環境土壌資源論

This course examines soil as a central component of the Earth system and develops a mechanistic understanding of how biogeochemical cycles—particularly those of carbon (C), nitrogen (N), and phosphorus (P)—regulate Earth system functioning and stability. Anthropogenic perturbations have accelerated global environmental change, including climate forcing, disruption of the N and P cycles, land-use change, and biodiversity loss. These processes are conceptualized within the framework of Planetary Boundaries, which defines the safe operating space for humanity within the Earth system.

The course begins with an overview of Earth system science and the Planetary Boundaries framework, explicitly positioning agriculture and soils as key regulators of elemental fluxes and feedbacks. Soil is then treated as a reactive biogeochemical matrix composed of minerals, organic matter, and microorganisms, in which coupled physical, chemical, and biological processes govern the transformation, stabilization, and loss of elements.

Core modules focus on the mechanistic basis of the C, N, and P cycles in soils, including processes such as mineral–organic associations, microbial transformation pathways, redox dynamics, and nutrient limitation. Emphasis is placed on how these processes scale to ecosystem and global fluxes, and how they interact with climate change and agricultural management. The course also examines how land-use change, fertilization, and soil management alter elemental cycling, greenhouse gas emissions, and soil functions.

In the latter part of the course, students work in groups to investigate topics at the interface of soil, agriculture, and Planetary Boundaries. Each group critically evaluates primary literature and case studies, and presents their findings for discussion.

By the end of the course, students will be able to interpret global environmental challenges through a soil-centric, process-based framework and evaluate strategies for managing soils to support Earth system stability and sustainable agriculture.

本講義では、土壌を地球システムの重要な構成要素として捉え、炭素・窒素・リンを中心とする生物地球化学循環と地球環境問題との関係を理解する。近年、人間活動の拡大により、気候変動、窒素・リン循環の撹乱、土地利用変化、生物多様性の損失など、地球システムの安定性に関わる環境問題が深刻化している。これらは「地球限界（Planetary Boundaries）」という概念によって整理され、人類社会が安全に活動できる地球システムの範囲が議論されている。本講義ではまず、地球システム科学および地球限界の概念を概観し、その中で農業と土壌が果たす役割を位置づける。続いて、土壌を鉱物、有機物、微生物からなる反応場として理解し、炭素循環、窒素循環、リン循環の基本プロセスと、それらが気候変動や農業活動とどのように結びついているかを学ぶ。また、土地利用や施肥管理などの農業活動が物質循環に与える影響についても議論する。講義後半では、学生がグループに分かれ、土壌・農業と地球限界に関わるテーマを選び、関連する研究論文や事例を調査して発表・討論を行う。本講義を通して、土壌を起点として地球環境問題と持続可能な農業を統合的に理解する視点を養う。