Perspectives on reviving waterlogged and saline soils through plantation forestry

Land degradation with water-logging and salinity is global problem especially in arid and semiarid regions. As an alternative for capital-intensive engineering approaches, plantation forestry has been advocated as an eco-friendly option to offset hydrological imbalances (bio-drainage) mainly for dryland salinity conditions. With robust monitoring world over, reforestation mainly with fast growing versatile Eucalyptus species have emerged as the most water profligate. These lower the water-table by extracting soil water throughout the year and even from deeper soil and phreatic zones. The annual evapo-transpiration of plantations vary from about 0.2 to 0.8 times OPE (Open Pan Evaporation) under dryland conditions and can equal or even exceed OPE under irrigated conditions. The factors like soil and climatic conditions, groundwater depth and its quality, growth rates of tree species; their stocking, patterns and the geometries and fraction of area under plantations define their effectiveness for water table draw-down and salinity control. Nevertheless, the emerging arguments against biomanagement include long time-lag, high land requirements and decline in their efficiency with salinity build-up underneath plantations. To overcome these constraints, shifting plantations in between discharge and recharge areas, reforestation with salt-tolerant species, integrating these with cropping systems and even with engineering measures in saline discharge areas are the alternate options. The gainful employment of bio-drainage demands the diagnosis of typical areas to be reforested in catchments using GIS/remote sensing tools, the development of decision support systems (DSS) for appropriate designing of reforestation strategies and their amalgamation with existing farming systems. Benefits of plantations beyond on-and off-site salinity control should aim at enhanced farm incomes, restoring biodiversity and particularly carbon trading when global interests are now targeting climate mitigation.