Background/objectives: The availability of nutrients to plants is one of the main constraints under calcareous soil. This study aimed to investigate the influence of humic acid on nutrients availability and fruit yield of apple trees. at district Ziarat using red delicious apple variety of same age. Methods: Six rates of humic acid were tested in randomized complete block design (RCBD) with three replications. These rates were included as T1 = Control (0.0 g Humic acid), T2 = 50 g potassium humate tree-1, T3 = 75 g potassium humate tree-1, T4 = 100 g potassium humate tree-1, T5 =125 g potassium humate tree-1 and T6 = 150 g potassium humate tree-1. Findings: The results showed that the apple trees received 125 and 150 g potassium humate tree-1 recorded statistically at par but higher fruit set (71.68 and 74.66%) and fruit yield (262.15 and 264.46 kg tree-1) and higher fruit retention (91.63%) with minimum fruit drop (8.37%) at 150 g potassium humate tree-1. However, control treatment resulted in greater fruit drop (72.43%) and minimum fruit set (21.10%). Similarly, the application of 125 and 150 g potassium humate tree-1 manifested higher leaf macro and micro nutrients concentration. There was positive and significant correlation between apple fruit yield and leaf nutrient concentration which evidenced the beneficial and stimulatory effect of humic acid on nutrient availability and yield. Applications/improvements: From this study it is suggested that different sources of humic acid need to be tested on apple so that the best source of humic acid can be found for quality fruit production of apple.
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