GIS could include the monitoring and mapping of yield data relative to discrete positions within the field. VRT could be used to vary the amount of N applied site-specifically within the field to reflect differing historical yield levels. All of these factors result in less total root growth and a more shallow placement of root growth in the no-till system. Any factor which results in low soil temperature during germination and establishment can result in slow crop development and a reduction in crop yield potential. This appearance in the top 13 to 18 inches indicates poor drainage critically-high in the root zone.
Poor drainage is a likely restriction on yield in that environment.
Sampling more intensively than this grid would be desirable where soil type is uniform but significant yield variability exists within an area. Such intensive sampling would produce additional information vital to either confirm or rule out variability in soil test levels as at least a partial contributor to the yield variability observed in these areas.