Rapeseed often forms a large number of "red leaf seedlings" in winter, and there are multiple reasons for the formation of "red leaf seedlings". The symptoms may be formed due to lack of properness and management and climatic factors, so farmers should be symptomatic.
In the absence of phosphorus and phosphorus deficiency, the plants are short, slow in growth, delayed in leaf emergence, small in leaf area, dark green in color, lack of luster, purple-red spots or plaques on the edges, and veins on the petioles and leaves on the back of the leaves turn purple.
Control measures: 25 to 30 kilograms of superphosphate is used for trenching or watering per acre. The earlier the effect is better, the later use of 1% superphosphate leaching solution.
The plants with nitrogen-deficient rapeseed are short, the new leaves are born slowly, the leaves are small and small, yellow-green to yellow, and the leaves are red.
Control measures: 8 to 10 kg of urea per acre or 20 to 30 kg of ammonium bicarbonate, or 750 to 1000 kg of human excrement with water; at the end of the nitrogen deficiency, spray with 1% to 2% urea solution.
When sulfur-deficient rapeseed is deficient in sulfur, the plant is short and pale green, similar to nitrogen deficiency; the leaf margin is uneven, shrinking, and the leaf back, veins and stems become purple-red.
Control measures: combined with cultivating, apply 1 to 2 kg of sulfur powder per acre, or 50 kg of gypsum powder.
When boron is deficient in boron, the leaves initially turn dark green, the leaf shape becomes smaller, the leaf quality thickens and becomes brittle, and the leaf ends are rolled back and collapsed. It then turns purple from the edge of the lower central blade and develops into the interior, which in turn turns blue-violet; the veins and their surrounding tissues turn yellow, resulting in a block of blue-purple spots. The last part of the leaf edge is dead, the whole leaf turns yellow and falls off early.
Control measures: spray with 0.1% to 0.2% borax solution.
Drought rapeseed encountered drought during the seedling stage, and the soil moisture was insufficient, which made it difficult for the roots of the rapeseed to absorb water and absorb the fertilizer, resulting in slow growth of the rapeseed, short plants and pale red leaves.
Control measures: timely watering, watering should be used for furrow irrigation, not flooding, to prevent dead roots and dead seedlings.
There is too much rain before the winter, or the transplanting in the plate field, the water filtration is not smooth, causing the waterlogging to damage the roots and the seedlings, the leaf color becomes dark red, and some will rotten the dead seedlings.
Control measures: timely ditch drainage, reduce groundwater level; cultivating loose soil, improving soil permeability and promoting root development.
When the winter temperature suddenly drops below 0 °C, the leaves will also appear red when frozen.
Control measures: Combine the cultivating and clearing ditch, cultivate the roots of the soil, increase the application of organic fertilizers, and reduce the freezing damage.
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