The Effect of Humic Acid Foliar Application on Morphophysiological Characteristics and Yield of Black Bean Plant Under Different Irrigation Regimes

Water deficit is one of the most important limiting factors of production in crops. The present study was conducted in 2019 to investigate the effect of different irrigation times and foliar application of humic acid on morphophysiological traits and yield of black beans as a split plot in a randomized complete block design with three replications at Zahak Agricultural Research Station in Sistan and Baluchestan Province. The main factor involves three irrigation treatments, including irrigation from planting to harvest, irrigation from planting to flowering, and irrigation from flowering to harvest, and the secondary factor includes foliar application at four levels of humic acid (0, 1, 2, and 3 per thousand). By increasing drought stress levels, plant height and width, fresh and dry forage yield, leaf area (in both stem and flowering stages), photosynthetic pigments, nitrogen, phosphorus (3.39%), potassium (20.6%), calcium of leaf, grain yield (11.27%), and biological yield (60.22%) has decreased, whereas proline content (31.88%) has increased, compared to the control. Also, by increasing humic acid levels, the values ​​of all studied traits has increased. Humic acid has had a positive effect on black bean plant traits under drought stress conditions, so that its concentration of three per thousand reduces the adverse effects of drought stress, increasing the tolerance of black bean crop. In general, complete irrigation and application of three per thousand humic acids for the production of black beans seems appropriate. It is suggested that in future research, soil application of humic acid consumption should be investigated to compare the efficiency of the methods used.