Effect of pond mud drying on mineralization and nutrients release

摘要

An experiment was conducted to recycle nitrogen (N) and phosphorus (P) nutrients accumulated in muds to water column through pond drying. Air dried and ground pond mud with 18.06 ±0.24 mg/g soil of organic carbon (C), 1.57 ±0.01 mg/g soil of total Nand 1.10 ±0.01 mg/g soil of total P was moistened with distilled water in four different soil:water ratio - 1:1, 1:0.7, 1:0.4 and 1:0.3 for the corresponding moisture content level of 100, 70, 40 and 30% on dry weight basis. Those mud moisture levels maintained were dried for 1, 4, 7 and 10 days during which muds were sprayed with distilled water twice daily to compensate evaporation loss. At the end of each drying period, muds were leached for twenty four hours. The highest mean concentrations of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) in leachate were 79.81 and 0.75 mg/kg mud, respectively, for 40% moisture level and 10 days drying. Considering 5 cm deep reactive layer of mineralization and bulk density of mud to be1 g/cm3, calculated N and P release were 39.9 and 0.38 kg/ha fish pond, respectively. Leachate analysis showed that 30-40% moisture level was optimal for the oxidation of organic matter in pond muds. Oxidation of pond mud enhanced the adsorption of mineralized P in mud in 1 to 4 days drying but SRP release increased after 4 to 10 days, indicating higher rate of mineralization than the rate of adsorption.