ANALYSIS OFWATER STRESS EFFECTS CAUSING SPATIAL YIELD VARIABILITY IN SOYBEANS

Abstract

Soybean yields have been shown to be highly variable across fields. Past efforts to correlate yield in smallsections of fields to soil type, elevation, fertility, and other factors in an attempt to characterize yield variability has hadlimited success. In this article, we demonstrate how a process oriented crop growth model (CROPGRO-Soybean) can beused to characterize spatial yield variability of soybeans, and to test hypotheses related to causes of yield variability. Inthis case, the model was used to test the hypothesis that variability in water stress corresponds well with final soybeanyield variability within a field. Soil parameters in the model related to rooting depth and hydraulic conductivity werecalibrated in each of 224 grids in a 16-ha field in Iowa using three years of yield data. In the best case, water stressexplained 69% of the variability in yield for all grids over three years. The root mean square error was 286 kg ha1representing approximately 12% of the three-year mean measured yield. Results could further be improved by includingfactors that were not measured, such as plant population, disease, and accurate computation of surface water run on intogrids. Results of this research show that it is important to include measurements of soil moisture holding capacity, anddrainage characteristics, as well as root depth as data layers that should be considered in any data collection effort.