Quantifying carbon and sulphate loss in drained acid sulphate soils

Approximately 25 years before they were sampled, one of a pair of adjacent and initially similar acid sulphate soils was drained. During the ensuing 25 years, the surface of the drained soil declined approximately 1.2 m relative to its undrained neighbour. The losses of carbon (C) and sulphur (S) from the drained soil were estimated as the difference between the amounts remaining in the drained soil and its undrained neighbour. I made these comparisons in two ways. Firstly, I determined the amounts of C and S by summing their volumetric concentrations to a common depth (relative to the Australian Height Datum) where these concentrations became equal. Secondly, I made comparisons using mass-based concentrations and a material coordinate defined by integrating the bulk density profile down from the soil surface. In this latter convention, the distance is the cumulative mass of soil solids per unit area of cross-section, measured to any depth from the soil surface. The former approach yields estimates of C loss almost 30% greater than the latter. The S loss based on volumetric calculations was approximately 25% greater than that based on mass-based coordinates. These overestimates of loss of C and S arise because the depth-based method fails to take account of the vertical movement of the soil solid accompanying drainage in these soils. As a result, chemical reactions and their products, which are uniquely identified with parcels of soil solids, have no unique depth in swelling soils over time. The material calculations are therefore correct, but I identify conditions where a conventional volume-based estimate might be used.     

Oxidation-induced leaching of sulphate and cations from acid sulphate soils

Leaching of sulphate and cations from horizon samples of two acid sulphate soils (0.9 to 1.6% S in subsoil) was studied in the laboratory. Samples were incubated and eluted with water at 20 °C and 5 °C until apparent exhaustion of leachable S resources. The leachates were analyzed for pH, SO₄-S, Fe, Al, Mn, K, Ca, Mg, and Na. Oxidation of sulphide was retarded at the lower temperature. From all the originally water-logged samples the sulphate formed was initially washed out with base cations (mainly with Mg), but the proportion of acid counter ions (predominantly Al) increased with proceeding oxidation and acid formation. In the most acid leachates, pH was 2.6 to 2.8. In the transition layer between reduced and oxidized horizons, sulphide oxidation had been going on for some time, and acid cations were the main counter ions for sulphate already at the beginning of the experiment. In the totally oxidized surface horizons, sulphate was leached only in moderate quantities, and the sum of cation equivalents (mainly base species) exceeded that of sulphate, suggesting some removal of other anions. Leaching losses in the laboratory experiment, corresponding to drainage-induced loading of waters in field experiments during the course of many decades, point out the environmental danger associated with deep drainage of potentially acid sulphate soils.     

Aluminium sulphate solubility in acid forest soils in Denmark

Ion leaching in 3 sandy spruce forest soils of different origin and pH was investigated in the laboratory. Zero-tension lysimeters containing undisturbed soil columns of varying soil depth were subjected to H₂SO₄ loadings for a period of 9 weeks. The analysis of the resulting leachate supports the hypothesis that Al-sulphate minerals may form in acidic soils when exposed to acid (H₂SO₄) deposition. In the B horizon of a glaciofluvial sandy soil (pH 4.2), both H⁺ and sulphate ions were retained to maintain 2pH + PSO₄ = 11.9 in the leachate solutions. This relation between H⁺ and sulphate activity may be due to an adsorption mechanism or a precipitation mechanism. The precipitation mechanism is favored by the good fit of leachate composition to the conditions for jurbanite [AlOHSO₄] formation from gibbsite [Al(OH)₃]. In the B horizon of a sandy till at pH 3.7, the Al in soil solution (0.5 mmol L^?1) was leached with sulphate. As the sulphate load was increased, some sulphate was retained. This may also be due to the dissolution and precipitation of an Al-sulphate mineral. The ion activity products of leachate solutions from the B horizon of this soil were close to the pK_s reported for jurbanite. The conditions for the possible existence and/or formation of Al-sulphate minerals in acidic soils are discussed.     

Response of acid sulphate soils to different liming treatments I. Solubility of sulphate and phosphate

In a preliminary laboratory experiment, samples from three cultivated and three virgin acid sulphate soils (pH 3.9-4.7) were treated with water or equivalent amounts of Ca(OH)₂ or KOH and incubated at about field capacity for three months. Both base treatments (133 meq/kg) similary reduced soil acidity and, thus, the same influence on the pH-dependent biological and chemical reactions was concluded. The liming-induced mineralization of organic S seemed to account for increased extratability of sulphate, being in most soils of the same magnitude in both treatments. Inversely, the solubility of P hardly was affected by the decomposition of organic matter but rather by the reactions of inorganic P. KOH markedly raised water-soluble P, whereas Ca(OH)₂ did not. The results of a rapid extraction test suggested that the poorer extractability of P in the soils amended with Ca(OH)₂ could partly be ascribed to a higher Ca saturation and its impact on the electrochemical properties of charged surfaces. In addition, a higher base-associated ionic strength created by Ca²⁺ was of great importance in reducing the P desorption in the Ca(OH)₂- treated soils.     

The importance of soil carbon and nitrogen for amelioration of acid sulphate soils

When exposed to air and adequate moisture, soils containing sulphides (sulphidic soils with pH > 4) become oxidized and generate sulphuric acid to form ‘sulphuric soils’ (pH < 4). Treatment of this acidity is undertaken by addition of lime. In this study, we investigated the effectiveness of adding plant organic matter, and simple carbon and nitrogen compounds, as alternatives to lime to sulphuric and sulphidic soils. In sulphuric soils under aerobic conditions, organic matter increased pH, the extent depending on the nitrogen content. Lucerne hay, which had the largest nitrogen content, increased the pH from 3.7 to 8.0, while pea straw and wheat straw effected smaller changes, in proportion to their respective nitrogen contents. Lucerne hay also caused the greatest reductions in soil redox potential and sulphate content, consistent with the action of sulphate‐reducing bacteria. Similarly, incorporation of organic matter under aerobic conditions effectively prevented sulphidic soil acidification and reduced the redox potential and sulphate content. The individual effects of carbon and nitrogen compounds were then examined and compared to plant organic material. Glucose was ineffective at both small and large concentrations, while molasses increased the pH slightly to 4.6 and acetate to 5.9. None of these carbon compounds was as effective as complex organic matter. Nitrogen added alone as nitrate or ammonia had little or no effect on pH, whereas organic nitrogen in the form of urea caused the pH to rise to 6.3 and reduced the redox to less than 0 mV but had no significant effect on sulphate content.     

Effects of live wetland plant macrophytes on acidification,redox potential and sulphate content in acid sulphate soils

Unless properly managed, acid sulphate soils can exert a range of negative environmental impacts, including soil acidification and mobilization of metals and metalloids. Incorporation of organic matter in the form of plant mulches can substantially neutralize sulphuric soils and prevent the oxidation of sulphidic soils. These positive effects of dead plants are largely mediated by bacterial reduction of sulphates to sulphides, using the organic matter as a microbial nutrient source. However, very little is known about the effects of live plants on acid sulphate soils. In this study, we compared pH, Eh and sulphate content of sulphidic and sulphuric soils that were not planted (i.e. unplanted) with those soils planted with the following three common wetland plants: Phragmites, Melaleuca and Typha. Each of these plants is capable of growth in aerobic and flooded soils. In all our experiments, the presence of plants correlated with an increase in soil acidification rather than neutralizing soil acidity when compared to unplanted controls. The mechanism for this appears to be transport of oxygen down the soil profile by aerenchymatous tissue formed in these species, and the release of oxygen into the rhizosphere.     

Response of acid sulphate soils to different liming treatments II. Exchangeability of soil cations

Liming-induced changes in cation exchangeability were studied in six samples from acid sulphate soils (pH 3.9-4.7) incubated with water or with equivalent quantities of Ca(OH)₂ or KOH. The extractability of acid cation species susceptible to hydrolysis was shown to be affected not only by increased pH but also by the kind of the cation and related electrochemical properties of the base used. Both liming treatments practically eliminated the exchangeable Al. In the virgin soils, however, the polynuclear Al-complexes formed by Ca(OH)₂ treatment seemed to have been hydrolyzed further. The superiority of Ca(OH)₂ was assumed to be due to the higher valency of its cation and its act of provoking a higher increase in ionic strength. The liming agents affected to varying extents also the extractability of base cations. Exchangeable soil K seemed to decrease by the KOH treatment and the soil Ca by the Ca(OH)₂ treatment, whereas K and Ca were only slightly, if any, affected by the Ca(OH)₂ and KOH treatments, respectively. Thus, the reductions were assumed to be attributable to other factors than increased pH. A fixation of K and a possible precipitation of Ca as CaSO₄ were discussed. Ca(OH)₂ decreased in all soil samples the exchangeability of Mg more than did KOH. The depression was not related to the Al polymerization and, thus, cannot entirely be ascribed to specific sorption on Al gel. The results imply that liming may affect base cation exchange reactions by neutralizing exchangeable Al of high bonding strength and by replacing it by cations of the liming agent.     

Extractability and adsorption of sulphate in soils

Virtually all of the indigenous sulphate (SO₄) in a range of UK soils with moderately high pH values (> 6) was found to be present in the soil solution and, as a consequence, was highly susceptible to leaching. For acid soils containing adsorbed SO₄, the extractability of SO₄ in NaCl and CaCl₂ solutions was dependent on both the ionic strength and cation species. Addition of small amounts (<～ 10^?2M) of either NaCl or CaCl₂ actually decreased the amount of SO₄ extracted, but SO₄ extractability increased sharply with concentrations of NaCl or CaCl₂ higher than about 0.1 M. At a similar ionic strength, more SO₄ was extracted by NaCl than CaCl₂. Sequential extraction with 1 M NaCl removed essentially all of the absorbed SO₄. The release characteristics of SO₄ were very different to those of phosphate and this difference in behaviour is not easily reconciled with the view that SO₄ is chemisorbed, as is phosphate. Except for a few acid soils with high oxide contents, the capacity of the soils to adsorb added SO₄ was quite small. None of the soils with pH values higher than 6 adsorbed a significant amount SO₄. The results raise questions regarding the efficiency of SO₄-containing fertilizers in correcting and preventing S deficiency in situations where leaching is important.     

The use of porous ceramic cup water samplers to measure solute leaching on chalk soils

Abstract. This paper reports results from a four year study to investigate the suitability of porous ceramic cups to measure solute leaching on shallow chalk soils. Measurements were carried out in one field following surface applications of nitrate and bromide tracers and in two fields after only bromide was applied. Soil water samples were collected from porous cups at 30,60 and 90cm depth after every 25 mm of drainage, and soil samples from 0–30, 30–60 and 60–90 cm were collected monthly eachwinter. Soil matric suctions andvolumetric moisture content were measured in one winter. Leaching losses, measured with ceramic cups were compared with those measured by soil analysis. Porous cups installed in chalk at 60 and 90 cm depth were only able to collect samples regularly when soil matric suctions were less than 15 kPa. Water held at such low suctions is likely to move quickly through relatively large fissures in the chalk. The slow rate of equilibration between solute concentrations in water moving in macrofissures and those in water moving through micropores of the chalk matrix, means that porous cups may not provide good estimates of leaching losses if they are installed in chalk rock.     

酸性硫酸盐土壤上施用磷矿粉对水稻养分有效性的影响

1998～2001年在已垦和未垦酸性硫酸盐土壤上连续进行6季作物的磷矿粉肥效试验,4种磷矿粉分别为摩洛哥CALCINE和BRUT,ALGERIA及昆阳磷矿粉,另外加上过磷酸钙和重过磷酸钙及对照。2000年起每小区均分成2个裂区,其中裂区Ⅰ继续按以前磷肥用量施肥,裂区Ⅱ则将后4季作物的肥料1次施下。试验结果表明,在未垦地上,施用磷矿粉处理水稻稻草P含量比对照显著提高,植株吸收N、P、K量、土壤含P量显著增加。磷矿粉为水稻生长提供了稳定有效的P源;水稻根部吸收P并主要储存于稻草中;2种施用方法无显著差异。已垦地上各处理间无显著差异。虽然缺P是制约水稻生长的一个关键因素,但在此类土壤上还存在更多的限制因子。     

Resurrection of Soil Surveys: a case study of the acid sulphate soils of The Gambia.

Abstract. Statistical techniques are used to test and re-interpret archival data from soil surveys of the tidal floodplain of the River Gambia. Key soil attributes include salinity, ripeness and the acid sulphate hazard. Soil taxonomic units derived by cluster analysis of all the validated data do not correspond with the intuitively-defined soil series of the original surveys. However they do correspond with practical soil mapping units, and distinguish areas of quite different geotechnical behaviour, kinds and degrees of salinity and acid sulphate hazard.     

Adsorption of phthalic acid and salicylic acid by two variable charge soils as influenced by sulphate and phosphate

Low‐molecular‐weight (LMW) organic acids exist widely in soils, especially in the rhizosphere, and the adsorption of these acids may affect their reactions in soils. The adsorption behaviour of phthalic acid and salicylic acid by two variable charge soils (a Rhodic Ferralsol and a Haplic Acrisol) was investigated. Both soils exhibited great adsorption capacity for these organic acids, with a greater affinity for phthalic acid. The Rhodic Ferralsol adsorbed more organic acids of both kinds than the Haplic Acrisol, which was consistent with the content of iron and aluminum oxides in the two soils. The iron oxides in these soils played a significant role in adsorption of the organic acids, whilst the soil aluminosilicate minerals, such as kaolinite, showed a small adsorption capacity. The presence of phosphate and sulphate caused a decrease in the adsorption of both organic acids because of their competition with them for sorption sites. The phosphate showed a bigger inhibition on the adsorption than sulphate as a result of a greater amount of phosphate adsorbed by the soils. The adsorption of both organic acids was affected by pH only slightly at pH < 4.5. However, the adsorption decreased with the increase in pH at pH > 4.5. A similar trend was observed for the phosphate system, but the opposite was seen for the sulphate system. This suggests that the inhibition of sulphate on the adsorption of the organic acids decreased with the increase in pH, because the adsorption of sulphate decreased strongly with increasing pH.     

The effect of aggregate size on water retention and pore structure of two silt loam soils of different genesis

Aggregate size distribution and pore structure affect many soil functions and root growth. The aggregate structure is associated with soil genesis and management practices applied. In this study the effects of various size ranges of aggregates (<0.25, 0.25–0.5, 0.5–1, 1–3, 3–5, and 5–10 mm) and undisturbed soil from the plough layer (0–15 cm) of two types of soils (Haplic Phaeozem and Eutric Fluvisol) of the same silty loam textural group on water retention curves (WRC) and pore size distribution (PSD) were assessed. A greater bulk density and lower humus content characterized the Eutric Fluvisol as compared to the Haplic Phaeozem. The WRC was determined using standard Richards chambers in drying process and expressed as the degree of saturation. Equivalent PSD was derived from the WRC. Resin impregnated sections from the layer of 0–8 cm showed that the Eutric Fluvisol, compared with the Haplic Phaeozem, had coarser pores and aggregates. The degree of saturation in beds of aggregates <0.25, 0.25–0.5 and 0.5–1 mm compared to beds of aggregates 1–3, 3–5 and 5–10 mm was greater at higher values of pressure head for both soils, and for undisturbed soil it was greater for the Haplic Phaeozem than for the Eutric Fluvisol at lower values of pressure head. The inverse relationship was true at higher values of pressure head. The derivative curves of PSD showed that the beds of aggregates and undisturbed soils exhibited multi-peak PSD. The pore radius peaks within the textural (primary) pore system were more defined in beds of aggregates <0.25 mm than in beds of coarser aggregates, whereas in the case of the structural and macropore peaks it was often the reverse. Greater magnitude and narrower shape of the peaks in the undisturbed Haplic Phaeozem compared to the Eutric Fluvisol indicated a more heterogeneous nature of the pore system in the former. The PSD data are discussed in relation to aggregate size distribution and stability of the soil aggregates. The results of this study can be helpful in predicting storage and transmission functions of surface aggregated soils.     

A simplified incubation method using chip‐trays as incubation vessels to identify sulphidic materials in acid sulphate soils

Acid sulphate soils (ASS) can pose a significant hazard to natural ecosystems and developed areas situated within ASS landscapes. Management techniques used to minimize these hazards rely on methods that can classify ASS materials. These methods have traditionally required complex and time‐consuming techniques. A new simplified incubation method, modified from existing ones, was therefore developed to classify ASS materials in a timely manner. The simplified incubation method was found to be a viable alternative where samples cannot be incubated to a stable pH because of logistical or time constraints, but where there is still a need to classify slowly acidifying sulphidic materials. The use of chip‐trays as incubation vessels was also examined. Chip‐trays offer many advantages in terms of transport, storage and analysis of soil samples compared with soil‐slabs. This study establishes an acceptable level of precision ( ± 0.1 pH units with 95% confidence) for pH measurements in the incubation method and confirms that an acceptable level of precision is obtainable when using chip‐trays in the pH incubation method.     

The use of dialysis cells for investigating pore water composition in wetland substrata,with particular reference to dissolved iron and sulphide

Abstract

Details and some evaluation are given of the use of a dialysis method for sampling pore water from depth in wetland substrata (peats), with particular reference to measurement of concentrations of ion species with stabilities dependent on redox potential. The method is based upon the burial and subsequent retrieval (after equilibration) of cells made from dialysis membrane filled with deionized water. Preliminary results of field investigations of concentrations of dissolved iron and sulphide in the pore water of base‐rich mires, as sampled by this method, are given. Results suggest that the method could have very considerable application and that its potential, and possible problems, deserve further examination.     

Microbial production of sulphate and sulphide in some Australian soils

Fifty-six Australian soils were examined for their ability to produce sulphate from sulphur and sulphide from added sulphur, sulphate and cystine. Selective liquid media were used to obtain initial counts and progressive activities of some of the principal organisms involved. Attempts were made to correlate soil properties, initial microbial counts, classes of micro-organisms detected and metabolic activities.Almost half of the soils oxidized sulphur very slowly or not at all, most probably due to absence of thiobacilli, particularly Th. thiooxidans. Even soils which oxidized sulphur rapidly never gave initial counts greater than 10⁴ cells/g. The majority of soils produced sulphide from sulphur, between one-half and two-thirds of them formed sulphide from cystine but sulphate reduction was very rare. Sulphide escaped more readily from aerobic than from waterlogged soils. Numerous genera were isolated including Desulfovibrio and Desulfatomaculum capable of reducing sulphur, both aerobically and anaerobically, particularly sporing and non-sporing mesophiles which were sometimes present at 10⁶ cells/g of soil. Sulphate reduction by the genus Desulfovibrio was uncommon, and by the genus Desulfatomaculum extremely rare. Many genera of sporing and non-sporing mesophiles seemed capable of producing sulphide from cystine when first isolated, but they quickly lost this ability on subculturing. Initial counts of 10⁶ cells/g of soil were occasionally found but usually much lower.No significant correlations, only trends, were found suggesting that any soil properties measured affected the occurrence or activities of organisms capable of producing sulphate or sulphide.     

Rice-soil interactions in Vietnamese acid sulphate soils: impacts of submergence depth on soil solution chemistry and yields

Abstract. The aim of this study was to investigate the effects of water submergence depth on radial oxygen loss (ROL), soil solution chemistry and rice growth performance in acid sulphate soils in southern Vietnam. ROL was measured in a solution culture. In a separate pot experiment the impact of water submergence depth on rice growth and soil solution chemistry was studied. Three submergence depths were used in the two experiments (5, 10 and 15 cm). ROL declined with submergence depth and was significantly greater in young roots (with no root hairs) than in older roots. In the pot experiment rice growth and soil solution chemistry were clearly affected by the submergence depth. During the first crop at 5 cm submergence, there was a significantly higher yield and a higher oxidation state (pe+pH) compared to 10 or 15 cm submergence. The Fe concentration was significantly greater at the 5 cm depth compared to the 10 or 15 cm depth. SO₄^2– reduction was delayed at the 5 cm depth. Rice yield was c. 25% less at the 15 cm than at the 5 cm depth. During a second crop, there was a substantial SO₄^2- reduction and H₂S formation and almost no significant effects of submergence depth on either soil solution chemistry or crop yield. In a field experiment with a dry-season rice crop, yield and Fe, Al and SO₄^2– concentrations were higher at a shallow submergence depth than at greater depths in the same field, showing similar depth trends to those found during the first crop in the pot experiment. Farmers should be advised to use a shallow submergence depth and, if possible, avoid deep-rooted rice varieties. A conceptual model is suggested, which summarizes the relationships between ROL and soil solution chemistry.     

人类活动对珠江三角洲酸性硫酸盐土壤发育的影响

In the Pearl River Delta with more than 1000 years of intensive land reclamation history,the development of acid sulphate soils has been generally limited in terms of their acid potential (pyrite content)and spatial extent.This is attributed to the rapid delta progradation,partially resulted from increasing sediment yield caused by deforestation within the catchment and the empolderment in the estuarine embayment.The empolderment practice accompanied by the clearance of mangroves stopped the upward growth of the pyritic layer on the one hand and limited the vertical accretion of non-pyritic freshwater sediments over the pyritic layer on the one hand and limited the vertical accretion of non-pyritic freshwater sediments over the pyritic estuarine sediments on the other.In such a case,the pyritic layer in the area is frequently thin and of shallow occurrence.Under forced leaching-recharge conditions for the paddy rice cultivation ,the leaching of acid sulphate materials prevails over its production and this leads to a net loss in pyrite oxidation products.Land excavation for fishpond farming accelerates pyrite oxidation due to the direct exposure of the pyrtic sediments to air on the pond bunds.Severe acidification can intensity the environmental degradation of estuarine ecosystems.     

Microbial activity in response to water-filled pore space of variably eroded southern Piedmont soils

Potential C and N mineralization and soil microbial biomass C (SMBC) are soil biological properties important in understanding nutrient and organic matter dynamics. Knowledge of soil water content at a matric potential near field capacity is needed to determine these biological properties. The objective of this study was to examine whether adjustment of soil water content to a common level of water-filled pore space (WFPS) may be an acceptable alternative that would require little prior analysis in comparison with adjustment based on matric potential. Potential C and N mineralization and SMBC were determined from 15 variably eroded soils of the Madison–Cecil–Pacolet association (clayey, kaolinitic, thermic Typic Kanhapludults) in response to WFPS. The levels of WFPS to achieve maximum activity and biomass under naturally settled conditions were unaffected by clay content and occurred at 0.42±0.03 m³ m⁻³ for net N mineralization during 24 days of incubation, 0.51±0.22 m³ m⁻³ for specific respiratory activity of SMBC, 0.60±0.07 m³ m⁻³ for cumulative C mineralization during 24 d of incubation, and 0.76±0.27 m³ m⁻³ for SMBC. Selecting a common WFPS level of 0.5 m³ m⁻³ resulted in 96±2%, 97±5%, 97±4%, and 88±10% of the maximum for these four properties, respectively, and was a reasonable compromise when attempting to estimate these properties during simultaneous incubations. Adjusting soil water content based on WFPS was simpler and nearly as reliable as based on matric potential, in which soil water content at −33 kPa varied from 0.16 to 0.30 g g⁻¹.     

Effective use of water in irrigated soils: Guidelines for soil salinity control

Abstract

Continued addition of irrigation water to the soil will add salts which may accumulate sufficiently to reduce plant growth and crop yields. Eventually, the accumulated salts may stop all growth, unless irrigation practices which move salts downward below the root zone are followed. Consequently, water is needed not only for growing plants but also for leaching salts out of the soil. The success of achieving these objectives primarily depends on the proper water management practices, which, in turn, depend on methods and timing of irrigation, quality and quantity of available water for irrigation, soil hydraulic properties, drainage systems, leaching requirement, and economics.