Saline Agroforestry: A Hanging Fruit for Saline Waterlogged Ecologies

Abstract

There are different sources of salt accumulation in the soil. The factors responsible for waterlogging in salt-affected soils include heavy rainfall and runoff accumulation, insufficient provision for drainage, faulty practices for management of irrigation water, shallow water table, unlined irrigation system, seepage from the upstream reservoirs and flat to concave land topography. These problems of waterlogging and soil salinity are common world over which have significantly reduced the productivity of lands. The engineering-based reclamation measures are effective for controlling these problems, but their large-scale adoption is constrained due to high investment, annual maintenance cost and problems due to disposal of harmful drainage effluents. Tree plantations have shown lot of potential to control salt-affected waterlogged situations. Different tree species are suitable for enhancing productivity and improvement of such sites by reducing salinity and lowering water table through biodrainage of excess water. Various factors such as type of tree species, tree spacing and method of planting should be considered while designing agroforestry measures for such sites. Tree species selected should develop a full canopy as quickly as possible and have deep roots and tolerance to salinity and waterlogging. Ridge-trench method is the best suited method for planting of trees in saline waterlogged soils. Different tree species have been found suitable for controlling salinity and waterlogging in various regions of the world. In Kenya, Balanites aegyptiaca was the most effective agroforestry tree species in the form of parkland where salinity problems were prominent. Some recommended species for wastewater irrigation in Egypt include Eucalyptus spp., Pinus spp., Populus spp. and Khaya ivorensis. In North America, six halophytes (Atriplex lentiformis, Salicornia bigelovii, Spartina gracilis, Distichlis spicata , Bassia hyssopifolia and Allenrolfea occidentalis) and some salt-tolerant forage species have been suggested for saline-sodic and waterlogged sites. In the USA, Atriplex plantations grown with high salinity water are highly productive. In Pakistan, Eucalyptus camaldulensis was the most appropriate species along with some other local tree species such as Acacia nilotica, Tamarix articulata and A. modesta. Elaeagnus angustifolia with more transpiration rate, tolerance to salinity and good growth was observed as the most potential tree in Uzbekistan. In Iraq, Tamarix plantations have been found most effective. In India, Eucalyptus and bamboo have been found as excellent biodrainers which could control the salinity and waterlogging problems of irrigated agriculture . Some other tree species selected for land reclamation and biodrainage in India are Terminalia arjuna, Casuarina glauca, Syzygium cuminii, Pongamia pinnata, Acacia nilotica, Tamarix troupii and Prosopis juliflora. In China, the tree species selected for land reclamation are Acacia nilotica, Prosopis juliflora, Tamarix troupii and various bamboo (Bambusa) and Eucalyptus species. Eucalyptus camaldulensis is being preferred for improvement of salt-affected soils in Australia. Some most useful pasture species for salt-affected soils in Australia include Thinopyrum ponticum, Puccinellia ciliata , Atriplex undulata and Atriplex lentiformis. In Europe, important species are willow (Salix), ash (Fraxinus), silverberry (Eleagnus), poplar (Populus) and black locust (Robinia). Major benefits accruing due to adoption of agroforestry on salt-affected waterlogged soils are being discussed. The growing of different tree species leads to timber production, fuelwood, fodder and other tree-based products and enhances the income of the farmers adopting agroforestry-based technologies. Biodrainage potential of tree species leads to lowering of water table and reduction in soil salinity. The planned plantation can help achieve optimum water as well as salt balance in saline waterlogged lands through biodrainage. The restoration of degraded salt-affected waterlogged soils under tree cover is also attributed to gradual improvements in their properties. These effects contribute to the productivity enhancement of salt-affected soils. However, saline agroforestry is still a hanging fruit, and its maximum potential can be extracted by adoption of saline agroforestry practices on a landscape scale in saline waterlogged areas.