Assessing maize production systems in Mexico from an energy, exergy, and greenhouse-gas emissions perspective

Highlights: • Four rain-fed and three irrigated maize production systems were investigated. • Energy, exergy, and GHG used as proxies for resources use and environmental burdens. • Diesel, synthetic fertilizers, and irrigation largely determine system performance. • Low-input maize systems have the lowest burdens per unit land area but low yields. • High-input maize systems have medium burdens per unit grain due to superior yields. -- Abstract: Maize is the most important staple crop in Mexico and is cultivated under varied agro-climatic and socio-economic conditions. The aim of this study is to estimate energy use, cumulative exergy consumption (CExC), and greenhouse gas (GHG) emissions of different maize production systems as proxies to compare their resource use and environmental performance. Based on average values, per-hectare energy use, energy intensity (EI), energy output-input ratio (ER), and net energy (NE) are in the range of 2.3–40.2 GJ ha⁻¹, 1.8–8.5 MJ kg⁻¹, 1.7–12.0, and 16.3–73.1 GJ ha⁻¹, respectively. Per-hectare CExC, exergy intensity (ExI), exergy output-input ratio (ExR), and net exergy (NEx) are in the range of 2.5–52.1 GJ ha⁻¹, 1.9–10.7 MJ kg⁻¹, 1.6–14.1, and 19.6–86.8 GJ ha⁻¹, respectively. Per-hectare GHG emissions, GHG intensity (GHGI), and GHG per unit energy input (GHGE_i) are in the range of 152.9–3475.8 kg CO₂e ha⁻¹, 116.5–601.9 kg CO₂e Mg⁻¹, and 63.1–117.2 kg CO₂e GJ⁻¹, respectively. Low-input rain-fed production systems perform better in EI, ER, ExI, ExR, GHGI, and GHGE_i though, they also show the lowest NE and NEx due to poor yields. High-input surface irrigated production systems have the highest NE and NEx coupled with medium values of EI, ExI, and GHGI due to high productivity.