Snow redistribution and soil water storage as impact by surface residue conditions

Hanxue Qiu

Water availability is a major limiting factor affecting agricultural productivity especially for the dryland farming regions of the Great Plains and the Pacific Northwest (PNW). Studies show that no-tillage (NT) practices result in more soil water storage by retaining more snow in stubble, enhancing infiltration and reducing evaporation in areas where winter is the primary recharge season, whereas conventional tillage (CT) practices result in considerable redistribution of precipitation with elevated surface runoff. We hypothesize that the residue effects on precipitation redistribution also affects the spatial variation of soil water. Studies show that spatial variation of available soil water has important environmental and economic effects and implications by affecting crop yield and quality and effective fertilization recommendation. Our objectives were to evaluate residue effects on snow redistribution and the spatial variation of soil water in the Palouse area of the PNW. Two side-by-side farms near Pullman, WA, one under NT, the other under CT, were surveyed for snow depth, snow water equivalent (SWE), and resultant soil water storage during the winter season of 2007-2008. Results indicated that snow pack on average was distributed more evenly and had less spatial variation under NT. Compared to CT, NT retained 10-20 cm more snow by its standing residue at the ridge top for the events surveyed. Snow water equivalents followed the same pattern of larger spatial variation in CT. The resultant soil water in the spring was the lowest at the ridge top areas, and highest at valleys in both treatments. However, under CT, soil water at the ridge top area was 6% less than, and in valleys 17% more than, the average over the whole treatment. Such variation was much smaller in NT where soil water at the ridge top was only 4% less than, and in valleys 6% more than, the average. Although many factors may have contributed to the spatial variation of soil water, residues under NT retarded the generation of runoff, retained more snow at the ridge top and steep-sloped areas, and likely reduced the soil water spatial variation.

Snow redistribution and soil water storage as impact by surface residue conditions

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