Keywords

19.1 Introduction

Soil salinity is foremost burden on agricultural lands, becoming hurdles for productive exploitation of agricultural lands for vigorous crop growth (Haque 2006; Lobell et al. 2007). Globally utilization of natural resources is increasing day by day and burgeoning population which severely influencing agriculture and different factors contributing toward worse soil conditions creating saline environment (Shahbaz and Ashraf 2013). Generally saline soils exhibit the characteristics of 4 dS m−1 and 15% exchangeable sodium percentage that inhibits the functioning of crops and ultimately result in retard growth and loss in yield (Munns 2005; Shahzad et al. 2017). Worldwide salt-affected soils cover the area of 20% of cultivable lands, and the problem on agricultural lands is 33%; moreover, it is increasing on annual basis due to change in climate. Several factors are currently under investigation which includes decreased supply of water and higher evaporation rate, weathering of rocks, saline water irrigation, and mismanagement of cultural practices (Jamil et al. 2011). No continent is free from saline problem (Table 19.1); it is estimated that 800 million lands are salt affected (FAO 2019), and salt affected land area would be increased by the year 2050 unless no precautionary measures cannot be taken with proper amendments (Ashraf 2009). It mostly occurs in arid and semiarid regions of the world which exist in all continents except Antarctica (Rengasamy 2006). Cotton (Gossypium sp.) is a cash crop named as white gold and king of fiber according its economic importance (Moseley 2001; Ahmad et al. 2014, 2017, 2018; Abbas and Ahmad 2018; Ahmad and Raza 2014; Ali et al. 2011, 2013a, b, 2014a, b). In addition to its fiber, its seed contains 15–20% oil contents, and seed cake is a rich source of protein for animal feed (Kothari et al. 2016). Cotton seed cake is used as manure having 6.5%, 3.0%, and 2.3% NPK. Cotton has significant importance for textile industry, and it is the oldest known crop employed for fiber (Amin et al. 2017, 2018; Bakhsh et al. 2012; Rahman et al. 2018; Tariq et al. 2017, 2018; Usman et al. 2009). Salinity obstructs its growth and quality traits (Ashraf 2010). Cotton is one of the salt-tolerant crops, but it is sensitive at early stages to salt stress, i.e., germination and seedling emergence as compared to later growth stages (Ahmad et al. 2002). Cotton has the ability of retaining sodium contents more than 95% in its tissues (Gouia et al. 1994). It is also reported to retain Na+ accumulation in leaves and roots of salt-tolerant cultivars (Sun and Liu 2001). Accumulation of salt in soils deters seed germination and plant growth and creates osmotic imbalance and toxicity leading to poor stand establishment (Ahmad et al. 2002; Bednarz et al. 2002). Under high salinity stress, it halts the physiological functioning of cotton by limiting photosynthesis and respiration which result in lower boll formation and poor fiber quality (Brugnoli and Lauteri 1991). Cotton is considered as moderately salt tolerant; however, it is depicted that its tolerance level varies from cultivars to cultivars (Leidi and Saiz 1997). Its tolerance level is also up to 7.7 dS m−1 (Maas and Hoffman 1977). Cotton salt tolerance level is dependent upon its ability of regulating sodium ion homeostasis in its tissues to minimize detrimental effects of cytotoxicity and by adjusting osmotic balance (Munns and Tester 2008). Salt stress disrupts photosynthetic machinery by firstly closing stomata of plants (Brugnoli and Lauteri 1991). Moreover, several reactive oxygen species (ROS) are formed under stress that further aggravates the oxidative stress to cotton (Meloni et al. 2003). On the other hand, contemporary modern approaches are available to cope with salt stress conditions to avail higher yield returns (Qadir et al. 2000; Gao et al. 2009; Shahzad et al. 2017). Saline soils can be reclaimed with plenty of good quality irrigation water (Murtaza et al. 2006). Chemical approach includes application of gypsum that improves the physical structure of soil and efficiently removes the soil from root zone (Murtaza et al. 2013). Arbuscular mycorrhizal fungi (AMF) are widely used to improve salinity tolerance in crops (Wu et al. 2010; Hajiboland et al. 2010; He et al. 2007). Improvements in cotton against salt stress tolerance is also conferred through biotechnological techniques (Zhang et al. 2011a, b, 2007; Ashraf et al. 2018a, b). It has broadened our horizon to understand the genes responsible for contributing stress tolerance (Liang et al. 2018).

Table 19.1 Salt affected soils in different continents of the world
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19.2 Saline Soil Genesis and Distribution

Salinization originate from number of variety sources, and primary sources include weathering of rocks and minerals in the earth crust which contributes soluble salt concentration to soil and sea (Van Breemen and Buurman 2002). Weathering of earth crusts is also distributing salts to ocean and other water bodies in its surrounding. Weathering of rocks is the primary origin of salinization, while secondary origins are irrigation with saline water (Bui 2013). Saline water irrigation deposits salts in soils under harch climatic conditions. Water evaporation increases resulting in accumulation of salts on the surface of the soil which give rise to saline soil (Fig. 19.1). Underground water utilized for irrigating crops is a principal source of soil sodication because it also contains sodium fairly in high concentration (Bauder et al. 2011). The other important process of saline soil genesis is the rise in ground table in some parts around the globe (Fan et al. 2013). Groundwater table is increasing at the rate of 1–2 m annually. It is mineralized with salts, and due to capillary action, water is moving upward and enhancing salts in the root zone of the plant and leave behind on the surface after evaporation (Xie et al. 2011). Fossil salts often forms in arid region due to earlier depositions of salts in the form of marine deposits (Thomas 2011). Seepage of salts from upper soil parts to the lower soil layer which ultimately finish their journey in underground water contaminates it with accumulation of excessive salt. Agricultural lands in the vicinity of ocean and seas absorb salt either via wind or groundwater movement (Ondrasek et al. 2011). It is chiefly responsible for movement of salts up to many kilometers in the surrounding area. It was observed that rate of deposition by this mean is 20–100 kg ha−1 per year in coastal areas (Rengasamy 2010). Anthropogenic activities disturb the natural environment and intentionally increasing salinity of soil. It comprises construction of roads, dams, canals, and other irrigation system on saline strata (Metternicht and Zink 2003; Oldeman et al. 1991). Likely all these human practices block the movement of water which causes severe increase to rise in water table creates water logging and finally salinization of land (Day Jr et al. 2013). Moreover, mostly farmers are unaware of the water requirement of the crops, and they tend to over-irrigate the crops which result in increase in water table (Carreira et al. 2014). Fertilization is another practice which works as a double-edged sword to increase yield of crop while on the other hand is harmful for soil health and properties leading toward contribution of salt to soil (Savci 2012). Poor waste management practices and dumping of animal waste on farm increase salt content for agricultural land. Salt stress declined agricultural productivity in many parts of world (Rozema and Flowers 2008). It was observed salinity covers more than 397 million hectares of land globally (FAO 2005). Salinity problem is exacerbated especially in arid regions because of less availability of moisture, and these regions also receive less rainfall (Pasternak and De Malach 1994; Villa-Castorena et al. 2003). Irrigated lands receive salts in the form of saline irrigated water with least leaching and poor drainage practices. Approximately 20% of the world’s land is irrigated with saline water (Sumner 1999). Almost 75 countries have been marked in the red zone of salinity stress with a moderate to severe salinity problems covering a total area of 831 million hectare, which was productive for crops in the past (Martinez-Beltran and LiconaManzur 2005; Qadir et al. 2000). Land coverage of salinity in across different continents is illustrated in Fig. 19.2 (Hoang et al. 2016).

Fig. 19.1
figure 1

Different sources contribution in forming soil salinity

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Fig. 19.2
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Distribution of salt affected lands in different continents

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19.3 Production of Cotton on Saline Soil

Cotton production halts due to presence of excessive salt concentration in soil, disturbing uptake of other essential nutrients for the growth and yield of crop (Jafri and Rafiq 1994). The main mineral ion that causes salinity stress is sodium chloride and sodium sulfate (Reich et al. 2017). Salinity influences soil nutrients for cotton by osmotic effect by increasing its concentration in the vicinity of cotton roots for uptake by plant and likely in the roots (Wang et al. 2015). On another hand NaCl deposition in roots creates dehydration by pulling out water from the roots (Younis et al. 2014). Moreover, it also disrupts the ion solution inside the plant cells that results in hindrance of physiological processes of cotton (Ashraf et al. 2017). Under saline environment, the nutrients that becomes inhibited are nitrogen, potassium, phosphorus, and zinc, so it is imperative to consider the application of these nutrients on such soils for ensuring better supply of these nutrients to combat with toxic effects of sodium and providing maintenance strategy to keep the other function of cotton to normal limits (Hu and Schmidhalter 2005; Dong et al. 2010c). Cotton is sensitive to salt at early growth stages such as during seed germination, emergence, and establishment in comparison to mature plant (Chen et al. 2010). It was suggested to take extensive measures during early growth stages to ensure robust growth for final fruitful yield (Ashraf 2010). Delayed and non-uniformity in emergence rate are the first gesture of salinity after sowing cotton seeds in saline soil (Dong et al. 2009). Decrease in germination of seed is obvious with the proportional concentration of salt concentration in soil (Ashraf et al. 2002). Complete failure of germination was observed at 16 dS m−1 (Kahlown and Azam 2002). Gossypium barbadense genotypes exhibited higher tolerance toward salinity as compared to Gossypium hirsutum and Gossypium arboreum cotton (Ahmad et al. 2002). Salinity has also mild effect on root length at low concentration, while higher concentration of sodium affects its root length (Chen et al. 2018a, b). Decreased root length and delayed secondary root growth have been reported (Cramer et al. 1987). Sodium is also a competitor of calcium to limit its uptake by cotton roots (Byrt et al. 2018). Cotton is salt tolerant, but its vegetative growth is severely affected on saline soil. Shoot is more sensitive to salt than roots. Decrease in leaf area per plant, stem thickness, and shoot and root weight reduction are important morphology traits significantly influenced by uptake of salt and higher accumulation in plants via roots (Anjum et al. 2005). On the other hand, application of calcium is beneficial for limiting Na+ uptake by plants (Reid and Smith 2000). Biomass production of cotton reduces with adverse salt stress. Boll formation also reduces with less number of fruits per plant (Gandahi et al. 2017). Salinization results in boll shedding and senescence of leaves (Rathert 1982; Brugnoli and Björkman 1992). Cotton fiber yield and length are important traits for textile industry; however, it results in poor lint quality due to interference of salts (Soares et al. 2018). Its seed also holds significant position for feed and oil sector which also becomes affected with saline conditions (Ashraf 2010). Cotton seed is a good source of oil. Decrease of cotton seed yield causes decrease in seed oil contents. It was reported that 50% decrease in seed yield was with a salinity level of 16.75 dS m−1 (Ali et al. 1986). Morphologically decrease in cotton was also reported with salinity conditions as enhanced sodicity hampered growth with a significant decrease in root length, fruit number, and ultimately lint yield (Dodd et al. 2013). Cotton is deemed to tolerate salt moderately within the range of 7.7 dS m−1 (Maas 1986), thereby it is efficient candidate crop against salt-affected soils for its growth (Ahmad et al. 2002). However, reduction in its growth and yield traits has been reported with the increase in its salinity threshold level (Khan et al. 2001; Dong 2012b; Higbie et al. 2010). Moreover, tolerance level varies among different genotypes of cotton (Ashraf 2010; Hanif et al. 2008). Cotton grown on saline soil for years exhibited elevation of Na+ concentration and decrease in phosphorus and potassium concentration in plant tissues (Rochester 2010). Similar negative correlation was observed from young and mature leaves at different growth stages of cotton (Dodd 2007). Its tolerance mechanism is dependent on genotypes for different growth stages. In order to make it tolerant, it is essential to have basic knowledge of cotton regarding tolerance at varying growth stages (Ashraf and Ahmad 2000). General perception is that halophyte plant accumulates enormous quantity of NaCl ions in tissues to adapt themselves to saline conditions, while mesophytes restrict the entry of these ions (Flowers and Colmer 2015). Higher Na+ concentration perturbs other nutrient in plants as mentioned earlier that it disturbs osmotic balance, thereby disturbed K+/Na+ uptake and its interference with each other for uptake is important mechanism for considering tolerance among cultivars (Leidi and Saiz 1997). Negative correlation of these ions uptake confers positive correlation toward salinity tolerance such as higher K+ allows lower Na+ ions uptake (Cramer et al. 1987). Moreover Na+ exclusion also resulted in tolerance, and it was also observed in tolerant cultivars that K+ concentration was measured to be higher in leaves (Ahmad et al. 2002). Oxidative stress also triggered with the entry of Na+ ion and disturbing other ions, so ROS needs to be eliminated or their effects needs to be suppressed; in this regard ROS scavenger comes to play their role which is mentioned later in this chapter. Another important strategy that is being adapted by breeders is development of salt-tolerant cotton cultivars to improve the characteristics of their local high-yielding cultivar (Harshavardhan et al. 2018). Breeding for salinity tolerance has reported potential results for improving yield of crops (Blum 2018). Cotton conventional breeding improved tolerance against salinity with a 7.4% increase in yield (Ledbetter 1987; Ashraf and Akram 2009). Later selection method was exploited which was also potential method for developing salt-tolerant cultivars (Da Silva et al. 1992).

19.4 Physiological Changes and Role of Antioxidant Enzymes

Salt stress is an environmental factor that interrupts physiological and biochemical changes in cotton (Meloni et al. 2003; Zhang et al. 2014). Salinity stress affects physiological processes by increasing respiration rate and disturbing mineral ion distribution especially displacement of calcium and potassium with Na+, sometimes leading to ion toxicity (Kinraide 1999). Salinity limits the photosynthesis process as well as cell growth (Munns et al. 2006). It directly inhibits CO2 availability due to limited diffusion via stomata, mesophyll, and disrupting metabolism of photosynthesis (Lawlor and Cornic 2002; Flexas et al. 2007). Salt interfere the photosynthetic machinery of cotton by decreasing its photosynthetic rate (Meloni et al. 2003). It results from the decline in chlorophyll contents of plants under adverse conditions (Jaleel et al. 2008). Foremost mechanism during salinity stress is the adjustment of stomata to limits transpiration and maintains cell turgor (Miller et al. 2010). Stomatal closure is the response against dehydration with the impaired supply of CO2 to shifting plants to water-saving strategy (Brodribb and Holbrook 2003). In this regard abscisic acid (ABA) plays a crucial role as a signaling molecule from its production site (roots) to the leaves for closure of stomata (Wilkinson and Davies 2002). Moreover, under saline conditions Na+ uptake is increased which halts the uptake of other essential nutrients such as potassium, calcium, and manganese (Hasegawa et al. 2000). Salt uptake in tissues of plant brutally influences older leaves with higher accumulation of salts (Munns 2002; Chaves et al. 2003). Decrease in nutrient uptake and impaired photosynthetic process was observed in cotton in response to salinity (Liu et al. 2014a, b). Salinity stress causes excessive production of ROS (You and Chan 2015). ROS are produced in different cell compartments of plant, generally the sites of its production are chloroplast and mitochondria (Jubany-Marí et al. 2009). It includes oxygen free radicals, i.e., singlet oxygen (1O2), superoxide anions (O2 •−), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH) (Zheng et al. 2009). These ROS species have detrimental effects on plant functioning by causing damage to DNA and protein (Foyer and Noctor 2005). Oxidative damages are alleviated by ROS-scavenging enzymes (Hussain et al. 2018). Antioxidant enzymes are superoxide dismutase (SOD), catalase (CAT), peroxidases (POD), and ascorbate peroxidase (APX) (Hossain and Dietz 2016). These enzymes work in a sequence to alleviate oxidative stress of cotton under salinity stress (Garratt et al. 2002). SOD is the first ROS-scavenger enzyme to start its function for alleviating ROS species; it dismutases O2 − into H2O2 and O2 (Azarabadi et al. 2017). Immediately after that POD starts catalyzing the H2O2 to H2O and O2 (Waszczak et al. 2018). Later CAT and APX capture H2O2 and convert in to H2O (Mittler 2017). Antioxidant enzymes work as indicator of salt-tolerant and susceptible cultivars (Ashraf and Harris 2004). It was observed that enzymes activities increased during salinity stress to cope with ROS species and aids in tolerance to stress (Koca et al. 2007). It was reported from studies on cotton that tolerant cultivar exhibited a higher level of antioxidant enzymes (Zhang et al. 2014; Liu et al. 2014a, b; Ibrahim et al. 2017). Increase in SOD activity in cotton alleviated oxidative stress caused by salinity (Xie et al. 2008). Lipid peroxidation results from ROS species where malondialdehyde is the product formed due to lipid peroxidation, and it represents how much damage has occurred to the plant in stress condition (Sharma et al. 2012). MDA is a marker for observing oxidative damage to the plants (Davey et al. 2005). Cotton exhibited increment in its amount due to salinity stress (Tang et al. 2007; Meloni et al. 2003). It also assists in differentiating the tolerant and susceptible cultivars (Liu et al. 2014a, b). Proline also accumulates during salinity stress to work in osmotic adjustment, alleviates free radicals, and maintains cellular redox potential (Ashraf and Foolad 2007). It accumulates normally in cytosol for osmotic regulations to cytoplasm (Ashraf et al. 2018a, b). Higher concentration of proline is correlated with tolerance of cultivar as tolerant cultivar depicts increase level of proline during salinity stress (Hayat et al. 2012). Furthermore, exogenous application also conferred significant results against salinity tolerance (Heuer 2003). Influence of proline for osmotic adjustment was observed in cotton (Meloni et al. 2001). Cotton was subjected to salt stress conditions, and marked increase proline concentration was observed to tolerate the stress (Golan-Goldhirsh et al. 1990). Proline is also associated for improving fiber quality of cotton (Xu et al. 2013).

19.5 Genetic Engineering and Molecular Biological Tool

Salts in high amount in soil result in higher uptake by plants and ultimately causing disruption of membrane functions and inhibit cell division, photosynthesis, and development of plants (Flowers 1999; Horie and Schroeder 2004). Plants as being immobile to move to favorable growth conditions thus have to survive under existing environmental conditions. First plant organs that come in contact with saline environment are root hairs from where it is taken up and transported to epidermis and cortex of plants (Cao et al. 2017). Sodium is transported to the shoots via transpiration stream in xylem, and rarely it is returned to the roots through phloem (Wu et al. 2018). Therefore, it is observed that its movement is unidirectional and results in higher accumulation of sodium in shoots (Ishikawa and Shabala 2019). Sodium accumulates in higher concentration in shoots as compared to roots, and from shoots it is transported to the leaves (Farooq et al. 2015). Potassium is a crucial nutrient for plant especially under salt stress because it is the competitor of sodium; if K+ concentration is higher, it inhibits the entry of Na+ in the plant cell and protects it from detrimental effects of Na+ (Adams and Shin 2014). Potassium is also essential for photosynthetic apparatus to aid in its functioning (Lu et al. 2016). Concentration of Na+ in high quantity disrupts the membrane functions causing disturbance in ion homeostasis which result in stunted growth and sometimes lead to death of cell (Flowers et al. 2014). Plants both halophytes and glycophytes utilize an identical strategy of regulating and maintaining Na+ ion homeostasis by coordinated functions of ion transporters for controlling the flow into the plants (Wang et al. 2017). Moreover, there are numerous selective pumps that favor the uptake of K+ compared to Na+ (Zhang et al. 2018). High-affinity potassium transporter (HKT) proteins are reported in numerous plants for playing selective role of K+ uptake against Na+ (Fairbairn et al. 2000; Golldack et al. 2002; Horie et al. 2001; Sunarpi et al. 2005). HKT was the first potassium-selective transporter found in plants (Schachtman and Schroeder 1994). It also plays function in Na+ exclusion from leaves and maintains K+ homeostasis in leaves (Horie et al. 2005). Currently Na+/H+ transporter located in tonoplast was identified that play role in outward movement of Na+ from cytosol to apoplast or vacuole (Zeng et al. 2018). However, it is an energy-consuming process for cell, and proton pumps give force for transporting Na+ contrary to electrochemical gradient (Blumwald et al. 2000). It was reported in cotton roots that Na+ concentration was lower due to higher influx of H+ via potential role of Na+/H+ antiporter (Kong et al. 2011). Another transporter is salt overly sensitive pathway (SOS); it also works as an exchanger in plasma membrane (Qiu et al. 2002). It becomes activated and plays crucial role in Na+ exclusion mechanism to render plant salt tolerance (Zhu 2000). Mechanism of Na+ transport by different pumps is depicted in Fig. 19.3. Engineered transgenic cotton is also worth mentioning for their contribution toward development of salt-tolerant cotton cultivars (Liu et al. 2014a, b). Transgenic plants contain any foreign DNA that plant does not contain naturally to improve traits and quality of plants (Rao et al. 2009). Transgenic cotton exhibited higher root development and minimized the transpiration rate; in that way it became tolerant to survive on saline soil conditions (Liu et al. 2014a, b). Cotton plants were transformed with H+-PPase gene exhibited tolerance in transgenic cotton lines by improving vegetative growth and higher photosynthetic rate resultantly lower ion leakage from the plants under salt stress as compared with non-transgenic plants (Bock 2010). Overexpression of Arabidopsis vacuolar pyrophosphatase gene (AVP1) in cotton contributed to 20% increase in fiber due to a number of boll formations under salt stress (Zhang et al. 2011a, b). Senescence results from decline in cytokinin contents in plant under stress conditions thereby isopentenyl transferase (IPT) gene has potential role in supplementing cytokinin and enhancing chlorophyll contents and delayed in senescence was reported in transgenic cotton to survive on salt affected soils (Liu et al. 2012a, b). Numerous studies have been accomplished successfully in manipulating cotton for salinity stress tolerance (Shen et al. 2015; Zhang et al. 2007; Yu et al. 2016; Cheng et al. 2018; Song et al. 2018). Plants sense stress environment and generate signals to try to adapt and adjust themselves to the salinity stress (Zhu 2016). Principal factor is regulation of genes that response under salinity stresses (Egea et al. 2018). However, it is a complex set of many genes that regulate to make the plant tolerant, while some genes are down regulated (Albaladejo et al. 2018). Salt stress induces gene expression; it was reported that the expression of salt overly sensitive (SOS2) gene and plasma membrane H+ ATPase (PMA2) gene was observed to be higher in cotton (Peng et al. 2016). In another study conducted on cotton gene expression profiles were documented for salt stress by exploiting microarray technique, and all the observed genes conferred cotton tolerant to salinity stress, furthermore some transporters also exhibited their role in rendering tolerance (Zhu et al. 2013). Genetic transporter expression is efficient for tolerance, and they also improve quality traits of cotton under adverse saline conditions (He et al. 2005). Some of the genes and their potential role under salt stress in cotton are given in Table 19.2.

Fig. 19.3
figure 3

Illustration of Na+ transport mechanisms against salt stress response and role of molecular transporters. Sodium concentration increases under saline conditions for uptake via plant roots. High-affinity potassium transporter (HKT1) unloads Na+ from the xylem. Na+/H+ exchanger (NHX) and salt overly sensitive (SOS1) assist in detoxification mechanism by decreasing the concentration of Na+ with H+ ion concentration

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Table 19.2 Genes for salinity tolerance in cotton and their functions
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19.6 Agronomic Practices to Circumvent Salinity for Cotton

Proper sowing method and good cultivation practices circumvent the effect of salt stress to cotton (Anjum et al. 2005). Cultivation methods such as mulching maintain moisture and protect from evaporation (Dong 2012b). Mulching practice to protect cotton from salinity effect is not new (Sandoval and Benz 1966). Straw mulching for 3 years reduced soil salinity (Benz et al. 1967). Mulching of cotton burr at the rate of 90 t ha−1 with intermittent sprinkling assisted in removing salts from root zone (Carter and Fanning 1964). This mulching technique is adapted for last many decades for growing cotton (Liu et al. 2012a, b). Plastic mulching with polyethylene is a general practice among cotton growers to protect seeds from complete failure of seed germination and safeguard early emergence on salt affected soils (Dong et al. 2009). Plastic mulching improved growth and lint yield of cotton by raising temperature of the soil (Dong et al. 2007). Benefits of conserving moisture are vital after its adoption that aided in control of saline environment in root zone (Bezborodov et al. 2010). Moreover, mulching is documented for unequal dispersion of salts which imparted suitable growth of roots and reduced damage of salt (Bezborodov et al. 2010). Sowing method has positive effect to overcome salinity stress (Sarangi et al. 2017). Cotton crops sown on ridges showed better growth and development as compared to crop sown on flat beds (Dong et al. 2010b). It was inferred that by exploiting this ridge sowing method there was non-uniform distribution of salts across the field as well as reduced deposition of Na+ in the root zone (Dong et al. 2008). Time of sowing is also important factor as cotton sown during normal growing season in temperate regions exhibited weak stand establishment and resulted in late maturity (Dong et al. 2007). However, late sowing efficiently enhanced seedling emergence and vigorous stand establishment due to rise in temperature with a declined Na+ contents in tissues of cotton (Dong et al. 2010a). Planting density also played a role in mitigating saline conditions. Cotton yield increase was observed by increasing planting density because enormous amount of salts might reduce plant size (Feinerman 1983). Increasing population density under severe salinity improved cotton seed yield (Dong 2012a). Plant density increased vegetative growth production, and it had positive effect for seed yield of cotton (Zhang et al. 2012a, b).

19.7 Reclamation Options and Fertilizer Management of Cotton for Saline Soils

Saline soils with excessive accumulated salts exacerbate soil physic-chemical properties which ultimately create harmful growth conditions for plants (Chabra 1996). Salinity deteriorates the soil physical structure by creating dispersion of particles, soil erosion, and sometimes water logged conditions (Warrence et al. 2002). In order to amend these soils, different reclamation strategies are in practice nowadays (Qadir et al. 2000). Reclamation can be done by considering different features appropriate in the selection of site, soil depth, and presence of hard pan and finally the most important presence of salt (Murtaza et al. 2006; Ghafoor et al. 2004). Freshwater availability free from salt can be used for removing salts from root zone and upper surface of soil with considerable leaching characteristics of soil (Bezborodov et al. 2010). It should also be considered that leaching should not be too much in order to protect the groundwater table form salts and also the amount of water applied for removal of salts. Proper irrigation management practices also contribute their role in minimizing salinity both for cotton crop and reclaiming soil to some extent (Wang et al. 2012). Sprinkler and drip irrigation are the preferred ways to remove the excessive salt from root zone of plant as well as protecting the groundwater table by limiting excessive leaching of salts as compared to flood irrigation (Karlberg and de Vries 2004). Leaching of soluble salts is an effective way of protecting rhizosphere from its toxic effects. It was documented from one study that drip irrigations conferred fruitful results for sustaining cotton productivity with the alleviation of sodium ion from roots of cotton at different growth stages (Kang et al. 2012). Chemical amendments are also beneficial of removing exchangeable sodium from cation exchange sites (Sahin et al. 2002). Gypsum is the most commonly used chemical amendment because it is cheap and easy availability (Ilyas et al. 1997). Organic amendments are also deployed for remediation of saline soils. Different organic amendments manure, mulch, and compost proved to have reclaiming characteristics of saline soil (Diacono and Montemurro 2015; Suzuki 1999). Emergence of cotton seedling increased on saline soil with organic manure application (da Costa et al. 2016). These amendments have multifaceted role in soil by enhancing aggregation of particles, improving water holding capacity to protect soil from drying via evaporation which causes accumulation of more Na+ in soil pockets (Lu et al. 2015). Moreover, they also provide nutrient that are essential to combat with Na+ for uptake by plant (Zhang et al. 2015). Therefore, fertilizer selection is crucial for saline soils. Potassium is normally applied as potassium chloride (muriate of potash) which is not suitable for saline soil. Potassium magnesium sulfate fertilizer is effective to cope with NaCl stress (Khare et al. 2015). Furthermore, nitrate has also potential to alleviate influence of higher chloride concentration in soil (Shrivastava and Kumar 2015). Management of fertilizers is a good option for cotton growing on salinized soils. Application of nitrogen to soil enhanced uptake by plant and confined Na+ uptake in cotton (Kawakami et al. 2010). Potassium and nitrogen foliar sprays are direct source of absorption by cotton leaves and bolls for sturdy growth of vegetative parts (Jabeen and Ahmad 2009). Interference of salt with nitrogen was illustrated by varying their levels and concluded that higher salt contents had profound effects on cotton plants (Chen et al. 2010). Good supply of nitrogen to the bolls either by foliar or basal resulted in higher lint yield of cotton on saline soils (Zhang et al. 2012a, b). Fertigation is another method for simultaneous application of water and fertilizers to crops (Castellanos et al. 2012). It is a modern agriculture approach for reduction of environmental pollution and feasible for cumulative chemical fertilizer usage efficiency (Hagin et al. 2002). It was employed for cotton growth to eradicate salt and give salt-free environment to the roots of cotton (Min et al. 2016). The benefits of fertigation for cotton crop was proved in another study that irrigation with suitable nitrogen fertilizer eradicated the devastating effecting of Na+ and provided nitrogen nutrient to the cotton for higher growth and yield (Min et al. 2017).

19.8 Conclusion

Salinity is an emerging global issue; cotton is being grown in more than 80 countries and plays a key role in the economy of various countries. Salinity is causing soil degradation at an alarming rate. Cotton productivity is severely hindered by degradation of soil. Cotton needs sustainable development under this situation; in order to cope with salinity, there are various mitigation tactics which can lead to sustainable productivity of cotton. Development of adaptable cotton cultivars is a basic step to face this challenge in the long run. Various scientists are keen to develop those techniques to enable crop to battle with various hazards faced during their life cycle. Adaptation in plants can be developed using various biotechnological tools. Development of appropriate surrounding situations for optimum development of crop is also considered; reclamation of soil, the use of appropriate fertilizer application, and good quality irrigation water are essential to minimize saline conditions and provide better growth of cotton.

Saline soils are formed; some decades now, the interference of human activities is worsening the already existing salt-affected soils. Moreover, adding increment to the salinized land area, proper control measures should be taken to control such activities polluting our natural environment and water resources. Salinity issues should be addressed, and awareness needs to create among farming communities directly involved for agriculture on such soils. Proper reclamation strategies potentially improved salt-affected soils and eradicating salts from root zone for improving growth of cotton. Irrigation water analysis should be done for irrigation saline soils. High EC water should not be applied to salt-affected soil. Sowing method for cotton is an efficient way for overcoming salinity problem. Likely density and plant methods should be considered. Fertilizer management is also important to supplement essential nutrients that become limited due to presence of sodium. High salt-tolerant cotton genotypes are suitable for growth on saline soil. Proper selection of cultivar also confers higher yield returns. If you don’t have any local salt-tolerant cultivar, breeding approaches should be exploited for improving traits of your local cultivar. The conventional breeding assist in fixing traits in susceptible but high yielding cotton genotypes it renders susceptible cotton genotype a tolerant one after several crossing for breeding. Physiological changes also occur in cotton due to the intake of Na+. Molecular approaches paved the path for improving antioxidant enzyme activities to combat salinity problem in cotton tissues. Development of transgenic also exhibited tolerance to salt stress which can be used growing cotton on salt-affected soil.