Yield and seed quality of Plantago ovata and Nigella sativa under different irrigation treatments

Employing locally adapted plants together with irrigation scheduling based on developmental stage in semi-arid and arid regions may provide an opportunity to optimize irrigation efficiency, and water savings in regions where water resources are limited. To investigate this water saving potential, the final seed yield and quality of two local plant species were investigated under water deficit conditions over two growing seasons (2003, 2004) in the northeast of Iran. In this study, black cumin (Nigella sativa L.) which is used locally as an anti-microbial and isabgol (Plantago ovata Forsk.) which is used as an anti-diabetic plant were exposed to four different irrigation regimes. Weekly irrigation was the control, and the three treatments based on developmental stage for both species were termination of irrigation at blooming (folded flowers), flowering, and seed formation. Isabgol seed yield was lower for all of the water deficit treatments compared to control, but black cumin showed tolerance to water deficit except when irrigation was terminated at seed formation. The lowest seed yield was obtained when irrigation was stopped at the blooming stage, and the number of seeds per plant was the main yield component affected. One thousand seed weight for both species was relatively stable across all irrigation treatments, and higher seed yield was consistent with higher straw yield and plant height. Our results did not show any reduction in oil concentration for black cumin or mucilage percentage for isabgol across all water deficit treatments.