The temperature requirements of hemp vary with the type of variety. Generally, from sowing to process maturity, the accumulated temperature of hemp greater than or equal to 0 ° C is 1900-2000 ° C, and to seed maturity, the accumulated temperature is 2700-3000 ° C; For early maturing varieties, the accumulated temperature of 1600-1700 ° C can reach the process maturity. Hemp seeds can germinate when the soil temperature is above 1 ° C, but they should appear neatly. Generally, they should be sown when the soil temperature is above 8-10 ° C. The optimum temperature for hemp seed germination is 25-35 ° C, and the maximum temperature is no more than 45 ° C. if the temperature is high, the germination is fast and uniform.
Hemp seedlings can withstand short-term low temperature of - 5 ° C, but it will seriously affect their growth process. The suitable growth temperature is 10-15 ° C at seedling stage; The rapid growth period is 18-30 ° C, and 19-25 ° C is the most suitable; The temperature from flowering to seed maturity is 18-20 ° C. in the flowering stage, when the temperature is - 1 ° C, the flower organs are damaged, and below - 2 ° C, the flower organs die, especially the male flowers. Seeds can withstand low temperature of 3-5 ° C and lower temperature within 10-15 days after germination; At a low temperature of - 5 ° C, its growth will be delayed. However, if sufficient water and nutrients can be supplied, the low temperature at seedling stage has little effect on future development and yield.
The East sowing experiment in Heilongjiang and Jilin provinces was successful. These show that the ability of hemp to resist low temperature at seedling stage is quite strong. Marijuana is not resistant to low temperature during flowering. It is easy to die in case of sub zero temperature during flowering, especially male plants. During the growth period, the day and night average temperature has a great impact on the growth of cannabis, especially from the beginning of bud to the end of flowering, the stem grows fastest and the dry matter increases greatly; During this period, the best temperature should be maintained at about 16 (night) - 25 (day).
Marijuana is a light loving crop. The influence of sunlight on marijuana includes two aspects: one is the total light exposure received by marijuana during the growth cycle, and the other is the daily sunlight exposure received by marijuana. In general, sunlight exposure has a greater impact on the dry weight of hemp than the total exposure, but the total exposure has a greater impact on the fiber quality (strength of primary fiber). In seed retention or oil cultivation, strong light is conducive to axillary bud germination and inflorescence development of hemp plant, so as to improve seed yield.
In hemp picking and cultivation, weak light can inhibit axillary bud germination and reduce the progressive top growth of branches, which is conducive to improving fiber yield and quality. The sun is abundant, the aboveground and underground parts grow well, and the dry weight and yield increase. But the sunlight is too strong, the fiber development is slow, and rough and hard. Therefore, in terms of fiber quality, it is appropriate to take cloudy days or cloudy weather with weak light. Marijuana is a crop with short sunshine, which can promote flowering, but the plant is short and the fiber yield is low; Prolonged sunshine can delay flowering. Due to the extension of vegetative growth period, the plant grows tall and has high fiber yield. There are also varieties that bloom under long sunshine.
Marijuana is a tall stalk crop with high water consumption. It needs 300-500 ml of water for each kilogram of dry matter, 1.5-2 times more than wheat and oats and 3 times more than corn. The water loss in marijuana leaves will increase the content of carotenoids including lutein, so the leaves turn yellow and the photosynthetic capacity decreases. Cannabis is resistant to atmospheric drought but not soil drought, so irrigation is particularly effective.
The precipitation of 50-70cm is required in the whole growth period of hemp. In the germination period and the first 6 weeks of growth period, the soil should have sufficient humidity. In the rapid growth period (the column height increases by 4-6cm / day), the soil humidity should be high. When the soil moisture is 70% - 80% of the field capacity of the soil, the growth and development is the best, which is conducive to improving the fiber yield. In the case of late sowing, cannabis develops faster than early sowing, and the water consumed in the main growth period accounts for 80-90% of the total water storage. Therefore, increasing soil moisture has a significant effect on increasing yield in this period. Light rain during seed maturity can increase seed yield; It is more drought tolerant when the stem height is 50-70cm, but drought and high temperature will promote early maturity, reduce plant height and low yield. However, from the peak of flowering to the maturity of male plants, too much rain is easy to cause mildew and blackening of hemp stems, which is not conducive to the filling and maturity of male seeds.
Hemp is not resistant to waterlogging during its growth, and waterlogging in hemp field for two days and nights will cause hemp plant death. Soil moisture not only affects fiber yield, but also has a close relationship with quality, but also affects the content of cannabinoid substances. When hemp plants were cultivated in soil moisture with total soil water holding capacity of 40%, 60% and 80%, the radius of cortex and xylem of male or female plants, the number and diameter of primary fiber and the yield of stem and seed increased with the increase of soil moisture; When the soil moisture is equivalent to 70-80% of the total water holding capacity of the soil, the fiber yield is the highest and the quality is the best.
The water demand of hemp is related to the nutritional conditions in the soil. Under the condition of good fertilization, the water demand is 575-985 cubic meters, while under the condition of poor fertilization or no fertilization, the water demand increases to 790-1180 cubic meters. Irrigation significantly increased the water consumption of cannabis, but the water consumption coefficient decreased with the increase of cannabis fiber yield and seed yield. Mineral and organic nutrients can effectively increase fiber yield and quality under irrigation conditions. All these show that irrigation and nutrition are mutually causal and promote each other.