Effects of various organic sources on plant growth and medium porosity were evaluated; alternatives to peat tested cannot be used for exported container plants but may be suitable for local use with some experimentation by the grower

Hensley, David

Yogi, Julie

ScholarSpace at University of Hawai'i at Manoa

Cooperative Extension Service Horticulture Research NoteNov. 1997HRN-11Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June30, 1914, in cooperation with the U.S. Department of Agriculture. Charles W. Laughlin, Director and Dean, Cooperative Extension Service, CTAHR, University ofHawaii at Manoa, Honolulu, Hawaii 96822. An Equal Opportunity / Affirmative Action Institution providing programs and services to the people of Hawaii without regardto race, sex, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or veteran status.Sphagnum peat is the primary organic componentof container media in Hawaii. It is expensive and willbecome even more so as ecological concerns about cur-rent harvest methods continue to be raised. This prob-lem is not unique to Hawaii, however. A number of re-searchers and nursery producers on the U.S. mainlandare searching for peat substitutes as more compostedorganic products become available.A number of organic materials have been success-fully substituted for peat (Henley and Ingram 1989).Bagasse was tested in Hawaii as a peat substitute in 1978(Uchida et al. 1979). Acceptable growth and quality wereobtained only from replacing 1⁄3 of the peat with fresh orcomposted bagasse.Replacement of 50% of the volume of peat in a stan-dard nursery mix in Minnesota produced quality plants(Jarvis et al. 1996). An alkaline, stabilized blend of sew-age sludge and peat blend gave growth comparable toSunshine Mix® for three bedding plants (Logan andLindsay 1996). Plants grown with up to 75% compostedpaper sludge from newsprint production grew as wellas or better than plants grown in peat-amended media(Tripepi et al. 1996). Composted yard trimmings suc-cessfully substituted for peat in azalea and pittosporummedia in Florida (Beeson 1996).Substitutions for peat in Hawaii nursery productionCoir pith and dust are the short fibers and dust re-maining after the long fibers of coconut are extracted.High-quality coir pith appeared to be an acceptable sub-stitute for sphagnum or sedge peat in soilless containermedia (Meerow 1995). Coir is already widely used inEurope and Australia. Fertilizer regimes and lime amend-ment will need to be adjusted if coir or any other or-ganic material is substituted for peat.We initiated a study to determine if several differ-ent organic materials might be substituted for peat inproduction of some nursery crops. Dwarf poinciana (ohaiali’i, Caesalpinia pulcherrima) seedlings were plantedinto 6-inch pots using various organic materials on De-cember 11, 1995. The media was a 1:1 (v:v) mixture oforganic material and medium perlite. The organic mate-rials tested are listed in Table 1. Each test medium wasamended with Osmocote® (18-6-12) at 143 g/ft3  and 43g/ft3 of gypsum (calcium sulfate) as a source of calcium.Two controls using sphagnum peat were prepared, onewith gypsum and the other with dolomitic lime. Plantswere pruned to 10 inches at planting. Each treatmentwas replicated five times. Plant heights were measuredon the following March 6, April 22, and May 30, andfresh weights were taken at the termination of the study.Porosities (air space) of the media were also measured.Table 1. Organic materials used in media study.Organic material DescriptionSphagnum peat with dolomitic lime Control medium (dolomite as Ca and Mg source and pH adjustment)Sphagnum peat with gypsum Control medium (gypsum as Ca source)Coir Coco-peat™ (coir from Sri Lanka)Composted municipal sewage waste (MSW) Bagged product from rapid aerobic compost of MSW (from Japan)Green waste compost Green waste compost (from Oahu)MSW+green waste compost MSW mixed with green waste and composted together (from Maui)Macadamia husk compost Composted macadamia nut husk (from Big Island)David Hensley and Julie Yogi, Department of HorticultureHorticulture Research Note HRN-11 CTAHR — Nov. 19972Porosity is the volume of the medium occupied by airafter the container has been saturated with water andallowed to drain freely.Plant growthGrowth of the dwarf poinciana seedlings was goodin each test media over the duration of the study (Tables2 and 3). There were no statistically significant differ-ences among the different media at any measurement.Growth of the plants in both peat mixtures was less thanthat achieved by the other organic materials at the lastmeasurement. The plants in the peat with lime mediawere noticeably smaller and less thrifty as indicated byfresh weight at the conclusion of the study (Table 3).The plants received no additional fertilization after plant-ing. The plants were able to utilize the higher levels ofnitrogen and other nutrients from the composts and coiras they became available.PorosityPorosity is a concern with organic materials to grow-ers for several reasons. First, the mix must have adequatelarge pore space to be well aerated for the roots. Exces-sive large pores, however, decrease the amount of waterthe media can store. The particles of organic materialmay become smaller with time due to decompositionand can sift down in the pot, clogging the pores andreducing aeration. The material needs to be relativelystable to avoid this problem.For outdoor production, container media should havelarge or drainable pore space of 20 to 30 percent of thevolume (Ingram and Henley 1989). This range providesgood aeration and water capacity and allows excess waterto drain away. The porosity of all of the media testedwas within the 20 to 30 percent range at both examina-tion dates (Table 4).All of the composted organic materials and coconutcoir tested produced dwarf poinciana growth equal toor better than that of peat. The plants in the compostwere larger than those grown in peat at the end of the173 day study. This was undoubtedly due to the releaseof nitrogen and other nutrients from their organicsources. Peat contains less nitrogen than composts. Sincewe wanted to look at the effect of the media, we did notadd supplemental fertilizer as would be done in nurseryproduction. The plants in the peat, and other media aswell, would have grown larger had supplemental fertil-izer been added.The goal of this study was to determine if coir, greenlandscape debris, and/or municipal composts could sub-stitute for peat in production of a woody plant. Thegrowth we saw indicated that any of the materials testedcould be an alternative for peat moss to grow dwarf poin-ciana seedlings. We do not mean to suggest from theseresults that this may be the case with every plant. Dosome experimentation with your material in your op-eration to determine the suitability of a substitute. Thereare a number of factors to consider.Table 3. Fresh weight at harvest of dwarf poinciana seed-lings grown in various organic materials.Organic portion Fresh weight (g)peat with lime 14.3 apeat with gypsum  27.5 abcoir 33.4 bMSW 42.4 bcomposted green debris 31.6 bcomposted MSW+green debris 35.8 bmacadamia husk compost 45.0 bMeans followed by the same letter are not significantly different when tested byTukey HSD (5% probability level)Table 2. Average heights of dwarf poinciana seedlingsgrown with different organic materials.Plant height (cm)Organic portion March 6 April 22 May 30peat with lime  14.3 ns  16.5 ns  21.5 nspeat with gypsum 14.7 19.0 29.4coir 15.2 21.0 30.0MSW 13.1 17.6 37.0composted green debris 14.0 23.0 35.8composted MSW+green debris 16.6 20.4 32.0macadamia husk compost 15.6 25.0 38.8ns = no statistically significant differences between for plant heights within col-umns (5% probability level)Horticulture Research Note HRN-11 CTAHR — Nov. 19973Table 4. Porosity (%) of media containing various organicmaterials.Porosity (%)Organic portion April 22 May 31peat with lime  26.7 ns 22.5peat with gypsum 20.8 19.4coir 31.8 29.5MSW 21.7 27.1composted green debris 26.7 24.7composted MSW+green debris 25.0 23.7macadamia husk compost 20.1 23.2Research conducted in Hawaii and elsewhere indi-cates that there can be differences in the quality of com-post. Variation can occur with batch, season, and changesin the raw inputs. Look particularly for stability in par-ticle size, pH, and soluble salts. Research has also indi-cated that these materials can successfully replace at leastsome of the peat in nursery mixes. Variation in batchesof compost diminishes dramatically as producers gainexperience and technology. Most commercial compostersin Hawaii have found stable sources of input materialand are producing a consistent product.If you are considering trying some of the locallyavailable composted organic materials, do some experi-mentation. Compost and coir have different chemicaland physical characteristics than peat. Adjust the amend-ments added to reflect the difference in pH. Supplementalfertilization may also require some fine-tuning.None of the organic materials tested, with the pos-sible exception of coir, would be suitable for producingcertified nursery material for export. All of the materi-als are produced or stored on the ground and thus do notmeet quarantine requirements for export. They appear,however, to have good potential for production of nurs-ery stock for local consumption.Literature citedBeeson, R., Jr. 1996. Composted yard waste as a com-ponent of container substrates. J. Env. Hort. 14(3):115.Henley, R.W., and D.W. Ingram. 1989. Characteristicsof container media components. The WoodyOrnamentalist 14(2). Univ. Florida Dept. Environ.Hort., Gainesville, FL.Ingram, D., and R. Henley. 1989. Engineering a containergrowth medium. The Woody Ornamentalist 14(3).Univ. Florida Dept. Environ. Hort., Gainesville, FL.Jarvis B., J. Calkins, and B. Swanson. 1996. Compostand rubber tire chips as peat substitutes in nurserycontainer media: effects of chemical and physicalmedia properties. J. Env. Hort. 14(3):122.Logan, T., and B. Lindsay. 1996. Growth of three bed-ding plant species in soilless mixes with alkaline sta-bilized sewage sludge. J. Env. Hort. 14(3):160Meerow, A. 1995. Growth of two tropical foliage plantsusing coir dusts as a container medium amendment.HortTechnology 5(3):237.Tripepi, R., M. George, A. Campbell, and B. Shafii. 1996.Evaluating pulp and paper sludge as a substitute forpeat moss in container media. J. Env. Hort. 14(2):91.Uchida, R., R. Criley, and F. Rauch. 1979. Substitutionof bagasse for peat in growing mediums. Horticul-ture Digest No. 52. Dept. of Horticulture, Universityof Hawaii at Manoa, Honolulu, HI.Mention of a trademark, company, or proprietary name does not constitute anendorsement, guarantee, or warranty by the University of Hawaii CooperativeExtension Service or its employees and does not imply recommendation to theexclusion of other suitable products or companies.

Substitutions for Peat in Hawaii Nursery Production

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Substitutions for Peat in Hawaii Nursery Production

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