1. Field Scale Fertilizer Recommendations and Spatial Variability

Fertilizer is usually applied at a single constant rate across a field. However, soil fertility may vary considerably within a field. Soil test calibrations (ie recommended fertilizer versus soil test ) are usually obtained from sites with low spatial variability of soil test values (ex. small plots ). These calibrations are then assumed to be valid for large fields with variable soil fertility. The effects of variable soil fertility on the relationship between average crop yield response, average...