The main objective of this research is to compare estimates of technical efficiency obtained from the stochastic frontier approach for two samples of farmers of private and water user associations in the Nefzaoua Oases region (Tunisia), which are characterized by a severe scarcity of water and especially a high degree of salinity. Technical inefficiency effects are modeled as a function of farm-specific socioeconomic factors. Results suggest that both systems are technically inefficient. On average, the private system is found to be slightly more efficient than the associative one. Date yield could be explained mainly by four variables: water quantity applied per palm tree, labor per palm tree, phosphate per palm tree, and water salinity. Output elasticities of all inputs are found to be positive and significant except for the farmyard manure. Water salinity has a considerable negative impact on date productivity. For the technical inefficiency model, none of the socioeconomic variables seem to matter.

Reclamation of saline lands seems difficult for climatic and economic reasons, but cultivation of salt-tolerant plants is an approach to increasing productivity and improvement of salt-affected wastelands. A five-year field study was conducted to evaluate the effects of growing a salt-tolerant species Leptochloa fusca (L.) Kunth (kallar grass) on chemical properties of a saline sodic soil irrigated with poor quality groundwater. Soil salinity, sodicity and pH decreased exponentially by growing kallar grass as a result of leaching of salts from surface (0–20 cm) to lower depths (>100 cm). Concentrations of soluble cations (Na+, K+, Ca2+ and Mg2+) and anions (Cl−, SO42− and HCO3−) were reduced through to greater soil depths. A significant decline in soil pH was attributed to release of CO2 by grass roots and solublization of CaCO3. Both soil salinity and soil pH were significantly correlated with Na+, Ca2+, Mg2+, K+, Cl−, HCO3− and sodium adsorption ratio (SAR). Significant correlations were found between soluble cations (Na+, Ca2+ and K+), soluble anions (Cl−, SO42− and HCO3−) and the SAR. In contrast, there were negative correlations between soil organic matter content and all chemical properties. The ameliorative effects on the soil chemical environment were pronounced after three years of growing kallar grass. Cultivation of kallar grass enhanced leaching and interactions among soil chemical properties and thus restored soil fertility. The soil maintained the improved characteristics with further growth of the grass up to five years suggesting that growing salt-tolerant plants is a sustainable approach to biological amelioration of saline wastelands.

Salt lakes are geographically widespread, numerous and a significant part of the world's inland aquatic ecosystems. They are important natural assets with considerable aesthetic, cultural, economic, recreational, scientific, conservation and ecological values. Some features, notably the composition of the biota, uniquely distinguish them from other aquatic ecosystems. The paper reviews the nature of environmental impacts and their effects upon salt lakes. Its aims are two-fold: to draw attention to the extensive damage that salt lakes have now undergone, and to indicate the likely status of salt lakes in 2025. Salt lakes develop as the termini of inland drainage basins where hydrological inputs and outputs are balanced. These conditions occur in arid and semi-arid regions (approximately one-third of total world land area). Many human activities threaten or have already impacted salt lakes, especially surface inflow diversions, salinization and other catchment activities, mining, pollution, biological disturbances (e.g. introduction of exotic species), and anthropogenically-induced climatic and atmospheric changes. The effects of such activities are always adverse and include changes to the natural character of salt lakes, loss of biodiversity and fundamental limnological changes. The effects are geographically widespread, mostly irreversible, and degrade the values of salt lakes. Four salt lakes are discussed, namely the Aral Sea in central Asia, Mono Lake in California, USA, and Lake Eyre and Lake Cantara South, in Australia. By 2025, most natural salt lakes will have undergone some adverse change. Many permanent ones will have decreased in size and increased in salinity, and many unnatural saline water-bodies will have appeared. In certain regions, many seasonally-filled salt lakes are likely to be drier for longer periods. The extent to which episodically-filled salt lakes will change by 2025 will largely depend upon the nature of climate change in arid regions. Objective cost/benefit analyses of adversely affecting salt lakes are rare, and international bodies have not properly recognized salt lakes as important inland aquatic ecosystems. To redress this situation, there is a need to raise awareness of: (1) the values of salt lakes, (2) the nature of threats and impacts from human activities, and (3) their special management requirements. More effective management and conservation measures need to be implemented. Mono Lake provides an example of what can be achieved in the conservation of salt lakes. Its conservation was largely brought about by (1) the commitment of a non-governmental organization which recognized its non-economic values, (2) the freedom to express views, (3) a legal system which took account of non-economic values, and (4) a legislature which implemented judicial findings. The conservation of Mono Lake was difficult; the conservation of other salt lakes is likely to be even more difficult. Only international pressure from appropriate organizations will be effective for the conservation of many.

Brackish water ponds for farming black tiger shrimp (Penaeus monodon) have recently proliferated in inland areas of Thailand's central plain, raising concerns about land and water salinization. The environmental impacts of inland shrimp farming were assessed by analysing the salt balance for an inland shrimp farm. Field data on water fluxes and pond salinity, collected from nine ponds in Chachoengsao Province from May–July 1999, were used to model the salt balance for a typical shrimp pond over one growout cycle. During growout, seepage represented 38% (11.5 tonnes crop−1) of salt losses, pond discharge 33% (9.7 tonnes crop−1), and accumulation of salt in pond sediment 6% (1.8 tonnes crop−1). About 23% of the initial salt content remained at harvest and could have been recycled. However, the majority (84% on average) was discharged to the irrigation canals. Much of the salt in pond sediment was also exported to the canal system through tidal flushing of the ponds. Field measurements of salinity were taken in adjacent canals and rice paddies to explore the impacts of salt exports from shrimp ponds. Pond discharge caused increases in canal salinity above levels that would impact on yields of irrigated rice and orchard crops, the main land uses in the region. Elevated soil and water salinity in adjacent rice fields was probably related to lateral seepage from the ponds. The salt budget was also modelled for a zero discharge farming system, promoted by proponents of inland shrimp farming as having few impacts. However, the results suggest that, even in zero discharge ponds, almost half of the initial pond salt content is exported through seepage (45%, 12.4 tonnes crop−1), with another 6% (1.8 tonnes crop−1) deposited in sediments. While techniques exist for mitigating much of the salt leakage, the likelihood of their uptake in Thailand is low. Further expansion of inland shrimp farming in the central plain is therefore likely to contribute substantial salt load to the area's land and water resources.