Type and Frequency of Excreta Application to Bahiagrass Swards Affects Herbage Yield and Nutritive Value.
Renee White1, Lynn Sollenberger2, Kenneth Woodard1, Don Graetz1, Yoana Newman1, Joao Vendramini1, and Sindy Interrante1. (1) University of Florida, P.O. Box 110500, Gainesville, FL 32611, (2) PO Box 110300, University of Florida, Agronomy Dept., 2185 McCarty Hall, Gainesville, FL 32611-0300
Most nutrients consumed by grazing livestock are returned to pasture in excreta, but excreta effects on forage responses are not well quantified. The objective was to determine the effect of excreta type and number of applications on bahiagrass herbage accumulation (HA) and nutritive value. Treatments were the factorial combinations of excreta type (dung and urine) and application frequency (1, 2, or 3/season). Dung and urine were collected from animals grazing bahiagrass and applied to ungrazed bahiagrass plots. A urine application was 2 L to a 60-cm diameter circle, while 2 kg of dung was applied to a 30-cm diameter circle. Concentric circles (radii of 0-15, 15-30, and 30-45 cm) to a distance of 0.45 m from center of excreta application were clipped monthly to measure forage response. Number of dung applications had no effect on HA (avg. 2820 kg/ha), but HA increased linearly (3910 to 4670 kg/ha) as urine applications increased from 1 to 3. Herbage N (1.36 to 1.61 g/100 g; linear and quadratic) and P concentrations (0.27 to 0.40 g/100 g; linear) increased as urine applications increased from 1 to 3, but number of dung applications had no effect. Percent recovery of N in excreta averaged 22% for urine and 2% for dung and decreased linearly (16 to 10%) as number of applications increased. Spatially, HA decreased linearly with distance from center of urine application (5330, 4850, and 3680 kg/ha for the three circles). The response was quadratic for dung (2330, 3060, and 2770 kg/ha), with lowest HA attributable to physical interference at the application site. Urine had much greater impact on grass growth than dung, likely due to greater nutrient availability and less physical interference. Greater N recovery with fewer excreta events per site emphasizes the value of management practices that increase uniformity of excreta deposition.