Sustainable agriculture in saline environments through serial biological concentration

• Pakistan Agricultural Research Council, Pakistan
• CSIRO Land and Water, Australia

The combination of irrigation-based agriculture and arid climates in parts of Pakistan and Australia has seen an unintended consequence - salinity. This is caused when naturally occurring salt, found in soil, is mobilised by rising water tables. The resulting discharge into top soils results in agricultural management for salt drainage or reduction, rather than production. Without this approach, however, either through saline effluent drainage, use of salt tolerant species or effective evaporation, the land becomes unproductive. Drainage can cause negative impacts to downstream users, shifting the problem rather than alleviating it. Evaporation also has drawbacks, working best for small quantities of water only. Discontinuing irrigation will not remove existing salt, nor ensure the continued agricultural viability of the land. Options for disposing of saline effluent, by rivers or through conjunctive groundwater processes are often difficult.

Combining options, releasing some saline effluent and capturing the heaviest salt load in a small quantity of effluent then diverted to an evaporation basin, is the best approach. Achieving this, in conjunction with existing and new measures can greatly increase the agricultural versatility of the affected land. Serial biological concentration (SBC) systems can play a central role in achieving this. The system is based on the continued reuse of saline effluent, flushing it through a series of biological chains. Each chain concentrates the effluent further by significantly reducing the volume of water but not the salt content. Effluent is cascaded through the chains, made up of plants and crops, until the heavily salted remainder is directed to an evaporation basin. Water use is maximised but saline residues in the soil reduced. Salt harvesting and the use of salt tolerant agriculture (for instance aquaculture of tolerant fish) offer potential income. SBC is already under trail in Australia at two locations in the Murray Darling Basin; part of a total approach to salinity management.

Proving the concept of SBC in appropriate areas of Pakistan for its incorporation into existing salinity management systems is underway in this project.

Proof of concept in Pakistan will be based on the installation of tile drainage systems, including field layout and drainage infrastructure at the two field sites. Site selection will be based on feasibility testing, with crop selection based on local knowledge of best bets and trialling of alternative options. Monitoring and data collection will be done through the National Agriculture Research Centre, with analysis shared with CSIRO. Economic assessments will be done by financial modelling. The combined analysis of scientific and financial data will inform analysis and the development of an analytical framework, resulting in economic and hydrological based guidelines for options selection at the farm level in the Murray Darling Basin.