Tuesday, November 14, 2006
217-28
Long-Term Effects of Continuous Stocking on Soil P Concentrations in Bermudagrass Pastures.
Maria L. Silveira, F. M. Rouquette, Vincent Haby, and Gerald Smith. TAMU Agricultural Research Center, 1710 N Hwy 3053, PO Box 200, Overton, TX 75684
Continuous deposition of animal wastes and repeated fertilizer application may lead to nutrient build up in grazed pastures and, therefore, increase the potential risks of edge-of-field P losses. Phosphorus losses have been identified as an important contamination source and responsible for serious environmental issues related to water quality. The objective of this study was to evaluate long-term changes in soil P concentrations and distribution in the profile in common and Coastal bermudagrass pastures subjected to different stocking and fertility managements. Bermudagrass stocking was initiated in 1968 and have been continuously stocked from late February to October. Stocking rates were low-, medium-, and high-grazing intensities, and the number of animals per ha was adjusted based on herbage mass and, thus varied among years. Pastures received annual P fertilization (44 kg P ha-1) from 1968 to 1985 and from 1997 to 2004. Because the soil test P levels were considered adequate for forage production, no P fertilizer was applied from 1986 to 1997. Temporal changes in extractable soil P from 1968 to 2004 in bermudagrass pastures were directly related to P fertilizer application regimens. There was no evidence of P build up in soils due to continuous stocking at any stocking rate. When P fertilizer was omitted from the pasture system, extractable soil P concentrations significantly decreased to levels comparable to those in 1985. Our results indicated that when properly managed, bermudagrass pastures grazed at different intensities could be slight exporters of P. At the current production level, bermudagrass pastures continuously stocked for more than 35 years (1969 to 2004) showed no apparent evidence of environmental risks associated with P accumulation in soils. Indeed, P was efficiently recycled through forage-animal-soil system and sustained adequate forage and animal productivity in bermudagrass pastures.
Handout (.pdf format, 107.0 kb)