Chloride and sulphate solutions as extractants for soil P: II Dependence of the relative extraction power of chloride and sulphate solutions on some soil properties 

Authors

• Helinä Hartikainen Department of Agricultural Chemistry, University of Helsinki, 00710 Helsinki 71
• Markku Yli-Halla Department of Agricultural Chemistry, University of Helsinki, 00710 Helsinki 71

DOI: https://doi.org/10.23986/afsci.72109

Abstract

The relative P extraction power of KCI and K2SO solutions of the same ionic strength was investigated in 102 mineral soil samples. By using the ratio of chloride soluble P to sulphate soluble P (”Cl-P”/”SO4-P”) instead of absolute differences it was possible to find out a more accurate relationship between soil properties and varying extraction efficiency of salt solutions. In the soils of low P intensity, the extractability ratio of P (”Cl-P’/”SO4-P”) seemed to decrease with an increase in the molar ratio of NH4F soluble P (CHANG and JACKSON’s method) to oxalate extractable Al, which indicates the improvement of the relative replacement power of sulphate. Conversely, in the samples of high or medium P intensity an increase in NH4F-P/AI had an opposite effect: the ratio ”Cl-P”/ √(”S04-P”) rather than ”Cl-P”/”SO4-P” was raised, suggesting a marked depression in the efficiency of sulphate. The superiority of sulphate, as compared to chloride, tended to be reduced also with increasing soil pH; the decrease seemed to be the greater the poorer the P status of the soil was. A theory explaining the variation in the relative extraction power of chloride and sulphate solutions was presented and the possible contributory influence of point of zero charge (pzc) was discussed.