Effects of Plant Density and Nitrogen on Physiological Growth Indices, Yield Components and Yield of Black Seed (Nigella sativa L.) as a Medicinal Plant

There is an increasing interest to produce medicinal plants as the demand for these natural products is also increasing in the world. Since the middle of the twentieth century, after identifying the negative side effects of chemical drugs, medicinal plants have been replaced by chemical drugs in many cases.  Due to the climatic diversity, Iran has a high potential for the production of medicinal plants, however, only a very small portion of the world’s market for medicinal plants is allocated to Iran. Considering the possibility of negative effects of chemicals on the quantity and quality of medicinal plants, it is necessary to use ecological principles. On the other hand, it seems that the cultivation of medicinal plants along with other crops would reduce weed and pest population due to the allelopathic properties of these plants. Cultivation of medicinal and aromatic plants has several advantages like higher net returns per area unit, low incidence of pests and diseases, improvement of degraded and marginal soils, longer shelf life of final products and foreign exchange earning potential. Black seed (Nigella sativa L.) is a widely used medicinal plant throughout the world which belongs to Ranunculaceae family. This experiment was carried out to evaluate physiological growth indices, yield and yield components of black seed affected by nitrogen rate and plant density under Mashhad climate conditions.

This experiment was conducted at the Agricultural Research Station of the Ferdowsi University of Mashhad, located in 10 km south-east of Mashhad (59° 36ˊ East, 36° 15ˊ N, 985 meters above sea level) during the 2016-2017 growing season. The experiment was conducted as factorial layout based on a randomized complete block design with two factors and four replications. Treatments were four plant densities (60, 120, 180 and 240 plants.m-2) and four nitrogen rates (0, 50, 100 and 150 kg N per ha as urea). Studied traits were leaf area index (LAI), dry matter accumulation (DM), crop growth rate (CGR), relative growth rate (RGR), plant height, yield components (such as number of branches per plant, number of follicles per plant, number of seeds per follicle and 1000-seed weigh), seed yield, straw yield and biological yield. SAS software was used to analyze the data and the comparison of means was done using Duncan multiple range test at 5% probability level. Charts were also drawn using Excel software.

The results indicated that the plant density and nitrogen rates affects leaf area index (LAI), dry matter accumulation (DM), crop growth rate (CGR), relative growth rate (RGR), plant height, yield components (such as number of branches per plant, number of follicles per plant, number of seeds per follicle and 1000-seed weigh), seed yield, straw yield and biological yield of black seed. The highest and lowest leaf area index was observed in 100 kg N and control, respectively. The fast period of vegetative growth, leaf area index and dry matter accumulation were observed at flowering stage with a small decline afterwards until physiological maturity. Also, crop growth rate reached to its peak in flowering stage followed by a decreasing trend afterwards. In addition, number of branches decreased sharply at high densities. The highest seed yield was observed from 150 kg N per ha (895.7 kg.ha-1) and the lowest was for control (689.9 kg.ha-1). Biological yield had high correlation with straw yield (r2=0.99) and seed yield (r2=0.97).

Agronomic management strategies had significantly effect on growth, yield, and yield components of black seed. Generally, plant density and nitrogen rates are two effective techniques for agronomic management of the medicinal plants. Further, investigations on quantity and quality of medicinal plants including black seed in association with agronomic operations will provide additional information.