Phosphate Adsorption by Ferrihydrite-Amended Soils (original) (raw)

2005, Journal of Environmental Quality

in the southern United States will be especially difficult due to a larger percentage of conventional till practices New technology and approaches for reducing P in runoff from than other regions, highly erodible, low organic matter high sediment yield areas are essential due to implementation of soils, and high rainfall amounts that occur primarily as increasingly rigorous water quality standards. The objectives of this research were to characterize ferrihydrite (Fe 5 HO 8 •4H 2 O) in terms of intense thunderstorms. In addition to elevated levels of its ability to adsorb P from soil solutions and relate its P adsorptive native soil P in some extensive areas, and the surface capacity to several soil properties that influence P mobility. A natuapplication of P fertilizers in expanding no-till farming rally occurring ferrihydrite, collected as an Fe oxide sludge by-product practices, this region has an ever-increasing feedlot and from a water treatment facility, was equilibrated with soil samples at poultry industry that produces enormous quantities of equivalent rates of 0, 0.34, 3.36, 16.80, and 33.60 Mg ha Ϫ1 for a 60-d manure that is applied to farmlands. This combination period. Individual 2-g subsamples of each soil were then equilibrated of factors represents a potential problem relative to the with 0, 5, 10, 20, and 40 mg kg Ϫ1 P in 20 mL of 0.01 M CaCl 2 on a contamination of surface and subsurface water supplies reciprocating shaker for 24 h. After 24 h, P in solution was measured through overapplication of P by either fertilizers or maby colorimetric methods, and designated as final P concentrations. The nures (Hansen et al., 2002; Sims et al., 1998). In terms data indicated that the unamended soils with a pH of Ͻ6.0 adsorbed, in some cases, 50 times more P than soils with a pH of Ͼ7.0. The of P leaching losses, Sims et al. (1998) report that the final P concentrations, averaged for all initial P concentrations and soil conditions most conducive to significant P leaching ferrihydrite rates, ranged from 0.09 to 4.63 mg kg Ϫ1 , and were most include those with high sand contents, high organic mathighly correlated with pH (r ϭ 0.844; P Յ 0.01), oxalate-extractable ter contents, reducing conditions, and preferential flow Fe (r ϭ Ϫ0.699; P Յ 0.10), and dithionite-extractable Fe (r ϭ Ϫ0.639; paths. The leaching of P in high organic matter soils is P Յ 0.10) contents of the unamended soils. In terms of individual due to both low Fe and Al contents, and the blockage soils, correlation coefficients (r) for final P concentrations versus of their associated exchange sites by organic matter. ferrihydrite amendment rates indicated a statistically significant (P Յ The use of Fe oxides to adsorb P on-site and reduce 0.001) negative relationship at all initial P concentrations for most A its concentrations in runoff and leachates is a proven horizons. The r values for the high Fe oxide content B horizon soils approach to potentially lowering P loadings of water did not show a statistically significant response to ferrihydrite additions. The results indicate that P adsorption, in soils amended with bodies (Moore and Miller, 1994; Elliott et al., 2002; ferrihydrite, will be greatest under acid pH conditions below the Gallimore et al., 1999). Numerous laboratory studies ferrihydrite zero point of charge (pH 5.77), and low incipient Fe have been directed at the sorption of phosphate on Fe oxide contents.