**1. Introduction**

Cotton, which is a prominent commercial crop in over 30 nations, is produced mostly in warmer areas and has large shareholdings in China, India, the United States, and Pakistan [1]. In 2014–2015, the top five cotton-productive nations were China, India, Pakistan, and Brazil, with 6.5, 5.4, 3.5, 2.3, and 1.5 M, respectively [2]. As a glycophyte, cotton is more tolerant than other main crops to abiotic stressors. However, e extreme conditions, such as drought, affect cotton growth, productivity, and fiber quality [3]. Cotton production is predicted to decrease owing to drought stress, according to a news release issued by the United States Department of Agriculture [4]. Similarly, cotton output decreased by 34% in Pakistan to only 9.68 million bales compared with 14.4 million bales in 2012, due to drought and high weather [5]. Other crops were harmed by drought in addition to cotton, as about 67% of crop losses in the United States were caused by drought stress in the last 50 years [6].

Water use efficiency (WUE) can be increased by reducing soil water evaporation and converting more moisture into biomass production through crop residue management, mulching, and target-based irrigation. Appropriate arrangement and improved water use is a possible measure for improving yield under water stress, and it assesses the way and depth of water application, and whether it was used at optimum level by the crop. Improved irrigation water use efficiency can be achieved by approving the best management practices of irrigation [7].

Potassium (K) is affianced in all the physiological developments of the plant, which need water. K supports water carrying and mineral translocation for the entire plant through the xylem. Under K-deficiency, the movement of minerals such as (NO3 − ), (PO4 3−), (Ca2+), (Mg2+), and amino acid uptake is abridged. One option is to use the normal rate of K application can support the plant to alleviate the effect of the water-deficit through better water use efficiency (WUE), which was related to the lower leaf ET [8]. Secondly, the option is to use K-efficient crop cultivars that can reduce the effect of water shortage and improve WUE without compromising the yield [9]. This can be achieved by the K-efficient cultivar by special proteins present in the cell membrane. These are called transporters and channels. Based on their affinity for K+ , K+ transport components can be classified as high-affinity components (transporters), which are active at a low concentration of external K+ , and lowaffinity components (channels), which are active at a higher concentration, usually at more than 0.3 mM external K<sup>+</sup> [10]. During water shortage conditions, root regulate their water and ion uptake by modifying these proteins and channels to cope with the water shortage [6, 11–32]. It is, therefore, K-efficient cotton cultivars that could perform better for sustainably cotton production under arid climatic conditions.

#### **1.1 Cotton is drought-sensitive crop**

Millions of people worldwide are involved with cotton directly or indirectly. Cotton is a severely susceptible crop under water stress conditions that reduces productivity [33]. Earlier, water stress reduced cotton growth and cotton yield due to lowered flowering and retention of the boll. Cotton is classified as a low drought-sensitive crop, according to FAO data; however, drought stress is dreadful when cotton is at the flowering and bolls formation stages [34]. In Pakistan, the cotton crop is mainly grown in arid and semiarid climatic conditions where annual rainfall is less than 250 mm. In the future, therefore, cotton productivity is estimated to drop due to severe water shortages, irregular patterns of rainfall, and other environmental impacts [35].

Drought has broad and variable effects on cotton, such that exact financial figures are hard to calculate. In 2008 and 2009, world production of cotton was extremely low and in 2009 stocks declined significantly. As a result, in 2010 and 2011, cotton prices increased, causing a 10% drop in cotton consumption in 2011. From 2010 to 2013, the output of cotton was more than demand, but from 2011 production declined significantly from 2014 to 2015 by 6.5 percent, while consumption grew by over 6.5 million bales per year. We thus need to set cotton production and consumption strategies. Furthermore, because too unpredictable situations in the future, stressful cotton types must also be produced. The focus must, on the other hand, not only be placed on the diversity of stress-tolerant of cotton, although plant survival is highly essential

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

**Figure 1.** *K status and crop removal in Pakistani soils [11].*

in the early stages of growth. It is widely recognized that improvements in yield and the stability in yields in cotton cultivations are vital for the expanding worldwide population under normal and drought conditions. Despite the complexities of the process of drought tolerance in cotton, the knowledge of the drought tolerance mechanism has been tremendously advanced. The drought-tolerant type of cotton might lead either to morpho-physiological, biochemical, and molecular modifications by nature or genetic engineering.

## **1.2 Current scenario of K-deficiency**

The soil contains on average 2% K; however, soil K may be quite low in older or drained soils. Soil K is usually available in four pools: 0.1–0.2% of the soil solution, 1–2% of the exchangeable K, 1–10% of the nonexchangeable K, and 90–98% of the soil mineral solution [36]. Plant roots collect K from variable pools and dynamically adjusted K solution for soil [36, 37]. The soil K in a solution pool of soil is filled by potassium released from interchangeable areas [36]. The nonexchangeable K may be found in the range of 2: 1 and 2: 1: 1 type clay minerals [37]. Some plant species have been discovered to utilize K from an unchangeable pool, such as sugar beet (Beta vulgaris L.) with exudates, which results in a K-influx of 7–20% higher than that for wheat and barley roots [36].

The deficiency of K in Pakistani soils is about 35% [38], which is continuously increasing due to the low use of K (<1.0 kg K2O ha−1) as compared to other countries of the world (15 kg K2O ha−1). In the year 2007–2008, about 43% of Pakistani soils were deficient in K, as reported by Ref. [39], but currently, it reached up to 90% and needs K fertilization for better crop production. Cotton requires K2O @150 kg ha−1 that almost equal to nitrogen from the soil, to get average crop yield [40] and is required @ 4.5 kg ha−1 day−1 during peak bloom by cotton [41]. Despite high-K requirements, K-use in cotton production is very limited in Pakistan. The total content of K varies from 50 to 150 mg kg−1 in the soil across the Punjab province. Adequate K nutrition upgrades the proficiency of photosynthetic rate and development of plant roots, as investigated by Ref. [42]. However, most of the farmers of developing countries, including Pakistan, do not apply K-fertilizer to crops due to their high-prices. Under this situation, the identification of K-efficient crop cultivars can improve production and reduce the demand for K fertilizers in the country (**Figure 1**).
