This is not correct. Most plants get their N from nitrates or ammonia salts, and only some plants (mostly leguminous ones) use a direct symbiosis with nitrogen

This is not correct. Most plants get their N from nitrates or ammonia salts, and only some plants (mostly leguminous ones) use a direct symbiosis with nitrogen-fixing bacteria to produce these from atmospheric N2. Most of the N in natural ecosystems comes from decay of proteins (from vegetable or animal origin), and in agriculture of course it is added as fertilizer.