An improved turbidimetric method for the estimation of sulphur in soil extracts

An improved manual turbidimetric method for the estimation of extractable soil sulphur was developed, which has higher sensitivity and rapidity over other manual turbidimetric methods evaluated. It involves destruction of extracted organic colloids and colour by using sodium peroxide and acetic acid, and gelatin as a stabilizing agent. The extractable soil sulphur contents measured by the proposed method were found to be more or less of similar magnitude as obtained from the ion chromatographic method. Gelatin used as stabilizing agent provided better stability to the barium sulphate colloidal system and higher sensitivity to the turbidimetric method of sulphur estimation at 420 nm wavelength as compared to Tween-80 (Polyoxyethylene sorbitan mono-oleate), glycerol, PVP (Polyvinylpyrrolidnone) and gum acacia. Irrespective of sulphur content and amount of stabilizing agent (Tween-80), consistently higher absorbance was recorded at 420 nm as compared to 600 nm wavelength. H₂O₂ or Na₂O₂ treatment for removal of organic matter through oxidation resulted into recovery of higher sulphur contents. The proposed method gives quantitative recovery of added sulphur to soil extracts. The modified method can be easily adopted in the soil testing laboratories.