Simulating the influence of integrated crop-livestock systems on water yield at watershed scale

摘要

Integrated crop-livestock (ICL) systems are being promoted as environmentally favorable alternatives to traditional crop agriculture and livestock production. There are few, if any, evaluation studies of the hydrologic response of watersheds to the implementation of ICL systems. Thus, we applied the Soil and Water Assessment Tool (SWAT) model to simulate the potential impacts of ICL systems on water yield and its hydrological components using a large agricultural dominated watershed. In this study, the integration of grazing operations with cropping systems represented cattle grazing under three typical crop rotations: (i) continuous corn (Zea mays L.; 1-year rotation), (ii) conventional (corn-soybean [Glycine max (L.) Merr.]; 2-year rotation), and (iii) winter cover crops (corn-soybean-oats (Avena sativa L.)/winter barley (Hordeum vulgare L.); 3-year rotation). Modeling results showed a significant reduction in water yield over a long-term period simulation (31 years) when grazing of corn residue or winter barley was scheduled within the rotations. When compared to scenarios without grazing operations, the reduction in water yield was 14.7% under corn-soybean rotation (corn as the forage grazed), 12.5% under continuous corn rotation, 6.4% under corn-soybean-oats/winter barley rotation (corn as the forage grazed), and 3% under corn-soybean-oats/winter barley rotation (winter barley as the forage grazed). Of the three components that constitute water yield (Le., surface runoff, lateral and groundwater flow), only surface runoff was reduced when integrating grazing into the cropping system. Instead, lateral and groundwater flows increased when ICL systems were scheduled in the watershed. Groundwater flow was the hydrological component with the highest relative impact on streamflow. These results indicate that ICL systems can positively affect processes involved in soil water storage and transit. Runoff reduction benefits of ICL systems might be helpful in improving the environmental quality of receiving waterbodies and in reducing flood-risk potential. These systems over the long-term could benefit the watershed's hydrological cycle through increased baseflow. Overall, this study suggests new watershed-scale benefits of ICL systems with important hydrological implications that might be of interest for agricultural watershed planners.