Biological nitrogen fixation associated with rice production

Research on biological nitrogen fixation began in Western Europe during the nineteenth century, under conditions where a mere increase in nitrogen fertilization inevitably increased yields : it was the beginning of the triumphal era of fertilizers. In the thirties began the era of legume inoculation : and this again was due to a very simplistic situation in western countries : the absence of bacterial symbionts adapted to crops such as soybeans. Biological nitrogen fixation (BNF) appeared as an extension of nitrogen fertilization, with the same effects on farmers' incomes. The amount of nitrogen available was the limiting factor of the farmer's income, whatever its origin ; mineral nitrogen from soil or fertilizers as well as nitrogen derived from biological fixation. In a way, this very clear-cut situation allowed for the rapid development of our knowledge about BNF, and its use by farmers. Nevertheless, when the time came to extrapolate to tropical countries, some difficulties arose. Some were due to a lack of knowledge about BNF systems in warm countries. Other difficulties were due to the interference of many yield-limiting factors other than nitrogen. But the main difficulty resulted from a misunderstanding about the objectives : the goal of developing BNF is not to achieve the maximum nitrogen input, it is really to achieve the maximum income (money and/or food) for farmers. In many tropical countries, the farmer's income is not directly proportional to nitrogen availability. We, as scientists, are confined to scientific objectives (maximum nitrogenase activity) whereas countries, such as Bangladesh, must aim at a maximum farming efficiency, biological science being largely secondary to other disciplines such as sociology or economics. (Résumé d'auteur