| Summary: | Drip fertigation with reduced fertilizer and water inputs has been widely used in greenhouse vegetable production in China. However, farmers usually do not apply additional organic material with a high carbon content, although soil organic carbon (SOC) concentrations are mostly below the optimum level for vegetable production. Returning straw or biochar to fields is an effective strategy for sustainability and environmental friendliness. We tested whether drip fertigation, (DIF) combined with maize straw (DIF+S) or biochar (DIF+BC), is a suitable option to improve SOC sequestration over eight growing seasons, and how these options affect soil N<sub>2</sub>O emissions and yields or partial factor productivity of applied N (PFP<sub>N</sub>) of crops over three growing seasons. During the winter–spring growing season, DIF+BC significantly reduced soil N<sub>2</sub>O emission by 61.2% and yield-scaled N<sub>2</sub>O emission by 62.4%, while increasing the tomato yield and PFP<sub>N</sub> compared with DIF. Straw incorporation had similar trends but without significant effects. Conversely, straw and biochar incorporation increased N<sub>2</sub>O emission during the autumn–winter season. The structural equation model indicated N<sub>2</sub>O emission was dominantly driven by soil NH<sub>4</sub><sup>+</sup>-N concentration, temperature and moisture. The N<sub>2</sub>O emission factor decreased significantly with increased PFP<sub>N</sub>. Moreover, the contribution of biochar to the increased SOC was approximately 78%, which was four times higher than that of straw incorporation. Overall, the results highlighted the potential of drip fertigation with biochar incorporation to mitigate N<sub>2</sub>O emissions, improve PFP<sub>N</sub> and significantly increase SOC storage, which could all contribute to maintaining environmental sustainability and soil quality of greenhouse vegetable production.
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