Combined inoculation of rhizobia on the cowpea development in the soil of Cerrado

Éder Rodrigues Batista,Edna Maria Bonfim-Silva,Salomão Lima Guimarães,Analy Castilho Polizel De Souza

doi:10.5935/1806-6690.20170087

Abstract

BBiological nitrogen fixation (BNF) plays an important role in the cowpea cultivation. This study aimed to assess the foliar levels of chlorophyll and the yield components of cowpea subjected to combined inoculation of rhizobia in Cerrado soil. The experiment was carried out in field conditions, from December of 2014 to the march of 2015, in Rondonopolis, Mato Grosso, using randomized block design with ten treatments and three replicates. Were tested the single strains MT8 and MT15 (both of R. tropici), MT16 (R. leguminosarum), BR3267 (Bradyrhizobium japonicum), the strains combinations MT8+MT15, MT8+MT16, MT15+MT16, and MT8+MT15+MT16, nitrogen fertilization (70 kg ha-1 of N-urea), and absolute control (without inoculation of rhizobia and without nitrogen fertilization). Data were subjected to analysis of variance and the averages were compared by orthogonal contrast and F test (p≤0.05). Were assessed the Falker chlorophyll index (at the 40 and 60 days after sowing), number and dry matter of nodules (at the 40 days after sowing), number of pods per plant, grains yield, the concentration and accumulation of nitrogen in grains, and crude protein. The number of pods per plant was increased 33.6% in the combination MT8+MT15. The same effect was observed for the yield grain, which presented an increase of 8.7%, 13.8%, and 16.7% in the combinations MT8+MT16, MT15+MT16, and MT8+MT15, respectively. The nitrogen accumulation in the grains increased 42.7% with the inoculation of MT15 strain. The cowpea responds positively to the usage of combinations of rhizobia strains.

Highlights

In Brazil, cowpea is cultivated in an area of 1.3 million ha in North, Northeast, and Central-West regions, with a total production of 482,000 tons yr-1 (RUFINI et al, 2014)
This study aimed to assess the foliar levels of chlorophyll and the yield components of cowpea subjected to combined inoculation of rhizobia in Cerrado soil
According to Crusciol et al (2007), values between 30-50 g kg-1 indicates a satisfactory nutritional status of the plants, and shows the cowpea plants presented an adequate amount of nitrogen at the leaves. This indicates the effectiveness of the rhizobia strains, and reinforces the positive correlation between chlorophyll index (Falker) and the nitrogen content in the plant tissues as an indicator of the nutritional state of plants (MORAIS; FONTES; GONÇALVES, 2013)

Summary

Introduction

In Brazil, cowpea is cultivated in an area of 1.3 million ha in North, Northeast, and Central-West regions, with a total production of 482,000 tons yr-1 (RUFINI et al, 2014). This crop plays an important role in the feed of the most of the population at those regions, supplying the daily demand of vitamins, minerals, and proteins (FRIGO et al, 2014). Brazilian farmers can use four strains recommended by Ministry of Agriculture, Livestock and Supply belonging to the genus Bradyrhizobium. Cowpea is able to form, promiscuously, symbiosis with diverse rhizobia strains and, limiting the commercial use of inoculants (ZILLI et al, 2006)

Objectives

Methods

Results