Sorption of sulphate and distribution of total, sulphate and mineralisable sulphur in some tropical soil profiles in tanzania

Abstract

AbstractThe forest soils from Arusha generally contained more total S (129–439, average 277 μg S g−1) throughout the profile than the cultivated ones from Mbeya (32–408, average 143 μg S g−1). Total S in the surface horizons was in the range of 120–439, average 292 μg S g−1. The contents of total and organic S in the profiles were significantly (P <0.001) correlated with the contents of organic C and total N. Although both extractants—0.5M‐NH4OAC and 0.01M‐CaCl2—yielded nearly similar results, the latter tended to extract a little more sulphate than the former from organic matter rich soils. Sulphate distribution in a profile was related to sorption capacities of the soils from various horizons. Its content in the profiles was in the range of 1–34, average 15 μg S g−1, and was significantly (P <0.05) but negatively correlated with the ratios of C:N and C:S. Maximum S mineralisation occurred in the surface soil of most of the profiles. Less mineralisation or marked immobilisation took place in the subsurface soil. Mineralisation‐immobilisation relationship was mainly affected by C: S ratio of the soil. A soil C: S ratio of 200:1 was found to be critical below which net mineralisation and above which immobilisation took place.