Sodium removal from a calcareous saline–sodic soil through leaching and plant uptake during phytoremediation

Saline–sodic and sodic soils are characterized by the occurrence of sodium (Na⁺) to levels that can adversely affect several soil properties and growth of most crops. As a potential substitute of cost‐intensive chemical amelioration, phytoremediation of such soils has emerged as an efficient and low‐cost strategy. This plant‐assisted amelioration involves cultivation of certain plant species that can withstand ambient soil salinity and sodicity levels. It relies on enhanced dissolution of native calcite within the root zone to provide adequate Ca²⁺ for the Na⁺ Ca²⁺ exchange at the cation exchange sites. There is a lack of information for the Na⁺ balance in terms of removal from saline–sodic soils through plant uptake and leaching during the phytoremediation process. We carried out a lysimeter experiment on a calcareous saline–sodic soil [pH of saturated soil paste (pH_s) = 7.2, electrical conductivity of the saturated paste extract (EC_e) = 4.9 dS m⁻¹, sodium adsorption ratio (SAR) = 15.9, CaCO₃ = 50 g kg⁻¹]. There were three treatments: (1) control (without application of a chemical amendment or crop cultivation), (2) soil application of gypsum according to the gypsum requirement of the soil and (3) planting of alfalfa (Medicago sativa L.) as a phytoremediation crop. The efficiency of treatments for soluble salt and Na⁺ removal from the soil was in the order: gypsum ≈ alfalfa > control. In the phytoremediation treatment, the amount of Na⁺ removed from the soil through leaching was found to be the principal cause of reduction in salinity and sodicity. Copyright © 2003 John Wiley & Sons, Ltd.     

Driving forces for sodium removal during phytoremediation of calcareous sodic and saline–sodic soils: a review

Abstract. Sodic and saline–sodic soils are characterized by the occurrence of sodium (Na⁺) at levels that result in poor physical properties and fertility problems, adversely affecting the growth and yield of most crops. These soils can be brought back to a highly productive state by providing a soluble source of calcium (Ca²⁺) to replace excess Na⁺ on the cation exchange complex. Many sodic and saline–sodic soils contain inherent or precipitated sources of Ca²⁺, typically calcite (CaCO₃), at varying depths within the profile. Unlike other Ca²⁺ sources used in the amelioration of sodic and saline‐sodic soils, calcite is not sufficiently soluble to effect the displacement of Na⁺ from the cation exchange complex. In recent years, phytoremediation has shown promise for the amelioration of calcareous sodic and saline–sodic soils. It also provides financial or other benefits to the farmer from the crops grown during the amelioration process. In contrast to phytoremediation of soils contaminated by heavy metals, phytoremediation of sodic and saline–sodic soils is achieved by the ability of plant roots to increase the dissolution rate of calcite, resulting in enhanced levels of Ca²⁺ in soil solution to replace Na⁺ from the cation exchange complex. Research has shown that this process is driven by the partial pressure of CO₂ (P_CO2) within the root zone, the generation of protons (H⁺) released by roots of certain plant species, and to a much smaller extent the enhanced Na⁺ uptake by plants and its subsequent removal from the field at harvest. Enhanced levels of P_CO2 and H⁺ assist in increasing the dissolution rate of calcite. This results in the added benefit of improved physical properties within the root zone, enhancing the hydraulic conductivity and allowing the leaching of Na⁺ below the effective rooting depth. This review explores these driving forces and evaluates their relative contribution to the phytoremediation process. This will assist researchers and farm advisors in choosing appropriate crops and management practices to achieve maximum benefit during the amelioration process.     

Proton release by N2‐fixing plant roots: A possible contribution to phytoremediation of calcareous sodic soils

With a world‐wide occurrence on about 560 million hectares, sodic soils are characterized by the occurrence of excess sodium (Na⁺) to levels that can adversely affect crop growth and yield. Amelioration of such soils needs a source of calcium (Ca²⁺) to replace excess Na⁺ from the cation exchange sites. In addition, adequate levels of Ca²⁺ in ameliorated soils play a vital role in improving the structural and functional integrity of plant cell walls and membranes. As a low‐cost and environmentally feasible strategy, phytoremediation of sodic soils — a plant‐based amelioration — has gained increasing interest among scientists and farmers in recent years. Enhanced CO₂ partial pressure (P_CO2) in the root zone is considered as the principal mechanism contributing to phytoremediation of sodic soils. Aqueous CO₂ produces protons (H⁺) and bicarbonate (HCO₃^‐). In a subsequent reaction, H⁺ reacts with native soil calcite (CaCO₃) to provide Ca²⁺ for Na⁺ Ca²⁺ exchange at the cation exchange sites. Another source of H⁺ may occur in such soils if cropped with N₂‐fixing plant species because plants capable of fixing N₂ release H⁺ in the root zone. In a lysimeter experiment on a calcareous sodic soil (pH_s = 7.4, electrical conductivity of soil saturated paste extract (EC_e) = 3.1 dS m^‐1, sodium adsorption ratio (SAR) = 28.4, exchangeable sodium percentage (ESP) = 27.6, CaCO₃ = 50 g kg^‐1), we investigated the phytoremediation ability of alfalfa (Medicago sativa L.). There were two cropped treatments: Alfalfa relying on N₂ fixation and alfalfa receiving NH₄NO₃ as mineral N source, respectively. Other treatments were non‐cropped, including a control (without an amendment or crop), and soil application of gypsum or sulfuric acid. After two months of cropping, all lysimeters were leached by maintaining a water content at 130% waterholding capacity of the soil after every 24±1 h. The treatment efficiency for Na⁺ removal in drainage water was in the order: sulfuric acid > gypsum = N₂‐fixing alfalfa > NH4NO3‐fed alfalfa > control. Both the alfalfa treatments produced statistically similar root and shoot biomass. We attribute better Na+ removal by the N₂‐fixing alfalfa treatment to an additional source of H⁺ in the rhizosphere, which helped to dissolve additional CaCO₃ and soil sodicity amelioration.     

Sodicity‐induced land degradation and its sustainable management: problems and prospects

Currently at least 20 per cent of the world's irrigated land is salt‐affected. However, projections of global population growth, and of an increased demand for food and fibre, suggest that larger areas of salt‐affected soil will need to be cropped in the future. About 60 per cent of salt‐affected soils are sodic, and much of this land is farmed by smallholders. Ameliorating such soils requires the application of a source of calcium (Ca²⁺), which replaces excess sodium (Na⁺) at the cation exchange sites. The displaced Na⁺ is then leached from the root zone through excess irrigation, a process that requires adequate flows of water through the soil. However, it must now be recognized that we can no longer conduct sodic soil amelioration and management solely with the aim of achieving high levels of crop productivity. The economic, social, and environmental impacts of different soil‐amelioration options must also be considered. A holistic approach is therefore needed. This should consider the cost and availability of the inputs needed for amelioration, the soil depth, the level to which sodicity needs to be reduced to allow cropping, the volume and quality of drainage water generated during amelioration, and the options available for drainage‐water disposal or reuse. The quality and cost of water available for post‐amelioration crops, and the economic value of the crops grown during and after amelioration should also be taken into account, as should farmers' livelihoods, the environmental implications of amelioration (such as carbon sequestration), and the long‐term sustainable use of the ameliorated site (in terms of productivity and market value). Consideration of these factors, with the participation of key stakeholders, could sustainably improve sodic soil productivity and help to transform such soils into a useful economic resource. Such an approach would also aid environmental conservation, by minimizing the chances of secondary sodicity developing in soils, particularly under irrigated agriculture. Copyright © 2006 John Wiley & Sons, Ltd.     

Degradation processes and nutrient constraints in sodic soils

Accumulation of excess sodium (Na⁺) in a soil causes numerous adverse phenomena, such as changes in exchangeable and soil solution ions and soil pH, destabilization of soil structure, deterioration of soil hydraulic properties, and increased susceptibility to crusting, runoff, erosion and aeration, and osmotic and specific ion effects on plants. In addition, serious imbalances in plant nutrition usually occur in sodic soils, which may range from deficiencies of several nutrients to high levels of Na⁺. The structural changes and nutrient constraints in such soils ultimately affect crop growth and yield. The principal factor that determines the extent of adverse effects of Na⁺ on soil properties is the accompanying electrolyte concentration in the soil solution, with low concentration promoting the deleterious effects of exchangeable Na⁺ even at exchangeable sodium percentage (ESP) levels less than 5. Consequent to an increase in the use of poor quality waters and soils for crop production, the problems of sodic soils can be expected to increase in future. The mechanisms that explain sodic behaviour can provide a framework in which slaking, swelling and dispersion of clay together with nutrient constraints in sodic soils may be assessed so that the practices to manage such soils can be refined for long‐term sustainable agriculture. Copyright © 2002 John Wiley & Sons, Ltd.     

Amelioration of calcareous saline sodic soils through phytoremediation and chemical strategies

Abstract. The worldwide occurrence of saline sodic and sodic soils on more than half a billion hectares warrants attention for their efficient, inexpensive and environmentally acceptable management. These soils can be ameliorated by providing a source of calcium (Ca²⁺) to replace excess sodium (Na⁺) from the cation exchange sites. Although chemical amendments have long been used to ameliorate such soils, the chemical process has become costly during the last two decades in several developing countries. As a low‐cost and environmentally acceptable strategy, the cultivation of certain salt tolerant forage species on calcareous sodic and saline sodic soils, i.e. phytoremediation, has gained interest among scientists and farmers in recent years. In a field study conducted at three calcareous saline sodic sites (pH_s=8.1–8.8, EC_e=7.8–12.5 dS m^–1, SAR=30.6–76.1) in the Indus Plains of Pakistan, we compared chemical and phytoremediation methods. There were four treatments; two involved plants: Kallar grass (Leptochloa fusca (L.) Kunth), and sesbania (Sesbania bispinosa (Jacq.) W. Wight). The other two treatments were uncropped: soil application of gypsum and an untreated control. All treatments were irrigated with canal water (EC=0.22–0.28 dS m^–1). The plant species were grown for one season (5–6 months). Sesbania produced more forage yield (34 t ha^–1) than Kallar grass (23 t ha^–1). Phytoremediation and chemical treatments resulted in similar decreases in soil salinity and sodicity, indicating that phytoremediation may replace or supplement the more costly chemical approach. The soil amelioration potential of sesbania was similar to that of the Kallar grass, which suggests that moderately saline sodic calcareous soils can be improved by growing a forage legume with market value.     

胀果甘草原生境土壤盐分特征分析

 通过野外调查采样和土样化学测定,分析胀果甘草原生境下土壤盐分的特征。结果表明:研究区土壤盐分普遍较高且表聚作用明显,土壤表层0～10 cm土层盐分均值高达32+.08g/kg,属典型的强度盐渍化土;土壤盐分组成中,含阳离子Ca2+、Na+、Mg2+、K+和阴离子Cl-、SO24、HCO-3,不含CO2-3,土壤盐分的特征因子为Ca2+、C1-、SO2-4、NaCa+,其盐渍类型主要为硫酸盐-氯化物型,重碳酸盐是土壤盐分的次要成分;该生境土壤中在整个垂直剖面上Ca2+的含量丰富,属典型钙质土。     

Edaphic characterization and soil ionic composition influencing plant zonation in a semiarid Mediterranean salt marsh

Soil characteristics and plant zonation were studied in a semiarid Mediterranean salt marsh in SE Spain. According to topographic sequences and plants distribution, two transects were established from the border of La Mata lagoon to the upland vegetation limit and soils were described and analysed. Regularly spaced plots were established in these transects in accordance with the stands of vegetation and surface soil samples were taken every 2 months for 2 years. The following edaphic factors were determined: soil moisture content, pH and concentration of Cl⁻, SO₄²⁻, Ca²⁺, Mg²⁺, Na⁺ and K⁺ in the saturation extract. In addition, the groundwater level was measured and the duration of the flooding periods established in each plot. Soil–plant relationships were studied by means of canonical correspondence analysis. Based on rainfall data for the study period, dry and wet seasons were separated and the habitats of the plant communities were compared for salt quantity and quality independently for each season. Soils were classified, according to FAO (1998), as Hypercalcic, Sodic and Mollic Solonchaks and Hypercalcic Sodic Calcisols. The most important variables which explained plant zonation were: the flooding period, total salinity, minimum Ca²⁺/Na⁺ ratio and the mean sodium adsorption ratio. When the habitats of the main plant communities were compared, differences in salt quantity, quality and seasonal variations were found. Two chenopod shrubs, Arthrocnemum macrostachyum and Sarcocornia fruticosa, predominated in the most saline areas. More pronounced seasonal variations in soil salinity were found in the A. macrostachyum zone than in the Sarcocornia fruticosa zone. The highest value for K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were measured in the Suaeda vera stand. The Lygeum spartum zone was distinguished by the high Ca²⁺/Na⁺ and Ca²⁺/Mg²⁺ ratios in the wet period. Among the rushes, Schoenus nigricans predominated in the less saline areas, where the K⁺/Na⁺ ratio was higher and the Ca²⁺/Na⁺ ratio lower than where Juncus maritimus predominated. Limonium cossonianum communities occupied an intermediate position with respect to soil salinity, between the chenopod shrubs and the other communities.Our results suggest that salt marsh plant zonation is influenced by temporal and spatial edaphic gradients which must be jointly considered if soil–plant relationships in saline soils are to be fully understood.     

Soil Properties and Maize Growth in Saline and Nonsaline Soils using Cassava‐Industrial Waste Compost and Vermicompost with or Without Earthworms

The aim of this study was to investigate the effectiveness of compost and vermicompost as soil conditioners in alleviating salt‐affected soils and increasing maize productivity. A greenhouse trial, consisting of seven soil amendment treatments in a completely randomized design with three replications, was carried out at Khon Kaen University, Thailand, during the rainy season of 2011. Plant height and total dry matter of maize increased in treatments with compost and vermicompost application when compared with the control (no fertilizer) in two types of soils (saline and nonsaline) during the growing season. Soil pH and electrical conductivity in saturation paste extracts were decreased by compost and vermicompost amendments with or without earthworms when compared with unamended treatments in the saline soil. Compost and vermicompost amendments improved cation exchange capacity, soil organic carbon, total nitrogen and extractable phosphorus in both soils. These amendments also increased exchangeable K⁺, Ca²⁺ and Mg²⁺ while decreasing exchangeable Na⁺ in the saline soil, which suggested that Ca²⁺ was exchanged for Na⁺, exchangeable Na⁺, then leached out, and soil salinity reduced as a result. Soil microbial activities including microbial C and N and basal soil respiration were improved by the application of compost and vermicompost amendments with or without earthworms when compared with the control in both soils. This experiment showed that the compost and vermicompost were effective in alleviating salinity and improving crop growth. Copyright © 2013 John Wiley & Sons, Ltd.     

Enhancing the productivity of high‐magnesium soil and water resources in Central Asia through the application of phosphogypsum

Recent evidences from some irrigated areas worldwide, such as Central Asia, suggest that water used for irrigation contains magnesium (Mg²⁺) at levels higher than calcium (Ca²⁺). Excess levels of Mg²⁺ in irrigation water and/or in soil, in combination with sodium (Na⁺) or alone, result in soil degradation because of Mg²⁺ effects on the soil's physical properties. More than 30 per cent of irrigated lands in Southern Kazakhstan having excess levels of Mg²⁺ are characterized by low infiltration rates and hydraulic conductivities. The consequence has been a gradual decline in the yield of cotton (Gossypium hirsutum L.), which is commonly grown in the region. These soils require adequate quantities of Ca²⁺ to mitigate the effects of excess Mg²⁺. As a source of Ca²⁺, phosphogypsum—a byproduct of the phosphorous fertilizer industry—is available in some parts of Central Asia. In participation with the local farming community, we carried out a 4‐year field experiment in Southern Kazakhstan to evaluate the effects of soil application of phosphogypsum—0, 4·5, and 8·0 metric ton per hectare (t ha⁻¹)—on chemical changes in a soil containing excess levels of Mg²⁺, and on cotton yield and economics. The canal water had Mg²⁺ to Ca²⁺ ratio ranging from 1·30 to 1·66 during irrigation period. The application of phosphogypsum increased Ca²⁺ concentration in the soil and triggered the replacement of excess Mg²⁺ from the cation exchange complex. After harvesting the first crop, there was 18 per cent decrease in exchangeable magnesium percentage (EMP) of the surface 0·2 m soil over the pre‐experiment EMP level in the plots where phosphogypsum was applied at 4·5 t ha⁻¹, and a 31 per cent decrease in EMP in plots treated with phosphogypsum at 8 t ha⁻¹. Additional beneficial effect of the amendment was an increase in the soil phosphorus content. The 4‐year average cotton yields were 2·6 t ha⁻¹ with 8 t ha⁻¹ phosphogypsum, 2·4 t ha⁻¹ with 4·5 t ha⁻¹ phosphogypsum, and 1·4 t ha⁻¹ with the control. Since the amendment was applied once at the beginning, exchangeable Mg²⁺ levels tended to increase 4 years after its application, particularly in the treatment with 4·5 t ha⁻¹ phosphogypsum. Thus, there would be a need for phosphogypsum application to such soils after every 4–5 years to optimize the ionic balance and sustain higher levels of cotton production. The economic benefits from the phosphogypsum treatments were almost twice those from the control. Copyright © 2007 John Wiley & Sons, Ltd.     

IONIC DISPLACEMENT AND RECLAMATION OF SALINE‐SODIC SOILS USING CHEMICAL AMENDMENTS AND CROP ROTATION

Biological, chemical and bio‐chemical strategies have been tested in the past for reclamation of saline‐sodic and sodic soils. The efficiency of two crop rotations (rice‐wheat and Sesbania‐wheat) alone or in combination with either gypsum (CaSO₄.2H₂O) or sulfuric acid (H₂SO₄) was tested for ionic displacement from four saline‐sodic soils. Pure gypsum was applied at 50 per cent of soil gypsum requirement at the time of planting rice and Sesbania, whereas 95 per cent pure sulfuric acid was added at 50 per cent soil gypsum requirement as one‐third applications by mixing with the first three irrigations. The rice crop biomass decreased at a soil saturation extract electrical conductivity (EC_e) of 8 dS m⁻¹, whereas wheat and Sesbania were influenced at a sodium adsorption ratio (SAR) of ≥40. Gypsum treatment helped the crops flourish well at these EC_e and SAR levels. The infiltrated volume of water dropped with decrease in EC_e : SAR ratio of soils and increase in crop biomass production. Crops rotation treatments alone helped leach sodium (Na⁺) and other ions successfully at SAR ≤ 21 but were less effective at SAR ≥ 40 at which point plants growth was also curtailed. Gypsum and H₂SO₄ treatments significantly aided leaching of Na⁺ and other ions with water at SAR ≥ 40 under both the crop rotations. Hence, crops effectively reclaimed soil at low sodicity level, whereas at high SAR, chemical amendments are obligatory in order to reclaim soils. This study also suggests that the required dose of H₂SO₄ should be applied with pre‐planting irrigation for better yield of the first crop. Copyright © 2011 John Wiley & Sons, Ltd.     

Dynamics of Sodium in Saline and Sodic Soils

Abstract

Soil salinization and sodication affect large areas of agricultural land in the world. Amelioration of these soils to make them suitable for agricultural production depends on understanding sodium dynamics and chemical interactions governing nutrient availability. Three locations in eastern Croatia were characterized to the 5‐m depth. The two solonetz‐solonchak soils were alkaline, whereas the solonetz soil had near‐neutral A/E horizon and alkaline deeper horizons. Electrical conductivity of the saturated extract (ECe) was greater than 4 dS m^?1 in the top horizons in the solonetz‐solonchak soils. The solonetz soil had 2.8–4.7 dS m^?1 in shallow A/E, CG, and G horizons and up to 6.3 dS m^?1 below 1.5 m. Highly alkalinized sodic horizons (exchangeable sodium percentage, ESP >20) had 24–47% Ca²⁺ and 27–33% Mg²⁺ on the cation exchange complex. Sodium adsorption ratio (SAR) was high (18–26) in the P horizon and even more so in Bt,na horizon (35–36) of solonetz‐solonchak soils. A strong negative exponential relationship existed between soluble Ca²⁺ and SAR (SAR increased greatly when Ca²⁺ dropped to around 3 mg dm^?3). An increase in pH to greater than 8.4 resulted in an exponential increase in SAR. Leaching of Na⁺ with successive volumes of water was similarly effective for the P and Bt,na horizons in the solonetz‐solonchak soils, but SAR remained greater than 15 even after six successive cycles of leaching. In conclusion, extensive amelioration of tested soils with gypsum and leaching will be required to overcome poor physical and chemical characteristics caused by various degrees of alkalization and sodication to bring these soils into production.     

Effects of Zeolite on Soil Nutrients and Growth of Barley Following Irrigation with Saline Water

ABSTRACT

Soil salinity is a major abiotic factor limiting crop production but an amendment with synthetic zeolite may mitigate effects of salinity stress on plants. The objective of the study was to determine the effects of zeolite on soil properties and growth of barley irrigated with diluted seawater. Barley was raised on a sand dune soil treated with calcium type zeolite at the rate of 1 and 5% and irrigated every alternate day with seawater diluted to electrical conductivity (EC) levels of 3 and 16 dS m^?1. Irrigation with 16 dS m^?1 saline water significantly suppressed plant height by 25%, leaf area by 44% and dry weight by 60%. However, a substantial increase in plant biomass of salt stressed barley was observed in zeolite-amended treatments. The application of zeolite also enhanced water and salt holding capacity of soil. Post-harvest soil analysis showed high concentrations of calcium (Ca^{2 +}), magnesium (Mg^{2 +}), sodium (Na⁺), and potassium (K⁺) due to saline water especially in the upper soil layer but concentrations were lower in soils treated with zeolite. Zeolite application at 5% increased Ca^{2 +} concentration in salt stressed plants; concentrations of trace elements were also increased by 19% for iron (Fe^{2 +}) and 10% for manganese (Mn^{2 +}). The overall results indicated that soil amendment with zeolite could effectively ameliorate salinity stress and improve nutrient balance in a sandy soil.     

Potassium–sodium interactions in soil and plant under saline‐sodic conditions

About 7% of the total land around the globe is salt‐affected causing a great loss to agriculture. Salt stress refers to the excessive amount of soluble salts in the root zone which induce osmotic stress and ion toxicity in the growing plant. Among toxic ions, sodium (Na⁺) has the most adverse effects on plant growth by its detrimental influence on plant metabolism in inhibiting enzyme activities. An optimal potassium (K⁺) : Na⁺ ratio is vital to activate enzymatic reactions in the cytoplasm necessary for maintenance of plant growth and yield development. Although most soils have adequate amounts of K⁺, in many soils available K⁺ has become insufficient because of large amounts of K⁺ removal by high‐yielding crops. This problem is exacerbated under sodic or saline‐sodic soil conditions as a consequence of K⁺‐Na⁺ antagonism. Here K⁺ uptake by plants is severely affected by the presence of Na⁺ in the nutrient medium. Due to its similar physicochemical properties, Na⁺ competes with K⁺ in plant uptake specifically through high‐affinity potassium transporters (HKTs) and nonselective cation channels (NSCCs). Membrane depolarization caused by Na⁺ makes it difficult for K⁺ to be taken up by K⁺ inward‐rectifying channels (KIRs) and increases K⁺ leakage from the cell by activating potassium outward‐rectifying channels (KORs). Minimizing Na⁺ uptake and preventing K⁺ losses from the cell may help to maintain a K⁺ : Na⁺ ratio optimum for plant metabolism in the cytoplasm under salt‐stress conditions. It would seem a reasonable assumption therefore that an increase in the concentration of K⁺ in salt‐affected soils may support enhanced K⁺ uptake and reduce Na⁺ influx via HKTs and NCCSs. Although very useful information is available regarding K⁺‐Na⁺ homeostasis indicating their antagonistic effect in plants, current knowledge in applied research is still inadequate to recommend application of potassium fertilizers to alleviate Na⁺ stress in plants under sodic and saline‐sodic conditions. Nevertheless some encouraging results regarding alleviation of Na⁺ stress by potassium fertilization provide the motivation for conducting further studies to improve our understanding and perspectives for potassium fertilization in sodic and saline‐sodic environments.     

内蒙古河套灌区灌排水离子组成及淋洗盐分用水量评价

以河套灌区“盐分去向”为研究背景, 通过调查灌区土壤及各级灌排渠系水阳离子含量变化及室内模拟灌溉水淋洗土柱试验, 分析灌溉水经过土壤到排水阳离子组成的变化规律, 探讨用Na⁺浓度评价淋盐排灌水量比的可行性。结果表明, 与灌溉水相比, 各级排水干渠排水所含盐分中Na⁺所占比例明显增加, 平均约为87%; Ca²⁺所占比例减少, 平均约为7%。排水的全盐浓度(EC)和Na⁺浓度有显著相关关系, 说明Na⁺浓度对排水的全盐浓度有显著影响。灌溉水的2/3 Ca²⁺以非水溶性钙盐积聚在土壤, 排出量较少, 但灌区全年的Na⁺收支基本平衡。淋盐排灌水量比评价分析结果表明, 用Na⁺浓度评价淋盐排灌水量比要优于用全盐浓度(EC); 要维持灌区Na⁺收支平衡, 排灌水量比应保持在0.12~0.15, 针对现有灌区年引水量50 亿t, 年排水量要达到6~7 亿t。     

PHYTOTOXICITY OF SALTS IN COMPOSTED SEWAGE SLUDGE AND CORRELATION WITH SODIUM CHLORIDE,CALCIUM NITRATE,AND MAGNESIUM NITRATE

The phytotoxicity of salts in composted sewage sludge (CSS) was evaluated. Concentrations of sodium (Na⁺), chloride (Cl^?1), calcium (Ca²⁺), and magnesium (Mg²⁺) were present at levels that would induce salt stress in plants. Nutrient imbalances were also found that would adversely affect the use of CSS as a growth medium. To further understand the phytotoxic nature of these salts, sodium chloride (NaCl), calcium nitrate [Ca(NO₃)₂] and magnesium nitrate [Mg(NO₃)₂] solutions were used to simulate the composition of salts found in CSS in an investigation of radish (Raphanus sativus L.) seed germination. High concentrations of Ca²⁺ (92.1 mmol.L^?1) and Mg²⁺ (27.4 mmol.L^?1) inhibited seed germination to an equal extent as did Na⁺ (40.6 mmol.L^?1). The lower concentration of Ca²⁺ (10 mmol.L^?1), however, significantly relieved the stress caused by NaCl. These results indicated that the composition and total amount of Na⁺, Cl^?1, Ca²⁺, and Mg²⁺ in CSS should be carefully monitored before it is used as a soil amendment or growth medium.     

Cation treatment and drying‐temperature effects on nonylphenol and phenanthrene sorption to a sandy soil

The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na⁺, Ca²⁺, or Al³⁺ and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na⁺ led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca²⁺ and Al³⁺ decreased it. The ¹H‐NMR relaxometry analyses showed that Al³⁺ restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca²⁺ or Na⁺. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.     

Tillage Effects on Crop Yield and Physicochemical Properties of Sodic Soils

Tillage modifies soil structure and has been suggested as a practice to improve physical, hydrological and chemical properties of compacted soils. But little is known about effect of long‐term tillage on physicochemical soil properties and crop yield on sodic soils in India. Our objective was to investigate the effect of different tillage regimes on crop yield (wheat and paddy rice) and physicochemical properties of sodic soils. Two sodic sites under conventional tillage for 5 (5‐YT; 5‐year tillage) and 9 (9‐YT; 9‐year tillage) years were selected for this study. Changes in crop yield and physicochemical soil properties were compared with a control, sodic land without any till history, that is, 0‐year tillage/untilled (0‐YT). Five replicated samples at 0‐ to 10‐cm and 10‐ to 20‐cm soils depths were analysed from each site. In the top, 0‐ to 10‐cm soil depth 5‐YT and 9‐YT sites had higher particle density (Pd), porosity, water holding capacity, hydraulic conductivity, organic carbon, total nitrogen (N_t), available nitrogen (N_avail), phosphorus (P_avail) and exchangeable calcium (Exch. Ca⁺⁺) than 0‐YT, whereas bulk density (Bd), C : N ratio and CaCO₃ were significantly lower. Bd, pH, EC and CaCO₃ increased significantly with depth in all the lands, whereas Pd, porosity, water holding capacity, hydraulic conductivity, organic carbon, N_t, N_avail, P_avail and Exch. Ca⁺⁺ decreased. We conclude that continuous tillage and cropping can be useful for physical and chemical restoration of sodic soils. Copyright © 2014 John Wiley & Sons, Ltd.     

日光温室番茄缺镁与土壤盐分组成及离子活度的关系

研究了石灰性土壤日光温室不同栽培年限及番茄不同程度缺镁的土壤水溶盐分中离子组成、比例及Mg2+、Ca2+、K+离子活度等的变化及关系.结果表明:随着栽培年限的增加,温室土壤水溶盐分中Ca2+、K+、NO3-含量显著增加;水溶性盐分中阳离子以Ca2+为主,栽培5 a后NO3-成为阴离子主要成分;土壤中NO3-含量的增加是导致土壤盐分累积的主要因素.随番茄缺镁程度的加剧,土壤水溶性盐中Ca2+、K+、NO3-、全盐量及Ca2+/Mg2+、K+/Mg2+摩尔比均呈增加趋势,番茄出现缺镁的土壤含盐量达到盐渍化水平.随着土壤盐分含量增加,Ca2+、Mg2+活度均呈指数下降趋势,番茄缺镁的土壤溶液中Mg2+和Ca2+活度显著低于不缺镁土壤,(K+)/(Mg2+)、(Ca2+)/(Mg2+)活度比显著高于不缺镁土壤,(K+)/(Mg2+)活度比随缺镁程度加剧达显著差异,番茄缺镁的土壤溶液(K+)/(Mg2+)活度比大于1.盐分累积使Mg2+活度大幅降低以及K+富集对植物吸收Mg2+的拮抗作用是石灰性土壤上番茄缺镁的主要诱因.     

Using Organic Matter with Chemical Amendments to Improve Calcareous Sodic Soil

Abstract

Kangping soil in northeast China is a sodic soil characterized by a high pH and excessive sodium. The high pH and excessive sodium in sodic soils generally cause loss of soil structure, reduce hydraulic conductivity (HC), increase soil hardness, and make the soil unproductive land. After we mixed organic matter (rice straw) and chemical amendments (H₂SO₄, CaSO₄, and FeSO₄), a column experiment was conducted to evaluate the physical and chemical properties of the soil influenced by the changes in HC, penetrability of soil s`urface, pH, electrical conductivity, CO₃ ^2‐, HCO₃ ^?, Ca²⁺, Na⁺, sodium adsorption rate (SAR), available phosphorus (P) and iron (Fe), and leached P.

Organic matter decreased the concentrations of CO₃ ^2‐, HCO₃ ^?, and Na⁺ in soil solution and increased the total volume of the leachate. Organic matter also reduced the amount of available Fe and increased the available P. However, organic matter did not affect the penetrability of the soil surface as much as soil hardness, HC, and SAR within the short period of this experiment. Among the chemical amendments, H₂SO₄ and FeSO₄ were more effective than CaSO₄ to restore HC, electrical conductivity, Na⁺, and SAR. The chemical amendments, compared with organic matter, significantly leached P from the soil in this study, but the leaching was independent of the concentration of available P in the soil. The CaSO₄ had the strongest effect in increasing leached P from the soil without changing the concentration of available P in the soil. Organic matter with added CaSO₄ leached P from the soil more than all other treatments.