Assess the Effect of Humic Acid Foliar Application on the Seed yield Its Components of Cowpea (Vigna unguiculata) under Low Irrigation Conditions in Iran (Southern Khuzestan)

BACKGROUND: Water is the limiting factor for the production of agricultural products in arid and semi-arid climatic conditions, including Iran, and its optimal use is very important. The use of natural fertilizers, including humic acid without harmful environmental effects, can be effective to increase yield. OBJECTIVES: Current study was done to investigate the effect of different levels of low irrigation and humic acid foliar application on cowpea crop production. METHODS: This research was conducted according split plot experiment based on randomized complete block design (RCBD) with three replications. The main factor included different levels of low irrigation (I1:70 or control, I2: 90, I3: 110 and I4: 130 mm of evaporation from the surface of the Class A evaporation pan) and secondary factor included different amounts of humic acid fertilizer (F1: none use or control, F2:4 lit.ha-1, F3: 6 lit.ha-1). RESULT: The difference between different levels of low irrigation and humic acid in terms of plant height, pod length, number of sub-branches, number of pods per plant, number of seeds per pod, weight of 1000 seeds, seed yield, biological yield and harvest index are statistically significant at the probability level of 1% was significant. The interaction effect of treatments on plant height and number of pods per plant was significant at 1% probability level and pod length, 1000 seed weight and seed yield was significant at 5% probability level. The highest seed yield belonged to the irrigation treatment of 70 mm evaporation and foliar spraying with 6 lit.ha-1 with an average yield of 3755 kg.ha-1. The lowest seed yield was obtained from the irrigation treatment of 130 mm of evaporation and without foliar spraying with an average of 987 kg.ha-1. The highest and lowest harvest index belonged to the irrigation treatment of 70 and 130 mm of evaporation pan, respectively (with an average of 41.25 and 25.67%). CONCLUSION: Based on the results of the research, foliar application of 6 lit.ha-1 of humic acid at different levels of low irrigation increased seed yield compared to the control (no foliar application).