Managing Global Resources for a Secure Future

2017 Annual Meeting | Oct. 22-25 | Tampa, FL

332-9 High Crop Nitrogen-Use Efficiency Does Not Translate into Low Environmental Losses in the Midwestern US.

See more from this Division: SSSA Division: Nutrient Management and Soil and Plant Analysis
See more from this Session: Nitrogen Efficiency, Cycling and Environmental Impacts

Wednesday, October 25, 2017: 10:10 AM
Tampa Convention Center, Room 10

Rafael A Martinez-Feria1, Michael J. Castellano1, Matthew J Helmers2, Matt Liebman1, Ranae Dietzel1, Isaiah Huber1 and Sotirios V Archontoulis1, (1)Department of Agronomy, Iowa State University, Ames, IA
(2)Ag & Biosystems Engineering, Iowa State University, Ames, IA
Abstract:
Increasing nitrogen (N)-use efficiency (NUE) is necessary for improving crop production and environmental quality. Cropping system NUE is often evaluated based on the long-term balance between the inputs of N into soil and its removal in harvested yield. A long-term N surplus (i.e. N inputs > N yield) is widely accepted as indicative of environmental N losses. Here, we evaluate this assumption in the context of the predominant rainfed maize and soybean cropping systems of the Midwestern US. We used a process-based model (APSIM), trained and tested with experimental datasets from Iowa, US, to calculate N balances across cropping systems that differed in fundamental biophysical controls on N dynamics. Modeling results indicated that despite the high NUE (87%) and a low N surplus (21 kg N ha-1 yr-1) in these systems, the actual environmental N losses (47 kg ha-1 yr-1) were substantially greater than what would be predicted by these metrics. Because the soil N pool in these systems is not in long-term equilibrium (-26 kg N ha-1 yr-1), the N surplus did not adequately characterize environmental N losses. Additionally, efficiency improvements resulting from the inclusion of a rye cover crop, which mitigated environmental N losses by 22%, were not captured by the N surplus method. This suggest that mitigating the high environmental losses in these systems requires more than reducing the N surplus alone, but also enhancing the N recycling with practices such as cover crops. Results also highlight the need for developing NUE metrics that can concurrently evaluate the efficiency attributable to improvements in both fertilizer management and N cycling. This would aid in the identification of win-win management scenarios that increase production while mitigating environmental N losses.

See more from this Division: SSSA Division: Nutrient Management and Soil and Plant Analysis
See more from this Session: Nitrogen Efficiency, Cycling and Environmental Impacts