Effect of bamboo foliage on soil respiration, microbial biomass and N mineralization

Microbial N, CO2 evolution rate and mineral-N dynamics were determined in soils collected beneath the canopy of two different bamboo species in a 9-year-old bamboo forest developed on an abandoned sloping agricultural land in a humid tropical zone of north-east India. A laboratory incubation study was set up to determine the dynamics of microbial biomass, soil respiration and N mineralization rates as influenced by addition of bamboo residues (leaves and scale leaves). Soil nutrients and microbial biomass C, N and P were greater in soils under Bambusa pallida as compared to B. balcooa. Lignin and N concentrations were greater in B. balcooa. Scale leaves had low lignin and N concentrations than the leaf litter. The litter quality, particularly lignin/N, influenced the dynamics of soil mineral-N and, therefore, on the net N mineralization rate. CO2 evolution rate in the soil had a negative relationship with the N mineralization rate, while the microbial N showed weaker correlations with the dynamics of the mineral N. Overall, amendments using the sclerophyllous and slow decomposing foliage did not contribute to the increasing N mineralization in the soils. The study also suggests that soil management practices in bamboo forests should take into account incorporation of residues of good quality, probably of other plant species, failing which, soil quality may deteriorate over a long term that would be critical in productivity and nutrient cycling of secondary bamboo forests regenerating on nutrient-poor, fragile and marginal fallow agricultural lands.