Effect of Rill Erosion during Early Vegetative Growth on Winter Wheat Yield
- P.E. Rasmussen and
- C.L. Douglas
The long-term effect of soil erosion on lowering soil productivity is well documented, but little is known about how rill erosion occurring during the crop growing season affects yield. Rill erosion effects on winter wheat (Triticum aestivum L.) growth and yield were determined in six fields where rill erosion occurred during early vegetative growth. Soils were Walla Walla (coarse silty, mixed mesic Haploxeroll) or Athena (fine silty, mixed mesic Haploxeroll) silt loams at least 2 m deep. Rills were followed across landscape positions on slopes ranging from l to 15%. Rills paralleled rows in all six studies, and traversed rows in two of the six. Rill erosion reduced head density, dry matter yield, N uptake, and grain yield at all sites. The rill/non-rill (R/NR) grain yield ratio (per square meter) varied from 0.84 to 0.94. The R/NR yield ratio was not affected by slope steepness or aspect, but was weakly correlated with yield level (greater loss at higher yields) and landscape position (lower slope positions had larger rills and greater yield loss). The grain R/NR ratio decreased with increasing rill depth but was not dected by rill width. Soil loss measured with a rillmeter was correlated with rill depth. The estimated yield reduction per ha associated with average rill development (11.7 cm deep rills, 26.7 kg m−2 soil loss in rill area, and 10 rill transects ha−1) was between 0.9 and 1.2%. Assuming a 36 Mg ha−1 soil loss (the average for sloping Haploxeroll soils of the Pacific Northwest), the calculated yield reduction from winter wheat fields yielding 5.2 Mg ha−1 is 88 kg grain ha−1 (about $13 ha−1 for wheat valued at $0.147 kg−1). This erosion cost would encompass a significant percentage of the landscape with sloping topography and is additional to any costs associated with long-term loss of soil productivity.
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