Weed emergence patterns as affected by topsoil movement within an eroded landform

Soil erosion significantly affects within-field soil properties, crop productivity, weed emergence patterns, and weed growth. Spatial variability in weed densities, emergence timing, weed seed production, seed viability, herbicide bioavailability, and other factors complicate weed management strategies in eroded landscapes. Reversing soil erosion by replacing translocated topsoil (soil-landscape rehabilitation) is one method to improve crop productivity of severely eroded land, but bulk soil movement changes soil properties and weed seedbanks that influence weed spatial distribution patterns, emergence, and growth. We evaluated weed community responses to soil movement within a hilly landform. Soil-landscape rehabilitation was performed by moving 15–20 cm of accumulated topsoil from the lower slope and adding it to the upper slope positions (areas of net soil loss by erosion). Adjacent plots were left in their eroded condition. Weed density and species richness were monitored for 4 years. Annual grasses dominated the weed community in the upper slope, and weed abundance was highest in the most eroded landscape positions. Soil addition improved soil characteristics for crop growth but did not increase weed densities. The density of weeds was lower where soil was removed in the first 2 years after soil movement, likely through removal of weed seeds with soil. Within 3 years of soil movement, weed abundance and species richness were the same or lower in areas of soil removal and no soil removal. In these experiments, movement of soil (and entrained weed seeds) within an eroded landform to improve productivity did not exacerbate weed issues.