**5. Potassium as a drought stress ameliorating tool**

Increases the leaf photosynthetic of crops, crop maturity, and high-quality fibers among all plant nutrients, K has a key role in increasing vigorous cotton development [23]. Due to its negative effects on cotton's surface of leaves of plants, photosynthesis, and production of biomass, K was shown to reduce yield and fiber quality [132], because K plays a major role in cotton growth, development, and quality fibers.

#### *Enhancing Water Use Efficiency by Using Potassium-Efficient Cotton Cultivars Based… DOI: http://dx.doi.org/10.5772/intechopen.112606*

In addition, excess or insufficient K is vital to the normal function of the plants and also for the development of plants [9] in the growth medium to maintain the K level and its relation with other critical plant nourishment (particularly sodium (Na)). The management of K-fertilizer is, therefore, beneficial to enhance plant growth. Adequate K supplies influenced the overall growth of cotton substantially [133] because of their crucial function in the generation of biomass [134], an increase in its surface area, and the synthesis of photosynthesis [135].

Cotton is more vulnerable to low K and the most sensitive to K fertilization than other plants [81]. Ref. [133] He also found varied responses from conventional and Bt cotton cultivars to low K levels. In biomass output, four cotton cultivars are significantly different from K in a field test. Likewise, nutrient-efficient genotypes culture was proposed as a key strategy to enhance fertilizer efficiency [37]. By decreasing the usage of artificial fertilizers in agriculture, potassium intake and effective use of soil nutrients are anticipated to have good environmental benefits. The genotypes which are successful in K-uptake were proposed to have a broader root surface. This can lead to additional root-to-soil moves to maintain a broader root gradient. This might further enhance K translocation to different plant organs, which could maintain the optimum cytosolic K+ content. The enhanced selectivity from K to Na is the fundamental mechanism of better efficiency of use [37].

A sufficient supply of cotton K is not only necessary for water relations but also for improving the water use efficiency of (WUE) which can enable plants to live under drought stress [135]. Observed that WUE in cotton was enhanced by K but with cotton cultivars, this impact was different [136] shows that not all plants or K levels may have a favorable influence on every element of water in cotton stomach conductivity by fertilization with K under water-starved conditions.

Drought stress yields are a good tolerance to K applications, and they increased fiber yield and quality when compared with a well-watered control, under drought stress treatments [137]. Furthermore, it was observed that using K foliar spray, the micronaire, an indirect measure of fiber coarseness, was enhanced by 0.32. Drought stress saving the effects of drought stress and enhanced output was the use of foliar K. Although the reaction of cultivars was varied, the use of foliar K in the drought treatments increased fiber output and quality, to make it statistically comparable to well-watered control [138].

Both root development and the rates of K+ root diffusion were reduced during drought stress, reducing the uptake of K. Drought resistance as well as K absorption might be further depressed by the ensuing reduced levels of K. Consequently, maintenance of sufficient plant K is important for the dryness of plants. A strong relationship has been established between K's nutritional status and plant drought resistance. Adequate quantities of K can increase the overall dry mass accumulation under drought stress compared to lower K levels. The stomata control by K+ and the associated increased rates of photosynthesis may be related to this result. Furthermore, K is also crucial to the transfer of root development photo-assimilates. Root growth promotion was shown to enhance the root surface that was exposed to the soil as a consequence of improved absorption of root water by increasing adequate K supply under K-deficient soil. Lindhauer said that K nutrition not only enhanced the total dry mass of the plant and leaf area but also improved the retention of water in the drought of plant tissue. Drought stress has considerably decreased cell membrane stability [139]. Maize plants with a higher application of K were shown to respond more effectively to water stress in research [140]. These improvements were mostly due to K's function in enhancing stability and adjusting the capabilities of the cell membrane. A suitable supply of K is necessary to increase dryness by increasing root length and keeping the cell membrane stable.

Many studies have demonstrated that osmotic adjustment is positively linked to drought resistance in different plant types [141]. K+ plays a crucial function in developing the capacity to adapt to drought environments as one of the most prominent inorganic osmotic in plants [142]. Increasing the K<sup>+</sup> , Cl− , and Na+ absorption by root cells regulated cell turgor restoration under osmotically-generated stress, partially mediated by K+ transporters on the cellular plasma membrane [143]. Moreover, enough K promotes solvent accumulation, therefore decreasing the osmotic potential to sustain osmotic stress in plant cell turgor. In a word, an adequate K status can enable osmotic adjustments which maintain high turgor pressure, the relative water content, and reduced osmotic potential [144].

For seed adjustment to drought environments, rapid stoma closure and internal moisture conservation are critical. K plays a vital function during stomata activity in turgor control in guard cells [142]. Considering that stomata closure is preceded by the quick release of K+ from the protective cells into the leaf apoplast, it is fair to believe that stomata could hardly be left open in K-deficient circumstances. Some studies show that K shortage in various agricultural plants might cause stomata closures and decrease photosynthesis rates [98, 145]. Rapid stomatal closure and internal humidity conservation are important for seed adaptability to drought conditions. K plays a key role in the turgor regulation activities in guard cells [142]. Since the closure of the stomata is before the rapid release of K+ in leaf apoplast from the protecting cells, it is reasonable that under the K-deficiency situations, stomata could scarcely be left open. Some researchers have shown that K deficit may affect stomata closures and photosynthetic rates in different agricultural plants.
