Abstract The extent of salt-affected soils is proliferating because of different natural and anthropogenic factors like high temperature, low ra infall, poor quality of irrigation water etc. Different nature salts are being accumul ated at the surface of soils and make environment difficult for plants to grow on su ch soils due to the reduced hydraulic conductivity and the low permeability. Th is leads to alter physical and chemical properties of soils making them non-produc tive for general cropping. Different management and remedial technologies are available to combat with the problem but the most striving concern is to opt the most economical and environment friendly technology. Different halophytic species c an be used for the productive use of saline soils. Sodic and saline-sodic soils can b e reclaimed using different amendments, which can provide soluble calcium to re place exchangeable sodium adsorbed on clay surfaces. There are two main types of amendments: those that add calcium directly to the soil and those that dissolv e calcium from calcium carbonate already present in the soil. Studies demonstrated t hat under adverse conditions tree plantations may provide positive returns to investm ent and significant economic and social benefits to land users. These findings sugge st that there is an opportunity for capital investment in afforesting abandoned salt-af fected lands with multipurpose † Muhammad Zia-ur-Rehman * , Ghulam Murtaza, Saifullah, Muhammad Saqib and Javed Akhtar Institute of Soil and Environmental Sciences, Unive rsity of Agriculture, Faisalabad, Pakistan. * Corresponding author’s e-mail: ziasindhu1399@gmail. com Muhammad Farooq Qayyum Department of Soil Science, Faculty of Agricultural Sciences and Technology, Bahauddin Zakariya University Multan, Pakistan. Managing editors : Iqrar Ahmad Khan and Muhammad Farooq Editors : Muhammad Sabir, Javaid Akhtar and Khalid Rehman H akeem University of Agriculture, Faisalabad, Pakista Salt-affected Soils: Sources, Genesis and Managemen t 201 salt concentration in the root zone results in the saline stored water. As salinity increases, the osmotic stress of the plant increase s, which further reduces transpiration and thus plant dies when salts increa se continuously. In the presence of shallow water tables, deficienci es in D i + D r may be offset by D g . If movement of ground water is upward drainage beco mes zero. This situation cannot continue forever. Under the dynamic field condition s, upward water movement coupled with drainage remain continue alternately t hroughout the year especially in the cultivated areas. If upward flow continues whil e leaching remains insufficient, soil salinity will retard the plant growth and deve lopment and ultimately plants die. That is why if salinity problem prevails there is t he need of net downward water movement for the sustainability of the crop product ion. The conditions that control the inward water flow as well as outward from the r oot zone are not true for the steady-state conditions permanently. Due to these p rocesses salt concentration in the soil solution varies over time. The primary objecti ve of water management is the maintenance of this variation that controls the exc ess drainage as well as reduction of plant growth and development. 9.6.4. Salt precipitation The equation (2) shows that the salt balance of a r oot zone is influenced by the precipitation of soluble salts. As a result, concen tration of salts that leach down may be less than the applied quantity. At low leaching fractions (LF=0.1), almost ≥ 20% salts become precipitated from the irrigational wat er and thus not present into the drainage water. Therefore, salt precipitation compo nent is an important factor for the calculation of salt balance especially under less l eaching fraction. 9.7. Reclamation of Salt-affected Soils Several techniques are adapted to reclaim salt-affe cted soils. The fitness of each technique depends upon a number of factors, e.g., 1 ) Physical, chemical and mineralogical characteristics of the soil; 2) Inter nal soil drainage; 3) Presence of pans in the subsoil; 4) Climatic conditions; 5) Content and types of salts present; 6) Quality and quantity of water available for leaching; 7) Qu ality and depth of ground water; 8) Desired rate of replacement of excessive exchang eable Na + , if present; 9) Presence of lime or gypsum in the soil; 10) Availab ility and cost of the amendments; 11) Availability of the equipment for soil tillage , if needed; 12) Crops grown in the region; 13) Topographic features of the land; and 1 4) Time available for reclamation. Good internal soil drainage, land leveling, and dee p ground water (preferably below 3 m) are considered essential prerequisites for suc cessful reclamation. From reclamation point of view, the salt-affected soils may be divided into two categories; 1) saline and 2) sodic/saline-sodic. 9.7.1. Reclamation of saline, sodic/saline-sodic soils Saline soils restrain only higher concentration of soluble salts and their reclamation is done by leaching with excess of good quality irr igation water that carries salts intSalt-affected Soils: Sources, Genesis and Managemen t 211 For irrigation waters with EC values of 1, 2, 3, an d 4 dS m -1 , respectively, the LR will be 13, 25, 38, and 50%. These are the maximum values because rainfall, removal of salts by crops, and precipitation of salts in so ils are seldom zero. The predicted value of LR may reduce if these factors are properl y taken into consideration. Equation 1 must be used with great care as the prov ision of steady-state and/or longtime average in this case is assumed. In equati on 1 average EC of the irrigation water must be used over averaged longtime for the c onductivities of the rain water (EC rw ) and irrigation water (EC iw ) as described in the given equation: EC (rw+iw) = (D rw EC rw + D iw EC iw ) ∋ (D rw + D iw ) ...... (2) Where D rw and D iw are indicating the depths of rain water along with the irrigational water that enters into the soil respectively. In or der to restrain the soil salinity to cross a specified value, knowledge related to the consump tive use of water is an important factor if the LR concept has to be under considerat ion while determining either the depth of irrigation water that must be applied or t he minimum depth of water that must be drained. The depth of irrigation water (D iw ) is related to consumptive use (D cw ) and the depth of drainage water (D dw ) by the equation: D iw = D cw + D dw ...... (3) Using equation 1 to remove D dw from equation 3 gives: D iw = D cw / (1 - LR) ...... (4) Expressing the LR in equation 4 in terms of conduct ivity ratio in equation 1 gives: D iw = [EC dw / (EC dw - EC iw )] D cw ...... (5) Thus, the depth of irrigation water (D iw ) can explained using the EC of irrigation water, consumptive use and salt tolerance of a crop . The crop salt tolerance is taken into account by the selection of the permissible va lues of EC of the drainage water or EC of the soil saturation extract. 9.9.2. Crop selection for salt-affected soils In salt-affected soils, the wise selection of crops that can provide suitable yields (50% lower) under saline conditions may clearly differen tiate between success and failure of any management option, particularly during early phase of colonization of such soils. Plant’s ability to endure the hazards of soi l salinity within the root zone and provision of proficient growth is declared as the s alt tolerance of the plants. salt tolerance potential of various plants can be evalua te using the following criteria as: 1) The ability of the crop to survive on salt-affected soils. 2) The acceptable yield of the crop on salt-affected s oils, mostly 50 % reduced yield 3) The relative yield of the crop on a salt-affected s oil as compared with its yield on a normal soil under the similar growing co nditions. The salt tolerance of a plant is not an exact value . It depends on many factors, viz. environmental and edaphic factors (soil fertility, physical condition of soil, salt distribution in soil profile, irrigation practices, climate) and biological factors (stage of growth, varieties and rootstocks). The salt tole rance of some plants is given in Table 9.6. Table 9.6 Tolerance of some crops to saline conditions. Salin ity expressed as electrical conductivity Sensitive (0-4 dS m -1 ) Moderately tolerant (4-6 dS m -1 ) Tolerant (6-8 dS m -1 ) Highly tolerant (8-12 dSm -1 ) Almond Corn Figs Barley Bean Grain Sorghum Oats Cotton Clover Lettuce Pomegranate Olive Onion Soybean Sunflower Rye Potato Tomato Wheat Wheatgrass Source: Brady and Weil (2016) 9.9.3. Balanced fertilization Salinity, sodicity and their combination induce unf avorable nutrient ratios in soils. Excess of Na + and deficiency of many macro- and micro-nutrients are common in sodic and saline-sodic soils. The predominant facto rs responsible for low nutrient availability and mobility in sodic soils are high s oil pH and poor soil physical conditions due to dispersed soil matrix because of Na + dominance. For this reason, special fertilizer management practices are needed for optimum crop production. Low organic matter coupled with deficiency of nitro gen is the basic feature of the salt affected soils. Nitrogen deficiency can be met by adopting the green manuring technique using sesbania species that also decrease the harms and hazards of salinity/sodicity. During the reclamation of the so dic soils part of the N may also leach down along with the other soluble salts and N a + . Some studies that were conducting in Pakistan (Murtaza 2011) as well as in India (Yaduvanshi and Dey 2009) reveal that application of higher dose of nit rogen than the requirement for the crops growing under saline/sodic conditions endow w ith more yield and production may be due to stimulation of dilution effect couple d with enhanced salt tolerance potential of plants (Woyema et al. 2012). Yaduvansh i and Dey (2009) and Murtaza et al. (2014) reviewed a series of experiments and recommended that rice and wheat crops grown in sodic soils should receive 25-30% N over and above the recommended rates for non-saline/sodic soils. Sodic and saline-sodic soils usually have higher av ailable phosphorus than the normal soils because higher concentrations of Na 2 CO 3 results in the formation of soluble Na 3 PO 4 . On the basis of some studies, it has been propose d that the sodic soils after reclamation require less additional P f ertilizer for some years. Similarly, it has been suggested that a 50% reduction in the reco mmended dose of P may be practiced for a rice-wheat rotation grown up to thr ee years during reclamation without yield loss. Increasing sodicity nearly alwa ys results in a deficiency of Ca 2+ concentration in the soil. Fertilizers containing C a 2+ (calcium nitrate, single superphosphate) or those producing physiological ac idity (ammonium sulphate, urea) perform better than the equivalent rates of C a-free or physiologically less acidic Salt-affected Soils: Sources, Genesis and Managemen t 213 materials like NH 4 NO 3 etc. Generally, it is recommended that application of fertilizers, except P containing fertilizers, to th e marginal salt-affected soils should be done at higher rates (15-30%) compared to their counterpart normal soils in any agro-ecological zone. 9.9.4. Planting techniques Under field conditions, it is possible through the modification of planting practices to minimize the tendency of salts to accumulate aro und the seed and to improve the stand of crops those are sensitive to salts during germination. Seeds of a crop sprout only when they are placed so as to avoid excessive salt around them. The pattern of salt concentration changes with the shape of beds o n which seeds are sown. 9.9.5. Saline agriculture Saline agriculture is defined as the profitable and integrated use of genetic resources (plants, animals, fish, insects and microorganisms) and improved agricultural practices to obtain better use from saline land and saline irrigation water on a sustained basis. Saline agriculture presents a syst ematic approach for the utilization of salt-affected lands involving a combination of s alt tolerant crops, crop genotypes and salt tolerant grasses, trees and shrubs. The co mponents of this system are site- specific and are changed according to the farmer ne eds, land capability, locality, market availability and climatic conditions of the area. Salt-affected lands are mostly potentially productive although with a lot of spati al variability. Therefore, the potential of salt-affected land is evaluated and co nsidered to select plants and other genetic resources for its utilization. Slightly sal t-affected lands are used for salt tolerant varieties of different crops. Moderately s alt-affected lands are used for salt- tolerant trees and grasses and the highly salt-affe cted lands are used for salt-tolerant shrubs and bushes. In the world there are more than 1500 salt-tolerant plants species but in Pakistan less than 1% of these species are present. The major cro ps including rice, wheat, cotton and maize have different tolerance to salinity and associated problems. It has been observed that these major crops have little or no g rowth at EC e 15 dS m -1 . However, there is genetic difference among the genotypes of each crop. Rice cultivars KS-282 and NIAB-6 are moderately salt-tolerant which produ ce about 30-35% more paddy than ordinary varieties. But rice is only crop that gives best results in water logged and sodic soil conditions. Salt-tolerant wheat vari eties selected by Saline Agriculture Research Center at the University of Agriculture Fa isalabad include SARC-I, SARC- II, SARC-III, SARC-IV, SARC-V and SARC-VI. Cotton c rop is a salt tolerant crop but problems occur with the emergence in sodic or s aline-sodic soils condition. NIAB-78 and MNH-93 are best salt tolerant cotton va rieties. Salt tolerant trees and grasses include date palm ( Phoenix dactylifera ), sugarbeet ( Beta vulgaris ), wheat and semidwarf ( Triticum aestivum ), bermuda grass ( Cynodon dactylon ), kallar grass ( Diplachne fusca ), mesquite ( Prosopis juliflora ) and river salt bush ( Atriplex amnicola ). Many of the salt tolerant plants have the potent ial to rapidly grow at electrical conductivity EC e ≥ 30 dS m -1 . 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