Tillage practices, and temperature and moisture interactions affect earthworm populations and species composition

The objective of this study was to evaluate season;ll populations of earthworms using the hand-sorting method in a long-term irrigated field study. The population of earthworms over the season was greater in the no tillage treatment in die upper 10 cm than in the fall and spring tillage treatments. There were similar numbers of earthworms in all the tillage treatments at the lower depth. However, the similarity in earthworm numbers represented different percentages of the three species in each of the tillage treatments. In the fall tillage treatment at the lower soil depth, Aporrectodea turgida dominated the population for most of the season. Whereas, under no tillage, Aporrectodea tuberculata, and A. turgida dominated, and under spring tillage A.. turgida dominated for the first part, and Aporrectodea rosea for the last half of the season. These results indicated a preference for different habitats and associations by different species. The results showed that A. tuberculata had a strong preference for no tillage which was likely related to soil moisture and temperature differences created by no tillage compared with the other tillage practices. The disturbance by tillage also affected A. tuberculata more than the other earthworm species. It was concluded that seasonal variation in earthworm populations was a function of the interaction between soil moisture and temperature, which was strongly influenced by tillage.