Pasture management effects on nonpoint source pollution of Midwestern watersheds

Grazing management practices that allow cattle to congregate near pasture streams may result in the loss of vegetative cover and accumulation of manure near the streams. These conditions may cause loading of the streams with sediment, phosphorus, and pathogens carried in precipitation runoff. Furthermore, the loss of vegetation and increased compaction associated with concentrated cattle traffic may promote stream bank erosion causing further impairment of stream water quality. Lake Rathbun Watershed Forage •Annual stocking rates on the 13 sites averaged: •123 (range 0-290) cow-days/acre •3.66 (range 0-10.2) cow-days/foot of stream •Mean sward height (10.7 cm), bare ground (13.8%) and manure-covered ground (0.61%) differed between the 13 pastures. •Proportion of bare soil along stream banks was only mildly related to the annual stocking rate per acre (Y=4.55+0.150X-0.0004X2; r2=0.20). •The proportion of manure-covered ground increased: •as the annual stocking rate per acre increased (Y=-0.038+0.0077X-0.00001X2; r2=0.47) •as the proportion of tall fescue in pastures increased (Y= 0.22 + 0.008X; r2 = 0.24) •To maintain 4 inches of forage on stream banks, the annual stocking rate should not exceed 88 cowdays/acre in the area adjacent to a stream. Cattle Distribution •Across all farms cattle were in or within 50 or 100 ft of the stream 1.3, 6.6, and 6.9% of the time, respectively, during the grazing season. •At greater black globe temperatures the proportion of time cattle were within 50 feet of the stream increased (Y = 11.81 + 0.436X + 0.0056X2, r2 = 0.37) MATERIALS & METHODS Rhodes Research Farm Pastures •Six 30-acre cool-season grass pastures •Each bisected by a 642 foot stream segment •Three grazing management treatments •Continuous stocking with unrestricted stream access (CSU) •Continuous stocking with stream access restricted to a 16-foot wide crushed rock crossing (CSR) •Five-paddock rotational stocking with one paddock in the riparian zone (RS) •15 fall-calving Angus cows per pasture •Grazing mid-May through mid-October in 2005, 2006, and 2007 Data collection Cattle Distribution •Visual Observation •Monthly May through September •Two consecutive days per month, 12 hours per day (0600 to 1800 hours) •Cow herd location, number of cows, and observed defecations recorded at 10 minute intervals •GPS collars (AgTraXtm BlueSky Telemetry, Aberfeldy, Scotland) •One cow per pasture •Month May through September •Two weeks per month, Cow position recorded at 10 minute intervals 24 hours per day •Data Analysis •Location data analyzed using ArcGIS 9.1 •Cow location defined as within stream (stream), within 110 ft of the stream, 110 to 220 ft from the stream, and greater than 220 ft from the stream.