Biological aspects of soil fertility

Abstract

1. These researches were undertaken in order to analyse and define with precision the causes of infertility in a heath soil at Wareham Forest, Dorset.2. The presence of substances actively inimical to growth has been confirmed and the origin of the resulting toxicity established.3. A new technique for biological analysis, the nutrient-agar-film method, makes it possible to estimate the relative degree of toxicity in any given sample, thus facilitating development of methods of laboratory control for elimination and redistribution of the factor or factors responsible.4. It has been proved that the toxic substances are of biological origin and that they operate directly by inhibiting fungal growth. The resulting biological inertia is exemplified by almost complete cessation of cellulose decomposition. Following upon this inertia are indirect effects of a secondary character on growth of the higher plants, in the case of trees restricting root growth, impeding mycorrhiza formation, and curtailing supply of nutritive requirements.5. Justification for the use of organic composts for relieving the observed infertility under field conditions has been provided by laboratory experiments proving that removal of toxicity and profound alteration of the organic substrate and soil bionomics follow addition of compost. Changes so induced are self-propagating and the effects on growth persistent.6. The bearing of these results on fertility in other natural soils and in cultivated soils is discussed.