Soybean is a high-input crop that requires significant amounts of nutrients throughout its growth cycle. It absorbs large quantities of nitrogen, phosphorus, and potassium from the soil, along with essential micronutrients such as calcium, magnesium, boron, manganese, molybdenum, and zinc. A deficiency in any of these elements can lead to various symptoms, ultimately reducing yield and quality.
Nitrogen deficiency in soybeans is common, as although rhizobia can fix atmospheric nitrogen, they only supply about one-third of what the plant needs. When nitrogen is lacking, leaves turn light green, growth slows, and yellowing occurs. To correct this, apply 5–7.5 kg of urea per acre or spray a 1%–2% urea solution every 7 days for 2–3 times.
Phosphorus-deficient plants show dark green upper leaves, while lower leaves develop interveinal chlorosis, with small, thin leaves and delayed flowering. Apply 12.5–17.5 kg of calcium phosphate per acre or use a 2%–4% calcium superphosphate foliar spray, repeating every 7 days for 2–3 applications.
Potassium deficiency causes irregular yellow spots on older leaves, starting from the edges and spreading inward, while the veins remain green. This leads to shriveled, deformed grains. Apply 4–6 kg of potassium chloride per acre or spray a 0.1%–0.2% potassium dihydrogen phosphate solution every 7 days for 2–3 times.
Iron deficiency appears first as yellowing in the upper leaves with green veins, progressing to white new leaves with brown spots near the margins if severe. Spray a 0.4%–0.6% ferrous sulfate solution to restore balance.
Manganese deficiency results in stunted growth, with light green to white spots between the veins, but the veins stay green. Use a 0.01%–0.02% manganese sulfate foliar spray to address the issue.
Zinc deficiency causes chlorosis starting at the leaf veins and spreading outward, making it difficult to see green veins. Apply a 0.1%–0.2% zinc sulfate foliar spray to correct this.
Boron deficiency affects reproductive growth, causing young leaves to turn light green, become deformed, and shorten internodes. In severe cases, the meristem may die, preventing flowering. Spray a 0.1%–0.2% borax solution on the foliage.
Molybdenum deficiency leads to pale yellow leaves, poor growth, and symptoms similar to nitrogen deficiency, including necrotic veins and leaf deformation. Use a 0.05%–0.1% ammonium molybdate foliar spray.
For best results, apply foliar sprays on dry, windless days after 4 p.m., ensuring optimal absorption and minimizing runoff. Regular monitoring and timely intervention are key to maintaining healthy soybean crops.
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