Studies on the Relationship Between Earthworms and Soil Fertility

Abstract

Observations on earthworm populations in the Carse of Stirling indicate that there are definite differences according to soil type both in total population numbers and in the relative numbers of each species present. The light and medium loams appear to carry higher total populations than the heavier clay types or the more open gravelly sand or alluvial types. Within and between the respective soil‐type populations, species numbers are variable, but the actual numbers present on a soil type do not necessarily indicate the relative importance of each species. In all cases Allolobophora caliginosa is the dominant species, being more numerous on the light loam than elsewhere. A. longa is subdominant and forms a substantial percentage on the medium loam and clay. On the light loam A. longa is high in number, but forms a smaller percentage of the total population because of the abundance of A. caliginosa. A. longa is also of reduced importance on the open soils—gravelly sand and alluvium. This species does not differ very much from Lumbricus rubellus and L. terrestris, as a percentage of the population on these two later soils and the light loam. The percentages of these two species are similar within populations, though much lower on the clay than on the other soils, and the total Lumbricus population number is highest on the light loam and lowest on the clay. There is a fair similarity between the two populations on the two open‐textured soils, in both numbers and percentages.Areas of acid, natural pastures contain earthworm populations low in number and species variety. Some of the species typical of these areas are small active species, e.g. Dendrobaena rubida, D. octaedra and Bimastus eiseni, which are not found in well‐established field populations. When agricultural treatment improves an area the acid‐pasture species eventually decrease in relative number and importance as the species normally associated with good pasture land become established and build up their populations.