Interferência de plantas daninhas associadas a restrição hídrica no crescimento inicial do feijão-caupi (Vigna unguiculata (L.) Walp.)

Abstract

The cowpea has a great nutritional and economic importance, especially for the poorest population in the North and Northeast regions of Brazil. This crop is able to produce high yields of grains per hectare, however it can suffer influence of the cultivation conditions, which it is submitted. Thus, the objective of this research was to evaluate the competition effect of Brachiaria plantaginea at different levels of infestation and submitted a periods of water restriction, on the growth and development characteristics of cowpea. The experimental design was completely randomized design, using a 3x2 factorial scheme. The treatments were weed densities (0, 3, 6 plants per pot) and two water regimes (irrigated plants and water restriction period). In the control treatment, the plants were maintained irrigated by 47 days after. The rates of photosynthesis (Pmax), stomatal conductance (gs), internal carbon concentration (Ci), respiration (E), water use efficiency (US), intrinsic water use efficiency (EiUA) and chloroplastidic pigments, evidencing that the lower physiological indexes occurred due to the water restriction. The cowpea MST accumulation was higher when cultivated in the absence of B. plantaginea under irrigated plants regime, on average 7.3 g per plant. The total dry matter of the weeds was higher in the higher planting density, on average 2.3 plants per pot, independent of the water regime. The proline content in the cowpea leaves increased due the presence of three weeds with the water restriction period, possibly by the interspecific competition for water in the V5 phase of cowpea. The enzymatic activity of dismutase superoxide, catalase and ascobate peroxidase was higher in response to the density of three or six weeds, independently of the water regime. Key-words: Competition, B. plantagiena, density of plants, production.