BERMUDAGRASS MANAGEMENT IN THE SOUTHERN PIEDMONT USA. VI. SOIL-PROFILE INORGANIC N

Authors: Franzluebbers, Alan; Stuedemann, John

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2003
Publication Date: 7/1/2003
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2003. Bermudagrass management in the southern piedmont usa. vi. soil-profile inorganic n. Journal of Environmental Quality.

Interpretive Summary: Fate of applied nitrogen (N) in forage-based agricultural systems is important to long-term production and environmental impacts. A pathway of N movement that has received a great deal of attention, because of the detrimental consequences on groundwater quality, is through leaching below the rooting zone of plants. The loss of N through leaching is both an immediate economic loss to farm producers, as well as a long-term economic burden for society and an environmental tragedy. We determined the accumulation of inorganic N in the soil profile during each of five years under various bermudagrass management systems. When the soil profile was divided into the upper rooting zone (0-0.3 m), lower rooting zone (0.3-0.9 m), and the area immediately below the rooting zone (0.9-1.5 m), the distribution of inorganic N was 17, 26, and 57% in these depths initially and 18, 35, and 46% at the end of five years. We found no difference in inorganic N accumulation whether fertilizer was from inorganic, clover plus inorganic, or poultry litter sources. Although the change in inorganic N was relatively small (30%), unharvested management and high cattle grazing pressure were the only treatments with elevated concentrations below the rooting zone.

Technical Abstract: We evaluated the factorial combination of nitrogen (N) fertilization targeted to supply 200 kg N/ha/yr (inorganic, crimson clover cover crop plus inorganic, and chicken broiler litter] and harvest strategy (unharvested, low and high cattle grazing pressure, and hayed) on soil-profile inorganic N during the first five years of 'Coastal' bermudagrass management. Harvest strategy had much larger effects than fertilization strategy, most notably that soil-profile inorganic N was lower when hayed than under other systems. In the lower rooting zone (0.3-0.9-m depth), soil inorganic N (initially at 29 kg/ha) accumulated 2%/yr with unharvested and low and high grazing pressure, but remained unchanged with haying. Below the rooting zone (0.9-1.5-m depth), soil inorganic N (initially at 58 kg/ha) increased 6%/yr with unharvested and high grazing pressure, was unchanged with low grazing pressure, and declined 9%/yr with haying. Applied N appears to have been efficiently utilized by forage with subsequent sequestration into soil organic matter and little movement of inorganic N below the rooting zone (<2% of applied N).