Thermodynamic Efficiency Analysis of Nutrient Cycling in Contrasting Nigerian Agricultural Ecosystems

This study applies thermodynamic efficiency analysis to compare nutrient cycling processes in contrasting Nigerian agricultural ecosystems, developing an original theoretical framework that integrates thermodynamics with agronomy to advance understanding of ecosystem efficiency and sustainability. Standard agronomic nutrient use efficiency metrics focus on the ratio of nutrient removed in crop to nutrient applied as input, capturing only the economic efficiency dimension. Thermodynamic approaches that account for the quality and free energy of nutrient transformations provide a more complete measure of ecosystem function that can reveal hidden inefficiencies and sustainability risks. This study develops a nutrient thermodynamic efficiency framework adapted from industrial ecology principles for application to agricultural nutrient cycling. The framework is applied to six contrasting Nigerian farming systems, including slash-and-burn shifting cultivation in Borno State, intensive yam monoculture in Benue State, flood-irrigated rice in Kebbi State, cocoa agroforestry in Ondo State, peri-urban vegetable production in Lagos State, and pastoralist-crop integration systems in Niger State. Nutrient inputs, outputs, stocks, and transformation pathways are quantified through complete farm nutrient budget analysis combined with soil fractionation and isotope tracing. Thermodynamic efficiency indices are computed for nitrogen, phosphorus, and potassium cycles. Findings reveal that the cocoa agroforestry system achieves the highest thermodynamic nutrient cycling efficiency, approaching tropical forest analogue values, while intensive vegetable production shows the lowest efficiency, with 62 percent of applied nutrients accumulating in non-plant-available soil fractions. The study contributes an original nutrient thermodynamics framework for Nigerian agronomy and recommends its use in ecosystem service valuation.

Keywords: thermodynamic efficiency, nutrient cycling, agricultural ecosystems, Nigeria, sustainability.