Determination of sulphur in some agricultural soils in the Philippines by neutron activation analysis

Seven soil samples from different areas in the Philippines were extracted with 1N NH4OAsub(C) (pH4.8) and the extracts analyzed for S by turbidimetric and nuclear activation analysis (NAA), P by Trueg's method and Cl by Mohr titration. The P and Cl content were used to correct for effects on radioactivity of the samples after neutron activation using a multiple regression equation based on activation of standard samples of S, P, and Cl. The results showed that in some cases NAA gave higher S than turbidimetric method. At relatively lower S contents, NAA gave higher amounts of S. At higher S contents, the turbidimetric method gave higher amounts of S and the difference increased as S content by turbidimetric method increases. Based on the present results, it is difficult to determine which method underestimates or overestimates the S content of the soil extract. Further studies have to be undertaken to improve the NAA techniques as applied to S determination in soils, and to provide a good basis for comparison