Developing and evaluating management zones for variable rate fertilizer application

Variable rate fertilizer application technology (VRT) can provide an opportunity to more efficiently utilize N fertilizer inputs, defining management zones that characterize the spatial variability within a field may provide an effective use of VRT.; The initial objective of this dissertation was to evaluate management zones identified using soil color from aerial photographs and farmer experience. These farmer developed management zones were compared to soil and crop parameters at two fields. Analysis indicates that this method can be useful in identifying different management zones. Soil and yield parameters followed the trends indicated by the management zones at field one with the highest values found in the high productivity zones and the lowest the low productivity zones. Significant differences were found among the management zones. At field two the low productivity zone was significantly lower in the soil and crop parameters, however the high and medium productivity zones were generally not significantly different.; A second objective was to evaluate and compare prescription maps using the management zones described above with prescription maps developed from grid soil sampling. Six N treatments were applied on three center pivot irrigated corn fields in northeast Colorado in 1999 and 2000. There were no significant differences in yield between the treatments developed from management zones and the treatments developed from grid soil sampling. These data indicate that management zone based variable rate application is at least equally effective as grid based application. However, the cost of implementing the management zone based VRT program is much less making it a profitable alternative to grid soil sampling.; The final objective for the dissertation was to compare and evaluate prescription maps developed from soil color and farmer experience with prescription maps developed from apparent soil electrical conductivity. The soil and yield parameters followed the trends indicated by both methods at field one. Significant differences were found among the management zones. However at field two the high and medium productivity zones were not significantly different using the soil color approach while the soil conductivity approach was effective in identifying three distinct management zones.