Diversity and Productivity Effect on the Amelioration of Afforested Sodic Soils

New forests created on sodic wastelands, consisting of different community structure ameliorate the soil at various degrees according to productivity and diversity status. Three such forested sites were selected at Banthra Research Station of National Botanical Research Institute, Lucknow, India with different productivity and diversity indices descending from site I (S₁) to III (S₃), which were compared with a control (non forested) sodic soil site. Importance value index (IVI) decreased from 320 to 150 from site I to III. Shannon-Wiener's general diversity index was greatest in site I (1.85) and lowest in site III (1.37). Population density, basal area and biomass also declined accordingly. Dominant genera in these Forest stands were Acacia, Albizia, Dalbergia, Terminalia, Bauhinia and Syzygium whereas grasses/forbs viz.Sporobolus, Desmostachya and Dactyloctenium were common on barren sodic land. A remarkable reduction in soil pH and exchangeable sodium percentage (67-73%) was noticed in afforested sites compared to the control as a result of combined effect of increased diversity and productivity. Individual effects of diversity or productivity were measured as 42% and 58%, respectively in soil amelioration. The soil fertility increased 2 to 3 times in organic carbon and 2.7 to 3.7 times in total nitrogen content on afforested sites. However, these improvements were greatest in surface soil (0.15 m) for C and N (68 & 73%) in comparison to lower depths (51 & 65%). Among the exchangeable cations, Na⁺ reduced by 41-57% from the control in afforested sites (I and II) while Ca⁺⁺ content increased of 38-68% in these sites. In general, available Zn, Fe and Mn contents increased in forested sites I and II whereas Cu decreased significantly in site II but remains at par on site I from the control. A rapid ch!lnge in soil properties occurred on surface soil even on poor afforested site while the rate of improvement at depths below 0.3 m depicted a slow amelioration process. A combined effect of both biomass productivity and species diversity of about 92% ameliorated the soil more significantly instead of individual factors, which should be taken into account for the rehabilitation of such sodic soil sites.