ACCUMULATION AND MOVEMENT OF PHOSPHORUS FROM POULTRY LITTER APPLICATION ON A STARR CLAY LOAM

The poultry industry faces tremendous challenges for the economically sound and environmentally safe disposal of the massive amounts of waste it generates during production processes. This study was conducted to investigate the accumulation and downward movement of phosphorus (P) from surface application of poultry litter (PL) on a Starr clay loam (fine-loamy, mixed, thermic Fluventic Dystrochrepts). Poultry litter was surface applied to unimproved pasture at rates of 5.8, 11.4, 17.2, 22.9, and 28.7 mt/ha in 1991 and 4.1, 8.0, 12.1, 16.1, and 20.2 mt/ha in 1992, respectively. Cumulative P levels supplied by the PL over the two-year period were 105.8, 211.7, 317.5, 423.3, and 529.1 kg/ha. Phosphorus from both PL and inorganic sources accumulated in the zone of application. The Mehlich 3 (M3)-extractable P level varied with rate of P application for each of the two years of this study. In 1992, MS-extractable P levels were increased by 2-, 4-, 6-, and 8-fold over the control by PL application in the 0 to 5 cm depth. In 1993, the highest rate of PL application (20.2 mt/ha) increased M3-extractable P level by almost 18-fold over the control (192 mg P/kg versus 11 mg P/kg). In 1992, downward movement of P occurred into the 5.0 to 10.0 and 10.0 to 15.0 cm layers from the highest rate of PL application (28.7 mt/ha). By 1993, P moved into the 5.0 to 10.0 and 10.0 to 15.0 cm soil layers from the second highest PL application rate as well. This downward movement of surface-applied P in the Starr soil with a high fixation capacity was attributed to mobility of organic-bound P.