Prevent soybean flower and pod drop: early prevention is key

Soybean flower and pod drop is a major factor limiting soybean yield increases. In production, the rate of soybean flower and pod drop generally reaches about 45%-70%. The most flowers drop 3-5 days after flowering, and the most pods drop 10-15 days after flowering. To increase soybean yields, substantial effort must be devoted to preventing flower and pod drop.

1. Causes of flower and pod drop

1. Poor ventilation and light penetration: excessive planting density and poor planting techniques cause excessive vegetative growth and premature row closure, worsening the light conditions in the lower part of the plants, which causes leaves to yellow and drop, reduces nutrient production and accumulation, and results in flower and pod drop;

2. Imbalanced nutrient supply: the flowering and podding stage of soybean is the period of greatest nutrient demand. Insufficient or imbalanced nutrient supply will cause massive flower and pod drop;

3. Unreasonable water supply: too little water during the flowering and podding stage causes the plants to wilt, reduces their uptake of soil nutrients, and creates an imbalance in water and nutrient metabolism, resulting in massive flower and pod drop. However, too much water lowers soil temperature, increases humidity, shades the field, and weakens photosynthesis, affecting the synthesis and transport of organic nutrients and increasing flower and pod drop;

4. Damage from pests and diseases: these damage the plant leaves, reduce photosynthetic intensity, and decrease the production and distribution of nutrients, causing flower and pod drop.

2. Methods to prevent flower and pod drop

1. Reasonable close planting: reasonable close planting is the central link in coordinating the conflict between individual plants and the population, making full use of soil fertility and light energy, and achieving high soybean yields. Reasonable close planting allows the population per unit area to develop fully, achieving the highest degree of light energy utilization and land utilization. High yields are obtained because the number of pods, number of grains, and grain weight per unit area increase. The specific density should be determined according to soil fertility, water conservancy conditions, and variety characteristics.

2. Skillful application of flower fertilizer: the flowering and podding stage requires large amounts of nutrients, and the basal fertilizer and seed fertilizer applied alone often cannot meet the demand. Therefore, apply topdressing at the early flowering stage, especially in poor, thin soil or fields where the seedlings are weak and cannot close the rows in time, applying 8-10 kg of urea per 667 sq m. Foliar spraying can also be used, spraying 60-70 kg of 0.3% potassium dihydrogen phosphate solution per 667 sq m, or using 50 kg of water plus 20-25 g of ammonium molybdate to make a solution for foliar spraying.

3. Timely drainage and irrigation: the flowering and podding stage is precisely the period of most vigorous vegetative and reproductive growth, and also the critical period for water demand. Insufficient water severely affects transpiration and photosynthesis and will cause massive young pod drop. When soybean growth slows, the leaves remain dark green, and the leaves wilt at noon, this indicates a water shortage in soybean, and irrigation should be carried out promptly. If water accumulates in the field after a rainstorm, it should be drained promptly to prevent waterlogging.

4. Prevent excessive vegetative growth: because some fields have good water and fertilizer conditions, combined with relatively high density, the branches and leaves grow excessively and the field becomes closed and shaded. This must be controlled.

5. Pinching at the flowering stage: pinching can control the vegetative growth of soybean, promote the redistribution of nutrients, concentrate the supply to flowers and pods, help increase flowers and preserve pods, control excessive vegetative growth, and reduce flower and pod drop. It thickens soybean leaves, lowers plant height, increases the number of pods per plant, promotes early maturity, and improves yield and quality. According to experiments, pinching at the full flowering stage generally increases yield by 10%-15%. Pinching from the full flowering stage to the final flowering stage of soybean has the most notable effect. Generally, pinching off about 2 cm from the top of the soybean main stem is sufficient. However, for land that is poor and thin, with relatively poor water and fertilizer conditions, and where soybean growth is weak and shows premature senescence, pinching is not advisable, to prevent increasing the amount of flower and pod drop.

6. Control pests and diseases: the main disease harming soybean is leaf spot disease, and the main pests include soybean pod borer, soybean pod moth, and soybean aphid, among others, which should be controlled promptly.