Clay Soils, Clay Loams, Loam Soils
Clay Soils
Soils containing 60 per cent, or more of clay and silt are commonly
called clay soils. A large part of so-called clay soil may be silt. Some clay soils are 80
to 90 per cent clay and silt; these are usually worthless for farming. Clay soils are
exactly the reverse of sandy soils in nature and in agricultural value. The very small
spaces between the exceedingly fine grains admit air and water very slowly. When a clay
soil is once thoroughly wet it is sticky ; when dry it cracks and bakes and becomes
cloddy. Hence, such soils are not only hard to till, but they are also hard on plants,
often being too wet in a wet time and too dry in a dry time. The difficulty lies in the
slowness of clay soils to move water. The dark, bluish-gray colour which so many clays
possess is mostly due to the presence of iron oxide or iron sulphide; the red or yellow,
is due to the presence of peroxide and protoxide of iron. On the other hand, clay soils
are usually rich in plant food, especially in potash. Plants once established in them,
particularly deep-rooting plants, are carried ahead vigorously.
The farm crops that succeed most generally on clay soils are the cereals, grasses and some
tree fruits, notably the apple, pear and plum. Clay land is especially valuable for hay.
The treatment of a clay soil should be that which will remedy its chief defect —
heaviness. Under-drainage will do much to accomplish this result. Under-drainage removes
the surplus water in a dry time and promotes aeration and warmth in these soils, many of
which are sadly deficient in these respects. The fine particles of clay may be separated
from each other and the soil loosened and lightened by mixing them with particles of
humus or sand. Barnyard manure or a green manure crop will lighten a heavy clay soil, as
well as give body to a light sandy soil. Manures applied to clay soils in the fall lose
but little of their plant food by leaching. It is rarely practicable to haul sand upon a
clay soil and plow it under, because of the expense, but if this can be done expediently
the result will be gratifying.
It often happens that a muck bed, marking the place where a small swamp formerly existed,
is adjacent to clay land. Three or four inches of muck spread upon clay soil is of
immediate and lasting benefit. Extreme caution should be used in plowing and tilling clay
soils. If plowed when too wet they become cloddy. There is a certain point between wetness
and dryness when a clay soil crumbles quite readily; it should be tilled only at this
time, so far as is possible. The texture of a clay soil may be ruined for several years
by one injudicious plowing, when it was too wet. Unless the soil is very tenacious, and
"runs together" or "puddles" if left bare over winter, clay land may be fall-plowed to
advantage, leaving it rough and exposed to the mellowing action of freezing and thawing.
The crust that forms so easily over the surface of clay soil in summer should be
prevented by frequent shallow tillage. Something may also be done to improve the texture
of clay soils, in certain cases, by liming them. This causes many of the fine grains to
stick together, forming larger grains, thereby making the soil looser and more porous.
The liming of soils is considered in Chapter XIV.
Clay Loams
These are quite similar to clay soils, but they contain less clay
and silt, and more sand. A soil carrying 30 to 40 per cent, of clay is generally classed
as a clay loam, and a soil carrying 40 to 50 per cent, of clay as a heavy clay loam. A
clay loam usually has 25 to 35 per cent, of sand, and a heavy clay loam 10 to 25 per
cent, of sand. The fair proportion of sand mixed with the clay in this type of soils
makes them easier to handle than clay soils, and more porous. They are apt to be rich,
especially in potash, not only because of the store of native plant food, but also
because they are very retentive soils. The plant food in fertilisers that may be applied
to them is not quickly leached away, as it is on sandy soils, but is held very
tenaciously by this more compact soil. Crops upon clay loams are not likely to suffer
from drought as badly as on clay soils, because water moves through them more freely.
Some clay loams, however, are cold and wet. These soils more than any other type, are
benefited by under-drainage. The clay loams are suitable for a larger range of cropping
than any other soils, except the loams themselves. They are especially valuable for
grass, wheat and corn. In handling clay loams attention should be given to the details of
management that are beneficial to clay soils, and especially to under-drainage, judicious
plowing and the incorporation of humus.
Loam Soils
These are the most useful "all around" soils; they combine the
lightness and earliness of the sands, with the strength and retentiveness of the clays.
Loams contain from 40 to 60 per cent, of sand, and 15 to 25 per cent, of clay. They "work
up" easily, do not crust or crack, are well supplied with plant food, and, what is chiefly
important, water moves through them freely and still they are not leachy. Practically all
farm crops grow satisfactorily on a loam. It is especially suitable for potatoes, corn,
market-gardening crops, and small fruits; but grasses, cereals, clover, alfalfa, and
cotton, find it congenial. It requires no special treatment, except such attention to
good tillage, drainage, and the addition of humus as is a necessary part of the best farm
practice everywhere.
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