Bermudagrass Management in the Southern Piedmont USA. II. Soil Phosphorus

which can become exposed at the soil surface from a long history of erosion (Bruce et al., 1990). Plant production can be limited by low levels of available P due Poultry production in the Appalachian Piedmont is exto high P-fixation capacity in soils of the southeastern USA. On the tensive (U.S. Dep. of Commerce, 1992). Manure mixed other hand, there is increasing concern about excessive application with bedding material (i.e., litter) at the end of the proof P to soil, especially when manure application is based upon N duction cycle is cleared from confinement housing and content. We evaluated changes in Mehlich-I extractable soil P during 5 yr of bermudagrass [Cynodon dactylon (L.) Pers.] management applied to nearby land as a source of valuable nutrients varying in fertilization [inorganic and broiler chicken (Gallus gallus ) for crop and pasture production. Depending upon manlitter] and harvest strategy (unharvested, low and high cattle (Bos agement, however, repeated application of poultry litter taurus ) grazing pressure, and haying). Broiler litter supplied eight to the same land could become a source of excessive times more P than inorganic fertilization to meet the N requirement. nutrients that would threaten water quality (Sharpley At a depth of 0 to 6 cm, Mehlich-I extractable soil P increased 0.8 et al., 1993; Kingery et al., 1994). Environmental regula1.6 mg kg 1 yr 1 (4 8% of total P added) with inorganic-only fertions to protect water quality have and will continue to tilization, 2.4 3.0 mg kg 1 yr 1 (9 11% of total P added) with clover be developed, especially with the increased competition (Trifolium incarnatum L.) cover crop plus inorganic fertilization, and for water resources among agricultural-, urban-, wild8.7 9.8 mg kg 1 yr 1 (6 7% of total P added) with broiler litter. life-, and recreational-supporting sectors of our increasHaying kept Mehlich-I extractable soil P constant with time due to ingly affluent society. Unfortunately, details on nutrient removal of P with harvest of biomass. At the end of 5 yr of broiler litter application to grazed land, Mehlich-I extractable soil P was 135, accumulation and distribution in soils managed for pas50, 22, and 4 mg kg 1 higher than with inorganic fertilization at depths ture production with differences in harvest strategy are of 0 to 3, 3 to 6, 6 to 12, and 12 to 20 cm, respectively. Broiler litter limited. Such information is necessary for legislators to fertilization was effective at increasing Mehlich-I extractable soil P make rational decisions on land use and nutrient manto an agronomically productive level (50 to 60 mg kg 1 15 cm 1 ), but agement based on scientific evidence. continued application could lead to excessive P accumulation that Grazing of a forage crop compared with haying recould threaten water quality from surface runoff unless appreciable turns most of the manure directly to the land, which soil fixation or removal of forage biomass were to occur. affects nutrient distribution in soil (Haynes and Williams, 1993; Follett and Wilkinson, 1995). Animal behavior patterns in pastures suggest that preferential deL and vertical distribution of nutrients in pasposition of feces and urine near shade and water sources tures can either limit plant-animal productivity or would lead to a non-uniform distribution of nutrients pose environmental threats, depending upon quantities (Mathews et al., 1996). Further, the impact of whether available and the type of management employed. In the forage is mechanically harvested or not on total and southeastern USA, rainfall is abundant and soils are extractable soil P deserves attention, based on the extent weathered, which make nutrient applications susceptiof land currently managed under the Conservation Reble to both runoff and leaching losses. The eroded and serve Program. Harvest management would be expected weathered soils of the southeastern USA, in general, to alter the depth distribution of extractable soil P, beare low in available P, with applied P quickly fixed into cause of the presence of animal traffic, ruminant prounavailable forms upon exposure to clay-sized minerals cessing of forage (i.e., biological transformation of nutri(Anderson et al., 1996). Crop responses to fertilizer apents), or nutrient removal in hay. plication of P are generally large, but repeated applicaWe hypothesized that with equivalent amounts of tions are necessary because of the high anion adsorption total N applied, fertilization strategy (i.e., inorganic or capacity of these soils, particularly in the clayey subsoil, organic with differences in associated P content) could affect the availability of P to forage and its form and depth distribution in soil. Our objective was to characUSDA–ARS, J. Phil Campbell Sr. Natural Resource Conservation terize the temporal and spatial distribution of Mehlich-I Center, 1420 Experiment Station Road, Watkinsville, GA 30677-2373. extractable soil P in response to differences in fertilizaReceived 19 Feb. 2001. *Corresponding author ([email protected]. edu). Abbreviations: ICPS, inductively coupled plasma spectroscopy. Published in Soil Sci. Soc. Am. J. 66:291–298 (2002). 292 SOIL SCI. SOC. AM. J., VOL. 66, JANUARY–FEBRUARY 2002 Table 1. Characteristics and rates of fertilizer sources applied. 1994 1995 1996 1997 1998 5-yr mean Variable May July May July May July May July May July yr 1 Eq† Eq‡ g m 2 g m 2 yr 1 mg kg 1 yr 1