MANIPULATION OF RHIZOBIA MICROFLORA FOR IMPROVING LEGUME PRODUCTIVITY AND SOIL FERTILITY - A CRITICAL-ASSESSMENT

Inputs of biologically fixed nitrogen derived from the symbiotic relationship between legumes and their root nodule bacteria into terrestrial ecosystems amount to at least 70 million metric tons per year. It is obvious that this enormous quantity will need to be augmented as the world's population increases and as the natural resources that supply fertilizer nitrogen diminish. This objective will be achieved through the development of superior legume varieties, improvement in agronomic practice, and increased efficiency of the nitrogen fixation process itself by better management of the symbiotic relationship between plant and bacteria. This paper considers ways and means by which populations of root-nodule bacteria, established and introduced, can be manipulated ecologically agronomically, edaphically and genetically to improve legume productivity and, as a consequence, soil fertility.