Adventures in carbon neutral farming: mitigating potent greenhouse gas emissions from soils with rock dust

1.背景农业是全球主要的管理景观之一，有可能成为气候变化解决方案的一部分，也是问题的一部分。陆基增强岩石风化（ERW）是将研磨的硅酸盐岩石应用于土壤的过程，是联合国公认的适用于管理农田的大规模大气二氧化碳去除（CDR）策略（Beerling等人，2018年）。然而，玄武岩添加后土壤pH值的增加也可能产生“石灰效应”，减少土壤N2 O排放，增加单位作物产量减缓气候变化的潜力。在100年的时间范围内，每分子N2 O的变暖潜力几乎是CO2的300倍。正在进行的美国玉米带土壤肥沃、有机质丰富的田间试验支持这一假设（DeLucia等人，2019; Geophys Res. Abst. 21，EGU 2019 -4500）。然而，N2 O通量的减少也可能与其他温室气体（GHG）通量（CO2和CH 4）以及大气污染物HONO、NO和NH3排放量的变化有关，但这在很大程度上仍未得到评估。氮从土壤流失到大气和沃茨中代表了植物必需氮从土壤系统中的流失，可能会降低产量，并使农民用氮肥补偿这种流失的循环持续下去，导致进一步的排放。减少农田土壤N2 O排放可以提高作物生产的氮素利用效率.目标.该项目将调查令人兴奋的气候变化减缓假设，即按照战争遗留爆炸物为CDR提出的比率，用玄武岩改良农业土壤，减少联合王国可耕地作物和牧场的土壤N2 O通量。重要的是，他们将评估其他重要的温室气体通量（CO2，CH 4）和土壤氮痕量气体排放（HONO，NO和NH3）对这种处理的响应。该项目将通过使用既定协议和数值建模以及团队熟悉的方法进行小规模实验工作来解决这些关键问题。2.1实验将进行种植小麦的复制围隔生态系统土壤培养研究，以调查玄武岩改良剂、作物、土壤类型和土壤水分变化的影响，包括土壤含水量。干旱和洪水事件对土壤温室气体、氮素淋失（硝酸盐、溶解有机氮）、产量和氮素利用效率的影响。将对土壤的一个分区进行分析，以确定更难测量的大气污染物NO、HONO和NH3。将从一组目标土地使用（谷物、草地）中收集土壤，这些土地具有不同的pH值和不同的土壤类型。2.2建模：在该项目的第二阶段，实验结果将用于参数化和校准基于过程的地球化学模型DAYCENT。这将使我们能够了解玄武岩改良土壤对N2 O和其他温室气体和氮痕量气体排放的关键控制。目的是严格扩大我们的研究结果，以预测在当前和未来气候变化的情况下，含有玄武岩的战争遗留爆炸物如何影响英国农田的温室气体和痕量气体排放。新颖性据我们所知，我们正在进行的实地试验是第一个报告减少土壤N2 O通量从农业土壤与破碎的玄武岩粉尘修正，有可能改善集约农业的温室气体平衡。这可以大大降低农业单位产量对气候的不利影响，扩大战争遗留爆炸物缓解气候变化的潜力。但我们现在迫切需要了解这些发现的普遍性及其与英国/欧洲农业用地的相关性。很准时。减缓全球气候变化是人类面临的最大科学挑战之一。IPCC 1.5度特别报告得出结论，避免“危险”的气候变化意味着现在必须部署CDR技术。该项目解决了一个重要的CDR战略的新的N周期的共同利益。

1. Background. Agriculture is one of the dominant managed landscapes worldwide with potential for being part of the solution to climate change as well as being part of the problem. Land-based enhanced rock weathering (ERW), the process of applying ground silicate rock to soils, is a UN-recognized strategy for atmospheric carbon dioxide removal (CDR) at large-scale applicable to managed croplands (Beerling et al., 2018). However, increases in soil pH following basalt addition may also exert a 'liming effect' and reduce soil N2O emissions, delivering added climate change mitigation potential per unit crop yield. Per molecule basis, N2O has almost 300 times the warming potential of CO2 over a 100-year time horizon. On-going field trials with fertile, organic matter-rich US corn-belt soils support this hypothesis (DeLucia et al. 2019; Geophys Res. Abstr. 21, EGU2019-4500). However, it is also possible that reductions in N2O fluxes are associated with changes in other greenhouse gas (GHG) fluxes (CO2 and CH4) and the atmospheric pollutants HONO, NO and NH3 emissions but this remains largely unassessed. Loss of N from soil to the atmosphere and waters represents loss of plant-essential nitrogen from the soil system, potentially decreasing yields, and perpetuating a cycle in which farmers compensate for this loss with nitrogen fertilizers, resulting in further emissions. Reduced emissions of N2O from agricultural soils could increase the nitrogen-use efficiency (NUE) of crop production.2. Objectives. The project will investigate the exciting climate change mitigation hypothesis that agricultural soils amended with basalt, at rates proposed for CDR by ERW, reduce soil N2O fluxes for UK arable crops and pasture. Importantly, they will assess the responses of other important GHG fluxes (CO2, CH4) and soil nitrogen trace gas emissions (HONO, NO and NH3) to this treatment. The project will address these key issues by undertaking bench-scale experimental work using established protocols and numerical modelling with approaches familiar to the team. 2.1 Experiments. Replicated mesocosm soil incubation studies planted with wheat will be conducted to investigate the impact of basalt amendment, crop, soil type and changes in soil moisture, incl. drought and flooding events, on soil GHG, N leaching (nitrate, dissolved organic nitrogen), yield and NUE. A subsection of the soils will be analysed for the more difficult-to-measure atmospheric pollutants NO, HONO, and NH3. Soils will be collected from a targeted set of land uses (cereals, grasslands) with varying pH values and contrasting soil types. 2.2 Modelling: In phase two of the project, experimental results will be used to parameterize and calibrate the process-based biogeochemical model DAYCENT. This will allow us to understand key controls on N2O, and other GHG and nitrogen trace gas emissions, for basalt-amended soils. The objective is to rigorously upscale our findings to predict how ERW with basalt might affect these GHG and trace gas emissions from UK agricultural lands under current and future climate change scenarios.3. NoveltyAs far as we are aware, our on-going field trials are the first to report reduced soil N2O fluxes from agricultural soils amended with crushed basalt dust, with the potential to improve the greenhouse gas balance of intensive agriculture. This could substantially lower the adverse impacts of agriculture on climate per unit yield, amplifying climate change mitigation potential of ERW. But we now need to understand urgently the generality of these findings and their relevant to UK/European agricultural lands.4. Timeliness. Mitigating global climate change is one of the greatest scientific challenges facing humanity. The IPCC 1.5 Degree Special Report concluded that avoiding 'dangerous' climate change means deployment of CDR techniques is now essential. This project addresses new N-cycle co-benefits of a significant CDR strategy.