WATER-QUALITY IN LABORATORY SOIL-WATER MICROCOSMS WITH SOILS FROM DIFFERENT AREAS OF THAILAND

Forty-five soil samples were collected from aquaculture areas in 23 pr ovinces of Thailand to include six soil orders and wide variation in p hysical and chemical properties. Soil-water microcosms were prepared c ontaining 5 g of soil and 150 mt of distilled water. Microcosms were h eld on an oscillating table shaker (150 rpm) for 1 wk at 25 C in the d ark. Water pH and concentrations of dissolved nutrients, total alkalin ity, and total hardness were measured. Differences in properties withi n soil orders caused wide variation in composition of solutions and di fferences in concentrations of dissolved substances and pH were not re lated to soil order. Regression analyses revealed significant correlat ions between concentrations of soil nutrients extractable in dilute ac id (0.05 N HCl plus 0.025 N H2SO4) or in neutral, 1 N ammonium acetate and aqueous concentrations. Regression coefficients usually were high er for dilute-acid extractable nutrients than for ammonium acetate ext ractable ones. Regression coefficients based on dilute-acid extractabl e nutrients follow: soluble reactive phosphorus (r = 0.816); calcium ( r = 0.685); magnesium (r = 0.470); potassium (r = 0.959); sodium (r = 0.977); manganese (r = 0.462); boron (r = 0.399). The correlation betw een soil and solution iron was not significant and aqueous concentrati ons of copper and zinc were below detection limit, Hardness was correl ated with soil carbon (r = 0.710) and soil pH was a good predictor of alkalinity (r = 0.877). Soil pH and aqueous pH were highly correlated (r = 0.939). Findings suggest that soil characteristics can be used to predict pH and concentrations of several dissolved substances in soil -water systems under aerobic conditions.