Management effects on the nature of organic matter in agricultural soils

农业土壤的有机质（SOM）通常比原生土壤少50%，因此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，只要它们得到适当的管理以封存C。采用可持续的最佳管理实践来保护和提高土壤有机质水平，目前正在积极推广：减少土壤耕作的频率和强度，种植复杂的轮作系统和覆盖作物，以最大限度地提高作物投入的质量和数量，并最大限度地提高作物残留物和有机废物的回报。尽管有机质在土壤功能中的核心作用，有机质成分的性质和动态，以及它们如何受到农业管理措施的影响知之甚少。简单地说，这些做法在分子水平上对SOM的影响是未知的。因此，很难预测SOM如何应对当前的压力：（一）农业集约化导致土地管理的变化（这对于向世界预计的900万人口提供粮食至关重要），（ii）由于植物生物量用于生物产品和生物燃料生产，或（iii）气候变化下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措施如何影响SOM的化学性质和周转。该研究将包括三个支柱的基础上：（一）从正在进行的，长期的实地研究中采样的土壤中的SOM成分的化学表征，（二）控制实验室培养研究，以评估持久性SOM的形成和动态，以及（三）生物物理建模，以评估预测和测试SOM的概念。该研究将在分子水平上确定受农业实践影响最大的SOM成分，并确定它们的变化速度。例如，众所周知，在免耕耕作下，作物凋落物和残留物积累在表层土壤上，但如果土壤被耕作以管理压实或作物残留物，则会迅速降解。 能否更好地管理这一有机物池，以提高其转化为SOM的效率？这些知识对于理解控制SOM存储的机制以提出可持续农业生产策略至关重要。

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.