Wang Xiao, Lu Ping, Yang Peiling, Ren Shumei
College of Water Resources and Civil Engineering, China Agricultural University, Beijing, China.
College of Sericulture, Textile and Biomass Sciences, Southwest University, Chongqing, China.
PeerJ. 2021 Jul 20;9:e11674. doi: 10.7717/peerj.11674. eCollection 2021.
Di-nitrogen oxide (NO) emissions from soil may lead to nonpoint-source pollution in farmland. Improving the C and N content in the soil is an excellent strategy to reduce NO emission and mitigate soil N loss. However, this method lacks a unified mathematical index or standard to evaluate its effect.
To quantify the impact of soil improvement (C and N) on NO emissions, we conducted a 2-year field experiment using biochar as carbon source and fertilizer as nitrogen source, setting three treatments (fertilization (300 kg N ha), fertilization + biochar (30 t ha), control).
Results indicate that after biochar application, the average soil water content above 20 cm increased by ∼26% and 26.92% in 2019, and ∼10% and 12.49% in 2020. The average soil temperature above 20 cm also increased by ∼2% and 3.41% in 2019. Fertigation significantly promotes the soil N2O emissions, and biochar application indeed inhibited the cumulation by approximately 52.4% in 2019 and 33.9% in 2020, respectively. NO emissions strongly depend on the deep soil moisture and temperature (20-80 cm), in addition to the surface soil moisture and temperature (0-20 cm). Therefore, we established an exponential model between the soil moisture and NO emissions based on theoretical analysis. We find that the NO emissions exponentially increase with increasing soil moisture regardless of fertilization or biochar application. Furthermore, the coefficient a < 0 means that NO emissions initially increase and then decrease. The a < a indicates that fertilization does promote the rate of NO emissions, and the a > a indicates that biochar application mitigates this rate induced by fertilization. This conclusion can be verified by the sensitivity coefficient (SC of 1.02 and 14.74; SC of 19.18 and 20.83). Thus, we believe the model can quantify the impact of soil C and N changes on NO emissions. We can conclude that biochar does significantly reduce NO emissions from farmland.
土壤中一氧化二氮（NO）排放可能导致农田面源污染。提高土壤中碳和氮的含量是减少NO排放和减轻土壤氮素流失的有效策略。然而，该方法缺乏统一的数学指标或标准来评估其效果。
为了量化土壤改良（碳和氮）对NO排放的影响，我们进行了为期两年的田间试验，以生物炭作为碳源，肥料作为氮源，设置了三个处理（施肥（300 kg N/ha）、施肥+生物炭（30 t/ha）、对照）。
结果表明，施用生物炭后，2019年20 cm以上土壤平均含水量分别增加了约26%和26.92%，2020年分别增加了约10%和12.49%。2019年20 cm以上土壤平均温度也增加了约2%和3.41%。施肥显著促进了土壤N2O排放，而施用生物炭确实分别在2019年和2020年抑制了约52.4%和33.9%的累积。除了表层土壤湿度和温度（0-20 cm）外，NO排放还强烈依赖于深层土壤湿度和温度（20-80 cm）。因此，基于理论分析，我们建立了土壤湿度与NO排放之间的指数模型。我们发现，无论施肥与否，NO排放都随着土壤湿度的增加呈指数增长。此外，系数a<0意味着NO排放先增加后减少。a<a表明施肥确实促进了NO排放速率，而a>a表明施用生物炭减轻了施肥引起的该速率。这一结论可以通过敏感性系数（1.02和14.74的SC；19.18和20.83的SC）得到验证。因此，我们认为该模型可以量化土壤碳和氮变化对NO排放的影响。我们可以得出结论，生物炭确实显著减少了农田的NO排放。
