Tillage and cropping effects on the fate of crop derived-c and n and turnover of soil organic matter

三分之二的陆地碳以土壤有机质（SOM）的形式储存在农业、森林和草地土壤中，因此它是全球碳的主要储存库，SOM的动态变化可以影响全球大气二氧化碳（CO2）的水平。SOM对植物和动物的生命也至关重要，因为它改变了土壤的物理、化学和生物特性，包括养分和保水能力、抗侵蚀能力和土壤肥力。尽管有这一核心作用，但人们对受土地利用变化或全球变暖影响的土壤有机质的性质和动态知之甚少——它被认为是地球上最复杂的混合物。农业生态系统占土地面积的11%，管理做法直接影响土壤有机质的形成和周转。最近，这些土壤已经成为主要的研究焦点，因为SOM有减缓气候变化的潜力：土壤已经失去了30-50%的原始SOM，但可以成为大气二氧化碳的主要全球储存库，在那里，植物C被隔离为数百至数千年的SOM。我的研究项目是研究耕作方式和土壤特性如何影响SOM成分，这对于制定隔离c的策略至关重要。拟议的研究将在位于安大略省德里的一个长期田野收集的土壤和作物样本上进行。这些地块是1988年在一个自1933年以来实行烟草-秋季黑麦轮作的场地上建立的。土壤是壤土，使SOM成分的研究免于粘土的混杂影响。它包括三种耕作制度（玉米连作、大豆-小麦轮作和烟草-黑麦轮作），在两种耕作制度下，使用板犁-圆盘耕作的CT和NT。目标是确定从以前的烟草-黑麦CT轮作的种植顺序和耕作方式的转变所导致的SOM的数量和组成的变化。由于SOM池中可测量的变化发生缓慢，因此该站点已存在约20年的事实是无价的。它被认为是世界上唯一一个含有14C和15n标记的作物残留物的长期站点，并允许测量δ 13C，因为从C3（烟草-黑麦）到C4（玉米）物种的转换。

Two-thirds of the terrestrial C is stored as soil organic matter (SOM) in agricultural, forest and grassland soils, therefore it is a primary storehouse of global C and changes in the dynamics of SOM can influence global levels of atmospheric carbon dioxide (CO2). SOM is also critical for plant and animal life because of it modifies soil physical, chemical and biological properties, including nutrient and water retention, erosion resistance, and soil fertility. Despite this central role, the nature and dynamics of SOM as affected by land-use change or global warming are poorly understood - it is considered to be the most complex mixture on earth. Agricultural ecosystems account for 11% of the land area and management practices directly affect SOM formation and turnover. Recently these soils have become a major research focus because of the potential for SOM to mitigate climate change: the soils have lost 30-50% of their original SOM but could be managed to be a major global reservoir for atmospheric CO2 where plant C is sequestered as SOM that is hundreds to thousands of years old. My research program studies how farming practices and soil properties affect SOM constituents and is critical for devising strategies for sequestering C. The proposed research will be conducted on soil and crop samples collected at a long-term field site located at Delhi, ON. These field plots were established in 1988 on a site in tobacco-fall rye rotation since 1933. The soils are loamy sand, allowing study of SOM constituents free of the confounding affects of clay. It includes three cropping systems (continuous corn, a soybean-wheat rotation and a tobacco-rye rotation), under two tillage regimes, CT using mouldboard plough-disc tillage and NT. The goal is to identify changes in the quantity and composition of SOM resulting from a shift in cropping sequence and tillage from the previous tobacco-rye CT rotation. Since measurable changes in SOM pools occur slowly, the fact that this site has been in place for ~20 yr is invaluable. It believed to be the only long-term site in the world containing 14C- and 15N-labelled crop residues and allowing measurements of delta 13C because of the switch from C3 (tobacco-rye) to C4 (corn) species.