Farm Ireland

Saturday 16 December 2017

August is key to oilseed rape crop

Gerry Bird

This year's harvest has certainly kicked off with a certain degree of optimism for overall yields and prospective prices.

I receive practically daily email updates of LIFFE feed wheat future prices, which adds to the 'sell or store' debate among growers. With the winter barley harvest done and dusted, it's time to consider cropping options.

In my area (north midlands), yields ranged from 5.4t-10.3t/ha, with the bulk in the 8-8.5t region -- a good average considering the difficult growing season. A post-harvest review indicates a few pointers as to some of the reasons for the lower yields; higher than normal levels of take-all in the barley stubble due to a combination of the weather pattern, reduced phosphorous usage, poor wild oat and grass weed control, and poor root structure. I always notice that the second cereal after maize, or particularly oats, can suffer from take-all. The severity depends on the season and management.

The benefit of a break crop such as beans and oilseed rape is obvious again this year, with the subsequent cereal crops showing excellent yield potential. Winter barley in the rotation is an ideal entry for oilseed rape, and growers are gearing up to begin drilling soon -- on or around August 20. The hybrid varieties have excellent vigour and can tolerate a certain degree of late drilling up to early September. I always aim to have rape in by the last week in August as good establishment is vital. However, do not compromise on seedbed conditions. Rape needs a fine, consolidated seedbed which can hold moisture, have good seed-to-soil contact and also minimise slug activity, particularly to reduce below-ground grazing.


Rape will not tolerate compaction, low soil pH (below 6.5) and low soil fertility, especially the vigorous hybrids. Aim to establish 40-60 plants/m2 -- the lower figure for optimum early sowing -- hoping for even distribution and good ground cover.

Min-till technique is a popular method of establishment. Compaction near the surface or deeper must be eliminated -- also ensuring a fine seedbed. Watch for slugs and swathes of volunteer cereal, which can smother the emerging rape. It should be treated with reduced rates of a graminicide.

Oilseed rape has remarkable plant recovery capabilities, judging by some crops this season which were rendered non-existent by pigeons in the spring and subsequently produced well-branched plants with good pod development down the plant.

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Slurry or other organic manures have an excellent role in the nutrition of rape with good nitrogen usage and phosphorous for early root development. The importance of early root development is critical as it facilitates good canopy production and lays a foundation for rapid recovery in the spring if severely grazed.

The advice would be to get phosphorus and potash on early, the phosphorus primarily for root development. The big potash requirement is in the spring. I like to get some magnesium, sulphur and Boron on in the autumn, particularly on lighter land, though it is not as critical on heavier clays.

The past couple of seasons were concentrated on saving fertiliser costs, particularly phosphorous and potash. However, certain crops have suffered as a result. Recent soil results confirm my suspicions, with low pH, P and K values.

The lime status is first on the agenda. The damage to land due to compaction and water logging reduces the soil pH, which, in turn, limits the availability and crop usage of N, P, K and other elements.

Soil biological activity changes, resulting in a slowdown of organic nutrient release and general healthy soil activity. Lime provides the soil with calcium. As well as raising the soil pH, it also helps soil structure by the action on clay particles.

Soil samples could be a vital tool in getting the foundations right for next year's crop. They're also a lot easier to understand than feed wheat future prices.

Irish Independent