Elemental Sulfur Oxidation by Thiobacillus spp. and Aerobic Heterotrophic Sulfur-Oxidizing Bacteria

The prediction of the oxidation rate of elemental sulfur (S 0 ) is a critical step in sulfur (S) fertilizer strategy to supply plant-available sulfur. An incubation experiment was conducted to determine the rate and amount of S 0 oxidation in relation to the contribution of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria. After 84 days, 16.3% and 22.4% of the total S 0 applied to the soil were oxidized at 20 and 30-C, respectively. The oxidation of S 0 proved to be a two-step process with a rapid oxidation during the first 28 days and a slow oxidation from then on. The highest oxidation rate of 12.8 μg S cm-2 d-1 was measured during the first two weeks at 30-C. At 20-C the highest oxidation rate of 10.2 μg S cm-2 d-1 was obtained from two to four weeks after start of the experiment. On an average the soil pH declined by 3.6 and 4.0 units after two weeks of experiment. At the same time the electric conductivity increased nine times. With the oxidation of S 0 the population of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased. The corresponding values for Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased from 2.9 × 10 5 and 1.4 × 10 5 g-1 soil at the start of the experiment to 4 × 10 8 and 5.6 × 10 8 g-1 soil 14 days after S 0 application, respectively. No Thiobacillus spp. was present eight weeks after S 0 application. The results suggested that oxidation of residual S 0 completely relied on aerobic heterotrophic S-oxidizing bacteria.     

过量施用氯离子的扩散: I. 土壤湿度、容重及温度的影响

Diffusion coefficients of chlorde ions in four soils of different exture with varying effective moisture content and varying bulk density from 1.1 to 1.6 g cm^3 under three different temperatures were determined by the diffusion-cell method using ^36Cl-labelled CaCl2 solution.The result showed that activation energy decreased with water content,which indicated that the threshold fro diffusion was lower at a higher soil moisture rate .Therefor,the diffusion coefficient(D) of chloride ions in soil increased consistently with soil moisture,Although a near linear increase in the diffusion coefficient with increasing soil moisture or bulk density in all the soils was observed,the increase rate in different soils was not the same.The D value increased with teperature,and with temperature increased by 10℃ in the range from 5℃to 45℃ the D valve increased by 10%-30%,averaging about 20%.     

硫杆菌以及好养异养型硫氧化菌对元素硫的氧化

The prediction of the oxidation rate of elemental sulfur (S⁰) is a critical step in sulfur (S) fertilizer strategy to supply plant-available sulfur. An incubation experiment was conducted to determine the rate and amount of S⁰ oxidation in relation to the contribution of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria. After 84 days, 16.3% and 22.4% of the total S⁰ applied to the soil were oxidized at 20 and 30 ℃, respectively. The oxidation of S⁰ proved to be a two-step process with a rapid oxidation during the first 28 days and a slow oxidation from then on. The highest oxidation rate of 12.8 μg S cm^-2 d^-1 was measured during the first two weeks at 30 ℃. At 20 ℃ the highest oxidation rate of 10.2 μg S cm^-2 d^-1 was obtained from two to four weeks after start of the experiment. On an average the soil pH declined by 3.6 and 4.0 units after two weeks of experiment. At the same time the electric conductivity increased nine times. With the oxidation of S⁰ the population of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased. The corresponding values for Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased from 2.9 × 10⁵ and 1.4 × 10⁵ g^-1 soil at the start of the experiment to 4 × 10⁸ and 5.6 × 10⁸ g^-1 soil 14 days after S⁰ application, respectively. No Thiobacillus spp. was present eight weeks after S⁰ application. The results suggested that oxidation of residual S⁰ completely relied on aerobic heterotrophic S-oxidizing bacteria.     

Evaluation of Soil Labile Phosphorus Using a Double—Labeling （^32P and ^33P） Technique

Isotopic exchangeability of phosphorus in four Chinese soils with and without P application was studied by ^32P and ^33P double-labeling technique in relation to routine chemical extractions.The results showed that Bray-I and Bray-Ⅱ reagents could extract most of the fast exchangeable P.Not all of the Olsen-P belonged to fast exchangeable P,but it was about the same quantity of fast exchangeable P in a calcareous soil and a neutral soil without P application.Sequential fractionation of the soil phosphorus showed that most of the added radioisotopes in high P fixation red soils were tightly held by iron and aluminium oxides,which could be totally extracted only by 0.1M NaOH solution.In the neutral and calcareous soils most of the radioisotopes added were loosely held on the surface of soil particles and could be extracted by anion exchange resin.Phosphate application increased the resin-P fraction significantly for all the soils studied.     

氮肥、土壤湿度和温度对稻田土壤甲烷氧化的影响

Effects of nitrogen fertilizer,soil mosture and temperature and temperature on methane oxidation in paddy soil were investigated under laboratory conditions.Addition of 0.05 g N kg^-1 soil as NH4Cl strongly inhibited methane oxidation and addition of the same rate of KCl also inhibited the oxidation but with more slight effect,suggesting that the inhibitory effect was partly caused by increase in osmotic potential in microorganism cell,Not only NH4^ but also NO3^- greatly affected methane oxidation.Urea did not affect methane oxidation in paddy soil in the first two days of incubation,but strong inhibitory effect was observed afterwards.Methane was oxidized in the treated soil with an optimum moisture of 280 g kg^-1 ,and air-drying inhibited methane oxidation entirely.The optimum temperature of methane oxidation was about 30℃ in paddy soil.while no methane oxidation was observed at 5℃or 50℃。     

草坪缓冲带限制斜坡上葡萄园敌草隆向地表水和地下水迁移效果的研究

Trichloroethylene (TCE), as one of the most common chlorinated organic compounds in soils and aquifers at many industrial sites, is carcinogenic and often recalcitrant in environment. TCE degradation in artificially contaminated soil samples was conducted using Fenton-like processes, i.e., by addition of excess hydrogen peroxide (H2O2 ). H 2 O 2 could directly oxidize TCE without addition of ferrous iron in contaminated soil. Under the optimal condition (H2O2 concentration of 300 mg kg 1 , pH at 5.0, and reaction time of 30 min), the removal efficiency of TCE in the soil was up to 92.3%. When the initial TCE concentration increased from 30 to 480 mg kg 1 in soil, the TCE removal rates varied from 89.2% to 86.6%; while the residual TCE in soil ranged from 2.28 to 47.57 mg kg 1 . Results from successive oxidations showed that the TCE removal rate with the TCE concentration of 180 mg kg 1 increased slightly from 91.6% to 96.2% as the number of successive oxidation cycle increased from one to four. Therefore, increasing the frequency of H2O2 oxidation was perhaps a feasible way to increase TCE removal rate for TCE-contaminated soil.     

Autotrophic and Heterotrophic Nitri?cation in a Highly Acidic Subtropical Pine Forest Soil

The occurrence of nitri?cation in some acidic forest soils is still a subject of debate.Identi?cation of main nitri?cation pathways in acidic forest soils is still largely unknown.Acidic yellow soil(Oxisol) samples were selected to test whether nitri?cation can occur or not in acidic subtropical pine forest ecosystems.Relative contributions of autotrophs and heterotrophs to nitri?cation were studied by adding selective nitri?cation inhibitor nitrapyrin.Soil NH~+_4-N concentrations decreased,but NO~-_3-N concentrations increased signi?cantly for the no-nitrapyrin control during the ?rst week of incubation,indicating that nitri?cation did occur in the acidic subtropical soil.The calculated net nitri?cation rate was 0.49 mg N kg~(-1)d~(-1)for the no-nitrapyrin control during the ?rst week of incubation.Nitrapyrin amendment resulted in a signi?cant reduction of NO~-_3-N concentration.Autotrophic nitri?cation rate averaged0.28 mg N kg~(-1)d~(-1)and the heterotrophic nitri?cation rate was 0.21 mg N kg~(-1)d~(-1)in the ?rst week.Ammonia-oxidizing bacteria(AOB) abundance increased slightly during incubation,but nitrapyrin amendment signi?cantly decreased AOB amo A gene copy numbers by about 80%.However,the ammonia-oxidizing archaea(AOA) abundance showed signi?cant increases only in the last 2weeks of incubation and it was also decreased by nitrapyrin amendment.Our results indicated that nitri?cation did occur in the present acidic subtropical pine forest soil,and autotrophic nitri?cation was the main nitri?cation pathway.Both AOA and AOB were the active biotic agents responsible for autotrophic nitri?cation in the acidic subtropical pine forest soil.     

Responses of Soil Enzyme Activities and Microbial Community Composition to Moisture Regimes in Paddy Soils Under Long-Term Fertilization Practices

The effects of fertilization on activity and composition of soil microbial community depend on nutrient and water availability;however,the combination of these factors on the response of microorganisms was seldom studied.This study investigated the responses of soil microbial community and enzyme activities to changes in moisture along a gradient of soil fertility formed within a long-term(24 years)field experiment.Soils(0–20 cm)were sampled from the plots under four fertilizer treatments:i)unfertilized control(CK),ii)organic manure(M),iii)nitrogen,phosphorus,and potassium fertilizers(NPK),and iv)NPK plus M(NPK+M).The soils were incubated at three moisture levels:constant submergence,five submerging-draining cycles(S-D cycles),and constant moisture content at 40%water-holding capacity(low moisture).Compared with CK,fertilization increased soil organic carbon(SOC) by 30.1%–36.3%,total N by 27.3%–38.4%,available N by 35.9%–56.4%,available P by 61.4%–440.9%,and total P by 28.6%–102.9%.Soil fertility buffered the negative effects of moisture on enzyme activities and microbial community composition.Enzyme activities decreased in response to submergence and S-D cycles versus low moisture.Compared with low moisture,S-D cycles increased total phospholipid fatty acids(PLFAs)and actinomycete,fungal,and bacterial PLFAs.The increased level of PLFAs in the unfertilized soil after five S-D cycles was greater than that in the fertilized soil.Variations in soil microbial properties responding to moisture separated CK from the long-term fertilization treatments.The coefficients of variation of microbial properties were negatively correlated with SOC,total P,and available N.Soils with higher fertility maintained the original microbial properties more stable in response to changes in moisture compared to low-fertility soil.     

温度和水分对长白山不同海拔梯度土壤有机质分解的影响

Decomposition of soil organic matter(SOM) is of importance for CO_2 exchange between soil and atmosphere and soil temperature and moisture are considered as two important factors controlling SOM decomposition. In this study, soil samples were collected at 5 elevations ranging from 753 to 2 357 m on the Changbai Mountains in Northeast China, and incubated under different temperatures(5, 10, 15, 20, 25, and 30?C) and soil moisture levels(30%, 60%, and 90% of saturated soil moisture) to investigate the effects of both on SOM decomposition and its temperature sensitivity at different elevations. The results showed that incubation temperature(F = 1 425.10, P 0.001), soil moisture(F = 1 327.65, P 0.001), and elevation(F = 1 937.54, P 0.001) all had significant influences on the decomposition rate of SOM. The significant effect of the interaction of incubation temperature and soil moisture on the SOM decomposition rate was observed at all the 5 sampling elevations(P 0.001). A two-factor model that used temperature and moisture as variables fitted the SOM decomposition rate well(P 0.001) and could explain 80%–93% of the variation of SOM decomposition rate at the 5 elevations. Temperature sensitivity of SOM decomposition, expressed as the change of SOM decomposition rate in response to a 10?C increase in temperature(Q_(10)), was significantly different among the different elevations(P 0.01), but no apparent trend with elevation was discernible. In addition, soil moisture and incubation temperature both had great impacts on the Q_(10) value(P 0.01), which increased significantly with increasing soil moisture or incubation temperature. Furthermore, the SOM decomposition rate was significantly related to soil total Gram-positive bacteria(R~2= 0.33, P 0.01) and total Gram-negative bacteria(R~2= 0.58, P 0.001). These findings highlight the importance of soil moisture to SOM decomposition and its Q_(10) value,which needs to be emphasized under warming climate scenarios.     

氯离子在土壤中的扩散: Ⅱ.动力学及热力学性质

The amounts of chloride ions diffused in four soils of different textures at the same water content under different temperature and at varied time were measured by the diffusion cell method using ³⁶Cl-labelled CaCl₂ solution. Five kinetic models were used to fit the dynamic process of the diffusion of chloride ions in the soils. It was found that Elovich equation or power function equation was the best model to describe the process. The pseudothermodynamic parameters, i.e. the net reaction energy, the activation entropy, activation enthalpy and activation free energy of the diffusion, were derived from the absolute reaction-rate theory. The results showed that these parameters decreased in the order of loessal soil > black lu soil > lou soil > yellow cinnamon soil, which indicated that the force and the heat-energy barrier to be overcome for diffusion decreased, the diffusion rate increased and the disorder of the soil-solution-ion system due to diffusion decreased successively with the texture becoming heavier in the four soils.     

Vertical Distribution of Physico-Chemical Properties and Number of Sulfur-Oxidizing Bacteria in the Buried Layer of Soil Profiles with Marine-Reduced Sulfur Compounds

We observed the presence of reduced sulfur compounds in the buried soil layer of a paddy field on Sado Island, Niigata Prefecture. We sampled the paddy field soil from 0 to 300 cm depth and analyzed the physico-chemical properties of the soil and the numbers of sulfur-oxidizing bacteria and iron-oxidizing bacteria in order to elucidate both the sulfur-oxidizing mechanism and the function of sulfur-oxidizing bacteria in the subsoil. Based on the physico-chemical properties of the soil, layers 4 and 5, which were located below 1 m in depth, were found to be potential acid sulfate soils and to be under semi-anaerobic conditions. However, the concentrations of water-soluble sulfate ions in layers 4 and 5 (88.2 to 444 mg S kg⁻¹) were higher than those in layers 1 and 3 (16.1 and 8.29 mg S kg⁻¹, respectively) and a significant number of sulfur-oxidizing bacteria (10^2–6 MPN g⁻¹) was detected in layer 4. These results suggested that the oxidation of reduced sulfur compounds by sulfur-oxidizing bacteria had occurred in layer 4. Since no iron-oxidizing bacteria were detected in any layers, and it was reported that sulfur-oxidizing bacteria such as Acidithiobacillus thiooxidans could not oxidize pyrite directly, it was considered that the oxidation of the reduced sulfur compounds in layer 4 occurred through the following processes. At first, reduced sulfur compounds such as pyrite were oxidized chemically by ferric ions to intermediary sulfur compounds such as thiosulfate ions. Subsequently, sulfur-oxidizing bacteria in layer 4 oxidized these intermediary sulfur compounds to sulfate ions. However, it was considered that the oxidation rate of the reduced sulfur compounds in layer 4 was far slower than would occur under aerobic conditions.     

Developing a Technique to Quantify Heterotrophic and Autotrophic Nitrification in Acidic Pasture Soils

Abstract

A series of laboratory incubation experiments were conducted on soils from Maindample and Ruffy in northeast Victoria and from Whittlesea in the Plenty Valley, north of Melbourne, Victoria, Australia, to develop a technique for quantifying both autotrophic and heterotrophic nitrification in acidic pasture soils. The use of a specific inhibitor of the autotrophic ammonium oxidizers (N‐serve) did not completely inhibit autotrophic nitrification in its commonly recommended concentrations (10 and 20 µg g^?1 soil) in these soils. The N‐serve concentration, which completely inhibited autotrophic nitrification, was found to be 60–80 µg g^?1. Varying soil types, pHs, and organic‐matter contents affected the optimum dose of N‐serve required for complete inhibition of autotrophic nitrification. Mixing the inhibitor with the soil after application was also important for immediate inhibition of autotrophic nitrification. Using N‐serve in combination with ¹⁵N‐labeled glycine in the Maindample soil showed that heterotrophic organisms were using the organic route for nitrification, and N‐serve did not affect heterotrophic nitrification. A lag of 12 to 24 h in complete inhibition of autotrophic nitrification by N‐serve may have occurred suggesting nitrification studies using N‐serve should include pre‐incubation of the soils with N‐serve for at least 1 day.     

Influence of nitrogen and elemental‐sulfur fertilization on sulfur oxidation and mineralization in relation to soil moisture on a calcareous soil of the Inner Mongolia steppe of China

Grassland‐livestock farming is the main agricultural activity in the Inner Mongolia steppe of China. It has been estimated that more than 80% of the grasslands suffer from sulfur (S) deficiency in this region. In an incubation study and a greenhouse experiment with alfalfa, the influence of soil moisture (40% and 70% water‐holding capacity, WHC), nitrogen (0 and 200 mg N (kg soil)^–1 as NH₄NO₃), and elemental sulfur (eS; 0 and 300 mg S (kg soil)^–1) amendments on the apparent eS oxidation, eS‐oxidation rate, net S‐mineralization rate, and S uptake of alfalfa were studied. After 28 d of incubation, the eS‐oxidation rate was four times higher at 70% than at 40% WHC if no N was applied. With N application, soil moisture had only minor effects on eS oxidation during the whole incubation period. In the greenhouse experiment, lower values for eS‐oxidation rate and net S‐mineralization rate were found if no N was applied. Application of N and eS significantly increased alfalfa growth and S uptake. The results of both experiments suggest that combined N and eS applications are the best way to alleviate S deficiency on these calcareous soils.     

Conversion of forest to agricultural land affects the relative contribution of bacteria and fungi to nitrification in humid subtropical soils

Land-use and management practices can affect soil nitrification. However, nitrifying microorganisms responsible for specific nitrification process under different land-use soils remains unknown. Thus, we investigated the relative contribution of bacteria and fungi to specific soil nitrification in different land-use soils (coniferous forest, upland fields planted with corn and rice paddy) in humid subtropical region in China. ¹⁵N dilution technique in combination with selective biomass inhibitors and C₂H₂ inhibition method were used to estimate the relative contribution of bacteria and fungi to heterotrophic nitrification and autotrophic nitrification in the different land-use soils in humid subtropical region. The results showed that autotrophic nitrification was the predominant nitrification process in the two agricultural soils (upland and paddy), while the nitrate production was mainly from heterotrophic nitrification in the acid forest soil. In the upland soils, streptomycin reduced autotrophic nitrification by 94%, whereas cycloheximide had no effect on autotrophic nitrification, indicating that autotrophic nitrification was mainly driven by bacteria. However, the opposite was true in another agricultural soil (paddy), indicating that fungi contributed to the oxidation of NH₄⁺ to NO₃^?. In the acid forest soil, cycloheximide, but not streptomycin, inhibited heterotrophic nitrification, demonstrating that fungi controlled the heterotrophic nitrification. The conversion of forest to agricultural soils resulted in a shift from fungi-dominated heterotrophic nitrification to bacteria- or fungi-dominated autotrophic nitrification. Our results suggest that land-use and management practices, such as the application of N fertilizer and lime, the long-term waterflooding during rice growth, straw return after harvest, and cultivation could markedly influence the relative contribution of bacteria and fungi to specific soil nitrification processes.     

Effects of seed-placed sulfur fertilizers on canola,wheat, and pea yield; sulfur uptake; and soil sulfate concentrations over time in three prairie soils

The form of sulfur fertilizer can influence its behavior and crop response. A growth chamber study was conducted to evaluate five sulfur fertilizer forms (ammonium sulfate, ammonium thiosulfate, gypsum, potassium sulfate, and elemental sulfur) applied in seed row at 20 kg S ha^?1 alone, and in combination with 20 kg phosphorus pentoxide (P₂O₅) ha^?1, to three contrasting Saskatchewan soils. Wheat, canola, and pea were grown in each soil for 8 weeks and aboveground biomass yields determined. The fate of fertilizer was evaluated by measuring crop sulfur and phosphorus concentration and uptake, and supply rates and concentrations of available sulfate and phosphate in the seed row. Canola was most responsive in biomass yield to the sulfur fertilizers. Sulfate and thiosulfate forms were effective in enhancing soil-available sulfate supplies in the seed row, crop sulfur uptake, and yield compared to the elemental sulfur fertilizer. Combination of sulfur fertilizer with monoammonium phosphate may provide some enhancement of phosphate availability, but effects were often minor.     

The response of a high-yielding canola hybrid to sulfur fertilization in three contrasting Saskatchewan soils

Abstract

Canola (Brassica napus) is the primary oilseed crop in western Canada; however, it is often grown on sulfur (S)-deficient soils. Moreover, canola has a high S demand compared to cereals and, therefore, is particularly sensitive to S deficiency. This study examined the growth and nutrient uptake responses of a high-yielding canola hybrid cultivar to S fertilization when grown on three contrasting soils differing in S fertility, with and without the addition of fertilizer S. The soils were collected from three soil-climatic zones within Saskatchewan (Brown, Black, and Gray) and three different fertilizer S forms were used: ammonium sulfate (AS); ammonium thiosulfate (ATS); and a composite fertilizer containing nitrogen (N), phosphorus (P), and S (NPS; 50-50 blend of sulfate (SO₄) salt and elemental S). Sulfur fertilization increased the canola biomass, along with plant uptake of N, P, and S on all three soils. Fertilizer S use efficiency (i.e. recovery) ranged from 11-75%. For all three soils, the general trend among fertilizer S forms for biomass, nutrient uptake, and fertilizer use efficiency was AS?>?ATS?>?NPS. The greatest differences were observed with the Gray soil, which had the poorest S fertility. Residual soil SO₄ after harvest was greater for ATS and NPS; reflecting continued oxidation of thiosulfate and elemental S to SO₄. Principal component analysis demonstrated the importance of tissue N:S ratio as a key diagnostic measurement related to canola growth and nutrient uptake in S-deficient soils.     

土壤磷扩散规律及其能量特征的研究Ⅱ.施磷量及水肥温相互作用对磷扩散的影响

非饱和土壤在施磷量０－４００ｍｇ／ｋｇ下的磷自扩散系数随施磷量近线性增加,但增加的幅度以缓冲性能小的轻质土壤最高。不同土壤磷扩散受土壤水分,施磷量和温度等因素相互作用的影响程度不同,为表征这种差异利用其多元非线性拟合方程的偏微分,本文提出了磷扩散率的水分系数,肥料系数和温度系数等概念。     

长期定位施肥下黑土呼吸的变化特征及其影响因素

阐明长期不同施肥下的土壤呼吸特征及其影响机制对黑土区固碳减排研究至关重要。该研究基于1990年开始的国家土壤肥力与肥料效益监测网站-吉林省公主岭市黑土监测基地,选取不施肥(CK)、单施氮磷钾肥(NPK)、无机肥配施低量有机肥(NPKM1)、1.5倍的无机肥配施低量有机肥(1.5(NPKM1))、无机肥配施高量有机肥(NPKM2)和无机肥配施秸秆(NPKS)6个处理,明确了长期不同施肥下土壤总呼吸和异养呼吸的季节变化特征,并分析了土壤温度、水分、微生物量碳氮、铵态氮、硝态氮与土壤呼吸和异养呼吸的关系。结果表明:长期有机无机肥配施可以显著提高土壤有机碳、全氮、土壤速效磷、有效钾的含量和土壤活性有机碳库组分含量(P0.05);与不施肥相比,长期有机无机肥配施和无机配施秸秆处理分别显著增加土壤呼吸及异养呼吸碳累积排放量56.32%~86.54%和70.01%~100.93%;根系呼吸对土壤呼吸的整体贡献为23.68%~34.30%;相关分析表明,土壤呼吸速率和异养呼吸速率与土壤温度极显著正相关(P0.01),与土壤含水率呈显著负相关(P0.01),土壤温度可以分别解释土壤呼吸和异养呼吸变化的42.79%和39.61%;土壤微生物量碳氮、土壤硝态氮均与土壤呼吸速率和异养呼吸速率极显著相关(P0.01),土壤微生物量碳氮、土壤硝态氮可以分别解释土壤呼吸和异养呼吸变化的78.42%和77.18%,58.33%和56.79%,59.29%和59.14%;土壤铵态氮虽然显著影响土壤呼吸速率(P0.05),可以解释土壤呼吸变化的5.56%,但其对异养呼吸速率的影响不显著。综合来看,微生物量碳对土壤呼吸及异养呼吸的影响最大,而土壤含水率(15%)越高则土壤呼吸越弱;无机配施秸秆处理可以提高土壤碳库组分含量,且作物生育期内土壤呼吸及异养呼吸碳累积释放量均低于等氮量下施用有机肥(NPKM1)的处理,为最佳的农田管理措施。     

Influence of soil moisture on sulphur oxidation in brown earth soils exposed to atmospheric pollution

Summary Laboratory studies were conducted to determine the influence of soil moisture on S oxidation in atmospheric-polluted brown earth soils. Elemental S was oxidized to sulphate over a wide range of soil moisture treatments (10%–60% w/w), but occurred optimally at around 40%–50% soil moisture content (0.08 MPa). Thiosulphate and tetrathionate were found only in soils incubated at low moisture contents. S-oxidation generally acidified the soils, but an increase in soil pH occurred at high moisture levels, where soils were waterlogged. The S oxidative ability of soil samples collected at monthly intervals and incubated with elemental S in the field-moist state was also strongly influenced by soil moisture content. The rate of sulphate production was greatest in the brown earth soil exposed to heavy atmospheric pollution from a coking works.