EAGER: Self-Protection of Organic Carbon in Soil Pores under Organic Agricultural Practices

1220731(壮族)。在农业食品生产中，有机耕作是一种运用轮作、秸秆还田、免耕等多种方法，实现营养食品、生态系统健康和土壤高生产力目标的工程方法。该项目将提供有洞察力的信息和证据，包括评估标准，以帮助农民就应采用哪些农业工程做法或其组合来最大限度地实现土壤固碳，以及气候和土壤特性如何影响有机做法的有效性和潜力做出优化决策。土壤有机碳固存对土壤健康和粮食生产力有许多好处。由于农业对土壤健康的依赖，这一资源对社会至关重要。在作物生产中采用有机或保护措施可以增加土壤中有机质(OM)的输入，从而为优先考虑土壤质量和保护土壤中的有机碳(OC)创造了巨大的潜力。不幸的是，控制OC应计比率和能力的机制仍然不清楚。这项研究将使用一种新的综合方法来研究一种未经测试但可能非常重要的机制，该机制控制着纳米/微米土壤孔隙中碳固定的能力和稳定性。在有机耕作系统中，土壤有机胶体、水和氮素之间的孔隙调节反馈控制着土壤碳的去向和储存。研究的目标是：(1)量化不同有机或养护措施下有机质填充(包埋)的程度，以及不同有机质填充土壤孔隙的大小分布对水分滞后的影响；(2)评估不同温度、氮素有效性和水分含量下包裹的OM的生物降解及其对土壤呼吸的贡献；(3)将OM填充、水分滞后和碳-氮相互作用纳入土壤呼吸模型。研究将使用从两个气候和土壤条件不同的有机管理农业地点收集的土壤样本进行。研究将重点放在土壤微团聚体上，因为它们在长期保护有机碳不被分解方面起着关键作用。还将检查散装土壤和粉土/粘土部分，以供比较。孔隙填充很可能是控制生态系统(特别是生物质生产系统)土壤固碳潜力的关键机制。这项研究将首次利用最新的小角散射(SAS)技术和基于同位素的分子签名技术的互补优势来表征土壤中孔隙介导的碳-水-氮相互作用。所获得的结果将阐明土壤有机质和水分之间是否存在关于生化试剂可及性的反馈效应，这些生化试剂在控制土壤纳米/微孔中的长期碳保存方面发挥了关键作用。不同环境条件(如温度和水分)下不同大小孔隙中有机质分布的动态变化数据将揭示土壤有机质对分解的相对敏感性。对有机质孔隙填充和土壤呼吸之间关系的评估将为最新的土壤呼吸模型增加新的机理信息，并阐明在什么条件下土壤碳的累积可以预期在负担得起的生产成本范围内。对来自美国和中国的一系列农业现场的结果进行比较分析，将使这项研究适用于特定研究地点的边界之外。这项研究将为农民提供采用有机或保护措施的战略指导，以同时优化粮食生产和质量、土壤固碳和作物对不利环境的抵抗力。该项目将通过大胆的思维和在国家实验室和中国使用新技术的实践经验，为至少三名本科生提供教育和技术培训机会。这项研究的多学科、国际化方面将使本科生为研究生学习做好准备，并增强他们制定科学合理的可持续农业和气候变化缓解战略的能力和承诺。该项目将促进未来美国和中国在环境可持续性研究方面的大规模合作。

1220731 (Zhuang). In agricultural food production, organic farming practice is an engineering approach that applies various methods, such as crop rotation, crop residue return, no-tillage and others, to realize goals of nutritional food, ecosystem health, and high soil productivity. This project will provide insightful information and evidence including evaluation criteria that helps farmers make optimized decisions on what agricultural engineering practices or their combinations should be adopted to maximize soil carbon sequestration and how climate and soil properties affect the effectiveness and potential of organic practices. Soil organic carbon sequestration has many benefits to soil health and food productivity. Due the dependence of agricultre on soil health, this resource is vital important to society. Adoption of organic or conservation practices in crop production can increase the input of organic matter (OM) into soil and thereby create great potential for prioritizing soil quality and preserving organic carbon (OC) in soils. Unfortunately, the mechanisms controlling the rate and capacity of OC accrual remain unclear. This research will use a novel integrated approach to examine an untested but potentially very important mechanism that controls the capacity and stability of carbon sequestration in nano-/micro-sized soil pores. It is hypothesized that a pore-mediated feedback between soil organic colloids, water, and nitrogen dominates the fate and storage of soil carbon in organic farming systems. Research objectives are to: (1) quantify the extent of OM pore-filling (encapsulation) under different organic or conservation practices as well as water hysteresis as affected by the size distribution of OM-filled soil pores; (2) evaluate the biodegradation of encapsulated OM and its contribution to soil respiration at different temperatures, nitrogen availabilities, and water contents; and (3) incorporate OM pore-filling, water hysteresis, and carbon-nitrogen interactions into a soil respiration model. Studies will be conducted using soil samples collected from two organically-managed agricultural sites that have different climatic and soil conditions. Research will focus on soil microaggregates because of their critical role in protecting OC against decomposition over the long term. Also examined will be bulk soil and silt/clay fractions for comparison. Pore-filling very likely represents a critical mechanism governing the potential of soil carbon sequestration in ecological systems (particularly in biomass-productive systems). This study will be the first to characterize pore-mediated carbon-water-nitrogen interactions in soils by using the complementary advantages of state-of-art small-angle scattering (SAS) technique and isotope-based molecular signature technique. The obtained results will clarify whether a feedback effect between soil OM and water with respect to the accessibility of biochemical agents that play a key role in controlling long-term soil carbon preservation in nano-/micro-sized pores. Data on dynamic changes of OM distribution in differently sized pores under different environmental conditions (e.g., temperature and water) will reveal relative susceptibility of soil OM to decomposition. Evaluation of the relationships between OM pore-filling and soil respiration will add new mechanistic information to a latest soil respiration model and clarify the conditions under which soil carbon accrual can be expected within affordable production costs. Comparative analysis of results obtained from a spectrum of agricultural sites in the U.S. and China will make this research applicable beyond the borders of the particular study sites. The research will benefit farmers by providing strategic guidance on adoption of organic or conservation practices for the purpose of simultaneously optimizing food production and quality, soil carbon sequestration, and resistance of crops to adverse environment. The project will provide education and technical training opportunities to at least three undergraduate students through bold thinking and hands-on experience in using novel techniques at national laboratories and in China. The multidisciplinary, international aspects of this research will prepare undergraduate students for graduate study and enhance their capacity and commitment in developing scientifically-sound strategies for sustainable agriculture and climate change mitigation. The project will facilitate future large-scale US-China collaboration on environmental sustainability research.