GREEN AND ANIMAL MANURE-DERIVED DISSOLVED ORGANIC-MATTER EFFECTS ON PHOSPHORUS SORPTION

This study was conducted to investigate the effect of dissolved organi c matter (DOM) extracted from common soil amendments and citric acid o n the P sorption of an acidic soil. Hairy vetch (Vivia billosa L.) and crimson clover (Trifolium incarnatum L.) were used as sources for gre en manure-derived DOM. Cattle manure (Bos taurus) and poultry manure ( Gallus domesticus) were used as sources for animal manure-derived DOM, The negative charge density of the water-soluble DOM ranged from 4.6 to 13.4 mmol(c) g(-1) C. Estimated molecular weight ranges were 710 to 850 for the green manure DOM and 2000 to 2800 for the animal manure D OM, Phosphorus sorption experiments were conducted at 40 mmol P kg(-1) soil and 0, 5, 10, 15, and 20 mM total soluble carbon (C-TS) for each green and animal manure source. The DOM extracted from vetch and clov er, as well as citric acid, inhibited P sorption in the order citric a cid > clover > vetch, The DOM extracted from the animal manures did no t affect P sorption, The ability of the green manure DOM to inhibit P sorption was related to its ability to react with soil Al through liga nd exchange reactions at lower DOM concentrations and through complexa tion reactions at higher DOM concentrations. The average ratio of Al s olubilization to P sorption inhibition on a molar basis was 1.76 +/- 0 .44. Ultraviolet absorbance and fluorescence data suggested that the h igher molecular weight of the animal manure derived-DOM was a factor i a its inability to react with soil Al. The results of this study sugge st that management systems that use green manures may increase the ava ilability of P by decreasing the sorption of added P to soils.