Transformations of carbon and nitrogen during composting of animal manure and shredded paper

Abstract

Composts produced from animal manures and shredded paper were characterized in terms of their carbon (C) and nitrogen (N) forms and C mineralization. Total, water-soluble, acid-hydrolyzable and non-hydrolyzable C and N contents were determined on composts sampled on days 0, 11, 18, 26, 33, 40 and 59 after composting was initiated. Water-soluble and acid-hydrolyzable C and N decreased during composting, whereas non-hydrolyzable C remained relatively constant, and non-hydrolyzable N greatly increased during composting. The water-soluble forms of N were characterized by a decrease of ammomium (NH₄ ⁺-N) at the beginning of composting, followed by an increase of nitrate (NO₃ ^–-N) towards the end of composting. The mineralization of C in composted materials was generally higher at the beginning than at the end of composting, whereas no differences were observed for mineralization of C in non-hydrolyzable materials. The addition of N inhibited C mineralization in composts except in samples collected on days 40 and 59, while C mineralization was strongly stimulated by adding N to the non-hydrolyzable materials. The data suggest that the N forms in the non-hydrolyzable materials were chemically similar and not readily available to microbes, indicating that the C/N ratios often used to assess the biodegradability of organic matter and to develop compost formulations should be based on biologically available N and C and not on total N and C.