Runoff reduced, water retention increased by multi-paddock grazing

Writer: Kay Ledbetter, 806-677-5608, [email protected]
Contact: Dr. Srinivasulu Ale, 940-552-9941, [email protected]
Dr. Richard Teague, 940-552-9941, [email protected]

VERNON – Adaptive multi-paddock grazing has been found to be an effective conservation practice on grazing lands for enhancing water conservation and protecting water quality, according to a Texas A&M AgriLife Research study at Vernon.

The research results were summarized in the article “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,” published recently in the Agriculture, Ecosystems and Environment journal The full journal article can be found at http://bit.ly/2mCiqdl.

Conducting the AgriLife Research study funded by the Dixon Water Foundation were Dr. Srinivasulu Ale, a geospatial hydrology associate professor; Dr. Richard Teague, rangeland ecology and management scientist, both in Vernon; Dr. Jaehak Jeong, associate professor at Temple; and Dr. Jong-Yoon Park, a postdoctoral researcher at Vernon who is now with the Korea Environment Institute.

The Agricultural Policy/Environmental Extender, or APEX, model was used to evaluate the influence of continuous and multi-paddock, grazing practices on runoff, sediment and nutrient losses at both the ranch- and watershed-scales, Ale said.

“We found grazing management practices do have a significant influence on ecosystem services provided by rangelands,” he said. “Not only did the multi-paddock grazing practice provide several hydrological benefits such as increased soil infiltration, increased water conservation and decreased surface runoff, but also environmental benefits such as water quality improvement.”

Teague said this study was designed to help producers by assessing the hydrologic and water quality impacts of traditional and alternate grazing management practices and identifying best management practices for long-term sustainability of rangelands.

The study quantified runoff, sediment and nutrient losses under traditional continuous and adaptive multi-paddock grazing management practices in the rangeland-dominated Clear Creek Watershed in North Texas, he said.

The APEX model was initially evaluated at the ranch-scale using observed herbaceous plant biomass and daily soil moisture data at four study ranches – two under multi-paddock grazing and one each under light continuous and heavy continuous grazing practices – and the model output was consistent with field data, Teague said.

The model was further evaluated using monthly streamflow, sediment, total nitrogen and total phosphorus data measured at the watershed outlet, Ale said. 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 multi-paddock to heavy continuous grazing at one of the study ranches, he said the simulated average annual surface runoff, sediment, total nitrogen and total phosphorus losses from 1980-2013 increased by 148 percent, 142 percent, 144 percent and 158 percent, respectively.

“Most importantly, interannual variability in the simulated runoff, and sediment and nutrient losses, increased substantially when grazing management was switched from baseline multi-paddock to heavy continuous grazing,” Ale said. “Also, the increases in sediment and nutrient losses under heavy continuous grazing were found to be mainly due to the increase in surface runoff.”

He said at the watershed-scale, changing grazing management from the commonly adopted heavy continuous to multi-paddock reduced the average annual surface runoff, sediment, total nitrogen and total phosphorus loads at the watershed outlet by 39 percent, 34 percent, 33 percent and 31 percent, respectively.

“Changes to grazing management practices had a much larger impact on surface runoff and subsurface flow than any other hydrologic component,” Ale said. “The average annual subsurface flow increased by 48 percent, followed by a 40 percent reduction in surface runoff under the multi-paddock grazing when compared to the heavy continuous grazing. This was mainly because of increased infiltration and soil water storage under multi-paddock grazing.”

In addition, multi-paddock grazing reduced streamflow during the high flow conditions by about 20 percent, thus reducing the chances of flooding downstream of the watershed, Ale said.

“Overall, results from this long-term simulation study indicated multi-paddock grazing provides many benefits in terms of soil and water conservation, nutrient retention and the potential to reduce flood risk in the downstream areas,” he said.