Winter Rapeseed Fertilization — How to Do It Right?

At the same time, rapeseed is the most important oilseed crop cultivated across Poland. The quality of the root system plays a vital role during overwintering, which is why proper knowledge is essential to ensure correct development of the crop.

Soil requirements — how to prepare for sowing?

Soil for winter rapeseed cultivation should be rich in humus, microorganisms, calcium, and generally of high fertility. The best-performing rapeseed is obtained by sowing on rye and wheat complex soils of classes I–III.

Winter rapeseed also requires soil with an appropriate pH level. The pH should range from 6.0 to 7.0. When soil acidity is too high, the root system fails to develop properly, leading to significant yield losses.

If the soil conditions are not suitable for rapeseed cultivation, liming should be considered to improve the chemical and biological properties of poor soils. Failure to lime can lead to increased fungal diseases, a poorly developed root system, and cracking of rapeseed pods.

Nitrogen and phosphorus fertilization of winter rapeseed — what you should know

In autumn, phosphorus fertilization of winter rapeseed significantly supports proper root system development. Why is the root system so important? Because it ensures better winter hardiness and greater access to water and nutrients, resulting in well-nourished plants that are less susceptible to drought stress.

Nitrogen fertilization is one of the most commonly chosen forms of fertilization for rapeseed. Nitrogen is one of the most yield-forming nutrients. However, when fertilizing rapeseed, the amount must be calculated correctly, because high nitrogen levels affect the availability of other nutrients — for example, sulfur. Plant sulfur supply partially determines how well applied nitrogen is utilized, which in turn impacts plant size, resistance and quality.

Another important aspect is selecting the right form of nitrogen in the purchased fertilizer and proper timing. The choice of nitrogen form is most critical in the first application. It is recommended that a significant portion be in nitrate form (NO3), which enables efficient rebuilding of the leaf rosette.

Delayed soil fertilization will result in later flowering and abnormal vegetative development. Consequences of late fertilization may include:

• Weaker pod development
• Slower plant growth
• Poor root system
• Low plant nutrient status
• Reduced flower pollination
• Difficulties during harvest

Effective nitrogen utilization is possible only when proper application guidelines are followed. Attention should be focused on the spring dose, aimed at repairing damage sustained during winter. The first dose should constitute approximately 2/3 of the total planned nitrogen application.

The second nitrogen dose should be applied between 3 days and approximately 3 weeks after the first dose. Delaying the second dose can cause negative effects such as rapeseed lodging, prolonged flowering, or excessive vegetative growth.

Of course, a proper winter rapeseed fertilization strategy is only possible through a well-thought-out process. Sowing date, weather conditions during winter, and current forecasts must all be taken into account.

Formula for calculating the required fertilizer dose

Proper preparation for spring fertilization of winter rapeseed is essential, as nitrogen has a major impact on yield. To determine the correct fertilizer dose, a field test must first be conducted to assess nitrogen and other mineral content in the soil. To obtain an accurate reading, 3 soil samples should be collected at different depths:

• 0–30 cm
• 30–60 cm
• 60–90 cm

The recommended method for calculating the correct fertilizer dose uses the following formula:

Spring N dose = target seed yield (t) x nutrient requirements per 1 t of seeds + straw – mineral N in soil.

To produce 5 t/ha, rapeseed takes up approximately 250–300 kg N, as 1 tonne of seed requires about 50–60 kg of nitrogen. The dose should account for nitrogen from both mineral and organic fertilizers. It is also important to remember to split the applied fertilizer doses.

What else can be used to fertilize rapeseed?

An additional option for winter rapeseed fertilization is the use of phosphorus-potassium fertilizers. These are applied in the pre-sowing period so that the soil can absorb the minerals through soil water. Solubility issues most often affect phosphorus fertilizers or those containing phosphorus. This must be taken into account, as these fertilizers need more time to fully dissolve.

If the soil has low fertility, phosphorus fertilizers should be avoided. Fertilizing rapeseed with a two-component fertilizer containing magnesium and sulfur is often sufficient to provide plants with the autumn nutrients they need.

There are cases where phosphorus-potassium fertilizers are also used in spring. Plant responsiveness to potassium or other mineral fertilization largely depends on soil moisture.

In very wet soil, winter rapeseed will have brittle roots, and minerals are at risk of excessive leaching. Therefore, if spring potassium and phosphorus fertilization is applied, it will positively influence nitrogen uptake. For best results, work should begin in early spring, approximately 2–3 weeks before the start of vegetation.

Potassium, along with phosphorus and other nutrients, meets winter rapeseed's requirements for elements that positively affect plant development, strengthen winter hardiness, improve nitrogen processing efficiency and support rosette growth. Potassium is the element that thickens and enlarges cells. Thanks to potassium, farmers can rest assured during winter that their crops will survive. Potassium also manages soil water resources efficiently, protecting plants from drought.

It is also worth supplying additional microelements such as magnesium, manganese, molybdenum, boron, copper and zinc. These nutrients are applied in liquid form as foliar fertilizers.

Farmers also frequently use sulfur, applied through soil fertilization. Mineral nitrogen content in the soil, thanks to sulfur, increases its processing capacity, positively affects plant growth and has a significant impact on fat synthesis. Despite its benefits, it is important to remember that excess sulfur acidifies the soil, which can negatively affect rapeseed growth in spring.

Rapeseed grows poorly when the dose is incorrectly calculated. Sulfur-containing fertilizers should be applied at a rate of 1/3 to 1/5 of the nitrogen dose. Plant resistance is in the hands of farmers — it is worth preparing for nitrogen fertilization (basic fertilization), foliar feeding, potential disease factors that may appear as leaf browning, and autumn fertilization with other elements.

What is foliar feeding?

Foliar feeding is considered a basic preventive measure that delivers missing microelements directly to the parts of the plant where they are needed — such as leaves, stems and flowers. This type of fertilization should be carried out in autumn, at the 6–8 leaf stage.

Microelements recommended for use in Poland

Boron — delivers essential sugars to the roots, supporting winter hardiness. Boron deficiency is common in Poland, so it is frequently supplied through fertilizers. Boron also plays a significant role in building cell walls, which increases plant resistance to various diseases and pests.

Iron — builds stronger mechanical tissue, which positively affects plant lodging resistance. Iron also supports lignin synthesis and stimulates microelement uptake.

Zinc — is responsible for proper plant resistance, supports the process of photosynthesis and contributes to efficient nitrogen and hormonal management.

Molybdenum — incorporates nitrogen into protein structures, which improves hormonal balance — ensuring greater safety during winter and more efficient plant regeneration after the winter period.

Manganese — slows growth and prepares the plant for dormancy, supports proper phosphorus uptake and promotes correct root development.

Copper — supports plants through proper nitrogen and hormonal management, aids photosynthesis, making the plant stronger and more resistant to disease.

Foliar fertilizers should be split into at least two applications. By using microelement-containing fertilizers, we support the plant during winter for better overwintering, ensure proper development, and build the plant's immune system against various diseases.

The most commonly chosen element is boron, which supports cell wall rebuilding, reducing the risk of poor plant development and cracking. Fertilization should take place at the rosette stage and again at the budding stage.

Despite the additional cost, fertilizing rapeseed is worthwhile so that significant quantities of nutrients are properly utilized, protecting yields. Fertilization enables plants to reach their full genetic potential and improves rapeseed frost resistance. Significant amounts of microelements are especially welcome in soils of medium fertility.

Summary

In summary, winter rapeseed is a crop that requires considerable attention and care. Spring fertilization is just as important as pre-sowing autumn fertilization and late autumn applications. In the biological processes taking place beneath the soil surface, deficiencies of any micro- or macroelements can negatively affect the taproot system of winter rapeseed.

It is also important to remember that the spring nitrogen dose should be split into at least two applications. Rapeseed is cultivated so that pre-sowing fertilization supports the formation of a rosette that is appropriately large and well-nourished. Soil fertility must not be neglected — it should be addressed both in autumn and in spring.

The condition of the field in spring will be the result of earlier preparation. For this reason, our efforts must be refined to replenish nutrients that have been leached by heavy rainfall or acidic soil, while paying particular attention to fully utilizing the potential of applied nitrogen, which is considered the most important nutrient in rapeseed cultivation.