Sweet sorghum a source of sugar

Press, 27 January 1986, Page 26

Sweet sorghum a source of sugar

PA Wellington A tropical cereal crop grown in some parts of New Zealand is a potential source of sugar, but scientists say they want companies that could develop and use the new supply to show some interest before research continues. Even without further processing into sugar products, sweet sorghum has good potential on farms as a fodder-crop.

Trials to determine how much sucrose can be produced from sweet sorghum have been made by a Ministry of Agriculture and Fisheries scientist, Graeme Piggot, at Whangarei.

The juice extracted

from an average one-hec-tare, 20-tonne crop of sweet sorghum would provide more then two tonnes of sucrose, he said. The trials were conducted on 11 sites and a range of soils. The sugar syrup produced could be used by industry, but as yet there was no reasonable manufacturing process, Mr Piggot said.

Researchers want to establish a scaled-down pilot project on a 50ha plot, but are restricted by the cost. Mr Piggot said the best varieties of sweet sorghum for sugar production have now been verified, but work will not proceed unless there is some commercial interest. Trials have been con-

ducted on the effect of sowing date, seeding rate, row spacing, harvest regime, weed control, fertiliser needs, and land uses during winter after a sorghum harvest. Forage sorghums are fast-growing summer greenfeeds that have been used for several years in warmer areas of New Zealand. They provide an alternative to greenfeed maize and will regrow after cutting or grazing. Sorghum/ is a frosttender crop that performs best in hot, moist summer weather and is more suited to the north of the North Island and warmer areas of southern North Island, Nelson, and Marlborough. While well-adapted as a forage species to Northland, the sorghum grew with some variability depending on the cultivar or hybrid chosen, the soil type and the season, Mr Piggot said. Crop management strongly influenced growth and development. The key factors were the correct sowing date, about mid-November, and obtaining a weed-free seedbed by either sowing into well-fallowed land or through residual herbicides at sowing. Since the crop has notable regrowth characteristics, flexible harvesting or grazing regimes can be devised to provide multiple harvests. Sorghum can also be integrated with plans for regrassing in autumn or for growing of winter forage crops. Mr Piggot said crop yield data suggest regimes involving sugar or silage production appear promising but have yet to be commercially proven. Research is now being concentrated on increasing the amount of sweet sorghum cultivar seed.