Effect of liming on phosphorus in two soils of different organic matter content: I Changes of native and applied phosphorus in incubation experiment

Abstract

The effect of increasing lime quantities on reactions of native and applied P was investigated in an incubation experiment performed with two acid mineral soils of pH 4.8 (CaCl2). The soil samples differed considerably in the content of organic matter, which was reflected in their pH buffering power: in the fine sand, rich in organic matter (6.4 % org. C), liming raised the pH less than in the muddy fine sand (3.0 % org. C). The level of native water-soluble P was markedly lowered in the incubated soil samples treated with nutrient salts. In the muddy fine sand, the decrease tended to be the smaller, whereas in the fine sand the greater, the more intensive liming was. This held true also of added P. The changes in CHANG and JACKSON’s P fractions did not alone satisfactorily explain the dissimilar response of soil P to lime treatments. The fate of P was concluded to be controlled by the quality and quantity of Al species differing in their affinity for P sorption. The changes in the solubility of P are a net result of processes enhancing and of those depressing the sorption tendency. In the fine sand soil of high initial content of water-soluble P, the detrimental effect of liming seemed to be attributed to the abundance of polymerized Al the affinity of which for P retention increased with intensified liming. Further, the high pH buffering power of this soil reduced the efficiency of lime to produce OH- ions able to compete with phosphate for sorption sites. In the muddy fine sand soil, on the contrary, the formation of sorption-active sites was not equally marked and, owing to the weaker pH buffering, liming raised the OH- concentration more effectively.