Management effects on the nature of organic matter in agricultural soils

与本地土壤相比，耕作农业土壤的土壤有机质(SOM)一般是枯竭的(约少50%)，因此它们在过去一直是温室气体排放的主要来源。然而，农业土壤也有可能成为汇，如果它们被适当地管理以固定C。目前正在积极推动采用可持续的最佳管理做法来保护和提高土壤有机质水平：减少土壤耕作的频率和强度，种植复杂的轮作制度和覆盖作物，以最大限度地提高作物投入的质量和数量，并最大限度地回收作物残留物和有机废物。尽管土壤有机质在土壤功能中起着核心作用，但人们对土壤有机质成分的性质和动态以及它们如何受到农业管理实践的影响知之甚少。简单地说，这些做法在分子水平上对SOM的影响尚不清楚。因此，很难预测SOM将如何应对当前的压力：(I)农业集约化导致的土地管理变化(这对向世界上预计的900万人提供粮食至关重要)，(Ii)由于植物生物质用于生物产品和生物燃料生产而导致的种植系统的变化，或(Iii)气候变化下的温度和降水模式的变化。*我的研究计划的目标是确定农业管理实践如何影响SOM的化学性质和周转。这项研究将由三个支柱组成：(I)从正在进行的长期实地研究中采样的土壤中有机有机质成分的化学特征；(Ii)受控实验室培养研究，以评估持久性有机质的形成和动态；以及(Iii)生物物理模型，以评估有机质的预测和测试概念。这项研究将在分子水平上确定受农业实践影响最大的土壤有机质成分，并确定它们变化的速度。例如，众所周知，在免耕耕作下，作物凋落物和残留物会积累在表层土壤上，但如果耕作土壤以管理压实或作物残留物，则会迅速退化。能否更好地管理这一有机物质池，以提高其向SOM转化的效率？这些知识对于理解控制土壤有机质储存的机制，从而提出可持续的农业生产战略至关重要。

Soils cultivated for agriculture are generally depleted in soil organic matter (SOM) relative to their native counterparts (~50% less) so they in the past have been a major source of greenhouse gas emissions. However, agricultural soils also have the potential to be a sink provided they are managed appropriately to sequester C. Adoption of sustainable best management practices to protect and enhance SOM levels is currently actively promoted: reduced frequency and intensity of soil tillage, the planting of complex rotation cropping systems and cover crops to maximize quality and quantity of crop inputs, and maximizing return of crop residues and organic wastes. Despite the central role of SOM in soil functioning, the nature and dynamics of SOM constituents and how they are affected by agricultural management practices are poorly understood. Simply, the effects of these practices on SOM at the molecular level are unknown. Therefore, it is difficult to predict how SOM might respond to current pressures: (i) changes in land management due to agricultural intensification (which is essential for providing foodstuff to world's projected 9 million people), (ii) changes in cropping systems due to plant biomass use for bio-product and biofuel production, or (iii) changes in temperature and precipitation patterns under climate change.***The goal of my research program is to determine how agricultural management practices affect the chemical nature and turnover of SOM. The research will consist of three pillars based on: (i) chemical characterization of SOM constituents in soils sampled from on-going, long-term field studies, (ii) controlled laboratory incubation studies to evaluate the formation and dynamics of persistent SOM, and (iii) biophysical modelling to evaluate predictions and test concepts of SOM. The research will identify at a molecular level the constituents of SOM most affected by agricultural practices and determine how quickly they change. For example it is well known that crop litter and residue accumulate on the surface soil under no tillage farming, but rapidly degrade if soils are tilled to manage compaction or crop residues. Can this pool of organic matter be better managed so as to increase its efficiency of conversion to SOM? This knowledge is critical for understanding the mechanisms controlling SOM storage to propose sustainable agricultural production strategies.