Case studies on the accuracy of soil pH and lime requirement maps

Successful variable-rate applications of agricultural inputs, such as lime, rely on the quality of the input data. Systematic soil sampling is the most common method used for creating variable rate prescription maps. The low density of economically feasible sampling has been primarily responsible for the typical inaccuracy of soil pH and lime prescription maps. To increase sampling density, on-The-go sensing technology was developed for mapping the soil pH and other relevant attributes. In this study, three fields in eastern Nebraska were mapped using both on-The-go mapping and systematic grid sampling approaches. Ten additional samples were used to define site-specific relationships between sensor measurements and laboratory analysis results. Finally, at least ten random validation locations in each field were used to compare soil pH, buffer pH and the prescribed liming rates with lime requirements. The data collected were used to compare three soil acidity management scenarios: 1) uniform rate liming; 2) variable rate liming based on systematic grid sampling, and 3) variable rate liming based on sensor-based mapping. In general, sensor-based maps were better predictors of soil pH, buffer pH and lime requirements than field average or grid-based maps.