Abstract

Water availability is a major limiting factor for cowpea bean crops, especially in semiarid regions, where it is necessary to adopt more productive and tolerant genotypes and efficient strategies for water use. Thus, an experiment was carried under field conditions in the semiarid region of Pombal city, PB, Brazil. Using a completely randomised blocks design experiment and four replications, in a factorial scheme. The first factor was formed by four cowpea beans genotypes (Costela de Vaca, Pingo-de-Ouro, Paulistinha and BRS Marataoã), and the second factor consisted of five different irrigation strategies (40, 60, 80, 100 and 120% of actual evapotranspiration (ETr)). Gas exchange was evaluated at the V4 stage, dry biomatter formation at the R2 stage and crop yield until 90 days after sowing. The gas exchange from cowpea genotypes was reduced by lower irrigation amounts. For dry biomass formation, greater values in the Pingo-de-Ouro genotype were observed when irrigated with 120% of ETr. Thus, the treatment of 120% ETr improved the growth in dry matter independently of the genotype. The Costela de Vaca genotype had better CO₂ assimilation rates. Paulistinha had the highest productivity among genotypes, and Costela de Vaca had the greatest water use efficiency.

Key words: Assimilation rate, Vigna unguiculata, water productivity.