Site suitability and tolerance limits of trees, shrubs and grasses on sodic soils of Ganga-Yamuna Doab.
An evaluation of the soil and vegetation (both natural and planted) was carried out at 20 representative sodic sites in Aligarh, Mathura, Agra and Mainpuri Social Forestry Divisions, Uttar Pradesh, in 1989. One-year-old nursery stock of 8 tree species (Prosopis juliflora, Acacia nilotica, Butea monosperma, Terminalia arjuna, Azadirachta indica, Pongamia pinnata, Dalbergia sissoo and Albizia lebbek [A. lebbeck]) had been planted at the site in 1955, in 0.6×0.6×0.6 m pits at 3×4.5 m spacing. Prosopis juliflora, Acacia leucophloea, Tamarix sp., Sporobolus marginatus, Desmostachya bipinnata and Diplachne fusca grew on sodic soils with average values of pH<10, ESP (exchangeable sodium percentage) <60, ECe (electrolytic conductivity) <4 dS/m, CaCO3<10%, and compact and indurated kankar (CaCO3)/clay pan present beyond 1 m soil depth under rainfed conditions. Higher sodicity levels and kankar pan within 1 m soil depth caused failure of vegetation. Acacia nilotica, Capparis zeylanica, Crotalaria medicaginea and Cynodon dactylon grew successfully on soils with maximum values of pH 9.5, ESP 50, ECe 4 dS/m and CaCO3 5% under conditions of a deep groundwater table and absence of compact and indurated kankar pan in the subsoil. Mixed forest species (Terminalia arjuna, Azadirachta indica, Pongamia pinnata, Dalbergia sissoo, Albizia lebbeck, Butea monosperma, Phoenix sp., Calotropis procera, Prosopis cineraria, Cryptostegia grandiflora, Capparis decidua, Salvadora oleoides, Zizyphus mauritiana [Ziziphus mauritiana], Adhatoda vasica and Saccharum spontaneum) grew well on soils with lower sodicity (pH<9, ESP<35, ECe<4 dS/m) and absence of clay kankar pan throughout the root zone (20-140 cm depth).