The Changes in Various Physio-Biochemical Parameters and Yield Traits of Faba Bean Due to Humic Acid Plus 6-Benzylaminopurine Application under Deficit Irrigation

Abstract

Implementing the deficit irrigation pattern has become a major strategy in crop production systems. However, using less water than is required to irrigate crops is associated with changes in plant physiology and lower productivity. Therefore, the current research aimed to assess the integrated effect of humic acid and cytokinin on faba bean under water deficit. Under two irrigation levels (full irrigation, FI and deficit irrigation, DI), two humic acid treatments (without addition, H0 and with addition of 10 kg ha−1, H10) and two cytokinin concentrations (without spray, C0 and spraying with 25 mg L−1, C25), faba bean growth, physiology, and productivity were evaluated. The experiment was implemented for two winter seasons of 2019/20 and 2020/21 and performed in a split–split plots design with three replicates. The findings revealed that under low water supply (DI), H10 plus C25 was the most efficient treatment for enhancing faba bean growth. All physiological faba bean traits estimated under DI showed remarkable increases with the application of H10 plus C25 in both seasons. The increases in proline, catalase, and total soluble sugars under DI due to H10 plus C25 were 31.4 and 31.8%, 51.9 and 55.1% as well as 43.8 and 46.6%, in the first and second seasons, respectively. There was no significant difference between FI × H10 plus C25 and DI × H10 plus C25 in phosphorus content in both seasons. FI × H10 plus C25 and DI × H10 plus C25 in the second season produced a similar number of pods plant−1 and seed yield of faba bean. Conclusively, the combined application of humic plus cytokinin achieved physiological and nutrient homeostasis, adjusting the biochemical compounds in faba bean under water deficit.