Supporting Technologies of Improved Soybean Varieties and Methods for High-Yield Cultivation

1. Timely sowing

Select varieties with high yield-increase potential adapted to the local area, and sow at the right time. Apply herbicide before sowing soybeans, and apply herbicide again after sowing depending on the weed situation. Sowing time: spring soybeans from late April to early May, sowing depth 5 cm; soil moisture conditions must be given great attention at sowing. The conditions for soybean seed germination mainly include moisture, temperature and oxygen.

① Moisture: seed germination begins with water absorption, so water is an important factor for germination. When seeds germinate, the water absorbed equals 1.21-1.5 times the seed weight, that is, germination begins; water absorption reaching 130%-140% is more suitable. Soil moisture content is closely related to soybean water absorption. When soil moisture content is 20%-24%, germination is relatively fast; below 18%, emergence is difficult. If there is too much water, it also has adverse effects on germination.

② Temperature: soil temperature is also one of the important factors affecting seed germination. The optimum temperature for the seed germination process is the temperature at which enzyme activity is strongest. The optimum temperature for soybean germination is 25-32°C; too high or too low a temperature both affect soybean germination.

③ Oxygen: from seed germination to seedling growth, life activities are extremely active and require an adequate oxygen supply to promote respiration and release energy and to promote material metabolism.

2. Reasonable close planting

Reasonable close planting is one of the effective measures for increasing yield in soybean cultivation. At present, soybean planting density is rather low, and missing plants and broken rows are serious. Soybean yield is mainly composed of four factors: "number of plants per unit area, number of pods per plant, number of seeds per pod and seed weight." In actual production, these four factors influence and constrain each other. Therefore, to obtain high soybean yield, there must be a reasonable population structure.

Creating a reasonable population structure means adjusting density so that the number of plants per unit area and individual plant traits maintain a certain coordinated relationship. A reasonable density is also affected by variety type and fertility conditions. Soybean varieties are numerous, divided into early-maturing, medium-maturing and late-maturing types, and also distinguished by leaf size, number of branches and strength of luxuriance; different types of varieties should have different reasonable densities. Varieties with many branches and tall stature should be planted at lower density; varieties with few branches and a single-stem type should be planted densely. There is also another principle: "fertile land is suitable for sparse planting, poor land for dense planting." On dry, poor land, keep 20,000 plants per mu for soybeans, with a sowing rate of about 5 kg. On land with high water and fertilizer levels, spring-sown soybeans should keep 8,000-10,000 plants per mu, with row spacing 50 cm, plant spacing 12-15 cm, and seed rate 3-4 kg; summer-sown soybeans are generally 18,000-20,000 plants per mu, sowing rate 6-7 kg, row spacing 40-50 cm, plant spacing 10-15 cm.

3. Improving fertility

Soybean yield level is closely related to soil fertility. Returning straw to the field and applying large amounts of organic fertilizer should be advocated. Soybean rhizobia can fix nitrogen, but they cannot meet the nitrogen supply needed by soybeans, still less replace fertilization. When fertilizing, attention should be paid to improving the nitrogen-fixing efficiency of root nodules. According to experiments by Shanxi Agricultural University, applying large amounts of fertilizer to the preceding crop of soybeans is beneficial to soybeans; mixing organic fertilizer and phosphate fertilizer as seed fertilizer, and applying nitrogen fertilizer at the flowering stage both give good results. Generally, for a yield of 200 kg of soybeans per mu, it is necessary to apply sufficient organic fertilizer 2,000 kg and phosphate fertilizer 50 kg mixed as seed fertilizer, and apply nitrogen fertilizer 10 kg at the flowering stage. Practice has proved that combined application of nitrogen and phosphorus at the seedling stage, flowering stage and pod stage can all increase yield, with the best effect at the flowering stage. Of the fertilizer applied to soybean fields, part is directly absorbed and used by the plants, and another part first nourishes rhizobia and then indirectly nourishes the plant body through the action of rhizobia. Because phosphorus is the main substance constituting rhizobia and is also an indispensable element for nitrogen fixation, applying phosphate fertilizer can play the role of promoting nitrogen with phosphorus. Experiments show that where phosphate fertilizer was applied, both the nitrogen-fixing intensity and nitrogen-fixing amount of rhizobia were significantly higher than the control, with nitrogen-fixing intensity increased by 20.98% and nitrogen-fixing amount increased by 33.3%. The effect is better when phosphate fertilizer is mixed with organic fertilizer, with the nitrogen-fixing amount increased by 73.3% compared with the control. On the basis of applying sufficient base fertilizer, applying organic fertilizer mixed with phosphate fertilizer as seed fertilizer is a good method of promoting nitrogen with phosphorus. It is worth noting that at the seedling stage, that is, the early stage of rhizobia formation, applying excessive quick-acting nitrogen fertilizer not only affects the number of root nodules but also reduces their nitrogen-fixing ability.

4. Reasonable irrigation

When planting soybeans on irrigated land, it is necessary to irrigate enough bottom moisture to ensure full stands; irrigate fully at the flowering and podding stage to increase flowers and preserve pods; control water at the seedling stage for appropriate seedling restraint. Also prevent lodging caused by excessive rain during the flowering and podding stage. As the farming proverb says: "When soybeans bloom, you can catch shrimp in the furrows. Dry flowers and wet pods, harvest one dan eight per mu (indicating a bumper harvest). Wet flowers and dry pods, stalks but no fruit (indicating a poor harvest)." It can be seen that the water requirements of soybeans from flowering and podding to seed filling are very important. If soybeans lack water for one week 4-7 weeks after flowering, yield is reduced by 36%, so timely irrigation is needed. Theoretically, soybeans consume different amounts of water at different growth stages, and water consumption is greatest from flowering to the seed-filling stage.

Soybeans need the most water during the flowering and podding stage, and this period is the critical period for soybean water demand. During this period, on the one hand, vegetative growth and reproductive growth proceed simultaneously, and photosynthesis, respiration, and material transport and transformation all rapidly reach a peak, so water demand increases greatly. At the same time, transpiration gradually increases until it reaches a peak, and water consumption inevitably increases greatly as well. Compared with other crops, the critical period for soybean water demand can last as long as two months. This is because the flowering and podding period of soybeans is long; although soybeans have entered reproductive growth after flowering, vegetative growth still continues for a relatively long time, especially for varieties with indeterminate podding habit. On the other hand, 4-7 days after soybean flowering is exactly the period when reproductive cells undergo meiosis to form tetrads, and the demand for water is most sensitive. Drought at the flowering stage will cause a large number of flower drop; drought at the podding stage will cause pod drop; drought at the seed-filling stage will affect seed development and produce shriveled seeds. Therefore, the amount of rainfall and its distribution are closely related to soybean yield. In arid and semi-arid areas with annual precipitation of 600-800 mm, mostly concentrated in the latter half of summer, soybean cultivation is most suitable.

5. Advocating intercropping cultivation techniques