Effect of liming on the fate of applied superphosphate phosphorus in some mineral soils

Authors

• Armi Kaila University of Helsinki, Department of Agricultural Chemistry

DOI: https://doi.org/10.23986/afsci.71668

Abstract

The effect of liming on the distribution of superphosphate phosphorus in various fractions of soil phosphorus was studied. Samples of four mineral soils (pH 3.9 to 5.1) were incubated at room temperature for eight months with 0, 0.5, or 1.0 per cent CaCO3, and with 0.40 per cent superphosphate or without any phosphate application. Liming increased the soil pH-values to pH 6.1—7.3. Samples were analyzed for inorganic phosphorus by the fractionation method of CHANG and JACKSON. Results obtained after an incubation period of four months showed that, both in the fertilized and unfertilized samples, liming had increased the fluoride soluble, acid soluble and easily soluble fractions, but it had decreased the alkali soluble phosphorus. These effects were generally the more distinct, the higher the application of CaCO3 had been. During the prolonged incubation, the alkali soluble fraction tended to increase at the expense of the fluoride soluble phosphorus. The differences in the phosphorus content of various fractions in the respective fertilized and unfertilized samples showed that the »superphosphate phosphorus» was mainly recovered as the fluoride soluble and alkali soluble forms, the relative amount of the latter being the lower the heavier the liming had been. Yet, even at about pH 7, from one fifth to one fourth of the applied phosphorus appeared to be sorbed by iron compounds and ocurred in the alkali soluble fraction. The sum of the proportions of easily soluble and fluoride soluble phosphorus increased with liming. The small parts of fertilizer phosphorus recovered in the acid soluble form did not depend on the rate of liming. Thus, even at pH 7, no significant turning of superphosphate phosphorus in difficultly soluble apatite like secondary calcium phosphates could be detected. The effect of liming on the availability of the fertilizer phosphorus and on the phosphate retention pattern of the soil, was discussed.