Phosphorus Leaching in the Coastal Plain Soils of North Carolina.

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Title: Phosphorus Leaching in the Coastal Plain Soils of North Carolina.
Author: Kang, Ji-Hoon
Advisors: Robert O. Evans, Committee Member
Aziz Amoozegar, Committee Member
Deanna L. Osmond, Committee Chair
Dean L. Hesterberg, Committee Co-Chair
Abstract: Some soils in areas of intensive livestock farming have shown significant phosphorus (P) leaching. The objectives of this research were: i) to examine the relationships between soil properties and P sorption capacity, ii) to investigate leaching of P as affected by fertilizer sources, iii) to examine the effects of manure-derived dissolved organic carbon (DOC) on P sorption, and iv) to evaluate deep leaching of P. The P sorption maximum (Smax) of seventy two soil samples from various horizons of Coastal Plain soils of North Carolina (NC) was determined according to the Langmuir equation. Soil samples were analyzed for pH, clay content, organic matter (OM) content, oxalate extractable Al (Alox), Fe (Feox), and P (Pox), Mehlich-3 extractable Al (AlM3), Fe (FeM3), and P (PM3). The Smax was positively correlated with extractable Al (r = 0.76 for Alox and r = 0.86 for AlM3) and OM content (r = 0.61). The positive linear relationship between OM and Smax showed a change point where there was a two-fold decrease in the regression slope for OM > 42 ± 4 g kg-1. Results indicated that Al and Fe in organic-rich soils were likely to be less accessible for P sorption compared to those in mineral soils. Leaching of P as affected by fertilizer sources was investigated with repacked soil columns (10-cm long). The fertilizer sources were dairy lagoon liquid (DL), poultry compost (PC), poultry litter (PL), swine lagoon sludge (SS), swine lagoon liquid (SL), triplesuperphosphate (TSP), and dissolved KH2PO4 (KP). When these fertilizer sources were 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 (PC, PL, SL and SS). The loss of source-derived P was well correlated with water extractable P in source materials (r2 = 0.87). Enhanced P transport was observed in the soil columns treated with liquid wastes as compared to the KP. Concurrent sorption of P and DOC was investigated with batch sorption experiments using the aqueous extracts of PL and SS in Autryville sandy loam. The presence of manure-derived DOC did not inhibit P sorption, while the sorption of DOC decreased in the presence of manure-derived P. Results suggested that the formation of new surface sites through metal bridges between manure-derived OM and mineral oxides outweighed the competitive efficacy of DOC against P on the soil sorption sites. Deep leaching of P was evaluated with intact soil columns (90-cm long) collected from the Coastal Plain regions of NC. The selected sites were dominated by Autryville loamy sand, Cape Fear loam, and Goldsboro fine sandy loam, and Wasda muck. A limited pore volume of leached water (2.1 ± 0.1) resulted in low concentration of dissolved reactive P in most column leachates (< 0.02 mg L-1) except Wasda muck (0.034 mg L-1). The increased P concentration in Wasda muck was attributable to the higher Mehlich-3 P concentration in deep subsoils (22 to 69 mg kg-1 at 75-90 cm depth) than the other soils (0 to 7 mg kg-1 at 75-90 cm depth).
Date: 2007-11-01
Degree: PhD
Discipline: Soil Science

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