Document Type : Complete scientific research article
Authors
1
M.Sc. Student in Agrotechnology – Crop Ecology, Department of Agronomy and Plant Breeding, Faculty of Agriculture, Yasouj University, Yasouj, Iran.
2
Assistant Professor, Department of Agronomy and Plant Breeding, Faculty of Agriculture, Yasouj University, Yasouj, Iran.
3
Associate Professor, Department of Agronomy and Plant Breeding, Faculty of Agriculture, Yasouj University, Yasouj, Iran.
4
M.Sc. in Agrotechnology – Crop Physiology, Department of Agronomy and Plant Breeding, Faculty of Agriculture, Yasouj University, Yasouj, Iran.
10.22069/ejcp.2025.23737.2690
Abstract
Background and Objectives: The yield stability of red bean (Phaseolus vulgaris L.) in many regions of the world is seriously threatened by environmental stresses, especially drought. This stress, by affecting key physiological processes of the plant such as photosynthesis and nutrient uptake, causes a significant reduction in grain yield. In arid and semi-arid regions such as Iran, the water crisis resulting from climate change and excessive exploitation has created a serious challenge to the sustainable production of drought-sensitive crops like red bean. In response to this challenge, the use of low-cost, sustainable, and environmentally friendly agronomic practices has become increasingly essential. Humic acid, as an organic compound derived from the decomposition of natural materials, is among the emerging options considered in the management of abiotic stresses. By improving the physical and chemical properties of the soil, increasing water-holding capacity, facilitating nutrient uptake, and enhancing the plant’s defense mechanisms, humic acid plays an important role in improving plant tolerance to water stress. Therefore, the present study was conducted to evaluate the effect of foliar application of humic acid on some physiological and nutritional traits of red bean cultivar Yaghoot under deficit irrigation conditions.
Materials and Methods: This field experiment was carried out in 2023 in Boyer-Ahmad County (southwestern Iran). The experimental design was a split-plot arrangement based on a randomized complete block design with three replications. The main factor consisted of three irrigation levels based on the percentage of crop water requirement estimated through reference evapotranspiration using Class A evaporation pan: full irrigation (100% of crop water requirement), moderate stress (80% of crop water requirement), and severe stress (60% of crop water requirement). The subplots included foliar application of humic acid at four levels: 0 (control), 2.5, 5, and 7.5 L ha-1, applied at two growth stages—six-leaf stage and beginning of flowering. The evaluated traits included proline, soluble sugars, superoxide dismutase, chlorophyll a and b, chlorophyll index, seed nutrient contents (nitrogen, potassium, and phosphorus), and grain yield.
Results: The results showed that 60% irrigation increased leaf soluble sugar content by 33.94%, while reducing chlorophyll a and b content by 46.15% and 52.71%, respectively. The simple effect of severe stress also reduced seed phosphorus by 6.54% and increased seed potassium by 45.91%. Application of 7.5 L ha-1 humic acid increased chlorophyll a, chlorophyll b, and chlorophyll index by 65.62%, 52.38%, and 9.49%, respectively. The significance of two-way interactions indicated that under 60% irrigation, application of 7.5 L ha-1 humic acid increased proline by 56.97% and superoxide dismutase activity by 70.43%. Overall, higher levels of humic acid application improved grain yield by 37.41% under full irrigation and by 20.66% under severe stress.
Conclusion: The findings showed that deficit irrigation in red bean disrupts physiological balance, reduces photosynthetic efficiency, and decreases nutrient uptake, ultimately leading to yield reduction. However, foliar application of humic acid, as an effective biostimulant, enhanced the plant’s physiological and nutritional capacity, increasing stress tolerance and improving yield-related traits. Therefore, foliar application of 7.5 L ha-1 humic acid, by strengthening the defense system and improving nutrient uptake, improved the final yield of red bean cultivar Yaghoot under deficit irrigation conditions in Boyer-Ahmad County. To validate these findings, multi-year experiments are recommended.
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