Relationship among crop grain yield, topography, and soil electrical conductivity studied with cross-correlograms

The characterization of factors causing spatial variability of crop yield is a necessary prerequisite for successful implementation of precision agriculture. However, the existing tools for a quantitative description of these factors and their relationship to crop yield lack effectiveness and completeness. This study proposed to use the area under an experimental cross-correlogram as a single parameter to describe the spatial correlation between crop yield and topographical and soil variables. The developed parameter conveniently combines the information on the magnitude of the cross-correlogram values, the correlation range, and the cross-correlogram shape. We used the developed parameter to quantify the relationships between corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yield and soil apparent electrical conductivity (EC) and elevation in their spatial context. Variations in the strength and direction (positive vs. negative) of the relationship between yield and soil EC were found to be related to the amounts of precipitation observed early in the growing season. Crop yield was strongly and negatively related to EC in years with high March precipitation and positively or weakly negatively related to EC in years with low or moderate March precipitation. Results also indicated that in years with high March precipitation, the cumulative spatial correlation between soybean yield and EC was stronger than that between corn yield and EC. The range of significant spatial correlations between crop yield and elevation was related to the precipitation data as well as to the soil characteristics of the fields, such as soil organic matter content.