Estimating Within Field Variability of Wheat Yield Using Spatial Variables: An Approach to Precision Agriculture

Within-field variation of wheat yield and spatial pattern of weed density and soil nitrogen were evaluated by geostatistical methods. Samples were taken from a 90×120 m area located in a 3.8 ha wheat field. Soil nitrogen content and weed density at tillering and wheat yield at maturity were measured in 1 m2 plots located at the center of 10×10 m grids. Grain yield was varied between 1.5-4.9 t ha-1 with coefficient of variation (CV) 0f 29%. However, weed density and soil nitrogen showed a higher spatial variation with CV of 55 and 41%, respectively. Based on the results of multiple regression, weed density and soil nitrogen accounted for 80% of the observed yield variation. Semivariance was calculated for the studied variables with 10 and 20 m lag distances and spherical model was fitted to the experimental variograms. Comparison of statistical characteristics of the variogram models indicated that precision was decreased with increasing sampling distance. Based on the modeled variograms measurements were interpolated using ordinary kriging and the resulting yield maps were reasonably mached with spatial pattern of soil nitrogen and weed density. The accuracy of interpolated yields with kriging at 10 and 20 m sampling distance was validated against the observed yields. Yield prediction accuracy was improved with co-kriging particularly when soil nitrogen content was defined as covariate in both distances however, this method of interpolation was more efficient at 10 m sampling distance.