Sulfur Cycling in Agricultural Soils

Sulfur is a critical macronutrient in terrestrial ecosystems, influencing plant growth, protein synthesis and soil health. In agricultural soils, sulfur undergoes a complex cycle of transformations between organic and inorganic phases. Organic sulfur, largely bound in soil organic matter as sulfate‐esters and sulfonates, is mineralised by microbial enzymes to release inorganic sulfate (SO₄²⁻), the form most readily taken up by plants. Elemental sulfur (S⁰), often applied as a slow-release fertiliser, is oxidised by specialised bacteria to sulfate, a process sensitive to soil pH, moisture and redox conditions. Conversely, under anaerobic or waterlogged conditions, sulfate can be reduced by sulphate‐reducing bacteria to sulphide, which may volatilise or bind to soil minerals. The balance of these processes determines sulfur availability, with implications for crop yield, grain quality and environmental outcomes such as sulphate leaching or acidification. Management practices—ranging from organic amendments and precision placement of fertiliser to pH regulation—shape microbial communities and chemical conditions, thereby modulating the rate and direction of sulfur transformations.

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Sulfur Cycling in Agricultural Soils publication trend

The graph below shows the total number of articles in sulfur cycling in agricultural soils across all publications each year (not limited to Nature Index journals).

Technical terms

Sulfate (SO₄²⁻): The primary inorganic form of sulfur available for plant uptake.

Elemental sulfur (S⁰): A reduced, solid form of sulfur applied as a slow-release fertiliser that requires microbial oxidation to become plant-available.

Organo-sulfur compounds: Organic forms of sulfur in soils (e.g., sulfonates, sulfate-esters) that must be mineralised to sulfate.

Sulfur oxidation: Microbial conversion of reduced sulfur forms (S⁰, sulfide) to sulfate, influenced by pH and soil aeration.

Sulfur use efficiency (SUE): The ratio of sulfur taken up by crops to the amount applied, reflecting both agronomic performance and environmental loss.

References

1. Sulfur in agriculture. Revista Brasileira de Ciência do Solo (2012).
2. It Is Time to Develop Sustainable Management of Agricultural Sulfur. Earth's Future (2023).
3. Substrate control of sulphur utilisation and microbial stoichiometry in soil: Results of 13C, 15N, 14C, and 35S quad labelling. The ISME Journal: Multidisciplinary Journal of Microbial Ecology (2021).
4. Organic Amendments and Elemental Sulfur Stimulate Microbial Biomass and Sulfur Oxidation in Alkaline Subtropical Soils. Agronomy (2021).