(1) Yield components. The yield of hemp fiber depends on the number of effective plants per unit area, plant height (process length), stem diameter and hemp yield. In general, higher fiber yield can be obtained by more effective plants per unit area, high and neat plant length, uniform thickness of upper and lower hemp stems, high process length and hemp yield. Increasing planting degree is an important way to increase the number of effective plants. But if the density is too high, the plant height decreases. With the increase of dead hemp, the yield per plant decreased, and the yield per unit area also decreased with the increase of density.
The number of effective plants per unit area varies greatly. According to the survey, in the case of large sowing of 450-525 seeds / m2, from the relationship between the number of sown seeds, the number of retained seedlings, the number of adult plants and the number of effective plants with sudden harvest, the number of seedlings is generally about 70% of the number of sown seeds, the number of retained seedlings is about 50% of the number of seedlings, the number of adult plants is about 60% - 70% of the number of retained seedlings, while the number of effective plants actually collected is only 70% of the number of adult plants, The number of paid in plants is 600000-750000 plants / hm2, and the number of adult plants, small hemp and dead plants account for about 30%.
Plant height, stem diameter and hemp yield reflect plant yield. The effect of density on plant height is main. According to the experimental research, under different water and fertilizer conditions, the plant height maintains the peak within the range of 75-1.5 million seedlings per hectare, and the plant height is 160-270cm; More than 1 million plants, the plant height decreases with the increase of density; When the seedling density was 3-6 million plants / hm2, the plant height decreased from 130 cm to 80 cm. The stem diameter also decreased with the increase of density. According to the experimental research, the stem diameters of 30, 60, 90 and 1.2 million plants per hectare are are 0.849, 0.728, 0.667 and 0.578cm respectively. The hemp yield is greatly affected by stem diameter. Because there are more xylem cells differentiated from cambium and less phloem cells differentiated, the hemp yield of finer hemp stems is higher and that of thicker hemp stems is lower. Therefore, we should study the effective number of plants, plant height, stem diameter and hemp yield under specific conditions, so as to achieve combination and improve the yield of hemp fiber.
(2) Determine suitable and planting density. Reasonable close planting is to maintain a reasonable population structure in different growth and development periods according to the regional ecological conditions and the characteristics of cannabis varieties, so as to coordinate the leaf area and the growth of various organs, make effective use of soil fertility, sunlight and carbon dioxide, and obtain the efficiency of converting biological yield into economic yield. Reasonable close planting mainly includes three aspects: first, determine reasonable basic seedlings; Second, adopt appropriate sowing methods according to the soil fertility to ensure the cultivation density and sowing quality; Third, according to the growth law of hemp stem, make the initial growth, rapid growth and later growth of hemp have a reasonable population structure.
Soil fertility has a great relationship with close planting of cannabis. Hemp has high requirements for soil fertility. If the soil is good, the soil is fertile and the fertility is uniform, there will be high-yield and high-quality appearance with full seedlings, plant height, uniform stems, neat population growth and less small hemp. Where the soil quality is poor and the soil fertility is insufficient, the hemp plants often cannot grow, the buds bloom early, and the fiber yield is significantly reduced. It can be seen that the soil fertility foundation is an important index to determine the cultivation density.
Cannabis is more resistant to atmospheric drought than soil drought. It can grow well in areas with annual precipitation of more than 600-700mm. The soil moisture should be high in the rapid growth period. When the soil moisture is 70% - 80% of the field capacity of the soil, the growth and development can be realized. Among them, the plants in the bud and flowering stage are tall and consume more water, accounting for 50% - 55% of the total water consumption in the whole growth period. If the soil moisture is insufficient, the planting density should not be too large, and the moisture is sufficient (including rainfall), close planting should be implemented to achieve the purpose of increasing production. The suitable planting density also has some differences in each hemp area. Reasonable close planting is not invariable.