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1.
    
The disposal of coal combustion fly ash (FA) generated from thermal power plants is a worldwide problem. However, its low bulk density and presence of calcium and iron–aluminium sesquioxide make it a prospective ameliorant alternative to gypsum for amending degraded sodic soils. A field experiment consisting of eight treatments with variable doses of FA and gypsum along with green manure (GM) was conducted for evaluating the amelioration mechanism by measuring changes in pH, exchangeable sodium percentage, zeta (ζ) potential, and properties of meso‐aggregates (0.5–2.0 mm). The results showed that compared with control, FA significantly reduced ζ‐potential, bulk density, and pH. The GM with FA further decreased ζ‐potential and increased hydraulic conductivity. The hydrolysis of iron and aluminium sesquioxide, present in FA, functioned to lower soil pH, whereas the reduction in exchangeable sodium percentage is attributed to bioavailable Ca (27.4%). A lower FA application rate produced better crop yields. FA 2.5% (w/w) alone, compared to the FA 5% (w/w), resulted in higher yield of rice (1.96 tonnes ha−1), whereas 25% gypsum requirement (25GR) + FA 2.5% (w/w) and 25GR + FA 2.5% (w/w) + GM provided wheat yield on par with 50% gypsum requirement (50GR). The study identifies that where gypsum is scarce, the recommended amendment is 25GR + FA 2.5% or 25GR + FA 2.5% + GM when applied for sodic soil to achieve a similar yield response to standard 50GR. If gypsum is unavailable, a one‐time application of FA 2.5% (w/w) alone will improve the productivity of degraded sodic soils corresponding to more exchangeable calcium and organic carbon, which were found to be higher for meso‐aggregates (0.5–2.0 mm).  相似文献   

2.
    
Salinisation of land resources is a major impediment to their optimal utilisation in many arid and semi‐arid regions of the world including Iran. Estimates suggest that about 34 million ha, including 4·1 million ha of the irrigated land, are salt‐affected in Iran as the consequence of naturally occurring phenomena and anthropogenic activities. The annual economic losses due to salinisation in the country are more than US$ 1 billion. With variable levels of success, different approaches—salt leaching and drainage interventions, crop‐based management, chemical amendments and fertilisers and integrated application of these approaches—have been used to enhance the productivity of salt‐affected soils in the Country. From sustainable management perspective, it is revealed from the past research that integrated salinity management and mitigation approaches have the potential to successfully address the complex problems of salt‐induced land degradation in Iran. As the growing need to produce more food and fibre for the expanding Iranian population necessitates the increased use of salt‐affected land resources in the foreseeable future, there is an urgent need to develop and implement a pertinent National Strategic Plan. In addition to establishing networks for monitoring spatial and temporal changes in soil salinity and water quality, this plan should integrate the management of salt‐affected environments into the overall management of land and water resources in the country. It should also address different management aspects of salt‐affected land resources in a holistic manner by considering the biophysical and environmental conditions of the target areas as well as livelihoods of the affected communities. The involvement of the communities will facilitate in developing a greater understanding about the potential uses and markets of the agricultural products produced from salt‐affected areas. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
    
Considering extreme events of climate change and declining availability of appropriate quality water and/or highly productive soil resources for agriculture in dryland regions, the need to produce more food, forage and fibre will necessitate the effective utilization of marginal‐quality water and soil resources. Recent research and practices have demonstrated that effective utilization of these natural resources in dry areas can improve agricultural productivity per unit area and per unit water applied. This paper focuses on the following three case studies as examples: (1) low productivity soils affected by high levels of magnesium in soil solution and on the cation exchange complex; (2) degraded sandy soils under rainfed conditions characterized by low water‐holding capacity, organic matter and clay content and (3) abandoned irrigated soils with elevated levels of salts inhibiting growth of income generating crops. The results of these studies demonstrate that application of calcium‐supplying phosphogypsum to high‐magnesium soils, addition of clays to light textured degraded soils and phytoremediation of abandoned salt‐affected soils significantly improved productivity of these soils. Furthermore, under most circumstances, these interventions were economically viable, revealing that the efficient use of marginal‐quality water and soil resources has the potential to improve livelihoods amid growing populations in dry areas while reversing the natural resource degradation trend. However, considerably more investment and policy‐level interventions are needed to tackle soil degradation/remediation issues across both irrigated and dryland agricultural environments if the major challenge of producing enough food, forage and fibre is to be met. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

4.
    
In the early 20th century, when extensive areas of land were transformed from rainfed to irrigated agriculture, there was a severe lack of scientific and technical literature available on the effects of applying water to saline soils. This was the case of the Violada Irrigation District located in a semiarid region of NE Spain whose transformation started in the 1940s. We discuss the use of agronomical expertise and the limited knowledge of soils available prior to the transformation, the favorable and unfavorable scenarios encountered during the transformation, and the final success of irrigation despite the initial soil salinization and water logging. We attribute the technical success to the fact that gypsum is common in the soils and geological materials, and to the continued drainage efforts. Failures in the irrigation of saline lands are a frequent subject of discussion in the scientific literature; contrariwise, we present the history of a successfully irrigated district after 70 years.  相似文献   

5.
    
Increasing levels of CO2 and H+ proton in the rhizosphere from some legumes may play an important role in calcite dissolution of calcareous salt affected soils. Soils planted with white and brown varieties of cowpea (Vigna unguiculata L.) and hyacinth bean (Dolichos lablab L.) relying on either fertilizer N (KNO3) or N‐fixation were compared against soils to which gypsum was applied and a control without plants and gypsum application to study the possibility of Ca2+ release from calcite and Na+ leaching. As compared to plants relying on inorganic N, leachates from all pore volumes (0·5, 1·0, 1·5, 2·0 pore volume) in lysimeters planted with N‐fixing hyacinth bean contained significantly higher concentrations of HCO with lower concentrations from lysimeters planted with white cowpea relying on N‐fixation. However, the lowest concentrations of HCO were recorded in the gypsum and control treatments. In initial leaching, lysimeters planted with N‐fixing plants maintained similar leachate Ca2+ and Na+ concentrations compared to gypsum amended soils. However, gypsum amended soils were found to have a prolonged positive effect on Na+ removal. It might be concluded that some legumes that are known to fix N in calcareous salt affected soils may be an alternative ameliorant to the extremely expensive gypsum through calcite solubilization and a consequent release of Ca2+. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

6.
脱硫石膏施用下宁夏盐化碱土水盐运移特征   总被引：3，自引：1，他引：3  
为定量描述脱硫石膏施用下盐化碱土土壤剖面盐分与淋洗水量的关系,通过室内土柱淋洗试验开展了脱硫石膏施用下不同淋洗水量对宁夏盐化碱土水盐运移影响的研究。结果表明:施用脱硫石膏对增加水分入渗和降低0—20cm土层土壤pH、盐分含量产生了积极影响,土壤脱盐率84.39%~95.41%,但较大水量的淋洗有可能会加剧土壤碱化。连续淋洗条件下,最大脱盐深度位于60—80cm土层。脱硫石膏施用下,0—20cm土层Cl~-、Na~+溶脱率随淋洗水量的增加变化不大,低淋洗水量下,SO_4~(2-)溶脱率低于Na~+和Cl~-,高淋洗水量下,3种离子溶脱率接近;20—40cm土层主要盐分离子溶脱率由大到小依次为Cl~-、SO_4~(2-)、Na~+,各离子脱盐率随淋洗水量的增加先增加较快后趋于平缓。当淋洗水量达到60cm时,SO_4~(2-)和Na~+在80—100cm土层累积,Cl~-则运移至100cm土层以下。  相似文献   

7.
Soil salinization is one of the major causes of declining agricultural productivity in many arid and semiarid regions of the world. Excessive salt concentrations in soils, in most cases, cannot be reduced with time by routine irrigation and crop management practices. Such situations demand soil amelioration. Various means used to ameliorate saline soils include: (a) movement of excess soluble salts from upper to lower soil depths via leaching, which may be accomplished by continuous ponding, intermittent ponding, or sprinkling; (b) surface flushing of salts from soils that contain salt crusts at the surface, a shallow watertable, or a highly impermeable profile; (c) biological reduction of salts by harvest of high‐salt accumulating aerial plant parts, in areas with negligible irrigation water or rainfall available for leaching; and (d) amelioration of saline soils under cropping and leaching. Among these methods, cropping in conjunction with leaching has been found as the most successful and sustainable way to ameliorate saline soils. Cropping during leaching or between leachings causes an increase in salt‐leaching efficiency because a decrease in soil water content occurs under unsaturated water flow conditions with a concurrent decrease in large pore bypass and drainage volume. Consequently, anaerobic conditions in soil may occur during leaching that can affect crop growth. Thus, in addition to the existing salt‐tolerant crop genotypes, research is needed to seek out or develop genotypes with increased tolerances to salinity and hypoxia. Since salt leaching is interacted by many factors, evaluation of the traditional concepts such as the leaching requirement (LR), the leaching fraction (LF) and the salt balance index (SBI) demands incorporation of a rapid, efficient and economical way of monitoring changes in soil salinity during amelioration. Besides this, numerous models that have been developed for simulating movement and reactions of salts in soils need evaluation under actual field conditions. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

8.
脱硫石膏施用下宁夏龟裂碱土水盐运移特征   总被引：1，自引：0，他引：1  
通过室内土柱淋洗试验,开展了脱硫石膏施用下不同淋洗水量对宁夏龟裂碱土水盐运移影响的研究,结果表明：脱硫石膏施用下龟裂碱土随着入渗时间的增加,湿润锋深度和累积入渗水量呈先急剧增加再缓慢增加的趋势;0~20 cm土层土壤pH值、碱化度和全盐量均有较大幅度的降低;连续淋洗条件下,最大脱盐深度位于40~60 cm土层;0~40 cm土层,随入渗水量的增加土壤脱盐率缓慢增加,其中0~20 cm土层处理1到处理4土壤脱盐率分别为79.72％、89.88％、91.93％和92.22％;随淋洗水量的增加,0~20 cm土层主要盐分离子易于溶脱的顺序为Mg2＋>Cl－>SO2－4>Na＋> HCO3－, Mg2＋溶脱率最大,可达到100％,20~40 cm土层主要盐分离子易于溶脱的顺序为Na＋>Cl－>Mg2＋, Na＋溶脱率最大,可达到91.42％, HCO3－和SO2－4含量则先增加后降低,0~40 cm土层Na＋、 Cl－、 Mg2＋随淋洗水量的增加淋洗效果更为明显。  相似文献   

9.
    
Saline water has been successfully used for irrigation in arid, semiarid, and coastal regions, and drip‐irrigation is widely regarded as the most promising system to deliver such water, particularly for reclaiming saline soils, because drip‐irrigation saves water and leaches salts efficiently. As coastal regions continue to be urbanized rapidly, vegetation establishment in coastal salt‐affected wastelands becomes increasingly urgent, but information on plants suitable for the purpose is scanty. The effects of drip‐irrigation with saline water (EC 0.8–7.8 dS/m) on the leaching of salts and on the performance of 15 plants suitable for landscaping were evaluated. The field experiment comprises trees, herbs, and shrubs, and irrigation was scheduled on the basis of soil matric potential threshold set at −5 kPa in 2013, −10 kPa in 2014, −15 kPa in 2015, and −20 kPa in 2016. As a result of irrigation controlled thus, soil that was severely saline initially became mildly saline or even nonsaline in its profile up to a depth of 1 m irrespective of the salinity of irrigation water. However, the survival rates of plants differed with the salinity and SMP threshold: Survival was more than 80% in four herb species and three tree species when irrigated with saline water at 7.8 dS/m for 4 years but decreased, especially in shrubs, as the SMP threshold was lowered. The thresholds of ECiw (electrical conductivity of irrigation water) and SMP were set based on the response of plants to salinity, and some plants are recommended for the ecological environment establishment. A combination of controlled irrigation with saline water and the right mix of plant species are helpful in reclamation of saline coastal areas.  相似文献   

10.
    
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 (ECe) 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 ECe and SAR levels. The infiltrated volume of water dropped with decrease in ECe : 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.  相似文献   

11.
    
Soil parameters, measured before crop planting, are typically used to quantify the relationship between soil properties and crop yield and to identify factors limiting crop yield. However, soil properties during sensitive stages of crop growth may have a greater effect on crop yield than the initial values. We determined if inclusion of soil properties, measured during the reproductive stage, could improve the accuracy of crop yield prediction. Classification and regression trees were used to determine the explanatory power of different soil and rice variables for predicting rice yield in alkaline salt‐affected paddy fields in northeast China. The traditional method explained 77.5% of the rice yield variation and identified soil CO32− in the 0‐ to 10‐cm soil layer, with single explanatory power of 53.4%, as the most important predictor. The whole explanatory power of the methods including soil variables during the reproductive stage and yield components, with/without soil variables before planting, increased to 81.3%. The residual sodium carbonate, measured in the 0‐ to 10‐cm soil layer during the reproductive stage, was identified as the most limiting factor due to its single maximum explanatory power of 60.5%. We conclude that inclusion of soil properties, measured during the reproductive stage, has potential for improving the rice yield prediction accuracy by enhancing the explanatory power in identification of the most limiting factor. These results encourage further investigation of the role of soil properties during sensitive stages of crop growth in crop yield prediction under different soil and climatic conditions.  相似文献   

12.
    
Salt stress is a major problem happening in almost all the world, affecting soil metabolism and acting further negatively soil fertility and soil quality, causing land degradation and low ecosystem service functions and ecosystem productivity. In marshy area as one type of important marginal land resources, salt is also the main barrier to be improved and the driving force to make vegetation succeed. This commentary briefly reviews the main advance focusing on salt‐affected soil and introduced the publications in this Special Issue: Salt Soil Improvement and Efficient Development in Land Degradation & Development 29, 2018, to promote global cooperation for studying salt‐affecting soil quality, land degradation, and eco‐restoration.  相似文献   

13.
    
Salinization and sodication are abiotic soil factors, important hazards to soil fertility and consequently affect the crop production. Soil salinization is of great concern for irrigated agriculture in arid and semi‐arid regions of the world; sodicity is characterized by an excessively high concentration of sodium (Na) in their cation exchange system. In recent times, attention has been turned to study the impacts of these factors (salinity and sodicity) on soil microbial activities. Microbial activities play central role in degradation and decomposition of soil organic matter, mineralization of nutrients and stabilization of soil aggregates. To understand the ecology of soil system, therefore, it is important to be conversant with the soil microbial activities, which show quick response to little change in the soil environment. Microbial activities (generally measured as C–N dynamics, soil respiration–basal respiration, or CO2 emission), microbial abundance, microbial biomass, quotients (microbial and metabolic) and microbial community structure, and soil enzymes have been considered as potential indicators to assess the severity of the land degradation and the effectiveness of land use management. Therefore, it is important to synthesize the available information regarding microbial activities in use and management of salt‐affected soils. The reclamation and management of such soils and their physico‐chemical properties have been reviewed well in the literature. In this review, an attempt has been made to compile the current knowledge about the effects of soil salinization and sodication on microbial and enzyme activities and identify research gaps for future research. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

14.
    
The effects of mineral fertilizers and organic amendments on soil properties, carbon (C) sequestration, and crop yields are studied in a 37‐year field experiment, Phosphorus–Potassium‐balanced design, in Switzerland. Treatments included a control (mineral fertilization) without nitrogen (N) fertilizers (Min‐N0) and with optimal N (Min‐Nopt) and 5 organic amendments (green manure [Gm], cereal straw [Str], fresh cattle manure in 2 doses 35 and 70 t ha−1 [Ma35 and Ma70] and cattle slurry [Slu]) all receiving the same optimal N fertilization as Min‐Nopt. All mineral and organic treatments received optimum P–K fertilization. Nitrogen fertilization (Min‐Nopt vs. Min‐N0) increased soil organic C, microbial activity, and microporosity but decreased pH, magnesium, and macroporosity. All organic treatments with optimal mineral N resulted in higher soil organic C content compared with Min‐Nopt, however, these effects were significant only for the highest dose of manure. The organic amendments supplied 25% to 80% additional C input to the soil compared with Min‐Nopt, and their amendment‐C retention coefficients ranged from 1.6% (Gm) to 13.6% (Ma70). Chemical, physical, and biological soil properties were not or slightly significantly different among organic treatments. Nevertheless, soils fertilized with farmyard manure produced generally higher grain yield (up to 7.3%) compared with Min‐Nopt whereas the opposite effect was noted for Gm (−2.2%) and Str (−5.2%) treatments due to their negative effect on N availability. In conclusion, Gm and Str treatments were as effectives as Ma35 and Slu treatments to prevent soil degradation but required higher chemical fertilizer to maintain crop yield.  相似文献   

15.
为了探究不同绿肥品种之间的生长差异及其翻压后对后茬水稻养分的影响,通过选取7种不同绿肥（紫云英、白三叶草、金花菜、光叶苕子、箭筈豌豆、油菜、二月兰）,以冬闲田（CK）为对照,进行大田试验,分析不同绿肥品种的生长性状、土壤肥力和水稻的产量、养分、养分累积量等指标。结果表明：不同的绿肥作物品种存在着不同的生长差异,综合来看以光叶苕子、箭筈豌豆的生物量最高,分别为46.07 t/hm2、38.74t/hm2,二者养分含量及养分累积量显著高于其他绿肥品种,适合作为苏北地区种植的绿肥品种;种植绿肥具有提高土壤肥力的潜力,促进土壤养分累积,同时对改良土壤肥力具有积极的作用。箭筈豌豆翻压后的土壤pH比CK 高出0.71%,光叶苕子翻压后有机质含量、全氮含量比CK高出1.56%、8.86%;绿肥翻压后对水稻秸秆和籽粒的氮、磷、钾含量及其累积量有了显著的增加,其中以箭筈豌豆的综合效果最好,与CK相比,箭筈豌豆翻压后水稻秸秆全氮累积量、全磷累积量分别提高15.18%、14.98%,水稻籽粒全氮累积量、全钾累积量分别提高9.98%、15.02%,水稻地上部全氮总累积量、全磷总累积量分别提高14.75%、20.42%。综上,光叶苕子、箭筈豌豆的生物量、养分累积量较高,推荐作为该地区种植的绿肥品种;光叶苕子能够对土壤肥力有一定的提高,箭筈豌豆能够促进水稻养分含量及养分累积量。研究结果可为苏北地区绿肥的利用与推广提供理论依据。  相似文献   

16.
    
Understanding the relationship between fertilization and soil bacterial communities in a salt‐affected environment is essential for alleviating the adverse impact of excessive salinity on soil biochemical functioning. However, how soil bacterial communities respond to consecutive fertilization across nitrogen gradients in coastal agroecosystem has not yet been clarified. We conducted a field plot experiment with four nitrogen fertilization rates (0, 150, 300, and 450 kg N hm−2 yr−1) on coastal salt‐affected soil for three consecutive years. Temporal dynamics of soil chemical and microbial properties was characterized, and soil bacterial community composition against N fertilization rates was investigated using 16S rRNA gene sequencing. Results indicated that consecutive N fertilization significantly increased soil organic carbon, total nitrogen (TN), available nitrogen (AN), available phosphorous, microbial biomass carbon (MBC), microbial biomass nitrogen and net nitrogen mineralization rate (NMR). N fertilization rates and cultivation years exhibited interactive effect on TN, AN, MBC and NMR. Soil bacterial community richness and diversity increased with the nitrogen rates. Predominant bacterial classes were Deltaproteobacteria, Anaerolineae, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Actinobacteria and Planctomycetia. Increasing nitrogen fertilization resulted in an elevation in the relative abundance of classes Alphaproteobacteria, Gammaproteobacteria, Planctomycetia and Nitrospira, and a decline in Anaerolineae, Acidobacteria_Gp6, Cytophagia, Bacilli and Acidobacteria_Gp10. Community composition of Alphaproteobacteria, Planctomycetia and Nitrospira was significantly associated with potential nitrification rate (PNR), whereas that of Actinobacteria was relevant to carbon mineralization rate. Results underlined that nitrogen fertilization improved nutrients, biochemical characteristics and metabolic activities to create more suitable bacterial microhabitats in the coastal agroecosystem.  相似文献   

17.
脱硫石膏是燃煤烟气湿法脱硫的副产物,已广泛应用于盐碱地改良。宁夏地区龟裂碱土质地坚硬、渗透性差,不易改良利用。为了评价脱硫石膏改良宁夏地区典型龟裂碱土的有效性和可行性,以早熟粳稻\"吉特605\"为试验材料,在大田试验条件下,研究了脱硫石膏对土壤特性、水稻产量和品质的影响,以及脱硫石膏作为盐碱地改良剂的安全性。结果表明:施用脱硫石膏降低了土壤的pH值和碱化度;显著提高水稻产量(P0.05),2013年水稻产量由2 333.3提高到3 317.4 kg/hm~2;脱硫石膏对稻米品质的影响主要体现在整精米率、垩白度、垩白粒率、胶稠度和直链淀粉上,2013年加工品质中的整精米率由52.6%提高到59.7%;比较施用脱硫石膏和未施用脱硫石膏的籽粒中的重金属含量的变化,施用脱硫石膏的籽粒中重金属除Cr含量较高外,Cd、As、Hg、Pb含量均比对照低,且都符合联合国粮农组织和国家食品标准规定的人类摄入标准。综合评价脱硫石膏施用效果,以施用量3.15×104 kg/hm~2作用效果显著。该研究为脱硫石膏改良龟裂碱土,提高资源利用率提供参考。  相似文献   

18.
Saline sodic soil with a high content of soluble carbonates is one of the important agricultural soils on the Central Indo‐Gangetic plains and elsewhere. Conventional reclamation procedures using gypsum application followed by vertical leaching (GC) is uneconomic; high ECe and precipitation of applied gypsum, reacting with soluble carbonates, reduce the efficacy of gypsum in these soils. This paper reports results from a project designed to evaluate reclamation by irrigation of the ploughed soil and turning of soil with a power tiller followed by flushing of standing water after 24 h, a second flushing after 7 days and subsequent application of gypsum and vertical leaching (GF2). Average rice and wheat production after GF2 significantly increased (25 and 62%, respectively) over the conventional practice. Compared with conventional treatment, GF2 significantly reduced the ECe and SAR of the soil and improved physical properties such as ζ‐potential, dispersible clay content, water stable aggregates expressed as MWD, and saturated hydraulic conductivity. Split application of gypsum between flushing (GF1/2 and GF2/3) gave similar results to GF2 in terms of soil amelioration and crop production.  相似文献   

19.
运用数值模拟的方法,对明沟排水洗盐过程中土壤水盐运移动态进行了研究。在沟距一半处土壤水盐运移可近似视为一维运动,冲洗脱盐率与脱盐深度最小,并沿这一位置形成对称分布;整个冲洗过程中,含盐量的变化总是稍滞后于含水率的变化;分析冲洗后不同含盐量剖面的返盐率发现,返盐率与含盐量符合幂函数关系,含盐量较低时,返盐率较高,反之亦然;运用数值模拟方法,建立了区域不同含盐量情况下明沟排水洗盐沟距一半处的洗盐制度。  相似文献   

20.
    
Sodic soils are characterized by the occurrence of excess sodium (Na+) to levels that can adversely affect soil structure and disturb availability of some nutrients to plants. Such changes ultimately affect crop growth and yield. There are large areas of the world that exist under sodic soils and need attention for efficient, inexpensive and environmentally feasible amelioration. Sodic soil amelioration involves increase in calcium (Ca2+) on the cation exchange sites at the expense of Na+. The replaced Na+ together with excess soluble salts, if present, is removed from the root zone through infiltrating water as a result of excessive irrigations. Records nearly a century old reveal the use of water, crop, chemical amendment, electric current, and tillage as amelioration tools for such soils. Among the amelioration strategies, chemical amendments have an extensive usage. Owing to gradual increases in amendment cost in some parts of the world during the last two decades, this amelioration strategy has become cost‐intensive, particularly for the subsistence farmers in developing countries. In the meantime, phytoremediation with low initial investment has emerged as a potential substitute of chemical amelioration. Phytoremediation works through plant root action that helps dissolve native soil calcite (CaCO3) of low solubility to supply adequate levels of Ca2+ for an effective Na+−Ca2+ exchange without the application of an amendment. Although significant progress has been achieved in improving amelioration methods, a great deal of work remains to analyse the economics of such methods with focus on (1) the long‐term sustainability of the amelioration projects and (2) the consequences of amelioration for the farmer himself, other growers and society as a whole. Computer modelling may help assess economic viability of different soil amelioration methods to extend results broadly to other similar locations. In addition, computer modelling to stimulate movement and reactions of salts in sodic soils has been a potentially useful complement to experimental data. However, such models need evaluation under field conditions. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

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