Persistence and recovery of introduced Rhizobium ten years after inoculation on Leucaena leucocephala grown on an Alfisol in southwestern Nigeria

Abstract

Establishment of Leucaena leucocephala was poor at Ibadan (Transition forest-savanna zone) andFashola (savanna zone, 70 km north of Ibadan) in southwestern Nigeria as a result of low soil fertility and the presence of only a few native rhizobia capable of nodulating it. Inoculation with L. leucocephala at these two locations in 1982 resulted in striking responses with Rhizobiurn strains IRc 1045 and IRc 1050 isolated from L. leucocephala grown in Nigeria. The persistence of inoculated effective Rhizobiurn strains after inoculation is desirable since it removes the need for reinoculation. Because of the perennial nature of L. leucocephala and its use in long-term alley farming experiments, we examined the persistence of inoculated rhizobial strains after inoculation, and their ability to sustain N2-fixation and biomass production at Ibadan. In 1992, ten years after Rhizobium introduction, uninoculated, L. leucocephala fixed about 150 kg N ha -1 yr -~ or about 41% of total plant N compared to 180kg N ha -I yr -~ or 43% measured in 1982. Serological typing of the nodules using the Enzyme-Linked-Immunosorbent Assay (ELISA) and intrinsic resistance to the streptomycin test revealed that most of the nodules (96%) formed on L. leucocephala in 1992 were by Rhizobiurn strains IRc 1045 and IRc 1050, which were inoculated in 1982. Nodules were absent on uninoculated L. Ieucocephala grown on the adjacent field with no history of L. leucocephala cultivation. We conclude that the N 2 fixed by Rhizobium strains IRc 1045 and IRc 1050 persisted for many years in the absence of L. leucocephala and sustained effectively fixed N 2 which growth and yield of L. leucocephala after several years, thus encouraging a possible low-input alley farming system by smallholder farmers in Nigeria.

Persistence of Rhizobium inoculants originating from Leucaena leucocephala fallowed plots in Southwest Nigeria

“…The substantial increase in population and dominance of the introduced Rhizobium strains in the rhizosphere can be attributed to: (i) a non-specific rhizosphere effect indicating that plant roots provide a more favourable environment than soil for rhizobia and other microorganism, and (ii) nodule senescence which encourages rhizobia release and thus increase the population of the appropriate Rhizobium symbiont in the rhizosphere and seed inoculation strategy adopted for this study. This submission aligned correctly with previous observation of earlier investigators (Bushby, 1984;Sanginga et al, 1990Sanginga et al, , 1994.…”

“…The implications of the results obtained in this study were that Rhizobium strains IRC 1045 and IRC 1050 introduced with L. leucocephala seeds were more competitive in the soil environment than the native rhizobia and were detectable in the soil in high numbers as well as being able to effectively nodulate L. leucocephala 10 years after their introduction which agrees with the report of Sanginga et al (1994). Persistence of B. japonicum in a field soil for 2-year fallow period which sustained soybean yields after fallow without further inoculant or fertilizer nitrogen input has been reported by Ranga Rao et al (1982 We conclude that the inoculation of legume seeds with reasonably large population of effective and persistent rhizobial strains constituted an evident advantage over inorganic nitrogen fertilizer which has to be applied frequently for consistent high yields.…”

“…The main value of legumes is in building up soil organic nitrogen to the level that adequate amount can be made available for future crops (Mulongoy and Van der Meersch, 1988). Inoculation with an effective and persistent Rhizobium strain has numerous advantages, which includes nonrepeated application of nitrogen fertilizers (Sanginga et al, 1994). However, for many soil types adequate nodulation and N 2 fixation via Leucaena leucocephala require inoculation with the appropriate and specific Afr.…”

“…Changing environmental conditions and management practices such as pruning and cutting affects the survival of inoculants and legume yields in the field (Sanginga et al, 1990;1994). The selection of adapted inoculant strains and understanding of changes in Rhizobium populations as well as the factors influencing such changes would enhance the integration of L. leucocephala inoculants in the desired low-input farming system.…”

Optimisation of inoculation of Leucaena leucocephala and Acacia mangium with rhizobium under greenhouse conditions

“…Among these species, Acacia mangium and Leucaena leucocephala have shown great ability to grow quickly in marginal lands [6,11,27]. However, in order to ensure optimal exploitation of their economic and agricultural potential, it is necessary to go for inoculation 380 D. Diouf et al using effective symbionts [9].…”