The potential for rhizobial inoculation to increase soybean grain yields on acid soils in Ethiopia

Abstract

In Ethiopia, inoculation of soybean with rhizobial inoculants is not common practice, but could provide an option to increase grain yields in low nitrogen (N) acidic soils. In these acid soils, the selection of acid tolerant rhizobia is one strategy that may increase the performance of soybean. In this study, rhizobial strains isolated from Ethiopian soils were evaluated for their acid tolerance and symbiotic N fixation efficiency with soybean, in controlled environments. Following this, four isolated rhizobial strains were evaluated in six field experiments in major soybean growing areas of Ethiopia. Inoculation with the commercial strain or with one of two locally sourced isolates, that were developed as inoculants, improved soybean yield. The yield increase due to inoculation with the commercial strain was consistent and greater than other treatments, while the increase due to the two locally sourced strains was comparable to, or greater than, application of 46 kg N/ha in soils, where the resident rhizobial population was ≤1.4 × 10 3 cfu/g soil. For soils with high background rhizobial populations, there was no response to inoculation. In one of the experimental sites (Bako), the percentage of N fixed (%Ndfa) was 55 for the commercial strain and 35 for the local strain, ES3. This study demonstrated that field validation is a necessary step in the selection of acid-tolerant strains of rhizobia to increase soybean production for Ethiopia.

Microbial inoculants: reviewing the past, discussing the present and previewing an outstanding future for the use of beneficial bacteria in agriculture

“…Because the usually acidic, saline, and low organic matter of the SSA soils, the average soybean yield is usually well below the world average (Thuita et al 2012; Muleta et al 2017). Therefore, in addition to the soybean genetic breeding, further studies have been carried out aiming at increasing yields.…”

“…Therefore, in addition to the soybean genetic breeding, further studies have been carried out aiming at increasing yields. For example, in Ethiopia, Muleta et al (2017) searched for acid-tolerant rhizobia as strategy to increase soybean performance. A local isolate was able to improve soybean yield, indicating that search for indigenous or naturalized elite isolates might represent an interesting strategy to be adopted in other African countries.…”

“…Efforts have also been applied to improve the efficiency of microorganisms already available and in the identification of new elite strains to be used as inoculants under unfavorable and stressful environmental conditions, such as areas frequently experiencing drought, soils with low nutrient availability or with salinity, among others (Benidire et al 2017; Koskey et al 2017; Youseif et al 2017). There is an increasing number of studies aiming to isolate, identify and evaluate the capacity of plant-growth promotion of bacteria with a variety of plant species, with potential to be transformed into new microbial inoculants in a near future (Yanni et al 2016; Koskey et al 2017; Manasa et al 2017; Muleta et al 2017).…”

Plant Growth Promoting Rhizobacterial Biofertilizers for Sustainable Crop Production: The Past, Present, and Future

“…These microbial products are already in use successfully in some countries their use is expected to expand [242]. There is an increasing number of studies aiming to isolate, identify, and evaluate the capacity of PGPR with the potential of being transformed into inoculants for a variety of crops [243][244][245][246]. It is, therefore, reasonable to expect that soon, the extensive use of biofertilizers will offer various strategies for the overall development of sustainable crop production systems [11].…”

Influence of Seed Inoculation with Commercial Bacterial Inoculants (Bradyrhizobium Japonicum) on Growth and Yield of Soybean

“…Rampim et al (2015), in turn, did not show the effect of seed inoculation with symbiotic bacteria on 1000 seed weight and the size of soybean yield. Thuita et al (2012) and Muleta et al (2017) obtained different efficacy of the bacterial inoculants used. In addition, the effect of the bacterial inoculants used was dependent on the type of soil.…”