Response of Dry Bean to Nitrogen Fertilization and Inoculation with Rhizobium Tropici and Azospirillum Brasiliensis

ABSTRACT

The dry bean (Phaseolus vulgaris L.) has significant economic importance in Brazil and is one of the most important sources of income, especially for small producers. This study aimed to evaluate the response of dry bean to different nitrogen (N) sources, using a completely randomized design, with five replicates. Treatments comprised five N sources [ammonium sulfate [(NH₄)₂SO₄], calcium nitrate [Ca(NO₃)₂], potassium nitrate (KNO₃), ammonium nitrate (NH₄NO₃), and urea] applied at 300 mg kg⁻¹ N plus three additional treatments (inoculation with Rhizobium tropici, inoculation with R. tropici plus Azospirillum brasiliensis, and the control without N and inoculation). The yield components [grain yield (GY), shoot dry weight yield (SDWY), number of pods per pot (NPP), number of grains per pot (NGPt), pod weight (PW), and number of grains per pod (NGP)], and physiological components [water use efficiency (WUE), photosynthetic rate (A), and stomatal conductance (g_s)] were evaluated. Inoculation with R. tropici and R. tropici plus A. brasiliensis did not induce significant effects on yield components when compared to those of the control. (NH₄)₂SO₄ did not change the performance of most quantified yield components, whereas NH₄NO₃ showed increases in GY, SDWY, NPP, NGP, and PW as well as in WUE. KNO₃ and Ca(NO₃)₂ resulted in increased performance of GY, SDWY, NPP, A, and g_s compared to that in the control treatment and the isolated inoculant and its combination with A. brasiliensis. The amide source via urea showed the greatest increase in GY, with 56.5% more than that in the control.

KEYWORDS:

• Phaseolus vulgaris
• nitrogen fertilizers
• Rhizobium tropici
• Azospirillum brasiliensis
• grain yield

Acknowledgments

We thank the Santa Rita Laboratory for soil analysis and the Microbiology Laboratory of Embrapa Soja for the analysis of leaf and grain N concentrations.