Extended Abstract

Introduction:

Rice is the staple food of more than half of the global population. In Iran, rice production faces challenges such as water scarcity and weed infestation, particularly barnyardgrass (Echinochloa crus-galli). Although alternate wetting and drying (AWD) irrigation is an effective strategy for reducing water consumption, it can increase weed population and diversity. This study aimed to evaluate the effects of different AWD irrigation intervals (8, 12, and 16 days) and integrated weed management on yield and morphophysiological traits of rice cv. Hasti in Rasht city, Guilan provinve (North of Iran).

Materials and Methods:

The experiment was conducted over two cropping years in Rasht, Iran, as a split-plot arrangement in a randomized complete block design with three replications. The main factor included three irrigation intervals, and the sub-factor consisted of six weed management levels including herbicide once and twice, manual weeding twice, rotovator twice, herbicide + manual weeding, and herbicide + rotovator. The herbicides used were cyhalofop-butyl + penoxsulam. Measured traits included grain yield, plant height, grain filling rate using the Richards equation, amylose content using the iodine-spectrophotometry method, fertile tiller number, filled grain number per panicle, 1000-grain weight, and panicle length.

Results and Discussion:

Irrigation interval had no significant effect on grain yield, indicating relative tolerance of cv. Hasti to mild drought stress. Irrigation interval significantly affected plant height and grain filling rate. The highest plant height was in the 12-day interval (129.05 cm) and the lowest in the 16-day interval (126.33 cm). Grain filling rate increased under mild drought stress, with the highest values in 16-day (1.33) and 12-day (1.31) intervals, which were 15.7% and 13.9% higher than the 8-day treatment (1.15), respectively. Weed management had a highly significant effect on grain yield, grain filling rate, amylose content, and all yield components. The highest grain yield was in manual weeding twice (5324 kg.ha⁻¹), not significantly different from herbicide twice (5267 kg.ha⁻¹) and herbicide + manual weeding (5249 kg.ha⁻¹). The lowest yields were in herbicide once and herbicide + rotovator treatments. Manual weeding twice compared to herbicide once increased fertile tiller number by 16.2%, filled grain number per panicle by 9.2%, and 1000-grain weight and panicle length by 6.3%. Increasing irrigation interval from 8 to 12 days increased fertile tiller number by 8.6%, filled grain number by 9.5%, and panicle length by 4.2%. The interaction between irrigation and weed management was significant for amylose content; the highest amylose content (22.00%) was in the 8-day irrigation + rotovator treatment and the lowest (21.08%) in the 8-day irrigation + herbicide + manual weeding treatment.

Conclusion:

Twelve-day AWD irrigation is recommended as an effective water-saving strategy without significant yield reduction. The integrated treatment (herbicide + one manual weeding) with a yield of 5249 kg.ha⁻¹ is recommended as a sustainable approach with 50% reduction in herbicide use, reduced production costs, and maintaining grain quality within the desirable amylose range. Given the relative tolerance of cv. Hasti to drought stress, cultivation of this cultivar in the paddy fields of Guilan province is recommended.