How to prevent frost damage in rapeseed? Early prevention is key

Rapeseed, also known as oil Chinese cabbage or bitter cabbage, Latin name: Brassica campestris L., a plant of the Brassicaceae family and Brassica genus, native to our country, its stem is dark green, its petiole resembles that of Chinese cabbage, it is a variety of Chinese cabbage of the Brassicaceae family, and its flowers are yellow. In agronomy, multiple species of plants whose seeds contain oil are collectively called rapeseed. At present, the main cultivated (variety) types of rapeseed are: turnip rape (Brassica rapa (campestris) L.), Indian mustard (Brassica juncea L.), and rapeseed (Brassica napus L.).

Growing conditions for rapeseed

Temperature requirements: Rapeseed is a crop that prefers cool conditions and has relatively strong cold resistance. According to experiments, the minimum temperature for seed germination is 4-6°C, and at 20-25°C seedlings can emerge in 4 days; the flowering stage is 15-19°C, and the pod development stage is 12-15°C, and a large day-night temperature difference is favorable for flowering and pod development, increasing the accumulation of dry matter and oil content.

Water requirements: Rapeseed has a long growth period, a large vegetative body, and a large number of fruiting organs, so it requires more water. The water requirements at each growth stage are: during the germination and seedling emergence stage, soil moisture should generally be maintained at about 65% of field capacity; during the bud and stem stage and flowering stage, it is 76-85% of field capacity, and during the pod development stage, it is 60-80% of field capacity.

Fertilizer requirements: According to measurements, for every 100 kg of rapeseed produced, the ratio of nitrogen, phosphorus, and potassium is 1:0.35:0.95, and the demand for these three elements is equivalent to more than 3 times that of cereal crops. In addition, rapeseed is relatively sensitive to the trace element boron, and deficiency easily causes flowers but no seeds.

Soil requirements: Rapeseed is a taproot crop with a relatively developed root system, a main root that penetrates deeply into the soil, and many lateral and fine roots. It requires a loamy soil with a deep soil layer, good structure, rich organic matter, and both fertilizer and water retention as well as loose aeration. In weakly acidic or neutral soil, it is more conducive to increasing yield and improving the oil content of the seeds.

Frost damage in rapeseed requires early prevention

Rapeseed belongs to the Brassicaceae family, Brassica genus, and is an annual herb with a taproot system, an upright stem, relatively few branches, and a plant height of 30-90 cm. Frost damage can cause serious economic losses to rapeseed cultivation, so how should frost damage in rapeseed be prevented?

Enhance cold resistance

Take different measures for different seedlings; ensuring strong seedlings overwinter is the fundamental measure to defend against low temperatures. During the overwintering process, rapeseed leaves are most likely to freeze and die, resulting in fewer branches after the year and directly affecting yield. Therefore, every possible means must be used before the year ends to promote root growth and leaf development. For overly vigorous seedlings before winter, from Minor Snow to Winter Solstice, deep intertillage and turning of the soil between rapeseed rows to about 10 cm can cut some lateral roots, reduce their nitrogen uptake capacity, promote the accumulation of sugars and other organic matter in the rapeseed plant, and thereby improve cold resistance. Promptly carry out intertillage and earth banking for rapeseed to thicken the soil layer around the root system, which has a certain effect on blocking cold wind invasion and improving heat absorption, insulation, and cold resistance, especially after earthing up the base of tall seedlings, shortening the root crown helps with insulation. When entering the cold winter season, especially before low-temperature invasion, quick-acting nitrogen fertilizer should be controlled to limit the increase in the rapeseed nutritional area, so that the waxy layer of rapeseed leaves accumulates, which is beneficial for cold resistance.

Apply winter fertilizer early and heavily

Increasing the proportion of phosphorus and potassium fertilizer in the winter fertilizer can help increase the thickness of the waxy layer on the leaves. It is best to apply the winter fertilizer before the cold wave arrives. In the early overwintering period, applying organic fertilizers such as pig and cattle manure or farmyard manure between rapeseed rows can raise the ground temperature by 2-3°C and can also have the effect of being applied in winter and used in spring. Generally, applying 1000-1500 kg of pig and cattle barn manure or 2000-2500 kg of farmyard manure per mu is appropriate. Potassium can increase the concentration of cell sap and enhance the cold resistance of cells. Generally, 5-8 kg of potassium chloride and 10-15 kg of superphosphate are applied per mu in furrows or holes. Plant ash is rich in potassium and has strong heat preservation. When the weather suddenly turns cold and other measures cannot be implemented in time, spreading a layer of plant ash on the rapeseed leaves and in the field can not only protect the leaves but also increase the soil's heat absorption performance and raise soil temperature.

Timely foliar fertilizer spraying

Spraying phosphorus fertilizer on rapeseed leaves can significantly increase the thickness of the waxy layer on the leaf surface, with a notable cold-resistant effect. Generally, leaves that have turned purple due to low temperature can turn back to normal green 5 days after spraying phosphorus fertilizer, and can withstand low-temperature invasion of minus 5°C. The specific method is to use 2 kg of superphosphate or 0.5 kg of ternary compound fertilizer per mu, soak it in 30-40 kg of water for one week, filter out the fertilizer residue, and spray it on the leaves, then spray again every 7 days. The key targets for spraying are rapeseed fields that appear tender green due to excessive nitrogen fertilizer. For relatively weak rapeseed, 0.1-0.2 kg of urea can be added to the phosphorus fertilizer solution to promote rapeseed leaf growth, thereby improving the leaves' ability to produce a waxy layer and enhancing cold resistance.