Alteration of soil water content consequent to root-pruning at a windbreak/crop interface in Nebraska, USA

Root-pruning is generally recommended as an appropriate treatment to reduce competition for soil water and/or nutrients and suppression of crop yield in areas adjacent to windbreaks. Several recent studies suggest, however, that factors other than soil water might be causing yield reduction at the interface. For two consecutive years, we evaluated root-pruning effects on soil water at the windbreak/crop interface under both cropped (soybean [Glycine max(L) Merr.] variety 'Iroquois', 1997) and non-cropped (1998) conditions in Mead, Nebraska, USA. Volumetric soil water content near the windbreaks was systematically measured at various soil depths, distances from the windbreak, and windbreak exposures using Time Domain Reflectometry (TDR). Overall differences in soil water content between root-pruned and non-pruned plots in soybean were smaller in magnitude at all distances in both the west (windbreak on the east side) and the east (windbreak on the west side) exposures in 1997, compared with the non-cropped condition in the south exposure in 1998. With a soybean crop in 1997, volumetric soil water content in the east exposure averaged 2.3% greater in the top 30 cm of the soil profile at a distance of 0.75H (H=windbreak height) into the field from the windbreak when compared to the non-pruned treatment. In the west exposure, however, the differences were undetectable at corresponding distance and depth. The increase in soybean yield in root-pruned plots corresponded well with the observed differences in soil water content at various distances, especially in the east exposure. Under a non-cropped condition in 1998, soil water content in the root-pruned plots was significantly greater than the non-pruned plots in the top 45-cm profile, averaging 3.3% at 0.75H and 2.2% at 1.0H. Beyond 1.0H, the increase was not significant. These results agree with the previously reported range of crop yield suppression near windbreaks, indicating that soil water competition between the crop and windbreak is highly related to, and probably plays a leading role in yield suppression within the competition zone.