To help meet the country's increasing demand for soybeans for both human and animal food, Indonesia's soybean production has spread to marginal cropping areas. Although there has been an increase in average yield per hectare, the national average remains less than 1 t/ha and the gap between local production and local demand continues to widen. Diversification to new production areas has expanded the research challenge to provide suitable packages to suit the wider range of environmental conditions, especially those of lower rainfall and soils of low pH and nutrient status.
Soybeans are now intimately linked with rice production, providing not only a high-protein break crop in both lowland and upland rice rotations, but one that will potentially contribute nitrogen to the system. When used in association with two rice crops per year in lowland areas, soybean varieties must have short growing periods, thus limiting the time for active nitrogen fixation and the period in which soybean roots and nodules are present as important sources of increased rhizobial activity. Neither the role of rice roots nor the impact of periods of flooding on the population dynamics of free-living rhizobia has been studied in depth.
This project has the objective of increasing nitrogen fixation of soybeans, acting on the hypothesis that the amount of nitrogen fixed by soybeans in the acid soils of West Java and Sumatra is a constraint on yield. It will examine implications for the establishment of an elite strain of Rhizobium, or the maintenance of sufficiently high numbers of indigenous strains to promote maximum nodulation. Specifically, it will address the following hypotheses:
. That the symbiotic compatibility of locally selected high-yielding soybeans is limited by the rhizobia in current use;
. that the use of both nitrogen fertilizer and the multi-strain inoculant reflects the uncertainty of adequate nitrogen fixation;
. that the population dynamics of soybean rhizobia in upland and lowland rice rotations are sufficiently different to affect inoculation strategy; and
. that the method of producing inoculants affects not only the number of rhizobia in the inoculant, but also their subsequent survival on seed.
Because the successful introduction of new legumes in Australia has required simultaneous introduction of their rhizobia, there are many Australian scientists with expertise in the area. The Commissioned Organisation, NSW Agriculture and Fisheries, is doing relevant rhizobial ecological studies at the Horticultural Research and Advisory Station at Gosford. The laboratory has already identified potential acid-soil-tolerant rhizobia strains in vitro for a number of legumes, and techniques required for the field studies are already developed. Laboratory staff at Gosford also played a major role in an earlier ACIAR rhizobial ecological project (8306) involving the growth and survival of rhizobia in inoculants.
Field work will be done in Indonesia, laboratory work in Gosford, and experiments will be shared between Gosford and the Bogor Research Institute for Food Crops (BORIF) as appropriate. Collaboration between BORIF and NSW Agriculture and Fisheries will be organised by regular visits to Indonesia by the Australian project leader. The Indonesian project leader has already visited the Gosford Laboratories to familiarise himself with relevant research methods.
As a result of the project, Indonesia will benefit by the provision of high-quality inoculant, which will be the basis for improving the genetic potential for symbiosis in the field. The strains selected will have a proven capacity for symbiosis with available high-yielding varieties of soybeans, and be capable of nodulating them in acid soils. Increases in yield are likely to be associated with very little increase in costs, and in some cases with a decrease in costs owing to reduced input of nitrogen fertiliser.
Australia will benefit by gaining a better understanding of the reaction of soybean rhizobia with both the host and the environment, and refinements in the technology of producing inoculants in Indonesia will have applicability in Australia and other areas of the region. The studies on the ecology of rhizobia under different rice-management systems will also assist in understanding interactions between introduced and indigenous rhizobia in such rotations, wherever grown.