Volume 1 Part 1 Article 15
Title: Some Chemical Changes in Mushroom Composts
Author: S. Burrows
Analysis of mushroom composts used m cropping trials for the development of synthetic composts gave information on the losses of dry matter and nitrogen taking place Difficulty was experienced m accurately assessing losses of dry matter during the composting period, but over the limited number of composts for which figures were available there appeared to be an association between dry matter losses and yields, high losses corresponding to high yields On the other hand, there was a negative correlation between dry matter losses during composting and those during cropping In addition, over about thirty composts corresponding to about 100 cropping beds, there was a weak but significant positive correlation between yields and dry matter losses during cropping These three correlations are not contradictory’, but indicate that the cropping dry matter loss may be divided into two parts, one part being due to the growth of mushroom mycelium and being related to yields, and the other part being due to the activity of other organisms and being affected by the magnitude of the dry mattei loss during composting.
Dried blood or nitrochalk was normally used as nitrogen source m these synthetic composts but hide meal was used m some and these showed a much lower dry matter loss during cropping, although yields were normal This may have been due to restricted bacterial action.
Big variations in dry matter losses during composting, caused by composting for different periods of time, were considerably reduced by a peak heating treatment m which a maximum temperature of 50°C was maintained for about 24 hours Mushroom yields tended to be more uniform m this experiment, thus again suggesting a connection between y iclds and composting losses.
During the composting process losses of nitrogen often occurred and these depended upon the original nitrogen content of the compost and also upon the temperature m the stack during composting Losses of dry matter were independent of nitrogen levels m these composts and thus there was a tendency for variations m C/N ratios to be reduced during composting During cropping, losses of nitrogen always took place but the amount was considerably greater than could be accounted for by its transference to the mushrooms or the casing soil Nitrogen losses incieased with increasing nitrogen m the compost but losses from hide meal composts were much lower than from other composts Composts which did not crop still sustained high losses of nitrogen The evidence points strongly to the loss of nitrogen as gas by bacterial demtnfication.
See also MRA. Report 1946-1948, p.49 et seq MRA Report 1949, p.18 et seq