**I. Causes of Reduced Scarring and Fewer Kernels**
1. **Low Temperatures**
Soybeans thrive in temperatures between 15°C and 25°C, with the ideal temperature for flower bud differentiation around 20°C. If temperatures drop below 15°C after this stage, plant growth is stunted, which negatively affects pollination and seed development. The optimal flowering temperature ranges from 24°C to 29°C, with nighttime temperatures ideally between 18°C and 24°C. Nighttime temperature has a greater impact—when it drops below 15°C, even high daytime temperatures may prevent blooming. Spring weather can be unpredictable, so protective measures are essential. If low temperatures affect the flower buds or flowers during critical stages, it leads to fewer pods and smaller kernels.
2. **Nutrient Deficiency**
Rhizobia in legumes help fix atmospheric nitrogen, enriching the soil. The early flowering stage marks the peak of nitrogen uptake. However, if early-maturing soybeans are planted too early in cold conditions, rhizobial activity is reduced, leading to nitrogen deficiency and poor growth, including severe calyx loss. Soybeans also require significant phosphorus, especially during branching and flowering. A lack of phosphorus during these periods reduces the number of nodes, branches, and flowers, and increases calyx drop. Additionally, phosphorus-deficient plants have fewer root nodules, reducing nitrogen fixation efficiency.
3. **Soil Drought**
Flowering and podding are the most water-intensive phases of soybean growth, requiring soil moisture to be maintained at 60-70% of field capacity. Dry soil hinders carbon dioxide absorption and disrupts normal photosynthesis. Drought during the early flowering stage can impair vegetative growth, reduce flowering and pod numbers, and cause flower bud drop. During grain filling, drought can block nutrient transport, leading to poor kernel development and pod abortion.
**II. Preventive Measures**
1. **Protected Cultivation**
Early-maturing soybeans benefit from double-membrane protection, such as greenhouses or small arch shelters. Soil temperatures should remain above 12°C from mid-February to early March. Throughout the growing season, remove or ventilate the cover according to the temperature needs of each growth stage. Proper planting density is also crucial—planting 20,000 seedlings per acre with spacing of 22 cm x 22 cm helps increase node numbers, promote grain filling, and boost yield.
2. **Fertilizer Application**
A balanced approach of base fertilizer and top-dressing is recommended. Base fertilizer depends on soil fertility, typically 1,000–1,500 kg of compost, 30 kg of compound fertilizer, and 100–150 kg of wood ash per mu. During the growing season, apply liquid manure (10%) during the seedling stage, and 10–20% decomposed human urine before flowering. Urea (0.3–0.5%) can also be applied. At the early flowering stage, spray a 0.02–0.05% ammonium molybdate solution and apply 25 kg per acre.
3. **Proper Irrigation**
During dry periods, follow the principle of "frequent but light watering," applying water 2–3 times. Consistent moisture ensures healthy plant development and better yield outcomes.
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