SEASONAL PATTERNS OF NITRATE REDUCTASE AND NITROGENASE ACTIVITIES IN ARACHIS-HYPOGAEA

The relationship between nitrate reduction and nitrogen fixation of two field-grown peanut (Arachis hypogaea L.) cultivars was investigated throughout the growth season. Leaf nitrate reductase activity declined rapidly post-flowering. In contrast, N fixation activity of root nodules increased post-flowering, reaching a maximum at the end of pod-filling. Nitrogen fixation activity per plant followed the pattern of nodule development. The Virginia type cultivar exhibited higher nitrate reduction and N fixation levels than the Spanish type. The reciprocal relationship of nitrate reduction and N fixation suggests that nitrogen fixation plays a crucial role in N assimilation during the post-flowering stages of peanut plant development.