Geospatial modeling of conservation tillage and nitrogen timing effects on yield and soil properties

Crop growth simulation can complement field research for adapting and targeting practices to diverse production areas. Two simulated experiments of 30-year duration were conducted with CERES and CROPGRO to evaluate the effects of fertilizer N practices and conservation tillage (CT) alternatives on maize (Zea mays L.) grain yield, soil organic C and soil organic N for seven technology extrapolation domains (TED) in Ethiopia. Mean maize grain yield was 663 kg ha(-1) more with three compared two N applications per season for high rainfall TED in western Ethiopia. Tillage did not affect response to N. Averaged across TED, maize yield was 33% more with a combination of conservation tillage, rotation and additional N application (CTr+N) compared maize monoculture with conventional tillage and the recommended N rate (CPmm), primarily because of crop rotation. Maize grain yield increased over time with the conservation tillage under rotation (CTr) but declined under CPmm. Soil organic C and N declined over time, but the rate of decline was lower with CTr+N compared to CPmm. Stored soil organic C and N were 8543 and 594 kg ha(-1) more with CTr+N compared with CPmm, respectively, averaged over the 30 years. First order stochastic dominance analysis from maize grain partial net returns showed that maize rotation dominated maize monoculture. Second order stochastic dominance analysis for partial net return indicated the absence of an unambiguous dominant of conservation tillage for a farmers' preference of low risk to higher net return or high net return to low risk.