Fallow management effects on soil water storage and wheat yields in the Pacific northwest

Conservation tillage practices are adopted by farmers to control soil erosion and in some cases to reduce production costs. Conventional tillage practices usually rely on extensive tillage to control weeds and conserve water. In other cases, grazing animals may be used to control weeds and utilize crop residues for animal fodder on the fallowed land. These intensive systems leave the soil surface bare and susceptible to erosion. A five-year study was conducted in the winter wheat (Triticum aestivum)-fallow area of eastern Washington to evaluate the effects of tillage, weed control, and residue management on soil water storage and wheat yields. Tillage treatments were (i) conventional (early spring sweep and summer cultivation), (ii) delayed spring (late spring sweep and chemical weed control), and (iii) no-till (chemical fallow). Residue management treatments were (i) all residues removed at the beginning of the 22-mo fallow, (ii) all residues and vegetation removed after the first winter rainy season, and (iii) residues not removed. Weed control treatments were (i) weeds not controlled during the first winter rainy season but controlled thereafter and (ii) weeds controlled throughout the fallow period. Soil water storage was greater every year where crop residues were not removed, or removed after the first winter of the fallow period, compared with residue removal at the beginning of the 22-mo fallow. Weedy fallow (weeds allowed to grow during the first winter rainy season) had no effect on fallow efficiency or wheat yields compared with fallow with weed control. Wheat yields were increased in one year out of five by the retention of surface residues and in one year by tillage and, thus, for the most part did not reflect differences in water storage efficiencies. Weedy fallow provided greater residue cover through erosive periods, but did not adversely affect soil water storage and wheat yields compared with fallow with weed control.