NOTE:
These narratives that provide a detailed description of the parameter,
the rationale for its inclusion, specific test methods, and other
information.
pH: pH is the numerical measure of the acidity
(or alkalinity), or hydrogen ion activity of the soil. The
pH scale ranges from 0 to 14, with a pH of 7 indicating neutrality.
Most compost has a pH of between 6 and 8. Since specified
plant
species can persist and flourish when grown within a specific
pH range, and based on typical compost application rates,
it is
understood that the addition of compost can affect the pH
of growing media. Therefore, to estimate the effect, which
in turn will affect
maintenance practices or system management, pH is a necessary
parameter to be aware of. pH is adjusted through the use
of such
materials as lime (alkaline) and sulfur (acidic). If liming
agents are used in the production of your compost product,
this information
should also be provided to end users. Although the addition
of lime in the composting process may not dramatically effect
the
compost's pH, it will have a pronounced effect on calcium
availability. pH adjustments of limed composts are much more
difficult, due
to its higher buffering capacity, and therefore, may not
be appropriate for specific applications.
Soluble Salts (salinity): Soluble salts
concentration is the concentration of soluble ions in a solution,
which is measured by the ability to carry an electric current.
Many nutrients are supplied to plants in salt form, while some
soluble salts are more detrimental to plants than others. Most
plant species have a salinity tolerance rating and maximum tolerable
quantities are known. Excess soluble salts can cause phytotoxicity
to plants. Soluble salts are measured in mmhos/cm or dS/m. Compost
may contribute to, or dilute, the cumulative soluble salts content
of growing media or soil. Manure compost tends to be low in soluble
salts, where sludge (biosolids) and yard debris composts are more
variable. Reduction in soluble salts content can be achieved through
thorough watering (leaching). However, management practices for
leaching will be dependent on the salinity of the irrigation water.
Nutrient Content (N-P-K): Nitrogen
(N), Phosphorous (P), and Potassium (K) are the three nutrients
used by plants in the greatest quantities (macronutrients), and
therefore, are the nutrients most often applied through fertilization.
These three nutrients are measured and expressed in a dry weight
basis in the form of a percentage (%). The content of phosphorous
should be expressed as P2O, and potassium as K20,
which are the plant available forms. The total nitrogen content
should be expressed and the amount of water soluble (N03
and NH4) and insoluble nitrogen forms should be known.
The content of these nutrients, as well as magnesium and calcium,
should be known to allow end users to make correct decisions regarding
supplemental nutrition and pH adjustment. Providing data relative
to the content of other nutrients can also be helpful, and may
be necessary for specific applications. Although large quantities
of nutrients are not typically found in compost, in comparison
to most fertilizer products, compost is usually applied at greater
rates and, therefore, can have a significant cumulative effect.
Water Holding Capacity: Water holding
capacity is the ability of a given volume of compost to hold water
under one atmosphere of pressure. Water holding capacity measures
the potential benefit of reducing the required frequency of irrigation,
as well as gross water requirements. The water holding capacity
should be known to allow end users to monitor, or estimate, the
compost's effect on their crop watering regime and growing media.
Water holding capacity is measured as a percent of dry weight.
Bulk Density: Bulk density is the weight
per unit volume of compost. Bulk density is used to convert compost
application rates from tonnage to cubic yards. In a field application,
cubic yards per acre would subsequently be extrapolated to express
an application rate represented as a depth in inches (i.e., 1
inch application rate). Bulk density is also used to determine
the volume of compost which may be transported on a given occasion,
taking into account that most vehicles have a specific maximum
gross weight which may not be legally surpassed. A product's bulk
density may also affect other handling issues. Bulk density is
typically measured in grains per cubic centimeter, then converted
to pounds per cubic yard.
Moisture Content: Moisture content
is the measure of the amount of water in a compost product, expressed
as a percent of total solids. The moisture content of compost
affects its bulk density, and, therefore, may affect transportation.
Moisture content is also relevant because it affects product handling.
Compost which is dry can be dusty and irritating to work with,
while compost which is wet can become heavy and clumpy, making
its application more difficult and delivery more expensive.
Organic Matter Content: Organic matter
content is the measure of carbon?based materials in compost. Organic
matter content is typically expressed as a percentage of dry weight.
To derive more accurate measure of organic matter content, materials
that are combustible, but also considered to be man-made inerts,
should not be considered organic matter in the expressed figure.
Being aware of a product's organic matter content is necessary
for determining compost application rates on specific applications,
such as soil incorporation and topsoil production. In these applications,
standard agricultural soil test kits are often used to determine
the recommended application rate of compost. However, these application
rates are specified as the quantity of organic matter needed per
acre. Typically, rates are not specified for specific types of
organic matter. Therefore, the compost product's organic matter
content must be known to convert the application to usable form.
Particle Size: The specificity in which
compost particle size is measured should be based on the product's
end use or your customer's specific needs. For most applications,
merely specifying the product's maximum particle size or the screen
size through which it passes, is sufficient. However, for specific
applications, such as potting/nursery media component, a full
particle size distribution may be required. A compost's particle
size distribution may be required. A compost's particle size distribution
will effect the porosity of the media to which it is added. Porosity
is related to the ability of a potting/nursery mix to resist water
logging, and low media oxygen levels. Particle size distribution
measures the amount of compost meeting a specific particle size
range, by using a series of sieves (screens) to capture compost
particles of specific size. Particle size distribution figures
are expressed as the percent of materials retained per sieve size.
A compost product's particle size may also determine its usability
in specific applications. For example, a compost product with
a maximum particle size of 1/2 inch or greater may not be acceptable
as a turf topdressing, whereas a product with a maximum particle
size of 3/8 inch or less would be acceptable.
