By Calvin Chong, University of Guelph, Department of Plant Agriculture - Vineland Horticultural Research Institute of Ontario, Vineland

This is a summary of Calvin Chong's presentation at the 2001 Landscape Ontario Congress.

Getting rid of garbage and waste is one of society's biggest challenges in the 21st century. Recent research and technological developments indicate that much of this waste can be re-used and developed into soil amendments for field and landscape plantings and potting mixtures for production of nursery and other horticultural crops.

     Additionally, some Ontario farms are now being "audited" for excess nutrients in run-off that may pollute the ground water. New state-of-the-art technologies will allow the nursery industry to recycle 100 per cent of all run-off water while using up to 80 per cent less fertilizers.

Farm, industrial and consumer wastes
During the past 16 years, I, like many researchers all over the world, have been investigating and evaluating various types of raw or composted farm, industrial and consumer waste by-products for use as amendments in field soils and potting mixes, and more recently in rooting mixes, for production of woody nursery plants. These uses (a) offer alternative ways for our society to dispose of or re-use organic by-products and thus conserve landfill space, and (b) place our green industry at the top of the "environmentally-friendly chart" by being proactive in dealing with the complex waste problem.

1. Spent mushroom compost
   For a long time homeowners have been using spent mushroom compost to amend and "enrich" their garden soils. It is a good source of organic matter (45 per cent) and rich in certain nutrients such as potassium and calcium.
   
        In the early 1980s, researchers used spent mushroom compost as a soil or potting mix supplement to grow a diversity of crops including fruit, vegetable and field crops, and potted foliage and greenhouse flower crops. Prior to this, researchers expressed pessimism and concern for the use of spent compost in container culture, primarily because of its high salt content and its potential for "burning" plants.
   
        In early trials at Vineland, we were surprised to observe growth of container grown nursery stock in #2 (6-L) containers increasing in proportion with the amount of spent compost in the substrate. In fact, the results - substantiated also in later trials - showed that the best growth often occurred in 100 per cent mushroom substrate medium, or in substrates with a high proportion of the compost. While spent mushroom compost has physical properties, such as aeration and water-holding capacities, comparable to or better than those of bark, the pH (8.0-8.2) and concentrations of soluble salts (4.9-8.3 dS/m, as measured in 1:2 by volume substrate: water extracts) exceed recommended values (pH, 5.5-7.0; salts, 1.0 dS/m).
   
        The key to our results was that, with normal irrigation practices, the salts leach quickly from the small nursery containers, declining to values that were benign to plants within days after potting.
   
        While growers often report successful use of spent mushroom compost under both container and field growing conditions, some also indicate various degrees of deleterious effect due to the salts. Thus, when using spent compost, we recommend that (a) the salt level in the mix be monitored, particularly during the first several to 14 days after potting when hazard level is highest; (b) the mix never be allowed to dry out since this increases the hazard level; (c) no more than 50 per cent of the mix should be spent compost; and (d) use only with smaller containers since salts leach slowly from large containers.
   
   
2. Paper mill wastes
   In the U.S., research on use of paper mill wastes and sludges began in the 1950s in marginal land reclamation, forestry, and agriculture. In Canada, paper mills in the Niagara area first began to distribute and incorporate this by-product in farm soils and rehabilitation sites in the early 1980s. In the 1990s, other paper mills introduced this practice to other regions of Ontario and Canada.
   
        Prior to its use in Ontario agriculture, paper sludge was landfilled until tipping fees of $90-95 per tonne made this practice uneconomical, or landfilling became prohibitive. Alternative uses were considered such as: energy source in incinerators; animal feed supplement because of its high cellulose content; manufacture of flower pots, skeet targets, and building blocks; and restoration of gravel pits, building and industrial sites.
   
        Our early trials at Vineland indicate that raw paper mill sludge mixed with soil, bark or other ingredients can be used effectively for container growing. As a rule, we recommend no more than one-third of the mix as sludge. However, any amount of a good composted paper mill sludge can be used. Plant growth was little affected by sludge-derived compost at different stages of maturity (immature or aged).
   
        It is a common misconception that paper mill sludge is laden with heavy metals and toxic organic chemicals such as dioxins and PCBs. The mineral composition of Ontario paper sludges is generally comparable to that of cattle manure, and contains very low quantities of heavy metals and organic chemicals, or low enough to meet thresholds set by the Ontario Ministry of the Environment. At the recommended rate of 30 wet tonnes/ha - a rate similarly recommended for cattle manure - paper mill sludge can be surface-applied to the same field annually as long as (a) sufficient nitrogen is present in the sludge (about 1.2 per cent dry weight), and (b) the field is adequately fertilized (about 100 kg of nitrogen/ha). In our field trials, crops such as corn, grapes and other fruits were successfully grown this way.
   
        The high organic matter content in paper sludge makes it suited for improving soil properties. According to one Niagara nursery, a long-time user of the by-product to grow landscape trees and shrubs on very heavy soils, "We couldn't farm without it. Tile drainage has been disappointing." The waste is distributed over the field and ploughed under several times. The fields are planted for one or two years to a rye cover crop, which is worked into the soil. Nursery trees and shrubs are then planted and grown into the amended field soil which has a consistency similar to that attained after adding peat moss.
   
        Since 1993, my research program has been involved in a long-term project initiated by an area mill to rehabilitate a 1,400-ha strip of wasteland about 10 km long, located along the Welland Canal. Heavy clay backfill from this realigned portion of the canal was incorporated with very high rates of sludge (600-800 tonnes/ha) and planted over the years with various types of seedling nursery and forest tree. At one experimental site, poplars and silver maple trees now exceed four metres in height.
   
   
        In good agricultural Vineland soil incorporated with paper mill sludge, field-grown nursery trees have thrived equally well, regardless of rates incorporated up to 250 tonnes/ha. More recently, we demonstrated an alternative use of the sludge as rooting medium amendment in summer propagation.
   
        Notwithstanding these successes, the results on use of paper mill sludge in Ontario agriculture has been variable and sometimes detrimental to crops, due in part to insufficient agronomic and research knowledge about its use. Different sources of sludge, or even batches of the same sludge, vary in chemical and physical characteristics. Agronomic responses are not always similar at different locations or in different years, or when another sludge other than the one tested is used.
   
   
3. Waxed corrugated cardboard
   Packaging material, including waxed corrugated cardboard, accounts for over 20 per cent of landfill wastes. Unlike other types of cardboard, waxed corrugated cardboard typically is not recycled in paper making because of interference by the wax. Chemical analysis indicates that waxed corrugated cardboard is low or lacking in nutrients and, in this respect, desirable as an amendment for container production.
   
        Our first study in the 1990s showed that certain substrates consisting of 25 or 50 per cent by volume of uncomposted waxed corrugated cardboard mixed with spent mushroom compost and/or sawdust supported growth of container-grown nursery species equal to a bark control medium or a commercial nursery mix. We later formulated and monitored composts containing 12 different combinations of spent mushroom compost, wood wastes, corrugated cardboard, and various nitrogen-rich wastes during two separate composting periods. In growth trials, the composts suppressed seed germination and growth of green­house-grown bedding plants, but two of three container-grown nursery crops grew better in them than in control substrates. This research demonstrated that cardboard packaging waste can be successfully composted and reused to grow container nursery plants.
   
   
4. Municipal waste composts
   In Canada, as in other countries across the world, composting is considered a key to the management and reduction of municipal wastes. Composts have been used in farms and gardens since ancient times. Studies in the early 1940s showed that municipal waste compost amended to soils almost always increased yields of field crops, but to a lesser extent than animal manures. Researchers all over the world have since confirmed these results and other benefits for horticultural crops, including container and field-grown nursery crops and turf (see sidebar). In view of legislation such as that in Ontario requiring a 50 per cent reduction in waste by year 2000 (a goal not fully realized), and the composting of all garden and yard waste by all municipalities with 50,000 in population, most of the composts produced in the future will be from municipalities.
   
        An early trial at Vineland in the mid-1980s, showed that growth of various container nursery species increased progressively with increasing amounts of composted municipal residential waste in the media up to 100 per cent by volume. Unfortunately, small (unspecified) amounts of plastic and synthetic materials made the product somewhat visually unattractive and, in recent years, the presence of contaminants such as plastic and glass residues has severely curtailed the use of municipal waste composts in the U.S.
   
        Since 1995, we have routinely and successfully used waste compost from Metro Toronto Solid Waste Division, Keele Valley Landfill, and more recently waste compost from the City of Guelph, in our experimental container mixes. Nursery plants typically grow well in these substrates mixed with paper mill waste, bark and/or other ingredients. Other trials also indicate that municipal waste composts make good rooting substrates, as long as the substrates are leached to reduce levels of salt to 0.2dS/m, the threshold value considered desirable for rooting nursery cuttings.
   
        Excess salts, high pH, and variability of com­position are major deterrents against use of municipal composts in nursery propagation and plant culture.
   
   
5. Other waste by-products
   We have also investigated other types of waste by-products in container nursery cropping systems including: softwood tree barks; apple pomace; industrial waste by-products from the manufacturing of polyvinyl chloride resins and compounds; turkey litter compost; organic fertilizers manufactured from animal wastes and meat by-products; wood chips from pallets and furniture and demolition wastes; food wastes; and various animal manures.

Run-off and irrigation wastewater:
Ground water pollution caused by run-off from farms and nurseries is becoming a major environmental concern in the new millennium. Legislation controlling run-off exists in Europe and certain parts of the U.S., but not yet in Canada.

     According to Extension Specialist, Dr. James Green, "Often less than 10 per cent of the water (typically applied overhead) and fertilizer in container plant production is taken up by the plant. Waste discharge can be eliminated and 90 per cent less water and fertilizer applied through targeted and protected applications while achieving equal or greater plant growth." In 1998, the Landscape Ontario membership at large indicated that water conservation and irrigation/fertilizer run-off were two of four major research priorities of this industry. Although a few commercial nurseries have wastewater and nutrient recirculating systems in place, most would consider a zero-run-off strategy as being too costly and/or impractical.

1. State-of-the-art technology
   In 1992, we initiated research on a "closed-loop, zero run-off" subirrigated water and nutrient recycling system for container nursery production - the first of its kind for nurseries in Canada. This system effectively eliminated run-off, but was manually operated. Without the proper equipment, recirculating nutrients is labour-intensive, and achieving a good nutritional balance may be difficult.
   
        A new computer-controlled, multiple-fertilizer injector that effectively recirculates nutrients may be the answer. In 1996, we began testing this state-of-the-art, Canadian patented technology. The equipment, specifically designed for research, cost $25,000 and is smaller than a typical commercial model, which may cost twice as much.
   
        After fertigation, the leachate run-off from the containers is collected in a reservoir. The machine takes some of the leachate; recharges it with fresh nutrients from nine separate fertilizer stock solutions; mixes it with fresh water and pumps it back to the crop.
   
        In an early growth trial, 'Darts Gold' ninebark grew better with recirculated than with non-recirculated nutrients of similar composition, or with non-recirculated liquid 20-8-20, or with a slow-release fertilizer.
   
        Nutrient recirculation eliminated leachates from entering the environment and resulted in a 57 per cent to 77 per cent reduction in major nutrients compared with non-recirculation. With the computerized fertilizer injector, container growers can take advantage of the benefits of water-soluble fertilizers without the environmental risks - provided there's an efficient recycling system with impervious collection beds, channels and irrigation storage.
   
        Growers can also program the machine to apply customized nutrient formulas for each taxa. To properly use this state-of-the-art computerized fertilizer injector, however, growers need to consider the nutrient needs of each taxa, but there is little information in this regard. Such needs will require future investigation.
   
   
2. Compost wastewater
   Our research program has been examining the recycling of wastewater from other perspectives. In a three-year experiment, we successfully used compost leachate collected in a pond at a commercial composting operation to irrigate a variety of ornamental trees and grasses, planted on adjacent land rehabilitated with waste compost. In both the second and third year, the leachate significantly increased growth of the plants.
   
        In hydroponic investigations, we also obtained surprisingly good to excellent growth of tomato and marigold seedlings in compost wastewater fortified with nitrogen and phosphorous, two nutrients that were present in limiting quantities in the wastewater.

Discussion and conclusion
Our research demonstrates that we can effectively recycle farm, industrial and consumer wastes in nursery and horticultural growing systems, and provides valuable information as basis for future advances in this area.

     While the results are encouraging, there are important regulatory, environmental, health and public concerns that must be addressed before raw, processed or composted waste by-products can become more widely used in horticulture:

• There are concerns about the poor or inconsistent quality of composts and other wastes being sold or used in cropping systems. Results are sometimes disappointing.
• While very high rates of compost or raw waste may yield satisfactory or apparent beneficial results in the short-term, repeated high application rates over the long-term may pose environmental and related problems. The leaching of nutrients and heavy metals into the ground water may not be apparent until 20 years or more after application.
• The consumer's perception about food crops grown on waste will likely always be a delicate subject. Because of potential health risks, some states in the U.S. ban the use of any compost with food waste to be applied to land where food crops (root vegetables and vegetables normally eaten raw) are grown, or will be grown within 24 months.
• The "high-end" horticultural market - nursery, landscape, turf, and garden and greenhouse sectors - has the greatest potential for utilizing high quality composts and waste-derived potting mixes to their fullest extent. However, it is becoming clear that the size of this market is limited and unable or reluctant to pay the high costs (estimated up to $170 per tonne) for processing and making some of these composts.
• What to do with all of this waste-derived material is a challenge for the new millennium.

     As we become more and more urbanized, the importance of nursery and horticultural crops will increase, as also will the need for amendments in potting and growing substrates. Thus, the demand and utilization of composts and waste-derived amendments will be driven primarily by the high-end horticultural crop sectors. Apart from environmental benefits, a prominent greenhouse operation in Leamington estimates savings of between $6,000 and $8,000 per acre ($15,000 and $20,000 per hectare) in fertilizer costs because of nutrient recycling practices. The impact of our research program will also take on new importance in the millennium as both public concern and the negative impact of run-off on the environment, and especially if - and when - legislation in Ontario and other parts of Canada restricts nutrient and irrigation wastewater run-off, as in Holland and Europe.

Benefits of municipal compost

• Many farmers say that good compost is worth more than plain manure. When applied continuously over many years, one tonne of good compost is worth as much as 20 tonnes of manure.
• Over a nine-year period, municipal compost increased yield of field crops on average of 11.4 per cent over those supplied with chemical fertilizers.
• Municipal composts amended to soils may eliminate the need for chemical fertilizers, at least in the first year of cropping, 40 tons/acre (90 tonnes/ha) of municipal compost increased yield as much as 50 lbs (57 kg) of nitrogen.
• 150 tons/acre (330 tonnes/ha) of municipal compost applied over two years increased soil organic matter from 1.6 to 4.2 per cent.
• 2.5 per cent increase in organic matter improves soil water-holding capacity by 300 per cent.
• Many composts suppress plant diseases and may contain antibiotics and other beneficial substances.