Optimizing Manure Nitrogen Application Timing in Corn Production for Sustainability and Profitability – Livestock and Poultry Environmental Learning Community

Purpose

Nitrogen (N) application timing is crucial in balancing crop productivity and environmental sustainability. While fall applications are typical among Iowa corn producers due to favorable field conditions, they pose a high risk of N loss through denitrification, volatilization, and leaching. Spring and in-season sidedress applications offer improved nitrogen use efficiency (NUE) by aligning N availability with crop demand.

This study evaluates the effects of different N application timings—fall, spring, and sidedress—on corn yield and NUE. Using data from 65 site-years, we assess how application timing influences yield, economic returns, and environmental impacts. The findings provide insights into best management practices for improving profitability and sustainability in corn production.

What Did We Do?

A review of studies comparing N application timing in corn production was conducted, including a long-term experiment from the University of Minnesota (1960-1996) and additional datasets totaling 65 site-years. Treatments were separated into three categories: fall, spring, and sidedress. Relative yield was used to normalize data across years, and yield response was modeled using a Mitscherlich-Baule equation (Figure 1).

Figure 1: Yield response curves for 65 site-years of relative yield response data, categorized by season of N application

Economic impacts were analyzed using maximum return to nitrogen (MRTN), which identifies the N rate that maximizes economic return (Figure 2). Corn prices ($4.62/bu) and anhydrous ammonia prices ($0.45/lb N) were used to estimate profitability in each application scenario. The environmental effects were assessed by examining N-loss pathways and the potential for emission reduction of nitrous oxide (N2O), a greenhouse gas estimated to be 273 times more potent than carbon dioxide.

Figure 2: Net income per acre for fall, spring, and sidedress N application. Maximum return to nitrogen (MRTN) is plotted as a circular point on each curve, with the profitable N rate (low and high) within $1/acre bounded by diamond points.

What Have We Learned?

Results show that year-to-year, sidedress applications consistently produce the highest corn yield, followed by spring applications, with fall applications being the least effective. Yield differences are particularly evident in wet years (November to June rainfall > 1 inch above average), where sidedress applications outperform fall by an average of 9% (Figure 3). MRTN analysis shows that sidedress applications require 25% less N than fall applications while achieving higher yields, demonstrating their economic advantage.

Figure 3: Reduction in relative yield between fall and sidedress application in different weather conditions: Dry (greater than 1 inch below average November-to-June precipitation), Average (within ±1 inch of average precipitation), and Wet (greater than 1 inch above average precipitation). Interpreted as the yield loss due to increased exposure of applied N to precipitation.

The environmental analysis indicates that reducing N application rates through improved timing could cut N2O emissions by up to 25%. With a carbon credit of $30/metric ton CO2e abated the reduction in N2O equates to a $2.66/acre credit for a reduced N application rate. Fall-applied N is most susceptible to losses due to prolonged exposure to wet conditions, while spring and sidedress applications minimize the risk of loss by reducing time in the field and matching crop demand.

Future Plans

Further research is needed to refine N application strategies by incorporating real-time weather data and precision agriculture tools. The development of high-clearance application equipment, such as 360 RAIN from 360 Yield Center, offers opportunities for more flexible and targeted in-season applications, potentially enhancing NUE and reducing losses.

Additional studies should assess the risk of spring or sidedress applications from year to year. Weather conditions often limit pre-plant N application, so a thorough analysis of the frequency and financial impact of interrupted field management operations should be conducted.

Future studies should also explore the economic feasibility of split applications, which combine the benefits of multiple timings to reduce risk. Additionally, expanding MRTN models to include seasonal effects would improve decision-making for producers seeking to optimize N application timing while minimizing environmental impact.

Authors

Presenting author

Jacob R. Willsea, Graduate Research Assistant, Iowa State University Department of Agricultural and Biosystems Engineering

Corresponding author

Daniel S. Andersen, Associate Professor, Iowa State University Department of Agricultural and Biosystems Engineering, dsa@iastate.edu

Additional Information

Talkin’ Crap Podcast Episode:

https://talkincrappodcast.buzzsprout.com/2163071/episodes/15629592-the-power-of-manure-timing-enhancing-nitrogen-efficiency

Andersen Lab Poster Repository:

https://iastate.box.com/s/4s9gjhkd93d95yvqip8q5rr46frshtln

https://iastate.box.com/s/icg6clbamksfzciw8ze3lc301p8homg1

Acknowledgements

USDA-NRCS

Brent Renner

360 Yield Center

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