Introduction: The excessive use of chemical fertilizers in agricultural lands has caused many environmental problems such as the destruction of the physical structure of the soil, soil nutrient imbalance, and eutrophication of waters. Therefore, animal manures can be used as a suitable alternative to chemical fertilizers in agriculture. Drought stress is one of the most important and common abiotic stresses that limits agricultural production and consequently reduces crop yields in arid and semi-arid regions such as Iran. Drought, as the most important growth limiting factor, has adverse effects on the growth and development of crop plants. Therefore, this study aimed to investigate the effect of animal manure on ecophysiological traits and grain yield of black cumin under irrigation interruption conditions.

Material and Methods: The experiment was conducted in form split plot based on a randomized complete block design (RCBD) with three replications, at Research Farm of the Campus of Agriculture and Natural Resources, Razi University during 2022. The treatments included fully rotted sheep manure (0, 10, 20, and 30 ton ha-1) as the main plot and irrigation interruption (complete irrigation, interruption of irrigation from flowering stage, interruption of irrigation from grain filling stage) as the subplot. The measured traits included leaf area index (LAI), radiation absorption, relative growth ratio (RGR), crop growth rate (CGR), total dry weight (TDW), radiation use efficiency (RUE) and grain yield. The RUE in g MJ-1 was calculated by calculating the slope of the regression line between cumulative total dry weight (g m-2) and cumulative total radiation rate (MJ m-2) for each treatment separately.

Results and Discussion: The results showed that the application of manure and irrigation treatments had effects on the evaluated traits significantly. The highest (2.34) and lowest (1.1) maximum LAI were related to the treatment of 30 tons ha-1 and complete irrigation and the conditions of no manure application and interruption of irrigation from flowering stage, respectively. In all manure application treatments, the radiation absorption improved with increasing irrigation water. The highest and lowest radiation absorption were observed in the conditions of 30 tons ha-1 of manure and complete irrigation and the treatment of no manure application and interruption of irrigation from the flowering growth stage, respectively. The highest and lowest RGR and CGR were related to 30 tons ha-1 of manure and full irrigation (0.094 g g-1 d-1 and 6.2 g m-2 d-1, respectively) and no manure application and interruption of irrigation from the flowering growth stage (0.066 g g-1 d-1 and 2.3 g m-2 d-1, respectively). The highest RUE (0.5539 g MJ-1) was obtained with 30 tons ha-1 of manure and complete irrigation, and the lowest (0.4565 g MJ-1) was obtained with no manure and interruption of irrigation from the flowering growth stage. The interaction of manure application and irrigation interruption on grain yield was significant. The highest and the lowest grain yield were 108.7 g m-2 and 44.3 g m-2 that were observed in the treatment of 30 tons ha-1 of manure and complete irrigation, and the treatment of no manure application and interruption of irrigation from the flowering growth stage, respectively.

Conclusion: In general, the results showed that in order to achieve maximum RUE and grain yield, the treatment of 30 tons ha-1 of manure and complete irrigation was better. However, in the condition of 30 ton ha-1 of manure, there was no significant difference between interruption of irrigation from the grain filling stage and complete irrigation. Therefore, instead of completely irrigating in the field without reducing yield, irrigation can be stopped at the grain filling stage, which in turn reduces the amount of water consumed in the field.