Soil Biological Indicators as Predictors of Agro-Ecosystem Function and Resilience in Nigerian Farming Systems: A Multi-Scale Analysis

This study develops and validates soil biological indicators as predictors of agro-ecosystem function and resilience in Nigerian farming systems, contributing an original multi-scale analytical framework that links soil biological diversity to ecosystem service provision. Soil biological communities, encompassing bacteria, fungi, protozoa, nematodes, and macro-fauna, perform fundamental ecosystem functions including nutrient cycling, carbon sequestration, disease suppression, and structural stability that underpin crop productivity and agricultural resilience. Current soil health assessment in Nigeria relies almost exclusively on chemical indicators, neglecting the biological dimensions that are often more sensitive indicators of management-induced soil degradation. This study develops a hierarchical biological indicator framework across micro, meso, and macro scale dimensions. Biological indicators including microbial biomass, fungal bacterial ratio, nematode food web analysis, earthworm density, and macro-arthropod diversity are measured at 180 sites spanning six farming systems across all geopolitical zones. Using the framework, relationships between biological indicator composites and ecosystem functions measured through enzyme activity, nitrogen mineralisation rate, water infiltration, and crop yield stability are quantified using structural equation modelling and machine learning variable importance analysis. A minimum dataset of biological indicators providing maximum predictive accuracy at minimum measurement cost is identified. Findings reveal that a composite of five biological indicators (microbial biomass carbon, nematode enrichment index, earthworm density, enzyme activity composite, and fungal hyphal length) predicts 73 percent of ecosystem function variation across all systems and zones. The study contributes an original Nigerian soil biological indicator framework and recommends its adoption as the standard for soil health assessment in agricultural land evaluation.

Keywords: soil biological indicators, agro-ecosystem function, resilience, farming systems, Nigeria.