Spring Oilseed Rape

Nitrogen, Phosphorus and Potassium

Nitrogen, P and K advice for oil seed rape is shown in Table 1. The first split of N should be applied in late February and the remainder in the first week of April. The first split should be about 30% of the total. It is unlikely that the application of N at sowing time is justified, but if it is used, it should not exceed 40 kg/ha of N. Fertilizer applications should not be combined drilled as this may delay germination.

The pH for oil seed rape should be above 6.5.

Sulphur

Oil seed rape responds to the application of S on sandy soils. A dressing of 25 kg/ha S should be adequate.

Magnesium

If the soil Mg is Index 1, apply a source of Mg. Use magnesium limestone if the pH is low or 75 kg/ha of calcined magnesite or kieserite every three years.

Boron

Boron should be applied for oil seed rape especially when the soil test is below 1 mg/l. Severe B deficiency causes stunting and brittle petioles, but relatively mild deficiency results in poor seed set and a reduction in seed numbers per pod and seed weight. These conditions can be induced by severe summer drought.

A spray at sowing and in the spring should prevent the occurrence of B deficiency.

Phosphorus (P) and Potassium (K) Removals for Oilseed Rape

P and K removed in seed and straw for oilseed rape. The majority of P and K is removed in the seed at harvest time (6.0kg P /tonne & 9.1 kg K /tonne). The straw contains small amounts of both P and K (0.44kg P /tonne & 5.0 kg K /tonne).

The table below shows the P and K removed in seed and straw based on crop yield (t/ha) and the total removal of P and K by the crop.

* Take note the figures in the above table do not take account of additional P and K required to build soil fertility at low soil indexes (Index 1 or 2). Consult the Teagasc Green Book for additional P & K for building soil fertility to the optimum soil index 3.