Effect of Planting Dates and Irrigation Level on Growth Criteria, Yield and Yield Components of Isabgol (Plantago ovata L.) under the Weather Conditions of Sarakhs

Proper planting date and irrigation rate are the most important factors for better use of rainfall and soil moisture and thus increase crop yield. Production of medicinal and aromatic plants and the demand for natural products in the world is increasing, so that the twentieth century has been named as a return to nature and the century of using herbal medicines. Proper growth and development of medicinal plants in agricultural conditions requires knowledge of the ecological characteristics of these plants, careful study of planting techniques and the use of agricultural inputs, especially irrigation, fertilizers, suitable planting and harvesting times and their management. Such factors also affect the amount of secondary metabolites in medicinal plants. The aim of this study was to investigate the effect of four planting dates and four irrigation rates on the yield traits of isabgol in Sarakhs.

In order to investigate the effect of irrigation levels and planting dates on the growth characteristics and yield of isabgol (Plantago Ovata L.) as a medicinal plant, a field experiment was performed in Research station, Sarakhs, Khorasan Razavi province during growth season 2015-16. This experiment was performed as strip plots based on a randomized complete block design with three replications. Irrigation treatments at four levels of 40, 60, 80, and 100% of the water requirements were placed in horizontal plots and four planting dates were on March 5, 2016, March 20, 2016, April 3, 2016 and April 18, 2016 in vertical plots. Irrigation was applied as furrow system at every 7 days. Irrigation treatments were applied at the time of complete establishment of seedlings in 3-4 leaf stage and continued until physiological maturity stage. The amount of irrigation water in each irrigation turn was calculated by AGWAT software. Measured traits included leaf area index, crop growth rate, dry matter accumulation, plant height, number of spikes per plant, number of seeds per plant, 1000-seed weight, grain yield, biological yield and harvest index.

The results of growth indicators showed that the maximum leaf area index (3.4 and 3.3), the crop growth rate (22.12 and 22.18 g m-2 d-1) and the accumulation of dry matter (444.9 and 445.4 g m-2) were obtained in the treatments of 100% and 80% of the water requirements, respectively. Also, the maximum leaf area index and crop growth rate were observed in the treatments of April 18 and April 3 (1.86 and 2). The treatments of March 20 and 5 also had the highest crop growth rate (14 and14 g m-2 d-1) and dry matter accumulation (270 and 261.3 g m-2). The results also showed that the interaction effects on plant height, number of seeds per plant, 1000-seed weight, grain yield, biological yield, and harvest index were significant at the 1% level of probability. Maximum plant height (24.57 cm) was obtained in the 100% of the water requirement and planting date of March 20 treatment. The highest number of seeds per plant (1210.36), grain yield (1891.4 kg), biological yield (5607.8 kg), number of spikes per plant (29.67) and 1000-seed weight (2.05 g) were obtained in the treatments of 80% of water requirement and planting date on March 20.The highest harvest index (36.4%) belonged to the treatment of 100% of water requirement and planting date on March 5.

general, it can be concluded that different characteristics of isabgol plant were affected by planting date and irrigation water amount so that with a delay in planting date and also reducing the amount of irrigation water, growth and yield characteristics were significantly reduced. As a result, deficit irrigation at 80% of the crop water requirement and planting date of March 20 were more effective in saving irrigation water along with a good yield of the isabgol plant compared to 100% of the crop water requirement treatment in the study area.