Land degradation, resulting from soil salinisation, sodicity, waterlogging and combinations of these, is a major impediment to land utilisation in many countries with semi-arid and arid climates. These problems, particularly irrigation-induced salinity, have led to the development of unproductive wasteland in Pakistan and India and caused serious declines in crop productivity there and in Thailand. All three countries urgently need to increase the rate of afforestation - to provide fuelwood, timber and forage as well as utilising these salt-affected soils and perhaps ameliorating the problems. However, suitable fast-growing and salt-tolerant species have yet to be identified.

The CSIRO Division of Forestry and Forest Products has been involved in the collection of seed of salt-tolerant trees and shrubs for some years. This project seeks to extend the range of tree and shrub germplasm for saline and saline-sodic soils often subject to seasonal waterlogging and to identify nutritional and other constraints limiting establishment of these soils.

Field trials will establish seedlots as either single-tree or multiple-tree row plots in randomised blocks at 6-7 locations - in Thailand (1-2), Pakistan (4) and Australia (1) - in experimental areas of up to 1 ha. The scientists will sample the soils for nutrient, salinity and physical status, both pre- and post-planting, and will measure tree survival, height and stem diameter at regular intervals. At two locations, they will apply various treatments - such as additions of gypsum and/or fertiliser, mulching and weed control - to determine how these affect establishment and early growth.

These trials should identify the most suitable tree and shrub species for afforestation of different types of salt-affected soils in Thailand, Pakistan and Australia and provide a rational basis for developing large-scale production of those species on saline 'wastelands' and in provincial forests. They will also determine the most suitable cultural techniques for optimising survival and early growth on saline sites to enable such large-scale afforestation, ascertain the categories of salt-affected soils most amenable to it and provide preliminary data on the processes and rates of amelioration of soil salinity by trees.

Glasshouse experiments in Australia will provide some basic information on the nutritional requirements of selected important tree species under non-saline, saline and saline-sodic conditions and characterise the adaptive attributes of native trees to salinity, sodicity and waterlogging. Additional studies on Rhizobium spp. at Queensland University and on Frankia spp. at the CSIRO Division of Soils in Townsville will extend the tolerance of these nodulating symbionts to soil chemical and nutritional stresses and strains. This work should provide more robust inoculum for a range of sites.