The Relationship of Soil Sulfur with Glomalin-Related Soil Protein and Humic Substances under Different Mineral and Organic Fertilisation

In recent years, sulfur inputs into the soil have greatly diminished due to the significant decrease in SO2 emissions. Plant nutrients, like sulfur, can be released by the mineralisation of soil organic matter (SOM), which is a complicated mixture of substances (or fractions) like glomalin-related soil protein (GRSP) and fulvic acids (FA), humic acids (HA), humic substances (HS) and others. GRSP, FA, HA, and HS content, as well as the content of mineral and organic fractions of sulfur, was determined in different mineral and organic fertiliser treatments of the long-term field experiment. Using these results, the sulfur content in GRSP was calculated based on the soil's organic matter carbon and soil's organic bound sulfur (CSOM/SORG) ratio. Sulfur content in GRSP was 4.08-5.46 (easily extractable GRSP), 9.77-15.7 (difficultly extractable GRSP), and 13.9-21.1 (total GRSP) mg S/kg of soil. Overall, the application of the organic fertiliser caused an increase in S content bound to GRSP. A strong significant relationship was also observed between GRSP fractions and soil organic sulfur. A similar relationship was also observed for the HA and HS with organic sulfur.