Comparative assessment of physico-chemical properties influencing microbial biomass as biomarker in monitoring soil status on chronosequences of iron mine overburden spoil

Mining activities led to nutritionally deprived habitats with different metal contaminations. The clay percentage, water holding capacity, moisture content, OC, TN and AP is found to be higher in forest soil as compared to chronosequences of iron mine overburden spoil. Comparative assessment with respect to variation in MB-C, MB-N and MB-P were analyzed among four iron mine overburden spoil in chronosequences as well as nearby forest soil of Noamundi, Jharkhand, India. In the present study, the contributions of different physicochemical properties influencing the microbial biomass have been addressed. Wide variation in MB-C (55.586–252.638 μg.g⁻¹ spoil), MB-N (4.833–23.567 μg.g⁻¹ spoil) and MB-P (2.416–11.124 μg.g⁻¹ spoil) was exhibited among chronosequences of iron mine overburden spoil. Comparative analysis suggested an increasing trend in microbial biomass from a nutrient deficient situation (FMS) to an enriched soil (FS). Stepwise multiple regression analysis was performed to determine the contribution of different physico-chemical factors influencing the variability in microbial C, N and P across the sites. The microbial biomass C, N and P were positively correlated with OC (r = 0.999; p<0.01). The proportion of OC contained in microbial biomass-C ranged from 3.1%-3.9%. The microbial C:N ratio ranged from 10.72 to 11.63, where as the microbial C:P ratio varies from 22.71 to 23. However, microbial C:N, C:P and MBC/OC ratio in forest soil was found to be 9.5%, 22.02 and 2.6 respectively. Further, principal component analysis was able to discriminate four different chronosequences of iron mine spoil as well as forest soil into five independent clusters based on their physico-chemical properties and microbial biomass. The variations in microbial biomass have strong implications with the extent of land degradation and can serve as a useful indicator of soil fertility status.