Characterization of leaf boron injury in salt-stressed Eucalyptus by image analysis

Symptoms of boron toxicity (i.e., necrosis of leaf tips and margins) have been observed on eucalyptus trees in the San Joaquin Valley of California where the trees are being tested for their effectiveness at reducing the volume of agricultural drainage effluents. In a controlled, outdoor sand-tank study, Eucalyptus camaldulensis Dehn., Clone 4544 trees were grown and irrigated with combinations of salinity and B to determine their influence on tree growth and water use. Irrigation water quality treatments were prepared to simulate the Na-sulfate salinity, high B nature of these drainage effluents. Electrical conductivities (EC_iw) of the waters ranged from 2 to 28 dS m-1 and B concentrations ranging from 1 to 30 mg L-1. As an integral component of this study , we developed a method to quantify and correlate foliar damage with leaf B concentrations. By scanning both injured and uninjured leaves into computer files and processing with image analysis, we were able to simultaneously correlate salinity stress with its overall effect on leaf area as well as to quantify the relative fraction of leaf area affected by specific-ion (i.e., B) injury. Leaf area was unaffected by B stress but was reduced by salinity only in the younger leaves. Boron injury was correlated with increasing irrigation water B only in older leaves. The relative injured area (RIA) of the older leaves was related to the B concentrations of leaves from trees grown at various salinities . A regression equation was developed from injury data obtained from trees grown under boron and salinity stress for 223 days (r2=0.90). From this relationship, we were able to estimate leaf boron concentrations from injury symptoms in leaves selected at random from main trunk branches of trees grown for 333 days under the same stress conditions. The results suggest that this method may have potential as an effective tool for monitoring the response to toxic levels of boron in eucalyptus, once B toxicity has been established by analytical means. The RIA appears to be mitigated by increased salinity of the irrigation water and is consistent with the general reduction in leaf B by salinity. The interactive effects of boron and salinity on foliar injury depends on the physiological age of the leaf.     

Crop production and management under saline conditions

Summary This review evaluates management practices that may minimize yield reduction under saline conditions according to three strategies: (I) control of root-zone salinity; (II) reduced damage to the crop; (III) reduced damage to individual plants. Plant response to salinity is described by an unchanged yield up to a threshold soil salinity (a), then a linear reduction in relative yield (b), to a maximum soil salinity that corresponds to zero yield (Y_o). Strategies I and II do not take into consideration any change in the parameters of the response curve, while strategy III is aimed at modifying them.Control of root zone salinity is obtained by irrigation and leaching. From the review of existing data it is concluded that the effective soil salinity parameter should be taken as the mean electrical conductivity of the saturated paste extract or of the soil solution over time and space. Several irrigation and leaching practices are discussed. It is shown that intermittent leaching is more advantageous than leaching at each irrigation. Specific cultivation and irrigation practices that result in soil salinity reduction adjacent to young seedlings and the use of water of low salinity at specifically sensitive growth stages may be highly beneficial. Recent data do not show that reduced irrigation intervals improve crop response more under saline than under nonsaline irrigation. Alternate use of water of different salt concentrations results in mixing in the soil and the crop responds to the mean water salinity.Reduced damage at the fiel level when soil or irrigation water salinity is too high to maintain full yield of single plants requires a larger crop stand. For row crops reduced inter-row spacing is more effective than reduced intra-row spacing.Reduced damage at the plant level while the salinity tolerance of the plants remains constant shows up in the response curve parameters as larger threshold and slope and constant salinity at zero yield. This is the effect of a reduced atmospheric water demand that results in reduced stress in the plant under given salinity. Management can also change the salt tolerance of the crop. This will show up as higher salinity at zero yield, as well as changes in threshold and slope. Such changes in the response curve were found at different growth stages, under different atmospheric CO₂, under different fertilization, and when sprinkler irrigation was compared with drip irrigation.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1111-E 1984 series.     

Overcoming Salinity Barriers to Crop Production Using Traditional Methods

Salinity is a major problem in arid and semi-arid regions, where irrigation is essential for crop production. Major sources of salinity in these regions are salt-rich irrigation water and improper irrigation management. The effects of salinity on crops include inhibition of growth and production, and ultimately, death. There are two main approaches to alleviating the adverse effects of salinity on agricultural crops: (i) development of salt-tolerant cultivars by screening, conventional breeding or genetic engineering, and (ii) the traditional approach dealing with treatments and management of the soil, plants, irrigation water, and plant environment. The success of the first approach is limited under commercial growing conditions, because salt-tolerance traits in plants are complex. The present paper reviews, analyzes, and discusses the following traditional approaches: (i) improving the plant environment, (ii) exploiting interactions between plant roots and bacteria and fungi, and (iii) treating the plant directly. With respect to improving the plant environment, we review the possibilities of decreasing salt content and concentration and improving the nutrient composition and concentration in the root zone, and controlling the plant's aerial environment. The interactions between salt-tolerant bacteria or mycorrhizal fungi and root systems, and their effects on salt-tolerance, are demonstrated and discussed. Discussed treatments aimed at alleviating salinity hazard by treating the plant directly include priming of seeds and young seedlings, using proper seed size, grafting onto tolerant rootstocks, applying non-enzymatic antioxidants, plant growth regulators or compatible solutes, and foliar application of nutrients. It can be concluded from the present review that the traditional approaches provide promising means for alleviating the adverse effects of salinity on agricultural crops.     

Practical salinity management for leachate irrigation to poplar trees

Landfill leachate can be beneficially reused for irrigation of fiber crops with appropriate attention to nutrient and salinity management. The Riverbend Landfill in Western Oregon has been effectively practicing irrigation of landfill leachate to poplar trees since 1993. Over that time, the site has been adaptively managed to control salinity impacts to the tree crop while beneficially utilizing the applied water and nutrients during each growing season. Representative leachate irrigation water has ranged in concentration of total dissolved solids from 777 to 6,940 mg/L, chloride from 180 to 1,760 mg/L and boron from 3.2 to 7.3 mg/L. Annual leachate irrigation applications have also ranged between 102 and 812 mm/yr. Important conclusions from this site have included: 1) Appropriate tree clone selection and tree stand spacing, thinning, and harvest rotations are critical to maintaining a productive tree stand that is resilient and resistant to salt stress. The most effective combinations have included clones DN-34, OP-367, 184-411, 49-177, and 15-29 planted at spacing of 3.7-m x 1.8-m to 3.7-m x 3.7-m; 2) Leaf tissue boron levels are closely correlated to soil boron levels and can be managed with leaching. When leaf tissue boron levels exceed 200 to 250 mg/kg, signs of salt stress may emerge and should be monitored closely; 3) Salinity from leachate irrigation can be managed to sustain a healthy tree crop by controlling mass loading rates and providing appropriate irrigation blending if necessary. Providing freshwater irrigation following each leachate irrigation and targeting freshwater irrigation as 30 percent of total irrigation water applied has successfully controlled salt impacts to vegetation; and 4) Drip irrigation generally requires more careful attention to long-term soil salinity management than spray irrigation. Moving drip irrigation tubes periodically to prevent the formation of highly saline zones within the soil profile is important. In this paper, a fifteen year record of monitoring and operational data are presented that can be used by others in managing irrigation of saline water to poplar trees. When salinity is carefully managed, tree systems can help to provide sustainable leachate management solutions for landfills.     

咸水灌溉条件下土壤水盐分布特征

通过设置3种灌水量水平（100%ET_c、80%ET_c、60%ET_c）和3种灌水水质水平（0.7、3和6 g·L^-1）,研究了咸水灌溉条件下春小麦120 cm土层内水分动态和盐分累积特征.结果表明：水分在农田土壤中的分布主要受灌水量和土壤质地的影响,充分灌溉使水分存贮在较深土层中,而非充分灌溉则使水分存贮在表层;在相同灌水量的条件下,土体内的盐分积累程度随着灌溉水矿化度的增大而加剧;在相同矿化度条件下,土体内的盐分含量及积盐深度随着灌水量的增加而增大.在作物整个生育期内,连续使用咸水灌溉将导致土壤积盐,且非充分灌溉较充分灌溉更易使土壤表层积盐.     

Foliar and root absorption of Na+ and Cl− in maize and barley: Implications for salt tolerance screening and the use of saline sprinkler irrigation

Above-canopy sprinkler irrigation with saline water favours the absorption of salts by wetted leaves and this can cause a yield reduction additional to that which occurs in salt-affected soils. Outdoor pot experiments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and barley plants exposed to four treatments: nonsaline control (C), salt applied only to the soil (S), salt applied only to the foliage (F) and salt applied to both the soil and to the foliage (F+S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m^–1 (30 mM NaCl and 2.8 mM CaCl₂) and for barley in 1994, 9.6 dS m^–1 (47 mM NaCl and 23.5 mM CaCl₂). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling and drip irrigation supplied nutrients in either fresh (treatments C and F) or saline water (treatments S and F+S).Saline sprinkling increased leaf sap Na⁺ concentrations much more than did soil salinity, especially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, leaf sap Cl^– concentrations were increased similarly by saline sprinkling and soil salinity in maize, and more by saline sprinkling than saline soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na⁺ when sprinkler irrigated with saline water. Moreover, maize leaves selectively absorbed Na⁺ over Cl^– whereas barley leaves showed no selectivity. When foliar and root absorption processes were operating together (F+S treatment) maize and barley leaves accumulated 11–14% less Na⁺ and Cl^– than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption processes. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of similar magnitude for plants exposed only to saline sprinkling, or only to soil salinity; whereas in barley, saline sprinkling was more detrimental than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na⁺ and Cl^– transport to the shoot, may not exhibit the same tolerance in sprinkler systems which wet the foliage with saline water. ei]T J Flowers     

咸水灌溉对沙土土壤盐分和胡杨生理生长的影响

通过咸水灌溉沙土土质生长的幼龄胡杨,分析了咸水灌溉沙土土壤盐分分布累积特点、盐分胁迫对胡杨的耗水生长关系、叶绿素、Pro、MDA的影响,结果表明:(1)在1.2—3 g/L范围内,微咸水灌溉沙土处于脱盐状态,6—12 g/L咸水灌溉使沙土积盐大增。在整个生长周期内,微咸水和咸水灌溉,0—200 cm内土体的总盐都呈累积趋势。(2)咸水灌溉胡杨,不同盐分处理的生长耗水关系可以用对数模型描述。(3)盐分胁迫下,胡杨叶片内叶绿素含量呈抛物线递减,Pro和MDA含量则呈现抛物线递增趋势。说明短期内咸水灌溉对土壤安全和胡杨的生长影响有限,可用咸水解决生态缺水现状,3种生理指标可用来衡量胡杨的盐胁迫程度,以此为指导提高人工造林的成活率。     

咸水非充分灌溉对土壤水盐分布及玉米产量的影响

通过不同矿化度的咸水灌溉春玉米试验,研究了石羊河流域中游咸水充分灌溉和非充分灌溉对土壤水盐分布及玉米产量的影响. 结果表明: 土壤含水量峰值均出现在灌溉期, 充分灌溉变化幅度高于非充分灌溉;土壤含盐量随灌水矿化度的增大而增大, 相同灌水矿化度下,非充分灌溉处理的土壤含盐量均较充分灌溉处理低; 非充分灌溉处理土壤盐分累积层较充分灌溉处理上移; 80～100 cm土壤含水量和含盐量保持稳定,不受灌溉水量和水质的影响.与淡水充分灌溉相比,咸水灌溉下玉米产量降低约15%～22%;9 g·L^-1、6 g·L^-1、3 g·L^-1咸水非充分灌溉下玉米收获后1 m土层平均土壤含盐量分别比充分灌溉降低8.1%、12.4%和18.4%,而产量仅分别降低3.4%、6.8%和3.0%.     

Modelling of soil salinity and halophyte crop production

In crop modelling the soil, plant and atmosphere system is regarded as a continuum with regard to root water uptake and transpiration. Crop production, often assumed to be linearly related with transpiration, depends on several factors, including water and nutrient availability and salinity. The effect of crop production factors on crop production is frequently incorporated in crop models using empirical reduction functions, which summarize very complex processes. Crop modelling has mainly focused on conventional crops and specific plant types such as halophytes have received limited attention. Crop modelling of halophytes can be approached as a hierarchy of production situations, starting at the situation with most optimal conditions and progressively introducing limiting factors. We analyse crop production situations in terms of water- and salt limited production and in terms of combined stresses. We show that experimental data as such may not be the bottleneck, but that data need to be adequately processed, to provide the basis for a first analysis. Halophytic crops offer a production perspective in saline areas, but in other areas long-term use of low quality irrigation water for halophyte production can result in serious soil quality problems. An overview is given of potential problems concerning the use of (saline) irrigation water, leading to the conclusion that soil quality changes due to poor quality water should be considered in determining the areas selected for halophyte growing.     

Fertilization management of crops irrigated with saline water

Summary Available data concerning nutrition and fertilization effects on crops irrigated with saline water are presented and discussed. Published data on the salinity-fertility relationship are, at least to some extent, contradictory; both positive and negative effects as well as no effect of fertilization on salinity tolerance have been recorded. However, a great deal of the experimental work supports the view that standard fertilization recommendations for non-saline conditions are also suitable for saline conditions. In addition, available data indicate that the apparent salt tolerance of agricultural crops varies with soil fertility level. Consequently, crops showing exceptionally high apparent salt tolerance at a low fertility level become more sensitive when adequately fertilized, although the absolute yield may be greatly increased. On the other hand, some data seem to show a real increase in salinity tolerance under improved fertility conditions.Important information concerning the responses of plants to salinity under various fertility levels was obtained by tissue analysis. It should be kept in mind that this information may be influenced also by the plant species and by environmental conditions.Contribution from The Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1085-E, 1984 series.     

高水位区暗管埋设下土壤盐分适时立体调控的生态效应

高水位地区作物生长关键期采用微咸水或咸水灌溉被证明在一定条件下可以起到增产正效应,但同时却存在着土体盐分积累及其对下茬或次年种植影响的生态负效应.为探讨消除或抑制微咸水或咸水灌溉对土壤盐分积累的生态负效应,保证作物种植增产的正效应,本文在河北近滨海高水位盐碱区开展了为期2年的试验研究,探讨了旱季微咸水或咸水灌溉带来的盐分异位积累与离子分布变化特征,分析了雨季关键期暗管适时排盐对土壤盐分的立体调控生态效应.结果表明：旱季咸水灌溉后土壤经历“积盐-脱盐-二次积盐”3个阶段;灌溉初期,1 g·L^-1咸水灌溉处理下0～50 cm土体脱盐,土壤含盐量随土壤深度增加而增加,HCO₃^-含量增加,其他离子含量降低;6与13 g·L^-1咸水灌溉处理下0～50 cm土体积盐,土壤含盐量随土壤深度增加而降低,HCO₃^-含量降低,其他离子含量增加;雨季暗管适时立体调控脱盐效果显著,土壤脱盐率达16.0%～45.7%,同降雨量下,降水分布越集中,脱盐效果越好;周年时间尺度上,咸水灌溉小区土壤积盐量小于对照区;咸水灌溉处理小区冬小麦产量显著高于对照处理,1 g·L^-1 处理高于6与13 g·L^-1处理.     

Soil Salinity and Water Stress and Their Effect on Susceptibility to Verticillium Wilt Disease, Ion Composition and Growth of Pistachio

The effects of soil salinity and water stress on Verticillium wilt, ion composition and growth of pistachio were studied in a greenhouse experiment (18–32°C). Treatments consisted of three levels of salinity (0, 1200 and 2400 mg NaCl/kg soil), three levels of water stress (3, 7 and 14 day irrigation regimes) and two Pistachio cultivars (Sarakhs and Qazvini, common rootstocks in Iran). Infested soil containing 50 microsclerotia/g of a pistachio isolate of Verticillium dahliae was used for all treatments and non‐infested soils were used as control. The experiment was arranged in a completely randomized design with three replications. Eight‐week‐old pistachio seedlings were transferred to infested and non‐infested soil and then exposed to salt stress and thereafter water stress. Shoot dry weights of both rootstocks were reduced significantly with increasing NaCl levels; however, increasing irrigation regimes reduced salt injury. Salt stress significantly increased shoot and root colonization by V. dahliae in both cultivars. Moreover, increasing of salinity level was positively correlated with increasing concentrations of Na⁺, K⁺ and Cl^? in both cultivars, but negatively correlated with increasing irrigation regimes. Based on these results, Sarakhs and Qazvini were found to be sensitive and tolerant to the effect of irrigation regimes, salinity and Verticillium wilt disease, respectively. Although there were no interactive effects of irrigation and salinity on V. dahliae infection.     

Oil content and lipid composition of safflower (Carthamus tinctorius) irrigated with saline water under greenhouse and field conditions

An intensive process of land deterioration of some regions in Uzbekistan including the Aral Sea basin has led to a significant increase in soil salinity levels and consequently to a considerable reduction of total fertile soil area, as these lands are of little use for plant growth. The area is estimated to be more than 1.4 million ha of seabed. As a result, there was an immediate need to cultivate new crops capable of stopping the movement of sands and the enlargement of saline soils. Safflower (Carthamus tinctorius) is considered to be a moderately salt‐tolerant crop and, as such, one of a few crops well suited to the cropping systems of salt‐affected soils. It is used in Uzbekistan as a reserve crop when the culture of the main crop fails. In spite of the great economic importance of this oil, there is almost no available information in the literature on the effect of salinity on oil quality and its chemical ingredients. The purpose of the present study was to determine, in greenhouse and field experiments, how irrigation with saline water would influence content of oil, lipids and other lipophylic components in safflower. We found that irrigation of safflower with moderate concentrations of saline water seems feasible, as far as oil and lipid composition is concerned. Consequently, safflower might be a potential crop for lands of little use for plant growth in Uzbekistan or other similar sites in the world.     

盐渍化灌区土壤盐分的时空变异特征及其与地下水埋深的关系

土壤盐分空间变异特征和地下水埋深状况是指导灌区合理用水和防治土壤盐碱化的重要依据。运用经典统计学和地质统计学方法,结合GIS技术,分析了河套灌区沙壕渠灌域0-20 cm、20-40 cm、40-60 cm土壤EC值的空间变异特征及地下水埋深对土壤盐分分布的影响。结果表明:沙壕渠灌域土壤盐分Cv值在不同灌溉时期和不同土壤深度均大于36%,表现为强变异特征;各灌水时期和不同土壤深度土壤EC值均表现为中等强度的空间自相关性,表层0-20 cm土壤空间自相关程度最高;秋浇前不同层次土壤EC值的空间分布在灌域内从南到北呈增大趋势,秋浇后土壤含盐量的高值区在西北部或东北部;土壤盐分受地下水埋深影响显著,灌域内地下水埋深南深北浅,土壤盐分随地下水埋深的增大而减小,二者之间满足指数关系。因此,应采取合理措施控制地下水埋深,防止区域土壤盐渍化加剧。     

Halophyte crop cultivation: The case for Salicornia and Sarcocornia

Increasing soil salinization and the growing scarcity of fresh water dictate the need for a creative solution to attain sustainable crop production. To accomplish this aim, the domestication of inherently salt tolerant plant species with economic value is proposed as a straightforward methodology. Most studies investigating salt tolerance mechanisms are linked to small, experimental systems that cannot be generalized to the real agricultural context. The crops Salicornia and Sarcocornia, however, with their extreme salt tolerance and long history of consumption by humans, make the ideal model plants on which to base a halophyte growth strategy. New applied technologies were developed for leafy vegetable production using small-scale greenhouse and in-field studies. Several cultivation systems adapted to the irrigation water salinity and the available soil conditions are described. Daylength manipulation and a repetitive harvest regime partially elucidated the flowering patterns of Salicornia and Sarcocornia and showed that flowering should be prevented for maximal vegetable production. Additionally, the beneficial effect of saline irrigation on quality parameters via the enhancement of stress-induced secondary metabolites with antioxidant capacity should be considered during cultivation. This review summarizes the recent developments in growing halophytes for food production with saline irrigation, using Salicornia and Sarcocornia as a case study.     

再生(污)水灌溉生态风险与可持续利用

作为一个农业大国,水资源贫乏及地域分布不均匀造成了我国严重的农业用水危机。为缓解我国农业用水危机,污水灌溉及再生水灌溉已成为解决农业灌溉水源不足的一项重要措施。在总结污水灌溉及再生水灌溉生态风险的基础上,针对国内研究现状,分析了我国再生水灌溉利用的可行性。研究发现,再生水灌溉的污染风险远小于污水灌溉,且再生水灌溉还具有回用成本低、减少农作物生产成本等经济效益,以及减少污染物向水环境中排放、改善土壤质量等环境效益。与污水灌溉相比再生水在农业灌溉上具有较大的应用前景,应加大其推广与应用的力度。最后,根据国内外的研究现状,提出了一些再生水灌溉可持续管理措施及其安全利用的相关建议。     

Leaching requirement conceptual models for reactive salt

Accurate prediction of the leaching requirements (Lr) of crops and striving to attain them is essential for efficient irrigation water use. Solute modeling was extended to develop four Lr conceptual models that do not neglect solute reactions in the root-zone, surface evaporation, and the influence of immobile wetted pore space. The models were based on: (i) the water movement equation which included an exponential water-uptake function (-e) or the 40-30-20-10 water-uptake function (-4); (ii) the solute movement equation for a reactive salt of a linear reaction term (the Lrchem-e and Lrchem-4 models); or the employment of output (salinity of soil solution, EC vs concentration factor, CF) of the SAO comprehensive chemical model (the LrSAO-e and LrSAO-4 models); and (iii) the inclusion of an effective soil solution volume in the transport equations. The root-zone average relative effective soil solution volume νeff (L | L50, p) was of sigmoidal response to leaching fraction (L) with two adjustable parameters L50 and p; the root-zone average reduced retention coefficient decreased linearly with L; and salt concentration at soil surface was related to salt concentration of irrigation water (ECi) by the fraction of irrigation water that evaporated (∈). The resulted concentration profiles indicated the salt behaved as a conservative one down to a threshold depth (xs) below of which salt was retained and precipitated. The depth of the conservative-salt front, xs increased with L and the 40-30-20-10 water-uptake pattern overestimated the xs depth relative to the exponential pattern. Concentration profiles were integrated to compute the root-zone average salinity, which was converted to crop salt-tolerance threshold (AE). The four conceptual models were successfully calibrated using experimental AE/ECi vs. Lr data with the input parameter values: ς = 0.27, p = 1.44, L50 = 0.16, ω = 2, and ∈ = 0 or 0.1 for the exponential or the 40-30-20-10 pattern, respectively; where ς is relative root length parameter and ω is a weighing parameter. No significant difference existed between the four model correlations at the 0.05 level. The four models require ECi and AE of the crop as input for Lr prediction. Sensitivity analysis revealed predicted Lr was sensitive the least to error in ∈. For tolerant and moderately tolerant crops Lr was sensitive the most to ς, and for sensitive crops to L50 and p. Model verification and validation were discussed. In deriving the present Lr models, no osmotic adjustment was required and both the exponential and the 40-30-20-10 water uptake patterns were, equivalently, applicable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the salt tolerance of some flower crops grown under glass

Summary The salt sensitivity of carnations, gerberas, anthuriums, chrysanthemums and hippeastrums was studied in an investigation. The crops were grown in basins filled with soil and irrigated with the aid of low level sprinklers. Two different cultivars of each crop were included in the experiments. The crops were irrigated with water containing different levels of salts. The EC of the irrigation water (EC_w) ranged between 0.2 and 3.9 mS.cm^–1 at 25°C.The salt applications had a deleterious effect on the development of all the flower crops used in the investigation. Carnations and chrysanthemums proved to be the least sensitive. Gerberas and hippeastrums showed a medium sensitivity and anthuriums proved to be the most salt sensitive. The latter crop also showed a specific sensitivity to sodium chloride.The salinity threshold values were low for most crops,i.e. EC_w<0.6. Slightly higher values were found for carnations only. The salinity decrease values of EC_w showed very wide variations and ranged from 6 to 34%. A method is proposed for the conversion of EC_w values into EC values for the saturation extract (EC_e) with the aid of the soil analytical results.The results of tissue analyses showed that the sodium and chloride contents in particular were affected by the salt applications. The effects of the salt applications on the uptake of the major nutrient elements varied from crop to crop.     

Oxygation Enhances Growth, Gas Exchange and Salt Tolerance of Vegetable Soybean and Cotton in a Saline Vertisol

Impacts of salinity become severe when the soil is deficient in oxygen. Oxygation (using aerated water for subsurface drip irrigation of crop) could minimize the impact of salinity on plants under oxygen-limiting soil environments. Pot experiments were conducted to evaluate the effects of oxygation (12% air volume/volume of water) on vegetable soybean (moderately salt tolerant) and cotton (salt tolerant) in a salinized vertisol at 2, 8, 14, 20 dS/m ECe. In vegetable soybean, oxygation increased above ground biomass yield and water use efficiency (WUE) by 13% and 22%, respectively, compared with the control. Higher yield with oxygation was accompanied by greater plant height and stem diameter and reduced specific leaf area and leaf Na+ and Cl-concentrations. In cotton, oxygation increased lint yield and WUE by 18% and 16%, respectively, compared with the control, and was accompanied by greater canopy light interception, plant height and stem diameter. Oxygation also led to a greater rate of photosynthesis, higher relative water content in the leaf, reduced crop water stress index and lower leaf water potential. It did not, however, affect leaf Na+ or Cl- concentration. Oxygation invariably increased, whereas salinity reduced the K+ : Na+ ratio in the leaves of both species. Oxygation improved yield and WUE performance of salt tolerant and moderately tolerant crops under saline soil environments, and this may have a significant impact for irrigated agriculture where saline soils pose constraints to crop production.     

Root-zone constraints and plant-based solutions for dryland salinity

Limitations to agricultural productivity imposed by the root-zone constraints in Australian dryland soils are severe and need redemption to improve the yields of grain crops and thereby meet world demand. Physical, chemical and biological constraints in soil horizons impose a stress on the plant and restrict plant growth and development. Hardsetting, crusting, compaction, salinity, sodicity, acidity, alkalinity, nutrient deficiencies and toxicities due to boron, carbonates and aluminium are the major factors that cause these constraints. Further, subsoils in agricultural regions in Australia have very low organic matter and biological activity. Dryland salinity is currently given wide attention in the public debate and government policies in Australia, but they only focus on salinity induced by shallow groundwater. However, the occurrence of transient salinity in root-zone layers in the regions where water tables are deep is an important issue with potential for larger economic loss than water table-induced seepage salinity. Root-zone constraints pose a challenge for salinity mitigation in recharge as well as discharge zones. In recharge zones, reduced water movement in sodic horizons results in salt accumulation in the root zone resulting in chemical and physical constraints that reduce transpiration that, in turn, upsets salt balance and plant growth. High salinity in soil and groundwater restricts the ability of plants to reduce water table in discharge zones. Thus plant-based strategies must address different kinds of limitations in soil profiles, both in recharge and discharge zones. In this paper we give an overview of plant response to root-zone constraints but with an emphasis on the processes of salt accumulation in the root-zone of soils. We also examine physical and chemical methods to overcome subsoil limitations, the ability of plants to adapt to and ameliorate these constraints, soil modification by management of agricultural and forestry ecosystems, the use of biological activity, and plant breeding for resistance to the soil constraints. We emphasise that soil scientists in cooperation with agronomists and plant breeders should design site-specific strategies to overcome multiple soil constraints, with vertical and lateral variations, and to develop plant-based solutions for dryland salinity.