Chloride and sulphate solutions as extractants for soil P: III Effect of increasing sulphate concentration on P desorption 

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.72136

Abstract

The effect of increasing sulphate concentration on P desorption was studied in 102 mineral soil samples with: a) solutions of a constant ionic strength I=0.1 adjusted with KCI and b) 0.1 M and 0.033 M sulphate solutions of different ionic strengths. Further, the efficiency of chloride and sulphate solutions of equal anion concentration (0.1 M) was compared. At a constant ionic strength, P desorption was enhanced as the sulphate concentration of the extractant increased. Even despite a much higher ionic strength the extraction power of the K2SO4 solution was greater than that of the KCI solution of the same anion concentration. Comparison of the 0.1 M and 0.033 M K2SO4 solutions revealed in 53 soil samples the extractability of P to be depressed by an increase in sulphate concentration (and ionic strength). In 49 samples, on the contrary, the 0.1 M K2SO4 solution extracted equal or greater P amounts than did the 0.033 M K2SO4. It was observed that the lower the P coverage on the oxide surfaces in the soil was, the more obviously the promoting effect of increasing sulphate concentration overruled the depression induced by increasing ionic strength, and the more superior the K2SO4 solution was as compared to the KCI solution.