| Hemp (Cannabis sativa L.) is an important economic crop that is used in medicine, food, textile and other fields. As the attention of people are gradually increased, hemp is widely used. Because the optimum demand for potassium (K) in hemp cultivation is unclear, the situation of blindly applying potassium fertilization is very common. In addition, a large area of farmland soil is potassium deficiency, and the potassium resources are shortage in China. Therefore, studying the suitable potassium level for hemp growth and screening hemp varieties with the resistant to low potassium stress is a way of solving the inadequate abuse of potash as well as potassium sources deficiency. In order to reveal the best potassium level for hemp growth and compare the capability of resistance under low-potassium stress among different varieties, hemp variety Yunma 1 was used to study the potassium nutrition feature under different potassium levels and 6 hemp varieties were analyzed for the growth status under low potassium stress by the method of water culture. It would provide potassium nutrition theory and experimental materials for a high yield and efficient in hemp cultivation. The main results are as follows:1. Feasible potassium level for hemp growth and developmentIn the condition of hydroponic nutrient solution,0.5,1.0,1.5,2.0,2.5 mmol/L potassium treatments were set. With the increase of the application amount of potassium, the plant height, stem diameter, leaf area of hemp increased at first and then decreased, and reached the optimal level in 2.0 mmol/L potassium treatment. The potassium utilization efficiency and SOD activity decreased. While the content of chlorophyll increased, the content of sucrose and the activity of sucrose increased at first and then decreased. The dry matter and potassium accumulation amount in hemp reached the maximum level in 2.0 mmol/L potassium treatment.2. Differences in tolerance to low potassium stress of hemp varietiesTest was set into low potassium (0.4 mmol/L K+) and control (2.0 mmol/L K+). Under low potassium stress, hemp was significantly short, leaf area and stem diameter decreased, and root/shoot ratio increased; Chlorophyll content, nitrate reductase activity and soluble protein content decreased; Soluble sugar content, relative electrical conductivity, SOD activity and acid phosphatase activity increased with different extent. Variation among different varieties was different. Fiber cells developed not well, cord diameter and tube diameter were both small in the stems of hemp under low potassium. But the stem microstructure of the hemp varieties with a strong resistance to low potassium developed well.Under low potassium stress, the potassium content of hemp reduced, the high tolerance varieties had high ability in potassium absorption and utilization. Different hemp varieties had a different distribution of potassium in different organs. Bama had the potassium content as leaf> stem> root under control condition, and stem> leaf> root under low potassium condition. But the other varieties in both potassium treatments were stem> leaf> root. With the membership function evaluation test, the ability of low potassium stress resistant in hemp varieties from large to small was:Bama>Yunma 1>Wanma 1>Yunma 5>Yunwan 6>Jinmal.In conclusion, the optimal potassium concentration for the growing of hemp variety Yunma 1 was 2.0 mmol/L hydroponic solution, and potassium deficiency or excess would inhibit its growth. The varieties with high tolerance to low potassium stress had obvious advantages in the growth, biomass, physiological and biochemical activity, potassium absorption, transportation and utilization. |
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