EVALUATION OF SULFUR FERTILITY OF SOILS UNDER RICE-BASED CROPPING SEQUENCES AND RICE RESPONSE TO SULFUR APPLICATION

Studies on S status of soils under rice-based cropping sequences revea led that out of 39 soils sampled from rice-growing areas in the distri ct of Sheikhupura, none was deficient in S. The sulphur status of the soils under various cropping systems was very similar with slightly gr eater amounts of total, NaHCO3 and KH2PO4 S being determined in the ri ce-fallow than in the rice-wheat sequence. The lowest value of these f orms was observed for the rice-berseem sequence. Soil properties such as EC, pH, CaCO3 and CEC were not correlated with NaHCO3, KH2PO4, orga nic and total S. However, clay showed significant correlation with org anic and total S. Similarly organic matter display low but significant correlation with organic S in the soils. Flood water, NaHCO3 (aerobic and anaerobic) and KH2PO4 S were significantly correlated with S conc entration in dry matter but organic and total S were not correlated wi th it. None of the S forms was correlated with dry matter yield and S uptake. Dry matter yield was significantly correlated with S uptake bu t not with S concentration. At a constant level of N application, eith er from urea or ammonium sulphate, S concentration and its uptake both in straw and grain and productive tiller, and straw and grain yield w ere better with ammonium sulphate than with urea. This indicates a pos sible response of rice to S application even when the native S status of the soil is well above the critical level.