Abiotic Stress Tolerance in Cotton

*Aamir Hassan, Muhammad Ijaz, Abdul Sattar, Ahmad Sher, Sami-Ullah, Iqra Rasheed, Muhammad Zain Saleem and Ijaz Hussain*

## **Abstract**

Cotton (*Gossypium hirsutum* L.) is a vital fiber crop that is being cultivated under diverse climatic conditions across the globe. The demand for cotton and its by-products is increasing day by day due to more consumption of this fiber in the textile industry and the utilization of cotton seed as a source of edible oil. However, the average seed cotton yield in the world is below that of the potential yield of cultivars. The factors responsible for low yield includes shortage of approved seed, pest and disease attack, weed infestation, unwise use of nutrients, and the incidence of abiotic stresses (including drought, heat, and salinity). Among these, the abiotic stresses are a single major factor, which is responsible for reducing the yield now and will affect the productivity of cotton in future. In this scenario, it is necessary to adopt ways to improve the tolerance of cotton against abiotic stresses. The strategies for improving tolerance against abiotic stresses may include the wise use of macroand micronutrients, the use of osmoprotectants, the use of arbuscular mycorrhizal fungi, and the plant-growth promoting rhizobacteria.

**Keywords:** nutrient management, PGPRs, osmolytes, plant hormones, fiber

#### **1. Introduction**

Abiotic stresses are major limiting factors that affect the growth, yield, and development of cotton. It is a fiber crop. It is cultivated in many countries across the globe. Medicinal products, home stuff, and cloth products are being processed from cotton crop. The raw material for the textile industry and also human oil consumption requirement are fulfilled by this crop. Extreme temperature, salinity stress, and water depletion are the main abiotic stresses that are considered the primary factors, which limit the productivity of cotton. The worldwide reduction of cotton crop is 50% due to the abiotic stress [1].

For maximum yield of cotton crops, they require optimum growth conditions like other field crops. For example, a temperature of 27–32°C is preferred by cotton crop during the formation of boll. At ≥36°C [2], the major reduction in carbon fixation was found in cotton crop, and for optimum photosynthesis, the optimum temperature is ~33°C. Poor yield and growth of the plant are caused by the major impact of salinity and alkalinity. The water stress in cotton is caused by salt acting as an osmoticum.

Specific ion toxicity is also a major cause of low yield in this crop. Inequity of nutrients is also a major cause. Plant metabolism is affected by impairing the photosynthetic process and membrane thermostability due to high temperature management. At the higher temperatures, the protein may be denatured and the activity of enzyme is more sensitive. Due to the effect of drought stress, the cell growth is influenced by the decrease in turgor pressure in cotton crop. The carbohydrate metabolism as well as photosynthesis is influenced by the drought stress directly or indirectly. Any change in carbon uptake also changes the process of photosynthesis resulting in the decrease of boll maintenance of the cotton plant and also the area of leaf that is a response to the stress due to drought [3]. The fiber quality, yield, and growth of this crop are affected by different abiotic stresses. In this chapter, we have discussed the impacts of different abiotic stresses on cotton performance and have enlisted possible improvement in its performance through application of plant hormones (auxin, cytokinins, abscisic acid, brassinosteroids, ethylene, and gibberellins) and plant nutrients (macronutrients and micronutrients).

## **2. Salinity stress**

Throughout the biosphere, the salinity stress has been the most important restrictions for the productivity of agriculture [4]. The cultivated area affected by the stress of salinity all over the world is 20% [5]. Because of decline in water uptake by emerging seeds, plant roots, photosynthesis, respiration, and protein synthesis, germination is reduced due to impact of salt stress. It also affects productivity and growth of the cotton crop [6]. In mitochondria and chloroplast, the undue accumulation and generation of reactive oxygen species [ROS; like superoxide anion (O<sup>−</sup><sup>2</sup> ), the hydroxyl radicals (OH), and hydrogen peroxide (H2O2)] are a result of the effect of soil salinity stress [7, 8]. Excessive salts in soil affect negatively the productivity and growth of cotton [9]; however, cotton is one of the most salt-tolerant crops. Plants own a number of antioxidant enzymes such ascorbate peroxidase (APX), glutathione reductase (GR), and superoxide dismutase (SOD) for fortification against the damaging effect of ROS (e.g., superoxide anion (O2<sup>−</sup>)) [10]. Under the unfavorable condition, the osmolytes metabolize the function in cotton to produce sugar alcohol [11]. Glycinebetaine and Proline serve as scavengers of ROS and also well-suited protectants, osmolytes for the macromolecules under the condition of salt stress. With specific references to stress and photosynthesis metabolism for controlling the survival and productivity, little information is present on biochemical and physiological features of cotton under the salt stress conditions. At the persistent salinity of 17 dS m<sup>−</sup><sup>1</sup> , the yield reduction is 50%, and when the salinity is at threshold level, which is 7.7 dS m<sup>−</sup><sup>1</sup> , a notable decline in seed cotton yield occurs. In conclusion, soil salinity negatively impacts the cotton growth and yield by affecting the plant physiological and biochemical traits.

## **3. Drought stress**

For all the agricultural commodities, the availability of water is a determining factor for the yield and growth of the cotton plants under stress situations. Increasing human demand for water availability and demands for water for agriculture purpose in increasing and changing climate condition are the main factors restraining accessibility to water for agriculture. The shorter plants with small number of nodes resulted due to the drought stress in the cotton plants during the squaring period. With the help of drought stress treatments, there would be highest yields of the cotton plants. Except the full application of irrigation, the fiber quality parameters were significantly improved. The poor fiber quality, lowest fruit retention, and lowest yield production at the flowering stages are more sensitive to

#### *Abiotic Stress Tolerance in Cotton DOI: http://dx.doi.org/10.5772/intechopen.89622*

drought stress. There is poor fiber quality and yield losses at the squaring as a result of stress due to drought [12]. The severity and timing of the drought determine what will be the effect of water stress on yield. Photosynthesis process is slowed down because of a decrease in the number and size of cotton leaves. Krieg [13] showed that water stress reduced crop growth rate.

The variability in genotype responses to drought stress in cotton has been reported [14]. Compared to drought tolerance, many morpho-physiological characters have been recommended as significant selection criteria for cotton crops. The distance from the first main lateral root to transition zone is increased due to drought stress in cotton, and also the increase in taproot weight, seedling vigor, the amount of lateral roots, and also the development of root system is rapid [15]. The temperature of canopy, the discrimination of carbon isotope, leaf water content, conductance of stomata, and rate of photosynthesis also reduce the rate of transpiration due to the effect of drought [16]. Cotton crop has taproot system. In cotton seedlings, a number of lateral roots are produced, which depends on the xylem poles for water absorption [17]. The amount of vascular bundles increases due to the increase of branching intensities of lateral roots in the cotton crop [18]. In cotton, decreasing leaf transpiration by stomatal transpiration (TRst) and cuticular transpiration (TRcu) is the important physiological indicator of water stress [19].

Stomatal conductance controls stomatal transpiration (TRst) under water stress conditions. Leaf surface characters like morphological structure and the thickness of the wax layer affect the cuticular transpiration (TRcu) [20]. Lewitt showed that stomatal closing can avoid drought in plants. Stomatal closing and opening are regulated by the help of guard cells. Overproduction of reactive oxygen species (e.g., superoxide and peroxide) is followed by drought stress. Inhibition of photosynthesis and cellular damage are a result of this. This process is known as oxidative stress and is a major cause of plant damage due to stresses of environment [21] in many crops. According to McMichael et al. [17], in the present cotton cultivars, genetic variability is low for many drought-tolerant characters. So, under high rainfall and humid situations, much of the current cultivars are opted. Potential sources of traits associated with drought tolerance are considered as primitive race stocks of upland cotton [22].

## **4. Heat stress**

By virtue of its geographical position, the cotton belt of Pakistan is present in the area of high level of temperature. In the Kharif season, the temperature approaches 50°C. The water stress and high temperature increase the impact that reduces the yield or quality of fiber, and fewer plants per unit area are a result of the heat stress with the other environmental stresses [23]. It is estimated that the harmful effect of heat stress causes the cotton crop to achieve only about 25% of yield potential [24]. The effect of these stresses is location-specific, exhibiting variation in frequency, intensity, and duration. The environmental stresses are site-specific, exhibiting frequency variation, light intensity, and duration of light. It is the practical approach to estimate the responses of heat responses by field evaluation of cotton under high temperatures with appropriate irrigations [10]. The ability to screen for heat tolerance might be affected by the timing of heat stress. It has been suggested that the identification of relative cell injury level from leaf disks at high temperature is the screening technique for heat tolerance in plants [25]. Plant development rate is much increased at high temperature, which reduces the life period besides other detrimental effects like denaturing of membranous structures [26]. Lint yields and quality are negatively correlated with the high temperature [27, 28]. The first and foremost requirement is to identify the suitable stock(s) to be used in breeding in

any crop improvement program [29]. It was reported that in most dry land cotton production areas seedling heat tolerance is essential. Under heat conditions, emerging cotton seedlings poorly develop root system and show burning effects on the leaves; particularly, the younger leaves are adversely affected [11]. When plants grown in pots are exposed to high air temperatures, the shoots and the roots are challenged with hot condition, and it was observed that optimum temperature for leaf area development was 26°C for cotton [30].

## **5. Waterlogging stress**

In areas with poor drainage or level, due to the excess of drainage and rainfall, the soil surface becomes saturated with water and this state of land is called waterlogging. Every year, the land area of the world experienced by waterlogging is about 10% [31]. The following are the two conditions: one is anoxic (oxygen absent: energy gain by fermentation is the only condition) and the other is hypoxic (low oxygen concentration: mitochondrial respiration is reduced and the process of fermentation takes place) because the microbial activity and plant activity use maximum amount of oxygen. During the conditions when the soil is waterlogged, the physicochemical properties such as the redox potential and pH are strongly changed due to the lack of oxygen concentration [32]. The effect of waterlogging on the salt-containing soil is more than 50% and these soils are mostly used for high-value crops such as cotton [33]. There are many drawbacks of the consequences of waterlogging for the plants of cotton, which may include terminated growth and the death of root apices, and also, increasing nutrient patterns may also be changed. For the growth of cotton, a waterlogged environment is lethal because it stops exchanging of gas and also results in energy problems [34]. Through the process of waterlogging, yield formation and the growth of cotton are strongly affected. But also these processes are complicated and remain unclear. It is reported that the adoption of cotton to the waterlogged stress is very poor [35]. But the cotton crop is that type of species that has indeterminate growth habit and has the large ability to compensate after the effect of abiotic stress.

#### **6. Improving abiotic stress tolerance in cotton**

#### **6.1 Plant hormones**

#### *6.1.1 Auxins*

For the development of the body and for the life cycle of plants, auxins are essential. These hormones play a critical role in the coordination of behavioral process and also in the growth of the plant. These hormones are present in all parts of plants. For the different process, the amount of these hormones is also different; for example, the most dominating and effective auxin is indole acetic acid (IAA). For the growth of cotton plants in abiotic stress, the dynamic and environment-responsive pattern of this hormone distribution within the plants of cotton is a key factor for their growth. These are also very important for the development of plant organs such as leaves or flowers and for the environmental reaction under the abiotic stress. Through the plant body, the process of polar auxin transport is achieved by the complex and well-coordinated active movement of these hormones from cell to cell in the plant body. Indole-3 propionic acid, indole-3-butyric acid, phenylacetic acid, indole-3-acetic acid, and 4-chloroindole-3-acetic acid are the five naturally occurring auxins, which are endogenous in nature [36]. For the proper development of plant growth, these hormones are

#### *Abiotic Stress Tolerance in Cotton DOI: http://dx.doi.org/10.5772/intechopen.89622*

very essential and contribute to giving the shape to the organ. Plants would be merely successful heaps of similar cells without hormonal regulation and organization of auxin hormone. The development of primary growth poles and future buds are formed by the auxin application. The employment of auxin begins in the embryo of the plant, and for subsequent growth, the distribution of the hormone is directional under the abiotic stresses [37]. This hormone is very important for proper growth and development. Also, with the help of this hormone, fruit senescence is delayed. In cotton, auxin plays a small role in initiation of the flowering and for reproductive organ development. Under the abiotic stress condition, when there is low concentration of auxin hormone, the senescence of the flower is delayed. In cotton, the lower concentration of this hormone can inhibit the formation of ethylene and also higher concentration can disturb the synthesis of ethylene. In cotton plants under abiotic stress, the auxin hormone influences a different kind of process such as the developmental and physiological. Through the auxin hormone application under stress conditions, rapid alteration in the roots of cotton occurs. Under abiotic stresses, in the cotton plants, various signaling auxin components appear that mediate diverse physiological and developmental processes. The target of various auxin-signaling components might be the strategy of potential to enhance the tolerance in cotton plants under abiotic stresses.

## *6.1.2 Cytokinins*

Cytokinins are naturally occurring type of plant hormones. Under the drought condition, with the help of that hormone, the production of cotton is increased under stress. This increases the cell division and growth. The growth of the plant's main stem and branches is motivated in cotton by these hormones. For the growth and yield of cotton, there are many commercially produced hormones available, which are applied under the stress condition. In the area where there is absence of water or no irrigation, through the application of these hormones, the growth is also improved under stress conditions. Half of the production of cotton from Asia is in arid high water-shortage areas. The 60–65% of the acreage in the area is dry and depends on the rainfall for the moisture of the soil in short growing season. There is more difficulty for the cotton plants to absorb the soil water because the young cotton plant seedlings have small root systems under stress conditions. In the young plant, the defense for the water is promoted by that hormone. Also for the absorption of the soil moisture, it helps to promote the plants to build a strong and deep root system. To prevent the loss of water under stress conditions, it stimulates the growth of protective wax on the surface of the plants. Under water-stressed conditions, it has been reported that the application of cytokinins increases the yield by 5–10%. The cytokinins can be applied in the early season when conducting normal weed management practices, and no extra work is involved for the grower. It should be applied at a relatively low concentration to cotton seeds or to cotton plants at an early stage of development. The developmental and various physiological processes in the cotton plants are done by cytokinins. The division of the cell in plants also increases under the abiotic stress [38].

Cytokinins have a vital function in seed and root development. This hormone also retarded fiber elongation at elevated concentration in ovule culture. Cotton fiber and seed yield were improved by slightly raising the level of endogenous cytokinins. This also decreases the expression of cytokinin dehydrogenase [39]. Plant hormones play a significant role during interaction with physiological and developmental 'switches' involved in fiber growth. Cytokines also help in cell elongation by loosening the cell wall and supplying structural materials under stress conditions. During this process, secondary cell wall deposition and increased cellulose formation are key roles of that hormone. The opposed effect of some hormones may act as a restraining factor for fiber cell development under the abiotic stress conditions. The exogenous application of plant growth regulators at a particular time may be helpful for the appropriate cell development. Little is known about how some of the cells are differentiated into lint (long fibers) and others into fuzz (short fibers) from the same ovule epidermis. Selective utilization of nutrients for elongation of long fibers is the main reason under the stress. When a number of cells differentiate into fiber, some substances from ovule epidermal cells are transferred into fuzz, which affects other cells to develop into full-length fibers, which is another important reason under the stress condition.

#### *6.1.3 Abscisic acid*

The role of the abscisic acid (ABA) in the fiber development is an inhibitor. The growth of the fiber is also decreased when using the ABA to unfertilized cultured ovules [40]. The inhibitory function of ABA is somewhat balanced in the presence of cytokinins, which inhibits fiber development in the absence of ABA. At the time of boll formation, the concentration of ABA is low and also decreases during the next 2 days [41].

It was found that the ABA level was higher in mature cotton fruits as compared to young healthy fruits [42]. It was concluded that the internal ABA level exhibited a reverse correlation with the rate of fiber elongation. Among the different cotton cultivars, it is shown that high internal ABA contents result in shorter fiber and the reverse relationship exists between ABA contents and fiber length. Dasani and Thaker [43] tested the fiber of different cultivars of cotton under stress condition. The function of the ABA is revealed in both in vitro and in vivo situations for the improvement of fiber. The inhibitory effect of ABA on fiber length was reduced due to the addition of growth promoters like naphthaleneacetic acid (NAA) and gibberellic acid (GA) along with ABA. From the results of in vivo and in vitro experiments, it can be concluded that ABA may be playing an inhibitory role in fiber elongation and is a positive indicator of the onset of cell wall thickening.

#### *6.1.4 Brassinosteroids*

Brassinosteroids are naturally occurring hormones with steroid chemistry and are found throughout the kingdom Plantae. They elicit growth stimulation at nanomolar concentrations. Brassinosteroids enhance cell elongation and affect cytoskeleton and cell wall structure.

It is stated that adding a minute concentration of brassinosteroid (brassinolide (BL)) to cultured cotton ovules increased cotton fiber elongation, while the use of brassinazole 2001 (BRZ) and also the inhibitor of BR biosynthesis retarded fiber length and ovule size [44]. The application of BR biosynthesis inhibitor (brassinazole 2001) hindered fiber initiation probably due to alteration in the differentiation of ovule epidermal cells into fibers. The exogenous application of BL increases the formation of fiber, while the application of BRZ reverses the effect [45]. BR signal transduction plays a role in determining cotton fiber length. Transgenic plants with altered brassinosteroid insensitive 1 (BRI1) expression produce fibers similar in length to wild-type plants. The thicker secondary wall with fiber is produced by the plants that overexpress BRI1. These are the changes in fiber cell growth correlated with changing in expression of cellulose formation gene in fiber development.

#### *6.1.5 Ethylene*

Ethylene biosynthesis is the most important pathway that is upregulated during cotton fiber cell elongation in accordance with recent physiology and gene expression analysis [46] under optimal and suboptimal conditions. During the 10–15 DPA

#### *Abiotic Stress Tolerance in Cotton DOI: http://dx.doi.org/10.5772/intechopen.89622*

(days post anthesis), the involvement of 1-aminocyclopropane-1-carboxylic acid oxidase 1–3 (ACO1–3) was predicted very effective for fiber growth elongation under the abiotic stress condition. The exogenous application of the ethylene inhibitor, 2-aminoethoxyvinyl glycine (AVG), inhibits the growth of fiber, and ethylene increased fiber cell expansion under the stress condition [45]. According to the results, under the stress condition, this hormone has a significant role in supporting cotton fiber growth and elongation. Additionally, ethylene might enhance cell elongation by escalating the expression of tubulin, sucrose synthase, and expansion genes [46]. Detection of ethylene in fibers proved that it affects fiber elongation.

Ethylene biosynthesis genes (ACO1–3) are expressed at fiber elongation stage. According to that, it may interact with BR and ROS signaling pathway. Experiments on cultured ovules have shown that exogenous application of ethylene ameliorate the problem of fiber elongation caused due to BR biosynthesis inhibition. The exogenous application of both ethylene and BR on cultured ovules triggered the expression of genes for biosynthesis of other phytohormones. This cross-talk between hormones and genes may regulate fiber development in both negative and positive perspectives [47].

## *6.1.6 Gibberellins*

The combination of auxin and gibberellins has been found to increase the fiber growth in in vitro cultured ovules [48]. Under abiotic stress, the application of auxin and gibberellins from exogenous source is vital for fiber growth in unfertilized ovules [49]. Studies on gene expression also explored the role of gibberellins and auxin in fiber growth. In DNA microarray, a cupin super family protein was found to be upregulated in 10 DPA ovules [50]. Because the plants have tissue sensitivity to improve the crop yield and quality, the transgenic approach has increased the manipulation of the hormones' concentration [51]. At a molecular level, to improve the fiber length and micronaire value, much effort has been made by scientists. Also the increased fiber for lint percentage and elongation was observed in cotton crop [52]. The targeted expression of an IAA biosynthetic gene under floral binding protein promoter (FBP7) was also shown in several studies and amplified the endogenous IAA levels at the fiber initiation stage under the abiotic stress [53]. The main aim of cotton-producing countries is to improve the yield of crop. By developing the seed that gives more yield of fiber under abiotic stress conditions, this aim of high yield can be fulfilled. The development of plant hormones plays an important role for the maximum growth and development of the crop [54]. The exogenous application of GA3 not only promotes the fiber length but also enhances the thickness of cell wall significantly. During abiotic stress, long length cotton fibers with thicker cell wall and increased dry weight per unit cell length were obtained.

## **6.2 Plant nutrients**

### *6.2.1 Macronutrients*

## *6.2.1.1 Nitrogen*

Nitrogen is a significant constituent of nucleic acids and amino acids and is required in high concentrations to plants. Maximum yields are not obtained from optimum nitrogen supply in the absence of adequate water, and optimum water supply will also not give maximum yield in the absence of adequate nitrogen supply [55]. Cotton that grows in different moisture stress levels in sandy soil shows similar special interactive effects of nitrogen supply and drought stress. Nitrogen shows

#### *Advances in Cotton Research*

genetic variation, selection, and breeding of lineages that are more effective in their N uptake. It is the more efficient strategy in arid land than in temperate zone [56]. When salinity is not severe, the addition of nitrogen enhances the growth and yield of crops [57].

Nitrogen also plays a key role in the synthesis of chlorophyll and proteins as well as in cell division. But cotton production can also be improved by foliar application in salinity stress [58]. Root development, germination, senescence, respiration, cell death, disease resistance, and hormone responses in crops are also influenced by nitrogen application. During abiotic stress in cotton, nitrogen plays an important role to activate the antioxidant defense in cotton [59]. Therefore, when the supply of nitrogen is adequate, root restriction increases the root activity. It also increases the availability of photoassimilates to above-ground plant parts. Hence, with the application of nitrogen to cotton, shoot growth and the ratio of shoot and root are enhanced.

#### *6.2.1.2 Phosphorus*

Phosphorus (P) is an essential component of nucleic acids, phosphor-lipids, and adenosine triphosphate. It also plays an important role in the storage, energy transfer, and also transport of carbohydrate. The pH is high and soils are calcareous in arid areas. Under the drought stress condition, phosphorous application can improve the growth of cotton crop [13]. The foliar application of urea and diammonium phosphate is the main source of phosphorous for the improvement of growth and development of cotton crop [60–62]. Improvement of fiber in cotton crop under the stress conditions can be obtained by the foliar spray of phosphorous at the boll formation stage [63]. In addition, boll weight and seed cotton yield are increased under stress [64].

Phosphorous is constituent of cell nuclei, and it is essential for cell division and development of meristematic tissues [65]. Phosphorous also influences the formation of nucleic acid, protein, and lipids as well as photosynthesis. In biotic stress conditions, the application of phosphorous improves the quality parameters of cotton. Cotton shows positive and economical response to phosphorous application [66]. Hence, plant height, shoots, and roots in cotton plants in abiotic stress conditions are enhanced by the application of phosphorous.

Phosphorous is efficiently applied to soil by fertigation as compared to broadcast application. However, in abiotic stress conditions, cotton yield can be improved with adequate amount of phosphorous fertilizer application at appropriate time. The reduced canopy is the result of the unbalanced nutrients in soil from the improper input of nutrients. Therefore, under abiotic stress conditions, photosynthesis rate and the yield of the cotton are reduced [67].

In abiotic stress conditions, the rate of leaf expansion and photosynthesis per unit leaf area of cotton crop are reduced due to phosphorous deficiency [68]. Crop growth, nitrogen and potassium uptake, total chlorophyll content, and dry matter yield of cotton plant are significantly enhanced by phosphorous [69]. The application of phosphorous leads to increased phosphorous uptake and content in leaf, stem, and reproductive parts such as seeds [70]. Phosphorous has a stimulating effect on number of flower buds and bolls per plant as well as is essential for cell division. Plant height, number of sympodial branches, seed index, boll weight, and seed cotton yield vary in all cotton cultivars due to genotypic variation [71, 72].

Cotton is facing decline in yield and quality because of abiotic stresses. Several genes for genetic engineering have been made from the cloning technology such as those related to fiber development (cytokinin dehydrogenase), disease resistance

(PR-3 and PR-10), and stress responses (GbRLI)3 . These genes play an important role in successfully generating transgenic cotton lines with greater abiotic stress tolerance [73].

## *6.2.1.3 Calcium*

Calcium plays a vital role in maintaining the many physiological processes that impact both the growth of cotton plants and also the responses to environmental stress. All the biotic and abiotic stresses and damages are repaired and act as defense for the cotton plants by the processes of translocation and respiratory metabolism. Concentration of water and the movement of the solutes influence these processes. These processes are also influenced by the Ca2+ on the structure of membrane and on the function of stomata. The uptake of calcium is minimized under stress conditions as compared to other elements. Hence, the accumulation of calcium is decreased to small extent as compared to phosphorous and potassium and this accumulation was in the range of 40, 71, and 91% for phosphorous, potassium, and calcium, respectively, in dry conditions in the mature cotton crops. The direct application of calcium is an efficient method for increasing the fiber yield of cotton. The incidence of fungal pathogens is reduced leading to increase in yield, and several physiological disorders are minimized by the application of calcium salt.

## *6.2.1.4 Potassium*

The optimal supply and the good source of potassium (K) are very critical for increasing the growth and yield of the cotton crop. With the help of stomatal cell, the turgor pressure and osmotic pressure are increased with the help of K under the drought stress condition [74]. Soil salinity problem widely affects all the agronomic and physiological parameters of the cotton crop. These effects were lowered by the optimal application of potassium fertilizers [75]. Potassium increases the uptake of other essential nutrients, so the productivity of cotton is badly affected through the low application of potassium [76]. With no application of potassium, the cotton yield and also yield-contributing factors and fiber quality will reduce [77]. It was suggested in a study that under drought stress, the application of potassium influences the physiological functions of cotton [78]. The two cultivars of cotton were planted in drought stress and well-watered conditions with three potassium rates (0, 150, and 300 K2O kg/ha) and these plants were showing higher leaf water potential, stomatal conductance, photosynthesis rate, and the maximum and actual quantum yield of PSII. With the application of potassium, the cotton plants were showing lower lipid peroxidation, higher antioxidant enzyme activity, as well as increased proline accumulation as compared to nonapplication of potassium, and a significant relationship was observed between photosynthetic recovery and potassium application.

Maintaining surplus water pressure within the boll also decreases the incidence of disease and improves the water use efficiency and fiber quality with the application of potassium [79]. Potassium application in cotton is also believed to extend the absorption of nitrogen, which causes vigorous vegetative growth and seed cotton yield. Also, the use of potassium in cotton enhanced the metabolic activity and improved the staple length, tensile strength, and fiber length and decreased the amount of damaged fiber [14]. Several other studies have reported an improvement in yield of cotton seed and quality of fiber due to potassium input in cotton under optimal and suboptimal conditions [80–82]. Combined foliar application of magnesium in combination with potassium and nitrogen improved the seed cotton yield, fiber quality, leaf nitrogen, potassium and magnesium concentration, and water use efficiency of cotton. The improvement in fiber quality was also visible through improvement in fiber strength, staple length, and fiber uniformity index owing to combined foliar application of magnesium in combination with potassium and nitrogen in abiotic stress in cotton crops [83].

Potassium plays a role in maintaining nitrogen metabolism and osmotic adjustment to sustain growth in soil under drought conditions [78]. Cotton plants under drought stress with potassium application not only showed higher osmotic adjustment with accumulation of osmolytes as well as maintaining higher enzyme activity, soluble proteins, and chlorophyll content but also regulate the nitrogen metabolism as compared to the plants without K application [84].

#### *6.2.1.5 Micronutrients*

As the cropping intensity increases, magnesium (Mg) deficiency occurs more frequently. Deficiency symptoms of sulfur are associated with the decrease in atmospheric sulfur. The uptake of magnesium and sulfur nutrients is reduced in cotton crop under drought stress. It has severe consequences for S nutrition and crop production. The plants uptake micronutrients through the process of diffusion decline because there is low soil moisture [85]. Cotton crop needs smaller quantities of micronutrients. Therefore, the effect of drought stress on micronutrients (Mg and S) is not the same as for macronutrients (P and N). Due to drought stress, deficiency of boron occurs in cotton crop. Due to the accumulation of silicon under drought conditions, the growth of cotton is improved and silicon is accumulated due to the reduction in transpiration rate [86, 87]. The main factors of saline and sodic soil on which they depend for availability of micronutrients are solubility of the micronutrients, pH, and the nature of the binding sites on the organic- and inorganic-particle surfaces. Salinity stress also affects the concentration of micronutrients in cotton plants, and soil salinity levels are also influenced by the salinity stress [88]. Inorganic nutrients play a significant role in determining plants' resistance to drought or salinity. Hence, both growth and development of cotton plants are similarly influenced by drought and salinity.

### **7. Use of osmoprotectants**

The accumulation of organic osmolytes has been reported in many plants under abiotic stresses. These include polyhydroxylic compounds and zwitterionic alkyl amines. The accumulation of osmolytes is widely discussed nowadays especially in cotton crops [89, 90].

Osmotically active solute is completed by the entry of water into the cell. This water provides sufficient concentrations for turgor pressure, which is necessary for the expansion of cells.

Cotton plants remain fit under stressful environmental conditions due to osmotic adjustment [91]. Therefore, high concentrations of several but not all compatible solutes protect the crop from oxidative damage. Their damage is reduced by scavenging free radicals in addition to their rules in preservation of osmotic equilibrium without disturbing macromolecule solvent relations.

The resistance against the oxidative stress of cotton has recently increased with the action of chloroplast accumulation of mannitol as well as consistent with high diffusion rate limited reactivity of hydroxyl radicals toward the most metabolic intermediates [92]. A significant role is played by the compatible solutes

#### *Abiotic Stress Tolerance in Cotton DOI: http://dx.doi.org/10.5772/intechopen.89622*

in terminating free radical chain reaction. The stress tolerance appears due to the critical element glycinebetaine in the cotton plants.

The growth of cotton plants is strongly influenced by the drought and saline environments with the osmoprotectants. Osmoprotectants are enormously proficient compatible solutes. The accumulation of glycinebetaine is induced and improves the tolerance to abiotic stress conditions [93]. The treatment of cotton seeds with the external application of glycinebetaine at increased the cotton seed yield by 18 and 22%, respectively. The growth and survival of extensive varieties of plants such as cotton crops are improved by the exogenous application of glycinebetaine.

## **Author details**

Aamir Hassan, Muhammad Ijaz\*, Abdul Sattar, Ahmad Sher, Sami-Ullah, Iqra Rasheed, Muhammad Zain Saleem and Ijaz Hussain Bahauddin Zakariya University, Layyah, Pakistan

\*Address all correspondence to: muhammad.ijaz@bzu.edu.pk

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **References**

[1] Bita C, Gerats T. Plant tolerance to high temperature in a changing environment: scientific fundamentals and production of heat stress-tolerant crops. Frontiers in Plant Science. 31 Jul 2013;**4**:273

[2] Bibi AC, Oosterhuis DM, Gonias ED. Exogenous application of putrescine ameliorates the effect of high temperature in *Gossypium hirsutum* L. flowers and fruit development. Journal of Agronomy and Crop Science. Jun 2010;**196**(3):205-211

[3] Leakey AD, Ainsworth EA, Bernacchi CJ, Rogers A, Long SP, Ort DR. Elevated CO2 effects on plant carbon, nitrogen, and water relations: Six important lessons from FACE. Journal of Experimental Botany. 28 Apr 2009;**60**(10):2859-2876

[4] McGrath JM, Lobell DB. Reduction of transpiration and altered nutrient allocation contribute to nutrient decline of crops grown in elevated CO2 concentrations. Plant, Cell & Environment. Mar 2013;**36**(3):697-705

[5] Liu J, Zhu JK. Proline accumulation and salt-stress-induced gene expression in a salt-hypersensitive mutant of Arabidopsis. Plant Physiology. 1 Jun 1997;**114**(2):591-596

[6] Wang SL, Heisey PW, Huffman WE, Fuglie KO. Public R&D, private R&D, and US agricultural productivity growth: Dynamic and long-run relationships. American Journal of Agricultural Economics. 14 Jun 2013;**95**(5):1287-1293

[7] Miller G, Shulaev V, Mittler R. Reactive oxygen signaling and abiotic stress. Physiologia Plantarum. Jul 2008;**133**(3):481-489

[8] Masood A, Shah NA, Zeeshan M, Abraham G. Differential response of antioxidant enzymes to salinity stress in two varieties of Azolla (*Azolla pinnata* and *Azolla filiculoides*). Environmental and Experimental Botany. 1 Dec 2006;**58**(1-3):216-222

[9] Qadir M, Shams M. Some agronomic and physiological aspects of salt tolerance in cotton (*Gossypium hirsutum* L.). Journal of Agronomy and Crop Science. Oct 1997;**179**(2):101-106

[10] Asada M, Kanaya T, Nakatsuji M, Kamaguchi R, Iwamoto Y. Method for Storage of Seeds. United States Patent Application US 13/378,792. Morishita Jintan Co Ltd, Niigata University, assignee; 31 May 2012

[11] Ashraf MF, Foolad M. Roles of glycine betaine and proline in improving plant abiotic stress resistance. Environmental and Experimental Botany. 1 Mar 2007;**59**(2):206-216

[12] Lv F, Liu J, Ma Y, Chen J, Wang Y, Chen B, et al. Effect of shading on cotton yield and quality on different fruiting branches. Crop Science. 2013;**53**(6):2670-2678

[13] Ackerson RC. Osmoregulation in cotton in response to water stress: III. Effects of phosphorus fertility. Plant Physiology. 1985;**77**(2):309-312

[14] Ali H, Afzal MN, Muhammad D. Effect of sowing dates and plant spacing on growth and dry matter partitioning in cotton (*Gossypium hirsutum* L.). Pakistan Journal of Botany. 2009;**41**(5):2145-2155

[15] Cook D, Herbert A, Akin DS, Reed J. Biology, crop injury, and management of thrips (Thysanoptera: Thripidae) infesting cotton seedlings in the United States. Journal of Integrated Pest Management. 1 Oct 2011;**2**(2):B1-B9

[16] Nepomuceno AL, Stewart JM, Oosterhuis D, Turley R, Neumaier M, *Abiotic Stress Tolerance in Cotton DOI: http://dx.doi.org/10.5772/intechopen.89622*

Farias JR. Isolation of a cotton NADP (H) oxidase homologue induced by drought stress. Pesquisa Agropecuária Brasileira. Jul 2000;**35**(7):1407-1416

[17] McMichael BL, Quisenberry JE, Upchruch DR. Lateral root development in exotic cottons. Environmental and Experimental Botany. 1 Oct 1987;**27**(4):499-502

[18] Longenberger PS, Smith CW, Duke SE, McMichael BL. Evaluation of chlorophyll fluorescence as a tool for the identification of drought tolerance in upland cotton. Euphytica. 1 Mar 2009;**166**(1):25

[19] Eickmeier WG, Casper C, Osmond CB. Chlorophyll fluorescence in the resurrection plant *Selaginella lepidophylla* (Hook. & Grev.) Spring during high-light and desiccation stress, and evidence for zeaxanthinassociated photoprotection. Planta. 1 Jan 1993;**189**(1):30-38

[20] Richards RA, Rebetzke GJ, Condon AG, Van Herwaarden AF. Breeding opportunities for increasing the efficiency of water use and crop yield in temperate cereals. Crop Science. 1 Jan 2002;**42**(1):111-121

[21] Sunkar R, Bartels D, Kirch HH. Overexpression of a stress-inducible aldehyde dehydrogenase gene from *Arabidopsis thaliana* in transgenic plants improves stress tolerance. The Plant Journal. Aug 2003;**35**(4):452-464

[22] Basal H, Smith CW, Thaxton PS, Hemphill JK. Seedling drought tolerance in upland cotton. Crop Science. 1 Mar 2005;**45**(2):766-771

[23] Rahman HU. Number and weight of cotton lint fibres: Variation due to high temperatures in the field. Australian Journal of Agricultural Research. 13 Jun 2006;**57**(5):583-590

[24] Burner DM, MacKown CT. Nitrogen effects on herbage nitrogen use and

nutritive value in a meadow and loblolly pine alley. Crop Science. 1 May 2006;**46**(3):1149-1155

[25] Toews MD, Tubbs RS, Wann DQ, Sullivan D. Thrips (Thysanoptera: Thripidae) mitigation in seedling cotton using strip tillage and winter cover crops. Pest Management Science. Oct 2010;**66**(10):1089-1095

[26] Boex-Fontvieille E, Davanture M, Jossier M, Zivy M, Hodges M, Tcherkez G. Photosynthetic activity influences cellulose biosynthesis and phosphorylation of proteins involved therein in Arabidopsis leaves. Journal of Experimental Botany. 19 Jul 2014;**65**(17):4997-5010

[27] Reddy KR, Hodges HF, McKinion JM. A comparison of scenarios for the effect of global climate change on cotton growth and yield. Functional Plant Biology. 1997;**24**(6):707-713

[28] Singh SK, Badgujar G, Reddy VR, Fleisher DH, Bunce JA. Carbon dioxide diffusion across stomata and mesophyll and photo-biochemical processes as affected by growth CO2 and phosphorus nutrition in cotton. Journal of Plant Physiology. 15 Jun 2013;**170**(9):801-813

[29] Burke JJ. Evaluation of source leaf responses to water-deficit stresses in cotton using a novel stress bioassay. Plant Physiology. 1 Jan 2007;**143**(1):108-121

[30] Volkov VA, Bulushev BV, Ageev AA. Determination of the capillary size and contact angle of fibers from the kinetics of liquid rise along the vertical samples of fabrics and nonwoven materials. Colloid Journal. 1 Jul 2003;**65**(4):523-525

[31] Volkov SV, Grinchenko OS, Sviridova TV. The effects of weather and climate changes on the timing of autumn migration of the common crane (*Grus grus*) in the north of

Moscow region. Biology Bulletin. 1 Dec 2016;**43**(9):1203-1211

[32] Pezeshki SR, DeLaune RD, Patrick WH Jr. Flooding and saltwater intrusion: Potential effects on survival and productivity of wetland forests along the US Gulf Coast. Forest Ecology and Management. 1 Jun 1990;**33**:287-301

[33] Jackson MB, Drew MC, Giffard SC. Effects of applying ethylene to the root system of *Zea mays* on growth and nutrient concentration in relation to flooding tolerance. Physiologia Plantarum. May 1981;**52**(1):23-28

[34] Voesenek LA, Bailey-Serres J. Flooding tolerance: O2 sensing and survival strategies. Current Opinion in Plant Biology. 1 Oct 2013;**16**(5):647-653

[35] Brodrick R, Bange MP, Milroy SP, Hammer GL. Physiological determinants of high yielding ultra-narrow row cotton: Biomass accumulation and partitioning. Field Crops Research. 12 Aug 2012;**134**:122-129

[36] Alvarez S, Marsh EL, Schroeder SG, Schachtman DP. Metabolomic and proteomic changes in the xylem sap of maize under drought. Plant, Cell & Environment. Mar 2008;**31**(3):325-340

[37] Schachtman DP, Goodger JQ. Chemical root to shoot signaling under drought. Trends in Plant Science. 1 Jun 2008 ;**13**(6):281-287

[38] Rupp HM, Frank M, Werner T, Strnad M, Schmülling T. Increased steady state mRNA levels of the STM and KNAT1 homeobox genes in cytokinin overproducing *Arabidopsis thaliana* indicate a role for cytokinins in the shoot apical meristem. The Plant Journal. Jun 1999;**18**(5):557-563

[39] Zhao J, Bai W, Zeng Q, Song S, Zhang M, Li X, et al. Moderately enhancing cytokinin level by downregulation of GhCKX expression in

cotton concurrently increases fiber and seed yield. Molecular Breeding. 2015;**35**(2):60

[40] Haigler CH, Zhang D, Wilkerson CG. Biotechnological improvement of cotton fibre maturity. Physiologia Plantarum. Jul 2005;**124**(3):285-294

[41] Haigler CH, Betancur L, Stiff MR, Tuttle JR. Cotton fiber: A powerful single-cell model for cell wall and cellulose research. Frontiers in Plant Science. 21 May 2012;**3**:104

[42] Gokani SJ, Thaker VS. Accumulation of abscisic acid in cotton fibre and seed of normal and abnormal bolls. The Journal of Agricultural Science. Dec 2001;**137**(4):445-451

[43] Dasani SH, Thaker VS. Role of abscisic acid in cotton fiber development. Russian Journal of Plant Physiology. 1 Jan 2006;**53**(1):62-67

[44] Sun Y, Veerabomma S, Abdel-Mageed HA, Fokar M, Asami T, Yoshida S, et al. Brassinosteroid regulates fiber development on cultured cotton ovules. Plant and Cell Physiology. 1 Aug 2005;**46**(8):1384-1391

[45] Shi YH, Zhu SW, Mao XZ, Feng JX, Qin YM, Zhang L, et al. Transcriptome profiling, molecular biological, and physiological studies reveal a major role for ethylene in cotton fiber cell elongation. The Plant Cell. 1 Mar 2006;**18**(3):651-664

[46] Shi R, Wang JP, Lin YC, Li Q, Sun YH, Chen H, et al. Tissue and cell-type co-expression networks of transcription factors and wood component genes in *Populus trichocarpa*. Planta. 1 May 2017;**245**(5):927-938

[47] Stiff MR, Haigler CH. Recent Advances in Cotton Fiber Development. Flowering and Fruiting in Cotton. Tennessee: The Cotton Foundation; 2012. pp. 163-192

*Abiotic Stress Tolerance in Cotton DOI: http://dx.doi.org/10.5772/intechopen.89622*

[48] Seagull RW, Giavalis S, Seagull R, Giavalis S. Molecular biology and physiology pre-and post-anthesis application of exogenous hormones alters fiber production in *Gossypium hirsutum* L. cultivar maxxa GTO. Journal of Cotton Science. 2004;**8**:105-111

[49] Beasley CA, Ting IP. Effects of plant growth substances on in vitro fiber development from unfertilized cotton ovules. American Journal of Botany. Feb 1974;**61**(2):188-194

[50] Ji SJ, Lu YC, Feng JX, Wei G, Li J, Shi YH, et al. Isolation and analyses of genes preferentially expressed during early cotton fiber development by subtractive PCR and cDNA array. Nucleic Acids Research. 2003;**31**:2534-2543

[51] Ruan YL, Xu SM, White R, Furbank RT. Genotypic and developmental evidence for the role of plasmodesmatal regulation in cotton fiber elongation mediated by callose turnover. Cell Biology and Signal Transduction. 2004;**136**(4):4104-4113. DOI: 10.1104/pp.104.051540

[52] Xiao YH, Yan Q, Ding H, Luo M, Hou L, Zhang M, et al. Transcriptome and biochemical analyses revealed a detailed proanthocyanidin biosynthesis pathway in brown cotton fiber. PLoS One. 21 Jan 2014;**9**(1):e86344

[53] Yang Z, Zhang C, Yang X, Liu K, Wu Z, Zhang X, et al. PAG1, a cotton brassinosteroid catabolism gene, modulates fiber elongation. New Phytologist. 2014;**203**(2):437-448

[54] Luo M, Xiao Y, Li X, Lu X, Deng W, Li D, et al. GhDET2, a steroid 5α‐reductase, plays an important role in cotton fiber cell initiation and elongation. The Plant Journal. Aug 2007;**51**(3):419-430

[55] Mengel R, Bacher M, Flores‐ de‐Jacoby L. Interactions between stress, interleukin‐1β, interleukin‐6 and cortisol in periodontally diseased patients. Journal of Clinical Periodontology. Nov 2002;**29**(11):1012-1022

[56] Cairns JE, Crossa J, Zaidi PH, Grudloyma P, Sanchez C, Araus JL, et al. Identification of drought, heat, and combined drought and heat tolerant donors in maize. Crop Science. 2013;**53**(4):1335-1346

[57] Papadopoulos CE, Lazaridou A, Koutsoumba A, Kokkinos N, Christoforidis A, Nikolaou N. Optimization of cotton seed biodiesel quality (critical properties) through modification of its FAME composition by highly selective homogeneous hydrogenation. Bioresource Technology. 1 Mar 2010;**101**(6):1812-1819

[58] Chen W, Hou Z, Wu L, Liang Y, Wei C. Effects of salinity and nitrogen on cotton growth in arid environment. Plant and Soil. 1 Jan 2010;**326**(1-2):61-73

[59] Floryszak‐Wieczorek J, Arasimowicz M, Milczarek G, Jelen H, Jackowiak H. Only an early nitric oxide burst and the following wave of secondary nitric oxide generation enhanced effective defence responses of pelargonium to a necrotrophic pathogen. New Phytologist. Sep 2007;**175**(4):718-730

[60] Ravindra S, Mohan YM, Reddy NN, Raju KM. Fabrication of antibacterial cotton fibres loaded with silver nanoparticles via "Green Approach". Colloids and Surfaces A: Physicochemical and Engineering Aspects. 5 Sep 2010;**367**(1-3):31-40

[61] Shahid MA, Pervez MA, Balal RM, Ahmad R, Ayyub CM, Abbas T, et al. Salt stress effects on some morphological and physiological characteristics of okra (*Abelmoschus esculentus* L.). Soil and Environment. 1 Jun 2011;**30**(1)

[62] Jabran K, Mahajan G, Sardana V, Chauhan BS. Allelopathy for weed control in agricultural systems. Crop Protection. 1 Jun 2015;**72**:57-65

[63] Singh R, Sharma RR, Tyagi SK. Pre-harvest foliar application of calcium and boron influences physiological disorders, fruit yield and quality of strawberry (Fragaria × ananassa Duch.). Scientia Horticulturae. 26 Mar 2007;**112**(2):215-220

[64] Rajakumar D, Gurumurthy S. Effect of plant density and nutrient spray on the yield attributes and yield of direct sown and polybag seedling planted hybrid cotton. Agricultural Science Digest. 2008;**28**(3):174-177

[65] Sawan ZM, Fahmy AH, Yousef SE. Effect of potassium, zinc and phosphorus on seed yield, seed viability and seedling vigor of cotton (*Gossypium barbadense* L.). Archives of Agronomy and Soil Science. 1 Feb 2011;**57**(1):75-90

[66] Gill SS, Tuteja N. Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants. Plant Physiology and Biochemistry. 1 Dec 2010;**48**(12):909-930

[67] Jiang Y, Yang B, Harris NS, Deyholos MK. Comparative proteomic analysis of NaCl stress-responsive proteins in Arabidopsis roots. Journal of Experimental Botany. 1 Oct 2007;**58**(13):3591-3607

[68] Casadevall R, Rodriguez RE, Debernardi JM, Palatnik JF, Casati P. Repression of growth regulating factors by the microRNA396 inhibits cell proliferation by UV-B radiation in Arabidopsis leaves. The Plant Cell. 1 Sep 2013;**25**(9):3570-3583

[69] Sawan ZM, Mahmoud MH, El-Guibali AH. Influence of potassium fertilization and foliar application of zinc and phosphorus on growth, yield components, yield and fiber properties of Egyptian cotton (*Gossypium barbadense* L.). Journal of Plant Ecology. 1 Dec 2008;**1**(4):259-270

[70] Deshpande AN, Masram RS, Kamble BM. Effect of fertilizer levels on nutrient availability and yield of cotton on Vertisol at Rahuri, District Ahemadnagar, India. Journal of Applied and Natural Science. 1 Dec 2014;**6**(2):534-540

[71] Ghoneim AM, Gewaily EE, Osman MM. Effects of nitrogen levels on growth, yield and nitrogen use efficiency of some newly released Egyptian rice genotypes. Open Agriculture. 2018;**3**(1):310-318.s

[72] Baloch MJ, Khan NU, Rajput MA, Jatoi WA, Gul S, Rind IH, et al. Yield related morphological measures of short duration cotton genotypes. Journal of Animal and Plant Sciences. 1 Aug 2014;**24**(4):1198-1211

[73] Zimmermann MR, Mithöfer A, Will T, Felle HH, Furch AC. Herbivoretriggered electrophysiological reactions: Candidates for systemic signals in higher plants and the challenge of their identification. Plant Physiology. 2016;**170**(4):2407-2419

[74] Pervez H, Ashraf M, Makhdum MI. Effects of potassium rates and sources on fiber quality parameters in four cultivars of cotton grown in aridisols. Journal of Plant Nutrition. 2 Jan 2005;**27**(12):2235-2257

[75] Teotia P, Kumar V, Kumar M, Shrivastava N, Varma A. Rhizosphere microbes: Potassium solubilization and crop productivity–Present and future aspects. In: Potassium Solubilizing Microorganisms for Sustainable Agriculture. New Delhi: Springer; 2016. pp. 315-325

[76] Mullins GL, Burmester CH, Reeves DW. Cotton response to in-row subsoiling and potassium fertilizer

#### *Abiotic Stress Tolerance in Cotton DOI: http://dx.doi.org/10.5772/intechopen.89622*

placement in Alabama. Soil and Tillage Research. 1 Jan 1997;**40**(3-4):145-154

[77] Bradow JM, Davidonis GH. Quantitation of fiber quality and the cotton production-processing interface: A physiologist's perspective. Journal of Cotton Science. May 2000;**4**(1):34-64

[78] Zahoor R, Zhao W, Abid M, Dong H, Zhou Z. Potassium application regulates nitrogen metabolism and osmotic adjustment in cotton (*Gossypium hirsutum* L.) functional leaf under drought stress. Journal of Plant Physiology. 2017;**215**:30-38

[79] Lin ZX, He D, Zhang XL, Nie Y, Guo X, Feng C, et al. Linkage map construction and mapping QTL for cotton fibre quality using SRAP, SSR and RAPD. Plant Breeding. Apr 2005;**124**(2):180-187

[80] Pervez H, Ashraf M, Makhdum MI. Influence of potassium nutrition on gas exchange characteristics and water relations in cotton (*Gossypium hirsutum* L.). Photosynthetica. 1 Jun 2004;**42**(2):251-255

[81] Pettigrew WT. Potassium influences on yield and quality production for maize, wheat, soybean and cotton. Physiologia Plantarum. Aug 2008;**133**(4):670-681

[82] Tsialtas IT, Shabala S, Baxevanos D, Matsi T. Effect of potassium fertilization on leaf physiology, fiber yield and quality in cotton (*Gossypium hirsutum* L.) under irrigated Mediterranean conditions. Field Crops Research. 1 Jul 2016;**193**:94-103

[83] Chen W, Feng C, Guo W, Shi D, Yang C. Comparative effects of osmotic-, salt- and alkali stress on growth, photosynthesis, and osmotic adjustment of cotton plants. Photosynthetica. 1 Sep 2011;**49**(3):417

[84] Wang H, Chen Y, Xu B, Hu W, Snider JL, Meng Y, et al. Long-term exposure to slightly elevated air temperature alleviates the negative impacts of short term waterlogging stress by altering nitrogen metabolism in cotton leaves. Plant Physiology and Biochemistry. 1 Feb 2018;**123**:242-251

[85] Irshad MU, Gill MA, Aziz TA, Ahmed I. Growth response of cotton cultivars to zinc deficiency stress in chelator-buffered nutrient solution. Pakistan Journal of Botany. 1 Jun 2004;**36**(2):373-380

[86] Läuchli A, Epstein E. Plant responses to saline and sodic conditions. Agricultural Salinity Assessment and Management. 1990;**71**:113-137

[87] Ma BL, Wu TY, Tremblay N, Deen W, McLaughlin NB, Morrison MJ, et al. On-farm assessment of the amount and timing of nitrogen fertilizer on ammonia volatilization. Agronomy Journal. 1 Jan 2010;**102**(1):134-144

[88] Oertli JJ. Nutrient management under water and salinity stress. In: Proceedings of the Symposium on Nutrient Management for Sustained Productivity. Ludhiana, India: Depart. Soils Punjab Agric. Unver.; 1991. pp. 138-165

[89] Bartels D, Phillips J. Drought stress tolerance. In: Genetic Modification of Plants. Berlin, Heidelberg: Springer; 2010. pp. 139-157

[90] Naranjo MA, Forment J, RoldÁN M, Serrano R, Vicente O. Overexpression of *Arabidopsis thaliana* LTL1, a salt‐induced gene encoding a GDSL‐ motif lipase, increases salt tolerance in yeast and transgenic plants. Plant, Cell & Environment. Oct 2006;**29**(10):1890-1900

[91] Boyer JS, James RA, Munns R, Condon TA, Passioura JB. Osmotic adjustment leads to anomalously low estimates of relative water content in wheat and barley. Functional Plant Biology. 19 Dec 2008;**35**(11):1172-1182

#### *Advances in Cotton Research*

[92] Lang J, Hu J, Ran W, Xu Y, Shen Q. Control of cotton Verticillium wilt and fungal diversity of rhizosphere soils by bio-organic fertilizer. Biology and Fertility of Soils. 1 Feb 2012;**48**(2):191-203

[93] Zhang K, Wang J, Lian L, Fan W, Guo N, Lv S. Increased chilling tolerance following transfer of a betA gene enhancing glycinebetaine synthesis in cotton (*Gossypium hirsutum* L.). Plant Molecular Biology Reporter. 2012;**30**(5):1158-1171

## Chapter 4

## Bioenergy Recovery from Cotton Stalk

Rafat Al Afif, Christoph Pfeifer and Tobias Pröll

#### Abstract

Cotton stalk (CS) plant residue left in the field following harvest must be buried or burned to prevent it from serving as an overwintering site for insects such as the pink bollworm (PBW). This pest incurs economic costs and detrimental environmental effects. However, CS contains lignin and carbohydrates, like cellulose and hemicelluloses, which can be converted into a variety of usable forms of energy. Thermochemical or biochemical processes are considered technologically advantageous solutions. This chapter reviews potential energy generation from cotton stalks through combustion, hydrothermal carbonization, pyrolysis, fermentation, and anaerobic digestion technologies, focusing on the most relevant technologies and on the properties of the different products. The chapter is concluded with some comments on the future potential of these processes.

Keywords: cotton stalk, thermochemical, biochemical, bioenergy

### 1. Introduction

Worldwide energy demand and greenhouse gas (GHG) emissions are predicted to increase by 70 and 60%, respectively, between 2011 and 2050 according to the International Energy Agency (IEA) [1]. An increase in GHG emissions is unequivocally the largest anthropogenic contributor to exacerbating climate change [2]. Currently, the majority of energy is derived from fossil fuels. As reported in 2017, it is estimated that if consumption of fossil fuels persists at 2016 levels, reserves of coal, gas, and oil will last only 153, 52.5, and 50.6 more years, respectively [3]. Therefore, other forms of energy such as biomass have significant potential to offset traditional energy sources [4]. Biomass, as a zero CO2 emission fuel, can offer one solution in the reduction of CO2 atmosphere content. In 2016 renewable energy accounted for 18.2% of the 576 exajoules (EJ) of total primary energy supply (TPES), of which 13% came from biomass [1, 5]. Biomass provided 46.4 EJ of TPES in 2016, and expert scientific analysis predicts that by 2050 the bioenergy share of TPES could reach 100–300 EJ per year (year<sup>1</sup> ) with the highest theoretical share proposed at 500 EJ year<sup>1</sup> [5, 6]. Although renewable energy makes up only a small percentage of current TPES, it has the theoretical potential to provide all of the human energy requirements on earth [7]. By 2035, biofuels could realistically provide at least a quarter of the estimated world's TPES of 623 EJ. To increase the proportions of renewables in the TPES, innovative feedstocks or inputs are required [8]. A significant source of biomass for renewable energy is available globally in the form of agricultural waste. Agricultural wastes pose expensive and challenging

issues for crop producers. With exception to the fraction of residues tilled back into the soil to increase soil organic carbon (SOC) content and enhance other soil physical characteristics, many of these wastes have little to negative value, and knowledge of revenue streams are sparse [9, 10]. For example, cotton biomass waste is an abundant and available waste from agricultural production at a high estimate of roughly 50 million tons annually [11]. Similarly, other crops produce even more abundant waste, such as rice husks which sum up to 822 million tons of waste with no real end of use application [12].

It has been reported that cotton residues left during harvest are carriers of the pest; therefore, adequate disposal of these residues is necessary [13]. However, it is worth considering that one of the major complications of cotton production is the management of the pink bollworm (PBW) (Pectinophora gossypiella). It is considered one of the most detrimental cotton pests because of its hardiness to insecticides [14]. PBW's life cycle consists of four stages: egg, larva, pupa, and adult. During the first stage, females lay 200–500 tiny eggs in single or small groups of 5–10 each on cotton plants which hatch 3–4 days later. During the second and most destructive stage, the larvae bore into the bolls to grow before cotton boll blossoming occurs. Here the larvae feed on seeds for 12–15 days where they mature to 12 mm long as a fully developed larva. The most significant damage occurs to the seed and lint. Before pupation, the larva experiences diapause during the winter for 2–4 months in which they do not feed or move. They may be found in bolls, in stems, or in the soil in which they are safe in a silken cocoon until spring. During the pupation stage, spring conditions cause the larva to drop to the soil beneath the cotton plants where they pupate; the pupa is roughly 7 mm long and brown, and the pupal period is between 7 and 8 days. During the adult stage in spring, first-generation adults develop from the pupae and are gray brown small moth which mate and lay eggs. In the summer, larvae from the previous generation fall to the soil, pupate, and emerge as second-generation moths, completing the life cycle. The entire cycle from egg to egg takes roughly 32 days, and the PBW can persist, on average, for up to six summer cycles [15, 16]. This pest is distributed globally where cotton is grown and is considered the key cotton pest. Its main effect on cotton crops is preventing flowering buds to open, shedding of the fruit, seed loss, and damage to lint. Trials in the USA have shown that the potential loss of harvest without control was 61%, whereas losses of 9% were estimated when the pest was controlled through insecticide application. In 1998, the total US crop yield of cotton was reduced by 2.7%, while in Egypt it is estimated that the PBW causes losses of about 10–20% of cotton crop annually [13, 15]. In 2014, it was reported that the PBW had been eradicated from California, Arizona, New Mexico, and Texas in the USA as well as Chihuahua in Northern Mexico. The eradication is attributed to a combination of insecticides and genetic modification of the cotton crop as well as releases of sterile PBW throughout the region [17]. In countries without robust pest management strategies, the most common method of PBW prevention is through burning the residues in the field or by shredding and plowing the residues to a depth of 6 inches into the soil, the latter of which is time and energy intensive [11, 15]. In light of the global challenges associated with cotton agricultural residuals, a promising method of cotton waste disposal is through their utilization as an energy source.

Studies indicate that undebarked cotton stalks are unsuitable for the production of fine paper and dissolving pulps [18, 19]. Furthermore, cotton stalks and other agricultural residues are unsuitable for hardboard and particle board due to their high water absorption and thickness swelling (deteriorated dimensional stability) [20, 21].

In contrast, the usage of cotton waste as an energy feedstock has become a subject of numerous studies in recent years [22–24]. Researchers generally focused on the production of biogas, ethanol, and the production of fuel pellets or

#### Bioenergy Recovery from Cotton Stalk DOI: http://dx.doi.org/10.5772/intechopen.88005

briquettes. Several studies on the subject of cotton waste pyrolysis indicate that pyrolysis of cotton stalks is deemed to have potential as one of the technological solutions for its management.

The purpose of the study is to review current bioenergy conversion technologies and to provide quantitative data and interpretation of the heating value, proximate and elemental analysis, and product yields specific to bioenergy recovery from CS. The hypothesis is that resulting data will be consistent with past research proving that CS residues have a high potential for use as an energy source. Moreover, some products from the conversion (e.g., biochar from pyrolysis) can be used as soil additive to recover nutrients and carbon to the soil. The latter can additionally act as water storage. This subject is important because there are significant quantities of CS waste from agricultural production globally, which is a potential source of revenue. Furthermore, other risks associated with cotton waste such as farm hygiene by pesticide remnants and soilborne pathogens can be addressed. Therefore, utilizing CS biomass has the potential to be a significant source of energy and an opportunity to reduce their environmental issues and financial costs [11]. This study contributes to the needed understanding of energy derived from thermal and biological conversion products of cotton stalks.

## 2. Cotton stalk residues for energy

Cotton stalks are a common agricultural residue with little economic value. They may be utilized without direct competition to food or feed provision. It is a renewable lignocellulosic biomass produced during cotton production. Daud et al. report values of 58.5% cellulose, 14.4% hemicellulose, and 21.4% lignin, which makes it a particularly attractive feedstock for thermochemical conversion processes [25]. Based on biomass classifications, cotton agricultural waste is a primary residue and herbaceous biomass fuel [26, 27]. Cotton crop cultivation occurs between July and February, while harvesting occurs from October to March [28]. Cotton agricultural wastes consist of the main stem, branches, bur, boll rinds, bracts, peduncle, roots, petioles, and leaf blades (Figure 1) left as residual biomass after harvesting the floral cotton bolls for commercial purposes, equivalent to roughly 3–5 times the weight of the produced cotton. The roots are 23.2% of the whole plant in average with the measured values ranging between 14.3 and 29.1%. However, based on observations of the amount of the soil stacked on the roots during fieldwork, it was decided in most studies to investigate the possibility of collecting only the aerial part of the residue, leaving the roots in the field. It was anticipated that the collected

Figure 1. Cotton residual wastes after harvesting.

material would be free of soil and with less moisture content. These factors would make its storage easier and its use for energy production by thermal conversions more attractive [29].

The separated CS consists of the main stem, branches, burs, boll rinds, bracts, and peduncles [28, 30]. The stem has an outer fibrous bark weighing 20% of the weight of the stalk as well as an inner pith [11, 31]. It reaches between 1 and 1.75 m long, and the diameter above ground varies between 1 and 2.5 cm. On average depending upon species and crop conditions, 2 to 3 tons of CS are generated per each hectare of land annually; it's worth noting that the moisture content was found to drop from 50% to under 20% when the stalks were left in the field, after harvesting, for 3 weeks [28].

According to the US Department of Agriculture (USDA), the total global production of cotton was roughly 26.9 million metric tons for the reporting year of 2018 from August 1, 2017, to August 1, 2018, which has been relatively steady for the last 5 years of data collection. The three largest global producers of cotton in 2018 were India, China, and the USA. India produced 6.3 million metric tons of cotton, China produced 6.0 million tons, and the USA produced 4.5 million tons. The remaining countries produce less than 2 million tons year<sup>1</sup> [32].

To determine the total CS residue or collectable dry residue from the cotton production values, several factors are required. These are the annual production, residue to the crop factor, dry weight factor, and the availability factor [33]. The annual production is reported yearly by each respective country and collected by the USDA [32]. The residue factor is based on the ratio of the fresh weight of residue to the grain weight harvested at field moisture. It describes the relationship between crop grown for product and the residual biomass leftover after harvest. The relationship is specific to the type of crop variety [33, 34]. As mentioned previously, the residue typically weighs three to five times the harvested cotton [31]. Klass and co-workers estimate the residue factor to be 2.45 [33]. The availability factor is based on the end use of the CS residue and how much is available for collection. The availability of crop residues may be limited due to tilling some residues into the soil to reduce erosion risk; to provide structure; to preserve fertility; to use as a fertilizer, as fibrous material for various agricultural uses; or to feed to livestock [34]. Therefore, it can be best described as the sustainable removal rate of a residue [35]. Typically, in areas with low SOC, more crop residues will be tilled into the soil, while in areas with high SOC, more crops can be sustainably removed [34]. Many studies assume roughly 25% of total available agricultural residues can be recovered; however, recovery percentages may be higher or lower depending on the crop [35, 36]. It is estimated that in the USA, up to 70% of the residues are tilled back into the soil for nutrient cycling and soil health, whereas in India 15% is used for fuel, while the remainder is burned in the field [28, 30]. Klass et al. report a residue factor of 0.6 for cotton agriculture. Lastly, the dry weight factor is the amount of moisture in the freshly harvested cotton residue. Therefore, collectable dry biomass can be calculated with all of these values [33]. It is worth noting that harvesting crop residues for energy has been shown to be efficient and the energy required to collect and process residues is a small percentage of the energy content of the residue itself [37].

### 3. Characterization of cotton stalks for determination of energy potential

In order to get an overview of the main fuel properties of cotton stalks, proximate as well as ultimate analyses need to be performed. Schaffer et al. [24] compared data from cotton stalks to data for wheat straw and beechwood (Table 1). In


#### Table 1.

Fuel properties of cotton stalks, wheat straw, and wood on a dry basis.

comparison with wood, the agricultural by-products are characterized by higher ash contents. The lower heating value (LHV) of dry cotton stalks is equivalent to poorquality wood and varies from 16.4 to 18.26 MJ/kg [38]. Compared with wheat straw (LHV of 17.28–18.41 MJ/kg [38]), the cotton stalk can be considered as a biofuel with respect to its energy content. However, a clean and energy-efficient utilization in combustion plants is counterindicated by high contents of elements like Cl, K, and Na that decrease the ash melting point of SiO2 and lead to fouling and corrosion in the boiler plant. Although straw and stalks are, therefore, not suitable for conventional combustion plants, low-temperature thermochemical conversion could be applied with the effect to yield biologically stable biochar containing the critical ash constituents and also plant nutrients, while the ash-free volatiles can be used in high-temperature conversion routes such as combustion in gas boilers or cofiring in pulverized coal boilers. In this respect, it is important to notice that the fixed carbon content obtained in the proximate analysis is higher for cotton stalks than wheat straw and beechwood. This observation holds true also when looking at other fuel samples available in the literature cited in Table 1. Furthermore, it is seen that cotton stalks possess high amounts of carbon (47.05%) and oxygen (40.77%) and its composition is relatively similar to wheat straw and wood. The presence of these elements in biomass leads to more char formation as well as to the high calorific value of the product. Therefore, because cotton stalks, wheat straw, and wood have high carbon and oxygen contents, they are suitable for energy production and could be combined with the supply of biochar.

Proviso studies have shown that raw CS provides higher combustion efficiency and longer burn time than some other agricultural residuals; furthermore, the energy needed to collect and process these residues is a small percentage of the energy contained within them [11]. To summarize, cotton stalk can be considered a typical biofuel with respect to its energy content.

#### 4. Bioenergy conversion technologies

Bioenergy carriers are solid, liquid, or gaseous fuels which can be obtained from the available technologies. Liquid fuels are commonly used in transportation vehicles but can also be used in stationary engines especially turbines. Solid fuels are

directly combusted to obtain heat, power, or combined heat and power (CHP). Gaseous fuels can be applied to the full range of end uses. As CS calorific value is equivalent to poor-quality woody biomass. A method of increasing the calorific value of the feedstock while simultaneously utilizing the residue is the technological processing through thermal and bioconversions to yield high-energy-content products which can be more easily transported and stored for use at a later time [11, 22]. CS can be converted into several useful forms of energy using different processes (conversion technologies). Bioenergy is the term used to describe energy derived from CS feedstocks. Several processing steps are required to convert raw CS into useful energy using mainly the two main process technology groups available: biochemical and thermochemical. Biochemical conversion encompasses two primary process options: anaerobic digestion (to biogas) and fermentation (to ethanol). For the thermochemical conversion routes, the four main process options presented here are pyrolysis, gasification, combustion, and hydrothermal processing (basically hydrothermal carbonization (HTC)). Figure 2 provides a broad classification of energy conversion processes for CS.

## 4.1 Thermochemical conversion

Thermochemical conversion of biomass is the process of utilizing heat and, in some cases, chemical reagents, to create more energetically useful products. The output from the process is heat, gaseous, liquid, or solid fuels [40]. The four major thermal processes for converting biomass to useful energy are combustion, gasification, pyrolysis, and hydrothermal processes (see Figure 2). Hydrothermal processes summarize three distinct processes such as hydrothermal carbonization, liquefaction, and gasification. Hydrothermal carbonization is the process which fits best to cotton stalks and is the most developed, and therefore the focus is here on this conversion route. Pyrolysis, gasification, and combustion can be seen as stateof-the-art technologies, although not implemented in demonstration scale for cotton stalks yet. All processes can be implemented in similar plant configurations (fix bed, fluidized bed, entrained flow). Pyrolysis seems to be the most promising thermochemical conversion route due to its robustness, flexibility, and the possibility to provide a method to recover nutrients. Thus, pyrolysis is described in more details.

Figure 2. Schematic diagram of the processes of energy conversion of cotton stalks.

#### 4.1.1 Combustion

Combustion, or direct burning, of biomass consists of full oxidation of combustibles in air or oxygen-enriched air. Generally, biomass combustion produces a variety of pollutants and particulate matter (PM), as well as flue gas which requires special treatment of unburned particles. In comparison to gasification and dependent on the feedstock used for fuel, combustion can release the acid rain contributing pollutants sulfur oxides (SOx) and nitrogen dioxide (NO2) at roughly 40 times and 9 times, respectively [41]. Combustion of biomass with high ash content has several drawbacks in comparison with low-ash biomass. The remnant ash content is left deposited on the internal heating surfaces, which forms slags and causes fouling to the process, affecting the heating rate negatively and decreasing process efficiency [9]. The inorganic compounds in the biomass feedstock may lead to an increase in particulate matter (PM) concentrations, such as crystalline silica, which has detrimental health effects in the air [9, 42]. With consideration to the detrimental impacts of ash on combustion processes, the ash content of the CS is relatively high with 5.5 wt% db. Although straw and stalks are, therefore, not suitable for conventional combustion plants, the ash problem can be avoided by separating it into biochar through pyrolysis at low temperatures prior to combustion [9]. This can be also done by air staging in the boiler to separate the oxidation of the gases from contact to the ash. However, it has been reported in a number of studies that CS provides the highest burning efficiency and longest burn time compared to corn stover and soybean residues. The greater the density, the longer the duration of combustion. This could lead to the necessity to pelletize the feedstock for certain applications. In the study by Coates [37], it was shown that cotton plant residue could be incorporated with pecan shells to produce commercially acceptable briquettes. However, changeover of the existing factories to facilitate utilization of CS would require an initial infusion of capital. This should be compensated by lower raw material costs in a reasonable period of time.

#### 4.1.2 Gasification

Gasification is the thermochemical conversion of biomass by partial oxidation with O2 and the reformation by steam, carbon dioxide, or other gasification agents, producing syngas as a chemical product or fuel. The biomass is exposed to less O2 than in combustion but more than in conditions of pyrolysis. Gasification may be allo- or autothermal; therefore, the heat required for endothermal processing is provided by ex or in situ combustion of char or gas [43]. Gasification is one of the most efficient methods for converting the chemical energy stored in biomass into heat and other useful forms of energy. Estimates of overall exergetic efficiency range from high estimates between 80.5 and 87.6% [44]. It is closely related to pyrolysis, in which both processes undergo devolatilization of biomass in the absence of O2 or air to yield suitable products for energy without entire combustion. However, the process is optimized for maximum gas yield through oxidation and subsequent reduction [41, 44]. Gasification is processed at temperatures of typically 750–900°C for fixed and fluidized bed, 1200–1500°C for entrained flow, and up to 3000°C for plasma applications.

The products yielded by gasification include a high proportion of gases, namely, carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), water (H2O), hydrogen (H2), gaseous hydrocarbons, minimal char residue, and condensed oil and tar. An oxidizing agent is added to the reaction in the form of air, O2, or steam; and the gaseous tar or oil in the gas is condensed to acquire the desired product, producer gas. The gas may have a low energy content for autothermal operation,

between 3 and 5 MJ/m<sup>3</sup> , 10% of the heating value of natural gas; however, it is enough to power gas engines and increases the value of feedstocks that would otherwise be considered wasteful [41, 44]. For allothermal operation heating values of 12–14 MJ/m<sup>3</sup> are achieved. The relatively low temperature of the process leaves a char residue, which can subsequently be gasified through burning it at a high temperature, such as at 1000°C, while simultaneously injecting steam into the process. This breaks down the steam into oxygen (O2) and hydrogen (H2) which react with the carbon (C) from the char to create CO and H2. By using O2 rather than air, high-quality syngas can be produced from the CO and H2 yield of the reaction, after impurities such as sulfur (H2S), ammonia (NH3), and tar have been removed. This syngas has the potential to be synthesized into methanol (CH3OH), a high value liquid fuel, as well as other types of hydrocarbon compounds through the Fischer-Tropsch process. The efficiency of the overall process varies from 40% in simple designs to roughly 75% in processes which are well designed [41]. Allesina et al. [45] indicate that cotton residue gasification represents the basis for local circular economy models.

#### 4.1.3 Pyrolysis

Pyrolysis is the process of thermochemical decomposition of a substance in the absence of O2 [46]. Pyrolysis is a similar process to gasification; however, gasification controls the O2 more precisely and generally; pyrolysis produces a significantly larger portion of biochar and is therefore sometimes called carbonization [47]. Pyrolysis is typically operated at 400–600°C. Pyrolysis produces a bio-oil liquid which can be used directly as a fuel and as a pretreatment intermediate step for converting biomass into a high-energy liquid which may be processed for power, heat, biofuels, and chemicals. Compared to the other technologies, pyrolysis is expected to offer more versatility, environmental stewardship, and higher efficiency [48]. Economically, periods of the energy crisis and fluctuating prices and availability have made biomass pyrolysis a more significant technology for development and research [49].

#### 4.1.3.1 Pyrolysis product yields

Cotton stalk pyrolysis in a fixed-bed reactor has been studied to demonstrate products yield variation for different temperature regions [50]. They indicate that temperature increase from 650 to 800°C favored gas production, while char production decreased from 66.5 to 26.73 wt%, as the temperature increased from 250 to 650 C. This effect can be thought of as more volatile material being forced out of the char at higher temperatures, thereby reducing yield but increasing the proportion of carbon in the char. As far as the liquid fraction of the products is concerned, there is an optimum temperature at which maximum oil yield obtained (41% at 550°C). Further temperature increases resulted in tar and liquid cracking into gases, and hence a high gas production is achieved. Similar results are also reported by [51]. The higher heating value (HHV) of pyrolysis oil is 16–23 MJ/l compared to fossil fuel which is 37 MJ/l. Pyrolysis oil has a low pH value of around 3, which must be taken into account in its handling and use. The (hydrophilic) bio-oil has water contents of typically 15–35 wt%. Typically, phase separation does occur when the water content is higher than about 30–45%.

#### 4.1.3.2 Pyrolysis system

Pyrolysis reactors can be operated in continuous or batch mode. Typical continuous pyrolysis reactors include fluidized-bed pyrolysis, auger/screw-type

#### Bioenergy Recovery from Cotton Stalk DOI: http://dx.doi.org/10.5772/intechopen.88005

pyrolysers, and rotary kilns. These reactors involve continuous input of feedstock and output of biochar, bio-oil, and syngas and often result in higher biochar yields and operational efficiencies than batch processes [52]. Compared to batch reactors, continuous reactors are more complex and expensive to design and operate and may require a reliable source of electricity [52, 53]. Therefore, continuous reactors are ideal for medium- to large-scale biochar production systems relying on centralized large quantities of feedstock. Additional information about the particularities of different pyrolysis systems can be found in the literature [48]. Nevertheless, some continuous reactor types are suitable for application in small to medium scale, too [53–56].

For the present study with cotton stalks as the feedstock, the continuously operated, indirectly heated rotary kiln reactor has been recommended according to Figure 3. The reasons for this decision are:


The elements chlorine and potassium, which are critical for combustion systems, remain quantitatively in the pyrolysis char fraction [55], and about 50% of the primary fuel energy can be exported with the gas and oil fraction, while less than 50% of the primary fuel energy stays in the char fraction. Thus, if the char is not further converted but returned to the soil, the problematic compounds may even have positive effects as nutrients and the related carbon will not be released as CO2. Therefore, researchers consider the potential application of the pyrolysis char as a soil additive to increase crop yield [56, 59] or as a negative emission technology [24, 60].

Figure 3. Example of an indirectly heated rotary kiln pyrolysis process scheme [58].

## 4.1.3.3 Char utilization from cotton stalks for sustainable soil enhancement and carbon storage

Currently, the cotton stalks are often burnt on the fields causing high local pollution. However, the solid residues of the stalks remain on the field supplying nutrients. The same effects can be reached by the application of biochar from stalks. Cotton crops typically grow in hot regions on sandy soils, where biochar addition has been reported to enhance the soil fertility [59]. Mild conversion conditions below 600°C avoid ash melting and keep nutrients available for microorganisms and plants. With respect to the carbon storage effect, biochar from pyrolysis at >500°C shows sufficiently low O/C ratios to promise longevity in the soil [61]. Generally, slow pyrolysis is preferred for increased char yield [40]. The steady-state process simulation environment IPSEpro was used by Schaffer et al. [24] to assess a virtual pyrolysis conversion of cotton stalks, and they indicated that 52.8% of the carbon contained in the biomass accumulates in the biochar, whereas 38% of the input energy can be exported as heat energy at temperature levels suitable for electricity generation or industrial heat supply. The pyrolysis char shows a low molecular O/C ratio of 0.07 and an H/C ratio of 0.26. The expected half-lives of biochar in the soil are in the order of 1000 years for O/C ratios below 0.2. This makes the presented approach an interesting low-tech negative emission option. The predicted net negative emissions through stored carbon amount to 2.42 t CO2 per hectare and year (Figure 4). The overall CO2 emission avoidance effect can be increased if fossil fuel is substituted by the energy exported from the pyrolysis process.

From Figure 5 one can see that 52.8 wt% of the total amount of carbon stored in cotton stalks is converted to char. Furthermore, the inorganic matter contained in the char, which includes important nutrients, remains in the char. The nutrients are then available for the new generation of plants if the char is used as soil additive.

The remaining part of carbon in pyrolysis gas and oil can be used for energy production as shown in the energy flow diagram in Figure 6. Energy streams are

#### Figure 4.

Net carbon removal from the atmosphere through pyrolysis of cotton stalks and soil application of the pyrolysis char [24].

Bioenergy Recovery from Cotton Stalk DOI: http://dx.doi.org/10.5772/intechopen.88005

#### Figure 5.

Carbon mass flow diagram for an indirectly heated rotary kiln pyrolysis process without condensation of pyrolysis oil [24].

#### Figure 6.

Energy flow through an indirectly heated rotary kiln pyrolysis process without condensation of pyrolysis oil [24].

assessed based on the lower heating value and sensible heat with a reference temperature (sensible heat of zero) of 273.

In conclusion, the use of agricultural wastes such as cotton stalks in distributed, small- to medium-scale, energy-autonomous pyrolysis plants will allow for quasipermanent soil storage of a part of the carbon contained in the biomass without the need for CO2 storage sites. As a side-effect, it is expected that soil quality can be maintained and even improved by the application of biochar.

#### 4.1.4 Hydrothermal carbonization

Nowadays hydrothermal carbonization is mentioned as a promising technology to convert biomass into a high-quality bioproduct, namely, hydrochar, as well as process water to recover nutrients (e.g., P, N, K, Si, etc.). Carbonization depletes compounds rich in oxygen and hydrogen and thereby increases the carbon content in the coal compared to the starting material. The depleted compounds are found essentially in the so-called process water and at low levels in the resulting process gas again. The product hydrochar is more hydrophobic than the source material,

and the drainage is less energy intensive than the dewatering of fresh biomass. In addition, essential reactions are exothermic, and upon carbonization, after initial energy input, heat energy is released. Due to the increased carbon content of the hydrochar, the heating value increases. The hydrothermal carbonization, e.g., of CS, kills the eggs of the pink bollworm and other pathogens. There is still a need for research in the area of reduction of impurities and in the accumulation of nutrients in the coal. The distribution of nutrients between the solid, liquid, and gaseous phase can be adjusted via the process conditions (pressure, temperature, residence time, heating rate, pH, additives, catalysts, etc.). The considered process is shown in Figure 7.

Al Afif et al. [62] investigate the use of HTC in the production of hydrochar from CS. They concluded that hydrothermal carbonization is a promising conversion technology to provide bioenergy from CS. And there was a strong dependence between the residence time and the char quality, as the LHV of the hydrochar from CS increased with increasing residence time, whereas the total amount of hydrochar was decreased.

## 4.2 Biochemical conversion

Cotton stalk, as lignocellulosic biomasses, is difficult to hydrolyze due to its complex structure and a large amount of lignin present in it. Basic steps involved in bioconversion process of lignocellulosic biomass are pretreatment (physical, chemical, biological, and their combination) for cell wall destruction for biogas production, hydrolysis (acid or enzymatic) for soluble sugar release, and fermentation (bacteria or yeast) for ethanol production. Due to recalcitrant nature of lignin and its binding with holocellulose, a pretreatment step is required for fractioning of different cell wall components. Pretreatment exposes the cellulose surface for enzymatic attack and improves enzymatic digestibility and subsequent processes. Pretreatment identifies one of the major economic costs in the biochemical conversion process [63]. Generally, both process routes as discussed in the following are technically feasible, but techno-economic assessments are missing.

## 4.2.1 Ethanol production

The six-carbon sugars, or hexoses, glucose, galactose, and mannose, can be fermented to ethanol by many naturally occurring organisms. Baker's yeast, or Saccharomyces cerevisiae, has been traditionally used in the brewing industry to produce ethanol from hexoses. Recently, engineered yeasts have been reported to efficiently ferment xylose and arabinose, as well as mixtures of xylose and arabinose. In order to effectively utilize cotton stalk as a feedstock for ethanol

Figure 7. System boundaries of the considered hydrothermal carbonization process.

#### Bioenergy Recovery from Cotton Stalk DOI: http://dx.doi.org/10.5772/intechopen.88005

production, optimal pretreatment is required to render the cellulose fibers more amenable to the action of hydrolytic enzymes. Generally, alkaline pretreatment is found to be more effective on agricultural residues and herbaceous crops such as cotton [64]. Christopher et al. [65] indicate that a hydrolytic efficiency of 80% was achieved for alkali-treated biomass using cellulase supplemented with betaglucosidase and concluded that cotton stalks have great potential as a bioethanol feedstock.

## 4.2.2 Biogas production

Anaerobic digestion is a technology widely used for treatment of organic waste for biogas production. Biogas is a combustible gas derived from decomposing biological waste in the absence of oxygen. Biogas normally consists of 50–60% methane. It is currently captured from landfill sites, sewage treatment plants, livestock feedlots, and agricultural wastes. There were only a few studies on the subject of biogas production from cotton wastes. Isci and Demirer [23] studied the biogas production potential of cotton wastes. They indicated that cotton wastes can be digested anaerobically yielding 65–86 lN CH4 kg<sup>1</sup> VS (24 days)<sup>1</sup> . A two-stage digestion technique for biogas production from co-fermentation of organic wastes (rice, maize, cotton) was also investigated [66]. This study indicated that under anaerobic conditions from the main components in CS, the cell wall carbohydrates were well preserved, while the level of soluble carbohydrate was low. Pretreatment of lignocellulosic biomass is a necessary step to overcome the hindrance of lignin and to increase solubilization [67]. Al Afif et al. [22] investigated the anaerobic digestion of cotton stalk (CS) using organosolv plus supercritical (SC) carbon dioxide pretreatment of cotton stalks for methane production. Results indicated that supercritical carbon dioxide pretreatment of CS is a potential option for improving the energy output, as the pretreatment of CS samples with organosolv plus SC-CO2 increased the methane yield up to 20% compared with the untreated samples. The highest methane yield of 177 lN kg<sup>1</sup> VS was achieved by pretreatment with organosolv plus SC-CO2 at 100 bars and 180°C for 140 minutes. It is worth noting that the quality of biogas was good and increased with pretreatment from 50 to 60% CH4. To summarize, cotton stalks can be digested anaerobically and is a good source of biogas; nevertheless, pretreatment of cotton stalks is a necessary step to increase solubilization hence the methane production.

### 4.3 Future perspectives

This study contributes to enhancing our understanding of the feasibility of bioenergy recovery from cotton stalks. The findings have the potential to lead to a sustainable solution for the treatment of cotton stalks.

Figure 8. The system boundary of coupling anaerobic digestion and pyrolysis process.

However, for higher bioenergy recovery, a study of the techno-economic feasibility of the integrated processes of anaerobic digestion and pyrolysis is recommended (see Figure 8).

## 5. Conclusions

It has been shown in this study that:


The findings have the potential to lead to a sustainable solution for the treatment of cotton stalks. However, for higher bioenergy recovery more studies are needed to prove the effectiveness of cotton waste utilization.

## Author details

Rafat Al Afif\*, Christoph Pfeifer and Tobias Pröll Institute of Chemical and Energy Engineering, University of Natural Resources and Applied Life Sciences, Vienna, Austria

\*Address all correspondence to: rafat.alafif@boku.ac.at

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Bioenergy Recovery from Cotton Stalk DOI: http://dx.doi.org/10.5772/intechopen.88005

## References

[1] International Energy Agency (IEA). Key world Energy Statistics. Paris: International Energy Agency; 2016. Available from: https://www.iea.org/ publications/freepublications/publica tion/KeyWorld2017.pdf

[2] Budinis S, Mac Dowell N, Krevor S, Dixon T, Kemper J, Hawkes A. Can carbon capture and storage unlock 'unburnable carbon'? Energy Procedia. 2017;114:7504-7515. ISSN 1876-6102

[3] BP. BP Statistical Review of World Energy June 2017. 2017. Available from: https://www.bp.com/content/dam/bp/e n/corporate/pdf/energy-economics/sta tistical-review-2017/bp-statistical-revie w-of-world-energy-2017-full-report.pdf

[4] Tripathi M, Sahu JN, Ganesan P. Effect of process parameters on production of biochar from biomass waste through pyrolysis: A review. Renewable and Sustainable Energy Reviews. 2016;55:467-481

[5] Renewable Energy Policy Network for the 21st Century (REN21). Renewables 2018: Global Status Report. Paris: REN21 Secretariat; 2018. Available from: http://www.ren21.ne t/wp-content/uploads/2018/06/ 17-8652\_GSR2018\_FullReport\_web\_fina l\_pdf

[6] Edenhofer O, Pichs R, Madruga Sokona Y, Seyboth K, Matschoss P, Kadner S, et al. editors. Special report on renewable energy sources and climate change mitigation. Intergovernmental Panel on Climate Change. ISBN: 978-92- 9169-131-9.2012

[7] Gasparatos A, Doll CNH, Esteban M, Ahmed A, Olang TA. Renewable energy and biodiversity: Implications for transitioning to a Green Economy. Renewable and Sustainable Energy Reviews, Volume. 2017;70(2017): 161-184. ISSN 1364-0321

[8] Xu J, Li M. Innovative technological paradigm-based approach towards biofuel feedstock. Energy Conversion and Management. 2017;141:48-62. ISSN 0196-8904

[9] Dunnigan L, Ashman PJ, Zhang X, Kwong CW. Production of biochar from rice husk: Particulate emissions from the combustion of raw pyrolysis volatiles. Journal of Cleaner Production. 2018;172: 1639-1645. ISSN 0959-6526

[10] Obour PB, Jensen JL, Lamandé M, Watts CW, Munkholm LJ. Soil organic matter widens the range of water contents for tillage. Soil and Tillage Research. 2018;182:57-65. ISSN 0167-1987

[11] Hamawand I, Sandell G, Pittaway P, Chakrabarty S, Yusaf T, Chen G, et al. Bioenergy from cotton industry wastes: A review and potential. Renewable and Sustainable Energy Reviews. 2016;66: 435-448. ISSN 1364-0321

[12] Dunnigan L, Morton BJ, Ashman PJ, Zhang X, Kwong CW. Emission characteristics of a pyrolysiscombustion system for the coproduction of biochar and bioenergy from agricultural wastes. Waste Management. 2018;77:59-66. ISSN 0956-053X

[13] CABI. Invasive Species Compendium: Pectinophora gossypiella (Pink Bollworm). 2018. Available from: https://www.cabi.org/isc/datasheet/ 39417#7BD9E856-BD8A-4AA5-9060- 4E6504EC8EEC

[14] Lykouressis D, Perdikis D, Samartzis D, Fantinou A, Toutouzas S. Management of the pink bollworm Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) by mating disruption in cotton fields. Crop Protection. 2005;24(2):177-183. ISSN 0261-2194

[15] El Saeidy E. Renewable Energy in Agriculture in Egypt: Technological Fundamentals of Briquetting Cotton Stalks as a Biofuel. Master [thesis]. Humboldt University of Berlin; 2004. Available from: https://edoc.hu-berlin. de/bitstream/handle/18452/15724/El-Saeidy.pdf?sequence=1

[16] Ellsworth P, Moor L, Allen C, Beasley B, Henneberry T, Carter F. Pink Bollworm Management. 2003. Available from: http://ag.arizona.edu/crops/ cotton/insects/pbw/NCCPBWnewsNo2. pdf

[17] Blake C.. Western Farm Press: Pink Bollworm Eradication in Cotton in 2017? 2014. Available from: https://www. westernfarmpress.com/cotton/pinkbollworm-eradication-cotton-2017

[18] Heilmann S, Davis H, Jader L, Lefebvre P, Sadowsky M, Schendel F, et al. Hydrothermal carbonization of microalgae. Biomass & Bioenergy. 2010; 34:875-882

[19] Bridgwater A. Biomass fast pyrolysis. Thermal Science. 2004;8: 21-49

[20] Algin H, Turgot P. Cotton and limestone powder wastes as brick material. Construction and Building Materials. 2008;22:1074-1080

[21] Zhang Y. Hydrothermal liquefaction to convert biomass into crude oil. In: Blaschek HP, editor. Biofuels from Agriculture Wastes Byproduct. Oxford: Blackwell Publishing; 2010. pp. 201-232

[22] Al Afif R, Wendland M, Krapf LC, Amon T, Pfeifer C. Organosolv plus supercritival carbon dioxide pretreatment of cotton stalks for methane production. In: Proceedings of the 10th International Conference on Sustainable Energy and Environmental Protection, Bioenergy and Biofuels. University of Maribor Press; 2017. pp. 22-33. ISBN: 978-961-286-048-6

[23] Isci A, Demirer G. Biogas production potential from cotton wastes. Renew Energy. 2007;32(5): 750-757

[24] Schaffer S, Pröll T, Al Afif R, Pfeifer C. A mass- and energy balance-based process modelling study for the pyrolysis of cotton stalks with char utilization for sustainable soil enhancement and carbon storage. Biomass and Bioenergy. 2019;120: 281-290

[25] Daud Z, Hatta MZM, Kassim ASM, Awang H, Aripin AM. Analysis the chemical composition and fiber morphology structure of corn stalk. Australian Journal of Basic and Applied Sciences. 2013;7(9):401-405. ISSN 1991-8178

[26] European Commission. Intelligent Energy Europe. Biomass Energy Centre. Solid Biofuels. Fuel Specifications and Classes. Graded Non-woody Pellets: Solid Biofuels. Fuel Specifications and Classes. Graded Non-woody Pellets. 2014. Available from: https://ec.europa. eu/energy/intelligent/projects/sites/iee projects/files/projects/documents/whs\_ summary\_of\_woodfuel\_standards\_en. pdf

[27] Khan AA, de Jong W, Jansens PJ, Spliethoff H. Biomass combustion in fluidized bed boilers: Potential problems and remedies. Fuel Processing Technology. 2009;90(1):21-50. ISSN 0378-3820

[28] Patil PG, Gurjar RM, Shaikh AJ, Balasubramanya RH, Paralikar KM, Varadarajan PV. Cotton Plant Stalk—An Alternative Raw Material to Board Industry. 2007. Available from: https:// wcrc.confex.com/wcrc/2007/techprogram/ P1506.HTM.

[29] Wang X, Qin G, Chen M, Wang J. Microwave-assisted pyrolysis of cotton stalk with additives. BioResources. 2016; 11(3):6125-6136

Bioenergy Recovery from Cotton Stalk DOI: http://dx.doi.org/10.5772/intechopen.88005

[30] He Z, Zhang H, Tewolde H, Shankle M. Chemical characterization of cotton plant parts for multiple uses. Agricultural & Environmental Letters. 2017;2: 110044. DOI: 10.2134/ael2016.11.0044

[31] Reddy N, Yang Y. Innovative Biofibers from Renewable Resources. Heidelberg, New York, Dordrecht, London: Springer; 2015. ISBN 978-3- 662-45136-6

[32] United States Department of Agriculture (USDA). Cotton: World Markets and Trade 2018. Available from: https://apps.fas.usda.gov/psd online/circulars/cotton.pdf

[33] Klass DL. Chapter 5—Waste biomass resource abundance, energy potential, and availability. Biomass for Renewable Energy, Fuels, and Chemicals, Academic Press, Pages. 1998: 137-158. ISBN 9780124109506

[34] European Commission (EC). 2016. Maximising the yield of biomass from residues of agricultural crops and biomass from forestry. Available from: https://ec.europa.eu/energy/sites/ener/ files/documents/Ecofys%20%20Final\_ %20report\_%20EC\_max%20yield%20b iomass%20residues%2020151214.pdf

[35] Scarlat N, Martinov M, Jean-François Dallemand JF. Assessment of the availability of agricultural crop residues in the European Union: Potential and limitations for bioenergy use. Waste Management. 2010;30(10): 1889-1897. ISSN 0956-053X

[36] Hoogwijk M, Faaij A, van den Broek R, Berndes G, Gielen D, Turkenburg W. Exploration of the ranges of the global potential of biomass for energy. Biomass and Bioenergy. 2003;25(2): 119-133. DOI: 10.1016/S0961-9534(02) 00191-5

[37] Coates WE. Using cotton plant residue to produce briquettes. Biomass and Bioenergy. 2000;18:201-208

[38] ECN. Phyllis2—Database for Biomass and Waste. 2019. Available from: www.ecn.nl/phyllis2

[39] Ahmed FA, Abdel-Moein NM, Mohamed AS, Ahmed SE. Biochemical studies on some cotton by products Part I—Chemical constituents and cellulose extraction of Egyptian cotton stalks. Journal of American Science. 2010;6: 1306-1313

[40] Bridgwater AV. Pyrolysis—State of the art. In: Bridgwater AV, editor. Success & Visions for Bioenergy: Thermal Processing of Biomass for Bioenergy, Biofuels and Bioproducts. Newbury, Berks, UK: CPL Press; 2007

[41] Boyle G. Renewable Energy: Power for a Sustainable Future. Oxford, England: Oxford University Press in association with the Open University; 2012

[42] Johansson LS, Tullin C, Leckner B, Sjövall P. Particle emissions from biomass combustion in small combustors. Biomass and Bioenergy. 2003;25(4):435-446. ISSN 0961-9534

[43] Salatino P, Solimene R. Mixing and segregation in fluidized bed thermochemical conversion of biomass. Powder Technology. 2017;316:29-40. ISSN 0032-5910

[44] Puig-Arnavat M, Bruno JC, Coronas A. Review and analysis of biomass gasification models. Renewable and Sustainable Energy Reviews. 2010; 14(9):2841-2851. ISSN 1364-0321

[45] Allesina G, Pedrazzi S, Allegretti F, Morselli N, Puglia M, Santunione G, et al. 2018. Gasification of cotton crop residues for combined power and biochar production in Mozambique. Applied Thermal Engineering. 2018; 139(5):387-394

[46] Kung CC, Zhang N. Renewable energy from pyrolysis using crops and agricultural residuals: An economic and environmental evaluation. Energy. 2015; 90(Part 2):1532-1544. ISSN 0360-5442

[47] Mohan D, Pittman C, Steele P. Pyrolysis of wood/biomass for bio-oil: A critical review. Energy. 2006;20:848. DOI: 10.1021/ef0502397

[48] Bridgwater AV. Review of fast pyrolysis of biomass and product upgrading. Biomass and Bioenergy. 2012;38:68-94. ISSN 0961-9534

[49] Qi Z, Jie C, Teijun W, Ying X. Review of biomass pyrolysis oil properties and upgrading research. Energy Conversion and Management. 2007;48:87-92

[50] Chen Y, Yang H, Wang X, Zhang S, Chen H. Biomass-based pyrolytic polygeneration system on cotton stalk pyrolysis: Influence of temperature. Bioresource Technology. 2012;107: 411-418. ISSN 0960-8524

[51] Kantarelis E, Zabaniotou A. Valorization of cotton stalks by fast pyrolysis and fixed bed air gasification for syngas production as precursor of second generation biofuels and sustainable agriculture. Bioresources Technology. 2009;100:942-947

[52] Brown R. Biochar production technology. In: Lehmann J, Joseph S, editors. Biochar for Environmental Management: Science and Technology. London: Earthscan; 2009. pp. 127-139

[53] Duku MH, Gu S, Hagan E. Biochar production potential in Ghana—A review. Renewable and Sustainable Energy Reviews. 2011;15:3539-3551

[54] Halwachs M, Kampichler G, Kern S, Pröll T, Hofbauer H. Rotary kiln pyrolysis—A comprehensive approach of operating a 3 MW pilot plant over a period of two years. In: Bridgwater AV, editor. Proceedings of the Bioten Conference on Biomass, Bioenergy and

Biofuels. Newbury: CPL Press; 2010. p. 2011

[55] Kern S, Halwachs M, Kampichler G, Pfeifer C, Pröll T, Hofbauer H. Rotary kiln pyrolysis of straw and fermentation residues in a 3 MW pilot plant— Influence of pyrolysis temperature on pyrolysis product performance. Journal of Analytical and Applied Pyrolysis. 2012;97:1-10

[56] Pandit NR, Mulder J, Hale SE, Schmidt HP, Cornelissen G, Cowie A. Biochar from Kon-Tiki flame curtain and other kilns: Effects of nutrient enrichment and kiln type on crop yield and soil chemistry. PLoS One. 2017;12: e0176378. DOI: 10.1371/journal. pone.0176378

[57] Meier M, Schmid K, Heger S. Pyrolyseverfahren in Burgau—eine Betrachtung aus Sicht der Überwachungsbehörde. In: Thomé-Kozmiensky KJ, Beckmann M, editors. Energie aus Abfall (in German). Vol. 11. Nietwerder, Germany: TK Verlag; 2014. pp. 780-795

[58] Pröll T, Al Afif R, Schaffer S, Pfeifer C. Reduced local emissions and longterm carbon storage through pyrolysis of agricultural waste and application of pyrolysis char for soil improvement. Energy Procedia. 2017; 114:6057-6066

[59] Schmidt HP, Pandit BH, Cornelissen G, Kammann CI. Biochar-based fertilization with liquid nutrient enrichment: 21 Field trials covering 13 crop species in Nepal. Land Degradation & Development. 2017;28:2324-2342

[60] Pröll T, Zerobin F. Biomass-based negative emission technology options with combined heat and power generation. Mitigation and Adaptation Strategies for Global Change. 2019. DOI: 10.1007/s11027-019-9841-4

[61] Spokas KA. Review of the stability of biochar in soils: Predictability of O:C Bioenergy Recovery from Cotton Stalk DOI: http://dx.doi.org/10.5772/intechopen.88005

molar ratios. Carbon Management. 2010;1:289-303

[62] Al Afif R, Pfeifer C, Ramadan M. An experimental study on hydrothermal carbonization of cotton stalks. In: Proceedings of the 11th International Conference on Sustainable Energy & Environmental Protection, Bioenergy and Biofuels. Glasgow, UK; 2018

[63] Alvira P, Tomás-Pejó E, Ballesteros MM, Negro J. Pretreatment technologies for an efficient bioethanol production process based on enzymatic hydrolysis: A review. Bioresource Technology. 2010;101:4851-4861

[64] Silverstein RA, Chen Y, Sharma-Shivappa RR, Boyette MD, Osborne J. A comparison of chemical pretreatment methods for improving saccharification of cotton stalks. Bioresource Technology. 2007;98:3000-3011

[65] Christopher M, Mathew AK, Kumar KM, Pandey A, Sukumaran R. A biorefinery-based approach for the production of ethanol from enzymatically hydrolysed cotton stalks. Bioresource Technology. 2017;242: 178-183

[66] El-Shinnawi MM, El-Houssieni M, Aboel-Naga SA, Fahmy S. Chemical changes during a two-stage digestion technique for biogas production from combinations of organic wastes. Resour Conserv Recycling. 1990;3:217-230

[67] Zheng Y, Shi J, Cheng Y. Principles and development of lignocellulosic biomass pretreatment for biofuels. Advances in Bioenergy. 2017;2:1-68

## **Chapter 5**
