Although S deficiency has been reported in plants worldwide, the belowground biogeochemical cycling of S is not well known. The combined use of mineral fertiliser and manure is regarded as a suitable fertilisation strategy to maintain agricultural soil productivity. A long-term (1964–2018) field experiment was selected to determine how manure application affects soil gross S mineralisation and immobilisation, and plant-derived organic S, cysteine (Cys), and methionine (Met) biological decomposition by ³⁵S, ¹⁴C, and ¹⁵N labelling. High organic manure application did not increase organic S content in the topsoil owing to the high mineralisation rate, but it increased the organic S content in subsoil where mineralisation rates were relatively lower. S immobilisation dominated gross S fluxes, and the highest SO₄²⁻ immobilisation rates were recorded under medium manure application. Most plant-derived protein S was decomposed to SO₄²⁻ after 15 min, and only approximately 30% was retained in the microbial biomass. Protein bioavailability may have a more dominant role in soil S mineralisation than soil S-containing amino acids, owing to its higher concentration. The immobilisation of SO₄²⁻ was considerably slower than that of proteins and amino acids, which indicates that the microorganisms preferred organic S over inorganic S and that the use is driven by C demand rather than S demand. Moreover, the microbial community released SO₄²⁻ and NH₄⁺ after taking up Cys and Met, and the imbalance of elements between substrates and microbes played a dominant role in soil S cycling. This process was strongly regulated by the nature of the substrate; less SO₄²⁻ was released from Met than from Cys. Among the three important processes for organic S decomposition—the uptake by microorganisms, SO₄²⁻ release, and SO₄²⁻ reuse—manure application had a greater effect on SO₄²⁻ release during organic S decomposition. Overall, manure application increased S bioavailability owing to high S fluxes, and high- and low-molecular weight organic S could be rapidly decomposed to SO₄²⁻.

尽管世界范围内的植物中都有硫缺乏的报道，但硫的地下生物地球化学循环尚不清楚。化肥与粪肥配合使用被认为是保持农业土壤生产力的适宜施肥策略。选择了一项长期（1964-2018）田间试验来确定施肥如何影响土壤总硫矿化和固定化，以及植物来源的有机硫、半胱氨酸 (Cys) 和蛋氨酸 (Met) 通过³⁵ S、¹⁴ C 和¹⁵N 标签。由于高矿化率，高施有机肥并没有增加表层土壤中有机 S 的含量，但它增加了矿化率相对较低的底土中的有机 S 含量。S 固定化主导了总 S 通量，最高 SO ₄ ^2-固定化率记录在中等施肥条件下。大多数植物来源的蛋白质 S在 15 分钟后分解为 SO ₄ ^2-，只有大约 30% 保留在微生物生物量中。与土壤含硫氨基酸相比，蛋白质生物有效性在土壤 S 矿化中可能具有更重要的作用，因为其浓度更高。SO ₄ ²⁻的固定比蛋白质和氨基酸慢得多，这表明微生物更喜欢有机 S 而不是无机 S，并且使用是由 C 需求而不是 S 需求驱动的。此外，微生物群落吸收Cys和Met后会释放SO ₄ ^2-和NH ₄ ⁺，底物和微生物之间的元素失衡在土壤S循环中起主导作用。这个过程受到底物性质的强烈调节。从 Met 释放的SO ₄ ^2-少于从 Cys 释放的SO ₄ ^2-。有机硫分解的三个重要过程——微生物吸收、SO ₄ ^2-释放和SO ₄ ^2-再利用——在有机硫分解过程中，施肥对 SO ₄ ^{2- 的}释放有更大的影响。总体而言，由于高 S 通量，施肥增加了 S 的生物利用度，并且高分子量和低分子量有机 S 可以快速分解为 SO ₄ ^2-。