TY - JOUR T1 - Spatial and agronomic assessment of water erosion on inland Pacific Northwest cereal grain cropland JF - Journal of Soil and Water Conservation SP - 347 LP - 364 DO - 10.2489/jswc.2022.00091 VL - 77 IS - 4 AU - M. Samrat Dahal AU - J.Q. Wu AU - J. Boll AU - R.P. Ewing AU - A. Fowler Y1 - 2022/07/01 UR - http://www.jswconline.org/content/77/4/347.abstract N2 - The inland Pacific Northwest (PNW) is characterized by high erosion rates attributed to hilly topography, highly erodible silt loam soils, wet winter seasons with frequent freeze-thaw events, and widespread use of conventional tillage practices. Historically, annual water erosion from cropland in the region’s Palouse River basin averaged 20.6 t ha-1, and more recent rates are 10, 13, and 11 t ha-1 for the low (<380 mm y-1), intermediate (380 to 460 mm y-1), and high (>460 mm y-1) precipitation zones. Identifying source areas for targeted, effective management requires understanding the factors affecting water erosion, especially how tillage practices and crop rotation interact in various topographic, soil, and climatic settings. The objectives of this study were to (1) understand how hillslope hydrological and water erosion processes are influenced by key environmental factors (soil, climate, and topography) and management practices (tillage and crop rotation), and (2) assess the spatial distribution of soil erosion at the county level and by precipitation zone over the last 30 years. We compiled various combinations of soil, climate, topography, tillage, and crop rotation, and simulated these combinations county by county with the Water Erosion Prediction Project (WEPP) model. Simulated average annual erosion rates were lowest in the low-precipitation zone and highest in the intermediate-precipitation zone, exceeding the USDA Natural Resources Conservation Service tolerable limit (11 t ha-1) in many cases. Temporally, high precipitation events and fallow periods in the rotation greatly increase erosion. Average annual erosion rates in Whitman County are 13.6, 19.0, and 15.4 t ha-1 in the three precipitation zones: low (<380 mm y-1), intermediate (380 to 460 mm y-1), and high (>460 mm y-1), respectively. The intermediate-precipitation zone produced a total annual erosion of 4.2 × 106 t, despite having the smallest area. Columbia County has the highest erosion rate with 23.7 t ha-1 y-1. Geospatial visualizations of the simulation results reveal critical source areas (“hotspots”) where estimated erosion rates are more than five times the average rates, providing crucial information for, and advancing our understanding of, targeting management and increasing efficiency of conservation practices. ER -