Earthworms (Aporrectodea spp.; Lumbricidae) cause soil structure problems in young Dutch polders

The presence of earthworms in relation to clay soil structure problems in arable fields in the Flevopolders (the Netherlands) was studied. Recently, farmers in this area have had difficulty in harvesting potatoes in predominantly wet years. After a dry period, soil particles in the top layer of the potato ridges form a platy structure and are difficult to sieve. Locally, this resulted in many clods, and sometimes harvesting proved impossible. In the field, significantly more earthworms (mainly Aporrectodea caliginosa and A. rosea) were observed in the problem parts than in the non-problem parts. A macrocosm study showed significantly more settlement and soil stickiness and an increasing number of large clods caused by greater numbers of A. caliginosa. The results of this study reveal earthworms to be the main factor affecting the state of the soil and causing the harvesting problems.