Improving USLE / RUSLE Estimations Using Runoff Plots Data to Consider the Effect of Soil Water Content
Long-term experimental data were obtained in three Argiudolls in runoff plots under natural rainfall in Uruguay: 1) Aguas Blancas, 1982-1986, five different Soil Management Systems (SMS), 89 erosive storms, 2) La Estanzuela, 1984-1989, six SMS, 144 erosive storms, and 3) Palo a Pique, 1994-1999, six SMS, 137 erosive storms; in all sites, it was completed one cycle of the longest rotation. The linear regression between annual soil erosion estimated with USLE/RUSLE and the experi-mental one was: EroEst = 0.958EroExp + 1.485, r2 = 0.96, close to 1:1.The highest erosion occurred in the permanently bare and tilled soil SMS, around 40, 50 and 90 Mg.ha-1.yr-1, respectively, when in the other SMS it was below 20 Mg.ha-1.yr-1. Bare soil water content was always close to field capacity due to the extremely low evaporation after the upper few cm of soil are dry. Not considering these three situations, the regression of the remaining 14 SMS situations having full evapotranspiration was EroEst = 1.447EroExp + 0.709, r2= 0.89, different of 1:1 relation, showing increasing overestimation with the magnitude of soil erosion: if estimation was 4 Mg.ha-1, the experimental value was 3.25 (23 % overestimation), if estimation was 8 Mg.ha-1, the experimental value was 6.02 (33 % overestimation). The model overestimation not considering soil water content variation is relevant around 7 Mg.ha-1, the most frequent tolerance value for Argiudolls; it is proposed to correct it using the regression obtained in the present work.