Exploring the Relative Importance of 4R Components in Achieving Agronomic and Environmental Benefits in US Maize Production.

Maize (Zea Mays L.) production accounts for the largest share of crop land area in the US and is the largest consumer of nitrogen (N) fertilizers. Routine application of N fertilizer has led to increased N surplus, and well-documented environmental problems and social costs. There is a potential to reduce these costs through implementation of the 4R concept. This study explores the relative importance of 3 of the 4R’s in reducing N surplus and environmental N losses: i) timing of N application; ii) use of Enhanced Efficiency Compounds (EEC); and iii) more precise N rate calculations (dynamic vs static N recommendation approach). For the analysis we have used Adapt-N, a computational tool that combines soil, crop and management information to estimate optimum N application rates for maize. The data spanned 3 soil textures and 7 years of climatic data (2010-2016) in 19 locations in the top 5 US maize production states – IL, IN, IA, MN and NE, resulting in a database of 12,000 simulations. Our results indicate that fall applications lead to the lowest N use efficiency, highest N surplus and lead to substantial amounts of N losses. The modeled EEC’s were found to have marginal benefits for fall applied N. Spring pre-plant N applications were found to have higher N use efficiency than fall applications, but could still lead to high N losses under wet spring conditions. These losses were significantly reduced when EEC’s were applied. Out of all simulated N management scenarios, applying a split N application and dynamically adjusting in-season N rates was found to have on average the lowest N surplus, lowest N losses and overall, highest N use efficiency. These results could be used to inform environmental policies and business models to reduce environmental costs associated with US maize cropping.