Potential of nine multipurpose tree species to reduce saline groundwater tables in the lower Amu Darya River region of Uzbekistan

Published source details Khamzina A., Lamers J.P.A., Martius C., Worbes M. & Vlek P.L.G. (2006) Potential of nine multipurpose tree species to reduce saline groundwater tables in the lower Amu Darya River region of Uzbekistan. Agroforestry Systems, 68, 151-165.
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Summary

This study investigated the potential of 10 deciduous tree species for creation of plantations on degraded land in the Khorezm region of Uzbekistan, Central Asia. It focussed on their suitability for lowering elevated groundwater tables (biodrainage) to counter salinization of soils that have developed due to evaporation of the shallow saline groundwater tables as a result of loss of natural vegetation, excessive irrigation and poorly maintained drainage systems. Such conditions prevail in many irrigated landscapes in this region.

Study site: The study was conducted in 2003-2004 at the Uzbek Forestry Research Institute Khiva Research Station (41º 41'N, 39º40'E).

Experimental plantations: Plantations, each 500 m apart, were established at two 0.14 ha sites on soil profiles representative of the two major soil textures (a light sandy soil and a more finely textured silt loam). Seeds of the selected tree species were collected locally and seedlings grown for one year at a nearby nursery; 50 saplings of each were then transplanted into plots (two rows of 25-30 trees, spaced 1 m x 3.5 m; six replications per species).

Selected trees: An effort was made to use species which combine a high water use with salinity tolerance, and an ability to produce high quality fodder and firewood to increase farmers' willingness to enter into tree-planting schemes . The 10 species (native and introduced) were: apricot Prunus armeniaca, black poplar Populus nigra var. pyramidalis, black willow Salix nigra, Eastern catalpa Catalpa bignonioides, Euphrates poplar Populus euphratica, Russian olive Elaeagnus angustifolia, salt cedar Tamarix androssowii, Siberian elm Ulmus pumila, swamp ash Fraxinus pennsylvanica and white mulberry Morus alba.

The groundwater table was monitored using four observation wells; in the study years, due to sufficient irrigation water and a high ground water table, the trees at the loamy site only needed occasional watering. At the sandy site the soil moisture remained high and irrigation was only necessary once at the onset of each growing season.

Transpiration rates and leaf area, and biomass production were recorded. Samples of leaves, twigs, stems, and roots were collected (as well as soil) to assess salt concentrations.

The best tree species with regards to their water use, root growth, salinity tolerance and suitability to other environment factors was E.angustifolia followed by U.pumila, P.euphratica and P.nigra (all potential candidates for biodrainage purposes). Additionally, E.angustifolia and U.pumila are N-fixing species, and have superior fodder (nutritious and fast growing) and firewood characteristics, thus providing added value to the farmer (financial returns are considered key to farmers’ uptake of such initiatives), which makes them the most suitable species for biodrainage purposes in this region.

The two typical fruit tree species in the region trialled (P.armeniaca and M.alba) though desirable from a farmers economic viewpoint, showed low biodrainage potential.

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