Simulation of a regional soil nitrogen balance in Swiss croplands

Abstract

Nitrogen (N) management in cropping systems needs adjustments because constraints to crop production are mostly related to high inputs and low recovery of N fertilizers. We used the DayCent model to predict regional N inputs, outputs, and balances of Swiss soils under (1) a range of N fertilizer input levels (0–300% of recommended crop-specific rates) and (2) organic fertilization, reduced tillage or cover cropping at the recommended input of N. The crops included wheat, maize, and root/tuber crops and legumes. Decreasing N inputs reduced the environmental impact by 13.5–51.3 kg N ha$^{-1}$, but it also reduced the yield by 6.8–44.8 kg N ha$^{-1}$. Increasing N inputs led to an increase in yield by 5.6–29.5 kg N ha$^{-1}$, but with additional losses of 14.9–181.8 kg N ha$^{-1}$ into the environment. Harvested crop N and $\hbox {NO}_3^{-}$ leaching accounted for 30–59% and 27–62% of fertilizer-derived changes in total N output, respectively. Converting conventional to organic cropping led to a mean increase in soil N balance by 0.3–62.6 kg N ha$^{-1}$. The soil N balance increased the most by using partially decomposed organic fertilizer in combination with cover cropping and reduced tillage. However, this positive N balance was mainly due to a reduction in N removal with harvest and $\hbox {NO}_3^{-}$ leaching. The use of highly decomposable organic matter and cover cropping did not lead to any N yield penalty while decreasing $\hbox {NO}_3^{-}$ leaching. These results highlight that organic practices combined with reduced tillage and cover cropping can optimize the use and recovery of N resources.