Legumes have a mutually beneficial relationship with the bacteria rhizobium. These bacteria infect legume root hairs, forming small nodules near the point of root elongation, or root nodes. These bacteria help remove nitrogen gas from the atmosphere and convert it to a plant-usable form.
This process is referred to as nitrogen fixation. Biologically fixed nitrogen is available to the legume once the roots have been infected and nodulated.
A good way to know if legumes in your pasture are fixing nitrogen is to dig up a plant with roots attached and physically cut open one of the nodules on the root system. If the color inside of the node is pinkish-red, then nitrogen is actively being fixed by the plan
Legumes can help provide a source of nitrogen for grasses in the system through a “give and take” relationship. As legumes are defoliated, either by grazing or mowing, this causes the roots to die back, releasing some nitrogen for surrounding plants.
Above ground legume leaf litter, or leaves that have fallen from plants over time, can degrade and go back to the soil. Grazing animals also recycle nutrients back to the soil while grazing mixed legume-grass pastures, which represents another source of nutrient retur
In other words, nitrogen fixed by forage legumes takes some time to become available to surrounding grass plants in a stand. It is generally recommended that legumes make up at least 30% of the pasture for no nitrogen to be applied. It is important that legume plants are well distributed across the pasture to see a more uniform response.
Annual use of legumes in pastures will help build soil quality, increase plant diversity in pastures and provide a high plane of nutrition in beef cattle grazing systems.
