Assessing spatial variability in an agricultural experiment station field: Opportunities arising from spatial dependence

Spatio-temporal field soil and crop processes are important for site-specific farming. The objectives of this study were to spatially evaluate selected soil physical and chemical properties and their relationship to wheat (Triticum aestivum L.) yield, and to discuss stochastic approaches to help identify processes underlying yield variability in heterogeneous field sites. Modified grid sampling included 330 sites including a primary transect. Soil properties measured for the Ap, E if present, and upper B horizons at each site included pH, P, Zn, Cu, exchangeable cations, percentage base saturation, cation exchange capacity, bulk density, soil water contents at -10, -33, and -1500 kPa, texture, and humic matter content. Wheat grain and straw were hand-harvested on 1- by 2-m plots centered on each site. Soil water content on the primary transect was determined by neutron attenuation on nine dates. Field and primary transect means and semivario-grams for a given soil or plant parameter were similar. The range of spatial dependence or autocorrelation of soil parameters ranged from 10 m for Ap horizon depth to 10 m for -1500 kPa water content of the Ap. Base saturation and available water storage capacity were cross-correlated with grain yield to a distance of ±15 and 12.5 m, respectively. State-space analysis was used to develop a grain yield model using these two variables. Spearman rank correlation of the soil water content data suggests that the temporal stability of soil water storage is less for shallow than for deeper soil layers.