Abstract
Cowpea can obtain N through biological nitrogen fixation (BNF) through symbiosis with rhizobacteria. However, nodulation and BNF are influenced by edaphoclimatic factors that may bring about benefits or damages to the process, and the availability of nutrients is among the main factors that affect BNF and phosphorus (P). Thus, the present study aimed to determine the effectiveness of doses and sources of soluble P on nodulation, accumulation of nutrients, N and P absorption and use efficiency in cowpea plants inoculated with or without rhizobacteria. The experiment was conducted in a greenhouse at the Federal Institute of Education, Science and Technology, Rondônia, Colorado do Oeste-RO Campus, Brazil. The experimental design was randomized blocks in a 5 x 2 x 2 factorial arrangement, corresponding to five P rates (0, 20, 40, 80 and 160 kg ha-1 of P2O5), two soluble sources of P2O5 [single superphosphate (SSP) and thermophosphate], absence and presence of inoculation, with four replication. The findings of this study show that inoculation with Bradyrhizobium sp. promotes increment in the dry matter production and increases N and P absorption efficiency in cowpea plants. The single superphosphate led to higher N and P absorption efficiency, production of shoot dry matter and production of nodules, when compared with thermophosphate. Inoculation with Bradyrhizobium sp. associated with SSP fertilization promotes higher P absorption efficiency in cowpea plants. Therefore, increase in P rates promoted increments in P concentrations in cowpea leaves. Key words: Vigna unguiculata (L.), Bradyrhizobium, phosphorus, fertilization, nutrition.
Highlights
Cowpea [Vigna unguiculata (L.) Walp], known as “feijão-de-corda”, constitutes one of the main leguminous crops cultivated in Brazil, predominantly in the north and northeast regions
The findings of this study show that inoculation with Bradyrhizobium sp. promotes increment in the dry matter production and increases N and P absorption efficiency in cowpea plants
Corroborating the results found in the present study, Zilli et al (2009, 2011) cultivated cowpea under field conditions and in greenhouse, respectively, and observed higher results of shoot dry matter in treatments inoculated with strains recommended for the cowpea crop
Summary
Cowpea [Vigna unguiculata (L.) Walp], known as “feijão-de-corda”, constitutes one of the main leguminous crops cultivated in Brazil, predominantly in the north and northeast regions. The participation of the cowpea crop in the North region in terms of, cultivated area and production is still low, in spite of the fact that, its yield is virtually equal to the national mean. Among the various factors that contribute to the low mean yield of this crop is, management of soil fertility, insufficient supply of nitrogen (N). Nitrogen is the nutrient required in largest amount by the bean crop and mineral fertilization is the main form of N supply to plants. The application of mineral N in tropical soils usually has low recovery efficiency by plants, normally lower than 50%, and may be limited to 5 to 10% in certain situations in sandy soils, due to the great losses through leaching and volatilization (Duque et al, 1985)
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