Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: August 1, 1997
Publication Date: N/A
Technical Abstract: The study used 18 0.7-ha paddocks of Coastal bermudagrass on severely eroded soil. Nitrogen (N) was supplied by either NH4NO3, poultry manure, or crimson clover. High (H) grazing pressure was 1000 to 1500 kg/ha and low (L) was >2000 kg/ha with a differential of about 1000 kg/ha between grazing pressures. Grazing pressure was adjusted at 28-d intervals by put-and-take. Three yearling Angus steers were randomly assigned as tester steers to each paddock. Steers were weighed at 28-d intervals. Soil measurements included bulk density, aggregate stability, carbon, N, phosphorus, and potassium at various depths. The GRAZE simulation model was used to simulate one year of the NH4NO3 treatment to determine grazing response at intermediate grazing pressures. GRAZE assumed that initial forage amounts and steer weights were identical for all stocking rates. Three intermediate rates were included between L and H. GRAZE calculated 896, 966, 1018, 998, and 818 kg gain/ha from L to H grazing pressure while actual gain/ha for L and H was 412 and 683 kg/ha. Estimated intake was 6515 and 8735 kg/ha as compared to GRAZE calculated intake 6835, 7229, 7585, 7807, and 7681 kg/ha from L to H. GRAZE predicted that the optimum grazing pressure was between grazing pressures used in the study and raises questions of how to interpret soil response measurements between the grazing pressures used.