The cluster bean (Cyamopsis tetragonoloba L.) is popularly known ‘Guar’. The word “guar” represents its derivation from the Sanskrit word “Guaahar” which means cow fodder or fodder for livestock. It is grown for various purposes such as vegetables, green fodder, green manuring and seed. Among leguminous crops, it is comparatively more drought hardy as it has long, deep root system that enables the plant to grasp the water available in the soil, thus offering better scope to be grown during the rainy season. In India, cluster bean is grown on 3.08 million hectares area with an annual production of 1.6 million tons and a productivity of 539 kg ha-1 (Anonymous, 2023-24). It accounts for almost 82.1 % area (4.9 m ha) and 70% production (2.2 million tonnes) in India whereas, Haryana and Gujrat have second and third positions, respectively. Productivity of cluster bean has stagnated or even declined due to decline in organic matter content, nutrients deficiency and non-availability of low-cost effective fertilizers. The deteriorated soil health also caused a decline in crop response to recommend doses of fertilizers. Cluster bean are generally grown on marginal and sub marginal lands by applying low inputs in the Indian farming system.
Potassium is described as the “quality element” for crop production (Usherwood, 1985; Pettigrew, 2000). Potassium exists in soil in different forms viz., water soluble, exchangeable K, non-exchangeable K (fixed K) and mineral K. Potassium is rarely applied to pulses despite of their higher K requirements and there is continued mining of soil K (Rao et al., 2014). Based on several field studies, it can be suggested that the application of 20-40 kg K2O ha-1 is beneficial for higher pulse production (Jat et al., 2022). Potassium is a dynamic ion in soil and plant system play an important role in plant growth, acting as an essential element. Cluster beans need large quantities of potassium to improve the crop quality, but nutrient status. The adequate supply of potassium during growth period, improves the water relations of plant and photosynthesis (Garg et al., 2005), maintains turgor pressure of cell which is necessary for cell expansion, helps in osmotic regulation of plant cell, assists in opening and closing of stomata, increases tolerance to water stress, (Epstein, 1972) and enhances water use efficiency. Potassium also activates the plant’s antioxidant system under cold stress to prevent damage of the cells. Many metabolic processes, like the rate of photosynthesis and translocation, enzyme systems and nutrient uptake by plant are adversely affected with inadequate supply of potassium ion (Marschner, 2002; Mengel, 1997).
