Volume 10 Part 2 Article 3: Influence of pH and Ammonia in Mushroom Compost

Volume 10 Part 2 Article 3
Year 1979
Title: Influence of pH and Ammonia in Mushroom Compost
Author: J.P.G. Gerrits


Two factors have a substantial influence on the composting process and hence can be considered as primary ecological factors. Their importance has already been described previously (Gerrits 1977a). At the same time a parabolic relationship between the NH4 content of the compost at filling and the yield was established. Using gypsum and a peak-heating period of 10 days a NH4 content of 0.4% is optimum. The pH is then about 8.3-8.5. During peak-heating the NH4 content decreases to about 0.1% or lower. This applies to horse manure compost as well as to synthetic compost.

If the NH4 content is 0.4%, the N content in horse manure compost is 1.5%, but in synthetic compost 2.0%. In both cases this is the level at which the N content remains constant throughout composting, neither increasing or decreasing. The difference between these two types of compost is brought about by their different ash-content. Expressed as percentage of the organic matter the N content is about the same. On average a NH4 content of 0.4% is achieved in horse manure compost by adding 100 kg of chicken manure per ton of horse manure and in synthetic compost by adding 1000 kg of chicken manure per ton of dry straw. The chicken manure can be replaced completely or partly by other N sources. In the Netherlands chicken manure is most economic.

Since the NH4 content decreases gradually during peak-heating, it is obvious to assume that the time required for the NH4 to fall below a certain value (e.g., 0.1%) will depend on the NH4 level at filling. To check this, composts with various NH4 levels were prepared and peakheated for various periods of time. In addition a series of trials was carried out to study the significance of gypsum in the compost. The results are discussed below first of all in relation to the significance of the NH4 content and the pH.

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