Yields of oilseed rape in the combine tank at harvest fail to reflect the year-on-year improvements to the genetic potential of the new and highly productive varieties. Here, Edward Long looks at on-going trial work that aims to shift the yield balance in favour of UK growers.

The average on-farm performance of the UK oilseed rape crop has, at best, been stagnant in recent years, yet in Germany yields continue to expand.

In NIAB/HGCA trials over the past 10 or so years there has been a 1-1.5% yield improvement from the control varieties each year, yet over the same period the average commercial production has declined annually by about 0.5%.

Now a major nationwide trial involving large tramlined strips in large blocks of crop is underway to discover what is compromising the on-farm performance on this side of the North Sea, and what can be done to bring UK yields back up to those combined by German rape growers. Crop Needs "The aim is not just to boost overall yield, but to maximise the economic yield," points out the trial`s co-ordinator CPB Twyford agronomist, Lee Bennett. "For the last two seasons rape grown on farms in Schleswig-Holstein, Saxony and just about everywhere else north of Frankfurt has given an average of 4t/ha of seed, yet here we only managed 3.1t.

The gap between us was even wider in 2004 when the German average was 4.2t/ha, and the UK crop struggled to reach 2.9t. "It seems a degree of complacency has crept in, some growers have taken their eye off the ball. So we need to sharpen the pencil and look again at how to grow and manage this important crop.

A lot of cost has been squeezed out of the system in recent years and it could be that this has gone too far, we may have thrown the baby out with the bath water, or we may have lost sight of the actual needs of the modern crop." The large-scale trial, in which CPB Twyford and machinery company Opico are collaborating, is geared to a `back-to-basics` approach from seedbed preparation through until the crop is ready for the combine. The nationwide trial comprises 14 sites on a range of soil types on farms as far apart as Nairn in Scotland and Sherborne in Dorset.

The effects on crop performance of different establishment and management techniques are being compared in large 1ha strips in 24m tramlines in commercial crops. The main variety that is common to all sites is the German-bred restored hybrid Trabant. It is growing alongside a development line. Trabant is the most widely grown variety on farms north of Frankfurt.  Sowing approaches A third of the Suffolk trial site at Brampton near Beccles, which followed wheat, was drilled with a Vaderstad Rapide into a seedbed prepared from ploughed land. Another third was prepared in the traditional min-till way using a Simba Solo, and the rest was put direct into stubble with Opico`s Variocast seeder mounted on a He-va subsoiler unit.

From the evidence gathered so far this season, the Opico system appears to work well as seed is placed into moist soil in the slot left by the tine. This avoids the risk of loss of tilth associated with cultivating ploughed land, and the risk of seed left on the surface in stubble not finding any moisture in a dry autumn. The target was to establish a population of 28 to 35 plants/sq metre, so a seeding rate of 50 seeds/sq metre was used.

All sites were sown at the normal time for the area and, with the warm late summer/early autumn weather and no lack of seedbed moisture, crops established rapidly and evenly and grew away well. "It made a pleasant change as conditions the previous autumn resembled the Somme which was a major shock as conditions in 2003 were Sahara-like with absolutely no sign of any water.

The biggest room for commercial on-farm improvement is to achieve optimum population every season," says Mr Bennett. To investigate the interaction between establishment method and agronomic investment/canopy management versus a typical UK disease management-only approach, Caramba was applied at the 2-6 true leaf stage and compared with Punch C. The growth regulator effects of Caramba encourage rooting in the autumn and helps with canopy management in the spring.

A big and sturdy root system provides the crop with the launch pad for the rest of the season, so Mr Bennett is keen to see if there are any lasting benefits to be gained from the German twin-track approach with Caramba going on in the autumn and again just before stem extension in the spring.

A routine treatment of Filan fungicide will be applied at the petal stage to protect against Sclerotinia. A 'hit-all' policy The plan is to work the crop hard, so it will be given 250kg/ha of nitrogen as ammonium nitrate prills. German rape growers apply trace elements as insurance treatments every year.

To UK growers this may seem a 'blunderbuss' approach but the effects of the hit-all policy with applications in both autumn and spring will be checked in another part of the trial in conjunction with Headland AgroChemicals. Where trace elements are used, boron plus cocktails of zinc, magnesium, manganese and sulphur will be applied.    

"This is a comprehensive trial conducted over a wide geographical area so it should unearth the clues needed to refine the way we grow rape in this country to boost yields. "I am convinced there is room for more precision in what we do, one possible way forward is to use hydroscopic pelleted seed to offset the effects of a dry seedbed and remove one of the main stumbling blocks faced by the UK crop," Mr Bennett concludes.