Suitable particle-size biochar enhances resilience of potato production and soil environmental to irregular precipitation in semiarid region.

Climate change has intensified the randomness of precipitation events, threatening the production stability of rainfed agricultural regions. The addition of biochar with a suitable particle size can effectively mitigate these adverse impacts. In this study, biochar of three particle sizes (SB, small: <0.5 mm; MB, moderate: 0.5-2.0 mm; and LB, large: >2.0 mm) were added to typical rainfed farmland to investigate its effects on potato source-sink relationships, yield, precipitation use efficiency (PUE), nitrogen use efficiency (NUE), soil micro-environment (NO3--N and NH4+-N contents, oxygen concentration, temperature, water-filled pore space), N2O emissions, and nitrogen leaching under varied precipitation patterns. Potato tuber yield was mainly governed by precipitation distribution, with biochar addition exerting a secondary effect. By contrast, biochar addition primarily reduced soil N2O emissions, and this mitigating effect was enhanced with increasing precipitation. The application of small and moderate particle size biochar under different precipitation patterns significantly improved the soil micro-environment, and promoted potato source-sink activity and assimilate demand. Among these treatments, MB achieved the best comprehensive effects, it significantly increased tuber yield, PUE, and NUE by 17.8 %, 17.1 %, and 60.8 %, respectively, while lowering soil N2O emissions, yield-scaled N2O emissions, and nitrogen leaching by 29.8 %, 40.2 %, and 20.6 %, respectively. In comparison, LB did not only fail to significantly increase tuber yield but also increased nitrogen leaching. Therefore, added biochar with a particle size of 0.5-2.0 mm can support sustainable potato production in Northwest China.