Simulation‐based Maize–Wheat Cropping System Optimization in the Midhills of Nepal

Abstract

Rainfed maize (Zea mays L.)–wheat (Triticum aestivum L.) production in the midhill region of Nepal is limited in the winter season by cool temperatures, low rainfall, and low fertility. Here, we use the Decision Support System for Agricultural Transfer Cropping System Model (DSSAT‐CSM) to simulate potential productivity for conservation agriculture (CA) and conventional practice (CP), contrasting N application rates, and wheat planting dates ranging from 1 September to 15 December under six different weather scenarios in the midhills of Nepal. Total maize plus wheat aboveground biomass increased up to 56% with longer vs. shorter duration maize varieties, but the subsequent dry‐season wheat failed 71% of the time after late‐planted, long‐season maize in areas where mean seasonal temperature was below 14°C. The optimal wheat planting date increased from August to December as seasonal rainfall amount increased. Increasing N application rate in wheat from 50 to 150 kg ha–1 resulted in significant yield and net profit gains for all weather scenarios given current grain and fertilizer prices in the midhills, especially where conditions were cool and rainfall exceeded 400 mm. Principal component analysis of soil and climate parameters indicated that CA benefits most from higher N application rates when conditions are cool and wet due to increased residue retention coupled with slow soil organic matter decomposition.Core Ideas Conservation agriculture out‐yields conventional practice in wheat for weather scenarios with high seasonal rainfall. Insufficient growing degree days may force earlier than optimal wheat planting in cooler midhill weather scenarios. Optimal wheat planting date occurs before October in warmer and drier midhill weather conditions.