Bridging the biophysical gap of Water-Energy-Carbon nexus in agricultural systems: A unified emergy-based framework for evaluating regenerative and demand-side interventions

The transition to sustainable agriculture requires navigating the complex trade-offs within the Water-Energy-Carbon nexus, especially as decentralized renewable energy reshapes the temporal and spatial dynamics of resource availability. However, current assessments often face the incommensurability challenge, where environmental costs (user-side) and ecological contributions (donor-side) are evaluated in isolated metrics, ignoring the potential of agricultural infrastructure to act as a functional buffer for the energy transition. This paper proposes a unified emergy-based framework to bridge this gap, moving beyond a conventional burden-oriented nexus evaluation toward an biosphere-work-oriented valuation logic. By introducing a phasic assessment approach, we capture the temporal dynamics of agricultural metabolism, redefining irrigation not merely as a resource sink but as a “virtual energy storage” component capable of synchronizing demand with renewable power profiles. Emergy, introduced by the ecologist H.T. Odum, is a measure of the biosphere's work in support of resource generation over time and spatial scales. Beyond standard accounting, we define two novel emergy-based indicators: the System-Wide Net Carbon Emergy Balance (USNCEB) to evaluate the shift from carbon load to ecological regulation service, and the Renewable Resource Substitution Emergy Efficiency (ƞRRSEE) to quantify the multiplier effect of the technological nexus. We applied this framework to a comparative case study of an integrated solar-wind-drip irrigation system versus conventional fossil-based farming across diverse intensive agricultural scenarios (China and Argentina). Results reveal a fundamental metabolic shift: the integrated system increases the renewable emergy share to ∼55%-70% and drastically reduces the Environmental Loading Ratio. The USNCEB shifts from a negative ecological debt to a positive value, confirming that the system functions as a net climate regulator rather than a passive emitter. Furthermore, an ƞRRSEE > 1.0 demonstrates a positive synergy, where the renewable infrastructure investment unlocks biophysical savings (fossil fuel and water) that exceed its own embodied cost. Our findings suggest that by aligning agronomic flexibility with precision resource management, agricultural systems can achieve a triple win of water productivity, decarbonization, and grid resilience. The study establishes emergy synthesis as a vital tool for revealing the donor-side value of low-carbon technologies, advocating for policy shifts from linear input subsidies to integrated payments for ecological regulation services.