Objective  Phsicochemical properties of composts with varied nitrogen (N) contents during tunnel composting were analyzed to provide the basis for optimizing the formula of Agaricus bisporus substrate.

  Method  Wheat straws and chicken manure were blended to result in starting compost materials with varied N contents at 1.15% (T1), 1.35% (T2), and 1.55% (T3) for the tunnel composting. Samples at different composting stages were taken for measurements on moisture, ash, and N contents as well as pH. Yields of mushrooms grown on the composts from Phase Ⅰ and Phase Ⅱ of the composting process were compared for evaluation.

  Result  In all cases, the N content in compost increased continuously during the fermentation process. Collected after Phase Ⅱ, the 2.28% of N content from T3 was significantly higher than T1. The generally weak alkaline compost had a pH increased initially followed by a decline. The pH of T3 in either Phase Ⅰ or Phase Ⅱ was the highest among all samples. A correlation between the pH and N content in compost was observed. The moisture content decreased continuously during the fermentation showing a minimum at 65.78% on T3 in Phase Ⅱ which was considered suitable for the mushroom cultivation. The ash content increased continuously along the composting. Among the various N levels, T1 had the lowest ash content at the beginning and remained the lowest with a content of 30.92% at the end of Phase Ⅱ. The compost with a higher N content during tunnel composting produced higher mushroom yield, as the greatest yield of 20.74 kg·m^-2 was found on T3.

  Conclusion  The physicochemical properties of the compost during tunnel composting changed significantly with varied N contents in the raw material. The mushroom yield reached the highest level under T3 when 1.55% N was formulated in the starting compost materials. Thus, T3 was recommended for commercial A. bisporus cultivation.