Bermudagrass Management in the Southern Piedmont USA: VI. Soil-Profile Inorganic Nitrogen

Fate of applied N in forage-based agricultural systems is important to long-term production and environmental impacts. We evaluated the factorial combination of N fertilization targeted to supply 20 g N m-2 yr-1 and harvest strategies on soil-profile inorganic N during the first 5 yr of ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] 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 upper rooting zone (0- to 0.3-m depth), soil inorganic N (initially at 3.1 g m-2) remained unchanged during the 5 yr under unharvested and low and high grazing pressures (0.00 ± 0.08 g m-2 yr-1), but declined with haying (-0.25 g m-2 yr-1). In the lower rooting zone (0.3- to 0.9-m depth), soil inorganic N (initially at 2.9 g m2) accumulated with unharvested and low and high grazing pressure (0.64 ± 0.20 g m-2 yr-1), but remained unchanged with haying (-0.06 g m-2 yr-1). Below the rooting zone (0.9- to 1.5m depth), soil inorganic N (initially at 5.8 g m-2) increased with unharvested and high grazing pressure (0.34 ± 0.03 g m-2 yr-1), was unchanged with low grazing pressure (-0.10 g m-2 yr1), and declined with haying (-0.50 g m-2 yr-1). 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), irrespective of inorganic or organic fertilization strategy designed to supply sufficient N for high animal production from grazing.