module_02 Carbon Transformations and Organic Matter
lesson_01 What are the advantages and disadvantages of adding organic materials?
objective Be able to identify benefits of organic matter in an aerobic and anaerobic setting.

Organic materials Organic materials added to the soil are the primary food source of soil organisms.  These organic materials gradually decompose and are converted into organic matter.

Role of organic matter Organic matter has a valuable role in aerobic and anaerobic soils as a nutrient source and for nutrient storage. First, nutrients like nitrogen, sulfur, and phosphorous mineralize and become available for growing rice plants as organic materials decompose. Second, organic matter has a high capacity to attract and store nutrients.  As a result, nutrients like calcium, magnesium, and potassium are available for plants instead of being leached away or immobilized.



Aerobic soil In an aerobic setting, organic matter is continually being oxidized. In order to maintain adequate levels of soil organic matter, new organic materials must be added.  Organic matter in aerobic soil plays a critical role in the formation of soil aggregates.  These aggregates influence soil pore space needed for good aeration and soil drainage.

Anaerobic soil In submerged soil, organic materials tend to accumulate due to slow anaerobic decomposition. The death and decomposition of aquatic organisms, such as algae, and the decomposition of crop residues provide organic materials contributing to the development and maintenance of soil organic matter. Addition of organic material is not necessary for formation of soil aggregates since soil structure is destroyed during puddling.

Methane release From Lesson 4, the addition of organic materials in an anaerobic environment can result in a significant release of methane during decomposition. By applying organic materials prior to flooding, some of the carbon compounds will decompose and be released as carbon dioxide. This reduces the amount of carbon that will be released as methane after the field is submerged.

Learning assessment This is the last lesson for Module 3. To get a brief assessment on what you have learned, click Next at the bottom of the screen.


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