Sulphur speciation and availability in long‐term fertilized soil: evidence from chemical fractionation and SK‐edge XANES spectroscopy

Abstract

SummaryKnowledge of sulphur (S) speciation in soil following applications of chemical and organic fertilizers is important for understanding the availability and fate of S in agricultural ecosystems. Sulphur speciation of the soil in three fields, which are part of the National Long-term Monitoring Network of Soil Fertility and Fertilizer Effects of China, was investigated with a combination of a wet-chemical fractionation scheme and S K-edge X-ray absorption near edge structure (XANES) spectroscopy. Treatments of the soil included no fertilizers (control), regular applications of nitrogen, phosphorus and potassium fertilizers (NPK), or of NPK plus organic manures (MNPK) since 1990. Soil samples were taken from the topsoil (0-20 cm) and subsoil (20-40 cm) horizons in 2011. Chemical fractionation showed that available sulphate was the predominant inorganic S species in the Eutric Cambisol, whereas HCl-extractable sulphate was the main inorganic S species in the Haplic Phaeozem and Calcaric Cambisol. Organic S accounted for up to 77% of total S in all soil samples. Results from the fractionation (inorganic S plus ester-S) and XANES analysis (oxidized S) were correlated (r = 0.585, P < 0.01), which confirmed the presence of HCl-extractable sulphate and the speciation of residual S in soil. Long-term application of organic manures facilitated significantly the accumulation of intermediate and reduced S species and increased total and organic S in the soil (P < 0.01). In contrast, the application of chemical fertilizers (NPK) had little effect on the distribution of organic S species compared with the control. Atmospheric deposition was identified as an important source of S. The combination of chemical fractionation and XANES spectroscopy provided complementary information on the availability and speciation of S in soil.

Sulfur Distribution and Availability in Alkaline Subtropical Soils Affected by Organic Amendments

“…Yang et al (2007) observed a significant increase in Cbonded S, organic S, and total S contents in the soil after FYM application. Xu et al (2016) reported that long-term use of organic manures significantly facilitated the accumulation of C-bonded S, residual S, and increased total and organic S contents in soils.…”

“…Organic C content, type of fertilizers used especially the organic fertilizers, and soil pH are the main factors influencing sulfur distribution to soil and its release into plant-available form (Gao et al 2017). Conversion of organic S into inorganic sulfate and the reverse processes play a vital role in the biogeochemical cycling of S and its bioavailability (Blum et al 2013;Xu et al 2016). Studies have shown that organic amendments help to maintain adequate soil S reserves, particularly in organic S forms such as the C-bonded S and ester sulfate S (Wyngaard and Cabrera 2015;Xu et al 2016).…”

“…Conversion of organic S into inorganic sulfate and the reverse processes play a vital role in the biogeochemical cycling of S and its bioavailability (Blum et al 2013;Xu et al 2016). Studies have shown that organic amendments help to maintain adequate soil S reserves, particularly in organic S forms such as the C-bonded S and ester sulfate S (Wyngaard and Cabrera 2015;Xu et al 2016). Both of these organic S fractions may be converted into inorganic sulfate through microbialmediated processes (Solomon et al 2011).…”

“…Concerns regarding changes in sulfur fractions in soil prompted studies on sulfur speciation under different management systems (Yang et al 2007;Blum et al 2013). Conflicting results were reported regarding organic amendments effect on S transformation and distribution in soil (Balik et al 2009;Xu et al 2016;Yang et al 2007). Two important questions in this regard were as follows: (i) how do organic amendments affect microbial properties and sulfur fractions in soils, and (ii) what is the relationship of sulfur fractions to available S pool in soil?…”

Sulfur speciation in a tropical soil under long-term no-till amended with lime and phosphogypsum

“…This way, Synchrotron-based X-ray absorption near-edge structure spectroscopy (XANES) emerged as an important noninvasive tool to direct determination of S forms in soils . XANES can help overcome the traditional methodology limitations and provide molecular-level information about S species in soil (Xu et al, 2016).…”