Impact of sheep bedding on soil nutrient dynamics in the Centennial Mountains of Montana and Idaho

Authors: Leytem, April; Seefeldt, Steven

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2008
Publication Date: 8/1/2008
Citation: Leytem, A.B., Seefeldt, S.S. 2008. Impact of sheep bedding on soil nutrient dynamics in the Centennial Mountains of Montana and Idaho. Soil Science. 173(8):503-510.

Interpretive Summary: The production of sheep is an important industry in the State of Idaho. The management of sheep grazinglands is important from an ecological and production standpoint. One practice that has been an issue of concern with grazingland managers is the use of sheep bedding areas and the impact they have on rangeland ecology. Sheep are concentrated in bedding areas at night to guard them from theft and predation which leads to concentrated grazing and manure and urine accumulation in the bedding areas. This heavy utilization of these areas has the potential to alter the soil nutrients over time which can also potentially influence the vegetative communities in the bedding areas. To address the effects of sheep bedding areas on soil nutrient status we monitored the nutrient status of soils from within and outside of sixteen bedding areas in the Centennial Mountains of Montana and Idaho, with a general survey performed in 2004 followed by more intense monitoring of six sites from 2005 to 2006. In the 2004 survey, soils were analyzed for total nutrients (carbon, nitrogen, phosphorus) as well as soluble nutrients (nitrate, ammonium, phosphorus). Over the period 2005-2006, six sites were monitored over time (before bedding, immediately after bedding, after winter) and the soluble nutrients (nitrate, ammonium, phosphorus) were tracked. The sixteen sites evaluated in the 2004 survey demonstrated that there was a significantly greater amount of total nitrogen, carbon, and organic carbon in non-bedding areas compared to the bedding sites. This was attributed to the removal of organic materials from these areas, which was greater than the nutrients returned by animal deposition. Soluble phosphorus and ammonium was significantly greater in the bedding areas, presumably due to the deposition of soluble nutrients by the sheep in the form of urine and manure. While concentrations of soluble nitrate were higher in bedding areas, these differences were not significant. When six sites were monitored over time there was no significant effect of bedding on soluble phosphorus concentrations over time or between bedding and control areas. There were significant changes in soluble nitrogen over time, depending on the sampling time bedding areas were either higher or lower than the non-bedding areas. Immediately after bedding, soluble N increased significantly in the bedding areas and then decreased again following winter. Although these results are preliminary, it appears as if sheep bedding can alter the nutrient content of soils both increasing some measures of soil nutrients, while decreasing others, which ultimately can affect the productivity and plant species diversity in these areas.

Technical Abstract: Sheep and lamb production is an important industry in the state of Idaho, with sheep grazing in the mountains during summer months a common practice. Sheep are concentrated in bedding areas at night to guard them from theft and predation which leads to concentrated grazing and manure and urine accumulation in the bedding areas. The effects of heavy grazing along with manure and urine accumulation have the potential to alter soil nutrient status over time which can ultimately alter the vegetative communities in these bedding areas. To address the effects of sheep bedding areas on soil nutrient status we monitored the nutrient status of soils from within and outside of sixteen bedding areas in the Centennial Mountains of Montana and Idaho, with a general survey performed in 2004 followed by more intense monitoring of six sites from 2005 to 2006. In 2004, soils were analyzed for total C and N, organic C, total P, Olsen P, water soluble P, soluble nitrate, and soluble ammonium. Over the period 2005-2006, soils were analyzed for soluble nutrients including Olsen P, water soluble P, soluble nitrate and soluble ammonium. The sixteen sites evaluated in 2004, showed significant differences in total N, C and organic C, with the control sites having greater concentrations. The Olsen P, WSP, and ammonium were also significantly different on the sixteen sites, with the bedding areas having greater concentrations than control areas. When six sites were monitored over time there was no significant effect of bedding on soluble P concentrations over time or between bedding and control areas, while there was a significant effect of time on soluble N concentrations but no significant differences between bedding and control areas. In general soluble N increased following bedding and then decreased again during the subsequent spring. Although these results are preliminary, it appears as if sheep bedding can alter the nutrient content of soils both increasing some measures of soil nutrients, while decreasing others, which ultimately can affect the productivity and plant species diversity in these areas.