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 physiological disorders, resulting in reduced yield and poor plant health.
Nitrogen deficiency in soybeans often manifests as pale green or yellowing leaves, stunted growth, and delayed development. While soybean plants can fix atmospheric nitrogen through rhizobia, this natural process only supplies about one-third of the plant’s total nitrogen needs. To correct this, applying urea at 5–7.5 kg per acre or using a 1%–2% urea solution for foliar application every seven days for two to three times can help restore plant health.
Phosphorus-deficient soybeans typically show dark green upper leaves, with yellowing between the veins on lower leaves, small and thin foliage, and delayed flowering. Applying calcium phosphate at 12.5–17.5 kg per acre or using a 2%–4% calcium superphosphate foliar spray every seven days for two to three applications can help alleviate the issue.
Potassium deficiency causes irregular yellow spots along the leaf edges, with the central veins remaining green. The grains may become shriveled or misshapen. To address this, applying potassium chloride at 4–6 kg per acre or using a 0.1%–0.2% potassium dihydrogen phosphate foliar spray every seven days for two to three rounds is recommended.
Iron deficiency first appears as yellowing in the upper leaves, with green veins. Severe cases cause the entire leaf, including the veins, to turn white, with brown spots forming near the edges. Spraying a 0.4%–0.6% ferrous sulfate solution can help restore iron levels.
Manganese deficiency leads to chlorosis between the veins, with the veins remaining green. Applying a 0.01%–0.02% manganese sulfate foliar spray can effectively correct this issue.
Zinc deficiency causes interveinal chlorosis, starting from the leaf margins and spreading inward. Using a 0.1%–0.2% zinc sulfate foliar spray can help improve plant condition.
Boron deficiency affects reproductive growth, causing young leaves to turn light green, leaf deformation, short internodes, and failure to flower. Spraying a 0.1%–0.2% borax solution on the foliage can help.
Molybdenum deficiency results in pale yellow leaves, poor growth, and symptoms similar to nitrogen deficiency, with necrotic veins. Applying a 0.05%–0.1% ammonium molybdate foliar spray is effective in correcting this.
For best results, foliar sprays should be applied on calm, dry days after 4 p.m. to ensure maximum absorption and minimize runoff. Proper nutrient management is crucial for achieving optimal soybean yields and maintaining healthy crops.
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