Monday, November 5, 2007
119-19
Phosphorus Mobility from Organic and Inorganic Soil Amendments: Rainfall Simulation Studies.
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.
Presentation