Effect of Disturbance on the Status of Soil Microbial Biomass in Tropical Sal Forest in Eastern Nepal
The present study was conducted to investigate the effect of disturbance on the status of soil microbial biomass and physico-chemical characteristics of soil in disturbed and undisturbed stand of tropical sal (Shorea robusta) forest during summer. The forest soil was sandy loam. The percentage of sand and silt increased as increases depth but clay decreased with increase in depth of soil in both forests. The pH value of both forests was (disturbed 5.41 and undisturbed 5.29) slightly acidic. Maximum Water holding capacity (WHC) was higher in undisturbed forest (60.14%) than disturbed forest (55.04). Undisturbed forest showed greater organic carbon (1.71%) and total nitrogen (0.138%) than disturbed forest (OC -1.44% and TN - 0.118%). The microbial biomass carbon and microbial biomass nitrogen of undisturbed forest (MB-C - 324.29 μg g-1and MB-N - 43.49 μg g-1) was higher than disturbed forest (MB-C - 207.74 μg g- 1 and MB-N - 35.84 μg g- 1). Organic carbon, total nitrogen, microbial biomass carbon and microbial biomass nitrogen decreased with increasing soil depth in both forests. The MB-C:
MB-N ratio indicate the bacterial dominance in disturbed stand (5.56) and fungal dominance in undisturbed stand (7.63). In the present work soil organic carbon and total nitrogen were reduced by 18% and 12%, respectively in the disturbed stand while soil microbial biomass carbon was reduced by 43% and microbial nitrogen by 18% for the same disturbed forest stand. It reflects a quick response of disturbance on soil microbial biomass.