Hemp is one of the most important green (i.e., environmentally sustainable) fibers. Planting density, nitrogen (N), phosphorus (P) and potassium (K) significantly affect the yield of hemp fiber. By optimizing the above main four cultivation factors is an important way to achieve sustainable development of high-fiber yield hemp crops. In this study, the effects of individual factors and factor × factor interactions on the yield of hemp fiber over two trial years were investigated by the central composite design with four factors, namely planting density, nitrogen application, phosphorus application, and potassium application rate. The influences of these four test factors on the yield of hemp fibers were in the order nitrogen fertilizer (X₂) > planting density (X₁) > potassium fertilizer (X₄) > phosphate fertilizer (X₃). To obtain yields of hemp with high-quality fiber greater than 2200 kg ha⁻¹, the optimal range of cultivation conditions were planting density 329,950–371,500 plants/ha, nitrogen application rate 251–273 kg ha⁻¹, phosphorus application rate 85–95 kg ha⁻¹, and potassium application rate 212–238 kg ha⁻¹. This study can provide important technical and theoretical support for the high-yield cultivation of hemp fiber into the future.

The present study aimed to explore the effects of exogenous gibberellins (GAs) on seed germination and subsequent seedling growth of hemp (Cannabis sativa L.) under drought stress. Seeds of two industrial hemp cultivars i.e., ‘Yunma 1’, (YM) and ‘Bamahuoma’, (BM) were treated with different concentrations of GA₃ solution (0, 200, 400, 600, 800 mg/L) at 20 °C for 8 h. The effect of pre-treatment was assessed on germination characteristics and physiological indexes on subsequent exposure to drought stress using 20% (m/v) polyethylene glycol (PEG) for 7 days. The results revealed that seed germination in hemp was sensitive to drought stress, as the germination indexes (germination rate and germination potential) decreased significantly, and seedling growth (hypocotyl length and radicle length) was impeded under 20% PEG-6000 condition. GA₃ pre-treatment affected germination rate, germination potential, hypocotyl length and radicle length. With increasing GA₃ concentration, these indexes first increased and then decreased. For seedling physiology characteristics in hemp, GA₃-pretreatment remarkedly increased the osmotic regulating substances (soluble sugar and soluble protein contents) and the activities of antioxidant enzymes (SOD, superoxide dismutase and POD, peroxidase), while sharply decreased the lipid peroxidation (malondialdehyde, MDA) in seedlings grown under PEG-6000 induced drought stress. These results suggested that seeds pre-treated with GA₃ could enhance the drought tolerance of hempseeds, and the optimal effect of GA₃ for seed pre-treatment of YM and BM could be obtained when the concentration of GA₃ solution reached 400 mg/L and 600 mg/L, respectively.

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.

Continuous cropping increases disease severity and causes arrested development of chilli plants and the decrease of yield and quality. Hemp-chilli rotation cropping evidently eased chilli diseases, but the causation remains unknown. This paper investigated the disease index (DI) of chilli’s anthracnose for hemp-chilli and continuous chilli cropping, the antifungal effect of water extract of hemp and chilli residues, and bacteria antagonistic to chilli anthracnose fungus from hemp and chilli rhizosphere. Hemp grown as a preceding crop decreased anthracnose DI from 35–39% for the continuous chilli to 14–15% for hemp-chilli rotation. Hemp residue water extract executed suppression of chilli anthracnose fungus and the efficiency increased as the extract concentration increased from 1% to 5%. Hemp extract concentration 5% gave a mean inhibition ratio (IR) of 32.34% to spore germination and IR 53.72% to mycelia growth, which was much greater than that of the chilli extract. Antagonistic bacteria isolated from the hemp rhizosphere evidently depressed the mycelia growth of the fungus with a mean IR 32.35%, while no antagonistic bacteria were obtained from the chilli rhizosphere. The stronger allelopathy of preceding hemp plants and antagonistic bacteria from the hemp rhizosphere synergistically suppressed the fungus growth and eased the disease in the succeeding chilli crop.