Table 9.1
Effects of Different Management Practices on Gains and Losses of Organic Matter, Beneficial Organisms, and Pests Management Practice
Gains
Losses
Enhance Beneficials
Increase
Decrease
(EB), Stress Pests (SP)
Add materials (manures, composts, other organic materials) from off the field
yes
no
EB, SP
Better utilize crop residue
yes
no
EB
Include high-residue-producing crops in rotation
yes
no
EB, SP
Include sod crops (grass/legume forages) in rotation
yes
yes
EB, SP
Grow cover crops
yes
yes
EB, SP
Reduce tillage intensity
yes/no*
yes
EB
Use conservation practices to reduce erosion
yes/no*
yes
EB
* Practice may increase crop yields, resulting in more residue.
all situations. In chapters 10 through 16, we will evaluate
with large root systems. Compared to aboveground
management options that enhance the soil environment
residues, the organic material from roots decomposes
and issues associated with their use. Most of these prac-
more slowly, contributes more to stable soil organic
tices improve organic matter management, although
matter, and, of course, does not have to be incorporated
they have many different types of effects on soils.
into the soil to achieve deep distribution. When no-till
is used, root residues, along with root exudates given
Using Organic Materials
off when they were alive, tend to promote formation
Amounts of crop residues. Crop residues are usually
and stabilization of aggregates—more so than surface-
the largest source of organic materials available to farm-
derived residue. One of the reasons that the many soils
ers. The amount of crop residue left after harvest varies
of the Midwest are so rich is that for thousands of years
depending on the crop. Soybeans, potatoes, lettuce,
prairie plants with extensive and deep root systems grew
and corn silage leave little residue. Small grains, on the
there—annually contributing large quantities of organic
other hand, leave more residue, while sorghum and corn
matter deep into the soil.
harvested for grain leave the most. A ton or more of crop
Some farmers remove aboveground residues such
residues per acre may sound like a lot of organic mate-
as small grain straw from the field for use as animal
rial being returned to the soil. However, keep in mind
Table 9.2
that after residues are decomposed by soil organisms,
Estimated Root Residue Produced by Crops
only about 10–20% of the original amount is converted
Crop
Estimated Root Residues (lbs/acre)
into stable humus.
Native prairie
15,000–30,000
The amount of roots remaining after harvest also can
Italian ryegrass
2,600–4,500
range from very low to fairly high (table 9.2). In addition
Winter cereal
1,500–2,600
to the actual roots left at the end of the season, there
Red clover
2,200–2,600
Spring cereal
1,300–1,800
are considerable amounts of sloughed-off root cells, as
Corn
3,000–4,000
well as exudates from the roots during the season. This
Soybeans
500–1,000
may actually increase the plant’s belowground inputs of
Cotton
500–900
organic matter by another 50%. Probably the most effec-
Potatoes
300–600
tive way to increase soil organic matter is to grow crops
Sources: Topp et al. (1995) and other sources.
89
Building SoilS for Better CropS: SuStainaBle Soil ManageMent