SEASON DISTRIBUTION OF ORGANIC SULFUR FORMS IN SOILS AS AFFECTED BY CROPPING

The results of rape rice rotations field trails conducted in hills region between Yangtze and Huaihe Rivers indicated that content of total organic sulphur, and C-S, C-O-S and inert S in soils sampled after harvesting rape decreased by 51.3%, 60.2%, 29.3%, and 73.4% respectively compared with soils sampled before trail; content of total organic sulphur, and C-S, C-O-S and inert-S in soils sampled after harvesting rice increased by 129%, 302%, 78% and 203% respectively compared with soils sampled after harvesting rape. Compared with soils sampled before trails, percent of total organic sulphur, C-S, C-O-S and inert-S in total sulphur in soils sampled after harvesting rape decreased by 12.6, 3.2 and 18.7 respectively; percent of C-S and inert-S in total organic sulphur in soils decreased by 2.3 and 18.7 respectively ; however percent of C-O-S in total sulphur and organic sulphur in soils increased by 8.9 and 20.7 respectively Compared with soils sampled after harvesting rape, percent of total organic sulphur, C-S and inert-S in total sulphur in soils sampled after harvesting rice increased by 7.4, 6.9 and 7.7; percent of C-S and inert-S in total organic sulphur in soils increased by 7 7 and 7 2 respectively; however percent of C-O-S in total sulphur and organic sulphur in soils decreased by 21.2 and 14.9 respectively Compared with soils sampled CK treatment in corresponding period,content of C-O-S, percent of C-O-S in total sulphur and total organic sulphur in soils sampled after harvesting rape and rape-rice rotations increased by 12.4% and 64.1%, 7.2 and 14.5, and 10.8 and 17.9 respectively; however percent of inert-S in total sulphur in soils decreased by 9.6 and 13.6, and percent of inert-S in total organic sulphur increased by 12.8 and 18.6 The organic sulphur in top layer soil during rape planting decreased significantly, and that during rice planting on the opposite side This showed that rape-rice rotation systems was one of better cropping systems for maintaining soil sulphur fertility in the area