Farm Ireland

Thursday 19 April 2018

Oilseed rape offers wide range of benefits


Patrick J Phelan

This week presents the last opportunity to sow oilseed rape this year. There is a huge resurgence of interest in the crop for a number of reasons.

For a start, it achieved a better gross margin than any of the cereal crops this year. It also provides a take-all break and leaves high levels of residual nitrogen for subsequent crops of winter wheat. It can also help control annual and perennial grass weeds. Finally, it spreads the harvest workload, since it will normally be cut before winter wheat.

Heavy to medium soils, similar to those required for wheat, will give good yield potential. However, rape will not tolerate water-logging. Crop rotation is important to minimise disease risk so rape should not be sown more often than one year in 4-5.

Crops isolated from other crops will also have less disease risk from wind-borne diseases. Hybrid varieties have extra vigour and should do better than conventional varieties when sown late. Seeding rate is dependent on variety, seed size and required plant stand but will range from 3kg/ha (60-70 seeds/m2) for hybrids to 6kg/ha (100-120 seeds/m2) for conventional.

Larger seeds will normally give better plant establishment and produce more vigorous plants. If this is your first year growing rape, it is particularly important to read all pesticide labels carefully so as to avoid risk to this year's crop either from chemicals you are applying now or indeed herbicides that were applied last spring to the previous cereal crop.

Plough or thoroughly cultivate before sowing if products such as Hussar were used during the past year. Sowing depth should be shallow at 20-30mm, but make sure there is at least 15mm soil covering if you are using pre-emergence weed control with either Butisan S or Katamaran.

Do not use pre-emergence herbicides if heavy rain is forecast. Pre-emergence weed control is best for both poppy and cleavers.


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Slugs will eat germinating and emerged seedlings. Firm seedbeds will reduce their activity but the recent rain has provided ideal conditions for slug activity so it is likely that slug bait should be applied to all crops.

Seedbed nitrogen is generally unnecessary, but may be beneficial in fields where straw was chopped as the breakdown of straw by soil micro-organisms utilises nitrogen, which would otherwise be available to the emerging crop. If soil phosphate or potash levels are down at index 1-2 it is preferable to place fertiliser with the seed.

Most of this year's spring rape has not been harvested yet. Crops that have not been desiccated should be sprayed at the next opportunity with glyphosate. A pod sealant such as Pod-Stik or Dessicote may provide some additional protection from shedding.

There is a requirement under the terms and conditions of your single farm payment to analyse all lands which are in tillage for at least six years for soil organic matter. You are also restricted from applying phosphorus in excess of index 3 requirements unless you have a soil analysis report confirming that the requirement is higher.

Despite these regulatory requirements, you should be wary of skimping too much on fertiliser applications.

Sub-optimal soil fertility is costing farmers substantial amounts of money every year.

Some of the problem is due to widespread deficiency within fields, but in many cases smaller areas within fields are causing the problem.

Those areas must be identified and treated separately in order to bring the lands to full potential and achieve the 5t/ac crops that your neighbours claim.

Tillage fields, and separated problem areas within them, should be sampled at least every three years and analysed for phosphate, potash, magnesium and lime requirement. Analysis for trace elements should also be done if the yields have been less than satisfactory in recent years, or if the field history is unknown.

When results and recommendations are received they should be utilised to prepare a fertiliser programme for the coming years. In too many cases results are filed away and not used until compiling records at the end of the year. Recording of results and recommendations on your farm map may be the best way of ensuring you exploit results fully.

Note that the latest date for the application of chemical nitrogen and phosphorus is this Thursday.

Patrick J. Phelan is a member of ITCA and may be contacted at

Indo Farming