Trials in three very different seasons confirm the need to increase wheat seed rates as sowing progresses through the autumn.

But the results, based on drilling only in the past two weeks of September and the first two of October, raise the question of how high a rate might be economically justified in later sowings.

Stressing that conditions for establishment had varied greatly from autumn to autumn for the 2006, 2007 and 2008 crops, Cambridge Aarable Technologies’ Paul Hickman said yields had averaged 9.6, 6.3 and 11.1t/ha, respectively.

In the first year the varieties were Alchemy and Solstice. In 2007 these were replaced by Humber and Mascot, Oakley replacing the latter in 2008.

Three seed rates were applied at each drilling – 100, 200 and 300/sq m.

For the September sowings yield was relatively unaffected by the rate, noted Mr Hickman. “In terms of economic yield the optimum was somewhere between 200 and 300/sq m over the range of varieties.

“For the October drillings it was quite a different picture, especially with the very high yielding varieties Oakley and Humber. With those we needed 300 for the optimum yield, and 100 produced a yield depression across all varieties.

“So for October 300 seeds/sq m is consistently the economic optimum, which begs the question of ‘what if we’d gone even higher?’.”