Sulphur-enriched municipal solid waste compost: strategies to enhance sulphur dynamics, soil biological activity and mustard productivity

Sulphur-enriched municipal solid waste (MSW) compost may contribute to soil fertility, but its agronomic performance depends on formulation and integration with mineral fertilizers. This field study conducted during the Rabi season of 2021–2022 evaluated soil sulphur fractions, enzyme activities andmustard ( Brassica juncea L.) productivity under six treatments in a randomized block design. Two compost formulations were tested: S1, comprising municipal organic waste and gypsum (2:1, w/w), and S2, comprising municipal organic waste, gypsum, phosphogypsum, pressmud and elemental sulphur (4:1:1:1:1, w/w). Each formulation was applied alone or with 50% of the recommended dose of mineral fertilizers (RDF), alongside unfertilized and 100% RDF controls. S2 combined with 50% RDF recorded the highest of available, water-soluble, HCl-extractable, and total sulphur, concentrations (17.2, 14.8, 15.6, and 98 mg kg -1 , respectively) and sulphur availability index (7.86). This treatment also noticed the highest arylsulfatase (217 µg PNP g -1 soil h -1 ) and dehydrogenase (17.3 µg TPF g -1 soil h -1 ) activities, with seed yield 11.6% higher than under 100% RDF. The highest post-harvest Walkley–Black concentration (0.56%) occurred with S1 combination with 50% RDF. These results support further evaluation of S2 with reduced mineral-fertilizer inputs for mustard production. However, differences between formulations cannot be attributed solely to sulphur sources, and the measurements do not establish sustained sulphur release or microbial mechanisms. Validation across sites and seasons is required before recommending mineral-fertilizer substitution.