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Soils vary
greatly and reflect the influence of both geology and vegetation.
TEXTURE
-
may be "light"
or "heavy": Feel a piece of soil between the finger tips. If it is
gritty, large particles (sand grains) are
present. A
high sand content means low fertility and low moisture retention,
but good aeration and rain penetration and easy working even when
wet or
cold (hence called light soil).
If it feels pasty, smooth, and soon dries your skin, it has a high
clay content (very small mineral particles). Clay has a high
attraction for and retention of water (will even steal it from your
skin) and of minerals (fertilizer). But too much clay means low
aeration, and clay
disturbed or
trampled when wet or cold may become hard. Such "puddled" soil has
lost what pores it had for air and water and root penetration.
ORGANIC CONTENT
-
A dark layer
indicates plant influences. If the soil is dark, light in weight,
and moist but crumbly (does not dry the skin), it has a very high
organic content and is called peat. Peat soils build up in sedge
meadows (and in the cold floating moss bogs of the north) because
waterlogging prevents aeration, retarding bacterial decay of plant
matter (just as cold climate can). Peat has high retention of water
and fertilizer, gives good aeration if well drained, and high
absorption of rain if not too dry, but may be deficient in some
available
minerals.
Disturbed peat has, in addition to ordinary weeds, special ones like
marsh nettles and giant ragweed.
A good loam
soil has an organized structure of coarse and fine mineral matter
and some organic matter too. The glaciers left us good loams in Dane
County, which the prairies enriched further with deep organic
incorporation. Some of the soil here is topsoil (loam) brought in
from farmland. In other places, there is almost pure peat, because
this marsh was once a waterlogged sedge meadow (see
sign 6). The
presence of nettles and dark soil color will indicate the peat. The
south knoll (sign 13) has a top layer of coarse sand brought in to
increase dryness.
Diagrams
of organic layers in some natural soils. (The soils you see here
were disturbed by construction and the bringing in of fill, but
can still be tested for texture and organic content).
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