ABSTRACT
Knowledge of the responses of bean plants as a function of N fertilization or seed inoculation with rhizobia can direct crops to different market niches in different technological levels. The roots nodulation and the yield grains of 10 bean cultivars on nitrogen fertilization and seed inoculation with Rhizobium freirei were evaluated aiming to identify, in terms of grain yield, the more efficient and responsive to nitrogen fertilization, as well to symbiotic N fixation in relation to N fertilization. Two experiments were conducted in two seasons (the 2012 dry season and the 2012/2013 rainy season) using a randomized block design in a 10 × 3 factorial arrangement with four replications. We evaluated the amount and mass of root nodules and grain yield of 10 common bean cultivars in the black marketing-group (IPR Gralha, IPR Tuiuiú, Rio Tibagi, BRS Esplendor, and IPR Uirapuru) and the carioca (beige with brown stripes) marketing-group (IPR Tangará, Iapar 81, IPR Campos Gerais, BRS Pontal, and Carioca) with three treatments with variations in N nutritional levels: control, without N; with N fertilization; and seed inoculation with R. freirei. Beans of the carioca commercial group are higher yielding and, regardless of nodulation with native or exogenous rhizobia, are more prone to symbiotic nitrogen nutrition. Nitrogen fertilization is especially harmful to nodulation of BRS Esplendor, Carioca, and BRS Pontal at lower water availability. In terms of grain yield, the cultivars Rio Tibagi, BRS Esplendor, BRS Pontal, and IPR Uirapuru are relatively more efficient with seed inoculation with R. freirei than with N fertilization, and the cultivars IPR Tangará and IPR Gralha stand out as responsive and efficient in respect to N fertilization.
Phaseolus vulgaris L.; urea; biological nitrogen fixation
