May Be Able To Do Without Legumes

Press, Volume CVIII, Issue 31760, 17 August 1968, Page 8

May Be Able To Do Without Legumes

\EW ZEALAND farmers save themselves a tremendous amount of money by using clover or other legumes to provide the nitrogen required by their pastures. Research now in progress at the Plant Chemistry Division of the Department of Scientific and Industrial Research may show how legumes can be made even more valuable for this purpose. It might also, conceivably, open the way to new methods by which pastoral farmers could become independent of legumes. A scientist whose studies are contributing toward these ends is Dr E. Moustafa, who recently returned to Palmerston North after 18 months’ work in the biological science department of Purdue University, Indiana.

Dr Moustafa’s main interest for several years has been the biochemistry of the root nodules of pasture legumes. In the nodules, atmospheric nitrogen is trapped and changed into a form that can be used by the plant. As nodules break off and disintegrate in the soil, the nitrogen they contain becomes available to other plants, including grasses. The whole process depends on soil bacteria known as rhizobia, which invade legume roots and cause the formation of nodules. The rhizobia then change from their free-living form to another form, bacteroids, which inhabit the nodules and produce enzymes responsible for nitrogen fixing. There are also some other nitrogen-fixing soil organisms whose activity does not depend on association with plants. The actual value of these free-living organisms has never been clearly determined, but they have an enzymic system similar to that used by the rhizobial bacteroids to trap nitrogen, and they provide a simpler source of material for laboratory study. Two such organisms, Clostridium and Azotobacter, as well as bacteroids, were used by Dr Moustafa in his work at Purdue. From these he isolated enzymes involved in

the nitrogen-trapping process.

He found that two enzymes were particularly important—one containing both iron and molybdenum, and the other iron but no molybdenum. Both must be present for nitrogen fixation to occur. Further study of them maythrow useful light on the place of molybdenum in soil management practice. Americans are very interested in these enzymes, mainly from the point of view of developing catalysts for use in the manufacture of nitrogenous fertilisers.

Dr Moustafa is more interested in improving the natural processes of nitrogen fixation so that they can be better exploited. He hopes that increased knowledge of the basic mechanisms involved will open up new possibilities on the practical level.

One of these possibilities might be the selection of strains of rhizobia that would promote nodulation more efficiently. This would increase the effectiveness of legumes in providing nitrogen for their own and other plants’ use. Another possibility might be artificial stimulation of the changeover of rhizobia to bacteroids. Dr Moustafa thinks that if this could be done the bacteroids alone, without association with leguminous plants, might fix sufficient nitrogen to meet the needs of grasses.

He emphasises, however, that this is still a rather remote possibility. In the laboratory, it has been shown that,' in certain conditions, bacteroids alone also can fix nitrogen, but it has yet to be shown that they can be made capable of a free-living existence in soil.