The significance of symbiotic nitrogen fixation in plant production

Abstract

Fixed nitrogen is probably the main plant nutrient that limits agricultural production worldwide. For most developed countries this limitation can be alleviated by the use of nitrogenous fertilizers. The increased cost of fertilizer nitrogen, concern about nitrates in water supplies, and the limited availability of fertilizer in developing countries are major factors influencing a desire to obtain more fixation by biological means. It is likely that nearly all plant species benefit from nitrogen fixation by bacteria associated with their roots. How much they benefit appears to be related directly to the degree of complexity of the interaction between the plant and nitrogen‐fixing bacteria. For example, some leguminous plants, which have root nodules containing rhizobia, can fix more than 100 kg N per hectare per annum, whereas some grasses which have nitrogen‐fixing bacteria associated with their roots may only support fixation of 10 kg N per hectare per annum or less. The role of biological nitrogen fixation in crop production will be reviewed and an attempt will be made to explore different ways in which it may be increased in the future.