are removed at the bottom. Some vermicomposting
operations are connected with livestock farms to process
manure for export of excess nutrients off the farm as a
dIseAse suPPressIon bY coMPosts
value-added product.
Research by Harry Hoitink and coworkers at Ohio State
University shows that composts can suppress root and
USINg cOMPOSTS
leaf diseases of plants. This suppression comes about
Finished composts generally provide only low relative
because the plants are general y healthier (microorgan-
amounts of readily available nutrients. During compost-
isms produce plant hormones as well as chelates that
ing, much of the nitrogen is converted into more stable
make micronutrients more available) and, therefore,
are better able to resist infection. Beneficial organisms
I don’t make compost because it makes me
compete with disease organisms for nutrients and
feel good. I do it because composting is the only
either directly consume the disease-causing organ-
thing I’ve seen in farming that costs less, saves time,
isms or produce antibiotics that kill bacteria. Some
organisms, such as springtails and mites, “actual y
produces higher yields and saves me money.
search out pathogen propagules in soils and devour
—CaM tabb, West virginia beeF and CroP FarMer
them,” according to Hoitink. In addition, Hoitink
found that potting mixes containing composts “rich in
organic forms, although potassium and phosphorus
biodegradable organic matter support microorganisms
availability remains unchanged. However, it should be
that induce systemic resistance in plants. These plants
kept in mind that composts can vary significantly and
have elevated levels of biochemical activity relative
some that have matured well may have high levels of
to disease control and are better prepared to defend
nitrate. Even though most composts don’t supply a large
themselves against diseases.” This includes resistance
amount of available nitrogen per ton, they still supply
to both root and leaf diseases.
fair amounts of other nutrients in available forms and
greatly help the fertility of soil by increasing organic
Composts rich in available nitrogen may actual y
matter and by slowly releasing nutrients. Compost
stimulate certain diseases, as was found for phy-
materials can be tested at selected commercial agricul-
tophthora root rot on soybeans, as well as fusarium
tural and environmental laboratories, which is especially
wilts and fire blight on other crops. Applying these
important if certification is sought. Composts can be
composts many months before cropping, al owing
used on turf, in flower gardens, and for vegetable and
the salts to leach away, or blending them with low-
agronomic crops. Composts can be spread and left on
nitrogen composts prior to application reduces the
the surface or incorporated into the soil by plowing or
risk of stimulating diseases.
rototilling. Composts also are used to grow greenhouse
crops and form the basis of some potting soil mixes.
Composting can change certain organic materials used
Composts should not be applied annually at high rates.
as surface mulches—such as bark mulches—from
That is a recipe for overloading the soil with nutrients
stimulating disease to suppressing disease.
(see discussion in chapter 7).
147
Building SoilS for Better CropS: SuStainaBle Soil ManageMent