|DANA O. PORTER, P.E.
WVU Extension Service
Agricultural Engineering Specialist
article is intended to help agricultural producers make
well-informed decisions about applying organic wastes,
and whether they should consider applying "raw"
untreated waste, partially treated waste, or treated
waste, such as compost. The focus will be upon two common
practices in production agriculture: direct land
application of raw waste and direct application of
composted waste. Keep in mind, however, that organic
wastes may prove beneficial or detrimental, depending
upon how wisely they are used and upon waste
characteristics. One waste material may provide valuable
nutrients and improve soil productivity if applied
appropriately, or damage soil productivity and possibly
contaminate water resources if applied inappropriately.
Another waste material may benefit one cropping system
and harm another. Still another waste may contain some
valuable nutrients, but also contain high levels of
undesirable elements, such as heavy metals or salts.
While the general discussion is about utilization of
animal wastes, these same concerns can be applied to food
processing wastes, domestic and municipal sewage and
sludges, and industrial organic wastes. Future articles
will explore waste handling, treatment, and utilization
alternatives in greater detail.
Benefits of organic waste utilization
Farmers and gardeners have long recognized the
importance of replacing nutrients and organic matter that
are depleted under continuous cropping. Renewed and
growing interest in "nutrient recycling" can be
attributed to high costs of synthetic fertilizers and the
increasing need for suitable disposal of wastes generated
by Concentrated Animal Feeding Operations (CAFOs).
Depending upon the material, organic wastes can supply
macronutrients (N, P, and K) and micronutrients to the
soil for use by crops. These materials can replace part
of or all synthetic fertilizers used in an operation.
Adding organic matter to mineral soils can improve their
physical properties (infiltration, water holding,
structure, etc.) and chemical properties (Cation Exchange
Capacity, fertility, etc.) Through agricultural
utilization of organic wastes, producers can benefit (and
possibly derive marketing potential) from materials that
otherwise may be placed into landfills or present
environmental pollution problems.
Direct land application
Direct land application of raw or partially treated
wastes is a well-known method of waste utilization.
Animal wastes and sewage sludges contain both
plant-available nutrients and immobilized nutrients
(which may become available as the organic material
decomposes). Waste characteristics, soil moisture, and
temperature will affect the rate of decomposition in the
field. Application rates should be based upon soil
fertility, crop requirements, and chemical
characteristics of the waste(s). Timing will depend upon
crop needs and the weather. Application method will
depend upon the physical characteristics of the waste and
upon equipment availability. Generally, solid wastes can
be applied with a manure spreader or common tillage
equipment. Liquid wastes may be injected, broadcast, or
applied through an irrigation system. Semi-solid or
slurry wastes may require special equipment or may be
modified so they can be handled with available or
Waste generators consider direct land application an
economical means of waste "disposal" in which
they may seek to minimize land area required for disposal
(i.e., apply waste at the highest allowable rates). For
example, a CAFO facility operator may be required to
demonstrate in his Pollution Prevention Plan that he has
sufficient land for environmentally safe application of
wastes generated at his facility. The size of his
operation, therefore, may be limited by the amount of
land available for waste application. Alternately, the
CAFO operator may seek alternate "disposal"
options, which include selling the animal waste as
A farmer who purchases the waste material as
fertilizer is interested not in maximizing the amount of
material that can be applied to his fields, but rather in
maximizing his net return on his input investment. It is
not in his best interest to overapply the waste. He will
supplement the waste with "complimentary"
wastes or synthetic fertilizers to provide a nutrient
balance appropriate for his crop. He will optimize the
value of the material by balancing costs of the waste
(including transportation and application costs) against
costs of synthetic fertilizers and the expected benefit
(in crop productivity) from the fertilizer application.
Composting is a biological treatment in which
microorganisms (bacteria, fungi, and actinomycetes)
decompose and stabilize organic material. Managing a
composting system generally involves providing an
environment that supports (maximizes) microbial activity.
As microbes consume organic material to grow and
metabolize, some of the waste mass (including nutrients)
is immobilized in the cells of the microorganisms. As a
result of microbial metabolism, water vapor, carbon
dioxide, and heat are released. Loss of water vapor
results in a gradual drying of the waste; loss of carbon
dioxide and water vapor result in reduction of mass. Heat
generated in composting increases temperature of the
material, which generally increases microbial activity.
High temperatures maintained in the composting process
also can destroy weed seeds, insects, and pathogens.
(Composting organic wastes will be discussed in greater
detail in an upcoming article.)
Because composted waste is "treated," it is
more stable than an untreated or partially treated waste.
Easily decomposed fractions in the material are
metabolized or "immobilized" in the bodies of
microorganisms. As a result, some nutrient loss may
occur. Under ideal aerobic conditions, however, nitrogen
may be transformed from an ammonia to a nitrate,
minimizing the volatilization loss of the ammonia.
Immobilized nutrients can become available with slow
decomposition of organic matter, in effect a "timed
release" of nutrients. The nutrient content of
compost will depend upon the nutrient content of the raw
materials, management of the composting system, and the
relative "decomposability" of the compost
materials. A chemical analysis is necessary to verify
the fertilizer value of the final compost product.
Since compost is a stable, bulky material, it is
relatively easy to handle and transport with conventional
equipment. Because it has a relatively low moisture
content, compost may be less expensive to transport than
many untreated high-moisture wastes. Further, because of
its biological stability, it is easy to store and
unlikely to smell at time of application.
Direct land application vs. composting: Which is
Comparing advantages and disadvantages of direct land
application of raw wastes with composted wastes may be
helpful in determining which is appropriate for your
operation. In general, untreated waste can be obtained at
lower cost than compost because composting involves some
investment of time, equipment, and labor. Untreated waste
may also contain higher concentrations of readily
available nutrients, especially nitrogen. However,
broadcast application without timely incorporation can
result in significant ammonia losses.
Compost can provide a farmer with greater scheduling
flexibility. While an untreated waste must be applied and
incorporated promptly to prevent nitrogen loss and
nuisance conditions, compost is stable and can be stored
safely. You can store, apply, and incorporate compost
when you and your operation are ready. Compost presents
little or no odor. Provided it is adequately treated and
cured, compost is not likely to "burn" plants.
Further, aerobic (high temperature) composting kills
pathogens and weed seeds, and will not contribute to pest
Organic waste utilization: Potential problems and
how to avoid them
Potential problems related to nutrient management in
agriculture can be avoided by following relatively simple
Nutrient overloading, through a one-time heavy
application or through accumulation of nutrients over
time, can contribute to pollution of surface or ground
water. Some micronutrients can even accumulate to levels
that may prove toxic to plants and/or grazing animals.
Before applying organic or inorganic fertilizers to a
field, collect soil samples and analyze them for
fertility levels. Contact your county agent for
assistance with soil sampling and analysis. Estimating
how much N, P, and K your crop will need and determining
residual nutrient content of your soil will help
determine how much supplemental fertilizer is needed.
Utilizing organic fertilizers (including wastes) is
similar to applying synthetic fertilizer in that you need
to know how much N, P, K, etc., you are applying. If the
material has not been analyzed, collect a representative
sample and have it tested at the West Virginia Department
of Agriculture Moorefield Field Office (HC 85, Box 302,
Moorefield, WV 26836); or send it to your preferred soil
testing laboratory. Be sure to note whether the lab
reports values in NO3-N, NH3-N, P2O5,
and K2O or elemental N, P, and K. You can save
money and reduce pollution risks by using your
fertilizers more efficiently.
Nutrient losses from applied organic waste can
result from volatilization and/or leaching. Ammonia
volatilization losses will be reduced if the waste is
applied through subsurface injection or, if
surface-applied, waste is incorporated soon after
application. Leaching losses will be reduced if the waste
is applied shortly before the crop needs it (in the
spring rather than in the fall). Careful control of
compost mixtures and aerobic conditions will limit
nutrient losses in composting.
High salt levels are found in some organic
wastes, including many animal wastes. In land affected by
high salinity and/or high sodicity (sodium content), it
is particularly important to monitor salt and sodium
levels in materials applied. When farming with saline
conditions, producers should consider salt levels in the
soil, in applied materials, in irrigation water, and the
"salt tolerance" of crops produced. In many
cases, salinity can be managed effectively through
Excessive heavy metals and/or other hazardous
materials may be found in some wastes, especially
industrial wastes, municipal sewage sludges, and dredging
products from contaminated lakes. Before you agree to
accept wastes from these sources, be sure that levels of
lead, cadmium, arsenic, copper, etc., are not excessive.
Contact qualified personnel from the Cooperative
Extension Service, the Natural Resources Conservation
Service (NRCS), or an agricultural consultant for
assistance with gathering and interpreting the
information you need to make an informed decision.
Pollution of surface waters may result from
runoff of applied waste materials. To prevent this, do
not apply waste to frozen or saturated soils.
Incorporating surface-applied waste and fertilizers into
soil will limit overland movement of nutrients and
organic matter detrimental to water quality. Check
"hydraulic loading" of waste application to
ensure that the volume of liquid applied does not exceed
the soil's percolation and water holding potential.
Imbalanced nutrient levels may interfere with
efficient use of the nutrients by the crop. An applied
waste that provides N, P, K, and micronutrients may not
provide them in appropriate ratios for many plants. Be
careful not to overload the soil with accumulated
phosphorus to supply sufficient nitrogen for your plants.
Generally, it is safer to add supplemental
"complimentary" wastes or synthetic fertilizers
to meet nutrient demands. Be aware that some wastes
contain high levels of organic matter (carbon sources)
but low nutrient levels. These wastes may temporarily
increase fertilizer demand and reduce nutrients available
to the crop, because the nutrients are used by soil
microorganisms as they "feed" on the organic
matter. The effect is to bind the nutrients, particularly
nitrogen, in organic forms not readily available for crop
uptake. Over time the nutrients may be released gradually
as the organic material decomposes. Also be aware that
nutrient availability and metal solubility may be
affected by pH of both the soil and the waste.
Nuisance complaints from neighbors or visits by
environmental agency personnel responding to complaints
of offensive odors are a common problem for producers
using untreated or partially treated wastes. Odor
problems can be minimized sometimes by scheduling
applications when wind will carry odors away from
neighbors. Wind can, however, also disperse odors. Timely
incorporation of applied materials and subsurface
injection of wastes reduce emissions of odorous gases.
Sometimes nuisance complaints are reduced through better
communication between neighbors. If possible, talk with
your neighbors so they understand what you are doing.
Perhaps you can agree on preferred application times or
even develop a cooperative waste application effort that
benefits all concerned. (Your neighbor may agree to an
application on Monday if you are willing to wait to
fertilize until after his weekend family reunion.)
Look out for your own interests, your land's
productivity, and the quality of the environment. Waste
suppliers are trying to eliminate a problem and
potentially make a profit. You are trying to optimize
your production system. Both parties can benefit from
proper waste utilization.
Where to go for more information
This list of references can help you locate more
information about utilization of organic wastes. Many
references may be ordered from publishers, some of which
are available at local and university libraries. The
World Wide Web provides access to many related materials
and experts. Your local agricultural consultants, county
agents, and NRCS personnel can also assist.
MidWest Plan Service. 1993. Livestock Waste Facilities
Handbook. MWPS-18. ($8) MidWest Plan Service, 122
Davidson Hall, Iowa State University, Ames, IA
50011-3080. (800) 562-3618
Northeast Regional Agricultural Engineering Service.
1994. Fertilizer and Manure Application Equipment.
NRAES-57. ($6) Northeast Regional Agricultural
Engineering Service, 152 Riley-Robb Hall, Cooperative
Extension, Ithaca, NY 14853-5701.
Northeast Regional Agricultural Engineering Service.
1994. Liquid Manure Application Systems: Design,
Management, and Environmental Assessment. NRAES-79. ($25)
Northeast Regional Agricultural Engineering Service, 152
Riley-Robb Hall, Cooperative Extension, Ithaca, NY
Northeast Regional Agricultural Engineering Service. 1992. On-Farm Composting Handbook. NRAES-54. ($15) Northeast Regional Agricultural Engineering Service, 152 Riley-Robb Hall, Cooperative Extension, Ithaca, NY 14853-5701.
("On-Farm Composting Handbook" is a good "how to" book for composting on the farm. Discussed are benefits, drawbacks, raw materials, equipment, and compost use. Contact Dana Porter, WVU Extension Service, for NRAES publications.)
BioCycle Journal of Composting and Recycling, 419 State Avenue, Emmaus, PA 18049, phone (610) 967-4135 (BioCycle, a monthly journal, addresses large-scale composting and recycling. Composting equipment is advertised and addresses of equipment manufacturers are listed. Single copy price (as of April 1996) is $6; the one-year subscription rate is $63. You may be able to locate the journal in a nearby public library or university library.
U.S. Environmental Protection Agency. Guide to Septage Treatment and Disposal. 1994. EPA/625/R-94/002. U.S. EPA Center for Environmental Research Information, Cincinnati, OH 45268.
("Guide to Septage Treatment and Disposal" is a handbook detailing procedures and regulations applicable to treatment and disposal of sewage sludge and liquid from septic systems.)
U.S. Natural Resources Conservation Service (formerly Soil Conservation Service). Personnel and publications are available for assistance and information.
WVU Cooperative Extension Service personnel and publications are available for assistance and information.