Madhav K. Shrestha; C. Kwei Lin
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Abstract: An experiment was conducted to determine the amount of P needed to saturate simulated fish ponds sediments, formulated to contain six levels of clay (0, 30, 41, 64, 73 and 81% by weight). A series of cylindrical cement tanks were filled to 20 cm depth with the six sediment types and triple superphosphate (TSP) solution was added to reach P saturation in sediment. Results showed that all sediment types reached a constant inorganic-P concentration in the upper 5 cm after 12 weeks of TSP application, and P adsorption capacity of sediment increased with increasing clay Content. Sediment P adsorption was slower and not significant (P>0.05) below 5 cm depth except in the sediment type containing 0% clay. Regression analysis showed that the rate and adsorption capacity of P in sediment are primarily governed by clay Content and its dominant minerals. While organic-P and loosely bound-P are commonly deposited in sediment, most inorganic-P is adsorbed by cations to form cation-P complexes. The linear relationship between cation-P saturation level and the percentage of clay in sediment is highly significant (r2 – 0.84, P<0.001) and, therefore, the maximum adsorption capacity of cation-P in pond sediment can be approximated by Y = 0.019X (where Y represents the 100% saturation level in mg P g-1 soil, and X is the percentage of clay in the sediment). In practice, the level of P saturation in sediment can be approximated by the intial cation-P and clay Contents in the top 5 cm of pond mud using the equation: P saturation (%) = initial cation-P (mg g-1 soil) x 100/P adsorption capacity (mg g-1 soil).