Response of cowpea (Vigna unguiculata (L.) Walp.) to water deficit during the establishment of nodulation and N-2 fixation

This study evaluates the effect of water deficit during the establishment o f N-2 fixation (N-2 D S) in cowpea and verifies the adaptive physiological response to stress. The experiment was conducted in the greenhouse in rando m blocks with subdivided plots. Each plot containing different stress level s (S-1 = -1.5 KPa, S-2 = -4.0 KPa and S-3= -10.0 KPa), divided in subplots containig different N-2 D S (E-1 = 0-15 days, E-2 = 15-30 days, E-3 = 20-35 days and E-4 = 30-45 days), with four blocks. The soil used was Yellow Lat osol, pH 6.3 and the crop was cowpea cv "IPA 204". Stress was applied by co ntrolling water potential through a porous cup. There was interaction among different N-2 D S and water deficit. The water deficit applied in stage E- 2 was the most negative. Even with high evaporative demand and limited soil water availability cowpea cv "IPA 204" could not induce an extremely low l eaf water potential (psi(w)). The stress applied by porous cup was gradual and the plant recovered its turgescence avoiding deleterious alterations in the cellular metabolism, even upon the most negative psi(m) (matrix potent ial).