The fate of water-soluble phosphate applied to some mineral soils

Authors

• Armi Kaila University of Helsinki, Department of Agricultural Chemistry

DOI: https://doi.org/10.23986/afsci.71630

Abstract

The distribution of applied water-soluble phosphorus in the various fractions of soil inorganic phosphorus was studied in an incubation experiment under the laboratory conditions. Samples of twelve soils were incubated for three months at room temperature with the applications of KH2P04 in amounts corresponding to 100, 200, or 500 mg P/kg of soil. The results of the fractionation showed that in most samples the applied phosphorus could be found almost completely in the fluoride-soluble and alkali-soluble fractions, the part of the former being the higher and that of the latter the lower the higher the rate of the phosphate application. Similar results were obtained also when the fractionation was performed after the samples had been in contact with the phosphate solutions only for two hours. Analyses of samples from two field trials were in accordance with these results. The soils tended to have a characteristic pattern of phosphate retention which in extreme cases means an almost complete sorption of the applied phosphate either as the fluoride-soluble form or as the alkali-soluble form. In most soils, however, the distribution was more equal. Usually the fluoride-soluble part of the recovered phosphorus tended to be somewhat higher than the alkali-soluble part. This tendency was more distinct in regard to the newly retained phosphorus. The effect of phosphate fertilizers in our soils is discussed on the basis of the results.