SOIL C, N, AND P FROM POULTRY MANURE ON GRAZED AND UNGRAZED BERMUDAGRASS IN THE SOUTHEASTERN USA

Authors: Franzluebbers, Alan; Stuedemann, John

Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: 8/20/2002
Publication Date: 8/14/2002
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2002. Soil c, n, and p from poultry manure on grazed and ungrazed bermudagrass in the southeastern USA. World Congress of Soil Science.

Interpretive Summary: The impact of animal manure application to grasslands is of portance to the understanding of agronomic and animal productivity, soil quality, greenhouse gas emissions, and environmental quality. Pastures have the potential to serve as a significant sink for carbon sequestered in soil organic matter. Efficient utilization of nitrogen is of concern agronomically and environmentally. Plant production can be limited by low levels of available phosphorus due to high phosphorus fixation capacity in soils of the southeastern USA. On the other hand, there is increasing concern about the excessive application of phosphorus to soil, especially when manure application rate is based upon nitrogen content. Broiler litter fertilization was effective at increasing extractable soil phosphorus to an agronomically acceptable level (50 to 60 mg/kg/15-cm depth) during the first five years, but continued application could lead to excessive soil phosphorus accumulation that could threaten water quality from surface runoff unless appreciable soil fixation or removal of forage biomass were to occur. Cattle grazing systems were effective at sequestering soil carbon and nitrogen in surface soil organic matter.

Technical Abstract: We evaluated the changes in soil carbon (C), nitrogen (N), and phosphorus (P) during the first five years of bermudagrass [Cynodon dactylon (L.) Pers.] management varying in fertilization [(1) inorganic, (2) crimson clover (Trifolium incarnatum L.) cover crop plus inorganic, and (3) chicken (Gallus gallus) broiler litter] and harvest strategies [(1) unharvested, (2) low and (3) high cattle (Bos taurus) grazing pressure, and (4) haying). Fertilization strategy had the greatest impact on total and extractable soil P, while soil organic C and total soil N were minimally affected. At a depth of 0 to 6 cm, extractable soil P increased at a rate of 0.8 mg/kg/yr (4 % of total P added) with inorganic only, 2.4 mg/kg/yr (9 % of total P added) with clover + inorganic, and 8.7 mg/kg/yr (6 % of total P added) with broiler litter fertilization. Soil organic C sequestration during the first five years of management was similar between low and high cattle grazing pressures (1400 kg/ha/yr), but much less in unharvested (650 kg/ha/yr) and hayed (290 kg/ha/yr) management. With cattle grazing of forage, fertilizer contributed to forage and animal production and 67-75% of the total N applied was subsequently stored as total soil N.