RESIDUE MANAGEMENT IMPACTS ON FIELD-SCALE SNOW DISTRIBUTION AND SOIL WATER STORAGE

Spatial variation of soil water affects crop performance, fertilizer use efficiencies, and other important economic and environmental factors. Soil water storage could be increased and field variability reduced by residue management practices such as no tillage (NT), as surface residues can retain more snow, enhance water infiltration, and reduce evaporation as compared to conventional tillage (CT). Our objectives were to evaluate the residue effects on snow distribution and the spatial variation of soil water storage for two adjacent fields near Pullman, Washington: one under NT, and the other under CT The fields were surveyed during the winter and spring of 2007-2008 to assess topographic variations in snow depth, snow water equivalent (SWE), and soil water storage. Standing stubble under NT retained 10 to 20 cm more snow on ridge tops and steeply sloped ground than CT, and the snowpack was distributed more evenly with less spatial variation. SWE followed the same pattern of larger spatial variation in CT than in NT Soil water (0 to 1.5 m) in the spring was lowest for ridge tops and highest in valleys for NT and CT Under NT, however, soil water varied less across different field locations than under CT, and overall water storage was 60, 29, and 13 mm more for NT than CT on ridge top, south slope, and valley locations, respectively. Although many factors can contribute to the spatial variation of soil water, standing wheat residue under NT retained more snow on ridge tops and steeply sloped areas reduced soil water spatial variation, and increased soil water recharge.