Spatially Applied Soil Amendments Decrease Soil Property and Crop Yield Variability on a Small-Plot Research Field

The variability of soil productivity is a problem in many agricultural experiment station fields, where field uniformity is needed for research conducted in small plots. The objective of this study was to evaluate the effects of applied amendments on the spatial variability of selected soil chemical properties and crop yield. Between 1993 and 1997, soil samples were collected from the top 6-inches of a 5-acre production field in a grid pattern and physical and chemical properties of the soil were determined following the application of ag-lime or S to adjust soil pH and fertilizer P and K to adjust soil test P and K availability index values. The initial soybean (Glycine max [L.] Merr.) seed yield ranged from 7.9 to 34.8 bu/acre with a CV of 20%, whereas the final soybean seed yield was significantly greater than that in 1993, ranging from 28.4 to 49.0 bu/acre, and had a lower CV of 11%. While field means for soil-test P and K were generally significantly greater in subsequent years compared to 1993 values, their uniformity did not improve greatly. Uniformity of soil pH and yield increased as measured by a decrease in the range and CV of these properties. Spatially applied soil amendments can be used effectively to improve crop yield uniformity, particularly in agricultural experiment station fields that require uniform soil-surface properties for small-plot research.