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Title: Runoff water quality from manured riparian grasslands with contrasting soil drainage and simulated grazing pressure

Author
item BUTLER, D - NCSU/UGA
item RANELLS, N - NCSU
item Franklin, Dorcas
item POORE, M - NCSU
item GREEN, JR, J - NCSU

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2008
Publication Date: 4/3/2008
Citation: Butler, D.M., Ranells, N.N., Franklin, D.H., Poore, M.H., Green, Jr, J.T. 2008. Runoff water quality from manured riparian grasslands with contrasting soil drainage and simulated grazing pressure. Agriculture Ecosystems and the Environment. 126(3-4):250-260.

Interpretive Summary: Globally, management of grazed streamside grasslands is of critical importance in terms of agricultural sustainability and environmental quality. However, the potential impacts of streamside grazing management on water quality are not well documented, particularly in the southeastern USA. Scientists from North Carolina State University and the USDA-ARS J. Phil Campbell Sr., Natural Resource Conservation Center quantified nitrogen and phosphorus (nutrient) losses from poorly-drained and well-drained streamside grasslands with heavy or light grazing by cattle. Volume of water in overland flow was generally greater from heavy grazing than from light grazing for both soil drainage types. Greater volume of overland flow was also observed from poorly-drained soils compared to well-drained soils for both light and heavy grazing. Rather low levels of sediment were lost from light grazing on both soils (10% that of heavy grazing). Total phosphorus loss was 4-fold greater from heavy grazing compared to light grazing on both soils. While loss of nitrate-nitrogen was unaffected by grazing and soil drainage, mean ammonium-nitrogen and total nitrogen losses from poorly-drained heavy grazing were more than 5-fold that observed from well-drained lightly grazed grasslands. Results indicate that heavy livestock grazing in streamside grasslands may cause large losses of sediments and nutrients, especially on poorly-drained soils. However, when high levels of cover are maintained on well-drained soils, sediment and nutrient losses may be of minimal environmental concern. With nearly 4 million acres of grazing lands in the Southern Piedmont, results reported here have a potential to be widely applicable to grazing management in the region. Results of this study will be most useful for resource management professionals such as the USDA-NRCS in the design of best management practices, as well as for farmers who wish to utilize streamside vegetation without causing environmental harm.

Technical Abstract: Globally, management of grazed riparian areas is of critical importance in terms of agricultural sustainability and environmental quality. However, the potential impacts of riparian grazing management on water quality are not well documented, particularly in the southeastern USA. The objective of this work was to determine sediment and nutrient export under simulated rainfall from poorly-drained and well-drained riparian soils where heavy or light grazing pressure by cattle was simulated. Plots were established on stands of existing vegetation to create grazing pressure treatments of a) light use (full ground cover, uncompacted), and with stands modified to establish b) heavy use (bare ground, compacted) treatments. Vegetation on poorly-drained soils consisted of several typical wetland species in the southeastern USA, whereas mixed tall fescue (Festuca arundinacea Schreb.) - dallisgrass (Paspalum dilatatum Poir.) stands dominated well-drained soils. Runoff volume was generally greater from heavy use than from light use for poorly-drained soils and for well-drained soils. Greater runoff volume was also observed from poorly-drained soils compared to well-drained soils for both light use and for heavy use treatments. Light use plots were remarkably effective at minimizing export of total suspended solids (TSS) (<30 kg ha-1) on both soils. Mean total Kjeldahl P (TKP) export was 4-fold greater from heavy use plots on both soils. While export of nitrate-nitrogen (NO3-N) was unaffected by grazing pressure and soil drainage, mean ammonium-nitrogen (NH4-N) and total N (TN) export from poorly-drained heavy use plots was more than 5-fold that from well-drained light use plots. Results indicate that livestock heavy use areas in the riparian zone may export substantial TSS and nutrients, especially on poorly-drained soils. However, when high levels of cover are maintained on well-drained soils, TSS and nutrient losses may be limited.