Peatmoss is one of the most commonly used substrate components in the greenhouse and nursery industry and has been used since the 1960s (Li et al., 2009; Shober et al., 2010). Currently, the environmental impacts of harvesting peatmoss are a concern since draining peatlands accelerates the decomposition process and results in the release of stored carbon to the atmosphere as carbon dioxide (Li et al., 2009). Wetlands, including peatlands, contain a vast pool of organic carbon, and currently hold about one-third of the global soil carbon stock (Freeman et al., 2004). Because of these environmental concerns, the restricted use of peat in some countries, rising cost (Sterrett, 2001), and peat scarcity issues during years of excessive precipitation (Jackson and Fonteno, 2013), a number of alternatives have been tested that include: coconut coir (Evans and Stamps, 1996), rice hulls (Buck and Evans, 2010), corn tassels (Vaughn et al., 2011), poultry feather fiber (Evans, 2004), tree-based products (Fain et al., 2008; Jackson et al., 2009), and different types of compost.
Compost has been used as a horticultural substrate additive since the 1970s and is a viable replacement for some components used in commercial substrates, specifically peatmoss (Benson, 1996; Bugbee, 1996). However, compost has not become a staple component of horticultural substrates used in the industry due to problems such as phytotoxicity, high concentration of heavy metals, chemical carry over, high salts, high pH, and inconsistency between batches (Hummel et al., 2014; Stoffella and Kahn, 2001). Since there are endless ingredients for making compost, the efficacy and rates for using each of these in greenhouse production are not well-understood (Murray and Anderson, 2004). Many of these problems can be avoided by using appropriate, high-quality, and consistent feed stocks, uniform production methods, followed by quality control testing. There are many positive impacts of using compost since it is created from recycled materials and places them back into the production stream; compost is typically locally produced, can provide supplemental nutrition, may suppress disease causing organisms, and can be used as a limestone substitute for pH establishment (Carrión et al., 2008; López-Lópeza and López-Fabal, 2013; Taylor, 2011; Wong et al., 1998).
Peatmoss has a low pH of 3.0–5.0 (Martinez et al., 1988) and typically needs 8 to 20 kg of lime per m3 to raise the pH to an acceptable level for most crops (Nelson, 2012). Compost pH, however, can range from 5.0 (Hue, 1992) to over 8.0 (Carrión et al., 2008), but is typically 7.0 or above. Because of the high pH of most composts, limestone rates can be reduced or even eliminated when compost is used as a component of substrate or as a peatmoss replacement (Bugbee, 2002; Taylor and Nelson, 2007). Many studies have shown that when compost is added to a peat-based substrate, the resulting pH is greater (Bugbee, 2002; DeKalb et al., 2014; Dolores Perez-Murcia et al., 2005; Jeong et al., 2011; Lopez et al., 1998; Taylor and Nelson, 2007; Wilson et al., 2001).
The pH buffering capacity of growing substrates may be affected when different materials, such as lime and/or compost, are used to establish substrate pH. Titration studies have been performed on pure compost with elemental sulfur and sulfuric acid to lower the high pH of the composts to make them more suitable for containerized crops and field-grown blueberries (Carrión et al., 2008; Costello and Sullivan, 2011b). However, these studies evaluated acidification of the compost directly, rather than after it was incorporated into a final blend. The direct impact on pH buffering capacity when compost is used to establish pH compared with limestone in horticulture substrates has not been determined. Determining the pH buffering capacity of substrates produced with compost is important for pH control and high-quality crop production. The objectives of this study were to: 1) determine the resulting substrate pH when using a range of compost and limestone rates and 2) compare the pH buffing capacity of substrates that had the pH established by the addition of compost, limestone, or a combination of both.
BuckJ.S.EvansM.R.2010Physical properties of ground parboiled fresh rice hulls used as a horticultural root substrateHortScience45643649
BugbeeG.J.1996Growth of rhododendron, rudbeckia and thujia and the leaching of nitrates as affected by the pH of potting media amended with biosolids compostCompost Sci. Util.45359
CarriónC.García de la FuenteR.FornesF.PuchadesR.AbadM.2008Acidifying composts from vegetable crop wastes to prepare growing media for containerized cropsCompost Sci. Util.162029
CostelloR.C.SullivanD.M.2011aDevelopment and validation of a simple method to determine the pH buffering capacity of compost. Thesis Oregon State Univ. 80–94
CostelloR.C.SullivanD.M.2011bEffects of acidified and non-acidified composts on highbush blueberry growth and nutrient uptake. Proc. of the ASA CSSA and SSSA International Annual Meetings
DeKalbC.D.KahnB.A.DunnB.L.PaytonM.E.BarkerA.V.2014Substitution of a soilless medium with yard waste compost for basil transplant productionHortTechnology24668675
Dolores Perez-MurciaM.Moreno-CasellesJ.MoralR.Perez-EspinosaA.ParedesC.RufeteB.2005Use of composted sewage sludge as horticultural growth media: Effects on germination and trace element extractionCommun. Soil Sci. Plant Anal.36571582
FainG.B.BoyerC.R.SibleyJ.L.GilliamC.H.2008Establishment of greenhouse-grown Tagetes patula and Petunia × hybrida in ‘WholeTree’ substratesActa Hort.782387393
FreemanC.FennerN.OstleN.J.KangH.DowrickD.J.ReynoldsB.LockM.A.SleepD.HughesS.HudsonJ.2004Export of dissolved organic carbon from peatlands under elevated carbon dioxide levelsNature430195198
HummelR.L.CoggerC.BaryA.RileyR.2014Marigold and pepper growth in container substrates made from biosolids composted with carbon-rich organic wastesHortTechnology24325333
JacksonB.E.AlleyM.M.WrightR.D.2009Comparison of fertilizer nitrogen availability, nitrogen immobilization, substrate carbon dioxide efflux, and nutrient leaching in peat-lite, pine bark, and pine tree substratesHortScience44781790
JeongK.Y.NelsonP.V.FrantzJ.BrintonW.2011Impact of composted dairy manure on pH management and physical properties of soilless substrateActa Hort.891173180
LiQ.DengM.CaldwellR.D.ChenJ.2009Cowpeat as a substitute for peat in container substrates for foliage plant propagationHortTechnology19340345
LiuM.KisselD.E.CabreraM.L.VendrellP.F.2005Soil lime requirement by direct titration with a single addition of calcium hydroxideSoil Sci. Soc. Amer. J.69522530
López-LópezaN.López-FabalA.2013Evaluation of urban solid waste and sewage sludge composts as components of growing mediaActa Hort.1013231238
McBrideM.B.1994Environmental chemistry of soils. Oxford Univ. Press. New York NY
MurrayR.AndersonR. G.2004Organic fertilizers and composts for vegetable transplant production. Floriculture Res. Rpt. 17–04. Univ. of Kentucky Ag. Exp. Sta
NelsonP.V.2012Greenhouse operation and management. 7th ed. Prentice Hall Upper Saddle River NJ
ShoberA.L.WieseC.DennyG.C.StanleyC.D.HarbaughB.K.2010Plant performance and nutrient losses during containerized bedding plant production using compost dairy manure solids as a peat substitute in substrateHortScience4515161521
SterrettS.B.2001Composts as horticultural substrates for vegetable transplant production p. 227–240. In: P.J. Stoffella and B.A. Kahn (eds.). Compost utilization in horticultural cropping systems. Lewis Publishers Boca Raton FL
Stoffella and Kahn2001Compost utilization in horticultural cropping systems. CRC Press Danvers MA
VaughnS.F.BerhowM.A.PalmquistD.E.DeppeN.A.2011Extracted sweet corn tassels as a renewable alternative to peat in greenhouse substratesIndustrial Crops and Products33514517
WilsonS.B.StofellaP.J.GraetzD.A.2001Evaluation of compost as an amendment to commercial mixes used for container-grown golden shrimp plant productionHortTechnology113135
WongM.T.F.NortcliffS.SwiftR.S.1998Method for determining the acid ameliorating capacity of plant residue compost, urban waste compost, farmyard manure, and peat applied to tropical soilsCommun. Soil Sci. Plant Anal.2929272937