Shrub legumes

• Balai Penelitian Ternak, Indonesia

Many tropical countries use shrub legumes as multi-purpose plants for fodder, living fences, hedges, shade, fuelwood and erosion control and as a source of nitrogen for other crops. In the southern Philippines and eastern Indonesia, the widely adopted alley cropping systems based on shrub legumes are among the few sustainable food production systems. However, shrubs such as Leucaena spp., being adapted to neutral to alkaline soils, do not thrive in the acid soils covering most of the tropics, and new lines are needed. Australia has one of the largest collections of Leucaena germplasm in the world, and a substantial collection of other shrub legumes. An ongoing program with such species is designed to identify elite lines and hybrids for further testing.
This project will seek to identify and provide high-yielding shrub legumes for a wide range of environments in developing countries. It will cover a wide range of species, including selected lines of Leucaena, Acacia, Gliricidia, Calliandra and Sesbania, initially provided from Townsville. Any promising local selections (of any genus) could also be included.
Research will concentrate on three goals: to evaluate the performance of these plants in diverse soil and climatic environments (multi-site testing); to characterise their nutritional requirements and define the soil factors limiting their growth; and to provide and maintain improved genetic resources of shrub legumes.
Multi-site shrub legume trials in progress as part of the Indonesian Forage Research Project, which involves UNE with ADAB support, have already provided substantial evidence of species x site interaction. In cooperation with that group, the ACIAR team will utilise some or all of their present test sites. Planned additional sites established in cooperation with other Indonesian research organisations, and in the Philippines, Thailand, Malaysia and northern Queensland. A total of ten sites is envisaged, covering a range of soil and climatic conditions.
The experiments will relate the performance of various species to chemical and physical characteristics of the sites and will be used to determine the best species for each site, and also to provide more precise selection criteria for future work. Adequate morphological and analytical chemical descriptions of the experimental sites will be prepared in conjunction with soil scientists in the countries concerned.
In characterising the nutritional requirements of the shrub legumes, the team will give priority to identifying the role of factors likely to be involved in soil acidity limitations to plant growth, namely low phosphorus, calcium, magnesium and molybdenum, low soil pH, and aluminium and manganese toxicities. A major aim will be to identify diagnostic criteria, in soil or plant, that can be used to predict the performance of species. Study of these aspects under glasshouse conditions in Brisbane will involve a small range of shrub legumes with known contrasting tolerance to acid soils. Feedback between this work and the multi-site trials will facilitate the future choice of appropriate species and the detailed examination of reasons for the success or failure of any species at a particular site.
The Division of Tropical Crops and Pastures already has considerable genetic resources, with one of the largest collections of Leucaena in the world (700 accessions) and a much smaller one of other shrub legume genera of potential value. These collections, held at the Lansdown Research Station near Townsville, will be used to provide improved genotypes to extend the climatic and edaphic range of the shrub legumes. New accessions will be sought, especially in the Gliricidia and Calliandra genera; these will be described and their seed multiplied. Seed multiplication will also be needed for any promising genotypes identified in the multi-site trials. Testing of the accessions will include monitoring their quality as animal feed to ensure that selected lines are neither toxic nor unpalatable.
The project will especially benefit farmers in marginal areas with low soil fertilityoften the poorest farmers, but will also have wider application throughout the region.