Evaluating the ranch and watershed scale impacts of using traditional and adaptive multi-paddock grazing on runoff, sediment and nutrient losses in North Texas, USA

Abstract

Grazing management practices have a significant influence on ecosystem services provided by rangelands. An assessment of hydrologic and water quality impacts of traditional and alternate grazing management practices facilitates adoption of best management practices for long-term sustainability of rangelands. A study was conducted to quantify the runoff, sediment and nutrient losses under traditional continuous and adaptive multi-paddock (MP) grazing management practices in the rangeland-dominated (71% rangeland) Clear Creek Watershed (CCW) in north Texas in the United States using the Agricultural Policy/Environmental Extender (APEX) model. The model was calibrated and validated using observed herbaceous plant biomass and daily soil moisture data at four study ranches in the CCW [two under MP grazing and one each under light continuous (LC) and heavy continuous (HC) grazing practices], and using monthly streamflow, sediment, total nitrogen (TN) and total phosphorus (TP) data measured at the watershed outlet. Both ranch- and watershed-scale results indicated a strong influence of the grazing practice on runoff and water quality. When the grazing management was changed from the baseline MP to HC at one of the study ranches, the simulated average (1980–2013) annual surface runoff, sediment, TN and TP losses increased by 148%, 142%, 144% and 158%, respectively. At the watershed-scale, changing grazing management from the baseline HC to adaptive MP reduced the average annual surface runoff, sediment, TN and TP loads at the watershed outlet by 39%, 34%, 33% and 31%, respectively. In addition, implementation of adaptive MP grazing reduced streamflow during the high flow conditions that have ≤10% exceedance probability, by about 20%, and hence reduced the chances of flooding downstream of the watershed. Adaptive MP grazing was therefore found to be an effective conservation practice on grazing lands for enhancing water conservation and protecting water quality.