|Bonta, James - Jim|
Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/27/2003
Publication Date: 7/1/2004
Citation: Owens, L.B., Bonta, J.V. 2004. Reduction of nitrate leaching with haying or grazing and omission of nitrogen fertilizer. Journal of Environmental Quality. 33(4):1230-1237. Interpretive Summary: Nitrate-N concentrations in excess of maximum contaminant levels (MCLs) can be found in groundwater under pastures that receive high N inputs. There are management options that will allow the NO3-N concentrations in groundwater to be reduced to acceptable levels. Two options include rotational grazing and forage being removed as hay. For these two practices to be effective, there should be little or no N inputs so that the N in the system can be reduced. Thus, N available for leaching will be reduced. This is still a multi-year process, 5 years in this study, and it recognizes that there are pathways of N loss besides leaching. Nitrogen is lost via N20 emissions, NH3 volatilization, and denitrification in grazing systems and in hay when it is removed. Even though the high NO3-N concentrations resulted from a grazing system, one with high N inputs, grazing is still an option to reduce this detrimental environmental impact. In other words, a livestock producer would not need to stop grazing an area in order to reduce the NO3-N leaching from a high fertility grazing system. But it must become a system with very limited N inputs. This information will be useful to livestock producers and agricultural advisors, e.g., the Natural Resources Conservation Service and university extension personnel.
Technical Abstract: In some high fertility, high stocking density grazing systems, nitrate (NO3) leaching can be great, and groundwater NO3-N concentrations can exceed maximum contaminant levels (MCLs). To reduce high N leaching losses and concentrations, alternative management practices need to be utilized. This research compares two management practices in terms of reducing NO3-N concentrations in groundwater following a rotational grazing management from which groundwater NO3-N concentrations exceeded water quality standards. Using four small watersheds (each approximately 1 ha), rotational grazing of a grass forage without N fertilizer being applied and grass forage without N fertilizer removed as hay were the alternative management practices used. Groundwater was sampled at spring developments, which drained the watershed areas, over a 7 year period. Peak groundwater NO3-N concentrations prior to the 7-yr study period ranged from 13 to 25.5 mg L-1. Groundwater NO3-N concentrations progressively decreased under each watershed and both management practices. Following 5 years of the alternative management practices, groundwater NO3-N concentrations ranged from 2.1 to 3.9 mg L-1. Both grazing and haying, without N fertilizer being applied to the forage, were similarly effective in reducing the NO3-N levels in groundwater. This research shows two management practices that can be effective in reducing high NO3-N concentrations resulting from high fertility, high stocking density grazing systems, including still maintaining a grazing option.