Effect of Nitrogen Supply on Growth and Nitrogen Utilization in Hemp (Cannabis sativa L.)

Yang Yang,Guanghui Du,Kailei Tang,Feihu Liu,Wenxin Zha,Gang Deng

doi:10.3390/agronomy11112310

Abstract

Hemp is a multipurpose crop that is cultivated worldwide for fiber, oil, and cannabinoids. Nitrogen (N) is a key factor for getting a higher production of hemp, but its application is often excessive and results in considerable losses in the soil–plant–water continuum. Therefore, a rational N supply is important for increasing N efficiency and crop productivity. The main objective of this paper was to determine the responses of four hemp cultivars to different levels of exogenous-N supply as nutrient solution during the vegetative growing period. The experiment was conducted at Yunnan University in Kunming, China. Yunma 1, Yunma 7, Bamahuoma, and Wanma 1 were used as the experimental materials, and five N supplying levels (1.5, 3.0, 6.0, 12.0, and 24.0 mmol/L NO3-N in the nutrient solution) were set by using pot culture and adding nutrient solution. The root, stem, and leaf of the plant were sampled for the determination of growth indexes, dry matter and N accumulation and distribution, and physiological indicators. The plant height, stem diameter, plant dry weight, and plant N accumulation of four hemp cultivars were significantly increased with the increase in exogenous-N supply. Root/shoot dry weight ratios, stem mass density, and N use efficiency decreased significantly with the increase in exogenous-N supply. Nitrogen accumulation, chlorophyll content, soluble protein content, and nitrate reductase activity in leaves were increased with the increase in exogenous-N supply. Among the four indexes, the increase in N accumulation was more than the increase in NR activity. The activities of superoxide dismutase and peroxidase in leaves were increased first and then decreased with the increase in exogenous-N supply, with the maximum value at N 6.0 mmol/L, while the content of malondialdehyde in leaves increased significantly when the level of exogenous-N supply exceeded 6.0 mmol/L. These results revealed that increasing the exogenous-N supply could improve the plant growth, dry matter accumulation, and N accumulation in hemp during the vegetative growth period, but N supply should not exceed 6.0 mmol/L. Among four hemp cultivars, Wanma 1 performed well at 6.0 mmol/L N application.

Highlights

As an important component of macromolecular substances such as proteins, nucleic acids, phospholipids, hormones, and chlorophyll in plants, nitrogen (N) is one of the essential macronutrients for plant growth and development
The plant height and stem diameter of hemp cultivars were increased with the increase in exogenous-N level, reaching the maximum value at 24.0 mmol/L, while the root/shoot dry weight ratio and SMD showed a contrary pattern
Plant height and root/shoot weight ratio did not change significantly when the N concentration was 12.0 mmol/L or more; the plant height of Yunma 1 (YM1) and SMD of Wanma 1 (WM1) did not change significantly when the N concentration was 6.0 mmol/L or more; the SMD of Yunma 7 (YM7) showed a significant difference among N concentrations (Table 1)

Summary

Introduction

As an important component of macromolecular substances such as proteins, nucleic acids, phospholipids, hormones, and chlorophyll in plants, nitrogen (N) is one of the essential macronutrients for plant growth and development. Papastylianou et al [12] reported that hemp biomass yield, stem dry weight, and inflorescence weight increased by 37.3%, 48.2%, and 16%, respectively, with the application of 240 kg N ha−1 when compared with the unfertilized control. The excessive N fertilizer impedes increase hemp productivity and reduces hemp yield caused by plant lodging and serious pests and diseases. Amaducci et al [15] reported that 100 kg ha−1 of N was the natural availability in the soil, and each additional kg of N supplied via fertilization increased hemp stem dry matter production by 20 kg but increased plant mortality. It is very important to understand the utilization capacity of exogenous-N for carrying out the high-yield and high-efficiency cultivation of hemp

Objectives

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Results

Discussion

Conclusion