Water Quality Improvements On Grazed Pasture Watersheds as Influenced by Agroforestry and Grass Buffer.

Agroforestry and grass buffers are believed to reduce non point source pollution from agricultural watersheds.  Agroforestry practice recently received increased attention in the temperate zone due to its environmental and economic benefits.  The objective of this study is to compare agroforestry and grass buffer effects on runoff, sediment, and nutrient losses from grazed pasture watersheds.  Six small watersheds located at the Horticulture and Agroforestry Research Center in Missouri were used for the study.  Treatments include: two with agroforestry buffers, two with grass buffers, and two control watersheds.  Vegetation in grass buffer and pasture areas include red clover (Trifolium pretense L.) and lespedeza (Kummerowia stipulacea Maxim.) planted into fescue (Festuca arundinacea Schreb.).  Eastern cottonwood trees (Populus deltoids  Bortr. ex Marsh.) were planted into fescue in agroforestry buffers.  Watersheds were instrumented with water samplers, flow meters and H-flumes in 2001 to collect runoff.  Soils at the site are mostly Menfro silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalfs).  Composite water samples were analyzed for sediment, total nitrogen, and total phosphorus after each runoff event to compare treatment differences.  Watersheds with agroforerstry and grass buffers significantly reduced runoff volumes as compared to the control watersheds.  The loss of sediment, total phosphorus, and total nitrogen were smaller for the buffer watersheds.  The results of the study suggest that establishment of grass and agroforestry buffers help reduce non point source pollution from grazed pasture watersheds.  It is anticipated as trees grow and roots occupy more soil volume, the reduction in N and P in runoff should increase on the agroforestry watershed.