Report No. CM-97-2

ACKNOWLEDGEMENTS

Landscape Architecture/Design Specifications for Compost Use was developed through funds provided by the CWC as part of its commitment to the composting industry and the development of sustainable compost markets.  Many other individuals and organizations also made this publication possible.  Additionally, thanks go out to The Composting Council, its staff, and Market Development Committee members for providing input, direction, and review of this publication.  Appreciation is also extended to the Landscape Architecture/Design industry who provided valuable input and review through leadership provided by the American Society of Landscape Architects (ASLA), the Washington (State) Chapter of the ASLA, and the Association of Professional Landscape Designers.

 

TABLE OF CONTENTS

Page

LETTER TO SPECIFIERS..............................................................................................................           1                                                                                                                                                                                                                    

SELECTING ORGANIC SOIL AMENDMENTS FOR LANDSCAPES........................................           2

GENERAL COMPOST INFORMATION

         INTRODUCTION..................................................................................................................           6

         1.0................................................................................................................................. BENEFITS OF COMPOST AND ITS EFFECT ON GROWING SYSTEMS.........................................................           8

                    Physical Benefits............................................................................................................           8

                    Chemical Benefits...........................................................................................................           8

                    Biological Benefits..........................................................................................................           9

                    Additional Benefits of Compost....................................................................................         10

         2.0      COMPOST SOURCE MATERIALS (FEEDSTOCKS).............................................         12

         3.0      COMPOST CHARACTERISTICS/PARAMETERS..................................................         15

                    Quantified Parameters..................................................................................................         16

                    Qualified Parameters....................................................................................................         20

                    Unspecified Parameters................................................................................................         21           

                    Other...............................................................................................................................                        23

         4.0      COMPOST SELECTION..................................................................................        24

                    The Compost Supplier.................................................................................................         24

                    Important Attributes of a Compost Supplier..................................................................         25

         5.0      COMPARING COMPOST TO OTHER HORTICULTURAL/

                    AGRICULTURAL PRODUCTS.................................................................................         26

         6.0      COMPOST USE ESTIMATOR.................................................................................         30

         7.0      SOIL/MEDIA TESTING....................................................................................        31

         8.0      COMPOST APPLICATION..............................................................................        32

         9.0      FERTILIZER APPLICATION....................................................................................         33

         10.0    NUTRIENT LOADING ESTIMATOR.......................................................................         35

         11.0    pH ADJUSTMENT.....................................................................................................         38

         12.0    HEALTH/ENVIRONMENTAL ISSUES....................................................................         40

                   

LANDSCAPE ARCHITECTURE/DESIGN SPECIFICATIONS

         SHORT SPECIFICATIONS

                    Turf Establishment with Compost..................................................................................         44

                    Planting Bed Establishment with Compost.....................................................................         46

                    Compost as a Landscape Backfill Mix Component.......................................................         48

                    Compost as a Landscape Mulch...................................................................................         50

Compost as a Soil Mulch for Erosion Control..................................................................        52

                    Compost as a Filter Berm for Sediment Control....................................................        54

         LONG SPECIFICATIONS

                    Seeding and Mulching..........................................................................................        57

                    Sodding and Sprigging..........................................................................................        65

                    Trees, Shrubs, and Ground Covers...............................................................................         74

                    Erosion and Sediment Control......................................................................................         92

LITERATURE CITED/ REFERENCES..................................................................................       100

APPENDICES

Appendix 1:  Part 503 Sewage Sludge (Biosolids) Regulations Summary

                       of Limits for Land Application  Quantified Parameters.......................................           i

Appendix 2:  Related Publications...........................................................................................          iii

Appendix 3:  List of Review Teams...................................................................................................           v

  

LIST OF COMPOST PRODUCERS AND MARKETERS.............................................................           ix

DISCLAIMER................................................................................................................................         xiii

December 1997

Dear Landscape Architect/Designer:

Thank you for your interest in the specification and use of compost.  Throughout the Country, compost has proven to be an excellent tool for landscapers to improve the environment in which plant materials are to be grown.  Compost is a unique product which can improve soil and other growing media physically, chemically/nutritionally, and biologically.  Today, it is estimated that approximately 5,000 composting facilities exist throughout the United States that manufacture product from various agricultural, municipal, and industrial source materials (feedstocks).  The use of compost has not only proven to dramatically improve soil quality, and therefore, turf and ornamental plant growth, but also reduce replacement costs in the field by improving plant survival rates.  Also, by providing and allowing for the proliferation of various microorganisms, compost has been shown to improve plant nutrient uptake as well as suppress many soil-borne diseases.

The enclosed package contains a series of short and long compost use specifications that were developed for various landscape applications.  Both product specifications and end use instructions are provided.  They may be used as is or modified to meet the specific needs of your client or project.  For instance, you or your customer may prefer a compost produced from a specific feedstock, or you may wish to adjust application rates based on manufacturer's recommendations or tighten up the product specifications based on personal preference.

Our goal is to provide landscape architects, landscape designers, municipal agencies, and other specifiers with compost use specifications which are written in a commonly used format, thereby allowing specifiers to "cut and paste" the appropriate information.  We hope that this will not only allow easy incorporation into your current project specifications, but also provide information that can be easily modified for different geographical areas, climatic conditions, and soil conditions.  We appreciate your support of compost, an annually renewable resource.  Please review the article that follows this letter.  It provides insight on how best to use compost under various soil conditions. 

 

Sincerely,

The Composting Council

P.S.      For additional information regarding compost use, composting, as well as test    methodologies used in its compost evaluation, please find The Composting Council's          publications list in the Appendix 2 of this document

SELECTING ORGANIC SOIL AMENDMENTS FOR LANDSCAPES

Francis R. Gouin, Professor Emeritus

University of Maryland College Park

Success in establishing landscapes is dependent upon knowing the soil that exists on site, knowing the species of plants to be planted, and knowing which organic amendment to use.  It is also important to understand that all three of these elements are of equal importance.

In new construction, the soil used in landscaping often contains little of what we classically consider to be topsoil.  Furthermore, areas surrounding the site are often heavily compacted due to construction equipment and practices.  In improving existing landscapes, especially if plants are not performing as expected, the problem can often be attributed to poor soil conditions.  Therefore, soil testing is necessary in order to determine how the soil can be improved and to provide guidance on selecting plants that can thrive under existing soil and/or improved soil conditions.

The auger that is used for taking soil samples can also be used to determine the degree of soil compaction.  If the auger is incapable of penetrating to a depth of 8 to 10 inches, it means that the soil is heavily compacted.  In addition to amending the soil with organic matter, it will be necessary to subsoil to a depth of 14 to 18 inches at 2 to 3 foot intervals when the soil is dry.  Subsoiling allows for fracturing of the hard pan layers without mixing the topsoil and the subsoil. Subsoiling should be done after the organic amendments have been added so that some organic matter drops down into the cavities created by the subsoiler.

Soil testing for laboratory analysis should be a composite of samples taken from an area spanning no larger than 10,000 square feet.  If the soil appears to be highly variable, more samples from the area to be landscaped should be submitted.  A minimum of 10 core samples should be taken, to a depth of 6 to 8 inches, from each area.  They should be mixed thoroughly together before extracting a pint sample for laboratory analysis.  The air‑dried sample(s) should be sent to a reputable laboratory for analysis and recommendations.  In addition to a general nutrient analysis and pH, one should also request testing for percent organic matter (O.M.).

Understanding the requirements of the various plants to be installed is also important in selecting which organic amendment(s) will be used.  There are species of plants that perform at their best when planted in acid soils (pH below 5.0), while others perform best when growing in only mildly acid soils (pH 6.5).  Aside from turf and ornamental grasses, most ornamental plants perform best at a pH of 7.0 or below.  Although the addition of large amounts of organic amendments to soils allows one to grow plants over a wider range of pH's,  it is important to remember that, in time, the roots of plants will extend far beyond their intended planted area, and the amount of organic matter in the soil will decrease with time.

It is important to remember that not all compost and other organic amendments are alike.  There is wide variation in the percent organic matter, pH, nutrient content, soluble salts, etc.  When selecting organic amendments, it is important to understand the characteristics of the organic amendments available.  This allows selection of the amendment that best improves the soil and meets plant requirements.  Plant nutrient requirements can often be satisfied when compost is used at the recommended rate.

Existing Soil Conditions and Plants to be Established

Soil pH is less than 5.0 & establishing non-acid loving plants

If existing soil pH is below 5.0 and the soil has less than 6% organic matter and only plants that grow best in mildly acid soils are to be planted, it will be necessary to add limestone in addition to compost unless compost made from lime dewatered biosolids is available.  If limed compost is available, there is generally sufficient lime in the compost to adjust the pH to the desired level.

Soil pH is less than 5.0 & establishing acid loving plants

If existing soil pH is below 5.0 and the soil has less than 6% organic matter, one should select a compost that has a pH at or below neutral (pH 7.0) and does not contain any liming agents (e.g., limestone, hydrated lime, ash, etc.).  Although the compost will raise the pH of the soil to above the desired range, the increased organic matter content will compensate for the difference.

Soil pH is greater than 5.0 & establishing non-acid loving plants

If existing soil pH is above 5.0 and non‑acid loving plants are being grown, compost containing liming agents should not be used except in areas where turf and ornamental grasses are to be established. Only compost not containing liming agents should be used for amending soils in ornamental plantings of ericaceous crops and plants that prefer mildly acid soils.  Ornamental grasses and turf species are more tolerant to high pH's than are most broadleaf species.

Soil pH is greater than 5.0 & establishing acid loving plants.

Most acid loving plants perform best when planted in soils having an abundant supply of organic matter.  However, despite the pH buffering capacity of organic matter, it is important to maintain a pH as close to ideal as possible.  Under such soil pH conditions, it if is often better to use peat moss or pine fines and not compost as a soil amendment and supply nutrients using chemical fertilizers.  Using a 1:1 blend (v/v) of peat moss or pine fines and compost (unlimed) can also be beneficial.  Since most peat moss (Canadian, Sphagnum) have a pH near 3.5, there is often sufficient acidity in the peat moss to neutralize the higher pH of the compost.

Using Compost to Meet Nutrient Needs.

Compost made from biosolids often has a higher nitrogen (N) and phosphorus (P) concentration than compost made from animal manures and yard trimmings.  Composts made from animal manures and yard trimmings generally contain elevated levels of potassium (K) and lower levels of P.  Knowing this information can provide guidance in selecting a compost that would be most beneficial and reduce chances of creating nutrition related concerns in the future.  Although not a typical occurrence, compost that contains extremely high levels of calcium (Ca) has the potential of binding P and essential trace elements in both the compost and soil, thus preventing their uptake by plants.

The overall best compost to use can also be further determined through soil test results.  If soils are low in P, using a compost made from biosolids can eliminate the need for having to add commercial phosphate fertilizers.  If the soils are deficient in K but rich in P, then using a compost from yard trimmings and/or animal manures in place of biosolids is preferred.  For amending soils possessing high levels of Ca, one should avoid using a compost that contains additional liming agents.

Soluble Salts in Compost

Most commercial composts contain a significant amount of nutrients in the form of fertilizer salts.  These fertilizer salts are also referred to as soluble salts.  Since excessive amounts of soluble salts can stunt or kill plants, caution should be taken when using compost around salt sensitive plant species.  For composts that contain high levels of soluble salts (over 5 mmhos/cm), one should not exceed a 20% inclusion rate in a soil mix where salt sensitive species are to be established.  Greater amounts of compost can be used if they contain low to moderate levels of soluble salts.  Although salt-related injury is not common, thorough watering at the time of planting will significantly reduce potential risk.

Sand vs. Clay

Although it is difficult to use an excessive amount of compost on sandy soils, some have found the excessive use of compost on clay soils to be problematic.  When incorporating compost at a 20% inclusion rate or higher, some clay soils have been found to hold excess moisture.  This can make the soil slow to dry and difficult to work even when the soil is lightly wet.  In turf and other permanent planting areas, this would not be a concern.  However, it should be considered in areas where on-going mechanical cultivation is practiced (e.g., annual flower beds).

GENERAL COMPOST INFORMATION

INTRODUCTION

This landscape architecture/design specifications package has been developed to provide you with compost use instructions which have been verified through research and field experience.  Data used in the development of this package was made available through a series of nationally funded projects that culminated in the development of 13 technically based compost use guidelines.  These guidelines provided step-by-step instructions for compost use in specific applications.  Data from the landscape related compost use guidelines was then used as a basis for this specifications package.  Along with a series of long and short specifications, this package also provides associated information about the characteristics and benefits of using compost as well as several other related topics.  This associated information, which may also be found in the Field Guide to Compost Use, was provided with permission from The Composting Council.

What is Compost?

Compost is the product resulting from the controlled biological decomposition of organic material that has been sanitized through the generation of heat and stabilized to the point that it is beneficial to plant growth.  Compost bears little physical resemblance to the raw material from which it originated.  Compost is an organic matter resource that has the unique ability to improve the chemical, physical, and biological characteristics of soils or growing media.  It contains plant nutrients but is typically not characterized as a fertilizer.

How is Compost Produced?

Compost is produced through the activity of aerobic (oxygen-requiring) microorganisms.  These microbes require oxygen, moisture, and food in order to grow and multiply.  When these resources are maintained at optimal levels, the natural decomposition process is greatly accelerated.  The microbes generate heat, water vapor, and carbon dioxide as they transform raw materials into a stable soil conditioner.  Active composting is typically characterized by a high- temperature phase that sanitizes the product and allows a high rate of decomposition, followed by a lower-temperature phase that allows the product to stabilize while still decomposing at a lower rate.  Compost can be produced from many feedstocks.  State and federal regulations exist to ensure that only safe and environmentally beneficial composts are marketed.

1.0  BENEFITS OF COMPOST AND ITS EFFECT ON GROWING SYSTEMS

As more and more compost is produced and utilized and as the body of end-use related research grows, the benefits of using compost have become more evident and measurable.  Because of its many attributes, compost is extremely versatile and beneficial in many applications.  Compost has the unique ability to improve the properties of soils and growing media physically (structurally), chemically (nutritionally), and biologically.  Although many equate the benefit of compost use to lush green growth, caused by the plant-available nitrogen, the real benefits of using compost are long-term and related to its content of living-organic matter.

Physical Benefits

Improved Structure:  Compost can greatly enhance the physical structure of soil.  In fine-textured (clay, clay loam) soils, the addition of compost will reduce bulk density, improve friability (workability) and porosity, and increase its gas and water permeability, thus reducing erosion.  When used in sufficient quantities, the addition of compost has both an immediate and long-term positive impact on soil structure.  It resists compaction in fine-textured soils and increases water-holding capacity and improves soil aggregation in coarse-textured (sandy) soils.  The soil-binding properties of compost are due to its humus content.  Humus is a stable residue resulting from a high degree of organic matter decomposition.  The constituents of the humus act as a soil 'glue,' holding soil particles together, making them more resistant to erosion and improving the soil's ability to hold moisture.

Moisture Management:  The addition of compost may provide greater drought resistance and more efficient water utilization.  Therefore, the frequency and intensity of irrigation may be reduced.  Recent research also suggests that the addition of compost in sandy soils can facilitate moisture dispersion by allowing water to more readily move laterally from its point of application.

Chemical Benefits

Modifies and Stabilizes pH:  The addition of compost to soil may modify the pH of the final mix.  Depending on the pH of the compost and of the native soil, compost addition may raise or lower the soil/compost blend's pH.  Therefore, the addition of a neutral or slightly alkaline compost to an acidic soil will increase soil pH if added in appropriate quantities.  In specific conditions, compost has been found to affect soil pH even when applied at quantities as low as 10-20 tons per acre.  The incorporation of compost also has the ability to buffer or stabilize soil pH, whereby it will more effectively resist pH change. 

Increases Cation Exchange Capacity:  Compost will also improve the cation exchange capacity of soils, enabling them to retain nutrients longer.  It will also allow crops to more effectively utilize nutrients, while reducing nutrient loss by leaching.  For this reason, the fertility of soils is often tied to their organic matter content.  Improving the cation exchange capacity of sandy soils by adding compost can greatly improve the retention of plant nutrients in the root zone. 

Provides Nutrients:  Compost products contain a considerable variety of macro and micronutrients.  Although often seen as a good source of nitrogen, phosphorous, and potassium, compost also contains micronutrients essential for plant growth.  Since compost contains relatively stable sources of organic matter, these nutrients are supplied in a slow-release form.  On a pound-by-pound basis, large quantities of nutrients are not typically found in compost in comparison to most commercial fertilizers.  However, compost is usually applied at much greater rates; therefore, it can have a significant cumulative effect on nutrient availability.  The addition of compost can affect both fertilizer and pH adjustment (lime/sulfur addition).   Compost not only provides some nutrition, but often makes current fertilizer programs more effective.

Biological Benefits

Provides Soil Biota:  The activity of soil organisms is essential in productive soils and for healthy plants.  Their activity is largely based on the presence of organic matter.  Soil microorganisms include bacteria, protozoa, actinomycetes, and fungi.  They are not only found within compost, but proliferate within soil media.  Microorganisms play an important role in organic matter decomposition which, in turn, leads to humus formation and nutrient availability.  Microorganisms can also promote root activity as specific fungi work symbiotically with plant roots, assisting them in the extraction of nutrients from soils.  Sufficient levels of organic matter also encourage the growth of earthworms, which through tunneling, increase water infiltration and aeration.

Suppresses Plant Diseases:  Disease incidence on many plants may be influenced by the level and type of organic matter and microorganisms present in soils.  Research has shown that increased population of certain microorganisms may suppress specific plant diseases such as pythium and fusarium as well as nematodes.  Efforts are being made to optimize the composting process in order to increase the population of these beneficial microbes.

Additional Benefits of Compost

Some additional benefits of compost have been identified, and have led to new uses for it.  These benefits and uses are described below.

Binds Contaminants:  Compost has the ability to bind heavy metals and other contaminants, reducing both their leachability and absorption by plants.  Therefore, sites contaminated with various pollutants may often be improved by amending the native soil with compost.  The same binding affect allows compost to be used as a filter media for storm water treatment and has been shown to minimize leaching of pesticides in soil systems. 

Degrades Compounds:  The microbes found in compost are also able to degrade some toxic organic compounds, including petroleum (hydrocarbons).  This is one of the reasons why compost is being used in the bioremediation of petroleum contaminated soils. 

Wetland Restoration:  Compost has been used for the restoration of native wetlands.   Rich in organic matter and microbial population, compost and soil/compost blends can closely simulate the characteristics of wetland soils, thereby encouraging the re-establishment of native plant species.

Erosion Control:  Coarser composts have been used with great success as a mulch for erosion control and have been successfully used on sites where conventional erosion control methods have not performed well.  In Europe, fine compost has been mixed with water and sprayed onto slopes to control erosion.

Weed Control:  Immature composts or ones which possess substances detrimental to plant growth (phytotoxins), are also being tested as an alternative to plastic mulches for vegetable and fruit production.  While aiding in moisture conservation and moderating soil temperatures, immature composts also act as mild herbicides.

Benefits of Using Compost 1.         Improves the soil structure, porosity, and density, thus creating a better plant root environment. 2.         Increases infiltration and permeability of heavy soils, thus reducing erosion and runoff. 3.         Improves water holding capacity, thus reducing water loss and leaching in sandy soils. 4.         Supplies a variety of macro and micronutrients. 5.         May control or suppress certain soil-borne plant pathogens. 6.         Supplies significant quantities of organic matter. 7.                   Improves cation exchange capacity (CEC) of soils and growing media, thus improving their               ability to hold nutrients for plant use. 8.         Supplies beneficial microorganisms to soils and growing media. 9.         Improves and stabilizes soil pH. 10.        Can bind and degrade specific pollutants.

2.0  COMPOST SOURCE MATERIALS (FEEDSTOCKS)

Quality composts are being produced from many different materials or feedstocks.  Typical feedstocks include agricultural by-products, yard trimmings, biosolids (sludge), food by-products, industrial by-products, and municipal solid waste.  Some of these feedstocks, such as biosolids must be blended with wood chips, sawdust, paper, biodegradable packing, etc. to enhance the composting process.  The majority of composters in the United States primarily compost agricultural by-products, yard trimmings, or biosolids.  If prepared properly, composts produced from various feedstocks will be somewhat similar in nature and function.  However, composts produced from certain feedstocks do possess some unique characteristics.

Agricultural By-Products:  Agricultural by-products can include manure and bedding from various animals, animal mortalities, crop residues, cull fruits and vegetables, and processing/packaging by-products.  Composts produced from agricultural by-products, especially manures, are known for generally possessing higher nutrient concentrations as well as elevated salinity levels.  They are typically low in contaminants and are commonly available in both bulk and bagged form.

Yard Trimmings:  Yard trimmings compost consists of grass clippings, leaves, weeds, twigs, brush, tree and shrub pruning, Christmas trees, and other vegetative matter from land clearing activities and from residential, commercial, and institutional properties.  The compost generated may contain one or all of these source materials.  Yard trimmings composts are also referred to as "yard waste", "yard debris", or "green waste" composts.  Yard trimmings composts are typically lower in nutrients and contaminants.  The soluble salt concentration is typically low, but may be elevated where the feedstock is collected unbagged or uncontainerized in areas where road salts are commonly used.  Yard trimmings composts are popular with both professional users and homeowners and are often marketed in both bulk and bagged form.

Biosolids (sewage sludge):  Biosolids are the organic solid residue derived from residential, commercial, or pre-treated industrial wastewater processing.  Biosolids are treated to reduce pathogens and contain only minimal levels of heavy metals and organic contaminants.  Only biosolids that meet a "Class A grade" (exceptional quality) as outlined in the US EPA's 40 CFR Part 503 regulations can obtain permits for general distribution (see Appendix 1 for Part 503 contaminant parameters).  Compost produced from biosolids that contain greater levels of contaminants may be usable, depending upon state regulations, on a restricted use basis.  Biosolids composts are fairly rich in plant nutrients and typically possess a pH between 6.0 and 7.5.  Some biosolids used to produce compost have been treated with liming agents that can affect pH, buffering capacity, and soluble salts level, thus limiting their horticultural use to a degree.

Food By-Products:  Food by-products can be obtained from various sources, including food processors and restaurants or institutions which separate the food by-products from the general waste stream.  Although food by-product composting is increasing in popularity, it is currently only a small percentage of the composting industry.  Food by-products that are commonly composted included culled or damaged fruits and vegetables, coffee grounds, egg shells, fish residues, bakery items, among others.  Composts produced from food by-products are typically rich in plant nutrients, but may also possess elevated salinity levels.

 

Industrial By-Products:  Many corporations that produce organic residues have begun recycling these materials through composting.  Industrial by-products may include wood processing by-products, paper goods, biodegradable packaging materials, pharmaceutical by-products, paper mill sludges, forestry by-products, brewery residuals, and so forth.  These materials are typically unique in nature and may possess some excellent properties for plant growth or environmental improvement.  Their overall characteristics will vary widely based on their feedstock.

Municipal Solid Waste (MSW):  MSW is typically considered to be mixed residential or commercial refuse that has not been source-separated for the removal of specific recyclable items such as paper, glass, plastics, and so forth.   However, in most cases, mixed municipal solid waste that is intended for composting will be processed after collection to have recyclables and household hazardous wastes removed by  mechanical or hand separation.  MSW composts, especially those containing significant quantities of paper, possess a lower quantity of nutrients and higher pH (7.5-8.0).  Because MSW tends to be rich in paper, its compost often has a higher water holding capacity.  Communities that source-separate residential waste usually have lower contaminants and the compost has a higher plant nutrient content.

As composting grows and becomes a better understood science, more and more organic by-products will be used as feedstocks.  Although end users will have their own personal preferences regarding the type of product they utilize, it is important to stress that high-quality compost products have been produced from all of the feedstocks described.  We urge you to try different types of composts to better determine which product you prefer, based on performance, and which products may be best suited for a specific application.  It should be understood that the qualities of a particular compost are not indicative of the quality and characteristics of all products produced from that same feedstock.  For instance, if you purchase a yard trimmings compost that is not fully stabilized and robs available nitrogen from the soil, you should not assume that all yard trimmings-based composts would have the same affect.  As far as quality and usefulness of compost are concerned, it is typically more an issue of the completeness of processing than it is an issue of feedstock.

3.0  COMPOST CHARACTERISTICS/PARAMETERS

Described in this section are the compost characteristics or parameters that are important in compost quality evaluation.  These parameters represent the basic chemical, physical, and biological data needed to assure successful compost use and overall satisfaction.  The parameters are also necessary to assist you in determining which compost products possess the characteristics needed for your specific application or are of particular importance to you.  We should urge our compost suppliers to provide us with this data.

Since growing conditions and plant needs differ, we can benefit greatly from accurate characterization data pertaining to the compost products we use.  This data will allow us to use compost in a way that best meets our particular need or specific situation.  Specific characteristics of a compost dictate how and in which applications it can be used.  By obtaining accurate characterization data, we can obtain a compost that is appropriate for a specific application and use in a way that best meets our particular need.

The following table lists important compost parameters and their rationale for inclusion.  In the table, the term "necessary for system management" means the specific value associated with each parameter will allow end users to more effectively manage the "plant growing system."  For instance, specific crops grow best within a certain pH range.  Composts possess a specific pH and when used in specific quantities, can influence soil or media pH.  Therefore, by knowing the compost pH, users can better estimate its influence and more easily manage the system.  Soil or media testing can assist in this endeavor.

The compost parameters are characterized as quantified, qualified, and unspecified.  Quantified parameters are described using numerical values and qualified parameters are described using a qualifying statement, whereas unspecified parameters may be described either quantitatively or qualitatively once industry standard test methods are established.

Compost Parameters*

	Rationale for Inclusion:
pH	Necessary for system management, effect on pH adjustment.
Soluble Salt Concentration	Necessary for system management, potentially toxicity, effect on watering regime, effect on fertilizer application rates.
Nutrient Content (N-PET-K, Ca, Mg)	Necessary for system management, effect on fertilizer requirements.
Water Holding Capacity	Necessary for system management, effect on watering regime.
Bulk Density (lbs/yd3)	Product handling and transportation issues, estimation/conversion of application rates.
Moisture Content	Product handling and transportation issue.
Organic Matter Content	Necessary for system management, relevant in determining application rates.  Some use as a basis to measure cost effectiveness.
Particle Size	Necessary for system management, effect on porosity.  May determine usability in specific applications.
Trace Elements/Heavy Metals	Necessary for system management, effect on fertilizer requirements, potential toxicity.  Necessary to address and reduce public concern.
Stability	Necessary for system management, effect on nutrient availability (nitrogen), odor generation.
Growth Screening	Necessary for system management, effect on seed germination/plant growth.

* Recommended test methods for all proposed parameters may be found in the Composting Council's Recommended Test    Methods for the Examination of Compost and Composting.

Quantified Parameters

It is suggested that quantitative data (e.g. compost possesses a pH of 6.0-6.7), with respect to the eight qualified parameters, be routinely provided to compost users to help assure successful compost use and overall satisfaction.

pH:  pH is the numerical measure of the acidity (or alkalinity), or hydrogen ion concentration of a material.  The pH scale ranges from 0-14, with a pH of 7.0 indicating neutrality.  Compost typically possesses a pH between 5.0 and 8.5.  Specific plant species can flourish when grown within a specific pH range, and based on typical compost application rates, it is understood that the addition of compost can affect the pH of soil and growing media.  Therefore, to estimate the effect, which in turn will affect maintenance practices or system management, pH is a necessary parameter.  pH is adjusted through the use of such materials as lime, to increase alkalinity, and sulfur, to increase acidity.

Liming agents are sometimes used in the production of compost.  Although the addition of lime in the composting process may not dramatically effect the compost's pH, it will have a pronounced effect on calcium levels.  Therefore, pH adjustment of these composts is much more difficult due to the compost's higher buffering capacity, and for that reason may not be appropriate for specific applications.

Soluble Salts (salinity):  Soluble salts concentration is the concentration of soluble ions in a solution, which is measured by the ability of a medium to conduct an electric current.  Excess soluble salts can be phytotoxic (damaging) to plants, yet many nutrients are supplied to plants in salt form.  Some soluble salts, such as sodium and chloride, are more detrimental to plants than others.  Most plant species have a salinity tolerance rating and maximum tolerable quantities are known.  Soluble salts are measured in dS or mmhos/cm.  Compost may contribute to, or dilute, the cumulative soluble salts concentration of a growing medium or soil.  Manure compost tends to be higher in soluble salts, while soluble salt concentrations in biosolids and yard trimmings composts are more variable.  Reduction in soluble salts concentration can sometimes be achieved through heavy watering (leaching).  However, management practices for leaching will be dependent on the salinity of the irrigation water.  Most composts produced from municipal feedstocks possess a soluble salt concentration of 10 dS (mmhos/cm) or below.

Nutrient Content:  Nitrogen (N), phosphorous (P), and potassium (K) are the three nutrients used by plants in the greatest quantities (macronutrients), and are the nutrients most often applied through commercial fertilizers.   These nutrients are measured and expressed on a dry weight basis as a percent (%).  The percent of plant available phosphorous and potassium are expressed as P₂O₅ and K₂O, respectively.  Nitrogen in compost is predominantly in the organic form and must be mineralized to available forms (NO₃ and NH₄) for use by plants.  Nitrate and ammonium levels in stable compost are generally low.  The total nitrogen content should be expressed and the amount of water soluble (NO₃ and NH₄) and insoluble nitrogen forms should be known.  The content of these nutrients, as well as magnesium and calcium, should be known to allow users to make correct decisions regarding supplemental nutrition and pH adjustment.  Calcium (Ca) and Magnesium (Mg) may be applied through fertilization application or pH adjustment (e.g. lime, gypsum).  Providing data relative to the content of other nutrients can also be helpful, and may be necessary for specific applications or crops.

Water Holding Capacity:  Water holding capacity is the ability of a compost to hold water.  Water holding capacity is measured as a percent of dry weight.  Water holding capacity measures the potential benefit of reducing the required frequency of irrigation, as well as gross water requirements for the crop.  The water holding capacity should be known to allow users to monitor, or estimate, the compost's effect on their watering regime.  Most composts produced from municipal feedstocks possess a water holding capacity of 75%-200% of their dry weight.

Bulk Density:  Bulk Density is the weight per unit volume of compost.  Bulk density is used to convert compost application rates from tonnage to cubic yards.  In a field application, cubic yards per acre would subsequently be extrapolated to express an application rate represented as a depth in inches (e.g., 1 inch application rate).  Bulk density is also used to determine the volume of compost that may be transported on a given vehicle.  Bulk density is typically measured in grams per cubic centimeter, then converted to pounds per cubic yard.  Most composts possess a bulk density of 700-1,200 pounds per cubic yard; most would consider 800-1,000 pounds per cubic yard as preferred.

Moisture Content:  Moisture content is the measure of the amount of water in a compost product, expressed as a percent of total solids.  The moisture content of compost affects its bulk density and, therefore, will affect transportation costs.  Moisture content is also relevant because it affects product handling.  Compost that is dry (35% moisture or below) can be dusty and irritating to work with, while compost that is wet can become heavy and clumpy, making its application more difficult and delivery more expensive.  Most composts possess a moisture content of 30%-60%, while 40%-50% is preferred for product handling.

Organic Matter Content:  Organic matter content is the measure of carbon-based materials in a compost.  Organic matter content is typically expressed as a percent of dry weight.  Being aware of a product's organic matter content may be necessary for determining compost application rates on specific applications, such as turf establishment.  In this application, standard agricultural soil tests may be used to determine the recommended application rate of compost.  However, these application rates are specified as the quantity of organic matter needed per acre.  Therefore, the organic matter content of compost must be known to convert the application rate to a usable form.  Most composts possess an organic matter content of 30%-70%, with 50%-60% being preferred.

Particle Size:  The specificity in which compost particle size is measured should be based on the product's intended use or other customer requirements.  For most applications, merely specifying the product's maximum particle size or the screen size through which the compost passes is sufficient.  However, for specific applications, such as a component of potting media, a full particle size distribution may be required.  A compost's particle size distribution will effect the porosity of the media to which it is added.  Porosity is related to the ability of a potting mix to resist water logging, and low media oxygen levels.  Particle size distribution measures the amount of compost meeting a specific size.  Particle size distribution figures are expressed as the percent of material retained per sieve size.  A compost product's particle size may also determine its usability in specific applications.  For example, a yard trimmings compost screened through a 1/4-inch screen would probably not be appropriate to use as a mulch, whereas the same product screened through a 1-inch screen could be acceptable.

Typical Characteristics of Municipal Feedstock-Based* Composts

Parameter	Typical Range	Preferred Range for Various Applications under Average Field Conditions
PH	5.0 - 8.5	6.0 - 7.5
Soluble Salts	1 - 10 dS (mmhos/cm)	5 dS (mmhos/cm) or below
Nutrient Content (dry weight basis)	N 0.5 - 2.5% P 0.2 - 2.0% K 0.3 - 1.5%	N 1% or above P 1% or above
Water Holding Capacity (dry weight basis)	75 - 200%	100% or above
Bulk Density	700 - 1,200 lbs/yd3	800 - 1,000 lbs/yd3
Moisture Content	30 - 60%	40 - 50 %
Organic Matter Content	30 - 70%	50 - 60%
Particle Size	--	Pass through 1" screen or smaller
Trace Elements/Heavy Metals	--	Meet US EPA Part 503 Regulations
Growth Screening	--	Must pass seed germination, plant growth assays
Stability	--	Stable to highly stable

* Municipal feedstock-based composts are primarily derived from yard trimmings, biosolids, municipal solid waste, or food by-products, or a combination of one or more of these feedstocks.

Qualified Parameters

It is suggested that qualitative data, with respect to trace elements/heavy metals, be routinely provided to compost users, where appropriate, based on feedstock.

Initially, it is suggested that only qualitative data be provided to customers pertaining to trace element/heavy metals, as well as other regulated contaminants.  This approach is suggested because providing an all-inclusive chemical analysis to most end users is confusing, impractical, and would not be necessary in most situations.  Instead, a quality assurance statement could be offered in its place, for example, "our product meets the Federal EPA's definition for an exceptional quality product" or "our product is approved for unlimited distribution and, therefore, can be used on...".  It is further suggested that qualitative data describing trace element concentrations be made available upon users request.  This data may be necessary to assist specific users adjust their fertilizer programs to avoid phytotoxicity.

Trace Elements/Heavy Metals:  Heavy metals, are so named for their location on the Periodic Table of the Elements.  Heavy metals are trace elements whose concentration is regulated due to the potential for toxicity to humans, animals, or plants.  The quantity of these elements are measured on a dry weight basis and expressed in parts per million (ppm) or milligrams per kilogram (mg/kg).  Regulations governing the heavy metal content of composts derived from specific feedstocks have been promulgated on both the state and federal levels.  Trace elements, also referred to as heavy metals, are arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc.  The mere presence of these elements does not mean that the product is unsafe.  Rather, some of these elements are essential in the diets of plants, animals, and humans and many are included in common vitamin supplements.  Therefore, measuring the concentration of these elements, as well as other plant nutrients, will provide valuable management data relevant to the nutrient requirements of plants, and subsequent fertilizer application rates.  Certain heavy metals and trace elements are known to cause phytotoxic effects in plants, and some plant species are more sensitive than others.  These elements are boron, manganese, molybdenum, nickel, and selenium.  Although detrimental quantities of these elements are not typically found in compost, some can accumulate in the root zone over time.  To avoid potential plant damage, these elements should be monitored.  Potential damage is unlikely, however, since minimal amounts of trace elements are actually available to plants because they are tightly bound within the compost's organic matter.

In many ways, the concern surrounding the use of waste derived composts has been unwarranted, especially in recent years, since great effort has been placed in the reduction of contaminants in the waste streams.  The United States Environmental Protection Agency, with assistance from the United States Department of Agriculture, has studied this issue extensively using a full scale risk assessment and has developed a series of regulatory limits.  This risk assessment data is the basis for federal and many state regulations, and has helped assure the safety of the products being produced.

Unspecified Parameters

Unspecified parameters are compost parameters not classified as quantitative or qualitative because of a current lack of industry consensus regarding definitions, test methodologies, or correlation of data.  Yet these parameters are important and will be included as quantitative or qualitative parameters in the future.  Producers should measure these parameters using one or more test methodologies.

Growth Screening:  The growth screening test is an indicator of the absence or presence of phytotoxic substances, including volatile fatty acids, alcohol, soluble salts, heavy metals, or ammonia.  Many scientists use the term "maturity" specifically to relate to the absence or presence of volatile fatty acids.  Any of these substances may cause delayed seed germination, seed or seedling damage, plant damage, or death.  The growth screening test is not intended to identify the growth inhibiting compounds, but rather a general measure of acceptability.  Growth screening tests include germination, root elongation, and pot tests.  It is important to note that compost passing initial growth screening tests may fail a similar test later if stored improperly.  This is because specific growth inhibitors, such as volatile fatty acids and alcohol, may form in compost stored under anaerobic conditions.  Therefore, we should ask vendors how their compost is stored in order to avoid buying compost that has gone anaerobic.

Stability:  Stability is the level of biological activity in a moist, warm, and aerated compost pile.  Unstable compost consumes nitrogen and oxygen in significant quantities to support biological activity and generates heat, CO₂, and water vapor.  Stable compost consumes little nitrogen and oxygen and generates little CO₂ or heat.  Unstable, active compost demands nitrogen when applied to soil and growing media.  This can cause nitrogen deficiency and be detrimental to plant growth, even causing death to plants in some cases.  If stored improperly and left unaerated, unstable compost can become anaerobic and give rise to nuisance odors.

Until industry standards are developed, it is important that growth screening (including maturity) and stability tests be performed and used for process control and to qualify these parameters.  There is a great need to standardize test methods for maturity and stability, and to develop industry standard definitions for the terms.  Only then can we develop a full and measurable understanding of their effects on specific crops and in specific situations.

Other

It should be noted that this list of important compost parameters was developed to represent a wide variety of compost applications and composts produced from various feedstocks.  It is difficult to include each parameter of specific importance to every user, or relevant to composts produced from every feedstock.  Other compost characterization data may need to be provided for certain composts or for specific uses.  For example, porosity and weed seed viability may be important to nurserymen, while flowability, odor presence, ash content, or calcium carbonate equivalence may be important to landscapers and turf managers.  Also, where quantifying the concentration of man-made materials, such as glass, plastic, and metal, may be appropriate for MSW or yard trimmings compost, it may not be appropriate for biosolids or food by-product compost.  The presence of man-made materials may be an issue of worker safety and also a significant aesthetic issue that can affect the product's acceptability.  Aside from these other issues, the compost must also be properly composted to assure it has been sanitized, thus destroying any potentially harmful organisms.

4.0  COMPOST SELECTION

Compost produced from different feedstocks and with different levels of refinement may have different uses.  For example, compost produced from municipal solid waste will generally possess a greater water holding capacity than other composts  because the feedstock from which it is produced typically contains paper and paper products.  Therefore, this compost may be more suitable to use in areas where drought conditions exist (e.g., sandy soils) or low maintenance occurs (e.g., roadsides), or perhaps in erosion control.  Understanding that no two composts or applications are exactly the same will help you select a compost that best meets your specific requirements.  At the same time, one product may be versatile enough to use for a number of different applications.  In selecting a compost, it is important that you purchase from firms who test regularly and supply data to their customers.  The section entitled "Compost Characteristics/Parameters" provides a discussion of the compost characterization data we should be provided to help us use compost properly.  Aside from working with a company that manufactures a compost which meets your requirements and provides characterization data, you must be assured that they are capable of producing a consistent product.  Only the production and use of a consistent product can assure uniform results.  Even a compost product that is mediocre in quality, but is consistent in nature, can be used successfully as long as all parties understand its attributes and limitations.

As more compost is produced and marketed, users will have the task of evaluating suppliers.  Increased competition for your business should improve the quality and variety of available compost, stabilize prices, and improve customer satisfaction.

The Compost Supplier

It is critical to find a reputable supplier.  A supplier should have a history of providing good customer service, reliability, and a consistent compost.  A good supplier is always open to suggestions and will work to satisfy your particular needs.  Bear in mind that there is a cost involved in responding to customer needs and addressing quality-related issues.  Buying an inferior compost for a superior price is no deal.  If a supplier can provide you with technical assistance and service your needs, don't be afraid to pay for it.

Whether your compost supplier is a facility or a broker, they must be able to provide compost when needed.  This requirement is accentuated due to the seasonality of the green industry.  To assure product availability, it is helpful to know the production cycles and storage capacity of your supplier.  Other issues to consider include how the compost will be delivered, site hours, and whether the vendor can arrange for trucking and payment terms. 

Remember, every compost is different, every supplier is different, and so is every customer.  Seek out the ones that best suits your company's needs.

Important Attributes of a Compost Supplier

·        Produce compost possessing attributes/characteristics that meet end user or application requirements

·        Supplies/Produces a consistent product

·        Has implemented an on-going quality assurance or testing program

·        Can supply current compost characterization data (quantifying and qualifying their product's attributes)

·        Provides good overall customer service, employs a "service minded" staff

·        Can assure prompt and reliable delivery (size of truck and mode of unloading are also important)

·        Possesses adequate storage to ensure availability

·        Can provide technical assistance regarding end use

5.0 COMPARING COMPOST TO OTHER HORTICULTURAL/AGRICULTURAL PRODUCTS

Comparing compost to other horticultural/agricultural products is not an easy task.  The variability of the particular compost and the need to compare effectiveness in a specific application makes comparisons difficult.  Within this section is a discussion of various horticultural and agricultural  products that are used in conjunction with or instead of compost.  This section is included for reference purposes only and as a means to compare the general characteristics of compost to these materials.  Following are descriptions of these other horticultural/agricultural products.

Peat Moss is derived from Sphagnum that grows in bogs and becomes covered with water when it dies.  Because of the cold wet climate in which it grows, peat moss accumulates to great depths undergoing partial anaerobic decomposition.  Over the years, peat moss has changed both physically and chemically due to harvesting methods and location.  Coarse chunky peat with a pH above 5.0 is seldom available.  In its place is a finer material that possesses a pH between 3.3-3.5.  This finer peat moss shrinks rapidly and requires twice, and sometimes three times more, limestone to neutralize its acid concentration than in previous years.  Although peat moss initially starts with a high cation exchange capacity, it decreases with time, thus reducing its ability to hold nutrients as the aging process continues.

Sedge Peat or Native Peat generally consists mostly of sedges and grasses that grow in bogs.  When these grasses and sedges die, their tops sink into the water and undergo partial anaerobic decomposition.  Since these plants are high in cellulose and contain little lignin, they decompose more rapidly than peat moss and contain few fibers.  Although sedge peat and native peat can be used as a substitute for peat moss, they are generally not as satisfactory in certain nursery applications.  Also, they are highly variable from bog to bog and can be equally as acidic as peat moss.  The cation exchange capacity of sedge peat and native peat is similar to peat moss.

Softwood Bark has become a major source of organic matter for the ornamental horticultural industry.  Products such as pine, fir, hemlock, redwood, and cypress barks are used throughout specific regions of North America.  Because they are low in cellulose and high in lignins, they can be used either fresh or composted and do not decompose rapidly.  Cypress and redwood sawdust is also low in cellulose and can be used in much the same way.  However, only coniferous barks with less than 10% cellulose can be used fresh.  Coniferous bark with 10% or more cellulose must be composted.  For optimum growth, when used as a soil amendment or growing media component, the bark products should be milled to particle sizes no larger than 1/2-inch diameter.  Unlike peat moss, sedge peat, or native peat, the cation exchange capacity of bark improves with age.  However, not all barks are the same and their availability is diminishing in certain regions. The landscaping industry not only uses ground coniferous bark as a soil amendment but coarser materials are popular as decorative mulches.

Hardwood Bark, Sawdust, Shavings, or Wood Chips should never be used in blending potting media unless they have been thoroughly composted.  These materials are high in cellulose and low in lignins; therefore, they shrink rapidly and will rob plants of nitrogen.  The competition for nitrogen may not be effectively offset by supplying additional nitrogen in a fertilizer program.  It is important to note that the use of these materials in field applications should be limited to areas where planting will not occur for several months.  Using a fine-textured and well-aged or composted hardwood bark will minimize negative effects.

Topsoil is defined as "the surface or upper part of the soil profile."  Individuals who use topsoil often define it as a naturally produced medium consisting of sand, silt, clay, organic matter, trace amounts of nutrients, and other inerts capable of supporting plant growth.  However, in many parts of the Country, even in agricultural areas known for their productive soils, many of the soils purchased as topsoil and used for horticultural applications are not true topsoils.  Many of the materials purchased and used as topsoil are mineral soils obtained from below the true topsoil layer.  These subsoils are often devoid of organic matter and essential plant nutrients and do not possess the physical structure required for optimum plant growth.  These materials are typically processed to remove debris before marketing.  In some areas, sand and muck-type materials are sold as topsoils.  Neither of these materials possess properties essential for optimum plant growth.  Most topsoils that can be purchased today contain less than 2% organic matter.

Manures from a variety of livestock have been used as a source of nutrients and organic matter on agricultural soils for centuries.  Typically these materials have been applied in a fresh form, but are currently available for agricultural and horticultural usage in aged, dehydrated, or stabilized form.  Common manure feedstocks include beef and dairy cattle, chicken, turkey, and horse manures.  Raw manures are typically more odorous than composted manures, and may still contain viable pathogens and weed seeds.  When raw manures are applied, it is suggested that planting be delayed two-to-four weeks after application and incorporation to allow for stabilization.  Since raw manure has not been stabilized, the nitrogen is often readily available and subject to leaching.  Its organic matter is also subject to more rapid degradation. Composted manures will contain a more stable form of nitrogen and a lower content of organic matter than will raw manures.

[Source:  Adapted from Peat Moss and Peat Substitute, Dr. Francis Gouin, University of Maryland Bulletin]

General Comparison of Compost to Other Horticultural/Agricultural Products*