DETERMINATION OF PHOSPHORUS SATURATION LEVEL IN RELATION TO CLAY CONTENT IN FORMULATED POND MUDS

An experiment was conducted to determine the amount of P needed to sat urate simulated fish pond sediments, formulated to contain sh levels o f 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 an d triple superphosphate (TSP) solution was added to reach P saturation in sediment Results showed that all sediment types reached constant i norganic-P concentration in the upper 5 cm after 12 weeks of TSP appli cation 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 i n sediment, most inorganic-P is adsorbed by cations to form cation-P c omplexes. The linear relationship between cation-P saturation level an d the percentage of clay in sediment is highly significant (r(2) = 0.8 4, P<0.001) and therefore, the maximum adsorption capacity of cation-P in pond sediment can be approximated by Y = 0.019X (where Y represent s the 100% saturation level in mg P g(-1) soil, and X is the percentag e of clay in the sediment). In practice, the level of P saturation in sediment can be approximated by the initial cation-P and clay contents in the top 5 cm of pond mud using the equation: P saturation (%) = in itial cation-P (mg g(-1) soil) x 100/P adsorption capacity (mg g(-1) s oil).