1. Drought. Sunflower is a crop with strong drought tolerance. However, the maximum amount of water is required in the formation of the flower disk to the final flowering period, which accounts for about 60% of the water requirement in the whole growth period. The lack of water during this period will increase the number of empty shell grains, resulting in a serious reduction in production. Drought-stressed supplemental irrigation, which lacks water, is an important factor leading to an increase in empty space.
2, temperature. Sunflower has strong adaptability to temperature, and it is both thermophilic and drought-tolerant. It has stronger resistance to low temperature at seed germination to seedling stage. Seeds can germinate at 4°C, emerge at 5°C, and meet the need for normal emergence at 8-10°C. The suitable temperature for germination is 31-37°C and the maximum temperature is 38-44°C. Due to improper sowing date in the production, unfavorable temperature after sowing hindered the development of sunflower, which affected the coordinated development of vegetative growth and reproductive growth.
3, light. Sunflower is a short-day crop, and its young leaves, leaves and disk have strong light. Sunshine is sufficient. Seedling growth is robust. During the mid-fertility, the growth of stems and leaves can be promoted, normal flowering and pollination can be carried out, and the seed setting rate can be increased. In the late growth stage, the grains can be filled and full. However, due to climatic factors in production, the light intensity is affected, resulting in poor flowering and pollination and an increase in the empty rate.
4, continuous work. On the same plot, the sunflower was repeatedly planted, resulting in reduced yields due to pest and weed damage and imbalance in soil nutrient composition.
5, density. Due to the different types of sunflower varieties, the density requirements are very different. Generally, the edible varieties are tall and planted, and the oil-using varieties are short and should be planted densely. In order to pursue high yields, people in production have blindly increased their density, resulting in an irrational group structure, prominent conflicts in competing for water and competing for light, and reduced utilization of light energy. As a result, sunflower hollow grains have increased, production has declined, and quality has declined.
6, fertilization. Sunflower is a fertilizer crop. Cultivation must be applied with base fertilizer and top dressing in time. According to the measurement, every 100kg of sunflower seed grain produced consumes 4.4-6.5kg of pure nitrogen, 1.5-2.5kg of pure phosphorus and 6-18kg of pure potassium, which is 1-2 times more than cereal crops.
7, pollination. Sunflowers are cross-pollination crops. There are 1000-3000 strong florets in the flower disk, the self-pollination rate is very low, and the cross-pollination rate is high. And the normal fertilization process is determined by the appropriate temperature, light, atmospheric humidity, insect activity, and wind power. The high-temperature and dry weather from June to July can easily weaken pollen viability, affect the activities of bees and other insects, affect normal fertilization, resulting in poor seed setting rate due to poor pollination, and increase the empty rate.
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