Utilizing Microbes to Accelerate Corn Residue Decomposition

INSIGHTS

• On average, broadcast treatments designed to increase soil microbial activity had minimal effect on yield in this trial.
• Mechanically sizing corn residue with a chopper or disk significantly increased yield, however accelerated decomposition could not be confirmed.
• University research concluded that residue decomposition was influenced more by soil moisture and temperatures above 50℉ that supported the microbes involved in residue decomposition.

Figure 1. Heavy residue cover in continuous corn field that can reduce stand establishment, decrease nitrogen availability, and increase pest pressure.

Agronomics of Corn Residue

Corn residue from the previous year can have many positive agronomic benefits. It can provide ground cover to reduce soil erosion, conserve soil moisture, moderate soil temperature, enhance nutrient cycling, suppress weeds, sequester carbon, increase organic matter, and promote microbial activity. However, depending on the geography, some of these benefits from corn residue may have a negative effect on crop production. The high ratio of carbon to nitrogen in corn residue can immobilize soil nitrogen and make it less available that season. Colder and wetter soils can slow emergence and increase the risk of seedling disease and stand loss. Cooler spring soils can also delay mineralization and availability of other nutrients such as sulfur (S). Residue can also harbor pathogens from previous years that can develop into diseases. Corn residue has even been believed to have an allelopathic effect that can slow early season growth of the following corn crop. At planting, heavy levels of residue also create a physical barrier for seedlings to grow through (Figure 1).

In recent years, the level of corn residue remaining in the spring has increased significantly in many fields, which can be attributed to higher yields. Intensified management with better fertilization and increased plant populations has not only boosted yield but also led to more stover production. For perspective, a corn crop yielding 180 bushels per acre typically produces about 4.3 tons of stover per acre. As yields push towards 300 bushels per acre, stover accumulation can exceed 7 tons per acre. This trend highlights the growing importance of effective residue management.

Managing Residue

Historically, growers have utilized many options to manage residue. Corn residue can be physically removed by baling corn stalks. However, removing residue can also remove nutrients such as nitrogen (N) and potassium (K) that must eventually be replaced. Another option is to incorporate residue into the soil with tillage to speed up residue breakdown, as the smaller pieces increase the surface area and allow the microbes to break down biomass faster. Vertical tillage or chopping stalks with a mower can reduce residue size, but also requires an extra pass in the field. Attachments for corn heads can help break down residue while harvesting. Chopping corn heads, residue managing stalk rolls, and aggressive stalk stompers are combine attachments that can create more corn residue surface area for microbes to enter. There are also biological products on the market that either contain microbes or catalysts to increase the activity of microbes already present in the soil to accelerate the decomposition process. Corn stover contains a much higher amount of carbon than nitrogen (60:1) relative to other crop residues like soybeans (20:1), which break down much faster. Soil microorganisms need a C:N ratio diet of 24:1 to be able to survive and stay active. In cases where residue C:N ratios are greater than 24:1, such as with corn, soil microorganisms will seek out additional nitrogen to consume the extra carbon. This results in soil nitrogen being immobilized and unavailable until those microbes die.

Agronomy in Action Research Trial

In 2024, the Agronomy in Action research team implemented a trial focusing on products to increase microbial activity to accelerate corn residue degradation. Three products with three different modes of action were evaluated. Urea Ammonium Nitrate (UAN) was used to decrease the C:N ratio and increase microbial consumption of carbon. Feed grade dextrose was used as a sugar source to stimulate the microbe population already present in the soil. Meltdown™, by BW Fusion, is a product containing 1% nitrogen, 4.1% fulvic acid, and 4.9% mixture of six microbial strains designed to feed, stimulate, and add to the soil microbial population. All treatments were broadcast applied in the fall or spring.

Figure 2. Aerial photo of one replication of disked (orange), non-sized (white), and chopped (blue) residue blocks at Slater, IA in 2024.

1. Check – no treatments were applied
2. Fall UAN at 60 lbs/A of N
3. Fall Meltdown at 32 oz/A
4. Fall Sugar at 4 lbs/A
5. Spring Meltdown at 32 oz/A
6. Spring Sugar at 4 lbs/A

Trials were established in Waterloo, NE, and Slater, IA. At Waterloo, NE, treatments were either applied on October 24, 2023 or March 26, 2024 to no-till corn stalks. At Slater, IA, a mechanical residue sizing component was added to the trial. All treatments were applied to corn stalks after using a John Deere stalk chopper or running a Case IH disk implement on September 20, 2023 to compare mechanically sized residue to the check (Figure 2). The Slater, IA, broadcast treatments were either applied on September 22, 2023 or April 23, 2024. At Slater, neither the check nor the stalk chopper treatments received any pre-plant tillage, whereas the fall disking was the only tillage pass for the disked treatment. Corn hybrid G05U86 brand was planted at Slater, IA, on April 25, 2024 and hybrid G13B17 brand was no-till planted at Waterloo, NE, on April 23, 2024. All treatments were replicated four times.

Trial Results

Physical residue degradation was not measured due to the challenging nature of the collection process. Stand establishment was similar across all treatments. Yield was recorded using a research plot combine. At Slater, IA, mechanically sizing the residue had a significant effect on yield when averaged across all broadcast treatments. Using the stalk chopper or disk implement increased yield by 13 Bu/A compared to non-sized residue (Graph 1), but it cannot be assumed that the yield increase resulted from accelerated residue degradation. Mechanical treatments may have provided a better seedbed for rooting or reduced the physical residue barrier for seedlings to grow.

At Slater, there was no significant interaction between mechanical sizing method and broadcast treatment. When averaged across non-sized and the two mechanical treatments, none of the broadcast treatments significantly increased yield compared to the check (Graph 2). Only when the residue was sized with a disk did fall broadcast UAN significantly increase yield by 19 Bu/A (Graph 2). It cannot be assumed the additional N increased microbial consumption of carbon, as it is plausible that N was available during early spring for the crop to utilize. Disking potentially allowed the N to move into the soil when broadcast compared to the non-sized or chopping treatments where the N may have been absorbed by the residue and subjected to loss through volatilization. It is difficult to determine the direct agronomic cause of the yield increase.

At Waterloo, NE, there was no significant difference in yield between any of the broadcast treatments and the check (Graph 3). UAN and sugar applied in the fall tended to slightly increase yield but not significantly.

Graph 1. Effect of mechanical sized residue method on yield averaged across broadcast treatment at Slater, IA in 2024.

Graph 2. Effect of broadcast treatment and mechanical sizing method on yield at Slater, IA in 2024.

Graph 3. Effect of broadcast treatment on yield at Waterloo, NE in 2024.

University Field and Lab Trials

Previous university field and lab trials found no difference in residue breakdown resulting from tillage type, nitrogen application at various rates, or previous corn trait.^1,2 They concluded from controlled lab studies that residue decomposition was influenced more by soil moisture and temperature. These environmental factors directly impact both the biological processes and chemical activities necessary to breakdown the lignin, cellulose, hemicellulose, and macro- and micro nutrients in residue. A wide variety of microorganisms control these biological and enzymatic processes. Environmentally controlled lab studies showed that soil moisture at field capacity and warmer temperatures (above 50°F) increased microbial activity and decomposition and that microbial levels doubled for every 10°F increase in temperature.

Unfortunately, planting full season hybrids for a given area to maximize yield potential delays plant maturity and harvest dates to a point in time where temperatures favorable for microbial activity that would help break down corn residue begin to diminish.

Summary

Overall, the Agronomy in Action research trials showed minimal effect on yield resulting from UAN, Meltdown, or sugar applied in the fall or spring. Mechanically sizing the residue with a chopper or disk significantly increased yield over non-sized residue. However, the physiological reason for the yield increase could not be identified.

University results illustrate that residue decomposition is a dynamic process and is highly dependent on both temperature and moisture. Methods to increase or extend microbial activity present in the soil is the best opportunity for faster residue degradation.

References

¹Al-Kaisi, M.M. and J.G. Guzman. 2013. Effects of tillage and nitrogen rate on decomposition of transgenic Bt and near-isogenic non-Bt maize residue. Soil Tillage Res 129:32–39. https://doi.org/10.1016/j.still.2013.01.004

²Al-Kaisi, M. M., D. Kwaw-Mensah, E.Ci. 2017. Effect of nitrogen fertilizer application on corn residue decomposition in Iowa. Agronomy Journal 109(5): 2415–2427. https://doi.org/10.2134/agronj2016.11.0633