Collembola populations in an organic crop rotation: Population dynamics and metabolism after conversion from clover-grass ley to spring barley

Abstract

Summary Population dynamics of earthworms, enchytraeids, mites and collembolans were assessed over two years as part of a collaborative research project in an organic crop rotation at the agricultural Research Centre Foulum, Jutland, Denmark. The Collembola study presented here is restricted to the first growth season of a two-year study, i.e from just before conversion of a two year old clover-grass ley to seedbed until harvest of the barley crop. The results refer mostly to the four most abundant species. The project included experimental reductions of earthworm populations to test the effects on interactions between earthworms and mesofauna. Expulsion by electro-shocking resulted in modest reductions in earthworm density and biomass. No significant effect of the reduction was observed on the collembolan populations. Total collembolan density and density, mean weight per specimen, biomass and population metabolism of the four most abundant species decreased markedly between the first and second sampling date as an effect of the mechanical disturbance, and inversion of soil layers caused by soil preparation. The depth distribution for all Collembola species was inverted from highest concentration in the 0–10 cm layer to highest concentration in the 10–20 cm soil layer. After a population minimum in May, the density, mean weight, biomass and metabolism increased more or less regularly according to species. The net loss of biomass after conversion implied a mobilization of 5 mg N.m−2 from dead collembolan tissues. Together with an estimate for nitrogen due to excretion, the contribution of Collembola to nitrogen mobilization through the growth season was estimated tentatively as 10 mg.m−2. This amount was negligible compared with the contribution of earthworms. The possibility that indirect catalytic effects of collembolan activity could have any significant effect on nutrient availability for plants was not resolved but the collembolan population metabolism showed no obvious synchrony with the nutrient requirements of the crop.