A Comparative, Quantitative Study of the Micro-Arthropods in Different Types of Pasture Soil

Abstract

1. The differences between the pasture soils on plots A and B are especially evident in their physical composition and in the more acid nature and lower organic content of the soil in plot B. 2. The rainfall figures for the autumn and early winter months during the sampling period were considerably higher than the annual average. 3. The normal maximum of the micro-arthropods in local soils occurs during the late summer and early autumn (end of rainfall season), and the minimum during the late winter and early spring (dry season). 4. The fluctuations in biomass of the micro-arthropods are not always in accordance with the fluctuations in numbers. The highest mean biomass per m2 was recorded during November 1962, the insects (excluding Collembola) being the dominant group. 5. The Trombidiformes, represented by 27 families, were numerically the dominant group of the Acari during the entire sampling period. The Tarsonemidae, Tydeidae, Nanorchestidae and Tetranychidae were more abundant than the other families. 6. Twenty-six species belonging to seven families constituted the mesostigmatid population in the soil of plot A, the Aceosejidae, Rhodacaridae and Laelaptidae being the dominant families. 7. The oribatid fauna of plot A was composed of 19 species representing 16 genera. The soil in this plot supported a much larger population than in plot B. 8. The Acaridiae were represented by two species on plot A and by one on plot B; this group constituted a small portion of the acarine fauna in the soil. 9. The numbers of the Collembola on plot A were very low during the entire sampling period whereas they were more abundant on plot B. 10. The insects (excluding Collembola) were mainly represented by Corrodentia, Hymenoptera and Homoptera; they made a considerable contribution to the biomass of the soil.