What are the key technical points for fertilizing rapeseed during the bud emergence and bolting stage?
How should rapeseed be fertilized during the bud emergence and bolting stage? Please advise. When rapeseed enters the bud emergence and bolting stage, the period from bud emergence and bolting to flowering is when both vegetative growth and reproductive growth are vigorous. This period is called the double-vigorous stage. The main objective at this stage is steady spring growth, promoting thick stems, and maintaining a relatively high number of green leaves, to lay a foundation for high yield...
How should rapeseed be fertilized during the bud emergence and bolting stage? Please advise.
When rapeseed enters the bud emergence and bolting stage, the period from bud emergence and bolting to flowering is when both vegetative growth and reproductive growth are vigorous. This period is called the double-vigorous stage. The main objective at this stage is steady spring growth, promoting thick stems, and maintaining a relatively high number of green leaves, to lay a solid foundation for high yield. During the double-vigorous stage, rapeseed takes up a large amount of fertilizer, accounting for about half of its total uptake over its whole life. Reasonable topdressing during this period can achieve the effects of strengthening bolts, increasing branches, promoting flowers, adding pods, and filling seeds. The specific methods are
Steady application of nitrogen fertilizer. In spring, the application rate of nitrogen fertilizer should be strictly controlled according to the earlier fertilization situation. For weak seedlings, apply early and heavily with quick-acting nitrogen fertilizer. Topdressing should be carried out after "Start of Spring," applying 5 kg-6 kg of urea per mu, so that nutrient supply matches bolting and the seedlings turn from weak to strong. For strong seedlings, apply appropriately late and lightly. When the bolts reach 10 cm in height, apply 3 kg-4 kg of urea per mu to prevent insufficient later vigor from affecting seed setting and seed filling. For overly vigorous seedlings, generally do not topdress with quick-acting bolting fertilizer; only apply 1,000 kg-1,500 kg of farmyard manure per mu to prevent nutrient deficiency from affecting pod setting and grain increase. Topdressing of bolting fertilizer should be steady. Generally, in plots with sufficient winter manure where low winter temperatures reduce its effectiveness, bolting fertilizer may be omitted or applied lightly, allowing the fertilizer effect to gradually come into play as temperatures rise.
Increase potassium fertilizer application. The double-vigorous stage is the peak period of potassium uptake in the entire life of rapeseed. When potassium application was insufficient earlier, it should be increased during the bolting stage to help improve the plant's stress resistance, enhance rapeseed's resistance to lodging, pests, and diseases, while coordinating rapeseed growth and improving yield and quality. Generally, apply 5 kg-7.5 kg of potassium chloride per mu or 75 kg-100 kg of plant ash, and in potassium-deficient soils and paddy-field rapeseed, the amount should be appropriately increased. The application time is generally best in mid-to-late February.
Supplement phosphorus fertilizer. Phosphorus fertilizer should preferably be supplemented by foliar feeding. Soak 1 kg-1.5 kg of calcium superphosphate per mu in 50 kg of water for a full day and night, then filter out the residue and take the liquid for foliar spraying. Generally, spray 2 times, with an interval of 5 days-7 days.
Spray boron fertilizer. During the bud and flowering stages of rapeseed, foliar spraying of boron fertilizer solution can prevent "flowers but no seeds" and the production of secondary flowers, with a significant yield-increasing effect. It is advisable to spray once each during the bolting stage and early flowering stage, using 100 g of borax per mu each time, diluted with 50 kg-75 kg of water, spraying both sides of the leaves. Borax is generally not easily soluble in water. When preparing the boron fertilizer solution, first dissolve the borax with a small amount of warm water at 60°C-70°C, then add enough water to the required volume. After the borax solution is prepared, it should be sprayed immediately to avoid prolonged standing that causes boron to recrystallize and precipitate, reducing the effect of boron spraying.
Spray growth regulators. Overly vigorous seedlings with drooping leaves and soft tissues may suffer yield reduction due to excessive nutrition and weakened resistance. Therefore, chemical regulation must be used for overly vigorous seedlings. During the bolting stage, 50 g of 15% paclobutrazol per mu can be sprayed with 75 kg of water to control height and increase thickness, control vigor and turn plants strong, making overly vigorous seedlings become a high-yield field.
In addition, when excessively growing rapeseed has a fast leaf emergence rate, in order to slow the leaf emergence rate and control growth, one spray of 0.5% chlormequat solution can also be used.
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