Rapeseed often form a large number of "red leaf seedlings" in winter, and the formation of "red leaf seedlings" has multiple causes. The lack of factors and improper management and climatic factors may form the symptoms, so farmers should be symptomatic.
Phosphorus deficiency Phosphorus, the plants are dwarf, slow growth, delayed leaves, leaf area is small, dark green leaves, lack of luster, purple spots or plaques appear on the edges, petiole and leaf veins on the back of leaves turn purple.
Prevention and control measures: 25-30 kg of superphosphate per acre topdressing or pouring water, the earlier the better the effect; later with 1% superphosphate calcium leachate foliar spray.
The nitrogen-deficient rapeseed plants are short and young, and the new leaves are born slowly. The leaves are small and small, yellow-green to yellow, and the leaf margins are red.
Prevention and control measures: Measure 8 to 10 kilograms of urea per mu or 20 to 30 kilograms of ammonium bicarbonate, or use 750 to 1,000 kilograms of human feces and urine to pour water; late nitrogen deficiency, with 1% to 2% urea solution foliar spray.
In the case of sulfur-deficient rapeseed, the plants are dwarf and pale green, which is similar to nitrogen deficiency. The margins of the leaves are uneven, shrinking, and the leaves, veins, and stems become purple.
Prevention and control measures: In combination with cultivator, 1 to 2 kg of sulphur powder per hectare, or 50 kg of gypsum powder.
When boron is deficient in boron deficiency, the leaves initially turn dark green, the leaf shape becomes smaller, the leaf mass becomes thicker, becomes brittle, the leaf ends are rewinded, and the leaf is not evenly crumpled. Then it turned purple from the edge of the lower middle of the leaf, and developed into the interior, and then became blue-purple; the yellow veins and its nearby tissues turned yellow, resulting in the formation of blue and purple patches. The last part of the leaf margins died and the entire leaf turned yellow and fell off earlier.
Control measures: Foliar spraying with 0.1% to 0.2% borax solution.
The drought of rapeseed during the seedling stage and the lack of soil moisture will make it difficult for the roots of the rapeseed to suck up and absorb water, which results in the slow growth of the rapeseed, the dwarfness of the plants, and the turning of the leaves into pale red.
Prevention and control measures: Watering in time, furrow irrigation should be taken when watering, do not flood irrigation, to prevent rot dead seedlings.
If there is too much rain before winter, or if transplanted in paddy field, the filter water will not be smooth, causing waterlogging and root damage. The leaf color will turn dark red, and some will still be dead.
Prevention and control measures: timely drainage of water to reduce the groundwater level; cultivating loose soil, improve soil permeability conditions, and promote root development.
When the freezing temperature suddenly drops below 0°C in winter, the leaves will also appear red when they are frozen.
Prevention and control measures: Combine with cultivator clearing ditch, planting soil and removing roots, adding organic fertilizers to reduce freezing damage.
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