F. M. Rouquette1, Maria L. Silveira2, Vincent Haby3, and Gerald Smith1. (1) TAMU Ag'l. Res. & Ext. Ctr., PO Box 200, Overton, TX 75684, (2) Texas A&M Agricultural Res. and Ext, "1710 N Hwy 3053, PO Box 200", "1710 N Hwy 3053, PO Box 200", Overton, TX 75684, United States of America, (3) Texas Agricultural Expt. Stn., PO Box 200, Overton, TX 75684-0200, United States of America
Nitrogen is generally the most limiting nutrient for forage production in the Southern US. However, because of the increasing prices of commercial inorganic fertilizer and potential environmental problems associated with N losses, alternative sources of N have become an important management issue for grass-based beef production systems. Symbiotic atmospheric N2 fixation by cool-season legumes represents a reasonable economic and environmental alternative to provide N to the warm-season grass pastures. The objective of this study was to examine the long-term effects of various stocking rates and fertility regimens on soil NO3-N and nutrient cations in common and Coastal bermudagrass pastures. Bermudagrass pastures were initially stocked in 1968, and have been continuously stocked at low-, medium-, and high-grazing intensities. In 1985 bermudagrass pastures at each stocking rate were split into two fertility regimens: (i) overseeded with ryegrass plus inorganic N application and (ii) overseeded with clover and no inorganic N fertilization. During 19 years (1985-2004) of fertility regimens, soil NO3-N concentrations in bermudagrass pastures at the 0- to 120-cm soil depth were significantly greater in pastures overseeded with ryegrass and fertilized with inorganic N compared to pastures overseeded with clover and no applied N. Nitrogen fertilizer promoted soil acidity and more frequent limestone applications were required in the overseeded ryegrass pastures in order to maintain adequate pH for forage growth. Conversely, bermudagrass pastures overseeded with clover showed relatively constant soil NO3-N concentrations throughout the 19-yr study, and had moderate forage production. For all stocking rates, there was no significant effect of grazing intensity on soil NO3-N concentrations. Continuous stocking and fertilization history increased extractable soil K, Ca, and Mg levels in acid, low fertility Coastal Plain soil. Nutrients were effectively recycled in bermudagrass pastures and sustained satisfactory animal and forage production.
