Nitrification plays an important role in nitrogen turnover in composting process. It has been believed that nitrification occurs mainly during the maturation phase due to the elevated temperature during the active phase of composting. In this work, the intense biodegradation of organic matters is demonstrated to be another negative impact on the ammonia oxidation, the first step of nitrification. We investigated the ammonia oxidation in compost following organic matters addition at intermediate temperature. Different indicators of ammonia oxidation were studied, respectively. The accumulation of nitrite and nitrate was 10(2)-10(3) lower in composts with organic matters addition. The nitrous oxide emissions were absent or 40-fold inferior in these composts. The nitrogen mass balance indicated a less amount of oxidized ammonia after the addition. The ammonia-oxidizing bacteria declined following the organic matters addition. In contrast, the ammonia-oxidizing archaea were supported by the organic matters. Possible mechanisms of this impact were also discussed. (C) 2013 Elsevier Ltd. All rights reserved.