Morpho-physiological traits, antioxidant capacity and nutrient accumulation in hemp (Cannabis sativa L.) under varying levels of nitrogen nutrition

Abstract

Optimization of nitrogen fertilizer application is an important means of improving hemp (Cannabis sativa L.) production and economic benefits with minimum environmental loss. The method of fertilization with hydroponic could precisely control the amount of nitrogen applied, to understand how nitrogen application can affect the growth and physiology of industrial hemp. A hydroponic experiment was conducted in 2017 to investigate the effects of different nitrogen treatments (0.30, 0.75, 1.50 and 12.00 mmol/L) on different regions and types, cultivars of hemp (“Wanma 1(WM1)”, “Bamahuoma (BM)’, “Ynuma 5 (YM5)” and “Yunma 7 (YM7)”). The main objective was to determine the effectiveness of nitrogen fertilizer application for improvement of the morpho-physiological traits, antioxidant capacity and nutrient accumulation of industrial hemp. In general, increasing N application rate positively impacts hemp total dry biomass, plant height and stem diameter. Total dry weight, stem diameter and plant height increased by 26.16%-238.94%, 11.43%-34.09% and 4.51%-54.73%, respectively, with the application of 1.50 mmol/L when comparing with the low N rate (0.30 mmol/L). Nitrogen deficiency leads to cell membrane lipid peroxidation (MDA) and increases in superoxide dismutase (SOD) activity. The activity of nitrate reductase (NR) in hemp leaves and the accumulation of nitrate nitrogen are related not only to the nitrogen supply but also to the form of nitrogen. In addition, increasing nitrogen supply has a significantly negative effect on the utilization efficiency of nitrogen and potassium, but positively on the phosphorus utilization efficiency. Nitrogen supply and cultivar proved to be relevant to the growth, physiology and nutrient accumulation in hemp under hydroponic conditions. Increasing nitrogen supply within a reasonable range is beneficial to hemp, whereas excessive nitrogen supply has an inhibitory effect, and the nutrient utilization efficiency significantly reduces.