Potential for Cultivating Various Legume Species in Controlled Environment Agriculture

Legumes are among the most important plants capable of biological nitrogen fixation. However, there is a significant knowledge gap regarding the specifics of cultivating legumes in hydroponic systems under controlled environment conditions, particularly nitrogen metabolism at different growth stages, which this study addressed. Chickpeas, faba beans, lentils, soybeans, and sugar peas were cultivated in deep-water hydroponics without rhizobia, with a nutrient solution as the nitrogen source. The legumes displayed significant variations in growth patterns and nitrogen dynamics. Among them, soybeans had the longest growth cycle, characterised by extended vegetative and early reproductive phases, while sugar peas developed the fastest. In all species, nitrate was the dominant form of nitrogen found in the roots, stems, and leaves, followed by ammonium (NH3–N) and nitrite (NO2−). The levels of NH3–N varied among species, peaking early in faba beans and later in chickpeas. NO2− concentrations were low and decreased with development. The activities of nitrate reductase and nitrite reductase also varied across species, plant organs, and growth stages. The highest enzyme activity was consistently observed in the leaves. Notably, peas exhibited high enzyme activity across all organs, while the leaves of soybeans showed the highest activity in the studied legumes.