Evaluation of the response of rice cultivars in some functional and physiological traits using different nutritional sources (chemical, organic) under drought stress conditions

A factorial experiment was performed as a randomized complete block design with three replications in Sari Research Farm during 2016-2017. Three levels of stress, including drought stress on the time of tillering initiation (15 days after transplanting), in remobilization stage (the end of flowering and the beginning of grain filling stage), and no drought stress (control), were considered as the main factors. Four fertilizer sources, including vermicompost, Azolla compost, humic acid, and chemical fertilizers of nitrogen, phosphorus, potassium, along with two local Tarom and Shirodi cultivars, were considered as the sub-factor. The maximum paddy seed yield was obtained in the non-stress condition using humic acid in Shirodi and local Tarom cultivars. The highest harvest index in the first year under non-stress conditions was obtained from the use of humic acid fertilizer resources in the Shirodi cultivar (54.08%), and the maximum concentrations of chlorophylls a, b, and total chlorophyll were obtained under non-stress conditions. With applying stress, especially drought stress at the complete heading stage, the chlorophyll concentration significantly reduced, so that under drought stress at the heading stage, chlorophyll a, b, and total chlorophyll concentrations reduced by 3.8, 2.6, and 3.3, respectively, compared with the control. the use of humic acid is recommended to obtain the maximum functional and physiological traits of the studied rice cultivars under drought stress.