title: Bermudagrass management in the Southern Piedmont U.S. IV. Soil surface nitrogen pools.
abstract: The fate of nitrogen (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 [Trifolium incarnatum L.] cover crop plus inorganic, and chicken [Gallus gallus] broiler litter pressure and four types of harvest strategy (unharvested forage, low and high cattle [Bos Taurus] grazing pressure, and monthly haying in summer) on surface residue and soil N pools during the first 5 years of 'Coastal' bermudagrass (Cynodon dactylon [L.] Pers.) management. The type of N fertilization used 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 x kg(-1) x year(-1) greater with inorganic fertilization than with other fertilization strategies. We could account for more of the applied N under grazed systems (76-82%) than under ungrazed systems (35-71%). As a percentage of applied N, 32 and 48% were 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 6.8 and 10.3 g x m(-2) x year(-1). Sequestration rates of total soil N under the unharvested-forage and haying strategies were negligible. Most of the increase in total soil N was at a depth of 0 to 2 cm and was due to changes in the particulate organic N (PON) pool. The greater cycling of applied N into the soil organic N pool with grazed compared with ungrazed systems suggests an increase in the long-term fertility of soil.
authors.affiliation: U.S Department of Agriculture-Agricultural Research Service, Natural Resource Conservation Center, Watkinsville, GA 30677-2373, USA. afranz@arches.uga.edu
authors.forename: A J
authors.initials: AJ
authors.lastname: Franzluebbers
authors.forename: J A
authors.initials: JA
authors.lastname: Stuedemann
mesh_terms: D000821:Animal Feed; D000822:Animal Husbandry; D000818:Animals; D002417:Cattle; D002645:Chickens; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods; D005308:Fertilizers; D005845:Georgia; D016014:Linear Models; D009584:Nitrogen / Q000378:metabolism*; D006109:Poaceae / Q000254:growth & development / Q000378:metabolism*; D012987:Soil / Q000032:analysis*
chemical_list: D005308:Fertilizers; D012987:Soil; D009584:Nitrogen