Nearly 15,000ha of sugar beet being grown this season in Germany is destined for biogas production, equivalent to about one-tenth of the total area in the UK given over to sugar beet.

It is part of the German government's drive over the past decade to increase renewable energy generation, explained Volker Utesch of KWS SAAT at the recent World Association of Beet and Cane Growers (WABCG) conference held in Cambridge.

At the heart is the feed-in tariff, which gives generators a guaranteed price for their gas/electricity for 20 years. This is the scheme that the UK feed-in tariff introduced earlier this year, was modelled on.

German experience

There are 4780 anaerobic digester plants in Germany generating 1600MW, the equivalent of one-and-a-half nuclear power plants, he said.

Of these, there are about 800 on-farm plants producing biogas using energy crops grown on 700,000ha, most of which is maize for maize silage topped up with rye, sorghum and sugar beet.

Hybrid rye tends to be grown in droughty areas of Germany where maize would struggle, said Mr Utesch.

However, in the past two years, sugar beet has received more attention, as growers discovered the advantages this crop offered. Sugar beet yields 400 litres of methane/kg of dry matter - 100 litres more than maize - because of its higher sugar content.

With beet, 95% of the carbohydrate is converted to gas while for maize and sorghum, it is nearer 70% because of the higher lignin and cellulose content.

Another benefit of sugar beet is the speed of degradation, which three to four times faster than maize.

Trials have so far found that a mixture of 75% maize and 25% sugar beet works best in practice, he said.

To help the biogas sector, KWS has embarked on breeding programmes to develop specialist varieties in the four crops, such as an energy beet.

We are currently looking at digestible dry matter output/ha, but there may be other traits we need to consider as we learn more. We still don't know what an energy beet will look like. Will it be more like a fodder beet? We are still refining what direction to go in.

However, Mr Utesch added that growers can already boost yields by 9-14% by tweaking management. As quality is not as crucial for biogas as for sugar production, growers can apply more nitrogen fertiliser and gain an extra 5-6% yield. If you include crowns, that's a further 5-8%.

Practical lessons

One practical problem encountered by German growers was preventing soil going into the digester, which impairs its performance. The solution? We invented a mobile beet washer that can process 50-70t/hour.