Evaluating soil movement using Cesium-137 and the revised universal soil loss equation

More complete information is needed on the rates and patterns of soil movement in Palouse watersheds to better guide conservation planning. Water erosion has historically been predicted from rates using the Universal Soil Loss Equation (USLE) or the Revised USLE (RUSLE). These equations, however, do not account for deposition or tillage erosion. This study was conducted to assess patterns of soil movement in an open Palouse watershed during a 27-yr period using the Cs-137 tracer technique and to statistically compare transect- and point-based RUSLE soil loss rates with Cs-137-based soil loss rates measured at 74 Cs-137 Sampling points located on 89 landscape profiles. One hundred fifty-eight soil samples were collected from a modified grid pattern and analyzed for Cs-137 activity. Soil movement rates were interpolated at 8025 points in the sample grid using ordinary point kriging. Hillslopes were classified into geometric and geomorphic components. The kriged mean net soil movement rate for the 27-yr period was -3.3 kg m(-2) yr(-1). Doubly convex landscape positions have experienced the most severe erosion, apparently due to tillage erosion. The measured Cs-137 and transect-based RUSLE median soil loss rates were both significantly higher than the point-based RUSLE median; however, no significant difference existed between the transect-based RUSLE and measured Cs-137 median soil loss rates (a = 0.05). Meaningful comparisons between Cs-137 and RUSLE soil loss rates can only be made if a tillage movement rate, history of crop management, and the accuracy of RUSLE relationships and operating files are known.