As technology in seed, fertilizer, crop monitoring, and data collection continues to advance, nitrogen recommendation systems will need to adapt. The influence of source, timing, and placement on rate is essential to consider in recommendations. Additionally, the influence of weather, soil, and other conservation practices on yield and efficiency measures like nitrogen recovery efficiency needs further consideration in the advancement of nitrogen recommendation systems.
Improving nitrogen management in cropping systems is important for the economic, environmental, and social goals of 4R Nutrient Stewardship. Increasing nitrogen recovery efficiency (NRE) is part of this [NRE = (nitrogen accumulation with fertilizer – nitrogen accumulation without fertilizer)/nitrogen rate; Mueller et al., 2017]. Corn grain yield increases with increased nitrogen application. Recent research conducted as part of the 4R Research Fund reported that from 0 to 200 lb N/ac, grain yield increased by 42%, but beyond that rate, no further grain yield response to nitrogen fertilizer was seen (Omonde et al., 2017). As fertilizer nitrogen application rates increase, nitrous oxide (N2O) emissions are likely to increase linearly. Nitrous oxide emissions are negatively related to NRE; as NRE increases, N2O emissions decrease (Omonde et al., 2017). Increases in NRE can be driven by greater uptake of nitrogen by the plant or reduced nitrogen rates, but the largest gains in NRE will be achieved by higher nitrogen uptake and lower nitrogen rates.
The source, placement, and timing of nitrogen fertilizer can all impact nitrogen uptake by the plant. The magnitude of the decrease in N2O emissions with increased NRE varied depending on the number of 4R management practices considered. When only nitrogen rate was adjusted, N2O emissions decreased by 0.011 lb N/ac for every 1% increase in NRE (Omonde et al., 2017). However, N2O emissions decreased by 0.017 lb N/ac for every 1% increase in NRE when rate and timing of nitrogen application were adjusted (Omonde et al., 2017).
In-field research has shown that NRE consistently improves with a late split nitrogen fertilizer application, but corn grain yield does not (Mueller et al., 2017). Further research is needed on the impact of combining source, rate, time, and placement changes in a single experiment and their impact on NRE.
Sally Flis, Ph.D. and CCA, Director of Agronomy, The Fertilizer Institute, Washington, DC