Soil organic matter
Upon successful completion of this course, students will be able to

  • Understand basic composition of SOM
  • Know factors affecting SOM dynamics
  • Explain functions of SOM in soils

Hello, we are Hok Lyda and Sambo Pheap and currently lecturers at Royal University of Agriculture. I would like to introduce you to an online course “Introduction to Soil Organic Matter (SOM).” This course consists of three modules and provides an introduction to SOM and the importance of SOM in agricultural soils. This course is designed for students interested in taking online courses. This course contains lectures and quizzes for students' practices.

No prerequisite for this course


  1. During the conversion of dead plant and animal materials into organic matter, biological processes occur first, followed by chemical and physical processes which occur in parallel and enable the stabilization of organic matter.

    • Biological processes refer to the action of macro-fauna and micro-organisms which fragment, bury, decompose and mineralize organic compounds. The 3 main biological processes are the fragmentation, the decomposition and the mineralization.

    • The stabilization of soil organic matter occurs then through physical and chemical processes, which are the occlusion within aggregates, the adsorption onto minerals and the selective preservation through biochemical recalcitrance.

    All those processes happen at the same time in the soil, even though they concern organic material at different stage of degradation. Thus, the SOM can be considered as a continuum including different sizes of particles at different stage of degradation from fresh residues to humus.

    The speed at which those processes occur is influenced by different factors. We will first see what are those factors, and then study in detail the different processes mentioned above.

  2. We remind you that an increase of the amount in SOM in the soil means that there is also an increase in the content of total organic carbon. Organic carbon influences many soil characteristics including color, nutrient holding capacity (cation and anion exchange capacity), nutrient turnover, and stability, which in turn influence water relations, aeration and workability.

    The role and functions of SOM will be described in the following sections. We will first emphasize the influence of SOM on soil characteristics and then detail its role in nutrient budget.

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