Final Disposition – Session Chair: Chuck Franks

The following abstracts were prepared for the Symposium on Composting Mortalities and Slaughterhouse Residuals

Portland, Maine

May 24-25, 2005

BSE in Washington- Discovery, Response, and Disposal Issues

Primary Contact: Chuck Matthews (Washington State Department of Ecology, P.O. Box 47775, Olympia, WA, 98504-7775)

Kip Eagles (Washington State Department of Ecology, 15 West Yakima Avenue, Suite 200, Yakima, WA, 98902-3387)


On December 23, 2003, the U.S. Department of Agriculture (USDA) announced the first confirmed case of Bovine Spongiform Encephalopathy (BSE) in the United States. The USDA was responsible for tracking down related animals that might carry or be affected by the disease. Potentially adulterated meat and animal byproducts already in circulation also had to be traced. The discovery resulted in the destruction of a significant number of animals, rejection of U.S. beef and beef by-products by many trading partners from around the Pacific Rim and other regions, and concerns about the safety of rendered materials that may have been produced from the processing potentially contaminated animals. Many domestic consumers have also turned away from mainstream beef in favor of paying higher prices for meat from producers that have carved out a niche market of providing grain raised beef produced without growth hormones and antibiotics. There is debate as to whether this beef truly offers any real added protection against BSE specifically, but perception that this is the case by consumers appears to have solidified a place in the market for these producers.

Some countries continue to impose a total ban of U.S. beef and byproducts until all animals are tested for BSE prior to export. These bans continue to have major economic impact to the beef industry in the Pacific Northwest. The USDA and U.S. Food and Drug Administration (FDA) have imposed restrictions on what can be included in animal feed and on feed production facilities. Canada and the United States continue to wrangle over import restrictions of Canadian-born cattle and beef products into the U.S. Some estimate the economic impact on the Canadian beef industry of up to seven billion dollars. While federal officials from both countries debate whether to re-open the border to Canadian products, three additional animals have tested positive in Canada for BSE in the past year. In addition to the economic and political fallout, the announcement of a positive BSE test in the U.S. spawned a media feeding frenzy that fueled consumer distrust of the government agencies involved, accusations of a cover-up, and skepticism about the ability to guarantee the safety of U.S. beef in general. While disposal issues were responded to relatively quickly, the political and economic repercussions from the incident continues a year and a half later.

By the time the investigation was complete, about 650 animals had been destroyed and approximately 2000 tons of meat and bone meal (MBM) were identified as potentially adulterated and were prohibited into the marketplace. Responsibility for detailing disposal options for the animal carcasses and MBM fell on state officials from the Washington State Departments of Agriculture, Ecology, and Health. These efforts were conducted in cooperation with local jurisdictional health departments and landfill operators managing Subtitle D compliant

landfills in both Eastern and Western Washington. Similar efforts were made in Oregon in case the event expanded to such a scale that depopulation efforts widened into a substantial part of the Oregon herds or the needs for disposal overwhelmed capacity in Washington. After reviewing disposal options, a decision was made to landfill the carcasses and MBM. Because of concerns about the durability of prions, composting was quickly ruled out. Inadequate regional infrastructure existed to manage the materials through incineration in a timely manner. Due to the large volume of material, alkaline digestion was not a practical option at the time either. Once the decision was made to landfill suspect carcasses and MBM, state officials identified suitable landfills and issued standards and precautions that should be applied during burial.


Once the USDA concluded its investigation and identified animals and byproducts that would require isolation and disposal, state agencies were looked to for guidance on what state law allowed regarding disposal of carcasses and recalled MBM. Because of the potential regional nature of incident, state officials from both Washington and Oregon became involved in identifying suitable landfills in both states where the waste could be taken. There was a sentiment among some state officials that federal investigators could have been better served at the local level if federal official had communicated more openly about the scope of their investigation and the potential volume of material requiring disposal. State officials assumed the worst case in their initial efforts to identify landfills and get local health departments and landfill operators on board and prepared in the event their services became necessary. A list of eleven Subtitle D landfills on both sides of the Cascade Range was provided and ultimately pared down to five facilities in Washington and one in Oregon. State officials worked with operators to determine what volumes of waste could be managed at their respective facilities in order to be prepared for the worst case. One of the Washington facilities was dropped after determining it could not meet all the published guidelines issued by the Department of Ecology (Ecology). Eventually, questions about volumes were answered and all the material was disposed of at the Roosevelt Regional Landfill overlooking the Columbia River on the Washington side. This 1800 acre facility is located in Eastern Washington in a remote arid region of the state. The landfill sits atop a layer of clay and basalt. Depth to groundwater is at least 450 feet. Leachate produced is recirculated back into the landfill to promote the generation of methane which is collected and used to produce energy.

The guidelines published by Ecology were essentially for use by local jurisdictional health departments (JHD) and operators to ensure worker safety, thorough entombment of the material, and adequate control of leachate. The location of the animal trenches and MBM within the landfill was logged in the event the need to exhume the materials arises in the future. It should be noted that Washington State is one of a handful of states in the country where authority for solid waste facility permitting and oversight is delegated by statute to JHDs. Ultimately, it was the JHD that decided whether or not to allow burial of potentially infected animals and byproduct at a facility within their jurisdiction. Ecology’s published guidelines promoted the following:

  • Disposal should occur only at lined Subtitle D landfill facilities
  • The landfill should collect leachate in a closed system for recirculation
  • The placement cell should have at least 20 feet of waste in place.
  • Delivery of whole animals, offal, or recalled meat must be by appointment only. This allows preparation by landfill staff to immediately deal with disposal of the delivered waste. In the case of whole animals, it is more desirable to have them delivered to the landfill live and euthanized on site.
  • Whole animals must only be disposed one layer thick. They must be immediately
  • covered with at least three feet of regular garbage.
  • Offal shall be placed on a 12-inch layer of Department-approved absorbent material such as a dry pulp sludge or dry soil. In certain cases municipal solid waste may be able to be utilized as absorbent material. This absorbent material is in addition to the twenty feet of waste required to be in place. The offal shall be immediately covered with at least three feet of regular garbage.
  • Large quantities of recalled meat (typically shipped from central locations) shall be placed on in-place garbage and immediately covered with at least three feet of regular garbage.
  • The disposal area for any of these wastes shall be covered with a minimum of twelve inches of soil at the end of the operating day. Alternative Daily Cover (ADC) cannot be utilized to cover this material at the end of the operating day.

(Since the Washington event, a concern has emerged regarding the suitability of placement of animals suspected to be infected with a prion-related disease such as BSE, Scrapies, Chronic Wasting Disease, in landfills that discharge leachate to waste water treatment facilities or surface waters. At the request of the Environmental Protection Agency’s (EPA) Office of Water, the Office of Solid Waste revised its guidance in November of 2004 for landfill disposal of animals potentially affected with CWD. The revision promoted limiting landfill disposal to facilities that recirculate leachate rather than discharge to a treatment plant or directly to surface water under a NPDES permit.)

Early in the week of January 6th, animals were trucked approximately 150 mile north of Mabton to a secluded closed processing plant in Wilbur Washington. Depopulation efforts occurred largely in secret and were performed by lethal injection. Carcasses were loaded into truck to be hauled south about 200 miles back south to the landfill. The operator, who was on call for this event, received a call at about 3:00 a.m. informing him that the carcasses were in route. The time of the call put the operator in the difficult position of securing a crew to bury the animals because the facility is about an hour’s drive from any of the communities where most of the workers lived and the region had experienced a snow storm that evening. As soon as there was adequate light to work, burial commenced at under gray skies, a shroud of fog, and a blanket of snow. The facility was closed to other customers that day.

By the time investigation and disposal were complete…

  • A total of 449 animals were depopulated from the bull calf raising premises.
  • A total of 131 at-risk animals were depopulated from the index premises in Mabton, WA.
  • A total of 39 animals were depopulated from the facility in Mattawa, WA
  • A total of 15 animals were depopulated from the facility in Connell, WA.
  • A total of 20 animals were depopulated from a facility in Boardman, OR.

In addition to disposal of animal carcasses, approximately 2000 tons of recalled meat and byproducts were disposed of. Before these materials were allowed to be transported to Roosevelt Regional Landfill, Baker Commodities and Darling International were each required to submit a disposal plan and obtain approval from the FDA’s Center for Veterinary Medicine. These plans detailed the specific location of potentially adulterated products, quantities and types, transportation methods, contacts, and facility location.


  • The discovery of BSE in Washington set in motion a sequence of events that exposed the need to plan for such incidents before they happen. Much of this planning is already taking place in states throughout the country under Homeland Security and other mandates. Officials need to understand risks associated with any animal disease that may require urgent response containment and perhaps mass depopulation ahead of the emergence of an incident warranting emergency response. Questions about necessary safeguards to protect human health and the environment, personnel protection, biosecurity, etc. in an emergency event should be answered and documented to help responders assemble necessary equipment and take appropriate precautions. Numerous animal diseases of concern have been identified and characteristics identified by national and international organizations. An understanding of disease characteristics such as how the disease spreads, it’s potential to affect humans and nearby animal populations, whether quarantine is required, whether immediate destruction is necessary all are critical to good response planning should an outbreak occur. How should the risks be communicated to the public? Such planning will go a long way towards swift and efficient responses and may also prevent an overreaction to the incident.
  • It’s critical that agencies at all levels of government be prepared to work together in such a response. Planning noted above should clearly identify roles and responsibilities under specific circumstances. Communication between the federal investigators and state officials must be open, direct, and reliable. No less than seven state and federal agencies were directly involved with the response, in addition to numerous local agencies asked to assist in finding a solution to disposal issues. The need to communicate within agencies is as compelling as the need to communicate among agencies. Larger departments will frequently have many divisions within its agency that may have overlapping (and sometimes conflicting) responsibilities. Also, as with any emergency situation, elected officials at all levels of government will become involved out of concerns for constituents or simply to be seen as “on the job”.
  • Poor communications and turf issues among involved agencies provide the media with fodder to fuel speculation about what is “really going on”. The speculation erodes public trust that officials are being truthful about the scope of the problem and efficacy of the solution. The behavior of officials towards media can be critical. Officials become discredited when the message is delivered with arrogance and when conflicting stories emerge from seemingly credible people. The public, when dealing with such conflicts, is far more likely to believe a story from a citizen asserting they had direct involvement who claims “cover up” over agency personnel who appear to deliver what is perceived a “company line” to protect the interests of the affected business over public safety.
  • In retrospection, many state agency staff wonder if destroying the potentially infected cattle might have precluded an opportunity to study the development of the disease and advance the bank of knowledge about its transmission and symptoms in bovine animals among a typically bred population. Once isolated from commercial breeding and production, the animals posed very little risk to humans and to other animals. The focus of the response to the discovery of BSE was obviously on tracking down related animals and products as quickly as possible. However, once accomplished, there arguably was no real urgency to destroy them. Costs to maintain the herd and fears about possible impacts and future use of property hosting the herd would need to be considered, but the maintenance of the herd could provide deeper understanding of the disease.
  • Finally, there was a sense that federal agencies should have relied more on the knowledge of state officials when seeking a disposal solution. Due to the nature of the business, solid waste staff in government and solid waste facility operators all understands the difficulty of the delivery of messages in the situation faced by the federal investigators. It is in no way uncommon that special situations arise that put the solid waste system in a situation of managing some of the less savory cast-offs of American society. It is unlikely that the disposal option eventually selected would have been different than what was ultimately selected, but the efficiencies of getting there would definitely have been improved. State solid waste professionals, both regulators and operators, routinely work closely together to ensure safe facility operations. Relationships exist that without question, could have been utilized and eased at least a portion of the anxiety and uncertainty of the situation experienced by all involved.

Agronomic Utilization of Compost — Growing Plants and Protecting the Environment

Harold M. Keener

Dept. of Food, Agricultural, and Biological Engineering, The Ohio State University, Wooster, OH. 44691, <>


Many composts are marketed and priced based on their nutritive value, which is largely fixed (except for N) by the initial compost mix. This paper presents information on the chemical properties of composts generated from municipal and agricultural sources. In addition, it provides information on erosion control uses, plant responses to compost maturity, disease suppression from compost used in potting mixes, pathogen destruction and antibiotic breakdown during composting.

Chemical Properties of Composts During Utilization

During composting, the plant nutrients P, K, Ca, Mg, as well as heavy metals do not disappear appreciably from the system as the dry matter decomposes (unless leaching occurs). However, N is lost during composting via numerous pathways, with ammonia volatilization being the most common. Its loss is directly related to total N content of manure and by C/N ratio. Numerous studies have shown C/N ratios near 40 or above will minimize N loss (Michel et al., 2004). Also, if the compost mix starts with N < 1%, N is generally retained by the biomass as dry matter disappears from the mix such that N percentage in the compost increases. However, waste with high nitrogen content such as caged layer manure and biosolids generally have C: N ratios well below 40:1 for any reasonable level of amendment. To prevent N losses, unamended caged layer manure can be composted in an enclosed structure with high atmospheric NH3 to reduced N losses (Keener et al., 2002). A second approach is acid scrubbing and reintroducing the NH3 salt back into the finished compost. Still another approach has used alum (Eckinci, 2002) for controlling nitrogen loss, although it has been shown to reduce the solubility of P by >50 %.

Historically, mature compost has nutrient contents of approximately 2% N, 2% P and 1 % K (4.6% P2O5, 1.8% K2O). However, these values are greatly influenced by the starting compost mix, additives to mixes, and stage of stabilization. Also, reported nutrient values for compost are meaningful only if reliable samples have been taken. Discrepancies between initial mixes and final compost composition often arise with heterogeneous composts as noted by Keener et al. (2000) for compost made from blended materials. Since compost nutrient values can vary within the size ranges of the cured compost (Elwell, et al., 1994), screening can also be used to modify NPK levels in products. Table 1 is a summary of properties of compost from yard waste, biosolids, municipal solid waste (MSW) and livestock manures that have been studied along with paper mill sludge. These results illustrate how compost properties are related to initial properties of the compost mixes and length of composting time. It should be also noted composting may increase plant availability of macro and micronutrients, although biomass N is not as readily available as the NH3 form of N.

The US Composting Council (USCC, 2004) has developed detailed protocols for the composting industry to verify the physical, chemical, and biological condition of composting feedstocks, material in process and compost products at the point of sale. This protocol is called TMECC, Test Methods for the Examination of Composting and Compost.

Table 1. Chemical properties of compost made from yard waste, biosolids, MSW, animal manures, and paper mill sludge amended with yard waste, wood chips, sawdust or straw.

Description1,2 Initial C/N Timeday N% db C/N P% db K% db NH4-N(μg g-1) NO3-N(μg g-1)
Yard waste Michel et al., 1996
le/gr/br(4:1:1) 26.4 140 1.32+0.19 19.1 0.11+0.02 0.59+0.09 1.8+0.9 17+12
le/gr/br(4:2:1) 25.9 140 1.61+0.06 16.1 0.23+0.02 1.08+0.10 2.9+1.6 122+23
le/gr/br(4:3:1) 25.9 140 1.63+0.10 14.2 0.23+0.01 1.01+0.06 1.3+0.1 144+10
Biosolids Elwell et al., (1994)
bs/wc (< 0.375″) 14 21 4.26+0.09 2.17+0.05 0.77+0.02 5400+850 288+17
Bs/wc/l20 (< 0.375″) 12.4 21 3.60+0.02 1.44+0.04 0.71+0.01 3650+71 253+32
MSW Keener et al. (1992)
kw/yw (4% inerts) 16.7 53 1.85+0.14 8.6+0.6
msw/cm (19% inerts, <0.375″) 19.3 31 2.01+0.04 12.8
so/le 1:1 (9% inerts) 32 54 2.3 12 0.35 0.91
Swine manure Keener et al., 2001
sm/sd 20.6+2.6 106 2.14 16.9 2.20 1.80 3818 117.0
Dairy manure Wang et al., (2004),Michel et al. 2004
dm/sd 33.0+1.22 112 3.39+0.06 12.7+0.3 0.54+0.01 2.3+0.04 89.0+7.8 90.6+14.6
dm/st 25.1+0.85 105 4.24+0.54 8.5+1.01 0.84+0.02 4.77+0.15 116+90 128+99
Poultry manure Keener et al. (2002)
cm (unamended) 5.8+0.6 56.00 5.58+0.57 5.80 1.80+0.25 2.51+0.23 4850+1245 213+37.4
Chicken manure Elwell et al., (1996)
cm/yw 22 27 1.6+0.0 11.8+0.1
cm/fw/yw 20.7+6.1 27 1.55+0.07 11.2+0.1
Horse Manure Keener et al. (2004)
hm/cb 30,6+3.4 70 2.33+0.25 16.7+1.6 0.63 2.84 49+13 5.1+7.1
hm/cb 30,6+3.4 90 2.32 17.3 0.64 2.53 27 16.7
Paper mill Brodie et al., 1996
Ps/pl/wc (< 0.5 in.) 31.5 245 0.95 17.0 0.67 600 0.7

1 br=brush, bs=biosolids, cb=cardboard, cm=caged layer chicken manure, dm=dairy manure, fw=food waste, gr=grass, hm=horse manure, kw=kitchen waste, le=leaves, msw=municipal solid waste, pl=poultry broiler liter, ps=paper mill sludge, sd=sawdust, sm=swine manure, so=store organics, st=straw, wc=woodchips, yw=yard waste.

2 <0.375″ indicates finished compost was screened to less than this size before analysis.

Compost Maturity

Composts prepared from wood industry wastes frequently have high C: N ratios and while technically “stable” may still immobilize N during utilization9. On the other hand composts from sewage sludges release significant levels of N early during crop production while a more mature compost from separated cow manure maintains a sustained level of N release over a longer time period (Chen et. al., 1996). Results (Wang et al., 2004) on dairy manure composted with sawdust or straw showed that a 100 day composting/curing time gave good growth responses. A growth trial (Wilkinson et al., 2004) conducted to identify the effect of cardboard/horse manure compost age on growth of cucumber seedlings (fig. 1) indicated that if fertilized at 200ppm N to overcome nitrogen immobilization, composting time should exceed 70 days. Results also showed the maturity or age of the compost in this study did not significantly affect the percent germination of cucumber seeds. In general total time for composting and curing will generally exceed 100 days to achieve well-stabilized, mature compost for use in potting mixes. For land application or other purposes, the time requirements could be less (See later discussion).

Fig. 1. Plants from the 100 ppm N fertilized group on day 22 versus age of compost used in potting mix.

Allelopathy, described as chemical warfare between plants, needs to be considered in composting. Tree barks in particular may be sources of such chemicals that inhibit plant growth. Fortunately, allelopathic chemicals responsible for this effect in both softwood as well as hardwood barks are destroyed within a few weeks of composting of barks from most tree species (Still et al., 1976).

Compost Toxicity.

Organic acids in compost, especially the low molecular weight fatty acids, negatively impact emergence of seeds. In practice, producing compost in properly aerated systems so that anaerobic pockets are prevented during composting/ curing/ storage avoid toxicity caused by organic acids. For the case where acids exist in the cured compost, removing and allowing the compost to cure for 1-2 weeks in smaller aerobic windrows can eliminate the problem. Ammonium from immature low C/N materials (e.g. composted manure, food waste, sewage sludge) and soluble salts can also cause toxicity. Using mixtures with high C: N ratio alleviates these two problems. Table 2 provides guidelines on allowable soil soluble salt levels to avoid salt toxicity and fig. 2 shows how ammonium toxicity limits use of compost for growing plants.

Table 2. Allowable soil soluble salts (mMhos/cm) to minimize salt toxicity.

Description Saturated Media Extract 2 : 1 Dilution
Satisfactory if soil is high in organic matter but too low if soil is low in organic matter Below 2 0.15 to 0.50
Satisfactory range for established plants but upper range may be too high for some seedlings 3 to 4 0.50 to 1.80
Slightly higher than desirable 4 to 8 1.80 to 2.25

Figure 2. Growth studies using compost made from hog manure/sawdust for growing Deutizia "Gracillus". Compost is limited to 4% of mix due to ammonium toxicity (Keener et al., 2000).

Utilizing Compost

Land Application. Using composts for crop production requires attention to the source of compost and the timing, method and rate of application. Dalzell et al. (1987) recommended that mixtures of mineral fertilizers and composts should be such that at least 30% of the N is supplied by each source. However, composts made from biosolids often contain high concentrations of nitrate-N such that these composts require no mineral N additions (Chen et al., 1996). The timing of application versus when a crop is grown on the amended soil is important. Immature compost with a high C/N ratio should be applied several weeks ahead of planting to prevent immobilizing soil N and inhibiting crop growth. The method of application, i.e. surface applied or mixed into the soil, is controlled by whether N loss will be excessive from surface application and the tillage program for the crop production system. Lastly, rate of application is important. For crop production a minimum of about 2.5 Mg ha-1 (2.2 ton/acre) is required before benefits of compost application become evident. However, rates 10 times or more higher than the stated minimum rate can be equally effective if applications are not made annually but only every three or four years. If the compost contains heavy metals, application rates should not exceed the permissible levels based on the USEPA 503 regulations for biosolid compost (eg. Copper 67, Lead 13, Hg 0.76 lb/ac/yr.

Container Media. Utilizing compost in container media and soil blending is determined primarily by the compost effects on hydraulic conductivity, water retention and air capacity (Spencer and Benson, 1982). Compost addition should maintain air capacities above 25% as air capacity of a potting mix directly affects plant growth and has an impact on root rot severity. For example, observations in nurseries indicate that Phytophthora root rots do not occur in media that contain tree barks having air capacities > 25% and percolation rates > 2.5 cm/min. Since the ratio of compost to soil in land application is small, compost’s physical properties usually have only marginal effects on soil physical properties for land application.

Mulches and Top Dressings. Organic mulches and top dressings effect the soil’s ecology and plant health. They do this by controlling temperature swings, increasing water infiltration, reducing water evaporation, assisting in weed control, providing food for soil microbes, nutrients for the plants, etc. However, the effect they achieve depends on the materials particle size, available carbon, nitrogen and other nutrients.

Herms (2005) noted that ground wood pallets and composted yard waste mulches both increased soil organic matter and microbial biomass activity when used on rhododendron and river birch trees. However, the composted yard waste increased, while the ground wood decreased nutrient availability and plant growth. Only the yard waste compost suppressed root rot disease. Figure 3 shows organics in the landscape. Not all mulches have positive impacts and Hoitink (1998) noted dry composts and mulches cause problems for the user if nuisance fungi grow in them and produce spores that detach and stick to house siding.

Figure 3. (a) Wood mulch used as a surface covering. (b) 1" of finished compost being tilled into soil prior to sodding to help establish the sod faster. 1" compost = 134 cubic yards/acre.

Erosion Control, Filtering. Compost is being actively market for erosion control for use along roadways, riprap channels, stream bank stabilization and gabions. In addition it is being used for filter cells to control runoff, bioretention ponds and bioremediation projects. Tyler (2005) noted: Bill Stewart pioneered filter berms and erosion control using compost in 1993; Maine Waste Mgt. Agency tests compost against others in Kennebec County – 1994; Clyde Walton, Maine DOT one of first to spec. berms in DOT projects – 1996; and EPA cites innovative uses for compost for erosion control- 1997. Novel approaches, such as Filtrexx™ socks10 (Tyler, 2005), control soil loss, allow rapid establishment of cover vegetation, and avoids non-organic structures in the environment such as plastic filter fence.

Disease Suppression

Disease suppression using compost occurs by three mechanisms, general suppression, specific suppression and induced suppression. It has been found that general (Natural) suppression will occur in about 90% of mature composts. The diseases most frequently controlled are Phytophthora and Pythium root rots (fig. 4). The second area, i.e. specific disease suppression, occurs in about 20% of mature compost and Rhizoctonia root roots are often the disease one is attempting to control. The third area is induced systemic resistance. It occurs in about 2% of the compost naturally and confers the ability to control foliar diseases (fig. 5).

Producing disease suppressive compost. It is recognized that control of root rots with composts can be as effective as that obtained with fungicides (Hoitink et al., 1997). The ornamental plant industry now relies heavily on compost products for control of diseases caused by soil borne plant pathogens. However, composts must be of consistent quality to be used successfully for biological control of diseases of horticultural crops, particularly if used in container media.

Effects of chemical properties of composts on soil borne disease severity are important but often overlooked. Highly saline composts such as those prepared from dairy manure or hog manure (Keener et al., 2001) enhance Pythium and Phytophthora diseases unless they are applied months ahead of planting to allow for leaching. Compost prepared from municipal sewage sludge has a low carbon to nitrogen ratio. They release considerable amounts of ammonium nitrogen and enhance Fusarium wilt diseases (Quarles and Grossman, 1995).

9 Standards for compost stability generally have not yet been adopted but an oxygen uptake rate less than 0.1 and 1.0 mg hr-1 gvs-1 of compost volatile solids (vs.) have been proposed. Compost maturity has many meanings and is usually assessed through the potential for plant growth (Keener et al, 2000).

10 Use of product name or trademark does not mean endorsement by The Ohio State University.

More to come.