Читать книгу Mountains and Moorlands - W. Pearsall H. - Страница 22

The lower nitrogen content which is characteristic of upland peats and humus is due partly to the slow breakdown of the original plant materials. These, as a general rule, are rich in carbon and poor in nitrogen, though these proportions vary with the plant species. Consequently undecayed plant remains reflect principally the low nitrogen content of the original material. On the other hand, the ultimate nature of the humus produced depends also on the relative rates of breakdown and removal of the two main components—which are the carbonaceous and nitrogenous compounds. In many peats the soil bacteria are unable to attack cellulose, one of the principal materials containing carbon—a substance which makes up the bulk of plant cell-walls and skeletal structures. Slow though the breakdown of nitrogenous matters may be, therefore, it still is often more rapid than that of the chief carbon compounds, so that the latter gradually become more abundant and the percentage of nitrogen remaining in the humus becomes less. This condition has a further harmful effect on the activity of the soil fungi and bacteria, for most of these organisms prefer a growth medium containing a low C/N ratio. Thus in order to facilitate the breakdown of dead leaves in a rubbish-heap, gardeners often mix with it nitrogenous manurial materials, a treatment that results in a greatly accelerated rate of bacterial decomposition of the plant remains.