Effect of liming on the mobilization of soil phosphorus

Authors

• Armi Kaila University of Helsinki, Department of Agricultural Chemistry

DOI: https://doi.org/10.23986/afsci.71643

Abstract

The effect of liming on the soil phosphorus fractions was studied under the laboratory conditions. 28 samples of mineral soils (pH in 0.01 M CaCl2 suspension 4.0 to 6.0) were incubated with 1 per cent CaCO3 or without lime for six months at about 18—20°C. In an other experiment, six samples (pH from 3.3 to 4.3) were incubated with 0, 0.5, 1, or 2 per cent CaCO3 also for six months. At the end of the incubation period the soil pH in the limed samples of the first experiment ranged from pH 5.9 to pH 7.5, in the second experiment the highest application kept the soil pH at 6.5 to 7.0. In the air-dried samples the content of organic phosphorus and the fractions of inorganic phosphorus were determined, and the increases or decreases due to the incubation and liming were calculated. Incubation without lime brought about decrease in the organic phosphorus content of several samples, and the presence of lime tended to intensify this effect, although only in a few cases the decrease due to liming was statistically significant. Liming also tended to increase the accumulation of NH4F-soluble inorganic phosphorus. The acid-soluble fraction was often increased in the limed samples but not in the unlimed ones. The alkali-soluble fraction was decreased in most soils in the limed samples, while it increased in some of the unlimed ones. In the second experiment the incubation caused marked decrease in the alkali-soluble phosphorus without a corresponding increase in the other phosphorus fractions determined in the subsoil samples. It was concluded that in these experiments the relatively heavy liming in the first place affected the distribution of inorganic phosphorus increasing the NH4F-soluble and acid-soluble forms at the expense of the alkali-soluble fraction. The effect on the mineralization of organic phosphorus seemed to be in most soils of minor importance.