Efeitos dos conteúdos de molibdênio da semente no potencial fotossintético das plantas de feijão-caupi cultivadas em solos coesos de baixa fertilidade natural

Abstract

Cowpea plants grown from seeds with high molybdenum (Mo) content are assumed to increase physiological responses and growth when grown in cohesive soils with low natural fertility. The aim of this study was to evaluate the effects of seed Mo contents on photosynthetic nitrogen use efficiency (PNE) and growth of cowpea plants grown in cohesive soil with low natural fertility. Seeds collected from the first harvest of the Guariba cultivar with three Mo contents produced in Viçosa-MG were used. In a factorial scheme, the three Mo contents (0.014 ± 0.005; 0.674 ± 0.151 or 1.987 ± 0.278 µg Mo seed -1) were combined with 0 or 60 kg ha-1 of N. A randomized block design was used, with four replications. Half of the 60 kg ha-1 dose was applied in the planting furrow and half was applied as a top dressing at 15 days after emergence (DAE). The plants were irrigated by drip irrigation to supplement the rainfall. In the R2 phase (beginning of flowering) and from 8:00 to 10:00, the Fv/Fm ratio, gas exchange (photosynthetic assimilation of CO2, Ci/Ca ratio, stomatal conductance, transpiration rate), instantaneous and intrinsic water use efficiency, leaf N content, specific leaf area, photosynthetic efficiency of N use, dry plant mass, harvest index and physiological efficiency were evaluated. With N, Mo contents did not influence photosynthetic assimilation of CO2 on an area or mass basis, EFUN and leaf N content. Without N, the averages of photosynthetic CO2 assimilation on an area basis and mass basis, EFUN and leaf N content of plants originating with 1.987 ± 0.278 µg Mo seed-1 were, respectively, 45.8%, 57.5%, 44.2% and 23.6% higher than those of plants originating with 0.014 ± 0.005 µg Mo seed-1. The results suggest that Mo-rich seeds increase EFUN and plant growth of cowpea plants grown in cohesive soils with low natural fertility when N is not used, but do not influence the harvest index.