Mixtures of coal ash and compost as substrates for highbush blueberry

Bottom ash from a coal-fired power plant and two composts were tested as components of soil-free media and as soil amendments for growing highbush blueberry (Vaccinium corymbosum L.). Combinations of ash and compost were compared to Berryland sand, and Manor clay loam, and compost amended Manor clay loam. The pH of all treatment media was adjusted to 4.5 with sulfur at the beginning of the experiment. In 1997, plants of ‘Bluecrop’ and ‘Sierra’ were planted in 15-dm3 pots containing the pH-adjusted treatment media. The first substantial crop was harvested in 1999. At the end of the 1999 season, one half of the plants were destructively harvested for growth analysis. The remaining plants were cropped again in 2000. Yield and fruit size data were collected in both seasons, and leaf and fruit samples were collected in 1999 for elemental analysis . The presence of coal ash or composted biosolids in the media had no detrimental effect on leaf or fruit elemental content. Total growth and yield of both cultivars was reduced in clay loam soil compared to Berryland sand, whereas growth and yield of plants in coal ash–compost was similar to or exceeded that of plants in Berryland sand. currently being under-used (Korcak, 1993). Bottom ash has a particle size ranging from 0.1 to 10 mm, and may contain usable levels of micronutrients. However, these materials may also have a basic pH and contain phytotoxic levels of some elements, or have appreciable levels of elements considered environmental contaminants. Elemental content of these products depends on coal source, and whether or not the coal was cleaned before combustion (Korcak, 1993). Bottom ash was used in our studies as a substitute for sand. A wide range of materials are now being composted by commercial facilities. We selected two commercial composts to represent different classes of materials. One was a sewage sludge or biosolids compost, and the other was primarily a leaf compost from a yard waste recycling program. We conducted a multiyear study to evaluate bottom ash and compost as components of soil-free media for highbush blueberry production. Comparison treatments included a typical blueberry soil, and an upland clay loam soil either alone or compost amended. Materials and Methods MEDIA TREATMENTS. Bottom ash was obtained from the PEPCO Chalk Point power plant in Prince Georges County, Md. A biosolids compost was obtained from a commercial composting facility at the Baltimore, Md., waste water treatment facility. A commercial leaf compost (Leafgro) was obtained from a yard-waste recycling program in Montgomery County, Md., and acid peatmoss was obtained from a commercial source. These components were then combined in the proportions listed in Table 1, to give six experimental media treatments. Controls included Berryland sand (Typic Haplaquad, Coastal Plain soil) obtained from the Philip E. Marucci Center for Blueberry and Cranberry Research and Extension, Chatsworth, N.J., and Manor clay loam soil (Typic Dystrocrept, Piedmont soil) collected from the Henry A. Wallace Beltsville Agricultural Research Center, Md. Properties of these soils have been previously reported (Korcak, 1986). Treatments of Manor clay loam with compost amendment at 25% and 50% of soil volume were also included. The initial pH of Berryland sand was 4.0 and the pH of the remaining media treatments were lowered with the addition of powdered sulfur. Samples of the ash–compost mixes and the soil– compost mixes were titrated with nitric acid, and sulfur requirements were calculated for a target pH of 4.5 (Brown and Chaney, Received for publication 29 Nov. 2001. Accepted for publication 24 Apr. 2002. The authors gratefully acknowledge the technical support of Ingrid Fordham and Philip Edmonds. We also thank Ron Korcak for helpful input through all stages of this project. We thank Rufus Chaney for reviewing the data presented here, and Mark Ehlenfeldt for helpful review of the manuscript. E-mail blackb@ba.ars.usda.gov. Retired. The cultivars of highbush blueberry have been derived primarily from selections of Vaccinium corymbosum L., which are naturally adapted to acidic, swampy conditions (Eck et al., 1990). Under cultivation, these plants prefer low-pH, moist, well-drained, sandy soils containing high levels of organic matter. These soil requirements effectively limit the number of suitable sites for commercial production to a few specific geographic regions (Eck and Childers, 1966; Pritts, 1992). In the more populated regions of the United States, direct marketing of fruit, either on farm or at local farm markets, is becoming more prevalent, as indexed by the growth in farm markets between 1994 and 2000 (Holley, 2000). In many regions however, the relatively specific site and soil requirements of highbush blueberry has limited their ability to be produced on diversified, directmarket oriented fruit farms. These farms, by nature, are located near population centers, and may or may not have sites suitable for highbush blueberry production. A number of research efforts have focused on these limitations. Extensive effort has been expended in breeding for upland soil adaptability (Finn et al., 1993a, 1993b; Korcak, 1988a, 1989; Korcak et al., 1982; Scheerens et al., 1999), which has yet to produce upland soil-adapted varieties. Other efforts investigated amending upland soils to improve soil properties (Dale et al., 1989; Goulart et al., 1998), optimizing management inputs to maximize tolerance to upland soil (Chandler et al., 1984; Erb et al., 1993; Korcak, 1983), and growing blueberries in a potting medium, similar to that used in the container nursery industry (Smolarz, 1985). However, the cost of potting mixes or their components as soil amendments may be prohibitively expensive for fruit production, even on a small scale. In regions with coal-fired electrical generation, coal combustion by-products may provide a relatively low cost substrate for plant growth. Several of these combustion by-products, such as fly ash, bottom ash, and fluidized bed combustion by-product, have desirable horticultural characteristics, are available at low cost, and are