Differential responses of two local and commercial guar cultivars for nutrient uptake and yield components under drought and biochar application.

Drought is one of the abiotic stresses that can reduce crop yields. It has a major impact on crop yield reduction. For crops under stress, organic modifiers such as biochar can be useful. Guar (Cyamopsis tetragonoloba L.), an annual legume from the Fabaceae Family, is highly adaptable to arid and semi-arid regions, with many applications in various industries. Field experiments were carried out in a randomized complete block design with three replications using a split-split plots arrangement. The aim was to evaluate the influence of irrigation levels (Ir1 = 10, Ir2 = 14, and Ir3 = 17 days irrigation cycle) and biochar (B1 = 0, B2 = 5, and B3 = 10 tons ha) application on physiological traits [(chlorophyll a and b, chlorophyll index (SPAD), relative leaf water content (RWC), electrolyte leakage (EL), canopy temperature, leaf area, water use efficiency (WUE)], morphological parameters (length and diameter of the stem, pod length, fresh weight of root and plant, root length), yield components (seed yield, number of branch plant, number of clusters plant, pod plant, seed pod, seed plant, 1000-seed weight, and gum contents), and leaf nutrient uptake (Ca, Mg, P, Na, and K) of two commercial and local cultivars (cv1 = RGC-936 and cv2 = Saravan) of the guar plant. It was observed that the Ir3 irrigation treatment produced the highest seed yield (1921.8 kg ha) in terms of water stress. However, the maximum pod plant (75.5), seed plant (454.2), seed yield (1871.1 kg ha), leaf area (861.8 mm), SPAD (92.2), Mg (49.8 mg g), Na (43.3 mg g) and P (0.49 mg g) were observed in RGC-936. The results also revealed that biochar was more effective than cultivars in terms of morphological traits. While yield and yield components were affected by cultivar, irrigation at different levels also had a significant effect on functional traits, physiology, and morphology. The addition of biochar appeared to have a positive effect on water stress alleviation and guar growth and leaf nutrient uptake. According to Pearson's correlation analysis, plant weight and length, root weight and length, stem diameter, seed pod, branches plant, and 1000-seed weight are moderately correlated with seed yield, while pod plant and seed plant are strongly associated with seed yield. On the other hand, the pod length, branches plant, and gum content showed a positive but not significant relationship.