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.
|Table 1: N, P and K for winter oil seed rape (kg/ha)|
|Soil N, P, K Index||N||P||K*|
|*K advice based on 3t/ha|
Oil seed rape responds to the application of S on sandy soils. A dressing of 25 kg/ha S should be adequate.
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 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.
|Nutrients removed in Oilseed Rape (seed & straw)*|
|Crop yield (t/ha)||2||3||4||5|
|Total P & K Removal in Seed & Straw|
* 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.