Green crop farm digesters were twice as efficient as official figures, according to a leading independent biogas consultant.

An East Anglian trial of more than a dozen varieties at a 'maize for biogas' trial near Mildenhall showed the performance gap between official figures and farm anaerobic digesters.

Richard Crowhurst, managing director of Enagri, told farmers and growers that the biofuel generating potential was much higher than official figures.

He said that the current projects would more than double the existing capacity of on-farm anaerobic digesters.

The Shropshire Group, which had staged the trials of 12 Syngenta varieties to assess the agronomic performance.

Mr Crowhurst said that politicians did not appear to understand the complete energy picture. 'It just shows that they do not understand how these crops are grown specifically as a biofuel source for efficient green energy production.'

The crucial factor for energy production from AD plants was the quality of feedstock, said Syngenta's maize specialist Nigel Padbury. 'When selecting suitable maize varieties for biogas feedstock it's all about the yield of digestible dry matter.'

In order to produce as much methane as possible from an AD plant, a variety with more concentrated energy was key.

'But as it doesn't make sense to harvest, ensile and handle more material than necessary, gross yield is not the best way to compare varieties for biogas production. From a movement and storage point of view, I would go for the concentrated energy of NK Bull every time.'

'An energy rich maize variety generates more output from any given volume going into the digester,' said Mr Padbury.