Introduction: Summer savory (Satureja hortensis L.) is an annual to perennial herbaceous and aromatic plant of the Lamiaceae family. The essential oil of savory is widely used as an antioxidant and antimicrobial agent in the food and pharmaceutical industries. Available water is one of the climatic factors that affects the distribution of plants around the world. Some studies have shown that water shortage reduces the yield of plants. It is important to achieve maximum yield in plants. Planting date by adapting the growth stages of the plant with soil and air temperature, day length, rainfall and other environmental factors affect crop growth and yield. Considering that Iran is located in arid and semi-arid regions and the production of vegetable seeds is of great economic importance, so determine the management methods that are compatible with regional conditions and can achieve maximum quantitative and qualitative performance, is important. Determining the best planting date by creating favorable growth and development conditions while making optimal use of water and soil resources will improve the growth status of the plant. Therefore, this study was conducted to investigate the effect of planting date and irrigation levels on savory grain yield in Birjand.
Materials and Methods: The experiment was conducted in Birjand in 2016-2017 as a split plot based on a randomized complete block design with three replications. Irrigation levels (100, 75, 50 and 25% evaporation from Class A evaporation pan at five-day irrigation intervals) and planting dates (March 16, April 11 and May 5) were as the main plots and sub plots, respectively. Each subplot consisted of four six-meter-long planting lines in which seeds were sown on either side of 50 cm wide ridges. The distance between subplots was 0.5 m, between two main plots was one meter and between two replications was three meters. Seed sowing was done by hand based on the date of sowing.
Results and Discussion: The results showed that reducing the amount of irrigation water to 50% of evaporation from the pan, did not have any significant effect on the most studied traits, but in the treatment of 25% of evaporation from the pan, number of lateral branches (13.7%), grain yield (51.5%), biomass yield (35.2%) and harvest index (25.9%) decreased compared to 100% evaporation treatment from the pan. Planting dates in March and April were not significantly different in terms of the most studied traits (except for remobilization rate and remobilization efficiency), but delay in planting to May 15, reduced plant height, number of lateral branches, remobilization rate, remobilization efficiency and grain and biomass yield, but increased flowering branches and total vegetative biomass. The interaction of irrigation levels and planting dates on crop growth rate (CGR), contribution of remobilization in grain yield and dry weight of seed branches were significant. The highest crop growth rate (CGR) was related to the treatment 75% evaporation from the pan and planting dates of April 21 and May 15 (10.3 and 11 g m^-2 day^-1, respectively). The highest dry weight of seed branches was related to treatment 100% evaporation from the pan and March 16 (621.7 g m^-2).
The results of comparing the means showed that decreasing the amount of irrigation water, remobilization rate and efficiency increased, so that in the treatment of 50 and 25% of evaporation from the pan compared to the 100% of evaporation from the pan, the highest amount of remobilization (3121.2 and 273.3 g m^-2, respectively) and the remobilization efficiency (1.15 and 0.99%, respectively) was obtained. Therefore, current photosynthesis was not enough to fill the seeds, thus the need for filling the seeds (especially carbohydrates) is compensated by re-transferring photosynthetic materials stored in different parts especially the stem. In some cases, current photosynthesis may not be enough to fill the seeds under optimal growth conditions, and the plant may be somewhat dependent on storage compounds. Delay in planting reduced remobilization content and its efficiency in savory, so that the delay in planting from march 17 to May 6 caused reduced it 44.8% and 57.6%, respectively.
Conclusions: Totally, the highest remobilization contribution in grain yield was related to the treatment 25% evaporation from the pan and planting dates April 11 (236.5%). On the other hand, considering save water in Birjand, aimed to maximum vegetative biomass production, irrigation levels of 50% evaporation from the pan at five-day irrigation intervals and planting on May 5 is recommended. In addition, planting on April 11 is recommended to achieve maximum savory grain yield.