Earthworms' Random Foraging Might Be Tamed by TillageBy
In their blind search for food, earthworms play an unseen but critical role
in agriculture. Someday, farmers might be able to boost this helpful role with
tillage methods that "herd" earthworms towards their food supply--and
help guard water quality.
Once a worm stumbles on its food source--decaying crop stubble--it keeps
coming back for more, according to a study at the
Agricultural Research Service. The
implication is, worms can be "taught" how to help soil--and
farms--become more productive and environmentally friendly.
Lab studies led by ARS soil scientist Dennis R. Linden in St. Paul, Minn.,
show that one common earthworm, Aporrectodea tuberculata, excavates 3
feet of tunnel per week. It swallows most of its work into its 2- to 2½-inch-long
body. The ten worms per square foot used in the study is equivalent to 435,600
worms an acre--enough to dig almost 250 miles of tunnels in a week.
Earthworm tunnels help loosen soil, create fertile soil clods or aggregates,
provide paths for roots, redistribute organic matter and drain and aerate soil.
Scientists have long known that the benefits can include better crop yields and
less soil erosion.
More recent ARS studies suggest tunneling may also help keep water free of
chemicals. Vertical tunnel patterns give water a relatively chemical-free route
downward, and the soil in the organic-rich burrows harbors more beneficial
microbes to degrade pesticides and fertilizers.
Linden and University of Minnesota graduate student Sabrina M.F. Cook
discovered that an earthworm searches randomly until it tastes food. Then it
keeps returning for more. The patterns of these return trips depend on the kind
of tillage. With reduced tillage, crop stubble is left on the ground. This
concentrates organic matter near the surface so the worms form a network of
burrows and depressions that funnel water vertically. Plowing, which buries
crop residue, leads to more horizontal, meandering burrows that slow down soil
water. Linden plans field studies to see how tillage can be designed to
encourage vertical tunneling.
Scientific contact: Dennis R. Linden, USDA-ARS
Water Management Unit, St. Paul, Minn., phone (612) 625-6798, fax 649-5175,