Dynamics and Contribution to Carbon Flows of Enchytraeidae (Oligochaeta) Under Four Cropping Systems

Abstract

(1) Enchytraeids were sampled in 1980-85 in an agricultural field experiment with four cropping systems: barley without nitrogen fertilization (B0); barley receiving 120 kg N ha-1 year-1 (B120); grass ley (GL); and lucerne ley (LL). The aim was to study the influence of the cropping systems on enchytraeid abundance and biomass and to calculate the contribution of enchytraeids to carbon flows in soil. (2) The enchytraeid fauna was composed of three widely distributed, sexually reproducing species of high reproductive capacity. Juveniles were mainly found in summer and early autumn. (3) Mean enchytraeid abundance in September in 5 years did not differ significantly between cropping systems but the dynamics did so. Mean abundance was 8400 m-2 in the top 20 cm of the soil and mean biomass was 0.45 g dry mass m-2. The vertical distributions of enchytraeid numbers and biomass in B0 and B120 were more uniform than in GL, where the enchytraeids were concentrated at the surface (0-4 cm deep). In LL, the vertical distribution was intermediate between those for GL and barley. The vertical distribution of enchytraeids reflected distribution of roots, and possibly organic matter and pore space. Towards the end of the experiment, abundance and biomass were greater in B0 than in B120. In the 2 months after ploughing, enchytraeid abundance increased in GL from 4700 to 28,000 m-2 and dry biomass increased from 0.3 to 0.9 g m-2. (4) Respiration of the total enchytraeid fauna was estimated at 1.2-2.6 g C m-2 year-1. This constituted 0.5 -1.6% of total heterotrophic soil respiration. Consumption (16-34 g dry mass m-2 year-1) corresponded to 3-12% of organic matter input to the soil.