nitrogen fixation method
Technical term in chemistry and biology for the process or method of converting atmospheric nitrogen into compounds usable by plants.
Leguminous plants perform nitrogen fixation in symbiosis with rhizobia.
窒素固定 refers to nitrogen fixation in general, while 窒素固定法 specifically refers to the method or technique of nitrogen fixation.
Compound of 窒素 (nitrogen) + 固定 (fixation) + 法 (method).