To investigate the effect of water-dispersible colloids derived from swine manure on the potential risks of phosphorus (P), migration behavior of P in saturated-flow columns was compared in the presence and absence of water-dispersible colloids of manure in influent. It was found that dissolved phosphorus (DP) accounted for a majority of total P (65-98%) in the effluent with deionized water treatments, while contributed between 21 and 45% to total P leaching with the manure colloid treatments. In manured soils, with the inflow of manure colloidal suspension, colloidal P in the effluent were 26.7 times higher than that of deionized water treatment (PM+W) and 1.9 times more than that of unamended soil treated with manure colloid (P0+M) in the end of the leaching experiment. Despite the initial reduction of DP concentrations in the effluent with the presence of manure colloid, the DP concentrations still increased smoothly and continued to transport with the effluent throughout the breakthrough experiment. This suggested that P sorption sites of the soil and the added manure colloid in the column were fastly saturated during initial stage of the experiment. In manure colloid treatments, higher colloidal P concentrations in leachate were related to larger P contents of leached colloids, which were in sorption equilibrium with larger concentrations of dissolved P. Furthermore, in deionized water treatments, good linear correlation between colloidal P and colloidal Fe indicated that Fe hydroxides could be served as a main medium for the transportation of colloidal P.
Key words: Dissolved P, colloidal P, water-dispersible colloids, manure, degree of phosphorus saturation (DPS).
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