ABSTRACT
Erythrina brucei has been applied as a green manure to improve soil fertility in southern Ethiopia. It has been nodulated by indigenous rhizobia. The objectives of this study were to evaluate the effects of E. brucei inoculation with microbial consortia consisted of Bradyrhizobium shewense, Acinetobacter soli and arbuscular mycorrhizal fungi (AMF)on E.brucei growth, soil nitrogen and phosphorous status after application as a green manure.A field experiment was conducted by inoculating E. Brucei with different microbial consortia. E. brucei inoculated with the microbial consortia were grown for 150 days. Its shoot length was measured at 60, 90, 120 and 150 days after planting. Then, plants were uprooted and mulched as a green manure. The soil nitrogen, available phosphorous and soil organic matter analysis were done. The experimental design was completely randomized block design with eight treatments comprised of three replications. Inoculated treatments did not show a significant (p < 0.05) difference in shoot length in the first 60 days. However, shoot length was increased between 19.1 and 41.3 %, 10.5-43.4 % and 8.7-37.6 %, respectively at 90, 120 and 150 days. The soil organic matter was improved in both inoculated and un-inoculated treatments. The improvements in the soil organic matter of un-inoculated treatments may be due to the decomposition of un-inoculated plants biomass in the soil. The B. shewense inoculation improved the soil nitrogen by 17 %. The soil phosphorous was improved in 57 % of inoculated treatments. The inoculation of E. brucei with microbial consortia enhanced its growth and improved soil fertility when applied as a green manure. Inoculating the green manure legumes with symbiotically effective rhizobia and plant-beneficial microbes can enhance the growth of E. brucei and its nutrient uptake.
ABSTRACT
Grass pea (Lathyrus sativus L.) is widely cultivated for food and feed in some developing countries including Ethiopia. However, due to its overexaggerated neuro-lathyrism alkaloid causing paralysis of limbs, it failed to attract attention of the research community and is one of the most neglected orphan crops in the world. But, the crop is considered an insurance crop by resource-poor farmers due to its strong abiotic stress tolerance and ability to produce high yields when all other crops fail due to unfavorable environmental conditions. This study was aimed at screening rhizobial isolates of grass pea and evaluating their symbiotic nitrogen fixation efficiency and tolerance to abiotic stresses. Fifty rhizobial isolates collected from grass pea nodules were isolated, screened, and characterized based on standard microbiological methods. The rhizobial isolates showed diversity in nodulation, symbiotic nitrogen fixation, and nutrient utilization. The 16S rRNA gene sequencing of 14 rhizobial isolates showed that two of them were identified as Rhizobium leguminosarum and the remaining twelve as Rhizobium species. Based on their overall performance, strains AAUGR-9, AAUGR-11, and AAUGR-14 that performed top and identified as Rhizobium species were recommended for field trials. This study screened and identified effective and competitive rhizobial isolates enriched with high nitrogen-fixing and abiotic stress tolerant traits, which contributes much to the application of microbial inoculants as alternative to chemical fertilizers.
