The Role of Legume-Rhizobium Symbiosis in Sustainable Agriculture

Abstract

The world’s population is increasing rapidly, and world food production needs to be commensurate with the demands of human consumption. To increase cultivated acreage would be very difficult, so we need to promote crop production, or the efficient use of existing croplands. The use of chemical nitrogen (N) fertilizers in the twentieth century promoted crop production by 4–10 times, and has supported food production over the past 100 years. However, the cost of chemical N fertilizers is high for farmers in developing countries, and their production requires a lot of fossil fuel. In addition, the inappropriate or excess application of chemical N fertilizers causes environmental problems, such as contamination of ground water by nitrates, and air pollution and global warming due to nitrous oxide. On the other hand, most leguminous crops, such as soybeans, beans, chickpeas, and groundnuts, and legume forage crops such as alfalfa and clover can fix atmospheric dinitrogen (N₂) by symbiosis with soil microorganisms (collectively termed rhizobia). The supply of N by symbiotic N₂ fixation via legume-rhizobium symbiosis is the most important source of N in agro-ecosystems. This renewable and environmentally sustainable N source also ensures soil restorative agents for maintaining soil fertility and sustainable crop production. Legume crops provide an important source of protein, oil and carbohydrate for human diets and livestock feeds. The production of legumes depends on symbiotic N₂ fixation, and this process is affected by various environmental conditions, as well as the supply of water and mineral nutrients, especially the availability phosphorous—the main theme of this book.