Enzymatic Activities Involved in S- Transformations and Their Mutualistic Relationships With Inorganic-S Components and Distributions in Salt Affected Soils

Abstract

A comprehensive experimental study was conducted at three locations reflecting the semi-arid conditions of Kafr El-Sheikh governorate.The selected soils are slightly salt-affected and irrigated in non-rational rates for a long-time with different sources of wastewaters, under different drainage conditions. A novel conceptual diagram was constructed to integrate the main labile and stable inorganic-S fractions and the ways by which their amounts are determined and calculated.The aim of this study was to assess the biochemical activity of some soil enzymes involved in S-transformations and gain informations about the standing stocks and distributions of all inorganic-S fractions in studied soils under different drainage conditions. Statistical of treatment of the obtained data, could be summarized as follows:  Grand mean value of biological enzymes activity was 328.4 nanomoles SCNreleased.g -1 soil.hour -1 for rhodanese, meanwhile, dehydrogenases activity was 9.41 µg TPF produced. g -1 soil. hour -1 .  Total-S pool recorded 300 mg S. kg -1 soil, its standing stock 257.48 kg S. fed -1 , which was within the normal range reported in other regions.  Inorganic-S value was 111.3 mg S. kg -1 soil, its standing stock 96.6 kg S. fed -1 .Percentage total-S in inorganic-S accounted for 37.7%, which was only a minor fraction compared to the major fraction of organic-S. However, the content of this fraction was higher than reported from temperate and subtropical regions.  Inorganic sulfate-S content was 106.2 mg S. kg -1 , its percentage distribution expressed as % of total-S and of inorganic-S accounted for 36.3% and 95.6, which was the dominate fraction of inorganic-S fraction. This fraction was more pronounced in studied semi-arid soils in comparison with those reported in other regions. Its value had a positive correlation with soil clay content.  Easily soluble and adsorbed sulfate-S contents were 82.1 and 1.8 mg S. kg soil, their percentage distributions accounted for 77.6% and 1.3% of inorganic sulfate-S. Soluble sulfate-S was the major S form of inorganic sulfate-S and at the same time was greater in comparison with reported in literature. Adsorbed sulfate-S had the opposite trend and negative correlation with soil pH as well as positive with clay content.  Dissolved sulfate-S fraction contains insoluble sulfate-S plus Co-precipitated/Cocrystallized with CaCO3. Its value was 22.3 mg S-kg -1 soil accounted for 21.1% of inorganic sulfate-S, which was positive correlated with CaCO3 content.  Inorganic non-sulfate-S value was 5.2 mg S. kg -1 , accounted for 4.4% of inorganic-S, which was greater than reported in other regions and had a positive correlation with CaCO2 content. Oxygenic highly oxidized-S form and lowly oxidized-S plus reduced-S forms were 4.2 and 0.99 mg S. kg -1 soil, accounted for 84.2% and 15.8% of inorganic non-sulfate-S.El-Kammah, M.A.M. 6218 Contents total-S pool and all fractions of inorganic-S as well as their percentage distributions had their maximum values in traditional drained soils in w...