Submitted to: The Scientific World
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2001
Publication Date: 9/24/2001
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2001. Bermudagrass management in the southern piedmont usa. iv. soil-surface nitrogen pools. The Scientific World.
Interpretive Summary: Nitrogen is the most limiting nutrient required by plants. Forage grasses respond dramatically to the application of additional nitrogen, either via inorganic fertilizers or animal manures. We tested how the type of fertilization affected the quantity, form, and depth distribution of nitrogen left in the soil. Fertilization types were inorganic, clover recycling, and chicken litter. We also tested the effect on soil nitrogen of how grass was utilized. Grass was either unharvested to simulate the conservation reserve program, harvested monthly in the summer to simulate haying, and grazed by cattle at two different levels to simulate low and high intensity grazing. Bermudagrass pastures were utilized for five consecutive years during this evaluation. More nitrogen was found in the surface soil with cattle grazing than with unharvested or haying systems. This implies that nitrogen was accumulating in the soil organic matter under cattle grazing, thereby improving the long-term fertility of soil. Most of the nitrogen applied was removed in plant biomass in the haying system. The fate of nitrogen when unharvested was less clear than in other systems.
Technical Abstract: The fate of N applied in forage based agricultural systems is important for understanding the long-term production and environmental impacts of a particular management strategy. We evaluated the factorial combination of three types of N fertilization (inorganic, crimson clover cover crop plus inorganic, and broiler litter) and four types of harvest strategy (unharvested, low and high cattle grazing, and hayed monthly in summer) on surface residue and soil N pools during the first five years of bermudagrass management. The type of N fertilization resulted in small changes in soil N pools, except at a depth of 0 to 2 cm where total soil N was sequestered at a rate 0.2 g/kg/yr greater with inorganic fertilization than with other fertilizer strategies. As a percentage of N applied, 32 and 48% was sequestered as total soil N at a depth of 0 to 6 cm when averaged across fertilization strategies under low and high grazing pressures, respectively, which was equivalent to 68 and 103 kg/ha/yr. Sequestration rates of total soil N under unharvested and hayed strategies were negligible. Greater cycling of applied N into the soil organic N pool with grazed compared with ungrazed systems suggests an increase in the longterm fertility of soil.