Modeling soil texture and residue management effects on conservation agriculture productivity in Nepal

Abstract Conservation agriculture (CA) is characterized by zero or minimum tillage, permanent land cover with crop residue or plant growth, and crop rotation. Only a few studies have addressed the impact of soil texture on relative CA:CP productivity, and none have simultaneously evaluated soil texture interactions with optimal residue retention rate. We simulated the interaction effects of soil texture and residue retention on crop yield for CA and conventional practices (CP) for a monsoon-season maize [Zea mays L.] and dry-season wheat [Triticum aestivum L.] double-cropping system in the midhills of Nepal. The simulation used 35 years of historical weather data, fifteen soil profile descriptions representing a range of soil texture classes, and variable rates of residue retention. Crop models were calibrated with field data and simulation results evaluated against measured field data from other published studies. Optimal maize residue retention rate was 60 % and optimal wheat residue retention rate was 10 %, regardless of soil texture. At optimal residue retention, CA maize yielded 0.37 Mg ha−1 less than CP on clayey soils and 0.25 Mg ha−1 less than CP on loam soils, equivalent to 5 % and 4 % yield loss, respectively. However, mean wheat yield was greater with CA than CP for all soil textures, with an average yield increase of 0.17 Mg ha−1, or 18 % increase in wheat yield. The time required for CA to produce equivalent maize yields to CP increased by approximately 1.23 yr per % of soil clay. Possible non-linearities exist in the relationship between soil clay and time-to-equivalent maize yield. Wheat yield was more stable, but maize yield less stable, with CA compared with CP for all soil texture categories.