Maize–Legume Intercropping Achieves Trade-Offs Between Productivity, Economic Return and Carbon Mitigation in Coastal Saline-Alkali Farmland of the Yellow River Delta

To alleviate the constraints of coastal saline-alkali soil on crop production and explore efficient and low-carbon planting patterns for vulnerable saline land ecosystems, a three-year continuous field experiment was carried out in the coastal saline-alkali farmland of the Yellow River Delta, Dongying City, Shandong Province, China. Using sole maize cropping (CM) as the control, this study systematically compared productivity, energy budget, economic benefit, carbon footprint (CF), and the carbon sustainability index (CSI) of maize–soybean intercropping (M/S) and maize–peanut intercropping (M/P), and further evaluated their comprehensive benefits based on the net ecosystem economic benefit (NEEB). The results showed that compared with CM, the three-year average economic yield of M/S and M/P decreased by 14.6% and 14.0%, with corresponding energy yield reductions of 12.0% and 9.1%. Notably, M/S and M/P significantly increased the maize equivalent yield by 9.4%. Relative to CM, the three-year average net income of M/S and M/P increased by 18.3% and 29.9%, respectively. For carbon-related environmental benefits, M/S and M/P reduced CF per unit maize equivalent yield by 14.0% and 18.1% and CF per unit economic benefit by 13.9% and 18.0%, while increasing the CSI by 6.0% and 8.4%, respectively. Comprehensive evaluation using the Z-score method demonstrated that M/P improved the NEEB by 9.4% and obtained a higher comprehensive score than CM, while M/S produced a marginally lower Z-score than CM. Overall, M/P exhibited the optimal multi-dimensional performance and represents a promising eco-friendly planting pattern for coastal saline-alkali regions.