Studies on composts prepared from waste materials I preparation, nitrogen losses and changes in ‘soluble nitrogen’

1. Changes in the pH and total soluble nitrogen of composts from waste materials have been examined during decomposition for periods up to two years. Losses of nitrogen dry matter and organic matter after 14‐16 weeks were also determined.

2. The rate of decomposition, based on the level of soluble nitrogen, in composts from straw and sewage sludge, increased as the initial nitrogen content increased from 1‐10 to 1‐97% above 1‐97% there was no increase in rate of decomposition and losses of nitrogen became excessive.

3. Nearly all the soluble nitrogen in mature composts was present as nitrate; the pH of the mature composts varied approximately inversely as the nitrate content.

4. Supplementary aeration slightly decreased the level of soluble nitrogen in mature composts and considerably increased losses of nitrogen in 14‐10 weeks. Aeration had little effect on losses of dry matter.

5. The soluble nitrogen in mature composts from straw and ammonium sulphate was much greater than in composts from straw and sludge prepared with the same initial nitrogen content.

6. The optimum conditions for preparing composts from straw and sludge in small cells are discussed, and the importance of the level of nitrogen, minimal aeration, duration of storage period and the influence of soluble nitrogen in the starting materials are emphasized.