Temporal and spatial dynamics of earthworm surface casting in a temperate soybean agroecosystem

Earthworm activity is expected to have a beneficial effect on soil structure and plant growth in agroecosystems, but active populations are temporally dynamic and spatially heterogeneous under field conditions. The objective of this research was to evaluate the temporal and spatial variation in surface casting by earthworms at the row-interrow scale in a temperate soybean agroecosystem. Earthworm populations were manipulated in 2.9 m2 field enclosures by applying carbaryl pesticide to reduce the naturally occurring earthworm population before juveniles and adults of Aporrectodea caliginosa (Sav.) and Lumbricus terrestris L. were added. Surface casting was measured weekly during a 14-week period. There was very little surface casting during the first 6 weeks of the study, possibly due to insufficient food resources and shade at the soil surface. We collected nearly 3400 casts from weeks 7 to 14, and surface casting rates during this period ranged from 0.95 to 2.51 g dry weight m−2 day−1. More casts were deposited within 30 cm of the soybean row than at distances up to 50 cm from the row, indicating that the planted row was a zone with greater earthworm activity than the inter-row. Better understanding of the timing and small-scale variation in earthworm activities will aid our understanding of how earthworms contribute to plant growth.