Most late-planted and weeded rapeseed crops are transplanted during the rainy season. Due to severe soil compaction, it's essential to cultivate the soil promptly to loosen it and improve root development. Cultivating the field after transplanting helps remove weeds, break up clods, and prepare a favorable environment for the seedlings. Once the rapeseed has recovered, deep cultivation should be carried out to ensure the soil is loose and well-drained. At the same time, the drainage ditches, furrows, and field channels must be cleaned to maintain smooth water flow and prevent waterlogging, which can help raise the ground temperature.
After transplanting, it's crucial to apply seedling fertilizer as soon as possible. The earlier, the better. Typically, 3-5 kg of urea per mu, 5 kg of potassium chloride, 300-500 g of boron fertilizer, and 750-1000 kg of diluted manure should be applied, either in one or two applications. Alternatively, 45-50 kg of ammonium carbonate per acre can also be used. Make full use of the warmer weather after the rain to promote healthy leaf and root growth.
A second application of wax fertilizer is mainly based on organic materials. For medium-fertility fields, 1000-1500 kg of pig manure per mu, 10-12 kg of superphosphate, and 5-7.5 kg of ammonium bicarbonate are mixed together and applied along the rows, combined with cultivation. This practice helps retain heat, promote root growth, protect the roots, and enhance oil content in the seeds.
Foliar application of phosphate fertilizer can improve the cold resistance of rapeseed. To prepare the solution, take 2 kg of fine phosphate fertilizer per acre, soak it in a container with enough water for a week, then mix in 200 grams of urea. Spray the solution directly onto the leaves during a sunny afternoon when there's no strong wind. If the solution is insufficient, add a little clean water. Spraying every one to two weeks ensures maximum absorption. Observations show that within three days of spraying, some yellowed leaves turned green again, and growth accelerated. After the second spray, the number of leaves increased from four or five to eight or nine, with stronger, thicker, and straighter foliage.
To control early flowering in both early and late rapeseed, especially when nutrient growth is excessive before winter, adjustments should be made accordingly. For fields with vigorous growth, deep cultivation can be performed. For underdeveloped fields, reapplying nitrogen fertilizer can delay vegetative growth, increase biomass, and prevent premature flowering.
Applying spring fertilizer and promoting strong seedlings is a key strategy for high-yield late-planted rapeseed. After the start of spring, 8-10 kg of urea per acre should be applied, followed by an additional 5-7 kg after the bolting stage. This helps build a strong seedling framework and supports high yields. It's also important to prevent downy mildew, especially in late spring rapeseed. During the flowering period, pesticides like virulence and chlorhexidine can be used for effective disease management.
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