This is a question I am often asked when discussing plans with growers and my most common response is, "Why wouldn't you?"
For me, as with any crop, it makes perfect sense to adopt variable rate drilling for OSR. Particularly for helping to create the optimum, even canopy as the correct seed rate can hugely contribute to this.
Today's modern varieties are very responsive to targeted input strategies, with husbandry guidelines to help growers achieve optimum results. The choice of varieties available comes following years of selection and careful management to produce homogenous plants that demonstrate particular characteristics or traits. However, when drilled into a field situation there can be vast differences in soil type and physical condition amongst other things, all of which can impact on the ability of the crop to reach its full potential.
To negate some of these effects, growers can variably drill the seed. This method allows for specific areas to be targeted at a rate suited to the soil type, to achieve an optimum canopy and help the crop to cope with different soil types and conditions.
Oilseed rape is generally considered to compensate when given space, but what about areas that then become too thick? The plant type, being indeterminate, will try to compete with itself and produce dense, leggy canopies in areas. This can then cause differences in standing ability and maturity, which is why I feel the crop lends itself perfectly to variable seed rate as it is an effective means for combating the above problems.
For example, if you have areas of poor or sporadic establishment you will know that they are far more prone to pest damage. This can reduce the plant population further, even below crop threshold levels. In such high-risk zones, adjusting to a higher seed rate can prove very effective for maintaining yields.
Therefore, in answer to the above question (and providing your drill is capable), winter oilseed rape is a great crop for variable seed rate.
Finding the seed rate that works for you
It's worth remembering the importance of finding the balance and what works best for your land.
A seed rate that is too high can, as is particularly true of OSR, result in thick canopies, increased lodging, high disease pressure, and reduced seed size and yield.
On the other hand, a seed rate that is too low can lead to reduced yields and a crop that suffers from increased weed pressure.
The best approach is to have a key target figure in mind and then use both your experience and any data you have recorded over the years to adjust the seed rate to suit your circumstances. Seed rate advice is given as the number of seeds per m2 to support average establishment, but you can vary this figure by up to 50% if it better suits your soil. Using our crop establishment tool in MySOYL, you can combine all of the above information to help produce a tailored, variable rate seed map in just minutes.
Don't forget the basics
Winter oilseed rape is no different to any other crop. It is optimum canopy we are aiming to achieve overall so it's important to get the first building blocks in place by removing any physical disparities caused by the variable nature of soil and pest pressures. If you have the right number of plants in every part of the field, you give yourself a much greater chance!