Harvest date and salicylic acid impact on peanut (Arachis hypogaea L.) properties under different humidity conditions

This study was conducted to investigate the effects of salicylic acid and harvest date on the yield and biochemical and physiological characteristics of peanuts in different humidity conditions, which is the novelty of this research. For this purpose, a split-plot factorial design during the 2018 and 2019 cropping seasons was conducted based on a randomized complete block design with three replications at the experimental field of the Agricultural and Natural Resources Research and Education Center of Guilan Province, Astara, Iran. Humidity regimes included rain-fed conditions (no irrigation), irrigation at the 10% flowering stage, 10% pod formation stage, and 10% flowering stage +10% pod formation stage in the main plots, and three salicylic acid levels (100, 200, and 300 µmol/l), and harvest dates (August 22, September 6, and September 21), were placed in subplots. Drought stress reduced the Chlorophyll Index, relative water content, seed, and pod yield but increased proline, Antioxidant enzyme activity, soluble sugar content, and H2O2 content. Conversely, Supplementary irrigation decreased proline, antioxidant enzyme activity, soluble sugar content, and H2O2 content, which increased the Chlorophyll Index, relative water content, seed, and pod yield. Also, salicylic acid foliar application enhanced guaiacol peroxidase, polyphenol oxidase, and ascorbate peroxidase antioxidant enzyme activity, mitigating the undesirable impacts of water deficiency. The maximum pod and seed production was obtained in all humidity conditions with 300 µmol/l salicylic acid. Under Humidity stress conditions, if water resources are available, two supplementary irrigations at 10% flowering and 10% pod formation stage are recommended. Also, for humid climates such as Astara and similar regions, in terms of climate, with limited rainfall in June and July (rainfall less than 10 mm during flowering and podding stages), one supplementary irrigation at 10% pod formation stage is recommended.