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Title: GRAZING IMPACTS ON NITRATE LEACHING FROM FERTILIZED GRASSLANDS

Author
item Owens, Lloyd
item Shipitalo, Martin
item Bonta, James - Jim

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/10/2005
Publication Date: 10/19/2005
Citation: Owens, L.B., Shipitalo, M.J., Bonta, J.V. 2005. Grazing impacts on nitrate leaching from fertilized grasslands [abstract]. ASA-CSSA-SSSA Annual Meeting, November 6-10, 2005, Salt Lake City, Utah. CD-ROM Agronomy Abstracts.

Interpretive Summary:

Technical Abstract: Some recent lysimeter studies indicate that intensive grazing has the potential to substantially increase nutrient leaching compared to ungrazed grassland. Our objective was to do a field-scale assessment of the impact of grazing on nitrate leaching from grasslands, the major pathway of N transport by water from pasture. Two small watersheds (< 1 ha) with underlying clay layers in a 13.8 ha area at the North Appalachian Experimental Watershed near Coshocton, OH were used. A spring development in each of the watersheds was sampled weekly to measure the impacts of surface management on the quality of water moving to groundwater. These orchardgrass (Dactylis glomerata L.) pastures received 224 kg N/ha as NH4NO3 annually for 5 years and were rotationally grazed by a spring calving beef cow-calf herd. During this period, NO3-N concentrations in groundwater increased to near or above 10 mg N L-1. Then alfalfa (Meticago sativa L.) was seeded into the orchardgrass and N fertilizer was no longer applied. With grazing on this grass-legume mixture and no N fertilizer, NO3-N concentrations decreased sharply at first and then gradually to below 2 mg L-1. After 18 years of no N fertilizer applications, the orchardgrass stand was reestablished; cattle were removed; 224 kg N/ha as NH4NO3 was applied annually; forage was removed as hay. Nitrate-N concentrations remained low when N fertilizer was applied to grass with haying instead of grazing. After 4 years, rotational grazing was resumed. Although NO3-N concentration changes in water at the spring developments are slowly occurring, water collected at monitoring wells in these watersheds are showing increased NO3-N concentrations. This watershed study indicates the potential for greater N leaching under a grazed management than an ungrazed practice, e.g. haying, with moderate to high N fertilizer additions.