John Grove, N122 Ag Science North, University of Kentucky, University of Kentucky, Department of Agronomy, Lexington, KY 40546-0091 and E. M. Pena-Yewtukhiw, Divison of Plant and Soil Sciences, 1104 Agricultural Sciences Building, West Virginia University, Morgantown, WV 26506-6108.
Precision soil fertility (nutrients/lime) management is based on greater information (more samples per field) regarding the soil fertility status of any given field area. That information includes both more soil tests and the positional information associated with those results, and comes at significant cost. How much fertilizer/lime redistribution occurs with typical 1-ha grid sampling, relative to “field-average” sampling, and what field characteristics are associated with the need for grid sampling? Our specific objectives were, using 46 grower fields located on alluvial soils, to determine: a) the magnitude of variation in grid soil pH and soil test P and K, relative to the “field-average”; and b) the potential redistribution of fertilizer and lime, relative to current “field-average” applications, applied to either the whole field or the individual grid cells. Grid sampling often, but not always, resulted in considerable redistributed lime and fertilizer. Redistributed lime and fertilizer were highest when the field's mean soil pH or soil test P or K values were close to the threshold where no lime or fertilizer P or K would be recommended. The greater benefit to grid sampling was not strongly dependent on the in-field variation in the soil test parameter. Given the average level of in-field variation observed, a preliminary sampling of only 3 to 5 grids would indicate whether one of these large river-bottom fields would benefit from grid sampling.