Evaluation of site-specific management zones on a farm with 124 contiguous small paddy fields in a multiple-cropping system

The identification of homogeneous management zones (MZs) within a field is a basis for site-specific management (SSM). We assessed the method of defining MZs based on the spatio-temporal homogeneity of six soil properties and above-ground biomass data from paddy rice, winter wheat and soybean over 3 years on a farm with 124 contiguous small paddy fields. The soil data were recorded at 372 soil sampling sites on a rectangular grid over the farm. A non-hierarchical cluster analysis was applied to the soil data and the algorithm grouped the sites into three clusters with similar soil properties. These clusters represent soil fertility and soil drainage. The three clusters were not randomly distributed across the fields, but formed contiguous areas associated with landscape position. This was due to the spatial variation of the soil in the study area. We delineated five MZs based on the spatial structure of the soil heterogeneity of the study area. The validity of the MZs was evaluated using the biomass data from paddy rice, winter wheat and soybean in each MZ; this depended mainly on soil fertility when conditions were dry. When the growing season precipitation was greater than the 10-year average, the biomass of winter wheat and soybean depended on soil drainage. This suggested that the delineation of MZs for site-specific management in fields under a paddy-upland crop rotation system should be based on several soil properties. The biomass data from the three crops over 3 years was not effective for delimiting MZs.