Conservation tillage enhances yield, energy efficiency, economic returns, and environmental sustainability in a rapeseed-maize rotation system in a subtropical karst region

Karst regions are highly vulnerable agroecosystems where soil degradation and resource limitation constrain sustainable crop production. In such fragile cropping systems, reducing soil disturbance through no-tillage is particularly important for conserving soil resources and maintaining agroecosystem functions. Using a representative experimental site in the Guizhou karst region, this study evaluated the effects of no-tillage and straw management on maize yield, forage quality, energy efficiency, life-cycle impacts, and economic returns during 2019–2021. Four maize cultivars were grown under no-tillage (NT) or conventional tillage (CT), combined with straw mulching (M) or no mulching (NM). Responses varied among cultivars, with Jinyu 519 showing the highest yield. On average, NT increased maize whole-plant dry-matter yield by 8.0%, whereas M improved silage quality, increasing relative feed value by 5.5%. The combined NTM treatment produced the best overall performance, increasing whole-plant dry-matter yield by up to 12.9%; at the annual rotation scale, it reduced energy input by 11.1% and increased net energy by 12.7%; during the maize phase, it decreased global warming potential and primary energy demand by 6.8% and 10.4%, respectively. Economic analysis showed that NTM increased net profit despite its additional straw-handling costs, with Jinyu 519 under NTM generating the greatest overall benefit. In the rapeseed-maize rotation, the integration of high-performing cultivars with NTM further enhanced yield stability, forage quality, energy output, profitability, and environmental performance. Overall, NTM was more effective than cultivar selection alone and provides a promising strategy for sustainable crop production in karst regions.