Earthworm collection from agricultural fields: Comparisons of selected expellants in presence/absence of hand-sorting
Résumé
The role earthworms play in soil fertility is under increasing scientific scrutiny, especially in light of the fact that farmers are seeking to reduce soil tillage. However, there are many discrepancies in earthworm sampling methods. The aim of this study is to compare the efficiency of three chemical expellants (formaldehyde, commercial ‘hot’ mustard and allyl isothiocyanate, abbreviated AITC), with two sampling methods: (i) a simple method that consisted in spreading an expellant solution on the soil and retrieving earthworms that emerged at the soil surface, and (ii) a combined method that consisted in applying a chemical to expel earthworms and then hand-sorting the remaining earthworms from the block of soil. Sampling efficiency was measured in terms of earthworm density and biomass, for endogeic and anecic earthworms. With the simple method, a higher density of earthworms was sampled using formaldehyde and AITC than with mustard. Formaldehyde, AITC and mustard expelled not significantly different biomasses of 47.7, 31.9 and 20.5 g m−2, respectively, on average over the three plots. The combined method did not yield a significantly different density or biomass with the different chemicals. Formaldehyde is toxic and commercial ‘hot’ mustard is difficult to standardise and inefficient when used without hand-sorting. Accounting for the accuracy of the sampling methods as well as the toxicity of the chemicals to users and soil organisms, AITC appears to be a reliable and promising chemical expellant whether or not in combination with hand-sorting. Its use would be a step towards standardizing earthworm sampling methods.