Time-limited soil sorting for long-term monitoring of earthworm populations

Hand sorting of soil blocks is a reliable but very labour intensive and ted ious method for estimating earthworm population sizes. A standardised, time -limited, intensive sorting procedure was adopted for a long-term earthworm field population study and the error in population estimates resulting fro m the use of this procedure was quantified during monthly sampling over one cropping cycle of conventional wheat and direct-drilling wheat-clover fiel ds. Compared to full soil sorting without time restriction, time-limited so rting achieved mean relative recoveries of 81-87 % of earthworm numbers and 94-97 % of earthworm biomass, but required only 36 % of the actual sorting time needed for full sorting. The earthworms which were missed during time -limited sorting were mainly unpigmented juveniles, accounting for 90 % of the numbers and 70 % of the biomass, and their mean individual biomass was 31-38 mg. It is concluded that validated time-limited soil sorting is a use ful, time-saving and also ergonomically advantageous approach for long-term studies of earthworm population dynamics.