Environmental Trade-Offs and Optimal Strategy of Hydrotalcite, Biochar, and Lactopeptide Use in a Cucumber Straw Compost-to-Field System: A Cradle-to-Grave Life-Cycle Assessment

Facility cucumber cultivation generates large quantities of straw residues in China, and composting represents a dominant recycling strategy for these organic wastes. However, conventional composting is accompanied by considerable greenhouse-gas emissions, severe nitrogen losses, and extra environmental burdens. Exogenous additives can mitigate such impacts, yet few studies have conducted systematic cradle-to-grave life-cycle assessment (LCA) across the full composting-to-field chain for various amendments. Moreover, the net environmental performance of lactopeptide remains poorly understood. Following ISO 14044, this study built an LCA model (functional unit: 1000 kg fresh cucumber straw). Ten scenarios integrated three additives (hydrotalcite, biochar, lactopeptide) with three application modes and were evaluated via CML-IA baseline (CML 2016) and China-localized distance-to-target (DTT) weighting. Results showed that at an identical 5% additive dosage, single-stage composting-phase addition outperformed field-only addition, whereas the dual-stage mode (10% total dose) carried higher comprehensive environmental burdens (1.9–9.1%). Lactopeptide yielded a 55.3% global warming potential (GWP) reduction, while hydrotalcite achieved 65.8% acidification potential (AP) mitigation. DTT screening selected single-stage hydrotalcite addition as optimal, cutting total environmental load by 63.8%. This study quantifies lactopeptide’s full-chain environmental benefits and supports sustainable agricultural straw residue management.