Applying the RZWQM2 in a Spatial Variability Study of a 4-Year Crop Rotation.

The Root Zone Water Quality Model (RZWQM2) has been widely used in field-scale studies to quantify the environmental impacts of soil and crop management. The strengths of this model are its wide applicability under different boundary conditions, the specific parameterization, and the detailed description of soil hydro-bio-geochemical and plant growth processes. Besides predicting processes precisely at the field scale, the model has not often been used in spatial variability studies, i.e., in situations, when processes need to be adequately described at different specific locations in a field, for which site-specific soil and other observations are available as parameter input. If RZWQM2 were sensitive to predict local soil and crop growth processes, it could be used as a tool for site-specific management decisions. The objective of this study was to find out, how RZWQM2 can be parameterized using site-specific input information and whether this parameterization supports enough sensitivity of the model to predict processes site-specifically. In a farmer’s field in Kentucky, RZWQM2 was applied to 45 locations for which soil textural and soil organic matter content information existed for four soil depth. These locations had been investigated over three years with corn, wheat and soybean crops. Special attention was given to soil textural variation and the parameterization of soil hydraulic properties, soil water processes, and crop growth and yield. Besides, measurements of mineral soil nitrogen were available and leaf area index for some points in time. For selected locations, we will show the model behavior in comparison to soil water content, and biomass development, and we will distinguish calibration of the soil hydraulic part using times of water infiltration and redistribution.