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Andrew Hoiberg, Ph.D.

Andrew Hoiberg, Ph.D.

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

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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).

 

Sources:

Al-Kaisi, Mahdi. 2014. Myths and Facts about Residue Breakdown. Iowa State University Extension and Outreach. (http://crops.extension.iastate.edu/cropnews/2014/04/myths-and-facts-about-residue-breakdown)

Bundy, L.G. and T.W. Andraski. 2002. Final Report to the Wisconsin Fertilizer Research Council. Project 175-99. (http://bulletin.ipm.illinois.edu/print.php?id=1565)

Coronel, E. and F. Fernandez. 2014. Effect of Fall Nitrogen on Corn Residue Breakdown in Illinois. SSSA Abstracts, Long Beach, CA. (https://scisoc.confex.com/scisoc/2014am/webprogram/Paper87666.html)

 

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Three Tips to Spot Sulfur Deficiency in Corn

Sulfur Deficiency

Now is the time to start scouting for sulfur deficiency in corn plants. As you’re out and about this spring, keep these three tips in mind to successfully identify sulfur deficiency.

  1. Check young corn plants. Sulfur deficiency is most obvious early in the growing season, when the plant is most vulnerable to nutrient shortages.
  2. Look at leaf color. From afar, plants with a pale green appearance should be inspected closer for nutrient deficiency symptoms. Both sulfur and nitrogen deficiency are marked by yellow striping between the veins of the leaf (interveinal chlorosis), which can cause confusion when diagnosing sulfur vs. nitrogen deficiency. The image above shows sulfur deficiency.
  3. Inspect plants’ youngest leaves. Sulfur deficiency shows up in the youngest leaves of the corn plant first, while nitrogen deficiency appears in the older leaves first. The difference is related to how each nutrient is mobilized in the plant.

The good news is that sulfur deficiency can be quickly corrected with a broadcast application of SuperCal SO4. An application rate of 100-150 lbs/acre will result in plant green-up in as little as seven days.

Keep in mind, corn needs sulfur throughout the growing season, so make sure you are supplying a source that offers flexible application timing and a release pattern that is compatible with plant requirements. For more details, click or tap to watch the video below comparing SuperCal SO4 and AMS.

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IPFS Presentation Sulfur Deficiency in the Upper Midwest

It's been a great week at the Iowa Power Farming Show. This year Dr. Andrew Hoiberg presented each day to growers on Sulfur Deficiency in the Upper Midwest

The key take a ways are:

Sulfur deficiency is often confused with Nitrogen deficiency, know what you are looking at.

Prior to 2005 little sulfur deficiency was observed

Sandy and loamy soils may exhibit more problems.

Soil tests may not adequately show a need for sulfur nutrition

Tissue tests of less than 0.25% Sulfur should show a response

Iowa State has documented yield increases of 7-18 bu / acre with applications of as little as 15 lbs /a sulfur

 

This Blogronomist article was written by Andrew Hoiberg, Director of Research and development. Here you will find a wide array of blog articles from Andrew and expert guests on topics related to soil and crop health, farming, and so much more. If it’s not here, ask us!

 

 

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Applying SuperCal Products on Snow Covered Ground

 

We are often asked about making application of our products on snow-covered ground. Applications in the late fall and early winter should have the same types of considerations as they do in other parts of the year.

When considering application timing, water should always be the preeminent issue. Water influences the movement of soil applied inputs, and when water has potential to run (and not infiltrate), then perhaps applications should be delayed. These events are not always easy to predict, so using your best judgment is the way to go.

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