Tufted vetch is a member of the family Leguminosae. Plants in this family often have nodules on their roots containing Rhizobium bacteria which 'fix' nitrogen from the air. Plants and animals need nitrogen to build proteins and other important chemials in the body. The air is full of nitrogen, however it is in an inert form that very few organisms can use directly. These bacteria perform a very useful task of converting atmospheric nitrogen into fertilizer for the plants, eventually animals eat the plants and so obtain their nitrogen.Some legumes such as peas and beans are grown as crop plants and they often need less nitrogen fertilizer because they produce their own. Indeed farmers sometimes innoculate the seeds with improved strains of the bacteria which are particularly good at fixing nitrogen. This is generally good for the environment as the production of nitrogen fertilizer in factories is very energy intensive.