Evaluation of extractants for predicting availability of sulphur to mustard in inceptisols

Mustard (Brassica juncea) is an important oilseed crop of northern India, which is widely grown in Delhi and adjoining States. This crop has a relatively high requirement of sulphur (S), and is sensitive to S-deficiency. For predicting response of mustard to S application, several extractants have been tried with variable results. Since selection of a promising extractant for a particular soil needs careful consideration, the present investigation was planned to select the most promising extractant to predict the availability of S to mustard grown on Inceptisols of Delhi. For this purpose, a greenhouse experiment was conducted with twenty soils (two from each of ten important soil series from the cultivated soil belt of Delhi. Nine extractants, commonly used for estimating the availability of S, were evaluated and S in soil extract and in plant digest was estimated using the turbiditimetric method. The results indicate that the phosphate salt methods extracted comparatively more S than other extractants. The amount of S extracted by these extractants was found in the following order: KH(2)PO(4)-500 ppm P > Ca(H(2)PO(4))(2)-500 ppm P > 0.001 M HCl > NaOAc+HOAc > heat soluble S > 0.15% CaCl(2) > 1% NaCl > water soluble S > NH(4)OAc+HOAc. Simple correlation coefficients of the amounts of S extracted by different extractants and the forms of S with the plant parameters were worked out. To determine the combined effect of soil characteristics on S extraction by different extractants, stepwise multiple regression analysis was carried out. Based on this study, the suitability of the extractants for mustard crops in Inceptisols of Delhi may be arranged as follows: 0.15% CaCl(2) > water soluble S > 0.001 M HCl > Ca(H(2)PO(4))2-500 ppm > 1% NaCl > NH(4)OAc+HOAc > NaOAc+HOAc > KH(2)PO(4)-500 ppm P > heat soluble S.