The potential of "precision" recommendations for sitespecific phosphorus, potassium and lime applications

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. Fertilizer/lime recommendations derived from soil testing were originally designed for "fieldaverage" sampling techniques. This might be a limitation to the use of these older recommendations for precision fertility management. Can additional agronomic, economic and environmental benefit(s) be captured with improved recommendations? Our specific objectives were, for a large number of grid-sampled grower fields, to determine: (a) the magnitude of variation in soil pH and bio-available P and K, relative to the "field-average"; and (b) the economic potential for "precision" fertilizer and lime recommendations, relative to current "field-average" recommendations applied to either the whole field or the individual grid cells. Results indicate that, taken together, grid sampling generated considerable economic value in redistributed lime and fertilizer, but savings due to reduced lime/fertilizer use were greater with conservative, "precision" recommendations. Economic benefits to a given field ranged from <$1/ha to nearly $60/ha and were more dependent on a field's soil test parameter mean than its in-field variation.