Geoscience Reference
In-Depth Information
Chapter 9
Agric Horizon
9.1
Introduction
The agric horizon is a subsurface horizon formed from cultivation. Known also as
the “plow sole,” the agric horizon is below the Ap plow layer. There are two major
requirements for the agric horizon: a thickness of
10 cm and either
5%
>
>
wormholes or
5 % lamellae. Formerly used at the great-group level in the Udalfs
(Agrudalfs), the agric horizon is not used currently as a prefix in classifying soils in
ST. Therefore, it is not possible at the present time to locate soil series from the
OSDs that contain an agric horizon.
>
9.2 Properties of Soils with an Agric Horizon
Figure
9.1
(top) shows a trench of soils containing an agric horizon in Outagamie
County, WI. The middle photograph shows the agric horizon below the plow layer,
and the lower photo shows the effect of the agric horizon on rooting of corn
(
Zea mays
). Trafficking leads to a reduction in macroporosity and saturated hydrau-
lic conductivity and an increase in penetration resistance, runoff, and bulk density
(Table
9.1
). These changes are often accompanied by a reduction in crop
production.
9.3 Classification and Distribution of Soils
with an Agric Horizon
Although many agricultural soils and some intensively managed forest soils in the
USA contain agric horizons, no soil series with agric horizons have been identified
to date.
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