The Relative Importance of Fertilizer Timing Vs. Form in Controlling Environmental N Losses in US Corn Production.

Routine application of N fertilizer in excess of crop demand has led to well-documented environmental problems in US maize production. There is a potential to reduce environmental losses by shifting both the timing (i.e. fall, spring, in-season sidedressing) and form (i.e. enhanced N efficiency products) of fertilizer N applications. However, the magnitude of this potential and the factors affecting it across different production environments is still not clear. This research gap is addressed here using the Adapt-N tool, a computational tool which simulates the relevant crop and soil processes throughout the growing season. Using results from a large synthetic dataset of 7200 simulations spanning six years (2010-2015), we have explored the agronomic and environmental efficiency of seven N management scenarios applied in the top five US Maize production states – IL, IN, IA, MN and NE. To cover a wide range of weather and production environments, all scenarios were applied at five locations in each state, using combinations of three soil texture and two organic matter percentages. Our results indicate that shifting the timing of N application had a much larger effect on environmental N losses than addition of any N inhibitors. Fall applications lead to the lowest N use efficiency and high N losses, and nitrification inhibitors were found to have a marginal effect on this result. Spring pre-plant N applications where found to have higher N use efficiency than fall applications, but could still lead to high N losses under wet spring conditions. In-season N application was found to have on average the lowest total N applied amount, lowest N losses and overall, highest N use efficiency. The results of this comprehensive analysis could be used to inform environmental policy and the promotion of split applications as an immediate step to reduce environmental costs associated with US Maize cropping.