Changes in physico-chemical, microbial and enzymatic activities during restoration of degraded sodic land: ecological suitability of mixed forest over monoculture plantation.

摘要

Degraded sodic lands in north India are rehabilitated under agriculture and forest sector as per national policies. Afforestation on such lands with monoculture and mixed species reclaims the soils with different efficiencies. We studied the physico-chemical and microbial properties along with enzymatic activities of degraded sodic land (control), rehabilitated sodic lands planted under Terminalia arjuna (R-TA), Prosopis juliflora (R-PJ) and mixed forest (R-MF) from two depths (0-15 and 15-30 cm). The properties of rehabilitated land uses were compared with the soils of corresponding reference (standard) land use under Tectona grandis (Ref-TG) plantation and mixed forest (Ref-MF) growing in the natural forest range of same biogeographic region to determine the status of improvement. The objective of the study was to determine efficient ecological model for the restoration of degraded sodic land. The bulk density, pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP) reduced during restoration under both, pure plantations as well as mixed forest. Increase in water holding capacity (WHC), organic carbon, soil nutrients, microbial biomass (MB) [carbon, nitrogen and phosphorus], microbial counts, CO₂ flux and enzymatic activities (dehydrogenase, beta -glucosidase, protease and acidic phosphatase) showed significant improvement in the soil quality of rehabilitated sites. At 0-15 cm soil depth in rehabilitated and reference land uses, in comparison to D-SL, organic carbon, nitrogen (total and available), available phosphorus, exchangeable cations (Na+, Ca++ and Mg++), MB (carbon and nitrogen) and activities of all enzymes, except alkaline phosphatase, were significantly greater, while other soil properties showed land use specific trends. The overall gain percent in physico-chemical soil properties varied from 54% under plantations to 77% under mixed forest (R-MF). Corresponding gain in microbial biomass was 21% (R-TA) and 34% (R-PJ) under plantation soils against 90% in mixed forest soil. The enzyme activities (on average) have also attained maximum gain% under R-MF (77%) followed by R-PJ (47%) and R-TA (35%) in decreasing order which indicates that afforestation with multiple tree species is a relatively good option for sustainable rehabilitation of sodic lands.