Submitted to: Soil Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2000
Publication Date: 6/1/2001
Citation: ZHANG, M., ALVA, A.K., LI, Y.C., CALVERT, D.V. ALUMINUM AND IRON FRACTIONS AFFECTING PHOSPHORUS SOLUBILITY AND REACTIONS IN SELECTED SANDY SOILS. SOIL SCIENCE, 166:940-948. 2001. Interpretive Summary: Soil properties influence the solubility and availability of phosphorus in soils. Soil pH and organic matter status are major factors to influence the phosphorus reactions. In this study, different depth soil horizons were sampled from different soil series. These soils represented a range of pH from 4.6 to 7.7. The soil samples were either unamended or amended with 44.5 mg phosphorus/kg soil and incubated for 30 days at field capacity soil moisture condition. Soil solution was separated for various analyses. The results showed the phosphorus form which accounted for a major portion of the phosphorus in soil solution and the variation in predominant phosphorus form in different soils. The study demonstrated that the soil management for crop production, particularly liming practice influences the soil pH and in turn result in variation in phosphorus availability. The need for phosphorus fertilization, therefore, depends on na number of soil factors and that a measure of bicarbonate form of phosphorus and the rooting depth of the crop in question are important to understand phosphorus requirements of crops.
Technical Abstract: Phosphate solubility and reactions were investigated in three horizon samples each from six cultivated soils representing Spodosols, Alfisols and Entisols, with pH ranging from 4.6 to 7.7. Soils were incubated for 30 days near field capacity moisture content without P application or with 44.5 mg P kg-1 soil applied as KH2PO4. Soil solution was extracted by centrifugation and the concentrations of anions and cations were determined. The ionic activities were calculated using the MINTEQA2 speciation program. Sequential-fractionation data suggested that amorphous forms of Al- and Fe- phosphates and P associated with crystalline Al- and Fe- oxides accounted for a significant portion of total P. The activities of Al3+ and Fe3+ in most cases were adequate to support the stability of wavelite, crandallite, variscite and strengite, and close to the equilibrium point of amorphous Al- or Fe- phosphate without applying P. Following the application of the equivalent of 100 kg P/ha, the soil solution chemistry from two Spodosols and one Alfisol suggest the formation of amorphous varscite- and strengite-like minerals. However, the soil solutions were under saturated with respect to amorphous Al- and Fe- phosphates in two Entisols and in another Alfisol with higher pH, where Ca- phosphate minerals appeared to control the soil solution phosphate activity. The research results suggested that liming practices under citrus production increase the soil pH of surface horizon, and in turn shift the control reaction and solubility of the phosphate minerals, and influence the availability of phosphorus in these sandy soils.