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United States Department of Agriculture

Agricultural Research Service

Title: Compost Maturity Index: a Classification Approach That Reflects Chemical and Biological Factors

item Thompson, W. - EDAPHOS INTL
item Watson, M. - OHIO STATE UNIV.
item Millner, Patricia
item Leege, P. - P.B.LEEGE CO., LTD.

Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: August 15, 2001
Publication Date: October 29, 2001

Technical Abstract: The maturity index is a 3-step decision tool for classifying composts by relative level of maturity. Three compost quality parameters are evaluated: 1) C:N ratio; 2) stability (be respirometry); and 3) potential phytotoxicity (by bioassay and/or chemical tests). Step 1 excludes material with a high propensity to immobilize N; material with a C:N ratio equal to or greater than 25:1 is categorized as immature; compost with a lower C:N ratio is further evaluated. Step 2 excludes material that is undergoing active microbial decomposition; a stability rating is assigned: very stable; stable; or unstable. Compost rated as unstable is classed as immature, whereas compost with a stability rating of very stable or stable is further evaluated. Step 3 screens for potentially phytotoxic compounds by considering chemical maturity indicators; a compost is assigned a maturity indicator rating of immature, mature or very mature. The outcome from Steps 2 and 3 are contrasted in a 2-way decision matrix and assigned a final maturity rating.

Last Modified: 4/21/2015
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