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The Effect of Cattle Grazing on Nutrient Losses in a Pacific Northwest Setting¹

ABSTRACT

Nutrient deliveries in runoff from a cattle-grazed and a nongrazed (check) watershed were measured for 3 years in the Pacific Northwest to determine nutrient contributions from each. Few runoff events occurred when animals were grazing during the 3-year study, since this is a winter-precipitation-summer-grazing area.

Total nitogen (TN) losses in runoff from the grazed watershed for water years 1977, 1978, and 1979 ranged from < 1 to 4 kg ha^–1 year^–1. During the same period TN losses from the check area were < 0.5 kg ha^–1. Generally, TN received in precipitation was equal to or greater than N lost in runoff from the grazed watershed. Nitrate-N levels in the runoff were normally < 1 mg L^–1. Total phosphorus (TP) losses in runoff from the grazed watershed during water years 1977, 1978, and 1979 ranged from 0.1 to 1.3 kg ha^–1 year^–1 and from < 0.1 to 0.17 kg ha^–1 year^–1 from the check area for the same period. Though grazing appeared to cause an increase in TN, TP, total organic carbon (TOC), chemical oxygen demand (COD), and chloride (Cl) losses in runoff, the quantities would not seem to be a significant threat to downstream water.

Key Words: nitrogen • runoff • nutrient delivery • phosphorus • water quality

¹ Contribution of the USDA-ARS in cooperation with the College of Agricultural Research Center, Washington State University, Pullman, WA 99164. Scientific Paper no. 6093. Work partially supported under interagency agreement no. EPA-78-D-X0249 between USDA-ARS and U.S. EPA.

² Graduate Research Assistant, Washington State Univ. (formerly soil scientist, USDA-ARS); Microbiologist and Research Hydrologist, USDA-ARS, Pullman; and Agricultural Engineer, USDA-Bureau of Land Management, Coeur D'Alene, ID 83814 (formerly Agricultural Engineer, Univ. of Idaho); respectively.

Received for publication January 7, 1981.