Evaluating farmer defined management zone maps for variable rate fertilizer application

In the U.S.A. intensive grid soil sampling has conventionally been used to develop prescription maps for variable rate (VRT) fertilizer application. Grid sampling can provide an accurate basis for variable rate application; however the cost and labor requirements suggest other approaches may be more economical. This research was initiated to determine if farmer-developed management zone maps based on soil color from aerial photographs, topography, and the farmer's past management experience can be effective in developing variable rate application maps. The accuracy of farmer-developed management zone maps was investigated on two center pivot irrigated fields near Wiggins, Colorado. Using aerial photographs as a template, the farmer defined high, medium, and low productivity management zones. Cluster analysis confirmed that management zones represent different suites of soil characteristics. In field one, soil organic matter (SOM), clay, nitrate, potassium, zinc, conductivity and corn yield data followed the trends indicated by the management zones. In field two, however, the medium productivity zone had the highest values for these parameters. Farmer developed management zones appear to be effective in identifying different management zones; however, ground truthing is needed to develop accurate VRT maps from the zones.