Growing Oilseed Rape
Crop Nutrition Advice

General aspects:

Nitrogen:

30-50 kg N/ha are often applied to support canopy development of weaker oilseed rape plants or heterogeneous crop stands. A useful combination can be made with phosphate and sulfate. With biomass sampling at the end of vegetation or in early spring, N uptake can be estimated and is regarded when calculating N fertilizer in spring. Oilseed rape can uptake up to 100 kg N/ha until late autumn. Therefore, oilseed rape is much more N efficient in autumn than winter cereals and takes on a function as catch crop reducing considerably the risk of N leaching over winter.

In spring, it is common practice to apply two N rates: the first N rate is spread at start of vegetation and the second at stem extension. This split N application is carried out with nitrate, ammonia or urea fertilizers. Spring N application can also be executed in one single rate. In this case, urea fertilizers with enhanced efficacy are often preferred. Urea efficacy is enhanced by coated fertilizer particles or fertilizers with nitrification and/or urease inhibitors.

Phosphate:

Phosphorus (P) in soil is prone to fixation in contrast to other macronutrients. P losses are mostly a question of eroded soil particles with wind and water from uncovered soils. P losses can be prevented effectively by green soil cover (with oilseed rape) or mulch layers. Even fully available P (100% water or citrate soluble) can be fixed. With optimum pH, the labile P fraction is released faster to soil solution. “Fresh” applied and slightly absorbed phosphate is much better plant available than stable fractions of aluminum/iron phosphates or calcium phosphates, resp. Oilseed rape can acquire phosphate very well but needs fresh P in autumn or spring to accelerate the canopy development.

Potassium:

On light sandy soils, potassium (K) is prone to leaching whereas on heavy clayey soils K can be fixed by clay minerals. Therefore, K on light soils should be fertilized in spring to reduce percolation losses. On heavy soils, K can be spread in autumn before sowing. In spring, oilseed rape takes up the highest K percentage during stem extension. Therefore, K fertilizers should be applied until stem extension.

Magnesium:

Magnesium (Mg) is essential for oilseed rape because Mg is the central ion of chlorophyll and activates many enzymatic processes. Mg deficient plants are mostly found on lighter coarse textured soils where Mg is prone to leaching. In spring, different K fertilizers containing Mg are suitable to close nutrient gaps. Especially after winter, weaker oilseed rape plants or crop stands with greater canopy losses are “grateful” for Mg fertilizers. With plant protection, small doses of Mg sulfate are often combined.

Calcium:

Up to 500 kg CaO/ha may be leached over winter under European conditions and must be balanced by liming (calcium carbonate or calcium hydroxide).

Calcium (Ca) is both soil and plant fertilizer: calcium ions enhance the soil structure by building bridges between clay and organic matter particles supporting the pore volume in soil, water infiltration especially with heavy rainfall events and increasing the soil water capacity. Also, oilseed rape removes comparably high Ca amounts from soil. Calcium sulfate fertilizers can be applied instead of lime if soil structural problems occur even with sufficient pH levels.

Ca fertilizers are spread typically in autumn before primary tillage and sowing. Mostly, Ca fertilizers are soil incorporated and spread to demanding broadleaf crops as oilseed rape in intervals of three to four years.

Sulfur:

Since air sulfur (S) emissions had been decreased extremely, oilseed rape showed sulfur deficiency first. Oilseed rape provides a very high S demand due to fatty acid synthesis in the seed as well as protein synthesis with S containing amino acids. Oil content is one crucial criterion for seed pricing. Therefore, many N fertilizers are combined with sulfate. Also, potassium or calcium sulfate fertilizers are very useful.

Later in the season at start flowering, N and S tissue contents can be assessed for the nutritional status of oilseed rape. For one plant sample, 20-30 fully developed leaves are collected (300-500 g fresh mass). Minimum contents are recommended as 4.0 g N/kg dry matter (DM) and 0.5 g S/kg DM. Lower values indicate at least latent deficiencies which cannot be corrected by high rates of solid fertilizers because nutrient accumulation precedes dry matter growth. Foliar application can only reduce deficiencies partly. Therefore, certain N and S amounts must be applied until stem extension because oilseed rape acquires high nutrient amounts in a short period of several weeks. Also, the status of other macro- and micronutrients can be assessed by tissue analysis.

Oilseed rape macronutrient removal (kg/ha)

Recommended oilseed rape nutrient contents at start of anthesis:

Uptake of nutrients (N, P, K, Mg) by the rapeseed in dependence of the physiological development stage (BBCH scale according to Hack 1993)

Micronutrients and foliar fertilization

Latent micronutrient deficiencies of oilseed rape in terms of boron, manganese and molybdenum can be prevented by foliar applications of 500-600 g B/ha, 200-300 g Mn/ha and 30 g Mo/ha. B application is then split in 150 g B/ha in autumn (4-6 leaves/plant), 300-450 g B/ha at stem extension and 75-150 g B/ha at “green bud” emergence (BBCH 51).
Boron is a very important micronutrient in oilseed rape fertilization. With autumn application, boron stimulates root formation. Boron is an integral component of cell walls. Good nutrition with this element enhances stem stability. Boron is involved in pollen and seed formation.

Micronutrients in oilseed rape are very often combined as foliar fertilizers with plant protection agents and/or growth regulators.
Foliar fertilizers are a common practice in fertilizing oilseed rape and may boost plant development and strengthen plants against abiotic factors (e.g., drought, heat, cold soils), and biotic factors (e.g., pests and diseases). However, foliar applications cannot replace the use of sufficient solid base fertilizers.