Tuesday, November 6, 2007 - 9:45 AM
144-2

Effect of Cattle Grazing Management on Runoff Water Quality.

Alan DeRamus1, Changyoon Joeng2, Terry Clement2, Lora Goodeaux2, and Calvin Berry3. (1) Dep. of Agricultural and Environmental Sciences, University of Louisiana-Lafayette, P.O.Box 44650, Lafayette, LA 70504, (2) Agricultural and Environmental Sciences, University of Louisiana-Lafayette, P.O.Box 44650, Lafayette, LA 70504, (3) University of Louisiana-Lafayette, Dep. of Mathematics, Lafayette, LA 70504

Two-0.8 ha plots for two grazing management treatments were established on Memphis silt loam soil to determine differences in runoff water quality. Conventional stocking (CS) and management intensive grazing (MIG) were used as treatments. Twenty 0.04-ha grazing paddocks were established with power fencing, allowing daily cattle rotation in MIG paddocks. Beef heifers (Bos tarus) grazed each plot as needed to maintain approximately 1500 Kg ha-1 of available forage dry matter (DM). Bermudagrass (Cynodon dactylon)(L.)Pers was grazed during the warm season, and ryegrass (Lolium multiflorum Lam.) was overseeded on the bermudagrass sod during October for winter and early spring grazing. Nitrogen was the only fertilizer used in this study. Forage production was measured monthly, and animal numbers were adjusted by “put and take” to maximize utilization of available forage DM. The total forage production reflected the improved management with an annual average of 19,275 Kg ha-1 DM for MIG and 16,513 Kg ha-1 DM for CS, a 14% advantage for MIG. Amount of rainfall, flow rate, and total runoff for each rain event were monitored and recorded for each plot with ISCO refrigerated samplers. Lab analyses conducted on water samples included: TSS, TCS, BOD, total nitrogen, ammonia (NH4), nitrate/nitrite (NO3/NO2), total phosphorous, reactive phosphorus (PO4), and fecal coliform. Water samples (230) were collected during 42 rainfall events from May 2001 through March 2004. Less total N and less total P were observed in the runoff (P<0.05) of MIG vs. CS plots. The MIG plots produced 21% less total runoff than from the CS plots. The water quality parameters of NO3/NO2, NH4, PO4, BOD, fecal coliform or sediments (TSS and TCS) revealed no significant differences (P>0.10) between treatments of MIG and CS. Observations and trends of improved productivity of animals, pastures, and general environmental conditions tend to support the practices of MIG as a Best Management Practice.