Rapeseed freeze damage should be prevented mainly through early prevention

Rapeseed is prone to freeze damage at low temperatures, especially rapeseed that has grown well in autumn, which is more susceptible to low-temperature freeze damage because its leaves are green and tender. According to surveys, the degree of freeze damage is closely related to the vigor of the rapeseed seedlings, the terrain and soil moisture, and the quality of transplanting. Doing a good job of early freeze prevention is the key to obtaining high rapeseed yields.

????Enhance cold resistance

Different measures should be taken for different seedlings, and ensuring that rapeseed overwinters as strong seedlings is the fundamental measure for defending against low temperatures. During overwintering, rapeseed leaves are most likely to freeze and die, which reduces the number of branches after the year and directly affects yield. Therefore, every possible effort must be made before the year ends to promote root growth and leaf development. For seedlings that grow excessively before winter, from Minor Snow to Winter Solstice, the soil between rapeseed rows can be cultivated and turned to a depth of about 10 cm, cutting some lateral roots and reducing their nitrogen uptake capacity, prompting the accumulation of sugars and other organic matter in the rapeseed plant, thereby improving cold resistance. Promptly carry out intertillage and hilling of rapeseed to thicken the root-zone soil layer; this helps block cold wind invasion and improves heat absorption, insulation, and cold resistance. This is especially true after hilling around the bases of tall-stemmed seedlings, as 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 rapeseed nutritional area, allowing the waxy layer of rapeseed leaves to accumulate, which is beneficial for cold resistance.

Apply winter fertilizer early and heavily

Increasing the proportion of phosphorus and potassium fertilizer in winter fertilizer can help increase the thickness of the leaf waxy layer, and it is best to apply the winter fertilizer before a 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 achieve the effect of winter application for spring use. Generally, applying 1000-1500 kg of pig and cattle manure pen 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 per mu should be applied in furrows or holes. Plant ash is rich in potassium and has strong heat-retention properties. When the weather suddenly turns cold and other measures cannot be carried out in time, a layer of plant ash can be spread on rapeseed leaves and in the field, which not only protects the leaves but also increases the soil's heat absorption performance and raises soil temperature.

????Timely foliar fertilizer spraying

Spraying phosphorus fertilizer on rapeseed leaves can significantly increase the thickness of the leaf waxy layer, with a notable cold-resistance effect. Generally, leaves that turn purple due to low temperature can return to normal green 5 days after phosphorus fertilizer spraying 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, then filter out the fertilizer residue and spray it on the leaves, then spray again every 7 days. The key target for spraying is 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.