Oilseed Rape

Nutrition check list

Good crop nutrition will help to achieve maximum crop productivity for maximum profits with minimal impact on the environment while adhering to all legislation. Some basic principles should be followed to achieve these goals:

  1. Identify the soil type in order to understand nutrient requirements.

  2. Analyse soil for nutrient content every 3-5 years and adapt nutrient inputs to maintain values of:

     
    pH 6.5 (5.8 peat soils)
    P Index 2
    K Index 2-
    Mg Index 2
  3. Determine the Soil Nitrogen Supply (SNS) either by Field Assessment Method or by sampling and analysis for Soil Mineral Nitrogen.

  4. Determine nutrient supply from organic sources and deduct available nutrient sources from total crop requirement.

  5. Apply Phosphorus and Potassium to maintain nutrients from crop removal and apply additional quantities if soil indices are low.

  6. Apply nutrients at the correct timing to match plant demand.

  7. Check that the fertiliser spreader or sprayer is calibrated to deliver nutrient accurately.

  8. Record all fertilisers and organic materials used.

Nitrogen

N Max limit

For crops grown in Nitrate Vulnerable Zones (NVZs) there are rules limiting the amount of nitrogen that can be applied. These limits are not necessarily the optimum for agronomic performance but are the maximum allowable in these areas.

In NVZ zones, the average nitrogen application rate (from manufactured fertiliser and crop-available nitrogen from any organic manure) must not exceed the N Max limit. It is also good practice to follow these guidelines for land outside of NVZ zones. The N Max limit applies to the average across the farm.

For full details of N Max limits please refer to the DEFRA document; Guidance on complying with the rules for Nitrate Vulnerable Zones in England for 2013 to 2016.

The table below highlights different N max limits depending on expected crop yield and soil type.

Crop Expected yield N max limits
Oilseed Rape 3.5 250
4.0 280
4.5 310
5.0 340
5.5 370

Maximum autumn application of 30kg N/ha (allowed as an exemption to the closed period for manufactured nitrogen fertiliser)

Optimising Canopy

A green area index (GAI) of 3.5 at flowering is the optimum to intercept incoming light and produce an optimum of 6-8000 pods/m2. Canopy development can be managed by adapting Nitrogen rates.
 
Nitrogen Requirements
50kg N/Ha is required to build each unit of GAI. Therefore, for an optimum of 3.5 GAI at flowering the crop must have taken up 175kg N/Ha. For predicted yields above 3.5 t/Ha, then additional N is required:
  • 4.0 t/Ha: an extra 30kg N/Ha
  • 4.5 t/Ha: an extra 60kg N/Ha
  • 5.9 T/Ha: an extra 90kg N/Ha

Calculating N Rates

Nitrogen requirement (kg N/ha) = Target N (175kg N/ha) - Soil Nitrogen Supply / Fertiliser N recovery (0.6) + Adjustment for higher yield potential

  1. First work out the crop available N before fertiliser application. This is done by adding the Soil Mineral N to the nitrogen already in the crop.
  2. Work out the shortfall of the target 175kgN/Ha for the crop. The additional fertiliser N to be applied should be based on a 60% efficiency.
  3. Then adjust for higher yield potential (see above values).

Green Area Index (GAI) can be estimated by  = Area of green material (green leaf and green stem) per m2 of ground.

Nitrogen Timings

  • Nitrogen needs to be applied early enough to allow sufficient uptake by flowering.
  • Where higher yield potentials are predicted nitrogen should be applied later (yellow bud or early flowering) to minimise risk of producing too big a canopy. However, this later timing needs to be balanced against the practicalities of evenly applying the fertiliser over a tall crop.

Nitrogen Inputs

The tables below highlight the nitrogen inputs required based on SNS and soil type.

The tables below highlight the nitrogen inputs required based on SNS and soil type.
 

Oilseed rape, Autumn and Winter sown - Nitrogen

SNS Index
  0 1 2 3 4 5 6
kg N/ha
Autumn 30 30 30 0 0 0 0
Spring  
All mineral soils 220 190 160 120 80 40-80 0-40
Organic soils       120 80 40-80 0-40
Peaty soils           40-80
 

Oilseed rape - linseed, Spring sown - Nitrogen

Nitrogen Timings

SNS Index
  0 1 2 3 4 5 6
kg N/ha
Spring oilseed rape
Light sand soils 210 180 150 120 70 40 0-40
Other mineral soils       120 70 40 0-40
Organic soils             0-40
Peaty soils              
Spring linseed
Light sand soil 80 50 0-40 0 0 0 0
All other mineral soils 100 80 50 0-40 0 0 0
Organic soils       0-40 0 0 0
Peaty soils           0

Foliar Nitrogen

In addition to the recommended rates of soil applied nitrogen, a foliar application of 40kg N/Ha has been shown to given 0.25t/Ha extra yield but a seed oil content reduction of 0.9%, giving an equivalent seed yield increase of 0.2t/Ha.

  Conventional foliar urea
Max N rate 40kg N/Ha
Timing Mid flowering - 2 weeks after end of flowering

Max air temperature at application to avoid scorch

 

18 deg celsius

Sulphur

Atmospheric deposition of sulphur has decreased following improved industrial processes and consequently sulphur is now frequently found to be deficient.
  • RB209 states that oilseed rape will respond to sulphur application when grown on all mineral soils.
  • HGCA Topic Sheet 66 recommends spring applications of a fertiliser supplying 75-100kg SO3/Ha.
  • Analysis of Sulphur Deficiencies (young fully expanded at early flowering stage): 0.4% S in dry matter, or N:S ratio of more than 17:1
  • Visual symptoms of sulphur deficiency: Stunting, Interveinal yellowing of upper and middle leaves, Pale flower petals

 

 

 

Crop nutrient removal

Significant nutrients are removed from the field during crop removal. The levels of these nutrients that are removed from the system will vary significantly depending on yield. In order to maintain soil nutrient levels the nutrients that are removed with the crop need to be replaced by either fertiliser applications and/or organic  additions.

The table below indicates the level of nutrients required to maintain soil indices at target Index 2 across a range of yield levels:

      Nutrient requirement (kg/ha)
Crop Straw management Yield (t/ha) P2O5 K2O MgO
Winter Oilseed Rape Straw ploughed-in/incorporated 3.5 60 45 7
4.0 67 51 8
4.5 74 56 9
5.0 81 62 10
Straw removed 3.5 65 85 No data
4.0 73 94 No data
4.5 80 103 No data
5.0 88 111 No data
Spring Oilseed Rape Straw ploughed-in / incorporated 2.0 45 35 4
2.5 52 41 5
3.0 59 46 6
3.5 66 52 7
Straw removed 2.0 50 70 No data
2.5 58 79 No data
3.0 65 88 No data
3.5 73 96 No data

Magnesium:RB209: At Mg Index 0 and 1, magnesium at 50 to 100 kg MgO/ha should be applied every three or four years.

Sulphur: RB209: Oilseed rape will respond to an application of sulphur on all mineral soils. Spring crops may be less susceptible to sulphur deficiency than winter crops.

Where deficiency has been recognised or is suspected, 50-75 kg SO3/ha as a sulphate containing fertiliser should be applied in early spring.