The behaviour of Phosphorus in Some Thailand Soils

Abstract

The Langmuir equation coupled with a Hofstee plot has been found to be more useful in studying phosphorus behaviour in soils than those of Freundlich and Bache and Williums method. Isotherms of P ranging from the lowest to the highest concentration can be examined with the merits of the Langmuir. Soils in humid tropical zones like Thailand, as found in some areas of southern peninsular, show higher fixing capacity of P in the sub-soils than in the top-soils. Adsorption sites have indicated that there are at least 2 regions. Of Both the top and the sub-soils, adsorption maxima (Am) in the Region I (Am) was lower than in Region II (Am). However, phosphate bonding energy in specific adsorption of phosphate takes place in Region through the processes called bidentate and monodentate in Region II. When phosphate is adsorbed at high concentration, the pH values tended to increase markedly under the Region I and II, and at a certain level of higher phosphate adsorption, decrease gradually again. This suggests that when adsorption maxima was reached, the disorganization of aluminosilicate structure occurs and provides new types of sites,