bedding or to make compost. Later, these residues
return to contribute to soil fertility as manures or com-
AboveGround croP resIdues
posts. Sometimes residues are removed from fields to
The amount of aboveground residue left in the field
be used by other farmers or to make another product.
after harvest depends on the type of crop and its
There is increasing interest in using crop residues as a
yield. The top table contains the amounts of residues
feedstock for the production of biofuels. This activity
found in California’s highly productive, irrigated San
could cause considerable harm to soil health if sufficient
Joaquin Val ey. These residue amounts are higher
residues are not allowed to return to soils.
than would be found on most farms, but the relative
Burning of wheat, rice, and other crop residues in the
amounts for the various crops are interesting.
field still occurs, although it is becoming less common in
the United States as well as in other countries. Residue
Crop Residues in the
San Joaquin Val ey (California)
is usually burned to help control insects or diseases or to
CROP
TONS/ACRE
make next year’s fieldwork easier. Residue burning may
Corn (grain)
5
be so widespread in a given area that it causes a local air
pollution problem. Burning also diminishes the amount
Broccoli 3
of organic matter returned to the soil and the amount of
Cotton
2.5
protection against raindrop impact.
Wheat (grain)
2.5
Sometimes important needs for crop residues and
Sugarbeets 2
manures may prevent their use in maintaining or
Safflower
1.5
building soil organic matter. For example, straw may
Tomatoes
1.5
be removed from a grain field to serve as mulch in a
Lettuce
1
strawberry field. These trade-offs of organic materials
Corn (silage)
.5
can sometimes cause a severe soil-fertility problem if
Garlic
.5
allowed to continue for a long time. This issue is of much
Wheat (after baling)
.25
more widespread importance in developing countries,
Onions
.25
where resources are scarce. In those countries, crop resi-
dues and manures frequently serve as fuel for cooking or
heating when gas, coal, oil, and wood are not available.
Residues of Common Crops in the
In addition, straw may be used in making bricks or used
Midwest and Great Plains
as thatch for housing or to make fences. Although it is
CROP
TONS/ACRE
completely understandable that people in resource-poor
Corn (120 bu.)
3.5
regions use residues for such purposes, the negative
Sorghum (80 bu.)
2.5
effects of these uses on soil productivity can be substan-
Wheat (35 bu.)
2
tial. An important way to increase agricultural produc-
Soybeans (35 bu.)
less than 1
tivity in developing countries is to find alternate sources
for fuel and building materials to replace the crop
—FroM various sourCes
residues and manures traditionally used.
Using residues as mulches. Crop residues or
composts can be used as mulch on the soil surface. This
90
Building SoilS for Better CropS: SuStainaBle Soil ManageMent
