Modeling the impacts of agricultural management strategies on crop yields and sediment yields using APEX in Guizhou Plateau, southwest China

Abstract The Guizhou Plateau, located in southwest (SW) China, is largely underlain by carbonate rocks and occupied by karst landscapes. Even though erosion rates are comparatively low, soil loss is still a serious land degradation problem on this plateau because soils are generally thin. Grain productivity is relatively low. Amounts of fertilizers applied, quantity of irrigation water supplied and tillage methods have changed for corn, rice and wheat at the Shaying Watershed on the Plateau during 1960–2010. So the APEX model was used to simulate grain yields of the three crops and sediment yields from the three crop-fields for the 50 years. The purpose of this study was to evaluate the impacts of these management strategies on crop productivity and soil erosion in the Watershed and thus applicability of APEX in this watershed and other similar watersheds on the Plateau. Results of 40 field experiments designed for different agricultural management strategies were selected for model calibration and validation. The calibrated model was able to replicate the annual crop yields with Relative Root Mean-Squared Error (RRMSE) ≥0.93 and Nash-Sutclifte efficiencies ≥0.48. The simulated grain yields have generally increased and sediment yields have decreased with increases of the amounts of fertilizers applied and quantities of irrigation water supplied and implementation of no-tillage during the 50 years. The simulated sediment yields have displayed similar changes in erosion to those revealed by a record of two reservoir-sediment cores within 1960–1970, 1970–1980 and 1980–1990 but different ones from those within 1990–2000. The results of this study suggest that the changes in agricultural management strategies have somehow altered grain yields and sediment yields in the Watershed and APEX is applicable in examining the impacts of different management schemes in this and other similar watersheds on the Plateau.