Morphological and yield responses of Silybum marianum L. to chemical and biological fertilizers in different planting dates

Introduction: Medicinal crops production is well interested in Iran due to market demand in recent years. Silybum marianum L. is an annual or biennial plant, native to the Mediterranean region, which now could be found in other warm and dry regions. Silybium marianum is used traditionally as a hepatoprotective agent and supportive treatment of liver disorders. Its fruits contain flavonolignan compounds, silymarin, which silybin is the main constitute (Abdolahzareh et al., 2012). Management of planting date and integrated nutrition systems in medicinal plants have to be considered. Sowing date affects the crop yields through changing weather parameters in the growth period. In addition to planting date, fertilizers rate and type, has an influence on crop production. Today continuous and excessive application of chemical fertilizers may have negative impacts on soil health and environment causing environmental problems (Mohammadpour Vashvaei et al., 2017). Bio-fertilizers are considered as sustainable alternative sources of nutrients compared to the synthesized fertilizers. The objective of the present study was to examine the effects of sowing date and fertilizing system (chemical, biological and integrated) on the morphological traits and yield of the milk thistle under Birjand, Iran conditions.
Material and methods: This research was carried out at the research farm of Birjand branch, Islamic Azad University, Birjand, Iran, in 2018. The experiment was conducted as a split plot based on a randomized complete blocks design with three replications. Three sowing dates (March 6, April 4 and May 5) and 6 fertilizing systems (non-fertilizer as control, NPK, vermicompost, Akadin, 50% NPK + 50% vermicompost, 50% NPK + 50% Akadin) were as main plots and sub plots respectively. In the study the responses of some morphological traits and yield of Milk Thistle were evaluated. Soil texture in the site of study was loam. Soil pH and EC were 7.4 and 2.3 mmos/cm respectively. Nitrogen, P, and K content of the soil were 3.8, 11.6 and 75.2 mg/kg at the depth of 0-30 cm, respectively. All data were analyzed by SAS statistical software and means were compared by LSD Test at 5% level.
Results and discussion: The first planting date (March 6) had the highest average morphological traits (plant height, capitol diameter and number of branches) and seed yield components (capitol number per m², number of seed per capitol, 1000-seed weight, seed yield). On the other hands the treatments 50% NPK and 50% vermicompost fertilizers had statistical superiority for most of the studied traits. The highest (3327.7 kg/ha) and the lowest (318.4 kg/ha) seed yield were related to the treatments NPK+ vermicompost at the first planting date and treatment of non-fertilizer application at the third planting date, respectively. It seems that seed yield declining for the planting date of May 5, was related to the shortening of growth season and the coincidence of pollination with summer heating. This caused a severe decrease in the number of capitol per m² and the number of seed per capitol. Normally, using organic fertilizers with chemical fertilizers improves physical aspects of the soil; increases microorganisms activity in the soil, nutrients availability, photosynthesis, yield components and eventually seed yield (Mohammadpour Vashvaei et al., 2017). Similar results also have been reported by Zarghani et al. (2019). Morphological traits quantity positively correlated to yield components and seed yield. Thus the highest value for these traits were observed for the first planting date under using NPK+ vermicompost. As a result, the superiority of seed yield of Silybum marianum in this treatment compared to other treatments, was to be expected. The results of regression analysis showed that traits capitol diameter, number of capitol per m², number of seed per capitol and 1000-seed weight were entered into the regression model, which explained 84.57% of total seed yield changes.
Conclusions: In general, the planting date of March 6 was superior to the other two planting dates and this planting date could be suggested as a suitable date for the cultivation of Silybum marianum L. in Birjand region under using 50% NPK+ 50% vermicompost.