ARS | Publication request: Grazing management effects on sediment, phosphorus, and pathogen loading of pasture streams

Submitted to: Iowa State University Animal Industry Report
Publication Type: Experiment Station
Publication Acceptance Date: March 1, 2011
Publication Date: March 1, 2011
Citation: Schwarte, K.A., Russell, J.R., Kovar, J.L., Morrical, D.G., Ensley, S.M., Yoon, K., Cornick, N.A., Cho, Y. 2011. Grazing management effects on sediment, phosphorus, and pathogen loading of pasture streams. Iowa State University Animal Industry Report. Report R2614.

Interpretive Summary: To evaluate the effects of cattle grazing management on pollution of pasture streams, six 30-acre cool season grass pastures bisected by a stream were grazed by 15 fall-calving Angus cows and soil, phosphorus (P), and pathogen losses from banks were monitored. Grazing was managed in one of three ways: i.) continuous stocking with full access to the stream; ii) continuous stocking with stream access limited to a stabilized crossing; or iii) rotational stocking. After two years, we found that as the amount of bare soil on stream banks increased, soil and P losses in rainfall runoff also increased. In general, results from the two years of measurements suggested that stream bank erosion and P losses to the stream were controlled by natural processes, rather than grazing management. Contributions from surface runoff and cattle manure were considerably less and could be minimized by grazing management practices that reduced congregation of cattle near pasture streams. Although bovine enterovirus was shed by an average of 24% of cows during the study period, it was collected in only a small percentage of runoff water samples. Fecal pathogens, such as Escherichia (E.) coli O157:H7, were not found in surface runoff. The results of this work will contribute useful information to cattle producers, local environmental groups, and Cooperative Extension and NRCS personnel interested in reducing the negative effects of agricultural production on water quality.

Technical Abstract: Erosion and precipitation runoff from pastures may lead to degradation of surface water. A two-year grazing study was conducted to quantify effects of grazing management on sediment, phosphorus (P), and pathogen loading of streams in cool-season grass pastures. Six adjoining 30-acre pastures bisected by a stream in central Iowa were divided into three treatments: continuous stocking with unrestricted stream access (CSU), continuous stocking with restricted stream access (CSR), or rotational stocking (RS). Rainfall simulations on stream banks resulted in greater (P < 0.10) proportions of applied precipitation and amounts of sediment and P transported in runoff from bare than vegetated sites across grazing treatments and from vegetated sites in CSU and RS pastures than vegetated sites in CSR pastures. Bovine enterovirus was shed by an average of 24.3% of cows during the study period and was collected in the runoff of 8.3 and 16.7% of the simulations on bare sites in CSU pastures in June and October of 2008, respectively, and from 8.3% of the simulations on vegetated sites in CSU pastures in April 2009. Fecal pathogens [Bovine coronavirus (BCV), Bovine rotavirus (group A), and Escherichia coli O157:H7] shed or detected in runoff were almost non-existent, as only BCV was detected in feces of one cow in August of 2008. Erosion of cut-banks was the greatest contributor of sediment and P loading to the stream; contributions from surface runoff and grazing animals were considerably less and minimized by grazing management practices that reduced congregation of cattle by pasture streams.