Rhizobia inoculants combined with organic and inorganic fertilizer amendments effects on nitrogen fixation and yields of beans in South Kivu, Democratic Republic of Congo
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In South Kivu Eastern of DR.Congo, most soils are highly weathered, leached and have low nutrients content resulting to low agricultural productivity. The objectives of the study was (i)to evaluate the effect of combining rhizobia inoculation and different fertilizer amendment on biomass and grain yields,(ii) to assess the nitrogen fixation efficacy of commercial rhizobia strains and (iii) to assess the effect of combining rhizobia inoculation and different fertilizer amendments on soil biochemical properties. The study sites were Lwiro in Kabare District and Kamanyola in Walungu District, located in South Kivu province, Eastern DR.Congo, respectively.The experimental design was a randomized complete block design with Rhizobia as a main factor and fertilizer amendment type as a subfactor. Rhizobia strains was applied at three levels; (i) without rhizobia, (ii) with CIAT 899 strains and (iii) with USDA 2667. Fertilizers amendments was a sub factor applied at 6 levels (none, manure, full TSP, TSP split; full NPK and NPK split). At planting the plots with full dose received N, P, and K ar a rate of 30 kg ha-1, 30 kg ha-1 and 25 kg ha-1 o respectively and half of the rate for plots with split dose (i.e. 15 kg ha-1, 15 Kg ha-1 and 12.5 Kg ha-1respectively for N, P, and K) and same amount of fertilizer top dressed just before flowering stage. The test crops were biofortified bush and climbing beans; CODMLB001 and MAC 44 varieties with three replications. Data were subjected to Analysis of Variance (ANOVA) using GENSTAT Version 14. Treatment differences were examined using Least Significant Differences (LSD) Test at P=0.05. Results showed that CIAT 899 rhizobium strain showed high competitiveness up to 259.3 % of symbiotic effectiveness. Treatments with full rates of NPK and manure were the best interactions with rhizobia leading to significant (P=0.05) an increase in soil pH, organic carbon, total nitrogen and available phosphorus by the end of the experimental period. The same treatments led to significant (P=0.05) increase in biomass yields (5.3 Mg ha-1 and 7.6 Mg ha-1, respectively), nitrogen fixation (38.5 and 37%, respectively) and grain yield (2.9 and 4.2 Mg ha-1) respectively for bush and climbing varieties. Combination of Rhizobia inoculants with different fertilizer amendements increased the nutrient status of the soil and equally enhanced the nitrogen fixation ability of the legumes. Based on the findings, combining Rhizobia strains with full dose of N, P, and K at planting and/or with manure was recommended for a sustainable legume production and soil fertility management at both Lwiro and Kamanyola.