https://practicalplants.org/An open encyclopedia of useful plants and how they grow.en https://practicalplants.org/articles/nitrogen-fixer/https://practicalplants.org/articles/nitrogen-fixer/is a function performed by some plants, most notably in the family Fabaceae, whereby they can convert atmospheric nitrogen into the form of nitrogen usable by the plant as a nutrient. This nitrogen is provided to the soil through leaf fall, root cycles, or when the plant dies and decays. https://practicalplants.org/articles/plant-association/https://practicalplants.org/articles/plant-association/A term used to describe the interaction of two plants. Associations are the fundamental principle behind a successful polyculture. https://practicalplants.org/articles/polyculture/https://practicalplants.org/articles/polyculture/The practice of interplanting a range of species according to their ability to co-exist or benefit one another spatially, temporally, nutritionally or environmentally. Polycultures are able to be a nutritionally self sustaining and provide crop redundancy, but have traditionally failed to convert to modern mechanised systems of agriculture, a contributing factor to the dominance of monocultures in modern agriculture. https://practicalplants.org/articles/use/https://practicalplants.org/articles/use/A use is the function a plant or part of a plant performs after harvest. https://practicalplants.org/articles/what-is-a-practical-plant/https://practicalplants.org/articles/what-is-a-practical-plant/Simply put: A plant which is cultivated to be used or perform a useful function, whether edible, medicinal or material.