Monday, November 5, 2007

Phosphorus Leaching in a Sandy Soil Affected by Fertilizer Sources.

Jihoon Kang, Dean Hesterberg, Aziz Amoozegar, and Deanna Osmond. North Carolina state university, Department of Soil Science, Campus Box 7619, Raleigh, NC 27695

Increasing emphasis on phosphorus (P)-based nutrient management underscores the need to understand P transport in soils amended with P fertilizer sources. The objectives of this study were i) to evaluate the water extractable P (WEP) in P source materials as a predictor of P leaching loss and ii) to characterize source-derived P transport by leaching in relation to the Langmuir sorption parameters. The miscible displacement of P under unsaturated condition was performed on repacked soil columns (6.35-cm diameter and 10-cm length) using seven P source materials: poultry compost (PC), poultry litter (PL), swine lagoon sludge (SS), triplesuperphosphate (TSP), dairy lagoon liquid (DL), swine lagoon liquid (SL), and dissolved KH2PO4 (KP). When these P sources were surface-applied on a total P basis (75 and 150 kg ha-1) as a pulse, inorganic P sources (TSP and KP) showed about two-fold greater P loss than organic P sources (DL, PC, PL, SL, and SS). The loss of source-derived P was well correlated with WEP in source materials (r2 = 0.87). For the columns treated with liquid P sources (DL, KP, and SL), we extrapolated one-dimensional P breakthrough curves (BTCs) from the Langmuir sorption parameters and the one-dimensional convective-dispersive equation model, and compared them with measured P BTCs. Enhanced P transport was observed in the columns treated with DL and SS as compared to KP. Results indicated that enhanced P transport in DL and SS may be attributable to the competition between DOC and P for sorption sites and mineralization of organic P.