Rapeseed leaves have a reason
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Rapeseed often develops a significant number of "red leaf seedlings" during winter. This phenomenon can be caused by several factors, each with its own set of symptoms and control measures. Understanding these issues is essential for effective management.
Nitrogen deficiency in rapeseed results in stunted growth, slow emergence of new leaves, and small, yellow-green to yellow leaves with red margins. To address this, apply 8–10 kg of urea per mu or 20–30 kg of ammonium bicarbonate, or use 750–1,000 kg of human manure. For late-stage deficiencies, foliar spraying with a 1%–2% urea solution is recommended.
Phosphorus-deficient plants are short, with delayed leaf development, dark green and dull leaves, and purple spots on the edges. The veins and petioles may also turn purple. Apply 25–30 kg of superphosphate per acre as topdressing, preferably early. If applied later, use a 1% superphosphate leachate for foliar spray.
Sulfur deficiency causes plants to be dwarfed and light green, similar to nitrogen deficiency. Leaves show large notches, collapse into cups, and their backs, veins, and stems turn purple. To correct this, mix 1–2 kg of sulfur powder per hectare with cultivation, or apply 50 kg of gypsum.
Boron deficiency initially causes dark green leaves that become smaller, thicker, and brittle. Leaf tips curl inward, and the edges develop purple discoloration, spreading toward the center. Yellow veins and surrounding tissues form blue-purple patches, eventually leading to leaf death. Foliar application of a 0.1%–0.2% borax solution helps manage this issue.
During the seedling stage, drought can hinder root water uptake, causing slow growth, dwarfism, and pale red leaves. Timely watering is crucial. Use furrow irrigation rather than flooding to avoid root rot.
Excessive rain before winter or transplanting in paddy fields can lead to waterlogging, damaging roots and turning leaves dark red. Drainage should be improved, and soil should be loosened to enhance permeability and promote healthy root growth.
Sudden freezing temperatures below 0°C can cause leaves to turn red due to frost damage. Preventive measures include ditch clearing, soil cultivation, root removal, and adding organic fertilizers to reduce cold stress.
By identifying the specific deficiency or environmental factor, farmers can take timely and effective actions to ensure healthy rapeseed growth.