Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2011
Publication Date: 11/16/2011
Citation: Owens, L.B., Barker, D.J., Loerch, S.C., Shipitalo, M.J., Bonta, J.V., Sulc, R.M. 2011. Inputs and losses by surface runoff and subsurface leaching for pastures managed by continuous or rotational stocking. Journal of Environmental Quality. 41(1):106-113. Interpretive Summary: Grazing management can affect forage quality and production, animal health and production, and reduce soil loss. Grazing management practices can also impact the quality and quantity of surface runoff and subsurface flow – positively and negatively, in some situations. In a multi-year study at the North Appalachian Experimental Watershed near Coshocton, OH, continuous stocking and frequent rotational (5 to 6 times per week) stocking systems were studied for their effects on NO3-N leaching into groundwater. Nitrogen fertilizer was applied twice each year for an annual total of 100 lbs N per acre. This is the same rate that was applied for 5 years prior to this study when the pastures were in a weekly rotational stocking system. Surface runoff, measured from small watersheds in the pastures, was minimal. Subsurface water was collected from developed springs within the grazing areas. Because precipitation was much above the long-term average for some years during the study, subsurface flow and NO3-N leaching were increased. Variations in flow and subsurface transport of N were greater among seasons than among stocking systems. Flow-weighted seasonal NO3-N concentrations did not exceed 7 ppm, which is below the maximum drinking water standard of 10 ppm. Variations in the amount of N leached from pastures were primarily due to variable precipitation rather than impacts of continuous, weekly rotational, or frequent rotational stocking practices. This suggests that there was no difference among these grazing practices in terms of nitrate leaching. This information is useful to grazing specialists and scientists as well as livestock producers.
Technical Abstract: Pasture management practices can affect forage quality and production, and animal health and production as well as impacting surface and ground water quality. In a 5-yr study, conducted at the North Appalachian Experimental Watershed near Coshocton, Ohio, we compared the effects of two contrasting grazing methods on surface and subsurface water quantity and quality. Four pastures, each including a small, instrumented watershed (0.51 to 1.09 ha) for surface runoff measurements and a developed spring for subsurface flow collection, received 112 kg N ha-1 yr-1 and were grazed at similar stocking rates (1.8 to 1.9 cows ha-1). Two pastures were continuously stocked; two were subdivided so that they were grazed with frequent rotational stocking (5-6 times weekly). In the 5 years preceding the study, these pastures received 112 kg N ha-1 following several years of 0 N fertilizer and were grazed with weekly rotational stocking. Surface runoff losses of N were minimal. During these two periods, some years had precipitation up to 50% greater than the long-term average which increased subsurface flow and NO3-N transport. Average annual NO3-N transported in subsurface flow from the 4 watersheds during the two 5-yr periods ranged from 11.3 to 22.7 kg N ha-1, which was similar or less than the mineral-N received in precipitation. Flow and transport variations were greater among seasons than among watersheds. Flow-weighted seasonal NO3-N concentrations in subsurface flow did not exceed 7 mg L-1. Variations in NO3-N leached from pastures were primarily due to variable precipitation rather than impacts of continuous, weekly rotational, or frequent rotational stocking practices. This suggests that there was no difference among these grazing practices in terms of nitrate leaching.