Microbial bio-fertilisers for sustainable and environmentally sound crop production in Vietnam and Australia

• Vietnam National University, Vietnam
• University of Western Sydney, Australia
• Centre for Application of Molecular Biology to International Agriculture, Australia

Using nitrogen-fixing legumes to enrich soil is an important agricultural tool, but in many Asian countries there is a reluctance to use legumes in rotation because of the consequent lower yields of crops in the short term. Biofertilisation, which involves inoculating plants or plant biomass with cultures of microbes selected for their nitrogen-fixing and other abilities, offers a promising alternative to legumes. This small project sought to confirm yield improvements that had been reported for a biofertiliser produced in Vietnam. In addition, the composition of the biofertiliser was analysed in Australia in order to understand more about the mechanisms responsible for the reported yield improvement.

The main objectives of the project were:
to assess the practical effectiveness and economic value of the pilot biofertiliser for rice and vegetables;
to obtain preliminary information regarding the mechanism of any yield increases from use of biofertiliser and to assess opportunities for other applications of microorganisms as biofertilisers to obtain nutritional or other benefits in Vietnam;
to assess the potential for application of such biofertilisers in Australia, comparing cultures obtained from Vietnam with similar inoculants available in Australia.

The project scientists conducted several field and laboratory experiments. The research methods involved activity in both Vietnam and Australia. Operations in Hanoi involved sowing and harvesting of two field trials, using the Vietnamese inoculant biofertiliser. The field data on vegetative growth and grain yield were collated and subjected to statistical assessment. Field trials involving local farmer groups were also conducted on Vietnamese farms.
Additional work at the University of Sydney involved identification of the inoculant microorganisms used in the biofertiliser. Trials were conducted in growth cabinets and in the greenhouse to investigate the mechanism of their effectiveness.

Research results were encouraging, although a cautionary result was obtained in one field trial. Confirmation was obtained that the microbial strains used in combination in the product have positive effects on the vegetative growth rate and the yield of rice. Yield increases were also demonstrated in a large number of farmer trials, where half a rice farm was treated with a recommended rate of biofertiliser plus a 50 per cent urea application then compared to the other half of the farm that was treated with the normal rate of urea.
In a large number of these farmer trials, yields of about 115 per cent on average were obtained when biofertiliser was applied. Such yields, if consistently obtained, would have clear potential to reduce input costs for farmers, improve total grain yield and possibly provide other benefits.
A similar yield increase from the application of biofertiliser was confirmed in one field trial using a split plot design. The results indicated that lower rates of inoculant biofertiliser would have been sufficient. However, a second trial at a different site using a different rice cultivar with lower rates of biofertiliser application actually showed a slightly negative effect with respect to the rate of biofertiliser application, coupled with a classical positive response to the rate of urea application.
This result in a single trial is not considered surprising. There are other factors involved in delivering an effective result. The biofertiliser product must meet certain quality criteria, and these are currently imperfectly met. Sufficiently high numbers of the most effective microbial strains must be present at inoculation, and in a viable form. Since non-sterile media are used, growth of the correct strain may not always be achieved. Such a cautionary result is not without benefits. Indeed, it justifies the decision to conduct a follow-up AusAID CARD project, focused on quality control of the biofertiliser product.
Laboratory research carried out in Australia has provided support for the efficacy of the biofertiliser product. Field trials in Australia using these Vietnamese strains will require permission from AQIS, which was not possible while questions about their taxonomic identity remained. Identification of the species involved using both nutritional and genetic approaches (PCR and 16s-r-DNA sequencing) now indicates that the three bacterial species (2N, 3C, 4P) selected from the rice rhizosphere for use in the biofertiliser are soil organisms potentially beneficial to the growth of non-leguminous plants. These identifications dispel concerns that the strains might be pathogenic on plants (or humans) and their physiological properties - such as nitrogen fixation, phosphorus solubilisation and phytohormonal effects stimulating plant root growth - are consistent with possible benefits.
All these effects have been observed in laboratory trials. In combination with local Azospirillum and Herbaspirillum strains, the strain known as the 'companion strain' (3C) has stimulated the yield of wheat grown in a typical Australian rice soil not amended with nitrogen or phosphorus fertiliser.