Table of Contents
From Trash to Compost
Properties of Compost
Effect of Compost on
Plant Growth Response
to Landfill Compost
How to Use Landfill Compost
James E. Shelton, Extension Specialist, Soil Science
North Carolina Cooperative Extension Service
July 1991 (TMD)
Last Web Update:
December 1997 (DBL)
Of the 160 million tons of
municipal solid waste produced in the United States annually about 85
percent is landfilled. In 1989, North Carolina produced 6
million tons of municipal solid waste. Land-filling poses many
problems, such as rising landfill maintenance and development costs, decreasing
availability of landfill sites, and an increasing risk that substances
leaching from landfills may contaminate groundwater and surface
From 25 to 40 percent
of these solid wastes could be composted and used in land based disposal
systems. Using this organic material to amend the soil could not only
improve soil quality but also serve as an environmentally safe and economically
sound method of waste disposal.
Composting is a natural biological process.
Carried out under controlled conditions, it hastens the decomposition
of organic waste and reduces its volume, creating a stable, soil-enriching
humus. A basic understanding of the composting process will help you appreciate
its beneficial effects on soil and crop growth.
The microorganisms that function in composting
have basic requirements. To achieve an acceptable product, adequate amounts
of air, water, and nutrients must be supplied. Proper control of surface
area, temperature, and acidity is also necessary.
Microorganisms involved in organic waste
degradation also need carbon as an energy source and nitrogen for protein
synthesis. The carbon-to-nitrogen ratio required by these microorganisms
is 30-to-1, whereas, municipal solid waste has a much larger
ratio of 150-to-1 or higher. Thus, nitrogen added to reduce
the carbon-to-nitrogen ratio will enhance the composting process.
Other elements needed by the microorganisms
may not be available during their initial rapid buildup. These elements
may be added as necessary. The addition of lime neutralizes some of the
organic acids released during decomposition, maintains a desirable acidity
range, and reduces the loss of nitrogen gas. The added nutrients combined
with the nutrients released during breakdown of the organic waste remain
in the compost as a valuable resource for plant growth.
The biological activity and temperatures
higher than 140°F destroy pathogens and most weed seed, resulting in a
final product that is safe to use.
Because landfill waste is composed of a high
percentage of noncompostible materials, composting must be followed by
screening. In a recent study of Buncombe County landfill compost, screening
removed the noncompostible and large wood particles, leaving a dark, friable
product containing a high percentage of unidentifiable organic constituents.
The composition of this material is shown in Figure
1. Table 1 gives an analysis
of the elements found in the compost. The following additions were made
to supply nutrients needed by the microorganisms and to achieve the necessary
pH and carbon-to-nitrogen ratio: 3 pounds of nitrogen, 2
pounds of P205 (phosphate), 2 pounds
of K20 (potash), and 5 pounds of dolomitic limestone
per cubic yard of raw material. The composting process reduced the volume
by approximately 50 percent and concentrated the basic elements
nitrogen, phosphorus, potassium, calcium, and magnesium as shown in Table
1. The finished compost had a pH of 7.3 and a
cation exchange capacity* of 63 centi moles per kilogram.
This high nutritive value and large cation exchange capacity suggest many
uses for improving soil quality and crop productivity. Also, heavy metal
concentrations were well below the United States Environmental Protection
Agency (USEPA) limits and safe for crop production.
1. Weight Composition of Buncombe County landfill
1. Elemental Composition of Buncombe County Landfill
*Cation Exchange Capacity is a measure
of the soil's ability to hold basic cations such as potassium, calcium,
When municipal solid waste compost was incubated
with a sandy or clayey soil, the bulk density of each soil was reduced
(Figure 2). Bulk density changed
proportionally to the rate of compost addition. Consequently, the soils'
structure, tilth, moisture retention capacity, and the water infiltration
rate of the clay soil were improved. Compaction and crusting were
2. Effect of Buncombe County landfill compost on
bulk density of a sandy and clayey soil.
The two soils' cation exchange capacities
were markedly increased by adding composted municipal solid waste (Figure
3). Adding 25 percent compost to a sandy or clayey
soil increased the cation exchange capacity 500 to 600
percent. Further compost additions continued to increase the cation
exchange capacity, but never as significantly as the first 25 percent.
At an optimum level of saturation the increased cation exchange capacities
would enhance the ability of the soils to hold potassium, calcium, and
magnesium in an available form. Potassium would increase from 195
to 1,014 pounds per acre; calcium from 1,200
to 6,240 pounds per acre; and magnesium from 180 to
936 pounds per acre.
3. Effect of Buncombe County landfill compost on
the cation exchange properties of a sandy and clayey soil.
The response of tomatoes grown in a variety
of pine bark and landfill compost mixtures are shown in Figure
4. At all rates of nitrogen fertilization, plant response improved
as the percentage of compost increased. In the first crop of tomatoes,
the following gains in biomass were seen as the compost increased: 1,900
percent when no nitrogen was applied; 1,420 percent
when 100 parts per million of nitrogen was applied; and 800
percent when 200 parts per million of nitrogen was
applied (Figure 4A). Along with positive responses as the compost levels
increased, the second crop of tomatoes grown in the same media showed
a greater response to nitrogen. The removal of much of the available nitrogen
contained in the compost by the first crop caused the increased effects
of nitrogen in the second crop. The response to increasing compost levels,
though not as great as in the first crop, was a direct response to the
organic components of the compost (Figure 4B).
Fruit production was also enhanced by increasing
the compost content of the growing medium (Figure 4C). At the highest
level of nitrogen supply (200 parts per million of nitrogen),
the fruit response varied with changes in the composition of the growing
medium. These changes may have been caused by high nitrogen levels, which
have been reported to reduce fruit set. Analysis of tomato fruit did not
show any heavy metal accumulation. Thus the fruit would be safe for human
4. Effect of landfill compost on dry weight of
tomato plants and fruit yield at three nitrogen levels.
Impatiens responded much differently to compost.
When no nitrogen was added, the best growth was attained in 100
percent compost. With nitrogen application rates of 100 or
200 parts per million, the maximum response to compost was
at the 75 and 50 percent levels, respectively
5. Effect of Buncombe County landfill compost on
dry weight of impatiens at three nitrogen levels.
Landfill compost can be used effectively
in many plant production systems. Field soils can be improved by incorporating
compost into the soil during land preparation or by applying it as surface
mulch. With field-grown nursery or sod crops, where significant volumes
of soil are removed at harvest, compost could replenish soil losses, thus
Container-produced nursery crops are frequently
grown in a medium of pine bark and peat moss. Compost could be used as
a substitute for the peat moss and, with some crops, as the growing medium
for container production. Compost could be used in greenhouse operations
as a medium or a medium amendment for production of floral crops and bedding
Composted municipal solid waste has been
used successfully to improve the physical and chemical properties of soils
and increase the growth of tomatoes, birch, maple, and bluegrass-fescue
sod. However, it was not found to increase the growth of azaleas because
the pH of the medium was too high for optimum growth. These studies indicate
that composted landfill waste has many potential uses in producing various
agricultural crops. Compost could be prepared to meet consumer demands
with minimal processing.