Abstract

The inoculation with Rhizobium together with nitrogen (N) fertilization during sowing can maximize common bean yield cultivated in the rainy season, but this interaction was not studied in the dry season cultivation. Therefore, the objective of this study was to evaluate the effects of biological nitrogen fixation (BNF) and or N fertilization on growth and yield of common bean cultivated in the dry season. Two experiments were conducted in a randomized block design with four replications. The first experiment, in 2013, had three treatments: F-25 (only fertilized with 20 kg of N ha^-1 at sowing and with 40 kg of N ha^-1 at 25 days after emergence - DAE), I-25 (only inoculated with Rhizobium tropici at sowing and fertilized with 40 kg N ha^-1 at 25 DAE) and IF-25 (inoculated with R. tropici and fertilized with 20 kg N ha^-1 at sowing and with 40 kg N ha^‑1 at 25 DAE). The second experiment, in 2014, had the same three treatments and an additional treatment I (inoculated with R. tropici with no N fertilization). Three plants were collected randomly weekly, for growth analysis, which showed the highest biomass and leaf area accumulation and, consequently, highest grain yield of common bean in the treatment IF-25. The results indicated that in the dry season, the inoculation with Rhizobium tropici might replace the N fertilization (20 kg ha^-1) at sowing without yield loss for common bean cultivation in a low-cost agriculture. Nevertheless, the N fertilization (20 kg ha^-1) together with inoculation with Rhizobium tropici at sowing did not inhibit root nodulation, increasing growth and yield of common bean for a high-cost agriculture. However, more studies are required with other cultivars and sites, to recommend these agronomic practices in the cultivation of common bean in the dry season.

Key words: Inoculation, fertilization, Rhizobium, Phaseolus vulgaris, growth.

Abbreviation

NN, Number of nodules; NDW, nodules dry weight; SDW, shoot dry weight; RDW, root dry weight; NP, number of pods per plant; NGP, number of grains per pod; DW100G, dry weight of 100 grains; GY, grain yield; TDW, total plant dry weight; LAI, leaf area index; CGR, crop growth rate; NAR, net assimilation rate; LSPC, leaf soluble protein content; DAE, days after emergence; BNF, biological nitrogen fixation.