Study on test methods for soil available S and critical levels of S deficiency

The methods and critical levels for assessing soil available S were investigated using correlation studies by pot experiments and calibration studies by field trials. In pot experiments,6 chemical extractants were selected to extract soil available S and determine S in the solution by ICP?AES and terbidimetric methods(T),respectively,for evaluation of soil available S with 18 soils by comparing the relationship between soil S test value and the total S uptake or relative dry matter yield of corn and rice. Results indicated that all extractants could extracted organic S and 0.5molL-1 NaHCO3 extracted the most. Phosphate solution could extracted more available S than chloride solution in acid soils. Soil available sulfur extracted by 0.01molL-1 Ca(H2PO4)2 solution and determined by terbidimetric method was found to be correlated well with corn and rice responses,and confirmed the superiority to other indices. In field trials,sulfur fertilizers could increase crops yield,such as winter wheat,corn,soybean,oil seed rape and rice. The critical levels of 90% relative grain yield by 0.01molL-1 Ca(H2PO4)2 T were 21 1mgkg-1 and 23 8mgkg-1 for upland soils and paddy fields,respectively.