What to Do About Soybean Flower and Pod Drop? Causes and Control Techniques

There are many causes of flower and pod drop in soybean, mainly:

Poor ventilation and light penetration. Under poor ventilation and light conditions, soybean is prone to flower and pod drop. When planting soybean, improper variety selection, early canopy closure, excessive density, mutual shading of branches and leaves, coupled with high humidity and poor light, leads to low leaf chlorophyll content, causing soybean plants to gradually turn yellow. With little nutrient accumulation, flowers and pods drop.

Nutrient imbalance. The flower and pod drop stage of soybean is the period of highest nutrient demand; if nutrient supply is insufficient, flowers and pods will drop. The fertilizer requirement pattern of soybean is generally as follows: from emergence to flowering, the plant needs 20% of the total fertilizer for the whole growth period; from flowering to pod filling, 55%; and from pod filling to maturity, 25%. According to this fertilizer requirement pattern, only rational fertilization can support normal growth and development of soybean. In fertilization, farmyard manure, chemical fertilizer and micro-element fertilizer should be applied in combination: soybean needs more nitrogen fertilizer throughout its life, followed by phosphorus fertilizer, and less potassium fertilizer. In application, nitrogen and phosphorus should be combined, using phosphorus to promote potassium and potassium to strengthen stems and prevent lodging. Combine base fertilizer, seed fertilizer and topdressing; combine flower fertilizer, pod fertilizer and grain fertilizer, to fully meet the needs of soybean for nutrient elements at different growth stages and prevent flower and pod drop.

Insufficient water. Sufficient water can not only accelerate the transport of nutrients and regulate plant temperature, but also directly participate in the metabolism of soybean growth and development; therefore, suitable water is beneficial to normal growth and development of soybean. During the flowering and podding stage of soybean, if it rains continuously and soil moisture is excessive, it will not only reduce sunshine hours but also lower soil temperature and increase relative humidity, causing the plants to grow excessively. As shading increases, photosynthesis decreases, affecting the synthesis and transport of organic matter and causing flower and pod drop; if water is too little, the plants cannot get enough water and will also wilt. In short, any imbalance will inevitably lead to flower and pod drop.

Disease and insect damage. Some directly damage the flower and pod organs and cause drop, while others damage the plants, affect growth and development, and cause flower and pod drop. However, storms and sudden temperature drops can also cause flower and pod drop.

Human-induced flower and pod drop. Improper field management in the later stage may break soybean stems and cause branches and leaves to fall off, resulting in artificial flower and pod drop.

So, how can flower and pod drop be prevented? In summary, there are the following technical measures:

Rational close planting. Rational close planting should be based on variety characteristics and soil fertility level. The requirement for soil fertility is that fertile land should be sparser and lean land denser. For soybean varieties currently promoted in Heilongjiang Province, under narrow-row close planting on small ridges, about 450,000 seeds per hectare should be sown, while for narrow-row close planting on large ridges or small ridges, about 400,000 seeds per hectare is appropriate.

Scientific topdressing. Because soybean is a crop with a relatively high nitrogen requirement, nitrogen fertilizer is usually applied once at the early flowering stage, which can reduce the flower and pod drop rate and prolong plant life. Generally, 150-180 kg of ammonium nitrate per hectare can be applied as topdressing, or 130 kg of urea; if foliar topdressing is carried out at the flowering and podding stage, use 0.5 kg of urea, 1.5 kg of superphosphate, 0.3 kg of potassium sulfate, and 30 g of boron nitrate per mu, or add an appropriate amount of plant nutrient regulators such as Genduozhuang, add 50 kg of water, and spray on the leaf surface, which can preserve flowers and pods and increase 100-grain weight.

Chemical regulation treatment. For soybean fields with excessively luxuriant growth, chemical regulation treatment can reduce nutrient and water consumption, optimize the growth environment, promote good growth and development, and prevent flower and pod drop.

Drought resistance and waterlogging removal. From flowering to podding, soybean absorbs the most water and at the fastest rate in its whole life. Irrigating in drought and draining in waterlogging during this period can reduce flower and pod drop.

Prevent and control disease and insect damage. In plots with a large area of continuous and alternating cropping and severe damage, disease and insects must be controlled in time to reduce flower and pod drop. At the same time, management such as cultivating soybean fields should be strengthened to promote good growth and development and prevent flower and pod drop.

In short, as long as soybean planting is based on the causes of flower and pod drop, timely prevention is carried out, problems are discovered early, and corresponding technical measures are taken for control, high and stable yield and good quality of soybean can be ensured, and considerable economic benefits can be obtained.