrogen in the fall to enhance corn residue decomposition occurs with some frequency in the Midwestern United States. The purpose of this application (normally applied as AMS or UAN) is to deliver a nitrogen source to feed microbes and increase the speed at which corn residue is decomposed. The main reason this topic seems more prevalent in recent years may be related to current hybrids and farming practices. Modern genetics have selected for stronger stalks and larger plants, while increases in corn-on-corn rotations and reduced tillage have resulted in more residual biomass. Combined, these result in greater demand on microbes to minimize the impact of residue on the following season's operations.

Rationale Behind "Stalk Burndown"

The rationale behind applying N to aid in stalk decomposition is related to the carbon-to-nitrogen (C:N) ratio, which indicates how effectively microbes decompose different materials. The C:N ratio is important because it denotes how many units of carbon are found in a given material in relation to the units of nitrogen. The ideal C:N ratio (think diet) for microbes is 24:1 and corn stover is about 60:1. This means that microbes must scavenge for additional nitrogen to keep things humming along when feeding on corn residue. Additional nitrogen typically comes from available nitrogen in the soil - and this is where the rationale of adding nitrogen to the corn stover comes from - to effectively narrow the C:N ratio of the residue and allow the microbes to more rapidly decompose the material as they wouldn't have to scavenge for available nitrogen.

Hurdles for Microbial Decomposition Rates

The problem is that the C:N ratio is not the only thing that governs microbial decomposition. Other factors such as moisture, and especially temperature (both soil and air) are very important with respect to biological activity. When liquid applications of UAN or AMS are made to corn stover, the nitrogen can be washed off by rain - defeating the purpose of the application. More importantly, microbial activity is reduced by decreasing air and soil temperatures in the fall, which can leave the applied nitrogen unused by microbes and susceptible to leaching with well-known environmental consequences.

Research Shows No Benefits from N Applications to Increase Stalk Decomposition

Several research projects have attempted to justify this practice to no avail. Researchers at the University of Wisconsin in 2002 found no benefit from fall application of nitrogen to increase microbial decomposition of corn stover (Bundy and Andraski, 2002). A collaborative research project between the University of Minnesota and University of Illinois ultimately concluded that fall applications of N had minimal to no effect in increasing residue decomposition and were not warranted, even when applied as early as September when air and soil temperatures were adequate to sustain microbial activity (Coronel & Fernandez, 2014). Lastly, a study conducted at Iowa State University found no differences in the rate of stover decomposition as a result of N application - from economic and environmental perspectives, N application had no effect in achieving the intended results of facilitating residue decomposition (Al-Kaisi, 2014).



Al-Kaisi, Mahdi. 2014. Myths and Facts about Residue Breakdown. Iowa State University Extension and Outreach. (

Bundy, L.G. and T.W. Andraski. 2002. Final Report to the Wisconsin Fertilizer Research Council. Project 175-99. (

Coronel, E. and F. Fernandez. 2014. Effect of Fall Nitrogen on Corn Residue Breakdown in Illinois. SSSA Abstracts, Long Beach, CA. (


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Having learned how much more efficient our pure, pelletized products are, you are probably left wondering how much SO4 you need. Fill in the appropriate fields below, and our custom calculator will do the rest.

  • SO4 Calculator Instructions

    Calculator gives you the ability to compare the costs of SO4 to other sulfur fertilizers. Follow these simple steps.

    • 1. Select your crop
    • 2. Input your yield goal
    • 3. Input your acres to be grown
    • 4. Select your alternate sulfur fertilizer
    • 5. Input the cost / lb for the alternate source
    • 6. Input the cost / lb for  SO4



Main Benefits of SO4
  • Improves soil structure
  • Helps reclaim sodic soils
  • Prevents crusting of soil and aids seed emergence
  • Improves compacted soil
  • Makes slightly wet soils easier to till
  • Stops water runoff and erosion
  • Decreases pH of sodic soils
  • Improves swelling clays
  • Prevents waterlogging of soil
  • Helps make stable soil organic matter
  • Makes water-soluble polymer soil conditioners more effective
  • Makes magnesium non-toxic
  • Corrects subsoil acidity
  • Improves water-use efficiency
  • Decreases dust erosion
  • Makes it possible to use low quality irrigation water
  • Has 17% sulfate
  • Helps plants absorb plant nutrients
  • Decreases heavy-metal toxicity
  • Increases value of organics
  • Improves fruit quality and prevents some plant diseases
  • Helps prepare soil for no-till management
  • Decreases bulk density of soil
  • Decreases the toxic effect of NaCl salinity
  • Decreases loss of fertilizer Nitrogen to the air
  • Keeps clay off tuber and root crops
  • Helps earthworms flourish
  • Safe for organic grower
Gypsum helps reclaim sodic soils
Gypsum is used in the reclamation of sodic soils. Where the exchangeable sodium percentage (ESP) of sodic soils is too high, it must be decreased for soil improvement and better crop growth. The most economical way is to add gypsum, which supplies calcium. The calcium replaces the sodium held on the cation exchange sites in the soil. The sodium can then be leached from the soil.
Gypsum prevents crusting of soil and aids seed emergence
Gypsum can decrease and prevent crust formation on soil surfaces which result from rain drops or from sprinkler irrigation on unstable soil. The gypsum is either surface applied or put on in the irrigation system. Prevention of crust formation means more seed emergence, more rapid seed emergence.
Gypsum improves compacted soil
Gypsum can help modify dispersive, compacted soil. This type of compaction in many soils can be decreased with gypsum, especially when combined with deep tillage. Addition of organic amendments also helps, especially in preventing return on the compaction.
Gypsum makes slightly wet soils easier to till
Soils that have been treated with gypsum have wider range of soil moisture levels where it is safe to till without danger of compaction or deflocculation. This is accompanied with greater ease of tillage and more effective seedbed preparation and weed control. Less energy is needed for the tillage.
Gypsum stops water runoff and erosion
Gypsum improves water infiltration rates into soils and also the hydraulic conductivity of the soil, which protects against excess water runoff from especially large storms that are accompanied with erosion.
Gypsum decreases pH of sodic soils
Gypsum immediately decreases the pH of sodic soils or near sodic soils from value often over 9 but usually over 8 to values of from 7.5 to 7.8. These values are in the range of acceptability for growth of most crop plants. Probably more than one mechanism is involved. Ca++ reacts with bicarbonate to precipitate CaCO3 and release protons which decrease the pH. Also, the level of exchangeable sodium is decreased which lessens the hydrolysis of clay to form hydroxides. These reactions can decrease the incidence of lime and bicarbonate-induced iron deficiency.
Gypsum improves swelling clays
Gypsum can decrease the swelling and cracking associated with high levels of exchangeable sodium on the montmorillonite-type clays. As sodium is replaced by calcium on these clays, they swell less and therefore do not easily clog the pore spaces through which air, water and roots move.
Gypsum prevents waterlogging of soil
Gypsum improves the ability of soil to drain and not become waterlogged due to a combination of high sodium, swelling clay, and excess water. Improvements of infiltration rate and hydraulic conductivity with use of gypsum add to the ability of soils to have adequate drainage.
Gypsum helps make stable soil organic matter
Gypsum is a source of calcium which is a major mechanism that binds soil organic matter to clay, which gives stability to soil aggregates. The value of organic matter applied to soil is increased when it is applied with gypsum.
Gypsum makes water-soluble polymer soil conditioners more effective
Gypsum complements or even magnifies the beneficial effects of water-soluble polymers used as amendments to improve soil structure. Like for organic matter, calcium, which comes from gypsum, is the mechanism for binding of the water-soluble polymers to the clay in soil.
Gypsum makes magnesium nontoxic
In soils having unfavorable calcium:magnesium ratios, such as serpentine soils, gypsum can create a more favorable ratio by displacing magnesium with calcium in the soil.
Gypsum corrects subsoil acidity

Gypsum can improve some acid soils even beyond what lime can do for them. The effects of toxic soluble aluminum can be decreased, including in the subsoil where lime will not penetrate. It is then possible to have deeper rooting with resulting benefits to the crops. The mechanism is more than replacement of acidic hydrogen ions which can be leached from the soil to give higher pH. Hydrogen ions do not migrate rapidly in soils containing clay. It is suggested that the sulfate from gypsum forms a complex (AISO4 +) with aluminum which renders the aluminum non-toxic. Also suggested is that the sulfate ions react with iron hydroxides to release hydroxyl ions which give a lime effect to increase soil pH. Gypsum is now being widely used on acid soils.

Gypsum improves water-use efficiency
Gypsum increases water-use efficiency of crops. In areas and times of drought, this is extremely important. Improved water infiltration rates, improved hydraulic conductivity of soil, better water storage in the soil all lead to deeper rooting and better water-use efficiency. From 25 to 100 percent more water is available in gypsum-treated soils.
Gypsum makes it possible to use low quality irrigation water
The effective sodium absorption ratio (SAR) of irrigation water should be less than 6 for some crops and less than 9 for others. When it exceeds these limits, gypsum should be applied to the soil or to the water. Use of reclaimed municipal waste water is important for conservation of natural resources. Reclaimed water can be satisfactorily used if amendments, such as gypsum and water-soluble polymers, are used. Care must be taken, however, to avoid sodium build up in the lower horizons of soil because of excessive leaching when swelling clays are present.
Gypsum decreases dust erosion
Use of gypsum can decrease wind and water erosion of soil. Severe dust problems can be decreased, especially when combined with use of water-soluble polymers. Less pesticide and nutrient residues will escape from the soil surface to reach lakes and rivers when appropriate amendments are used to stabilize soil.
SuperCal SO4 has 17% Sulfate
SuperCal SO4 has 17% sulfate, which is the most absorbable form of sulfur for plants.
Gypsum helps plants absorb plant nutrients
Calcium, which is supplied in gypsum, is essential to the biochemical mechanisms by which most plant nutrients are absorbed by roots. Without adequate calcium, uptake mechanisms would fail.
Gypsum decreases heavy-metal toxicity
Calcium also acts as a regulator of the balance of particularly the micro-nutrients, such as iron, zinc, manganese and copper, in plants. It also regulates non-essential trace elements. Calcium prevents excess uptake of many of them; and once they are in the plant, calcium keeps them from having adverse effects when their levels get high. Calcium in liberal quantities helps to maintain a healthy balance of nutrients and other compounds within plants.
Gypsum increases value of organics
Blends of gypsum and organics increase the value of each other as soil amendments, especially for improvement of soil structure. High levels of soil organic matter are always associated with liberal amounts of calcium, which is part of gypsum. Calcium decreases burn out of soil organic matter when soils are cultivated by bridging the organic matter to clay.
Gypsum improves fruit quality and prevents some plant diseases
Calcium is nearly always only marginally sufficient and often deficient in developing fruits. Good fruit quality requires an adequate amount of calcium. Calcium moves very slowly, if at all, from one plant part to another, and fruits at the end of the transport system get too little. Calcium must be constantly available to the roots. In very high pH soils, calcium is not available enough; therefore, gypsum helps. Gypsum is used for peanuts, which develop below ground to keep them disease free. Gypsum helps prevent blossom-end roots of watermelon and tomatoes and bitter pits in apples. Gypsum is preferred over lime for potatoes grown in acid soils so that scab may be controlled. Root rot of avocado trees caused by Phytophthora is partially controlled by gypsum.
Gypsum helps prepare soil for no-till management
Liberal application of gypsum is a good procedure for starting a piece of land into no-till soil management or pasture. Improved soil aggregation and permeability will persist for years and surface-applied fertilizers will more easily penetrate as a result of the gypsum.
Gypsum decreases bulk density of soil
Gypsum-treated soil has a lower bulk density compared with untreated soil. Organics can even decrease it more when both are used. Softer soil is easier to till, and crops will respond accordingly.
Gypsum decreases the toxic effect of NaCl salinity
Calcium from gypsum has a physiological role in inhibiting the uptake of Na by plants. For species of plants not tolerant to Na, Ca protects from toxicity of Na but not Cl.
Gypsum decreases nitrogen volatilization
Calcium from gypsum can help decrease volatilization loss of ammonium nitrogen from applications of ammonia, ammonium nitrate, UAN, urea, ammonium sulfate, or any of the ammonium phosphates. Calcium can decrease the effective pH by precipitating carbonates and also by forming a complex calcium salt with ammonium hydroxide which prevents ammonia loss to the atmosphere.
Gypsum keeps clay off tuber and root crops
Gypsum can help keep clay particles from adhering to roots, bulbs and tubers of crops like potato, carrots, garlic and beets. In combination with water-soluble polymers, it is even more beneficial.
Gypsum helps earthworms to flourish
Continuous supply of calcium with organics is essential to earthworms that improve soil aeration, improve soil aggregation and mix the soil. Earthworms can do the plowing for no-till agriculture.
Safe for organic growers
Our products are pelletized using calcitic lignin sulfonate which is acceptable worldwide.
Provides calcium nutrition for your crop.
Calcium fertility is often an afterthought in many cropping systems. However, proper calcium nutrition is vital to overall plant health and Triplicity delivers a pure and effective source of calcium for your crop’s needs.
Q: Can I use SO4 for a sulfur source?
A: SO4 is a great choice for sulfur nutrition. Sulfur exists in the sulfate form in SO4, which is the plant available form and is immediately available. 200 bu. corn will use 32 lbs. sulfur/A, and 80 bu. beans will use 36 lbs. sulfur/A, indicating the need for yearly sulfur fertility. Further, sulfate-sulfur is dynamic in the soil system, similar to nitrate-nitrogen and can be leached easily. SO4 is also a great calcium source. 200 bu. corn requires 42 lbs. calcium/A, 80 bu. beans require 136 lbs. calcium/A.
Q: What about using SO4 on alfalfa?
A: SO4 is an excellent way to get the required calcium to legumes, especially alfalfa. Since SO4 is soluble, it will be available for plant uptake sooner than other forms of gypsum. The addition of sulfur to alfalfa normally causes a jump in the feed value of the forage, so you now have more and better alfalfa.
Q: My soybeans show IDC. Will SO4 help?
A: Application of gypsum will, in most cases, reduce or eliminate signs of iron deficiency. Also, note that resulting vigorous plant growth will make plants less susceptible to many other diseases and environmental stressors. Research has also shown that gypsum will help reduce the effects of white mold in fields that exhibit a tendency toward that problem.
Q: My soil turns white to gray and cracks as soon as it's dry.
A: First, test your soil to see if either salt or an imbalance of your calcium and magnesium is causing the problem. In either case, regular applications of SO4 should alleviate either condition.
Q: I have a 'hardpan.' Will SO4 take care of that?
A: A good program using SO4 and deep tillage can help loosen hardpan soils. SO4 by itself can help alleviate the problem, but it will be a long-term project since SO4 is not normally mixed deeply into the soil; this may be one place where it’s OK to place the product lower in the soil if need be. Dispersion of soil colloids can be caused by excessive sodium or magnesium in soil and calcium can help alleviate compaction in that situation by replacing the sodium and magnesium and helping rebuild soil structure by helping clay particles aggregate and improve drainiage.
Q: I have lots of tile but still get 'ponding.'
A: This is primarily due to compaction, low spots, and high water tables that result in poor soil water penetration. Regular applications of SO4, along with tillage, should help alleviate this problem. SO4 will allow the passage of both water and air by helping change the soil structure.
Q: I have side hill seeps high in salt. Can I use SO4 to solve that?
A: The success of this depends on whether you can address the source of the salt first, and then address the areas most affected. This is best determined by testing an area to see if there will be any easement of the problem.
Q: I have a water source high in salt. Will SO4 address that?
A: If your water is the primary source of sodium buildup in your soil, it will become a case of "shoveling sand" as the removal must exceed the source. Only in cases where you use a clean source of water will you be able to fully remove the buildup of salts in the soil. Also, it must be noted that leaching and good drainage are needed to remove the sodium salt.
Q: I have high salt levels. Will SO4 take care of that?
A: In most cases, yes. First, it needs to be determined by the soil testing if sodium salt is the problem. If it is, regular applications of SO4 will reduce the sodium as long as there is a way for the soil to be leached and drain properly (i.e., tile or naturally occurring drainage).
Q: Will SO4 help in a high pH soil?
A: Yes. It will supply free, soluble calcium which will be available to the crop while existing calcium in the soil can be tied up due to the high pH. SO4 will not reduce soil pH, but will create a friendlier environment for the plant to grow. Your soil test will likely indicate that there is abundant calcium in the high pH soil, but that calcium can be tied up as a result of high soil pH.
Q: I want to deep till. Should I apply SO4 before or after that tillage?
A: Wherever possible, we recommend that tillage be performed first and then apply SO4 to the surface. Incorporating SO4 can reduce its overall performance in the top layers of soil.
Q: Will in-furrow application of SO4 hurt the seed?
A: No. SO4 contains nothing that will harm the germination of a seed or emergence of a seedling.
Q: Can I band SO4?
A: Yes, you can band SO4 either in a "T" band method or directly in the furrow. Keep in mind that the effects of the gypsum application will be limited to the area to which it is applied. If the problem is field-wide, broadcasting gypsum is recommended.
Q: Can I use SO4 in my deep placement program?
A: We do not recommend deep application of gypsum unless it is being used strictly as a sulfur source. The best benefits of gypsum are best realized by surface application.
Q: Do I need to incorporate SO4?
A: No. SO4 works best applied to the soil surface after any mechanical tillage is done. If it is fall applied, normal seed bed preparation will not affect gypsum's activity.
Q: Will SO4 lower my pH?
A: No, to lower your pH with sulfur, you need the elemental form, not the sulfate form, which is how it exists in SO4. The acidifying process of soil borne bacteria converting elemental sulfur to the sulfate form is what lowers pH.
Q: How long will SO4 last?
A: There are many factors involved in answering this question; soil type, weathering, specific problems to be addressed, crop grown, etc. In general, applications for most problems should be made yearly, however, sulfur deficiency in corn is becoming widespread in the Midwest and applications of SO4 should be made yearly to ensure adequate sulfate levels in the soil.
Q: Can I apply SO4 with other products?
A: As long as the other products are granular, SO4 can be mixed and applied at the same time and with the same equipment. We do not recommend application with liquid compounds unless they are suitable for impregnation on fertilizer, and then they may be impregnated on the SO4 also. This is applicable for most micro nutrients also.
Q: Can I put on too much SO4?
A: It is not likely that you will over apply SO4; we are not aware of any instances in which SO4 caused any harm to a plant-soil system by over application. Sulfate is dynamic in the soil system and excess will be leached, and calcium will also eventually leach if there is no room for it in the soil.
Q: How often should I apply SO4?
A: Yearly applications are recommended until the problems you are trying to alleviate have been addressed. At that time, you can reevaluate your situation and reduce application rates to maintenance levels or application frequency.
Q: How much SO4 do I need to use?
A: Normal rates are 300 lb/A per application unless you are addressing a high sodium situation, in which case the rate could be as high as 900 lb/A. As always, a soil test should be taken and analyzed before application.
Q: What is SO4?
A: SO4 is finely ground gypsum mixed with a binder to form a pellet. SO4 contains 21% calcium, 17.5% sulfur (in plant available sulfate form), and is 95% pure dihydrate gypsum. Dihydrate gypsum is much more soluble than other forms of gypsum, which makes it the right choice for any agricultural or horticultural application.
  • Bill Peterson of Little Falls, MN discusses how SuperCal SO4 improved his soil.

  • SuperCal SO4 and SuperCal 98G from the farmers perspective.

  • SuperCal SO4 and SuperCal 98G from users and dealers.

  • SuperCal SO4 on Canola.

What our clients say...

  • Jim has been using SuperCal SO4 as part of his fertility program on his alfalfa. He has an acre of alfalfa that is 30 years old and produces more than 6 ton per year.

    — Jim Jarosz, Cedar Rapids, Nebraska
  • We have been raising cattle on grass for many years, traditional fertilizer didn't seem to be giving us the response we were looking for. We started looked for other options and Gene Zimmerman recommended SuperCal SO4. We were looking for a good sulfur source, but also felt we needed the calcium. The grass responded quite well to 300 lbs/a. We could tell where the spreader ran out of SuperCal SO4, and we have seen a big difference compared to the ground we did not spread any SuperCal SO4 on.
    It has been pretty dry this year so we were not sure what kind of results we would see. The carrying capacity looked better than my neighbors, and the cattle seem to like the grass better, and even started grazing the weeds. I have cows that have never raised good calves; this year they have big calves. Two representatives from the local sale barn came to visit me. My calves were more robust, they wanted to know what I was doing.
    "I would use SuperCal SO4 again, it’s priced reasonably."

    — Morris Stokes, Sullivan County, Missouri
  • have been using SuperCal SO4 for 4 years now and have been seeing it right to the row where I have been using it as my pictures show, I have been banding it at 50 to 100 # rates and have seen anywhere from 5 to 11 bushels increase on my corn yields. The 50# rate was costing me about $3/acre and seeing a 5-bushel yield increase at $3/bushel corn is $15 for a $3 investment. A 5x return on investment works for me.
    Visit Jay’s website:

    — Jay Myers, Colfax, North Dakota