Effect of planting date and plant density on morphological traits, yield and yield components of Cannabis sativa L.

Cannabis has long been used for hemp fibre, hemp oils, medicinal purposes, and as a recreational drug. Given the importance of maximum utilization of environmental parameters during growth period, it is crucially important to choose an appropriate sowing date and plant density for crops cultivation. Hence, the objective of the present study was to evaluate the effect of sowing date and plant density on morphological and yield traits of canabis. This experiment was carried out as a split-plot based on randomized compelate block design with three replications at the field of agricultural research center of Birjand, Iran in 2013. In this research the main plots were sowing date at three levels of May 12, May 27 and June 11 and the sub-plots were plant densities at four levels of 7.4, 11.1 and 22.2 plants m-2. Measuring traits included the plant height, stem diameter, branch number of main stem, seed number per plant and m2, 1000-seed weight, seed yield, biological yield, harvest index and seed and biomass yields of single plant. The texture of the soil in research farm was loam with the pH of 8.28, electrical conductivity of 2.23 mmos/cm and organic carbon, total N, P, and K content was 0.18%, 0.035%, 6.04.4 ppm and 231 ppm at the depth of 0-30 cm, respectively. In the end, all data were analyzed by MSTAT-C statistical software and means were compared by Duncan Multiple Range Test at 5% level. The results showed that all traits were significantly affected by sowing date and plant density. Also, interaction effects of planting date and plant density significantly affected plant height, seed number per m2 and seed yield of cannabis. The delay in sowing from May 12 to June 11 significantly decreased stem diameter, branch number in main stem, plant height, seed number per single plant and m2, seed and biological yields per single and m2 and harvest index by 20.2, 22.2,20.3, 49.2, 43.2, 53, 36.9, 48, 36.9 and 32%, respectively. It can be said that with delay of sowing date from May 12 to June 11, because increasing of temperature and shortened days, the plants did not have enough time for vegetative growth and production of branches (Shafaroodi et al., 2012), and so the number of seed per plant and m2 and finally seed and biological yields decreased. Also means comparison showed that with decrease in density from 22.2 to 7.4 plants/m2, seed number, seed yield and biological yield traits per m2 decreased by 37.2, 13.7 and 19.5%, respectively, and stem diameter, branch number in main stem, seed number, seed yield and biological yield traits per single plant and 1000-seed weight increased by 40.7, 22.7, 72.7, 112.3, 141.4 and 32%, respectively. It appears that the increasing trend of seed yield with the increase in plant density was caused by by more leaf area, effective utilization of solar radiation during growth period (Niroomand Tomaj et al., 2012، Delarami & Moosavi, 2016) and photosynthetic capacity and production of more pods per unit area. As a result, longer growth period and production of more assimilates in earlier sowing dates can be mainly reason for better yield of cannabis. Moreover, higher plant density by maximum utilization of solar radiation, increasing in the photosynthetic capacity and source power was significantly increased seed yield of cannabis. Also, higher yield in first sowing date and 22.2 plants m-2 treatment related to effective utilization of solar radiation by more leaf area. In total, the treatment of sowing date of May 12 with the density of 22.2 plants m-2 had maximum of seed yield with an average of 356.60 g m-2.