Simulating nitrogen management impacts on maize production in the U.S. Midwest

Area of Science:

• Agricultural Science
• Environmental Science
• Agronomy

Background:

• Nutrient loss reduction strategies aim to decrease the environmental impact of nitrogen (N) fertilizer use in agriculture.
• These strategies often involve reducing N application rates and shifting application timing from fall to spring.
• The watershed-scale impacts of these practices on maize yield and N use efficiency (NUE) require further investigation using crop simulation models.

Purpose of the Study:

• To assess the spatiotemporal impacts of nitrogen fertilizer rate and application timing on maize grain yield (GY) and NUE at the watershed scale.
• To evaluate the effectiveness of shifting N application from fall to spring and reducing N rates on maize production in the U.S. Midwest.
• To understand the influence of winter rainfall on the performance of these nutrient management strategies.

Main Methods:

• Utilized the DSSAT-CERES-Maize model to simulate maize grain yield under various nitrogen fertilizer rates (0, 168, 190, 224 kg N ha-1) and application timings (fall, spring, split).
• Simulations were conducted across 3042 points in Illinois from 2011-2015.
• Model outputs were scaled to the watershed level to analyze spatiotemporal impacts.

Main Results:

• Spring-applied N (SN) increased average maize grain yield (GY) compared to fall-applied N (FN) in years with above-average winter rainfall (>500 mm).
• Nitrogen use efficiency (NUE) gains for SN over FN were more pronounced with higher winter rainfall (0.1-9.2 kg GY/kg N vs. 0.0-1.4 kg GY/kg N).
• Reducing N rates by 15% (224 to 190 kg N ha-1) combined with a shift to SN showed variable yield responses (<10% to >70% probability of increase) and only improved both GY and NUE in 60% of simulations.

Conclusions:

• Shifting nitrogen application from fall to spring can enhance maize yield and NUE, particularly under high winter rainfall conditions.
• Simultaneously reducing nitrogen fertilizer rates and altering application timing presents challenges for consistently improving both yield and NUE.
• Optimizing nutrient management strategies requires consideration of regional rainfall patterns and their interaction with fertilizer application practices.