Submitted to: American Water Resources Association Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/29/2001
Publication Date: N/A
Technical Abstract: Dryland winter wheat/fallow cropping systems on the Columbia Plateau are susceptible to runoff causing soil and nutrient loss. Nutrient loss is detrimental to crop production and contributes to water quality impairment. During the winter of 1999 - 2000, we collected rain fed runoff and sediment samples from long-term experimental plots. These plots were established in 1931 to test the effect of crop residue management and nutrient amendments on crop yields. Tillage in this traditionally farmed winter wheat/fallow cropping system consists of moldboard plowing, followed by multiple passes with a secondary tillage equipment to control weeds. The plots are duplicated at two slope positions, upslope with a 6 percent slope, and downslope with a 2 percent slope. Treatment differences in amount and quality of bedwash were tested using ANOVA and a mean separation test, and total carbon loss. Total carbon was significantly greater in the two treatments with burned residue and no nutrient amendments than from the stubble (non-crop year) treatment. These two treatments represent the worst-case scenario for soil carbon loss for this cropping system, but are not significantly different than the treatments wherein commercial fertilizer is applied and crop residue is not burned. The winter wheat/fallow system, under traditional tillage practices, leads to soil carbon loss by microbiological activity, which is exacerbated by highly erodible soil surface conditions. As soil quality declines, erosion increases with concomitant nutrient loss, leading to a downward cycle of increasing soil loss and decreasing soil quality.