Effects of Aporrectodea Caliginosa on Soil Hydraulic Properties and Solute Dispersivity

Earthworms have historically been absent from dryland agricultural fields in eastern Colorado, but their invasion or purposeful introduction may affect water retention and plant nutrient availability in soil. The objective of this study was to determine the effect of Aporrectodea caliginosa on hydraulic properties and solute dispersivity in soil from eastern Colorado (Adena [Ustic Paleargid]-Colby [Aridic Ustorthents] complex) that was amended with biosolids. Columns of repacked soil (50 cm in depth) were incubated with or without A. caliginosa for a period of 16 wk, after which columns were divided into 15-cm depth increments to determine soil-water retention curves and solute breakthrough curves (BTCs) under unsaturated and saturated conditions. Aporrectodea caliginosa and their burrows and casts altered soil water retention curves in the top 30 cm of the soil, where A. caliginosa were most active. Earthworms also affected BTCs within the top 30 cm of soil resulting in an approximately 35-fold increase in solute dispersivity under saturated flow conditions and a 4- to 10-fold increase with unsaturated flow conditions. Overall, A. caliginosa increased soil residual water content by 33 to 41% and altered soil physical properties so that water flow became more tortuous, solute dispersion increased under saturated and unsaturated conditions, and soil drained over a larger range of tensions. In conclusion, A. caliginosa has the potential to reduce upward losses of water, increase water retention, and increase dispersion of agricultural chemicals applied to the soil surface.