Monday, November 5, 2007
119-19

Phosphorus Mobility from Organic and Inorganic Soil Amendments: Rainfall Simulation Studies.

Thomas Rew1, Donald Graetz2, Manohardeep Josan1, Vimala D. Nair1, and Willie Harris1. (1) University of Florida, 4215 NW 20th Dr., Gainesville, FL 32605, (2) PO Box 110510, University of Florida, University of Florida, Soil & Water Scences, 106 Newell, Gainesville, FL 32611

 Agricultural watersheds in Florida and across the nation contribute excessive phosphorus (P) to surficial water bodies, particularly when amendments are applied at a nitrogen-based rate.  Our objective was to document P release and movement in the soil affected by different P sources. Surface soil from a poorly-drained unimpacted Immokalee fine sand was packed in rainfall simulation boxes (100 cm x 30 cm x 20 cm). Six P sources including dairy bedding (Black Kow), 2 biosolids (Milorganite and Orlando), triple super phosphate (TSP), poultry manure, and dairy manure were applied to the surface soil at a total P of 300 kg ha-1. Seven 30-min rainfall simulations were run at weekly intervals. Leachate and /runoff were collected and analyzed for soluble P. After the 7th simulation, soil cores were taken from each box, cores divided at 5 cm intervals, and Mehlich1-P (M1-P) and metals determined for each soil depth. Soil phosphorus storage capacity (SPSC) values were calculated from M1-P, Fe and Al concentrations. Cumulative P in leachate decreased:  TSP>Orlando biosolids>poultry manure>Black Kow>dairy manure>Milorganite>control. All applied P in the TSP treatment was leached. Runoff P was minimal for all treatments. Cumulative P leached was significantly correlated (p < 0.05) with water extractable P (r2 = 0.98) and M1-P (r2 = 0.93) of the P source. With successive rainfall events the amount of P leached increased for Black Kow, dairy manure, and Milorganite; but decreased for TSP and Orlando biosolid treatments. The SPSC values were negative for the surface soil (0-5 cm) for all P sources except the control and Black Kow treatments.  TSP treatment resulted in negative SPSC throughout the 20-cm soil profile. Since P sources affect the release and mobility of P in the soil, their solubility should be taken into consideration during land application of P.