A nitrogen compound production method includes the step of establishing at least one aquatic plant in a cell containing water and alternating a step of inhibiting photosynthesis inducing light from reaching the at least one aquatic plant and a step of allowing photosynthesis inducing light to reach the at least one aquatic plant. The step of inhibiting photosynthesis inducing light defines a dark phase. A concentration of oxygen is reduced in the water to define an anoxic condition. During the anoxic condition, the at least one plant releases nitrogen compounds into the water and these nitrogen compounds are collected from the water contained in the cell.