Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2009
Publication Date: 2/17/2010
Citation: Webber, D.F., Mickelson, S.K., Ahmed, S.I., Russell, J.R., Powers, W.J., Schultz, R.C., Kovar, J.L. 2010. Livestock Grazing and Vegetative Filter Strip Buffer Effects on Runoff Sediment, Nitrate, and Phosphorus Losses. Journal of Soil and Water Conservation. 65:34-41. Interpretive Summary: The amounts of sediment and nutrients, such as phosphorus (P), in surface runoff from agricultural lands are of concern because of the potential for siltation and eutrophication of waterways. At this time, there is limited information on total sediment, nitrogen (N), and P losses in runoff from pasture land in the Midwest. Because aboveground biomass limits soil disruption caused by the impact of raindrops and roots hold soil particles, forages harvested at an appropriate height through suitable grazing management should promote water infiltration and minimize sediment and nutrient losses in runoff water from pastures. In this three-year central Iowa study, we measured the amounts of sediment, nitrate, soluble P, and total P in runoff water from pastures managed three different ways. Data were collected from 12 natural rainfall events during 2001 to 2003. We found that forage management did not affect the amounts of sediment and P lost in runoff water. The amount of nitrate lost was greatest from the ungrazed paddocks in 2003. These results and other research findings suggest that the relatively higher amount of rain and subsequent runoff in 2003, as well as forage nutrient cycling processes, may have contributed to the elevated nitrate losses in the ungrazed areas. Results also suggest warm-season grasses, such as switchgrass, could be incorporated into certain paddock areas in a rotational grazing management program to improve grazing efficiency and reduce nutrient losses. The results of this research will provide useful information to cattle producers, local environmental groups, and Cooperative Extension and NRCS personnel.
Technical Abstract: This research quantifies the effects of grazing management practices and vegetated filter strip (VFS) buffers on losses of runoff (RO) with total solids (TS), nitrate-nitrogen (NO3-N), ortho-phosphorus (PO4-P), and total-phosphorus (TP) during natural rainfall events. Runoff data were collected from 12 events during 2001-2003 at an Iowa State University research farm in central Iowa, USA. Three grazing management practices (5.1-cm [2-in.] continuous grazing [con], 5.1-cm [2-in.] rotational grazing [rot], and no grazing [ng] control) and three VFS buffers (paddock area:buffer area ratios of 5:1, 10:1, and no buffer [NB] control) comprised nine treatment combinations. The nine treatments were replicated in three 2.75 ha (6.8 ac) plot areas for a total of 27 runoff collection units in a randomized complete block design. The plot areas were on uneven terrain with up to 15 percent slopes and consisted of approximately 100 percent smooth brome (Bromus inermis Leyss.). Average paddock and VFS buffer plant tiller densities were approximately 62M and 93M tillers/ha, respectively. Results from 2001 and 2002 show no significant differences (p < 0.10) in average losses of RO, TS, NO3-N, PO4-P, and TP among the nine treatment combinations. The 2003 results also show no significant differences (p < 0.10) in losses of RO, TS, PO4-P, and TP. However, the 2003 results indicate significantly higher (p < 0.01) losses of NO3-N from "10:1ng" treatments compared to all other treatment combinations and reflect a possible tendency towards elevated losses in some "ng" treatments from "con" treatments in 2001 and 2002. Runoff analysis results indicate grazing management practices did not significantly affect runoff losses (p < 0.10). These results and other research findings suggest the relatively higher 2003 event precipitation, antecedent moisture, concentrated surface flow conditions, dense cool-season smooth brome, and forage nutrient cycling processes may have contributed to the potential shift of elevated losses to the non-grazed "ng" treatments. Results also suggest warm-season grasses like switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii L.) could be incorporated into certain paddock areas in a rotational grazing management program to improve grazing efficiency and reduce RO and contaminant losses.