Biochar Mitigated Yield-Scaled N2O and NO Emissions and Ensured Vegetable Quality and Soil Fertility: A 3-Year Greenhouse Field Observation

Abstract

Biochar amendments have been widely used in agricultural soil for lowering N2O and NO emissions while improving soil fertility and crop performance. However, a thorough understanding of the longevity of the favorable effects would be a prerequisite for large-scale biochar application in agriculture. We conducted a three-year greenhouse vegetable trial in Southeast China to systematically investigate the impacts of biochar mixed with nitrogen (N) on soil N2O and NO emissions, vegetable performance, and soil fertility at an interannual scale. The field experiment was established in November 2016 with biochar (0, 20 and 40 t ha−1; C0, C1, and C2, respectively), applied once without/with 240 kg N ha−1 urea (N0 or N1, respectively). Soil N2O and NO emissions were monitored during the spring vegetable cultivation period, and vegetable yield, quality, and soil properties were measured after harvests in 2018, 2019, and 2020. Results indicated that N application significantly increased N2O and NO emissions and vegetable yield throughout the trial period. Biochar combined with N generally reduced N2O and NO emissions and emission factors while increasing the vegetable yield, leading to lower yield-scaled N2O and NO emissions in 2018 and 2019. Biochar markedly enhanced soil pH and organic carbon and persisted, but generally had no significant effect on N use efficiency (NUE), vegetable quality, and soil fertility index (SFI) among treatments in over-fertilized vegetable fields. Based on our results, biochar application at 20 t ha−1 combined with N seemed to achieve the highest agronomic and environmental benefits for intensive vegetable production in Southeast China.