Match variety to drilling date to get the most from oilseed rape crops

Download the OSR seed rate calculator on the right.

The tool is designed to help you decide your optimum seed drilling rate for your conditions and establishment technique. Adjust the target plant numbers you desire and input your seed germination, TGW and expected field losses.

OSR suggested drilling dates

Match variety to drilling date to get the most from oilseed rape crops

The relationship between plants per square metre and seed yield is largely well understood. It took a while to prove it, but there is probably no better example of the ‘less is more’ rule than oilseed rape plant populations.

It wasn’t always so however. Conventional thinking used to support the notion that thick crops based on a planting rate of 100 seeds per square metre were best. This had a lot to do with the desire to produce a thick canopy ahead of the winter in hope that it would make it difficult for pigeons to find an entry point. Today, however, we take a different approach to achieving the same goal.

Successive trials, for example, have demonstrated that crops with a seed rate as low as 30 seeds per square metre can and do go on to produce excellent yields. Then again, other trials in the same year, but in a different location performed best at a seed rate of 70-160 seeds per square metre. It is a case of matching seed rate to the seedbed conditions, but we have learned that the crop has great capabilities to compensate for low seed rates. There is a great deal of data on this subject on the AHDB Cereals & Oilseeds website for anyone with the time or inclination to read it.

What has been the subject of more recent investigations however, is the importance of plant spacing along the row, not just between rows. The same conclusions apply: oilseed rape doesn’t like being crowded either at its front and back or at its sides. Research by ADAS indicates that there is a large range in the optimum distance between rows due to the variabilities in establishment percentages and site conditions. In a favourable year and under good conditions crops are capable of delivering impressive performances on row spacings up to 72cm, but that 50cm is a sensible compromise when faced with the possibility of a less-than-kind-season.

Similarly, the optimum number of plants per metre is between six and 24. This is a large range, but supports what we know about the plant’s ability to compensate when populations are low. From a practical perspective, it also allows for inaccuracies in drill metering systems or miss-calibrations when calculating the intended seed rate.

An area that is less well understood is that of matching variety to drilling date. It stands to reason that some varieties will better suit the early August drilling slot while others will, such as Campus and Picto with their exceptional early vigour, can be comfortably drilled up to 21st September. We have long recognised this with varieties of wheat so why not with oilseed rape?

Our experience suggests that the differences between varieties only becomes truly evident once you get into September. Those growers who can who can be confident of drilling in August will see little difference between varieties. Take Barbados and Hasting, two varieties that combine excellent yields with outstanding light leaf spot and stem canker resistance, for example, both are well-suited to drilling throughout August.

In contrast, Flamingo a conventional type and the restored hybrids Harpege and Hawai, up for recommendation this autumn represent a step forward in yield and disease performance, but are better suited to drilling between 7th August and 10th September. Having the confidence of this extra week can be crucial.

We need to do more to understand the subtle differences between varieties that will become increasingly important as we seek to make the most of a plant’s natural ability to compensate for poor establishment or get ahead of threats such as cabbage stem flea beetle attack. Results this season demonstrate that some varieties have done significantly better than others even when separated by nothing more than a hedgerow and a ditch.

Oilseeds seed rate calculator