Improving the Nutrient Content, Physiological Indices and Grain Yield of Black seed (Nigella sativa L.) with the Application of Vermicomposting at Different planting Dates

One vital area of research about medicinal plants is to study the different environmental conditions affecting the quality of these plants. Also in the research of medicinal plants, it is necessary to investigate and find the optimal conditions to produce the plants with the highest possible yield. Knowing the proper planting date of medicinal plants for each region can be effective in increasing the yield. Cultivation date is one of the main factors in determining the yield of black seed. Accordingly, in different regions, different times have been suggested for the cultivation of this plant. On the other hand, due to the environmental problems caused by the use of chemical fertilizers, the use of organic fertilizers can be used as a solution to increase the yield of medicinal plants. Therefore, vermicomposting can increase yield by improving the condition of the soil bed.

The factorial experiment was conducted in the form of a randomized complete block design with three replications in the field of Fasa in 2021. The first factor includes six planting dates (3 February, 19 February, 5 March, 21 March, 4 April and 21 April) and the second factor includes vermicomposting at three levels (control, no fertilizer and vermicomposting 5 and 10 tons Per hectare). The Vertebrate application of vermicomposting was used. At the end of the growth period, nutrient concentrations, physiological traits and grain yield and yield components were measured.

The results showed that acceleration or delay in planting reduced the uptake of nitrogen and phosphorus in black seed. Delay in planting may have reduced nitrogen and phosphorus uptake by reducing root growth and nutrient uptake. Also, the highest nitrogen and phosphorus uptake of leaves was observed in the use of 5 and 10 tons of vermicompost fertilizer. At different planting dates, the use of vermicompost reduced ion leakage and increased the relative leaf water content and chlorophyll content. Consumption of vermicompost due to improved absorption of nutrients such as nitrogen has led to more synthesis of photosynthetic pigments. Therefore, considering the key role of elements such as nitrogen in the structure of chlorophyll, it seems that the supply of this element is the main reason for the increase in leaf chlorophyll in this study. Also, 10 tons of vermicompost increased the grain yield on planting dates of 19 February and 5 March by 13.2% and 17.8%, respectively, compared to the control. Production of higher yield at the vermicompost level compared to the control is due to the absorption of more nutrients as well as the improvement of photosynthetic pigments and the relative content of leaf water. Early sowing on 3 February and delay in sowing on 4 April and 21 April caused a significant decrease in harvest index and 1000-seed weight.

Late planting shortens the vegetative growth period, the plant enters the reproductive stage earlier and the plant is faced with a lack of photosynthetic resources. Also, the grain filling period is faced with drought stress and heat at the end of the season, and this end stress on grain weight causes a severe reduction in yield. On the other hand, vermicompost has been able to provide the plant with nutrients in an acceptable amount and has the right conditions for growth and increase yield. Therefore, vermicompost has increased the growth of black seed by providing a suitable growth environment. In total, the planting date is 19 February to 21 March and the use of vermicompost fertilizer 10 tons per hectare for planting black seed is recommended. Therefore, the use of vermicompost to increase the production of seed yield in Nigella sativa can be an interesting perspective in the production of this plant for industrial and pharmaceutical applications.