SALT AFFECTED SOILS, THEIR AFFORESTATION AND ITS AMELIORATING INFLUENCE

Abstract

Field experiments since 1979 showed the principal constraints on plant growth in highly sodic (alkali) soils of the Indo-Gangetic plains to be: toxicity of excess sodium, carbonates and bicarbonates; poor soil structure and moisture transmission characteristics of the profile; and a calcic horizon at about 1 m depth which impedes root growth. Planting selected tree species in auger-holes refilled with the original sodic soil mixed with gypsum and farmyard manure was an easier and more economic form of establishment than the previous pit method. The use of gypsum is essential. Acacia nilotica, Eucalyptus tereticornis (hybird) Prosopis juliflora, Casuar ina equisetifolia and Albizzia lebbek showed higher tolerance of sodic conditions than Azadirachta indica, Dalbergia sissoo and Syzygium fructicosum. Populus deltoides, Morus indica var. alba and Syzygium cuminii did not survive. Eucalyptus tereticornis (hybrid) grew well for 2–3 years after planting but its growth rate then declined. Biomass accumulation by Acacia nilotica and Prosopis juliflora was significantly higher than that of the other species.