The legume-rhizobia symbiosis and assessing the need to inoculate

Legumes are a major component of all agrarian systems throughout the world. They are particularly attractive to low input systems of agriculture because they take inert nitrogen from the air and (through rhizobia) transform it into proteins in a process that leaves no carbon footprint. But beware, legumes differ in their adaptation to infertile soils, and the right legume must be chosen for each environment. Legumes are many and varied. The grain legumes provide protein-rich food, and soybean and groundnut are also important oilseed crops (Table 1.1). Pasture or fodder legumes are important for livestock feed in various forms: in grazed systems, as feed concentrates made from their grains, or in cut-and-carry systems where animals are kept in stalls. Woody or tree legumes produce a number of useful products apart from poles and construction materials; they are important sources of feed and browse for livestock and several of them produce edible fruits. The other major uses of legumes are for soil fertility improvement, through cover crop protection of the soil from erosion, and as green manures contributing nitrogen to improve soil fertility.