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United States Department of Agriculture

Agricultural Research Service

Title: Transformation of Organic Matter and Its Effect on Nutrient Reserves

Author
item Smith, Jeffrey

Submitted to: Proceedings of the International Symposium on Integrated Nutrient Managemen
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 1999
Publication Date: N/A

Interpretive Summary: Soil organic matter plays a major role in terrestrial ecosystem development and functioning. In both undisturbed and cultivated systems, potential productivity is directly related to soil organic matter concentrations. The dominate effect that soil organic matter has on ecosystem structure and stability is clear evidence of the need to protect current soil organic matter levels and develop management practices which will enhance soils with declining soil organic matter contents. Organic matter contents range from less than 0.2% in desert soils to over 80% in peat soils. In temperate regions soil organic matter ranges between 0.4 and 10.0%, with humid region soils averaging 3-4% and semi-arid soils 1-3%. Although it is only a small fraction of the soil, components of soil organic matter are the chief binding agents for soil aggregates which, in turn, control air and water relationships for root growth and provide resistance to wind and water erosion. The dynamic nature and complex chemistry of soil organic matter makes it a major source of plant nutrients. With 95% of soil nitrogen (N), 40% of soil phosphorus (P) and 90% of soil sulfur (S) being associated with the soil organic matter fraction, decomposition and turnover can supply the majority of macronutrients needed for plant growth. During decomposition microorganisms assimilate complex organic substances for energy and carbon (C), and release inorganic nutrients. This process is controlled by temperature, moisture, soil disturbance and the quality of soil organic matter as a microbial substrate. These factors, together with the size and activity of the microbial population regulate the rate of decomposition and nutrient release.

Technical Abstract: Soil organic matter is a complex and dynamic entity that is ever changing. The interaction of soil organic matter with microorganisms, soil particles, nutrient elements, the abiotic environment and plants is the critical factor in ecosystem stability. Soil organic matter is a critical factor for agricultural crop production and timber forest growth. The loss of soil organic matter will seriously affect any plant growth and eventually the soil system. Crop residues are usually considered a problem but handled correctly can increase soil organic matter dynamics and nutrient cycling which creates a more efficient system. We are in grave danger of losing productive land by ignoring changes in the soil created by disturbance. The most significant disturbances are occurring from deforestation and agricultural production. These disturbances are causing biological, chemical and physical instability in the systems because of massive carbon loss and changes in nutrient cycling. A major research need is to be able to quantify a soil system as to its health and ability to function properly. Changes in soil organism diversity and functioning may be an avenue to assess the stability of disturbed and regenerating ecosystems. Quantification between systems is also needed, for example, deforestation causes permanent changes in plant communities disrupting organism population diversity whereas agroecosystems with periodic disturbance will change organism functioning. Techniques from molecular biology to community structure should be developed to provide a measure of system degradation and potential resiliency.

Last Modified: 10/24/2014
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