Effects of Pyrolysis Temperature and Residence Time on Vineyard Waste Biochar Properties and Short-Term Soil Physical Improvement

Grape cultivation and processing generate large amounts of pruned vine branches and grape pomace, which can be converted into biochar as an effective recycling strategy. This study aimed to investigate the effects of pyrolysis temperature (300–600 °C) and residence time (0.5–4 h) on biochar physicochemical properties and to evaluate the short-term impacts of biochar–manure co-application on vineyard soil physical quality. A total of 13 biochar variants were produced from vine branches (9 treatments, L9(32) orthogonal design) and grape pomace (4 treatments, L4(22) orthogonal design) under oxygen-limited pyrolysis. Biochar properties were characterized using Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Based on comprehensive evaluation, branch-derived biochar pyrolyzed at 300 °C for 4 h (BC4-300; specific surface area: 24.07 m2·g−1) and pomace-derived biochar pyrolyzed at 300 °C for 1 h (BP1-300; pH: 8.2–9.1) were selected as optimal soil amendments. A field experiment was then conducted using a randomized complete block design with ten treatment combinations (five for each biochar type), in which biochar was applied at 10 or 30 t·ha−1 and co-applied with cattle manure at 10 or 30 t·ha−1. After one growing season, BC4-300 significantly enhanced topsoil (0–20 cm) aggregate stability, increasing the mean weight diameter (MWD) by up to 27.8% compared with the control. In contrast, BP1-300 significantly improved subsoil (20–40 cm) aggregate stability, increasing the proportion of water-stable aggregates > 0.25 mm (R0.25) by 15.6%. Moderate application rates (10 t·ha−1 biochar + 10 t·ha−1 manure) reduced subsoil bulk density by 6.3%. These findings demonstrate that optimizing pyrolysis parameters enables feedstock-specific biochar production and provide practical guidance for short-term soil physical improvement in sustainable vineyard management.