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 Uni versal Soil Loss Equation (USLE) or the Revised USLE (RUSLE). These eq uations, however, do not account for deposition or tillage erosion. Th is study was conducted to assess patterns of soil movement in an open Palouse watershed during a 27-yr period using the Cs-137 tracer techni que and to statistically compare transect- and point-based RUSLE soil loss rates with Cs-137-based soil loss rates measured at 74 Cs-137 Sam pling 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 po ints in the sample grid using ordinary point kriging. Hillslopes were classified into geometric and geomorphic components. The kriged mean n et soil movement rate for the 27-yr period was -3.3 kg m(-2) yr(-1). D oubly convex landscape positions have experienced the most severe eros ion, apparently due to tillage erosion. The measured Cs-137 and transe ct-based RUSLE median soil loss rates were both significantly higher t han the point-based RUSLE median; however, no significant difference e xisted between the transect-based RUSLE and measured Cs-137 median soi l loss rates (a = 0.05). Meaningful comparisons between Cs-137 and RUS LE soil loss rates can only be made if a tillage movement rate, histor y of crop management, and the accuracy of RUSLE relationships and oper ating files are known.