EFFECT OF ORGANIC RESIDUE AMENDMENT ON MINERALIZATION OF SULFUR IN FLOODED RICE SOILS UNDER LABORATORY CONDITIONS

This study was undertaken to assess the mineralization of sulfur (S) i n laboratory conditions of three rice soils (Joydebpur, Faridpur, and Thakurgaon), receiving the following treatments: 1) control, 2) rice s traw (Oryza sativa L.), and 3) pea vine (Pisum sativum L.). The organi c residue (25 mg g(-1)) was added and mixed with soil and glass beads (1:1, soil to bead ratio) and placed into a Pyrex leaching tube. The s oils were flooded and incubated at 35 degrees C, after which they were leached with deionized water at 1, 2, 4, 8, and 12 weeks for analysis of SO4 and other chemical properties in the leachates. Potentially mi neralizable S (S-o) and C (C-o) pools and first-order rate constants ( K-s for S and K-c for C) in soils amended with rice straw and pea vine under flooded conditions were estimated using an exponential equation . The S-o and K-s varied considerably among the soils and types of add ed organic residues, and their values in rice straw and pea vine range d from 8.70 to 29.55 and 0.124 to 0.732 mg S kg(-1) wk(1), respectivel y. Except for the Thakurgaon soil, the S-o and K-s values in Joydebpur and Faridpur soils were higher in the unamended treatments. Higher S- o values in the unamended soils were probably due to less microbial ac tivity to mineralize organic S from organic residues. The results indi cate that the amount of SO4 in flooded soils amended with organic resi dues are dependent on soil type, nature of organic residues, and time of incubation. The C-o and K-c values under flooded incubation were hi gher in residue amended soils than in unamended soils. Pea vine treate d soils had higher C-o and K-c values than the soils treated with rice straw.