Characterization of sulfur retained by soils exposed to sulfur dioxide

Abstract

Soils have substantial capacity for sorption of sulfur dioxide (SO₂) but little is known about the nature of the sorbed S. Three surface soils varying in pH, organic matter, CaCO₃ equivalent and surface area were exposed to air containing 5% SO₂ and subsequently analyzed by ten different procedures to characterize the sorbed S. Most of the sulfur retained by soils after exposure to SO₂ could be recovered as CaCl₂‐extractable S, Ca(H₂PO₄)₂‐extractable S, or S released as H₂S by hydriodic acid (HI). Only small amounts of sulfur could be recovered as tetrachloromercurate (TCM)‐extractable S, S released as SO₂ by HCl, or S released as H₂S by HCl + Zn, HCl + Sn, or Raney Ni and NaOH. However, large amounts of S released as SO₂ by HCl were recovered from the air‐dry Webster and the moist Storden soils indicating that SO₂ sorption is influenced by organic matter in air‐dry soils and by CaCO₃ in moist soils.     

Evaluation of calcium dihydrogen phosphate solution as an extractant for inorganic sulfate applied to soils

Abstract

To evaluate conventional calcium dihydrogen phospahte [Ca(H₂PO₄)₂] solution containing 500 mg P/L as an extractant for soluble plus adsorbed sulfate (SO₄), we added known amounts of SO₄ to 10 soil samples differed in clay mineral composition and extracted with Ca(H₂PO₄)₂ solution. The experimental results showed that the five successive extractions at a soihsolution ratio of 1:10 could quantitatively recover the added SO₄, and there was little effect of air‐drying the soils after addition of SO₄. Based upon these experimental results, we concluded that the Ca(H₂PO₄)₂ extraction is an excellent method for determining soluble plus adsorbed inorganic SO₄ in soils.     

Comparison of some methods for determination of sulfate in soils

Abstract

Sulfate (SO₄ ^2‐) is present in soils as salts of various metals, and the different metals associated with sulfate may influence adsorption of SO₄ ^2‐by soils. The analytical method used for determination of SO₄ ^2‐could be affected by the type of metal associated with the SO₄ ^2‐. Four analytical methods based on different principles were evaluated for determination of SO₄ ^2‐in different metal salts and in soil extracts obtained with three extractants {0.1M lithium chloride (LiCl), 0.15% calcium chloride (CaCl₂), and 500 mg P/L as calcium phosphate [Ca(H₂PO₄)2]}. The analytical methods were: (i) a methylene blue (MB) colorimetric method after the reduction of SO₄ ^2‐to hyrogen sulfide (H₂S), (ii) an ion Chromatographie (IC) method, (iii) a turbidimetric (TD) method, and (iv) an indirect barium (Ba) atomic absorption spectrophotometric (SP) method. The recovery of SO₄ ^2‐associated with various mono‐, di‐, and tri‐valent metals was quantitative by the MB method. But, trivalent metals, such as aluminum (Al), indium (In), lanthanum (La), and scandium (IC), decreased the recovery of SO₄ ^2‐by the other three methods. The MB and IC methods gave similar values for SO₄ ^2‐in soils by using the three extractants. The TD and SP methods gave variable results and, in general, underestimated the amounts of SO₄ ^2‐in soils. Among the four methods, the MB and IC methods were the most accurate and precise.     

Extraction of soil‐available phosphate,nitrate, and sulphate ions using ion exchange membranes and determination by ion exchange chromatography

Abstract

In recent years, ion exchange membranes (IEM) have been used successfully to determine the availability of soil nutrient elements for plants. In general, the procedures proposed are applied to the determination of a single ion, and in only a few of these studies, the selectivity of these IEM was considered. Therefore, this work was conducted (a) to find the most suitable extraction conditions for phosphate (H₂PO₄ ^‐), nitrate (NO₃ ^‐), and sulfate (SO₄ ^2‐) in soils by IEM and their subsequent determination by ion chromatography, (b) to test the effectiveness and selectivity of IEM, (c) to compare the results obtained by IEM with the common procedure for determining the availability of the soil nutrient elements, and (d) to verify whether a relation exits between the concentration of phosphorus (P) extracted by IEM and the plant P requirement. The soil samples used for this study were Humic Cambisols located in four forest plots under natural conditions and four plots fertilized with 100 kg P ha^‐1 as triple superphosphate. The efficacy of the IEM was high (85% for SO₄ ^2‐, and 92% for H₂PO₄ ^‐ and NO₃ ^‐). Statistically significant correlations were obtained between the H₂PO₄ ^‐ extracted by IEM and the H₂PO₄ ^‐ obtained by the Bray P1 procedure (r²=0.936) and with the H₂PO₄ ^‐ extracted using Saunders and Williams (1955) procedure (r²=0.370). The correlation obtained between the amount of NO₃ ^‐ extracted with IEM and that obtained using 2M potassium chloride (KCl) was also highly significant (r²=0.828). The IEM extraction allowed to know in a single extraction process and a single subsequent measurement by ion chromatography the concentrations of soil available H₂PO₄ ^‐, NO₃ ^‐, and SO₄ ^2‐ ions, which are of great plant nutrition interest. Phosphorus extractable with IEM yielded a close relationship with biomass production and could be used for determining the P requirement of these forest trees.     

Ion chromatographic method for determination of oxyanions in solutions equilibrated with soils

Abstract

Methods based on simultaneous determination of oxyanions in soil solution are needed for studies of competitive adsorption of several oxyanions by soils. An accurate and precise ion Chromatographie (IC) method was developed for simultaneous determination of PO₄ ³‐, AsO₄ ³% SeO₄ ^2‐, WO₄ ^2‐, and MoO₄ ^2‐ in solution equilibrated with soil. The water extract obtained was analyzed by a Dionex 2002i IC after filtering (0.45‐μm membrane filter). The IC unit was fitted with a guard column (AG‐3), a separator column (AS‐3), a 50‐μL injection loop, and a micromembrane suppressor system eluted with 12.5 mM H₂SO₄. A solution made 3.0 mM NaHCO₃ + 6.0 mM Na₂CO₃ was used as an eluant, and conductivity was used as the mode of detection. The proposed method was tested by analyzing soil extracts obtained after equilibrating soils with a series of solutions containing mixtures of these oxyanions. Results showed that the elution times for PO₄ ^3‐, AsO₄ ^3‐, SeO₄ ^2‐, WO₄ ^2‐, and MoO₄ ^2‐ were 1.8, 2.5, 4.1, 6.6, and 8.0 min, respectively. The accuracy of the method was evaluated by spiking the soil extracts with standard solution of the oxyanions. The recovery of standards (made to correspond to 0.5 mM) added to the solution analyzed ranged from 95.4% to 104.6%, with coefficients of variation ranging from 0% to 10.5%. The detection limits of oxyanions studied ranged from 1 μM with PO₄ ^3‐ to 25 (μM with MoO₄ ^2‐. A single operator can analyze about 50 solutions of the five oxyanions in a normal working day.     

Ionic equilibria,selectivity and diffusion of cations in soil as influenced by anion additions

Abstract

An experiment was carried under controlled conditions to investigate the influence of the anions, H₂PO₄ ^‐. and Cl on the ionic equilibria, selectivity and effective diffusion of Rb, K, Na, Ca, Mg in two Indiana soils.

Additon of anions to the soils increased the concentration of cations in soil solution. In both the soils receiving H₂PO₄ ^‐, lower cation concentrations were found in the soil solution than in those receiving Cl^‐ . Additon of H₂PO₄ ^‐and Cl^‐ reduced the ion selectivity coefficient, k, for various homovalent (Rb/K, Rb/Na, K/Na, Ca/Mg) and mono‐divalent ion pairs (Rb/Ca, Rb/Mg, K/Ca, K/Mg). In Zanesville soil treatments receiving H₂PO₄ ^‐ had lower k values for mono‐divalent cations than treatments receiving Cl^‐. However, no such conclusions could be drawn for Raub soil. Soils treated with H₂PO₄ ^‐ had higher k values for homovalent cations than Cl^‐ treated soils. The differences in the selectivity of adsorption in these two soils might be attributable to the differences in the type and nature of exchange materials and cation concentrations on the exchange phase.

Addition of H₂PO₄ ^‐ or Cl^‐ enhanced the magnitude of effective diffusion coefficient. (De) of all the cations under considerations. The magnitude of effective diffusion coefficient for cations was lower for H₂PO₄ ^‐ treated soils than Cl^‐ treated soils. Such a reduction in De is related to the reduction in cation concentration in soil solution thereby increasing the buffer capacity for the ions under consideration.     

Chemical fractionation,water solubility and temporal distribution of sheep faecal sulphur fractions in grazed pastures receiving long‐term sulphate fertilization

Abstract

Although over 40% of excretal S is returned to intensively sheep ‐grazed pastures as faecal S, limited information is available on faecal S fractions, their water solubility and temporal distribution. This study reports results obtained from sheep faeces returned to grazed pastures which have received long‐term annual sulphate applications for 15–20 years. Five freshly‐voided sheep faecal samples (<100 g moist faeces per sample) per sampling were randomly collected at approximately one month intervals over a one‐year growing season. Faeces were fractionated into total S, inorganic SO₄ ^2‐, ester SO₄ ^2‐, Hi‐reducible S and C‐bonded S. Results obtained showed that faecal total S, ester SO₄ ^2‐ Hi‐reducible S and C‐bonded S fractions varied significantly throughout the year. Carbon‐bonded S was the dominant (>80%) faecal S fraction, regardless of faecal total S content or the time of year faecal samples were deposited. Faecal ester SO₄ ^2‐ and inorganic _SO₄ ^2‐fractions accounted for 3.3–7.1% and 0.1–14% of faecal total S respectively. Thus approximately 3.4–21.1% of faecal total S was estimated to be potentially leached or readily available to pasture plants. The Hi‐reducible faecal S fraction was significantly‐correlated (r = 0.59***; *** = P ≤ 0.001) with HCl‐extractable faecal inorganic S, which was considered to represent faecal total SO₄ ^2‐ (ester SO₄ ^2‐ and inorganic SO₄ ^2‐ fractions).

The solubility of different faecal S fractions was determined by sequential extraction of ground (< 1 mm) faeces three times (30 minutes per extraction) with water or 0.01 M Ca(H₂PO₄)₂ solution (1: 5 ratio of faecal DM: extractant). Both amounts of water‐extractable and Ca(H₂PO₄)‐extractable faecal S fractions were found to vary significantly throughout the year. Ca(H₂PO₄)₂ tended to extract more inorganic faecal S than water, attributed to the presence of phosphate and the low pH (pH=4) of Ca(H₂PO₄)₂ extractant. A significant proportion (15–25%) of faecal S was extracted by water and most (70%) of this water‐extractable faecal S was in the organic S fraction. Water‐extractable inorganic faecal S probably originated from the faecal total SO₄ ^2‐ fraction as shown by their significant correlation (r = 0.45** ‐0.63***; ** = P≤ 0.01; *** = P≤ 0.001). Some of the faecal S in water extracts may also originate from the faecal C‐bonded S fraction, as a significant correlation was obtained between C‐bonded faecal S and either water‐extractable faecal organic S (r = 0.53–0.57***; *** = P ≤ 0.001) or water‐extractable faecal inorganic S (r = 0.40–0.41*; * = P ≤ 0.05).

Significant amounts of faecal inorganic SO₄ ^2‐ and ester SO₄ ^2‐ fractions were removed by Ca(H₂PO₄)₂ extractant. The Ca(H₂PO₄)₂‐extractable faecal inorganic S was significantly correlated (r = 0.73***^; *** = P ≤ 0.001) with water‐extractable faecal inorganic S.     

Sulfur status of volcanic ash‐derived soils in Hawaii

Abstract

Several rainwater samples and 14 profiles of Hawaii's volcanic ash‐derived soils were analyzed for sulfur (S). Atmospheric deposition was an important S source at the coast (24 kg S/ha), but its contribution decreased with increasing distance from the sea (1 kg S/ha at 24‐km inland). The S concentration of rainwaters also decreased linearly with increasing rainfall.

Several thousand mg SO₄‐S/kg can be extracted from many volcanic ash‐derived soils of Hawaii, and it was often required at least four extractions [0.04 M Ca(H₂PO₄)₂, 1:10 soil to solution ratio] to completely desorb this SO₄. There was a close association of high SO₄ retention with high rainfall. This might have resulted from (1) the development of a solid phase with high SO₄ retention under intense weathering conditions, (2) more total SO₄ received by the soils from atmospheric deposition, and (3) past fertilization of sugarcane grown in high rainfall areas.

Low concentrations of soil solution SO₄‐S in relation to large amounts of P‐extractable SO₄ suggest that a S bearing mineral, such as basaluminite, may be controlling soil‐solution SO₄. Furthermore, SO₄ adsorption isotherms of these volcanic soils generally show a bi‐phasic property, and suggest that 40 to 80 mg SO₄‐S/kg is required to maintain 3 ‐ 6 mg SO₄‐S/L in the soil solution, a concentration range considered adequate for the growth of most crops.     

Water,NaHCO3−, NaH2PO4− and NaCl-extractable SO42− in acid forest soils

A variety of different methods have been used for the determination of inorganic soil SO₄^2? in the past, which makes it difficult to compare SO₄^2? contents of soils. Sulfate was extracted with the four commonly used extraction solutions 0.5 M NaHCO₃, 0.02 M NaH₂PO₄, 0.1 M NaCl and H₂O from A-, Bw- and Bs-horizons of six acid forest soils. 5 g of field moist soil were percolated with a flow rate of 5 ml/h and percolations were repeated as long as SO₄^2? was detectable in the percolate (> 0.5 mg SO₄·l^?1). NaCl and NaHCO₃ extracted highest amounts of total inorganic SO₄^2? in A-horizons, but NaHCO₃ caused analytical problems. NaHCO₃ and NaH₂PO₄ yielded highest amounts in B-horizons. With the exception of Bs-horizons more than 70% of the total inorganic SO₄^2? was H₂O-soIuble. Thus, if H₂O-soluble SO₄^2? is defined as reversibly bound, the greater part of the inorganic SO₄^2? in the investigated acid forest soils was reversibly bound. This SO₄^2? fraction can potentially be released, if SO₄^2? deposition decreases.     

Sulphate Adsorption in Soils of North and Northeast Iran

Abstract

Gypsum (CaSO₄ · 2H₂O) is used in agriculture both as a source of calcium (Ca) and sulphate (SO₄ ^2?) and as an amendment to improve soil structure. The effect of gypsum on the adsorption of SO₄ ^2? in irrigated and nonirrigated soils was examined. Almost all of the indigenous sulphate (SO₄) in a range of Golesthan and North Khorasan soils with moderate pH values (>6) was found to be present in the soil solution and, as a consequence, was highly susceptible to leaching. The adsorption of sulphate to the soils receiving no gypsum was greater with correlation coefficient of r=0.91 at 0 kg S ha^?1 as compared to the soils received 40 kg ha^?1 of gypsum as fertilizer with the value of r=0.88 in Golesthan Province. The same trend was observed in Khorasan Province with r=0.79 and r=0.75 with soils receiving 0 and 40 kg S ha^?1, respectively. The results were more pronounced in irrigated fields for both provinces. The amount of sulphate adsorption in Golesthan Province soils was comparatively greater than soils of Khorasan Province. The results raise questions regarding the efficiency of SO⁴‐containing fertilizers in correcting and preventing S deficiency in situations where leaching is a concern.     

A turbidimetric method for determining phosphate‐extractable sulfates in tropical soils

Abstract

Turbidimetric methods, using Ba ions to precipitate SO₄, are frequently used to determine soil sulfates extracted with phosphate solutions. These methods, as routinely performed, seriously underestimate SO₄ in some soils of the tropics because phosphate is removed from the extractant by soil adsorption and because many extracts fail to yield satisfactory precipitate even if the extracting procedure is adequate. Decolorizing the extracts with carbon black, treating extracts with strong oxidizing agents, adding SO₄ spikes, and seeding the extracts with BaCl₂ seed‐crystals improve precision, but some extracts, especially those from soils derived from volcanic ash, do not yield reliable precipitates even though these procedures are employed. This paper presents a method that consistanlty yielded more SO₄ than other turbidimetric procedures with which it was compared. The proposed method was further validated against an ion‐chromatographic method for SO₄ determination. The two methods yielded virtually identical results.

The proposed method consists of extracting SO₄ with 0.04 M Ca(H₂PO₄)₂ pH 4, at a soil‐to‐solution ratio of 1: 10. Repeated extraction is necessary for phosphate‐retentive soils. (A. single extraction was approximately 40% effective for removing indigenous SO₄ from a Hydric Dystrandept subsoil, approximately 78% effective for an Eutrustox.) Organic materials are removed from the extracts by adsorption on charcoal; SO₄ is concentrated in the extract by volume reduction; a SO₄ spike is added; BaCl₂‐seed crystal is added, after which volume is increased by adding BaCl₂ solution. Optical density is read at 600 nm.     

Comparison of Seven SO4-S Extraction Methods for Analysis by Turbidimetry or ICP Spectrometry

Soil sulfur (S) analyses for fertilizer recommendations in the northern Great Plains often do not reflect crop S requirements. Seven SO₄-S extraction methods with S determination by either turbidometry or inductively coupled plasma emission spectroscopy including Ca(H₂PO₄)₂ and KH₂PO₄ (both containing 500 ug/l P), 0.25 M KCl (40 ºC) and 0.25 M KCl (room temperature), H₂O, DTPA, and Mehlich 3 extractants. Three horizon depths of three soils from a previous field study were used for these comparisons. Average standard deviations for turbidometric determinations were 4.3 times greater than ICP determinations. With turbidometry, S values were H₂O > KH₂PO₄ > Ca(H₂PO₄)₂ > KCl (40 ºC) = KCl, while with ICP, the values were Mehlich 3 > KCl (40 ºC) = KCl > DTPA (diethylenetriaminepentaacetic acid) > KH₂PO₄ > H₂O > Ca(H₂PO₄)₂. Extraction with KCl at room temperature with ICP determination appears to show promise, but further method evaluation is necessary before it can be recommended as a SO₄-S test method.     

Anionic constituents of acid rain and microbial activity in soil

Soil amended with 1% glucose was treated with H₂SO₄, fuming H₂SO₄, HCl, H₃PO₄, HNO₃, fuming HNO₃ or with combinations of fuming and non-fuming H₂SO₄ and HNO₃ to lower the bulk soil pH to values ranging from 5.0 to 2.0. There was a difference in the amount of toxicity caused by the different acids at the same bulk pH of soils. Acidification to pH 2.8 or 2.9 prolonged the lag phase of glucose degradation; fuming HNO₃ had the greatest effect, and fuming H₂SO₄ was only slightly more toxic than non-fuming H₂SO₄. At pH 2.3–2.4, fuming HNO₃, alone or in combination with H₂SO₄, inhibited CO₂ evolution. Both fuming and non-fuming HNO₃ also reduced the amount of C mineralized to a greater extent than did fuming and non-fuming H₂SO₄. The amounts of C mineralized from soils treated with combinations of H₂SO₄ and HNO₃ were intermediate between those from soils treated with each of these acids alone. HCl and H₃PO₄ had a similar effect on prolonging the lag as did non-fuming H₂SO₄. H₃PO₄ was less toxic than the other acids and sometimes increased the total amount of C mineralized. The “anionic effect” of acid rain must, therefore, be considered in addition to the effect of the proton. When the soil was inoculated with a suspension of microbiologically-active soil, more C was mineralized, in general, and the inhibitory effects of acidification on C mineralization were less pronounced than in soil that had not been inoculated. The addition of montmorillonite, but not of kaolinite, enhanced the growth of Aspergillus niger in soils amended with 2:1 combinations of H₂SO₄ and fuming HNO₃ however, growth was inhibited completely at pH 3.4.     

SO42-和Cl-对稻田土壤养分及其吸附解吸特性的影响

利用长期定位试验 ,比较了长期施用含SO₄^2-和Cl^- 化肥 22年后稻田土壤的 pH值、养分状况及其吸附解吸特性。结果表明 ,长期施用含SO₄^2-化肥 ,土壤有机质、速效氮和速效钾的含量较高 ,但全量氮磷钾的含量较低 ;长期施用含Cl^- 化肥 ,土壤全量氮磷钾和速效磷的含量较高 ,但pH值相对较低。长期施用含上述二种阴离子的化肥后 ,土壤对H₂PO₄^-的最大吸附量均较大 ,且在Cl^- 处理下土壤对H₂PO₄^-吸附的结合能较大 ,而SO₄^2-处理下土壤在同等吸附量时对H₂PO₄^-的解吸量相应较多。长期施用含SO₄^2-的化肥亦使土壤对钾素的供应强度较大 (ΔK0的绝对值较大 )、缓冲能力增强 (AR0值较高 ) ,而长期施用含Cl^- 的化肥时则与SO₄^2-相反     

Determination of ammonium n and nitrate n in acid permanganate solution used to absorb ammonia,nitric oxide,and nitrogen dioxide evolved from soils

Abstract

Simple steam distillation methods are described for determination of ammonium N and nitrate N in acid KMnO₄ solution used to absorb NH₃, NO and NO₂ evolved from soils. They involve use of MgO for distillation of ammonia and of FeSO₄, Ag₂SO₄, and MgO for reduction of nitrate to ammonia. The methods are rapid and precise, and they permit nitrogen‐15 analysis of NH₃‐N and (NO + NO₂)‐N evolved from soils.     

Short‐Term Effect of Lime,Phosphorus, and Iron Amendments on Water‐Extractable Lead and Arsenic in Orchard Soils

Abstract

Lead arsenate was extensively used to control insects in apple and plum orchards in the 1900s. Continuous use of lead arsenate resulted in elevated soil levels of lead (Pb) and arsenic (As). There are concerns that As and Pb will become solubilized upon a change in land use. In situ chemical stabilization practices, such as the use of phosphate‐phosphorus (P), have been investigated as a possible method for reducing the solubility, mobility, and potential toxicity of Pb and As in these soils. The objective of this study was to determine the effectiveness of calcium carbonate (lime), P, and iron (Fe) amendments in reducing the solubility of As and Pb in lead‐arsenate‐treated soils over time. Under controlled conditions, two orchard soils, Thurmont loam (Hapludults) and Burch loam (Haploxerolls), were amended with reagent‐grade calcium carbonate (CaCO₃), iron hydroxide [Fe(OH)₃], and potassium phosphate (KH₂PO₄) and incubated for 16 weeks at 26°C. The experimental results suggested that the inorganic P increased competitive sorption between H₂PO₄ ^? and dihydrogen arsenate (H₂AsO₄ ^?), resulting in greater desorption of As in both Thurmont and Burch soils. Therefore, addition of lime, potassium phosphate, and Fe to lead‐arsenate‐contaminated soils could increase the risk of loss of soluble As and Pb from surface soil and potentially increase these metal species in runoff and movement to groundwater.     

Fractionation and distribution of selenium in soils

Abstract

A modified selenium (Se) fractionation procedure was used to study Se distribution in three soils (two silt loams and one silty clay). This sequential procedure consisted of: i) 0.2 M potassium sulfate (K₂SO₄)‐soluble fraction, ii) 0.1 M potassium dihydrogen phosphate (KH₂PO₄)‐exchangeable fraction, iii) 0.5 M ammonium hydroxide (NH₃H₂O)‐soluble fraction, iv) 6 M hydrochloric acid (HCl)‐extractable fraction, and v) residual fraction digested with perchloric (HClO₄) and sulfuric (H₂SO₄) acids. The fractionation procedure had high recovery rates (92.5 to 106%). The Se distribution in soil was controlled by soil properties, such as pH, oxide, clay, and calcium carbonate (CaCO₃) contents. In the untreated soil samples, residual Se fraction was dominant. In the Se‐enriched soils, the silty clay had significantly more Se in the NH₃H₂O and residual fractions while in the two silt loams the largest were KH₂PO₄ and residual fractions. The Se availability in the two silt loams was higher than in the silty clay. The Se availability pattern in the untreated soils was: unavailable (HCl + residual fractions) >> potentially available (KH₂PO₄ + NH₃H₂O fractions) > available (K₂SO₄ fraction), while in the Se‐enriched soils it was potentially available > unavailable > available.     

NITROGEN–PHOSPHORUS–POTASSIUM EFFECTS ON FORMS OF SULFUR IN LEAVES AND FRUITS OF CUCUMBER

ABSTRACT

The impact that nitrogen (N), phosphorus (P), and potassium (K) application rates on the sulfur (S) fractions in leaves and fruits of greenhouse-grown cucumbers plants (Cucumis sativus L. cv. Brunex) are presented. The treatments were as follows: N (N1=5 g NO₃NH₄/m², N2=10 g NO₃NH₄/m², N3=20 g NO₃NH₄/m², N4=40 g NO₃NH₄/m²), two levels of P (P1=8 g H₃PO₄/m² and P2=16 g H₃PO₄/m²), and two levels of K (K1=20 g K₂SO₄/m² and K2=40 g K₂SO₄/m²). The foliar and fruit contents were determined for total S, organic S and sulfate. The influence of the N treatments on the total S (St: organic S +sulfate) concentration, proved significant, showing a progressive increase in the leaf and fruit concentrations. In the leaves, the P slightly diminished the St concentration but values in the fruits did not appreciably differ from control. The K dosage did not cause the St concentration to differ from that of P, although in the fruit a slightly lower St concentration appeared in the K2 treatment. The response of the organic-S concentration in the leaves resembled that of St, and thus organic S should not be used as a diagnostic method for S status. In the relationship SO₄ ^2-/St, the SO₄ ^2- concentration proved more influential than did the St form, providing a more accurate representation of the potential status of this nutrient in the plant.     

Suitability of Extractants for Predicting Available Sulfur in Natural Grassland in the Inner Mongolia Steppe of China

Abstract

It was the objective of this study to compare the suitability of different extractants for predicting the availability of sulfur (S) in natural grassland in a sulfur response trial on three different soil types in the Inner Mongolia steppe of China. For soil analysis, seven different extractants have been employed. The inorganic SO₄–S concentration was determined by ion chromatography. Additionally, in the Ca(H₂PO₄)₂ extract the total soluble S was determined employing turbidimetry. Weak salt solutions (0.15% CaCl₂, Ca(H₂PO₄)₂, and KH₂PO₄) extracted similar amounts of SO₄–S. Extraction with 0.025 M KCl provided the lowest SO₄–S values. Deionized water dissolved significantly more SO₄–S in the control plots than most weak salt extractants. The concentration of soluble organic S decreased in the control plots after 100 days of plant growth, indicating that the organic S pool contributed significantly to the S nutrition of the forage crops. Significant relationships among the SO₄–S in the soil determined in different extracts and crop yield, sulfur content in the forage, and total sulfur uptake were only found for the Ca(H₂PO₄)₂ extract. In general, the correlation coefficients proved to be unsatisfactory for field experimentation.     

Sulphur Mineralization and Carbon,Nitrogen, and Sulphur Relationships in Some Alfisols of India

Abstract

The amount of sulphur (S), nitrogen (N), and organic carbon (C) in different layers of soils from some Alfisols varied considerably with location. The amount of S extracted by different extractants as a percentage of the total S was in the order of organic (3.5%)>0.05 (N) NH₄OAc+0.25 (N) HOAc (1.9%)>0.1 (N) H₃PO₄ (1.8%)>0.025 (N) CaCl₂ (1.8%)>0.03 (N) NaH₂PO₄ (1.7%)>0.001 (N) HCl (0.6%). In all the soil series SO₄ ^2?‐S mineralization decreased up to the second week after incubation, followed by a slight increase up to the fourth week, a subsequent decline up to the sixth week, and a slight increase up to the eighth week. The C:N, C:S, N:S, and C:N:S ratios averaged 9.4:1, 63.7:1, 6.9:1, and 94:10:2.08, respectively.