Selenium topdressing popular, M.A.F. says

Press, 2 August 1985, Page 20

Selenium topdressing popular, M.A.F. says

Farmers have responded quickly to the lifting of restrictions on aerial topdressing of selenium, according to a scientist at the Ruakura Agricultural research Centre, Dr John Watkinson. Selenium treatment has been accepted so quickly and widely that last year more than' 700,000 hectares were topdressed which represents about 20 to 30 per cent of the farmland that can receive benefit from treatment, he said. Selenium is a trace element, similar to cobalt, which is necessary to prevent white muscle disease and infertility in sheep. White muscle disease degenerates muscle tissue in young animals, and affects the heart tissues. In extreme cases the affected animal can die. Because it is more poisonous than cobalt, selenium had not been allowed to be topdressed until 1982. In fact New Zealand was the first country to allow this. Since then Finland and the Australian State of Victoria have followed suit Dr Watkinson said more

than 20 years of research was needed to prove that selenium in granular form was not toxic, and could be manufactured, handled and topdressed safely. The amount of selenium deficiency in an area depends very much on soil structure in each locality, but the most deficient areas are the entral plateau of the North island and almost all of the South Island. Only 10 grams a hectare of Selenium is needed annually and in some cases it can enrich the soil enough to make further topdressing unnecessary, Dr Watkinson said. Half a part of selenium to one million parts of soil would be enough for that to happen. Dr Watkinson said it could take about 30 years before a farmer could cut back to biennial topdressing, and even less would be required as time went on, if the doses were kept up. However he said using drenching or injections and waiting for the selenium in the animal excretions to enrich the soil would not be feasible.