On-Farm Composting: A Guide

8/9/2019 On-Farm Composting: A Guide

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Publication 452-232


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AKNOWLEDGEMENTS

The authors wish to thank the following faculty of the College of Agriculture and Life Sciences andVirginia Cooperative Extension (VCE) for their time and valuable contributions in reviewing the manu-script for this publication: Dr. Mark M. Alley, Extension Specialist, Department of Crop & Soil Environ-mental Sciences; Dr. Darrell Bosch, Assoc. Professor, Department of Agricultural and Applied Econom-ics; Dr. Eldridge Collins, Agricultural Waste Specialist, Department of Biological Systems Engineering;Charley Goodman, VCE Fluvanna County; Robert Lane, Engineer-Marine Industries, Seafood ExtensionUnit; and Jim Riddell, VCE Louisa County. Appreciation also goes to Dr. Leon Geyer, Professor, Depart-ment of Agricultural and Applied Economics, for his assistance in developing the section on contractissues in compost feedstock delivery and management.

This publication has been funded in part by the USDA Southern Region Sustainable Agriculture Re-search and Education Program.

DisclaimerCommercial companies and products are named in this publication for informational purposes only.Virginia Cooperative Extension does not endorse these companies and products and does not intenddiscrimination against others which may also be suitable.

COVER PHOTO: Turning compost at Cascades Farm, Rockbridge County, Virginia.Owners- C. Halliwill and B. Bressler.

ON FARM COMPOSTING:

A GUIDE TO PRINCIPLES, PLANNING AND OPERATIONS

Archer H. Christian and Gregory K. Evanylo

Department of Crop & Soil Environmental Sciences

James W. Pease

Department of Agricultural and Applied Economics


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TABLE OF CONTENTS

Introduction ..........................................................................................................................................................1

I. Principles ............................................................................................................................................................1

A. Overview ........................................................................................................................................................1

B. Fundamentals .................................................................................................................................................1C. Summary ........................................................................................................................................................4

II. Feedstocks ........................................................................................................................................................5

A. Feedstock materials.......................................................................................................................................5

B. Compost mixes ...............................................................................................................................................7

III. Systems ............................................................................................................................................................9

A. Windrow ........................................................................................................................................................9

B. Aerated static pile .........................................................................................................................................9

C. Passively aerated windrow ..........................................................................................................................12

IV. Processing and Quality Guidelines .............................................................................................................12A. Process management ....................................................................................................................................12

B. Troubleshooting .............................................................................................................................................12

C. Water quality protection ...............................................................................................................................12

D. Curing and storage .......................................................................................................................................13

E. Compost quality considerations ..................................................................................................................13

V. Application and Benets.................................................................................................................................15

VI. Planning and Siting .......................................................................................................................................16

A. Identify goals .................................................................................................................................................16

B. Understand the composting process ..........................................................................................................16C. Assess feedstock availability .......................................................................................................................16

D. Determine site suitability .............................................................................................................................16

E. Assess projected operation economics .......................................................................................................18

F. Assess the market potential if compost is to be sold ................................................................................. 19

G. Investigate local and state regulatory requirements ................................................................................20

H. Select technology level and establish operation size ...............................................................................20

I. Develop operation budget .............................................................................................................................20

J. Inform and educate neighbors ......................................................................................................................22

VII. Regulations: Understanding and Compliance .........................................................................................24

A. Yard waste composting facility regulations ..............................................................................................24

B. Solid waste management regulations .........................................................................................................26

Appendix A. Composting Process Record Table .............................................................................................27

Appendix B. Composting Troubleshooting and Management Guide .........................................................28

Appendix C. Contract Issues - Compost Feedstock Delivery/Management..............................................31

Appendix D. Composting Contacts and Resources ........................................................................................34

References..............................................................................................................................................................36


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B. FUNDAMENTALS

The natural process of breakdown can be accel-erated by gathering the organic waste materialinto piles. When organic wastes are gatheredinto sufciently large piles for composting, thenatural insulating effect of the material leadsto a conservation of heat and a marked rise intemperature. The heat given off by the micro-organisms further increases the temperature.The temperature rise inside the pile is due to thedifference between the heat generated by themicrobes and the heat lost to the surroundings.The dimensions of the pile, particle size of the

material, availability of nutrients (e.g. carbonand nitrogen), oxygen concentration, and mois-ture content are critical factors that affect thetemperature and, therefore, the microbial popu-lation and diversity within the pile.

Microorganisms. The microbes that inhabita compost pile are so small that a clod of soil thesize of a pea may contain millions of them. Theybreak down the complex compounds of thewaste material into simpler organic compounds.

Bacteria are the most important group of de-composing microorganisms in composting andare generally identied by the temperaturerange in which they are most active (Figure 2).The mesophilic bacteria thrive at temperaturesof 77-108F (25-42C), but they can survive athigher temperatures. During their short lifespan at the beginning of the composting process,these bacteria feed on the most readily availablecarbohydrates and proteins. The heat produced

INTRODUCTIONFarmers can effectively manage manures andother wastes and create a desirable end-productby producing their own compost from organicmaterials generated on-farm and off-farm. Thesematerials, many of which can be received fromoff-farm with minimal or no regulatory require-

ments, include municipal yard trimmings, fruitand vegetable residuals, and livestock manures.Composting yields an end-product that is usefulas a soil amendment, improves odor control andwaste handling in animal operations, and offersthe potential for additional farm income fromthe sale of nished material and/or the receiptof tipping fees for accepting off-farm wastes.This publication contains a discussion of basiccomposting principles, compostable materials,composting systems, the use of compost and itsbenets, guidelines for managing and solving

process problems, the steps for facility planningand operation, and the regulations that governon-farm composting.

I. PRINCIPLES

A. OVERVIEWComposting is the manipulation or control ofthe natural decomposition of organic matter. Itrequires optimizing the conditions for the mixedpopulation of microorganisms (mainly bacteria,fungi and actinomycetes) responsible for thedecomposition. These microbes, normally foundon the surface of leaves, grass clippings andother organic materials, thrive in a warm, moist,aerobic (oxygen rich) environment.

During decomposition, the microorganisms mul-tiply and liberate carbon dioxide (CO

2), water,

other organic products and energy. Some of theenergy is used in metabolism and the remainder

is given off as heat (Figure 1). Eventually, thereadily-available food supply is exhausted, mi-crobial growth and heat generation decrease, anda humus-like material remains. This material iscalled compost.

The following fundamental principles describethe decomposition of raw materials, and illus-trate how to optimize that process for efcientcomposting and the successful production ofcompost.

Organic matter

(including carbon

chemical energy,

nitrogen, protein,

humus), minerals,

water, microorganisms

Finished compos

Organic matter

(including

carbon chemical

energy, nitrogen,

protein)

Minerals (includ-

ing nitrogen and

other nutrients)

Water

Microorganisms

Raw materials

Water Heat CO2

Compost Pile

O2

Figure 1. The Composting Process (Reprinted withpermission from On-Farm Composting Handbook,

NRAES, 1992.)


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during metabolism raises the temperature in thepile beyond their viable range and causes theirdeath. These higher temperatures are conduciveto thermophilic bacteria, which perform best attemperatures ranging from 122-140F (50-60C).The most rapid decomposition occurs withinthis range. Thermophilic bacteria degrade the

proteins and non-cellulose carbohydrates. Ther-mophilic fungi, which break down the celluloseportion of leaves, also colonize the pile at thesetemperatures. In addition, weed seeds, insecteggs and larvae, and potential pathogens are de-stroyed when temperatures remain in the upperend of the thermophilic range for several days.If the temperature rises above 140F (60C), themajority of the bacterial population and manyother living organisms begin to perish. Attemperatures below 59F (15C), activity of theprimary decomposers is very limited.

process to ensure survival of the microorgan-isms. Incoming materials may be too dry andwater may need to be added as the piles areformed. However, it is not desirable for the pilesto be excessively wet. Too much water lls upthe air spaces, which creates undesirable anaero-bic (oxygen limiting) conditions. If compost-

ing material is too wet, mechanical mixing andaerating can facilitate drying. Absorbent bulkingmaterials can also be added. Breathable, but wa-ter impermeable, compost covers can be used toprevent unwanted precipitation from inltratingpiles and windrows.

A quick test to determine if the moisture con-tent of the composting material is appropriateis to squeeze a representative handful. If oneor two drops of water can be squeezed out withdifculty, it is sufciently moist. Although notessential, a moisture meter can be used for moreprecise measurement of water content.

Oxygen for the microbial population can beprovided by both natural convection and me-chanical aeration. Piles must be maintained withgood particle size distribution and porosity fornatural convection to occur (See Particle Size andStructure on page 3). Excess aeration can keepa pile too cool for optimum microbial activity.Without adequate oxygen, the aerobic bacterial

population dies off, anaerobic microbes becomeprevalent, and fermentation occurs. This leadsto the production of odorous and other undesir-able gases, lower temperatures, a slower de-composition rate, and incompletely compostedmaterial. The unnished compost can containorganic acids and other compounds harmful toplants (phytotoxic) and soil life.

C:N Ratio. Microorganisms use carbon(C) as an energy source and nitrogen (N) tobuild proteins and other cell components in aproportion that averages about 15 parts C to 1part N. These elements are found in all organicwaste materials; however, this ideal carbon-to-nitrogen (C:N) ratio is not found in any oneorganic source, nor is all of the carbon andnitrogen in organic materials readily available tomicrobes.An initial C:N ratio of approximately 30:1 (dryweight basis) is recommended for most efcientcomposting. This is achieved by combining

Figure 2. Temperature Ranges of Mesophilic and

Thermophilic Bacteria (Adapted from McNelly, 1989)

Thermophilic

Range

Mesophilic

Range

Weed seed destruction

Pathogenic destruction

Fahrenheit212o

Celsius100o

77o

63o

55o

43o

10o

170o

145o

131o

110o

50o

32o F 0o C

Macroorganisms. The outer portion ofany composting pile provides a cool enoughenvironment for the macroorganisms thatalso play a part in the decomposition process.Macroorganisms are many-celled organismsranging in size from microscopic (rotifers andnematodes) to the larger fungi,mites, springtails,

sowbugs, beetles and earthworms. The action oftheir chewing, foraging and moving through thepile helps to physically break up the materialsand create a greater surface area on whichbacterial action can occur.

Moisture and Oxygen. All living thingsrequire water, and microbes are no exception. Itis important to maintain a moisture content of 45to 65 percent throughout the entire composting


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various raw materials for which concentrationsof carbon and nitrogen are known. Care must betaken in establishing the mix, however, becausematerials vary not only in forms and concentra-tions of C and N, but in bulk density (weight perunit volume) and particle size, as well. A higherC:N ratio than 30:1 may be appropriate for mixes

with woodchips and sawdust, because much ofthe carbon is present in forms that are very dif-cult to degrade. If too little carbon is presentrelative to the nitrogen (C:N40:1), nitrogen becomeslimiting and the composting rate will decrease.

The C:N ratio decreases as decomposition pro-ceeds. The nal C:N ratio of the material willvary depending on the initial materials used,the technology employed, how completely thematerial decomposes, and whether screening outany large woody particles is conducted prior toproduct analysis. Few unscreened composts willhave ratios below 15:1.

Although C:N ratios are reported on a dryweight basis, materials are usually combined ona volume basis because most operations do nothave large scales for weighing trucks or vessels.

Conversions can be made when the bulk densityof feedstock materials is known (See Table 2 andCompost Mixes (Section II)).

Particle Size and Structure. Composting isaffected by particle size and structure of the rawmaterials. Particles that are too small will packtightly and reduce porosity in the pile. How-ever, smaller sized particles will provide moreexposed surface area than larger ones and accel-erate the composting process. Particles with toolittle rigidity may contribute to compaction.

The compost pile should be constructed of avariety of material sizes within the range of 1/8to 2 inches. Achieving this mix may requiregrinding or shredding of raw materials. The ac-tion of turning the compost pile will often breakup raw materials, such as leaves or grass, suf-ciently. In addition, pile mixing can help restorestructure and promote natural convection when

materials have compacted over time. Compost-ing with materials whose physical characteristics(i.e., particle size, moisture content and holdingcapacity) are diverse will enhance the processby optimizing aeration and moisture-holdingcapacity.

Temperature. When proper initial conditionsare established, the temperature of the com-posting material rises rapidly (Figure 3). Thetemperature must be monitored and the heatreleased to prevent high temperatures from kill-ing the decomposing microorganisms. This canbe achieved by mechanically turning the pile orforcing air through it when the average internaltemperature reaches 140F (60C). Mixing oraerating a compost pile daily may be necessaryinitially, but the required frequency will decrease

with time. Maintaining temperature above 131F(55C) for at least three days will ensure patho-gen destruction, and above 145F (63C) for threedays will kill weed seeds. Primary compostingis considered complete when internal tempera-tures have declined below approximately 105F(43C), and remain there even when the compostis aerated and maintained under optimum mois-ture conditions.

30 60 90 120 150 180 210 240 270

Days

Average Ambient Temperature

180

160

140

120

100

80

60

40

20

Temperature(oF)

Figure 3. Changes in internal temperature of a com-

posting pile over time. (Dane County Compost Recy-cling Network, 1988)


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Table 1.Recommended Conditions For Rapid Composting

(Adapted with permission from On-Farm Composting Handbook, NRAES, 1992)

Condition/Characteristic Acceptable Range Optimum Range

Initial carbon to nitrogen ratio (C:N) 20:1 to 40:1 25:1 to 30:1

Temperature 110-150 F 120-140 F

Moisture content 40 - 65 % 50 - 60 %

Oxygen concentration > 5% >> 5%

Particle size (diam) 1/8 - 1/2 varies with materials, pile size

Initial bulk density < 1100 lb/yd3

(40 lb/ft3)

pH. The acid-base balance can be describedby the pH scale. A pH of 7 (on a scale of 1 to 14)is neutral, pH values below 7 are acidic, and pHvalues above 7 are basic. The pH of compostfeedstocks is not critical. Proper compostingwill result in a pH near neutral (6.5-8.0) fornished compost.

The pH of the composting material can be usedas a diagnostic tool. If anaerobic conditions existfor an extended period, the pH will remain low(3 to 6), decomposition rate will slow, and odorswill be produced. If low pH conditions occurand persist, reoxygenation of the material canremedy the situation. Correcting for acidic con-ditions with the addition of lime to the materialis not generally necessary or recommended as ahigh pH will promote the production of am-monia gas. Adding lime may also raise the pHof the end product to a level too high for someplants.Inoculants and Other Additions. Inocu-lants are marketed as composting rate accel-erators. They typically contain bacteria and amedium on which the bacteria can grow. Themicrobes normally found on organic materialsare capable of degrading the material withoutthe addition of commercially available inocu-lants, if the requirements of proper C:N ratio,

moisture and oxygen are met. Finished compostcan be added to a newly formed windrow if onedesires to provide a concentrated population of

bacteria to the windrows; however, a microbialpopulation will develop readily without suchseeding.

Inorganic nitrogen fertilizer (e.g. urea) is notgenerally recommended as an additive for lownitrogen materials, such as in the composting of

leaves alone. This practice can initially create anappropriate C:N ratio, but this readily-availablenitrogen may be quickly transformed to ammo-nia, a gaseous and odorous form of nitrogen thatis easily lost to the atmosphere. A subsequentdeciency of nitrogen may result, and the pro-cess may again become limited by nitrogen.

Curing. A curing period for achievingcompost stability and maturity is an extremelyimportant part of the composting process.

Improperly or incompletely composted materialthat is not stable and mature may containphytotoxic organic acids or cause soil oxygendepletion and thus result in injury to plants.A curing period allows mesophilic bacteria torecolonize the pile, a more extensive populationof macroorganisms to develop, and nitrate-nitrogen (a plant-available compound ofnitrogen) to form. Further humus developmenthas been reported to occur more readily during

this period, as well.

C. SUMMARYA summary of the recommendations for opti-mum composting is presented in Table 1.


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II. FEEDSTOCKSRaw materials are combined to establish theappropriate initial carbon to nitrogen ratio andstructure. Table 2 lists the C:N ratio, moisturecontent and bulk density of common feedstocksfor composting on farms. Of course, materialsshould be analyzed for C and N concentrations,

rather than relying on averages. Laboratoriesthat conduct soil, environmental, animal manureand/or specialized compost testing can all pro-vide appropriate analysis for calculating propermixes of feedstock (See Appendix D).

A. FEEDSTOCK MATERIALSLeaves. Leaves are a commonly compostedmaterial due to the fact that they are usuallycollected separately by municipalities and can becomposted alone or in combination with otherorganic wastes. Their C:N ratio can range from40 to 80, making them a good carbon source

for on-farm composting with high nitrogenmanures. Some disadvantages associated withusing leaves in farm composting are that theymay contain trash or be compacted and wetwhen they arrive. Benets include the fact that

Table 2.Potential raw materials for farm composting.

Raw Materials C:N Moisture Content (%) Bulk Density (lb/yd3)

Bark - hardwoods 116-436

Bark - softwoods 130-1,285

Broiler litter 12-1 22-46 650-1,000

Compost


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their carbonaceous components are fairly easilydegraded and that some municipalities willpay a tipping fee to farmers accepting them.Frequent temperature-based turning with amechanical windrow turner will produce anished compost in the shortest time.

Mixing other organic wastes with leaves permitsrecycling of these other wastes, accelerates thedecomposition of leaves, and creates a nutrient-rich compost. High nitrogen sources that canbe composted successfully with leaves includegrass clippings or other plant wastes, animalmanures, sludges (biosolids), and institutionalfood wastes.

Composting leaves alone produces a soilamendment with a consistent nutrient contentand pH; however, the high C:N ratio of leaveslengthens the time required for full decomposi-tion into compost. Depending on the technol-ogy used, composting of leaves alone can takefrom ve months to three years.

Grass Clippings. Grass clippings are goodcomplementary materials to add to leaves orother coarse, high carbon compostables, becauseof their relatively high moisture content (82%average) and low C:N ratio (9-25). A mix of 3:1(volume to volume) of leaves to grass clippings

is generally optimum for rapid composting.Greater proportions of grass clippings promotecompaction, which can lead to anaerobic con-ditions. Grass clippings do have a signicantpotential for odor generation during collection,stockpiling, and composting.

The composting of leaves and grass requirespreparation to accommodate the differencesin the collection periods of these two materi-als through the year. During the early fall, theavailability of both leaves and grass allows forready co-composting. Stockpiled leaves collect-ed in the fall and early winter can be compostedwith grass clippings collected from the rst cut-tings through mid-summer.

Animal Manures. Animal manures areusually high nitrogen materials that should bemixed with high carbon materials for compost-ing. Establishing an appropriate mix can bedifcult because the composition of delivered

material can be variable. Several of the mostcommonly available manures are describedbelow.

Poultry litter has a high nitrogen concentration(2.5 to 4%), is generally moderately dry (25 to45%), and should be composted with a high

carbon material. It is a very good co-compostingamendment when managed to control ammoniageneration. Poultry houses are cleaned at vary-ing intervals depending on bird age and housesize. Litter haulers may deliver fresh housematerial or material that has been stored undercover for varying amounts of time. Once litterreaches the composting site, additional consider-ations, such as length of time before mixing andthe amount of precipitation on uncovered mate-rial, are important in determining the best mix.

Suitable composting mixtures of high carbonmaterials such as leaves and poultry litter haveranged from 3.5:1 to 9:1 (volume basis), depend-ing on the moisture and nutrient content of thelitter and the age and moisture content of theleaves. A mix of 4 parts leaves to 1 part litter iscommonly employed for aged leaves weighingroughly 500 lbs/yd3 and litter, at 650 lb/yd3 anda nitrogen concentration of approximately 3%.A ratio as high as 16 :1 (volume basis) may beappropriate for dry, newly collected leaves (~200

lbs/yd3

) mixed with very fresh, wet turkey litter.Frequent monitoring and timely aeration of pilesare essential, regardless of the mix.

Other sources of solid animal manures can alsoserve as nitrogen sources for composting. Horsemanure generally contains large amounts ofbedding and, thus, can have a high C:N ratio (30to 40:1), which often permits the materials to becomposted alone. The mix decomposes quicklyand has low odor potential when the bedding isstraw. Swine and dairy cattle manures are often

very wet (~80% moisture content) and have highnitrogen concentrations (up to 4%-dry wt. basis).Unless the manure is collected from beddedpack areas, these materials need to be compos-ted with a high-carbon, dry material. Handlinghigh moisture content manures is difcult, andcomposting them should be attempted only afterprevious composting experience. Other live-stock manures, such as sheep, goat and rabbit,are also good for composting when they contain


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some bedding or are mixed with high-carbonmaterials.

Other Yard Wastes and Woody Materials.Brush trimmings and woodchips are resistant todegradation, but can be excellent bulking agentsfor other feedstocks. Their large particle size im-

proves air ow in mixes with easily compactedmaterials or those with initially high moisturecontent. Some pieces of brush trimmings andwoodchips will generally remain after primarycomposting. Unless these composts are intend-ed as a mulch, they are often screened to removechips prior to land application or use in pottingmixes.

Other Compostable Solid Wastes. Manyother organic solid waste components can be

mixed with yard waste for composting. Theseinclude items such as waste paper, unmarketableold newsprint, and food processing wastes. Indi-vidual analysis of these highly variable materialsis necessary before establishing a compostingrecipe. Currently, Virginia operations mustsecure a solid waste composting permit from theVirginia Department of Environmental Qualityfor composting these wastes.

B.COMPOST MIXESProper compost mixes are based on feedstock

C:N ratios, moisture content, bulk density andparticle size distribution. The nal mix of choiceoften involves a trade off between C:N ratio andmoisture content because the optimum aerationand porosity achieved by adding bulking agentsfrequently gives higher than optimum C:N ra-tios. Average C:N ratios (Table 2) are sometimesused in preliminary mix ratio decisions but mustnot be expected to adequately characterize a ma-terial. For instance, generally one loader bucketof grass clippings is appropriate for mixing with3 buckets of deciduous tree leaves. A smallervolume of compacted, wet leaves may actuallybe needed because more carbon will be presentthan in the same volume of dry, loose leaves. Onthe other hand, a larger quantity of dry leavesmay be necessary to provide greater porosityand sufcient available carbon, when mixingwith wet, dense grass clippings.

The best approach for determining proper feed-stock proportions for a co-composting mix is to

have material analyzed and use the calculationsprovided in Table 3. Some of the parameterscan be evaluated on-farm, but samples must besent to a qualied laboratory to obtain C and Nconcentration values. (See Appendix D.)

Material moisture content (%) can be deter-

mined on-farm. The feedstock sample should beweighed and then dried at about 160oF (71oC) orless until the dry weight does not change withsuccessive drying attempts.

Example for determining moisture content:

(undried sample wt.) (dried sample wt.)5 ounces - 3.5 ounces

x 100 = 30%5 ounces (undried sample wt.)

(The general formula for determining moisture content for

a mix of materials is provided in Section II of Table 3.)

The calculations in Table 3 yield weight-to-weight ratios of materials. These must be con-verted using the bulk densities to a volume-to-volume ratio for actual mixing. Some bulk den-sity ranges are reported in Table 2. A sufcientlyaccurate measurement of bulk density can bedetermined on-farm by weighing a sample ofmaterial in a 5 gallon bucket (the weight ofwhich is already known), subtracting the weightof the bucket, and then multiplying by 40.5 to

convert to lb/yd3.Example: 18.5 lb. broiler litter/5 gal x 40.5 gal/yd3 =

749 lb. broiler litter/yd3

It is important to try to ll the sample containerso that the material is compacted to approxi-mately the same degree expected under com-posting conditions. Therefore, when sampling,feedstock should not be packed into the con-tainer tightly or uffed up. Determining bulkdensity for several samples will help establish arange and average.

When a calculated mix based on a desired mois-ture content of 55% results in a C:N ratio thatis too low (


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Table 3. Formulas for determining composting recipes.

(Adapted with permission from On-Farm Composting Handbook, NRAES, 1992.)

I. Formulas for an individual ingredient

Moisture content = % moisture content 100

Weight of water = total weight x moisture content

Dry weight = total weight - weight of water= total weight x (1 - moisture content)

Nitrogen content = dry weight x (%N 100)

% carbon = %N x C:N ratio

Carbon content = dry weight x (%C 100)

= N content x C:N ratio

II. General formulas for a mix of materials

Moisture content = weight of water in ingredient a + water in b + water in c +...

total weight of all ingredients

= (a x ma) + (b x m

b) + (c x m

c) + ...

a + b + c + ...

C:N ratio = weight of C in ingredient a + weight of C in b + weight of C in c +...

weight of N in a + weight of N in b + weight of N in c + ...

= [%Ca

x a x (1 - ma)] + [%C

bx b x (1 - m

b)] + [%C

cx c x (1 - m

c)] +...

[%Na

x a x (1 - ma)] + [%N

bx b x (1 - m

b)] + [%N

cx c x (1 - m

c)] +...

Symbols: a = total weight of ingredient ab = total weight of ingredient bc = total weight of ingredient c

ma, m

b, m

c, ... = moisture content of ingredients a, b, c, ...

%Na, Nb, Nc, ... = % nitrogen of ingredients a, b, c, ... (% of dry weight)%Ca, C

b, C

c, ... = % carbon of ingredients a, b, c, ... (% of dry weight)

III. Shortcut formulas for only two ingredients

1. Required amount of ingredient a per pound ofb based on desired moisture content:a = (m

b- M) / (M - m

a)

Then check the C:N ratio using the general formula.

2. Required amount of ingredient a per pound ofb based on the desired C:N ratio:a = %N

b(R - R

b) (1 - m

b)

%Na

X

(Ra

- R)X

(1 - ma

)

Then check the moisture content using the general formula

Symbols: a = pounds of ingredient a per pound of ingredient bM = desired mix moisture contentm

a= moisture content of ingredient a (e.g., woodchips)

mb

= moisture content of ingredient b (e.g., manure)R = desired C:N ratio of the mixR

a= C:N ratio of ingredient a

Rb

= C:N ratio of ingredient b


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III. SYSTEMS

A.WINDROWOn-farm composting is most often conducted bybuilding composting windrows - elongated pilestypically 4 to 9 feet tall, 10 to 18 feet wide, and aslong as needed for the volume of material to be

composted. Mechanical mixing and aeration areaccomplished with a) a front-end or skid loader;b) a backhoe; c) a tractor with bucket; d) a tractorwith manure spreader; e) a tractor-pulled wind-row turner; or f) a self-propelled windrow turner.

Windrows can be constructed with a front-endloader (or similar equipment), tractor with ma-nure spreader (Figure 4), or a dump truck (Fig-ure 5). An effective way to construct a windrowwith a front-end loader or tractor with a bucket

is to spread a layer of high carbon materialson the windrow site in the desired width andlength; follow this with a layer of high nitrogenmaterials; and then add another layer of carbonmaterials. Several layers can be applied to mini-mize initial mixing. The windrow is then mixedas thoroughly as possible with the bucket byrepeatedly lifting and slowly letting the materialtumble out.

The lifting and tumbling method is also em-ployed when using a bucket for windrow turn-

ing/mixing during processing. Care shouldbe taken to avoid traveling into the windrowand compacting materials. A tractor and ma-nure spreader can also be used with a loader(or similar equipment) for windrow mixing. Ifa windrow turner is to be used for processing,windrows must be constructed to accommodatethe height and width dimensions of the turneror additional time will be required for windrowmodication.

Some operators suggest that the minimal equip-ment requirements for turned windrow com-posting of about 3,000 cubic yards of materialare: a) a 50 to 90 hp tractor with as large a loader-bucket as possible, or a skid loader; b) a 60 to 80hp tractor with PTO and creeper gear, capableof pulling a manure spreader at slower than 1mph; and c) a PTO-driven manure spreader,preferably with low-speed setting (apron-chain,beater-type, single axle). Other on-farm com-posters have been successful without a manure

spreader. A windrow turner provides most ef-cient processing. These can range in price fromroughly $15,000 for a tractor-pulled type to about$25,000 for farm-scale, self-propelled models.Tractor-pulled windrow turners generally mustbe pulled by a tractor capable of very low speedsof as little as 1/2 mph.

Breathable compost covers, generally made ofgeotextile fabric, are used by some farmers as aneffective means of preventing excess precipita-tion from over-wetting the piles. If windrowsare left exposed to precipitation, more frequentmixing is often necessary to control moisturecontent and prevent anaerobic conditions. Com-post covers come in rolls of various widths andlengths, and are made of materials that allow airexchange. Although they are expensive (ap-proximately $0.25/ft2, $3/running ft.), their costshould be evaluated against the extra time, laborand equipment usage necessary to control mois-ture content without them.

B.AERATED STATIC PILESystem Description. Another method foron-farm composting involves using a system ofpipes and blowers to aerate elongated station-ary piles (up to 80 ft. long) (See Figure 6). A pileshould be no more than 8 feet tall including a

6-inch covering of nished compost or bulkingagent, such as a mixture of soil and sawdust orleaves. This additional covering serves as a lterfor potentially odorous gases and serves as aninsulating barrier against heat loss. The piles aretypically constructed over a 6- to 12-inch deepporous base material, such as woodchips, withinwhich a perforated aeration pipe (4 to 8 in. di-ameter) has been laid. The porous base shouldnot extend out to the edge of the pile, but shouldrange from 1/4 to 1/3 of the pile width and

reach to no closer than 8 feet from the end of thepile. The perforated aeration pipe is connectedto a blower operated on a time schedule (4-inchpipe diam.) or with temperature-based control(6-8 inch pipe diam.), and designed to either pullor force air through the pile at a recommendedmaximum velocity of 2000 ft/min. Air ow ratesrange from 15-25 ft3/min (time-based control) to100 ft3/min (temperature-based control) per dryton of material.


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Figure 4. Forming windrows with a manure spreader.(Reprinted with permission from On-Farm Composting

Handbook, NRAES, 1992.)

Figure 5. Move the dump truck forward slowly to

form the windrow. (Reprinted with permission from On-Farm Composting Handbook, NRAES, 1992.)


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Pipe Sizing/Air Flow. Pipe hole size andspacing can vary depending on pipe size andlength. The general formula for determininghole diameter is: [(D2xS)/(Lx12)]

(where: D=pipe diameter (inches); L=pipe length(ft.), and S=hole spacing (inches).)

Air ow rate and pipe specications are deter-mined according to Table 4.

Blower System. Basing blower control ontemperature is more expensive than using asimple time schedule, because it requires a largerblower (3 to 5 hp vs 1/3 to 1/2 hp) with more air-ow, a larger aeration pipe, and a more sophis-ticated control system. Temperature set-point isgenerally about 122 - 130F (50-54C). Continu-ous low ow blower operation is also possible,

but because predominant air channels develop,there is less even air distribution throughout thepile. A suction system (pulling air) generallyrequires a condensate trap (inexpensive) and anodor lter, which can be a pile of screened com-post. Although these components necessitate alarger blower, this system controls odors muchmore effectively than a pressure system (pushingair). Controlling any undesirable odors occur-ring with a pressure system is often addressedby increasing the outer cover depth.

Construction and Operation. Thorough ini-tial mixing of materials and proper particle sizeare critical for establishing sufcient and well-distributed air ow throughout the compostingprocess, because no physical mixing or turningtakes place after pile construction. Initial mixingcan be accomplished with a manure spreader,batch type feed mixer, or pug mill. Extra caremust also be taken with this type of process inorder to ensure protection of the aeration pipe.

The operation site must also be equipped toprovide electrical power. The pile can be builtin sections, and new feedstock can be depositedin place of nished material removed for cur-ing. Screening of the end-product is generallyrequired with static pile systems in order toseparate the base and cover material (when thelatter is not nished compost) from the nishedcompost.

System Costs. Aerated static pile compost-ing may be more attractive to operators whocannot afford the capital expense of a windrow

Table 4. Air ow rate and pipe specifcations (NRAES, 1992).

a) air ow (total ft3/min) = __ dry tons of material x __ft3/min./dry ton

[15-25 ft3/min for time-based control; 100 ft3/min for temperature-based control]

b) pipe area (in2) = [(___ total ft3/min) / (2,000 ft/min max.velocity)] x 144 in2/ft2

c) diameter (in) = [(__in2 x 4)/] (=3.1416; round result up to nearest available pipe size)

Figure 6. Aerated static pile layout and dimensions.

(Reprinted with permission from On-Farm Composting

Handbook, NRAES, 1992.)


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turner. Blower and piping costs to set up asystem to process up to 100 yd3 of cattle holdinglot bedding were approximately $2,000 in centralVirginia in 1996. The largest expenses were thepurchase of a blower and electrical system instal-lation. Costs can be lower than with a turnedwindrow system, because processing time is

much shorter (3 to 5 weeks) and less land area isnecessary. The cost of screening the nal mate-rial must also be considered. Screening unitscapable of processing from 25 to 50 yd3 per hourrange in price from $35,000 to $100,000.

C. PASSIVELY AERATED WINDROWThis system also does not involve turning thewindrows once they are constructed. Generally,a 6- to 9-inch base of straw, nished compost,or material such as peat moss is rst laid on the

ground surface. Sections of 4-inch diameter per-forated pipe, approximately 14 feet long, are laidon top of the base perpendicular to the lengthof the windrow, at 18-inch to 3-foot intervals.Septic system drain eld pipe (schedule 40 PVC)with 2 rows of half-inch diameter holes run-ning the length is often used. Some operationslay the pipe sections on the ground surface andcover them with 6 to 8 inches of wood chips. Awindrow approximately 10 feet wide and 3 to 4feet tall is constructed over top of the pipes andcovered with a 6- to 8-inch layer of compost or

peat moss, with or without a breathable fabric.Other windrow dimensions are also possible,and wider windrows will better accommodatethe 20-foot length pipes generally available,avoiding cutting costs. In all cases, however, thecovering layer is necessary for insulation andodor control. The open-ended pipes will extendout from the windrow on both sides and drawair into the pile as natural convection creates achimney effect. It is very important to choosematerials that have a wide range of particle sizesand to thoroughly mix the raw materials beforebuilding the windrow. Good porosity and struc-ture are far more critical in this system than inthose that are actively aerated. Approximately19,000 ft2 would be required to establish tenwindrows that are 3.5 feet tall, 10 feet wide, and75 feet long for composting a total of 500 yd3 ofmaterial.

IV. PROCESSING AND QUALITYGUIDELINESA. PROCESS MANAGEMENTThe four most important tools for compostprocess monitoring and management are: athermometer, ones hands, ones eyes, and ones

nose. Additional monitoring equipment enhanc-es process management but cannot replace these.Monitoring and management of the process ona regular and even daily (during the rst severalweeks) basis will allow an operator to maintainoptimum composting conditions and avoid sur-prises, such as the development of odors offen-sive to neighbors. Under optimum process man-agement a compost pile requires attention whenaverage temperatures fall outside the optimumrange of 100-140F (38-60C) or moisture contentis too low (65%). After some

experience, a normal pattern in the prole of thetemperature and changes in the composting ma-terial can be observed over time, and an operatorwill develop an invaluable sense of the process.A form similar to that in Appendix A can be usedto record process information. Records can pro-vide useful information for increasing efciencyby keeping track of successes and problems.

B. TROUBLESHOOTINGThe most common problems that occur in com-

posting are those related to odor generation anddecomposition rate. There are many interrelatedvariables that affect the process and contribute tothese problems. For instance, when the tempera-ture inside the pile does not increase to between110 and 140oF (43 to 60oC) within a day or so ofpile construction, one of the following may bethe cause: a) the C:N ratio is too high; b) too littlemoisture is present; or c) too much moisture andinsufcient oxygen are present. Correcting prob-lems is often a trial and error process. A concise,thorough tool for troubleshooting is presented in

Appendix B.

C. WATER QUALITY PROTECTIONThe composting site should be designed todivert surface water and to control runoff toprotect nearby surface waters. Site design mustmaintain all-weather conditions for equipmenttravel. The establishment of a grass lter strip


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below the composting area provides an inex-pensive method to manage runoff. The stripshould extend across the full length of the siteand be of sufcient width to capture the highestrainfall expected in a 24 hour period. This widthwill depend on the slope. Proper lter strip sizeis also dependent on soil type and grass cover

species. Fescue and reed canary are often recom-mended. Your Agricultural Extension agent orNatural Resource Conservation Service person-nel can assist in lter strip sizing. In order toavoid compaction and to maintain high inltra-tion rates, heavy equipment should never travelover the strip. Filter strip maintenance is alsoimportant. Sediment build-up can cause waterto pond behind the strip.

D. CURING AND STORAGEGenerally, when the interior temperatures havestabilized at or below approximately 105F(43C) under proper moisture and aerationconditions, then primary decomposition is con-sidered complete and the compost is ready for acuring period. A curing period of one to severalmonths is necessary before using the compost inorder to ensure material stability and maturity.Curing is considered complete when internaltemperatures decline (under proper moistureand oxygen conditions) to near ambient.

Curing piles can be larger than windrows and ofany shape, but must not be so large as to pro-mote anaerobic conditions. Periodic mixing ishighly recommended for material that is stock-piled for several months.

E. COMPOST QUALITYCONSIDERATIONSEnsuring nished compost quality is as impor-tant as maintaining optimum conditions duringthe process. Physical, chemical and biological

characteristics are used to assess compost qual-ity. The material should be free of foreign ma-terials, such as plastic bag remnants and othertrash. It should also be stable and mature, andhave concentrations of soluble salts and heavymetals below acceptable limits. Compostersshould be aware that some composts can containhigh concentrations of soluble salts which inhibitplant growth and are not remedied by the cur-

ing process. Having the nal material analyzedfor these and other parameters is important toensure that the compost is not used inappropri-ately, or that it is amended as necessary prior touse. Table 5 provides guidelines for several com-post quality parameters.

Immature or unstable compost can have nega-tive effects on soil and plant life. The curingperiod following active decomposition helps toensure compost stability and maturity. A stablecompost does not reheat upon turning/aerationwhen proper conditions are maintained, and amature compost will not injure plants.

There are both eld and laboratory methods fordetermining compost stability and maturity. Theleast costly means of determining stability is tomeasure temperature response to turning/aerat-

ing in the eld. It is advisable to conduct thistest several times once the temperature has sta-bilized while making sure optimum conditionsexist. Alternatively, there are devices that test acomposite compost sample and can be utilizedto determine stability within just a few days.One of these involves measuring temperaturerise in a properly moistened sample incubatedin a small, well-insulated vessel for ve to sevendays. The degree to which the temperature risesas compared to an established scale determines

the degree of stability. Information on thesedevices can be obtained through the resourceindividuals listed in Appendix D. Laboratorymethods for determining the stability of a com-post include measuring the generation of carbondioxide or consumption of oxygen to reveal theactivity level of the microbial population. Themost common method for determining if a com-post is mature is by conducting a simple seedgermination test, often with radish seeds.


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Table 5. Compost Quality Guidelines.

Potting Media Top Dressing

Characteristic Amendment Grade Grade Soil Amendment Grade

recommended formulating top dressing agricultural soil improvement;

uses growing media for turf establishment/maintenance of

potted crops landscape plantings; disturbedsoils restoration

particle size


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V. APPLICATION AND BENEFITSCompost can improve the biological, physical andchemical properties of soils and growing media.Vast quantities of microorganisms are introducedwith compost, helping to promote humus forma-tion and increase the availability of plant nutrients.Plant diseases, such as pythium and fusarium, as

well as nematodes can be suppressed by certain ofthe benefcial microorganisms present in composts(Grebus et.al., 1994; Logsdon, 1995; Hoitinket.al.,1993; The Composting Council, 1996). Compostsalso encourage macroorganisms, such as earth-worms, which improve soil aeration.

High quality composts improve the physicalstructure of soils and potting media by improvingaggregation, reducing bulk density, and increas-ing water-holding capacity as well as permeabil-

ity. These improvements result in greater resis-tance to compaction and erosion and potentialreductions in required irrigation water.

Another major benet to soil/growing mediaprovided by compost is through the addition of

organic matter, which buffers (stabilizes) pH,increases cation exchange capacity (better plantnutrient retention), and supplies plant macro-and micronutrients, such as nitrogen, phospho-rus, potassium, calcium, magnesium, manga-nese, boron, and iron. Utilizing composts as asole alternative to conventional fertilization is

not often feasible, however, because these nutri-ents are not typically present in concentrations(weight to weight basis) comparable to mostcommercial fertilizers, thus necessitating largevolumes of compost. In addition, many of thenutrients are tied up in slowly plant-availableorganic forms. Nonetheless, reductions in com-mercial fertilizer use and more efcient fertilizerutilization by plants have been well reported, ashave increases in crop yields and improvementsin growth of turfgrass and in nursery and green-house stock.

The Composting Council, a national trade orga-nization representing the composting industry,has established recommended application rates.Some of these are shown in Table 6.

Table 6. General Uses and Application Rates for Compost (Composting Council, 1994).

Market Applications Approximate Usage Rates

Landscapers new turf establishment 1-2 tilled to a 5 depth depending on soil type

turf renovation 1/8-1/2 topdressed after aeration

planting bed preparation 1-2 tilled into raised beds

mulching 2-3 around all landscape plants

backllfortreeplanting 30%ofplantingholevolume

outdoor planter mix 20-40% by volume

Nurseries eldapplicationasa 1-2incorporated5deep

soil amendment

band application for shade trees 2 applied in 2-foot wide band

liner beds - incorporated 1-2 incorporated pre-plant to 5 depth

liner beds - mulched 1-2 mulched post-plant

container mixes 5-40% of vol. depending on plants

Agriculture generaleldsoilamendment 1-2incorporatedto5-8depthspecialty crop production 1-2 incorporated to 5-8 depth

Retailers/ common landscape or garden 1 application or 20% of planting mix

Homeowners amendment

mulching 2-3 around all landscape plants

Topsoil blenders soil amendment for many beds 10-50% for blends depending on plant family

andspecications

Silviculture new seedling establishment 1-2 disked where possible

mulch 1-2 evenly applied


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VI. PLANNING AND SITINGEstablishing and managing a successful com-posting operation requires meeting a series ofobjectives concerning planning, assessing theeconomics, and siting of an operation. Many ofthe factors important in planning interact, anddecisions are often inuenced by multiple fac-

tors. The following steps provide a simpliedapproach to the planning process.

A. IDENTIFY GOALSDevelop your composting plan based on aclearly dened set of goals. Examples of goalsare: a) to produce a valuable soil amendmentor potting medium for on-site use; b) to im-prove livestock manure management; and c) toincrease farm economic potential through thesale of compost. Regularly revisiting goals will

permit timely changes that might be necessaryin order to maintain an efcient compostingoperation.

B. UNDERSTAND THE COMPOSTINGPROCESSBasic knowledge of the composting process isessential for making planning decisions. It isbenecial to consult many sources for informa-tion on composting principles and systems,feedstocks, and process management. A list ofother publications and resources is provided inAppendix D. Visit existing compost operationsto learn about the practical aspects of compost-ing (i.e., facility design and siting, equipmentoperation, troubleshooting the process, andachieving desired nished material quality).Valuable information can be gained throughthe experiences of other composters who can beidentied through the Virginia Organics Recycling& Composting Directory (VCE Pub.452-230) or bycontacting your Cooperative Extension agentand/or the Virginia Recycling Associations

Organics Recycling and Composting Committee(see Appendix D.). Internet resources are alsoimportant sources of information. Some of theseare also listed in Appendix D.

C. ASSESS FEEDSTOCK AVAILABILITYMost organic wastes can be composted, butmaterials that provide a balanced C:N ratioand achieve desired particle size distributionmay not be easily obtained. Locating numer-

ous sources of feedstock materials can improvethe overall dependability of materials ow andallow exibility in determining mixes. Stateagency representatives such as your local Exten-sion agent can be helpful in identifying wastestreams that are not readily apparent.

Some materials may be available free of charge(e.g. municipal leaves, sawdust), while in othercases, waste handlers may be willing to pay atipping fee to deposit materials on farm. Somefeedstocks may need to be purchased, such aspoultry litter, which can provide nitrogen for thefarm composting operation with an overabun-dance of high carbon content materials. Thecosts should be well researched and appropriatearrangements made for delivery. Obtaining acontract for materials delivery is recommended;therefore, assessing the potential for such con-tracts is important in the planning process. Is-sues important in developing a materials deliv-ery and management contract are presented inAppendix C. Any such contract should address:length of agreement, quantity, fees (if any),delivery schedule and conditions, quality, con-tingencies, and assignment of responsibility inthe event of damages. Securing the services of acompetent legal advisor is recommended.

Delivery mode and quality of materials are

critical issues. Many waste streams can containnuisance and even hazardous materials. Glass,metals and plastics can excessively contaminatemunicipal leaves collected with a vacuum truck.Some of these can damage equipment or im-pede mixing and processing, and can potentiallybecome projectiles thrown by windrow turners.Variations in moisture content and nitrogen con-centration may require using differing amountsof individual materials. In addition, processingraw materials prior to composting is sometimesnecessary. Being aware of these factors can help

one negotiate a workable contract.

D. DETERMINE SITE SUITABILITYSites should be evaluated based on the plannedand potential amount of wastes to be compos-ted, accessibility, the existence of or potentialfor creating an appropriate surface, proximityto a water source for wetting windrows or piles,and regulatory requirements for set-backs andwater quality protection. Specically, Virginia


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yard waste composting regulations require thatthe composting area not be within a designatedood plain and that it be at least 24 inches abovethe seasonal high water table.

The composting site must be large enough to al-low for receiving and handling of all feedstocks,for composting and curing, and for equipmentoperation. The various systems used in farmcomposting are presented in Section III. Site siz-ing should also take into account the possibilityof some event preventing the composting of theincoming material, as well as potential delaysin moving the cured compost off-site (Figure 7shows a sample facility layout). Approximately1.2 acres will be required for active composting

and curing of 1,000 yd3

of material processed infour windrows 100 yds. long, 4.5 ft. tall and 10 ft.wide. This includes space for material receiving,composting, equipment maneuvering, compostcuring, and a grass lter strip. This same areawould be adequate to compost 4,000 to 6,000 yd3annually, if feedstock delivery is spread over sev-eral months and rapid composting is practiced.An area of approximately 0.9 acre is needed foraerated static pile composting of 1000 yd3 of ma-terial in 10 piles that are 12 ft (w) x 6 ft (h) x 75 ft

(l) and covered with an additional 6-inch insulat-ing/lter layer. This includes space for materialreceiving, cover material stockpiling, compost-ing, blower pad, compost curing, and a grasslter strip. State regulations require certain

setbacks or buffer zones concerning proximity toneighbors. These are addressed in Section VII.

Composting can be conducted on the existingground surface, on some type of ground cover-ing material (such as woodchips), or on a pre-pared surface over compacted subsoil (such asa base of mixed rock plus rock dust, or a pavedarea). An area with moderate to well-drainedsoils is desirable for composting on existingground surface. A prepared surface minimizes

the development of ruts and ponding duringrainy weather, requires less maintenance, andprevents the inadvertent incorporation of soilor loose surface material for turned windrowcomposting. For turned windrow composting,a grade of 2-4% (4 ft. drop over a 100 ft. length)will permit runoff to drain adequately and willprevent excessive erosion when composting on anon-paved surface. The expense of grading willvary widely from site to site.

Figure 7. Compost operation site.

(Reprinted with permission from On-Farm Composting Handbook, NRAES, 1992.)

Farm pondPasture

Prevailingsummer winds

Direction of drainageGeneral slope of theland (0-8%)

Compostingpad

Wetlands

Proposed composting site

Pasture

Curing andcompost stor-

age

Stream

Rawmaterial stor-

age

Farmland

Possible visual screen

Existingtrees and

brush

Cropland

N

Farm house

Neighbors house Neighbors house Neighbors house Neighbors house

Farmr

oad


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Composting generally produces little leachateunless uncovered windrows or piles are exposedto heavy rains. Properly designed grass lterstrips will trap runoff and prevent surface watercontamination. Proper lter strip size is depen-dent on soil type and grass cover species. LocalExtension agents, Natural Resource Conserva-

tion Service personnel, or other agriculture agen-cies can assist in lter strip sizing.

E. ASSESS PROjECTED OPERATIONECONOMICSThe addition of a composting operation to acurrent agricultural enterprise is not simply amatter of adding a piece of equipment or onenew task for a worker. Composting can requiresubstantial investments of capital, labor, land,and management resources. A reduction in cur-rent activities or the addition of new personnelmay be necessary. Management of a compostingoperation may require daily attention duringcertain phases of the process. Depending uponthe scale of the planned composting operation,the initial investment could range from a fewhundred to tens of thousands of dollars. Keyeconomic variables to consider include:

benets of using compost on farm, such asincreased yields, reduced fertilizer orother input cost;

income potential from selling nished

compost; cost of any additional labor if needed; credit availability and cost, if

additional investment is needed; operating cost and purchase of

equipment and facilities, if needed.A business plan should be developed for anynew farm enterprise, including nancing, opera-tion and investment costs, and projected income.However, a series of questions should be an-swered before penciling out the numbers.

What quantity of suitable organic material isavailable, and at what price? Is a largequantity of high-nitrogen material such asanimal manure produced on farm thatrequires disposal in any case, or is manureavailable at low cost? What quantities ofcarbon sources are available, and at whatprice, if any? Might a municipality or busi-ness pay for a farm to receive compostableorganic wastes? What are the transportation

costs, if any, in bringing feedstocks to acomposting site?

Does the land area have easy access, ad-equate drainage, and suitable slope? Is itreasonable to sacrice whatever net return iscurrently derived from this land in order to

dedicate it to compost production? If only alittle land is available relative to the amountof compost that will be produced, is it rea-sonable to consider a more capital-intensive(and expensive) production system? Howmuch will it cost to prepare the site forcompost production, and to prepare entryand exit for delivery and sales?

How much labor and management time will

be required for compost production andmarketing? At what times of the year will

raw materials be available and do thesecoincide with targeted compost productionperiods? At what times of year will compostmarketing, loading or delivery efforts be

possible or necessary and will productavailability coincide with demand? Willcompost demand occur at the busiest

time of year for farming opera-tions? Is it possible and moreadvisable to put in more labor timeas opposed to purchasing more equipment?

What production system and level of technol-ogy would be best to use, and what are thecapital investments needed? Can someexisting farm machinery be used efciently?Are large capital investments affordable, or isit better to choose a simpler, smaller produc-tion system?

How much do government permits cost, and

what are the restrictions applicable to on-farm composting that affect cost?

Is it reasonable to risk money, time, and effort

on this venture? Would the failure of acomposting operation put this farm intonancial jeopardy?

In order to derive economic benet, the end-usevalue (whether it is in increased yields, reducedoff-farm fertilizer and pesticide inputs, reductionin irrigation requirements for crop production,or in sales of nished compost) must exceed the


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sum of lost revenue from land use changes plusthe costs for compost production and market-ing/utilization. Refer to Sections II and III for adiscussion of feedstocks and the various equip-ment and systems options available. A processfor developing a budget is presented in SectionVI.I. Keep in mind, however, that not all costs

are quantiable. For instance, long-term im-provements in soil quality are not readily trans-lated into dollar gures on a balance sheet.

Anticipating production costs can be difcultbecause they have been minimally reported andvary widely. Expenses are very dependent onthe quantities, types and characteristics of theincoming material, the production system em-ployed, and the equipment being used. (Refer toSection VI.I for some reported costs.)

In windrow composting, the cost ofpassivecomposting principally involves loss of the landto other uses and the initial investment in per-forated aeration pipes. However, when usingexisting farm equipment to actively manage com-posting windrows, the costs additionally includegreater site development and maintenance, labornot available for other activities, and increasesin equipment use, maintenance/repair, and rateof depreciation. Utilizing a windrow turner candramatically increase processing capacity (500-

2,000 yd3

/hr with a turner vs. approximately50 yd3/hr with a tractor and bucket), and thusreduce labor costs per yd3, while increasingefciency, and improving end-product quality.The cost to purchase and own such equipment,however, can represent considerable expense.

For on-farm static pile aerated systems, set-upcosts include site preparation, electrical serviceinstallation, and blower and piping costs. Oper-ating costs will vary greatly based on such thingsas the types of wastes, how well they are initially

mixed, and the blower control schedule.

F. ASSESS THE MARKET POTENTIAL IFCOMPOST IS TO BE SOLDMarket research is an essential part of any busi-ness venture (German, et al.1994). The rst steptowards assessing market potential is to deter-mine the cost of the potential product. A marketpotential exists when it can be determined thatcustomers have a need for the product and a

consistent, high quality product can be suppliedat a competitive price. An important market-ing message is that compost produces higherbenets per dollar purchased than competingproducts, is locally produced, and is environ-mentally desirable. If many potential customersalready accept this message, ready markets may

be available.

The three most important factors in market-ing are location, location, and location. Is thecomposting site close enough to urban andsuburban markets to avoid ruinous transporta-tion costs for the nished material? Do speciallocation advantages exist for establishing long-term agreements with clients? Does a compostmarket currently exist, or must it be created?Organic farmers, greenhouse operations, andlandscape businesses will likely be valuable

customers, since each has signicant soil amend-ment needs. Local Extension agents or appropri-ate farmer organizations can assist in estimatingthe size of the potential market and facilitatingcontacts with customers. Greenhouse operationsand landscape businesses should be contacteddirectly. Having product samples available todistribute and being willing to offer a low intro-ductory price for initial purchases can enhancesale opportunities. Other possible clients arenursery businesses, golf courses, municipalitiesand other government bodies. A large potential

for new clients is among homeowners, althoughthey must be educated about the benets ofusing compost as an alternative or additionto traditional soil amendments or landscapemulches. A market advantage can be gained byoffering custom compost blends using differentcomposts, woodchips, and/or topsoils. Land-scapers may want a coarse material (i.e. withsome chips) to utilize as mulch; gardeners maybe seeking very ne material; and homeowners,a compost/topsoil blend for ower beds. Inves-tigating the specic needs of different customers

will allow development of application-appropri-ate blends.

Target markets may initially depend on exist-ing delivery and distribution systems. Directbulk sales at the farm has been the most com-mon avenue for young operations. Selling bulkcompost through retailers such as garden shopsis an option for those with the capacity to deliverthe material economically. Small or mediumvolume compost producers generally cannot


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justify a bagging operation to sell compost in 25-or 40-pound bags, but this avenue can becomeattractive as an operation grows. In some cases,composters have found retail nursery operationswilling to cooperatively purchase a bagging ma-chine for customer self-service use.

Even if no clear market exists for compost,there may be opportunities to educate potentialcustomers and increase demand. Such an effortwill require generating the advertising creativ-ity, putting in the time, and incurring the costs ofcustomer education. Customers rst must knowa compost production business exists in theirarea in order for them to seek out the product.They also need information about the product.Distributing product samples, writing articlesfor local magazines, buying local radio spotsor newspaper ads, and giving presentations to

garden clubs or Master Gardener meetings areall possible avenues for building a market.

G. INVESTIGATE LOCAL AND STATEREGULATORY REQUIREMENTSUnderstanding regulations is essential forcompliance. Local ordinance restrictions mustbe investigated thoroughly, not only to ensurecompliance, but to maintain cordial relationswith neighbors who may not initially considera composting operation an asset for the com-

munity. Restrictions may include such thingsas maximum truck weights on roads leading tothe farm and set-backs or buffer zones for par-ticular agricultural practices. In addition, be-cause composting may not explicitly fall withinthe denition of existing controlled activities,planning commissions or other local governingboards may need to be consulted and petitionsfor changes to local ordinances may be neces-sary. Section VII gives a detailed treatment ofthe Virginia state composting regulations affect-ing agricultural operations.

H. SELECT TECHNOLOGY LEVEL ANDESTABLISH OPERATION SIZEComposters may choose among active windrowcomposting, passive windrow composting, andaerated static pile composting as the technologyto adopt. A discussion of these is provided inSection III.

I. DEVELOP OPERATION BUDGETA business plan, including an annual projectedcash budget, should be constructed, if a com-posting operation appears feasible and desirable.Remember that the cost of compost productionand the net revenue earned (if compost is sold)are very farm-dependent, subject to the produc-

tion system and equipment needs, the materialsused for composting, the distance the farm liesfrom available markets, and a host of other fac-tors.

To develop a composting budget, make realis-tic estimates of ALL the anticipated costs of theoperation, and dont become starry-eyed aboutthe revenue potential. No one wants to haveunwelcome surprises about costs or returns.The costs and returns should be penciled outto be sure that compost production costs will bebelow an acceptable level, and (if sold) that thecompost will earn a solid return. Area ExtensionFarm Management agents can be contacted forassistance. Such a budget can be organized asfollows:

Cost: Materials and supplies. For materi-als imported to the farm, the costs for purchase,transport, and other inputs associated with de-livery to the composting site should be included.When using ones own equipment, a hauling

cost which reects all the costs of fuel, oil, main-tenance and repairs, equipment taxes and depre-ciation should be included. As a rule of thumb,budgeting less than $0.10 per ton per loadedmile may be underestimating hauling costs.

Nitrogen sources: These costs should includethe total annual cost of organic materialsources such as animal manure. If purchasedfrom off the farm, include purchase, trans-port, and any other costs for delivery to thecomposting site. If manure is normallyproduced and spread on the farm, there maybe no additional costs with composting.

Carbon sources: The costs of materials andsupplies should also include total annualcost of high-carbon materials, which usuallyare not produced on the farm. The mostattractive high-carbon material for manyfarmers is yard waste that is provided, insome cases, at a subsidy (tipping fee) from


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local municipalities. Consider a tipping feeas a revenue or (equivalently) a negativecost. Other materials include paper andsome wood products, crop residues, hay orstraw, and seaweed or aquatic plants (seeTable 2).

Other supplies: Materials and suppliesassociated with process monitoring are alsonecessary. These include one or morethermometers and possibly product testingequipment and supplies.

Cost: Labor and Equipment. Labor andequipment costs are best considered togetheron an hourly basis, since composting operationsgenerally require a combination of labor andequipment. The rst factor to consider is thecost of labor. If hired labor will be conductingthe actual composting, their hourly wage shouldbe used. However, even if one is providing allthe labor, a wage cost of at least the currentskilled labor wage rate should be charged to thecomposting operation, so that any net returnsfrom composting can be considered prot,above and beyond any consideration of the costof that time.

Next, the costs of all equipment such as tractors,front-end loaders, and manure spreaders must

be considered. Equipment costs are often dif-cult to calculate. The rst type of equipmentcost to consider is the estimated cost to operatethe equipment in the composting enterprise.This should include any fuel, oil, or other lu-bricant cost, as well as any expected repair ormaintenance charges stemming from use of theequipment in composting. Typical operatingcosts of a $24,000, 60-HP diesel tractor used 500hours per year for 12 years are approximately$4-$5 per hour, while those of a $41,000, 100-HPdiesel tractor used at the same annual pace areapproximately $7-$8 per hour (calculated fromsimilar or identical equipment in Doanes Agri-cultural Report Newsletter, 1996).

The second type of equipment cost is the owner-ship cost an estimate of the cost of owningthe equipment, whether or not it is used. This

cost depends on the purchase price of the equip-ment, whether it was purchased outright orwith a loan, the useful life of the equipment, theinterest rate charged or opportunity cost of themoney invested in the equipment, and the costof insurance and housing. For the 60-HP trac-tor mentioned above, ownership costs might be

approximately $3,000 per year, or $6 per hour ifused 500 hours per year, while ownership costsof the 100-HP tractor might be $5,200 per year, or$9.50 per hour if used 500 hours per year (Doane,ibid.).

Dont forget to estimate costs for specialty equip-ment like tractor-mounted front-end loaders, ma-nure spreaders, and compost turners. The com-bined annual ownership and operating costs fora typical 1-yard bucket used 200 hours per yearwould be $3.50-$4.50 per hour, and for a smallmanure spreader used 200 hours per year wouldbe $8.50-$9.50 per hour (Doane, ibid.). If a com-post turner is to be purchased, its cost shouldbe a major focus of consideration. How large acomposting operation will be needed to repaythe investment of $15,000 or more in a compostturner? For a $15,000 tractor-pulled turner witha 12-year useful life, the annual ownership costswill be approximately $2150 per year. Assumingthat 50 yd3 of nished compost can be producedper hour of turner time1, the hourly ownership

and operating costs of the turner (without trac-tor or labor costs) when 7,500 yards of nishedcompost are produced will be approximately $20per hour (Doane, ibid.).

A few specic gures for system establishmentand compost production have been reported. Inactive windrow composting, creating compostfrom yard trimmings and yard trimmings plusmanures using standard farm equipment, andturning the material from one to a few times, hasranged from $3 to $7.50 per cubic yard of incom-

ing material (Gresham, et al., 1990; Dreyfus, 1990;DeMuro, 1995). For aerated static pile compost-ing, an investment of $2,000 was required for thepurchase and installation of a blower and pipingat one central Virginia farm in 1996 in order tobatch compost 80 tons of spent bedding froma cattle holding lot (T. Zentgraf, 1997). A 1992

1 Based on a windrow of 1000 yd3 of material being turned in 20-30 minutes, for a total of 25 times, and resultingin a material volume reduction of approximately 50% (from 1000 yd3 to 500 yd3).


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operating cost estimate for a static pile aerationsystem in the Northeast U.S. capable of han-dling approximately 200 tons of sh waste plusbulking agents was approximately $2700/yr(NRAES, 1992).

Cost: Other Capital Costs. Remember to

put a value on the land which is used for thecomposting operation. At a minimum, gurethe cost of the land as the typical rental rate forsimilar land in the community.

Large capital investments of many thousand dol-lars may be necessary for site preparation andestablishing all-weather road access to the com-posting site. These will vary greatly from siteto site. In one case, the cost to grade a portionof fairly level pasture measuring 25 x 75 yards(0.38 acre) at a farm in northern Virginia and layand compact a 5-6 inch base of roadbed-grademixed stone and 2 inches of rock dust was ap-proximately $10,000 in 1994 (E. Polishuk, 1994).When calculating the annual cost of compostproduction, divide the site preparation and roadaccess initial investments by the useful life ofthe principal equipment purchased (such as thecompost turner). Add an additional annual feefor any interest charges and maintenance costs.

Included on the next page are two simple work-

sheets to help organize cost estimates: Worksheet1 for recording labor and equipment use costs,and Worksheet 2 for computing the annual costof compost production.

If some or all of the compost produced is to besold, be conservative about both the sale pricesthat can be expected and the amount of compostthat can be sold. Its better to be surprised thatthe operation did better than projected than it isto be dismayed about not fullling unrealisticexpectations. If urban yard waste will be com-posted through a contract with a municipal au-thority, ones bargaining position depends on theexistence of other farmer-bidders, the distancemunicipal trucks must travel to the farm, andthe tipping fee for leaf waste disposal atlocal/regional landlls. If a contract is securedfor urban yard waste, make sure that eitherdebagging will be the responsibility of themunicipal authority or that debagging costs areincluded in determining contract rate, along

with extraction of visible, non-compostable trashlike toys, plastic bottles and rocks. Monitoringcosts should be expected in order to make surethat incoming trucks and their loads are countedand to extract trash not found by urban crews.Worksheet 3 can be used to detail revenues.

j. INFORM AND EDUCATE NEIGHBORSIt is extremely important to inform and educateneighbors about composting activities. Utilizingthe support of Extension agents and state agencypersonnel can assist in easing concerns regard-ing trafc, noise, dust, odors, and environmentaland health issues. Being prepared for discus-sions is very important in maintaining goodrelations. Accurately representing what changeswill likely occur in farm activities and the stepsbeing taken to minimize any potentially nega-

tive aspects of those changes will demonstrateconsideration for and a desire to help ease neigh-bors concerns.


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Worksheet 1: Labor and Equipment Tasks (simple windrow production system)

Task Labor Time Labor Cost Equip. Time Equip. Cost

Site Preparation

Debagging or Trash

RemovalWindrow Formation

Windrow Turning

Windrow Wetting

Windrow Monitoring

Cleaning and/or Bagging

Loading

Delivery

Worksheet 2: Composting Enterprise Annual Costs of Producing Units Compost

Item Quantity

Cost: Materials and Supplies

Nitrogen sources

Carbon sources

Other supplies

Cost: Labor and Equipment

Cost: Other Capital Costs

Worksheet 3: Composting Enterprise Annual Revenues

Annual Revenue Price Quantity Total

Bulk Sales

Pickup Sales

Bag Sales

Tipping Fees


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VII. REGULATIONS:UNDERSTANDING ANDCOMPLIANCE

At the statewide level, composting activities inVirginia are regulated by the Department of En-

vironmental Quality (DEQ). The Virginia YardWaste Composting Facility Regulations (9 VAC20-100-10 et seq.) and the accompanying statuteestablish the standards for siting, design, con-struction, operation, closure, and permitting ofyard waste composting facilities. These allow allagricultural operations to compost farm manuresand/or other agricultural wastes in combinationwith yard wastes. They also provide for someexemptions from operational and/or permittingrequirements for various agricultural operations.(Note: In 1997 the yard waste composting regu-

lations will be replaced by the Vegetative WasteManagement and Yard Waste Composting Regu-lations (9 VAC 20-160-10 et seq.). However, thesewill contain essentially the same requirementsfor agricultural operations.

The Virginia Solid Waste Management Regula-tions establish the requirements for compostingall materials other than yard and agriculturalwastes. These are more stringent than thosefor yard waste composting and result in greater

expense for permitting and compliance. Speci-cally, all composting sites must be hard-surfacedand provide for collection and treatment ofrunoff/leachate.

Following is a summary of some of the high-lights of these regulations and the exemptionsthat govern agricultural operations2. Copies ofall of these regulations are available from DEQ(See Appendix D).

A. YARD WASTE COMPOSTING

FACILITY REGULATIONS

Fully exempted facilities. Agriculturaloperations conducting composting are exemptfrom ALL the regulations (i.e. siting, design,construction, operation, closure and permitting)under 2 scenarios:1. When vegetative wastes and yard wastes

generated on site are being composted withor without on- or off-site agricultural solidwastes3, anda) all the compost is used at the operation,b) all applicable local ordinances are

observed, andc) no nuisance or threat to human health or

the environment results;OR

2. When vegetative wastes and yard wasteswhich are received from off-site are beingcomposted with or without on- or off-siteagricultural solid wastes, anda) all the material is composted and used

within 18 months after it arrives,b) no more than 6,000 cubic yards of

vegetative and yard wastes are receivedeach year,

c) the site has at least one acre available forreceiving yard wastes for every 150cubic yards of nished material gener-ated during a year,

d) composting is not conducted in a oodplain or located within 300 feet of aproperty line or 1,000 feet of an occupieddwelling,

e) all applicable local ordinances are ob-served,

f) no nuisance or threat to human health orthe environment results,

g) the owner submits a simple letter ofcertication (specied in the

regulations) to the DEQ before receivingmaterial for composting.

2 An agricultural operation is any operation devoted to the bona de production of crops, animals, or fowl,including but not limited to the production of fruits and vegetables of all kinds; meat, dairy and poultryproducts; nuts, tobacco, nursery and oral products; and the production and harvest of products fromsilviculture activities. (Code of VA, 9 VAC 20-10-10. Defnitions.)

3 Agricultural solid waste materials are dened as those normally returned to the soil, which are generated bythe growing and harvesting of agricultural crops [spoiled hay, peanut hulls, corn stover] and the raisingand husbanding of animals [e.g. animal manures, spent animal bedding] (Code of VA, 9 VAC 20-80-150.F).


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Regulated facilities. All agricultural opera-tions conducting composting, but not meetingeither of the 2 scenarios above must follow sit-ing, design, construction, operation and closurerequirements. Some of these operations maycompost without a permit; others may not.

Siting, Design, Construction, Operation,Closure:Operations that compost greater than6,000 cubic yards of yard waste per year and/or sell the nished compost must adhere to thefollowing requirements:

a) The site must not be within 200 feet of an occupiedstructure, in a ood plain or geologically unstablearea, or closer than 50 feet to a regularly owingstream.

b) The site must have a buffer zone of no less than100 ft between the process operations area and the

boundary of the facility.

c) The composting facility must be designed and op-erated such that non-vegetative wastes and othernon-compostable materials are separated fromthose to be composted, and disposed of properly.

d) No wastes other than vegetative and yard wastesand agricultural wastes may be composted.

e) If the seasonal high water table is within 24 inchesof the ground surface, the composting and han-dling areas must be hard-surfaced and bermed to

manage runon, runoff and leachate. No leachateor runoff must drain or discharge directly intosurface waters.

f) For other sites, the area need not be hard-surfaced,but must be graded to provide for the propermanagement of runon, runoff and leachate.

g) The roads serving the composting operation mustbe useable in all weather conditions.

h) A manager / worker must be on duty during op-eration hours.

i) A safety program, a re prevention and suppres-sion program, and controls for dust, odors andvectors must be in place.

j) An approved closure plan that minimizes theneed for future maintenance must exist. Thisclosure plan needs to include the steps requiredfor closing the operation at its peak, if that wereto become necessary. It need not specify a closuredate and can be amended as needed.

Permitting- Exempted facilities:Agricultural operations that compost greaterthan 6,000 cubic yards of yard waste per yearand/or sell the nished compost are not re-quired to secure a permit if:

a) Composting is not conducted in

On-Farm Composting: A Guide

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