Abstract
The soybean-Bradyrhizobium symbiosis can be very effective in fixing nitrogen and supply nearly all plant's demand on this nutrient, obviating the need for N-fertilizers. Brazil has been investing in research and use of inoculants for soybean for decades and with the expansion of the crop in African countries, the feasibility of transference of biological nitrogen fixation (BNF) technologies between the continents should be investigated. We evaluated the performance of five strains (four Brazilian and one North American) in the 2013/2014 and 2014/2015 crop seasons in Brazil (four sites) and Mozambique (five sites). The experimental areas were located in relatively similar agro-climatic regions and had soybean nodulating rhizobial population ranging from ≪10 to 2×105 cells g−1 soil. The treatments were: (1) NI, non-inoculated control with no N-fertilizer; (2) NI+N, non-inoculated control with 200kg of N ha−1; and inoculated with (3) Bradyrhizobium japonicum SEMIA 5079; (4) B. diazoefficiens SEMIA 5080; (5) B. elkanii SEMIA 587; (6) B. elkanii SEMIA 5019; (7) B. diazoefficiens USDA 110; (8) SEMIA 5079+5080 (only tested in Brazil). The best inoculation treatments across locations and crop seasons in Brazil were SEMIA 5079+5080, SEMIA 5079 and USDA 110, with average grain yield gains of 4–5% in relation to the non-inoculated treatment. SEMIA 5079, SEMIA 5080, SEMIA 5019 and USDA 110 were the best strains in Mozambique, with average 20–29% grain yield gains over the non-inoculated treatment. Moreover, the four best performing strains in Mozambique resulted in similar or better yields than the non-inoculated+N treatment, confirming the BNF as an alternative to N-fertilizers. The results also confirm the feasibility to transfer soybean inoculation technologies between countries, speeding up the establishment of sustainable cropping systems.
Highlights
Soybean [Glycine max (L.) Merrill] has potential to play a major role in responding to global food insecurity that results from mounting demographic pressures
The experimental sites in Brazil were in four textural classes, Clay, Sandy, Sandy clay loamy and Sandy clay, all of which were represented in Mozambique, apart from Sandy clay (Table 1)
Brazilian soils are originally devoid of rhizobia capable of nodulating soybean, but strain selection programs started early with soybean expansion in the 1960s (Hungria et al, 2006a; Hungria and Mendes, 2015)
Summary
Soybean [Glycine max (L.) Merrill] has potential to play a major role in responding to global food insecurity that results from mounting demographic pressures. Numerous reports testify that when soybean is grown for the first time in new areas outside Southeast Asia, its centre of origin and domestication, it generally requires inoculation with exotic strains (Pulver et al, 1985; Hungria et al, 2006b; Abaidoo et al, 2007; Giller et al, 2011; Hungria and Mendes, 2015). In Africa, where the distribution of inoculants represents another limitation, a strategy consisting in the use of promiscuous soybean genotypes—capable of forming nodules with indigenous rhizobia (Pulver et al, 1985; Abaidoo et al, 2007; Tefera, 2011)—has been used for decades; this strategy would be useful especially for smallholder farmers with no access to inoculants (Mpepereki et al, 2000). With cropping intensification, the search for soybean genotypes with higher yield potential but requiring inoculation is scaling up
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