Abstract
With high protein content, the cowpea is one of the most widely consumed legumes in northeastern Brazil. This study was aimed to evaluate the rhizobia inoculation effect on nitrogen accumulation and nodulation in cowpea subjected to water availability. The experiment was conducted in a greenhouse, in a completely randomized design, with six water availabilities (40%, 60%, 80%, 100%, 120% and 140% of maximum soil water retention capacity), with four replications. Soil moisture maintenance was performed by gravimetric method. The BR3267 strain (Bradyrhizobium japonicum) recommended for cowpea grown in Brazil was used. At thirty-five days after treatments implementation, the nitrogen nutritional status was assessed through SPAD reading, shoot nitrogen concentration and total accumulation. Nodulation was assessed by nodules number and dry matter. The increased water availability provided negative effect on SPAD reading and shoots nitrogen concentration. Shoot nitrogen accumulation was favored to up to 78.8% water availability, with subsequent decline. Nodulation was favored when soil water availability was between 85% and 87%. Water availability affects nodulation and cowpea nutritional status, although negative effects are more pronounced when there is soil water excess.
Highlights
Cowpea (Vigna unguiculata (L.) Walp.) is a rustic species which is well-adapted to tropical regions climate and soil conditions, having high genetic variability, being used in different production systems [1].In Brazil, cowpea bean production is concentrated in the northeastern and northern regions
Soil water availability affected all analyzed variables, confirming that soil water availability interferes with cowpea development
SPAD reading is directly related to plant nutritional status assessment, since there is a positive correlation with leaves nitrogen concentration [6]
Summary
In Brazil, cowpea bean production is concentrated in the northeastern and northern regions. This culture has been cultivated in the midwest region, due to the development of cultivars with features that allow mechanization [2]. When effectively nodulated by efficient strains, it can dispense other nitrogen sources, and through FBN, achieve high productivity levels [4]. According to reference [5], the inoculation of cowpea plants has shown gains in the increase of dry matter, and in total nitrogen and nodulation, confirming the importance of symbiosis between bacteria and cowpea, generating productivity gains. Nodulation and BNF may be influenced by factors that can maximize or minimize the process including soil water availability
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