Sulphur flow in soil-plant system with long-term agricultural practices on a Vertisol

Sulphur (S) deficiency is widespread in agricultural fields across the globe. Its flow in the soil-plant system under different management practices is too poorly understood to strategize S fertilisation with increased efficiency. Accordingly, an attempt was made to elucidate the pathways of S flow in soils and to plants under organic, inorganic, and integrated nitrogen (N) management practices using a 30-year-old long-term field experiment planted with sorghum in the semi-arid tropics. Partitioning soil S into pools, we observed that exchangeable (4.2%) and adsorbed (4.6%) pools constituted a small part of total soil S but contributed mainly to S nutrition (46% and 33%) of sorghum; it also contributed to the variability of S extractable by six commonly used extractants. Using multiple criteria, the superiority of monocalcium phosphate as an extractant for assessment of S in Vertisols was established. Among the N management practices, integrated N management performed better in supplying S in soils and to sorghum, and excelled, both in retention (35.9% of applied) and utilisation (13%) of S, curbing its losses (51.1%) from the system, over the organics (26%, 8.4%, and 65.6%, respectively) and inorganic (11.6%, 7.1%, and 81.3%, respectively) management practices. The integrated management practices with farmyard manure (FYM) excelled in improving S in soils, including economics. Out of the organics, FYM was more effective in improving S availability in soils and its nutrition of the crop over the crop residue, and green manure. Changes in organic C, and oxides and hydroxides of Fe and Al in soils are the keys governing the flows of S in the soil-plant system. A detailed pathway of the increased efficacy of S fertilisation upon conjoint application of N sources over the others was highlighted for adoption in Vertisols of semi-arid tropics.

Automated summary

Sulphur deficiency is a common problem in agricultural fields worldwide, and efficient fertilization strategies are still needed. Integrated nitrogen management performs better in supplying and retaining sulphur in soils and plants, while reducing sulphur losses. Farmyard manure is an effective method to improve sulphur availability in soils. Changes in organic carbon, iron, and aluminum oxides and hydroxides in soils are key factors influencing sulphur flow in the soil-plant system.