PASTURE LEGUMES, INOCULATION OF
Leguminous plants have a symbiotic relationship with certain bacteria, called rhizobia, that are able to extract nitrogen from the air, supply it to the host plant and eventually to all surrounding plants. Without nitrogen all plants die. Therefore these bacteria are particularly important in pasture establishment and growth, since the supply of nitrogen from clover plants is continuous and the cheapest that is available to the farmer. Though high fertility soils usually contain rhizobia that can inoculate clovers, they seldom have strains that are effective on lucerne, whereas lower fertility soils are deficient in most rhizobia. The correct strains of rhizobia for all leguminous plants can, however, be easily applied to the seed before planting. They establish themselves in small nodules on the plants' roots.
In 1927 the Mycological Laboratory of the Plant Research Station (now Plant Diseases Division, Department of Scientific and Industrial Research) commenced the distribution to farmers of cultures for the inoculation of lucerne. Demand increased steadily and by 1955 sufficient culture to inoculate more than 500,000 lb of lucerne seed was being used annually, together with experimental quantities of culture for the inoculation of other legumes, particularly clovers. When, in 1955, several firms showed the desire and ability to produce these legume cultures, the supply from the Department of Scientific and Industrial Research was discontinued and a scheme for the testing and certification of commercial cultures was instituted as a protection to the farmer. With the increase in development of second- and third-class land, especially that being brought into pasture from bush or scrub, together with the general realisation that such land required either annual applications of costly nitrogenous fertiliser or the inoculation of the clover seed with nitrogen-fixing bacteria, there has been a steady increase in demand for cultures to inoculate clovers.
by Douglas Winton Dye, B.AGR.SC., PH.D.(EDIN.), Plant Diseases Division, Department of Scientific and Industrial Research, Auckland.