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

在农业、森林和草原土壤中，三分之二的陆地碳以土壤有机质(SOM)的形式储存，因此它是全球碳的主要储存库，SOM动态的变化可以影响全球大气二氧化碳(CO2)的水平。SOM对动植物生命也是至关重要的，因为它改变了土壤的物理、化学和生物性质，包括养分和水分保持、抗侵蚀和土壤肥力。尽管发挥了这一核心作用，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了解甚少--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%，管理措施直接影响土壤有机质的形成和周转。最近，由于土壤有机质具有缓解气候变化的潜力，这些土壤已经成为一个主要的研究热点：这些土壤失去了原来土壤有机质的30%-50%，但可以成为全球大气二氧化碳的主要储存库，在那里，植物C以数百到数千年的SOM的形式被封存。我的研究项目研究耕作方式和土壤性质如何影响土壤有机质成分，对于制定封存碳的策略至关重要。拟议的研究将在位于安大略省德里的一个长期田间地点收集的土壤和作物样本上进行。这些田间地块于1988年在1933年以来的烟草-秋黑麦轮作地点建立。土壤是壤质沙土，可以研究有机质成分，而不受粘土的混杂影响。它包括三种耕作制度(玉米连作、大豆-小麦轮作和烟麦轮作)，在两种耕作制度下，采用翻耕轮作和免耕。其目标是确定由于上一次烟草-黑麦轮作的种植顺序和耕作方式的改变而导致的土壤有机质数量和组成的变化。由于SOM池中可测量的变化发生得很慢，因此该站点已经存在了大约20年，这一事实是无价的。它被认为是世界上唯一一个含有14C和15N标记作物残留物的长期地点，由于从C3(烟草-黑麦)物种转变为C4(玉米)物种，它允许测量增量13C。

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.