Pine bark substrates amended with parboiled rice hulls: Physical properties and growth of container-grown spirea during long-term nursery production

Abstract

The decline in the availability of pine (Pinus taeda L.) bark (PB) supplies andincreasing prices have caused concerns in the nursery industry. Research was conductedto evaluate the effect of parboiled rice (Oryza sativa L.) hulls (PBH) as a substrate amendmentto PB-based container substrates on the growth of Spiraea ·bumalda L. 'Anthony Waterer'and to examine the changes in physical properties of the substrates during long-termproduction cycles under outdoor nursery conditions. Six substrates were formulatedby blending PB with 0%, 20%, 40%, 60%, 80%, or 100%PBH (by volume). Substratecomposition affected plant growth components evaluated, generally decreasing growthas the amount of PBH increased. However, amending PB with up to 40% PBH did notresult in a significant decrease in plant growth or increase the volume or frequency ofirrigation for container-grown spirea. Physical properties of substrates amended withPBH improved over time. Based on these results, PB-based substrates amended with upto 40%PBH retained physical properties that were generally within current guidelinesfor nursery container substrates after one (25 weeks) and two (70 weeks) growingseasons.