New rhizobial strains for velvet bean (Stizolobium aterrimum) evaluated under greenhouse and field conditions

Ítalo Augusto Férrer Melo Santos,Giselle Gomes Monteiro Fracetto,Adeneide Candido Galdino,Mario De Andrade Lira Junior,Felipe José Cury Fracetto

doi:10.1590/1413-70542017414012917

Ítalo Augusto Férrer Melo Santos, Giselle Gomes Monteiro Fracetto + Show 3 more

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https://doi.org/10.1590/1413-70542017414012917

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Abstract

ABSTRACT The selection of efficient rhizobia for the inoculation of velvet bean may increase the use of this plant as green manure, maximizing the addition of nitrogen (N) to the crop. This study aimed to select rhizobia that nodulate velvet bean more efficiently than do strains currently recommended and for the potential of rhizobia to compose an inoculant. A greenhouse experiment evaluated 39 strains using non-sterile soil and was followed by a field experiment with the five most effective strains under field conditions on a dystrocohesive Yellow Argisol. Both experiments included non-inoculated and inoculated treatments with currently recommended strains and N-fertilized controls. Nodules, root and shoot dry mass, shoot N concentration and accumulation and relative efficiency were evaluated. The N dose corresponding to the shoot dry mass increase of the inoculated plants was also estimated. Under field conditions, the plants inoculated with the strains T2.19A and T1.17M had a shoot N concentration similar to that from the application of 80 kg ha-1 N, and the N concentration was significantly higher that of the other treatments; additionally, the N accumulation was significantly higher than that of the control (112 and 104% for the two strains, respectively), the recommended strain mixture inoculation (99 and 91%, respectively) and the mineral N application (58 and 52%, respectively). Inoculation with T2.19A and T1.17M presented promising results, showing the potential of these strains for recommendation and inoculation of velvet bean.

Highlights

Green manuring with legumes improves soil quality and increases available nitrogen by biological nitrogen fixation (BNF) through the symbiotic relationship between rhizobia and legumes
In addition to these treatments, we adopted the following treatments as controls: I-inoculation with the mixture of two strains recommended by the Ministério da Agricultura Pecuária e Abastecimento (MAPA) -Brazil for velvet bean, Bradyrhizobium spp. (SEMIA6156) and Bradyrhizobium elkanii (SEMIA 6158); III-four nitrogen fertilizations (60, 120, 180 and 240 kg N ha-1); and IV-noninoculated and non-fertilized control treatments
Velvet bean plants responded to increasing N doses in accordance with a quadratic regression (r2=0.94) (Figure 1), with a maximum shoot dry mass (SDM) of 4.28 g plant-1 with 160 kg N ha-1

Summary

Introduction

Green manuring with legumes improves soil quality and increases available nitrogen by biological nitrogen fixation (BNF) through the symbiotic relationship between rhizobia and legumes. Velvet bean (Stizolobium aterrimum) is recommended for green manuring of several crops due to the high biomass productivity and potential for nitrogen fixation under tropical conditions (Ambrosano et al, 2011, 2013; Andrade Neto et al, 2010; Queiroz et al, 2010; Zaccheo et al, 2016). Experiments indicate the shoot dry mass yield is between 6 and 9 Mg ha-1, resulting in up to 350 kg biologically fixed N ha-1 per crop (Formentini, 2008), but there is large variation depending on the soil and climatic conditions (Barros; Gomide; Carvalho, 2013). To inoculate with more efficient rhizobia, it is important to adjust the acidity and soil fertility to favor symbiosis, which increases BNF (Amado; Mielniczuk; Aita, 2002)

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