Amelioration of a highly alkaline soil by trees in northern India

A study was carried out to compare the impact of 6-year-old plantations of Prosopis juliflora (Swartz) D.C., Dalbergia sissoo Roxb. Ex. D.C. and Eucalyptus tereticornis Sm. on the physical and chemical properties of sodic soil in the Indo-Gangetic alluvial plains of Uttar Pradesh, India. Soil properties under the three tree species showed significant improvement through a reduction in the pH, electrical conductivity, exchangeable sodium percentage, CaCO3 and gypsum requirement, and by increase in organic C, total N, and available P and K. The six years of reclamation had achieved a marked reduction in exchangeable sodium (from 11.5 to 4.5 cmol(c) kg(-1)) to a depth of 1.5 m in the soil profile, whereas the levels of exchangeable calcium, magnesium and potassium had increased. There was also a significant reduction in soil bulk density (from 1.66 to 1.24 g cm(-3)) and increases in porosity, water holding capacity, field capacity, permeability and infiltration rate. The equilibrium infiltration rate after 455 min increased from 0.03 cm h(-1) in the control to 0.13 cm h(-1) under P juliflora and D. sissoo and 0.10 cm h(-1) under E. tereticornis. It is concluded that salt-tolerant tree species have a significant impact on soil properties, which could help to rehabilitate the sodic wastelands in the region.