ABSTRACT
The demands on modern agriculture to provide ample food, feed, and energy coupled with anthropogenic (human)-driven global climate change has greatly increased the importance of understanding and managing the dynamics of soil carbon (C) and nitrogen (N) cycling (C/N cycling). The world’s C and N supplies exist in a continuous and dynamic cycle, and key processes are constantly active in the soil beneath our feet. The amount of C in the top one meter of soil (the pedologic pool) is approximately 3.5 fold greater than that in the atmosphere; this C helps soil retain its structure and function including crop production and ecosystem stability. In contrast to C, the great majority of the Earth’s N is not in soil but in the atmosphere. However, most of the forms useful to plants are found in the soil. Plant productivity in natural systems is often N limited; in agriculture, farmers routinely supplement soil N with fertilizers and manure and, thus, perturb C/N cycles. The cycles of C and N in soil are linked and are controlled by microorganisms. As a result, microorganisms and their activity have a significant impact on some of our greatest challenges including sustaining food production and water quality and reducing soil emission of the greenhouse gases that drive climate change. This entry provides a new overview of the forms and locations of C and N in soil, emphasizes the biological factors controlling pedologic C/N cycling, and addresses how today’s anthropogenic activities stress the soil ecosystem, potentially impacting its stability.
