Substitution of chemical fertilizer nitrogen through Rhizobium inoculation technology

Nitrogen is one of the most essential elements for plants growth and development. Urea is commonly used as a substitute for chemical nitrogen. Rhizobium inoculation technology for legume crop was evaluated in a number of field experiments comparing with 80kg urea per hectare application. The inoculation and urea application trial showed almost similar biomass accumulation, nodule number and nodule dry weight compared to un-inoculated control. The symbiotic effectiveness with inoculated and urea application showed similar results. The inoculant strains isolated locally from Mucuna pruriens (velvet bean) were found suitable for inoculants production. The bio-technology of inoculation can be a promising and cheap alternative of urea for the legume crops.

Helping plants get more nitrogen from the air

Plants cannot themselves obtain their nitrogen from the air but rely mainly on the supply of combined nitrogen in the form of ammonia, or nitrates, resulting from nitrogen fixation by free-living bacteria in the soil or bacteria living symbiotically in nodules on the roots of legumes. Increased crop yields in the twentieth century required this biological nitrogen fixation to be supplemented increasingly by the use of fixed nitrogen from chemical fertilizers. The development of the Haber–Bosch process for catalytically combining atmospheric nitrogen with hydrogen from fossil fuels to produce ammonia enabled increased crop yields. However, energy and environmental concerns arising from the overuse of nitrogenous fertilizers have highlighted the need for plants to obtain more of their nitrogen from the air by biological nitrogen fixation. New systems are being developed for increased biological nitrogen fixation with cereals and other non-legumes by establishing nitrogen-fixing bacteria within their roots. This new inoculation technology is aimed at significantly reducing the use of synthetic nitrogenous fertilizers in world agriculture.

Bioremediation of agricultural and forestry soils with symbiotic microorganisms

Symbiotic micro-organisms are important in alleviating the limitations of nitrogen and phosphorus deficiency on plant growth in Australian soils. Maximization of the contribution of these micro-organisms can give important benefits for plant production. In some cases, optimization of the infectivity of the target organisms will be achieved most effectively through changing soil management stratregies. In soils where the infective organisms are absent, or where the indigenous isolates are not effective, inoculation with selected isolates may be appropriate. Adoption of inoculation technology depends on a well defined benefit and a reliable source of high quality inoculum at a cost which is appropriate for the overall cost structure and returns of the industry. Further, inoculation should not require additional complex technology or machinery and should fit easily into existing processes of production. Inoculation with rhizobia in legume production meets these criteria and consequently is widely used. By contrast, inoculation with VA or ectomycorrhizal fungi still only occurs on a small scale, in part due to practical difficulties of inoculum production but also due to the limited number of situations where the benefits of inoculation can be clearly demonstrated.

Competition for nodule occupancy of introduced Bradyrhizobium japonicum strain SMGS1 in French soils already containing Bradyrhizobium japonicum strain G49

The competitiveness of Bradyrhizobium japonicum strains G49 and SMGS1 was first studied in the greenhouse in sterilized sand, with or without added soil. Strain SMGS1 was more competitive than strain G49 with soybean (Glycine max L.) cultivar Labrador but the two strains showed equivalent competitiveness with cultivar Kingsoy. When soil was added, nodule occupancy of strain G49 was only 22% with this cultivar. In field experiments, conducted over 2 years in soils already containing strain G49 (1.5 × 103 to 4.0 × 104 cells/g of soil), nodule occupancy of inoculated strain SMGS1 ranged from 20 to 90%. Nodule occupancy was 3–22% higher when inoculation was done by peat seed coating or with liquid inoculation in the row than with peat-coated clay microgranulars. Nodule occupancy was also dependent on the physiological state of the inoculated cells. When an inoculum stored at 28 °C for 1 year was used at the same viable cell rate, nodule occupancy of strain SMGS1 was 4–20% lower than with a recently made inoculum. Pot experiments with soil from field experiments carried out in the 1st year showed that the inoculated strain continued forming nodules without further inoculation, with a recovery rate equivalent to that of field experiment in the previous year.Key words: Bradyrhizobium japonicum, interstrain competition, inoculation technology, ELISA, field trials.