Impact of land clearing methods and cropping systems on labile soil C and N pools in the humid zone Forest of Nigeria

Labile soil C and N play vital roles in soil–plant nutrient dynamics, especially in the low input cropping system and are vulnerable to perturbation. Surface (0–0.15 m) soils from three land clearing methods (slash and burn, bulldozed non-windrowed and bulldozed windrowed) and each with two cropping systems (5-and 4-year cropping/2-year cassava fallow) were collected in the humid forest ecosystem of Nigeria.The soils were analysed for total C and N, microbial biomass C and N (SMB C and N), particulate organic matter C and N (POM C and N), water-soluble C, potentially mineralizable N (PMN) and mineral N. The size of the labile C and N and their relative contributions to the organic C and total N differed significantly among land clearing methods, irrespective of the cropping system. Soils under slash and burn had a significantly (p > 0.05) higher particulate organic matter C, N (10.80 and 0.16 g kg⁻¹, respectively) and microbial biomass C and N (1.07 and 0.12 g kg⁻¹) compared to the bulldozed windrow, regardless of the cropping system. Four years cropping/2-year cassava fallow resulted in a significant higher labile C and N, relative to 5-year cropped plots across the land clearing methods. Effect of the treatments on the concentration of PMN and mineral N mirrored the SMB N and POM N. However, the quantity of most of the labile C and N pool and crop yield obtained from the slash and burn and bulldozed non-windrowed treatment did not differ significantly. Hence, bulldozed non-windrowed clearing could be a viable alternative to slash and burn in the case of large-scale farming in ensuring reduced losses of soil organic matter and nutrient during land clearing in the humid tropics.