A Detailed Guide to Watering Times and Top-Dressing Key Points for Spring Rapeseed

Rapeseed is currently mainly used as an oilseed crop, and is sometimes also used as animal feed. In addition, rapeseed also has ornamental value, and many places now have rapeseed tourism culture. Rapeseed is grown all over the world and does not have very high requirements for growing conditions. So during spring rapeseed cultivation, when is it generally watered? What are the key points for top-dressing?

1. When is spring rapeseed generally watered?

Reasonable irrigation and drainage are important measures to ensure high and stable rapeseed yields. Rapeseed has a long growth period, a large vegetative mass, luxuriant leaves, and many fruiting organs, and its water requirement throughout its life is relatively large. In rapeseed-producing areas, rainfall in autumn, winter, and spring is generally low, and the soil is dry, which is not conducive to sowing, seedling emergence, and cultivating strong seedlings. In northern regions, winter drought often aggravates freezing damage and causes seedling death. In southern regions, there is more rain in the later period, causing waterlogging damage or flood damage. Therefore, timely irrigation and drainage must be carried out according to the water requirement characteristics of rapeseed and local conditions.

2. What are the key points for top-dressing spring rapeseed?

1. Apply seedling fertilizer early

Apply seedling fertilizer early and frequently to promptly supply the nutrients needed by rapeseed seedlings, and take advantage of the brief period of relatively higher temperatures before winter to promote rapeseed growth, achieve strong seedlings for overwintering, and lay the foundation for high and stable rapeseed yields. Seedling fertilizer can be applied twice, in the early seedling stage and the late seedling stage. The early seedling fertilizer is applied at the time of final thinning or when there are 5 true leaves, generally 5-6 kg of urea per mu. In soil deficient in phosphorus and potassium, if no phosphorus and potassium fertilizer was applied as base fertilizer, phosphorus and potassium fertilizer should be supplemented; the late seedling top-dressing should be determined according to seedling condition and climate. Generally, 8-10 kg of high-nitrogen compound fertilizer is applied per mu. Varieties with strong spring habit or areas with relatively warm winters should be fertilized early, while areas with low winter temperatures or triple-cropping rapeseed areas may be fertilized appropriately later.

2. Apply bolting fertilizer steadily

The bolting stage of rapeseed is a period when vegetative growth and reproductive growth proceed together. The plant rapidly bolts and grows branches, leaf area increases, and flower buds differentiate in large numbers. It is the period with the greatest fertilizer demand, and also the key period for increasing branches and pods. Therefore, bolting fertilizer should be applied steadily according to the application of base fertilizer and seedling fertilizer and the growth condition. If base fertilizer and seedling fertilizer are sufficient and the plants grow robustly, bolting fertilizer may be applied less or not at all; if base fertilizer and seedling fertilizer are insufficient and there is a trend of nutrient deficiency, bolting fertilizer should be applied early. Generally, 15-20 kg of high-nitrogen compound fertilizer is applied per mu. The fertilization time is generally the middle bolting stage, when the bolting height is 15-30 cm. However, for weak growth, fertilizer may be applied at the early bolting stage to avoid premature senescence; for strong growth, it may be applied at the late bolting stage, when the bolting height is 30-50 cm, to avoid excessive growth during flowering and resulting canopy closure.

3. Apply flower fertilizer skillfully

After rapeseed bolts, it flowers while forming pods. The number and weight of seeds are closely related to the nutritional conditions after flowering. For vigorous growth with a large amount of fertilizer applied at the bolting stage, it may be applied less or not at all; for early-maturing varieties, it should not be applied, or only a small amount should be applied at the beginning of flowering; top-dressing at the flowering stage can be done by foliar spraying, spraying 0.1-0.2% urea or 0.2% potassium dihydrogen phosphate during the flowering and pod-forming period. In addition, 0.2% borax aqueous solution can be sprayed once each at the late seedling stage and bolting stage to prevent the phenomenon of “flowering but not bearing fruit” and increase yield.