Modified green waste compost as growing substrates on the effective components of medicinal plants perilla (Perilla frutescens (L.) Britt.) and mint (Mentha haplocalyx Briq.)

Abstract

Soilless substrates supporting plant production have been the research focus in recent decades. Green waste compost (GWC)-based substrates have shown the feasibility in improving plant production, but the research of GWC as growing substrate to improve the quality of medicinal plants was limited. The objective of this study was to explore the effects of GWC substrates modified by matured peanut shell (MPS, at 0, 10, 20 %; by vol.) and humic acid (HA, at 0, 3, 6 %; by weigh.) on the effective components of medicinal plants perilla (Perilla frutescens (L.) Britt.) and mint (Mentha haplocalyx Briq.). The 100% GWC substrates was used as control. The hydrologic-physical and biochemical properties of growing substrates and the biomass accumulation, secondary metabolite synthesis, essential oil production, and chemical composition of both herbs were investigated. Results showed that both perilla and mint grown in GWC substrates amended with MPS and HA had better performance than the control. The addition of additives (MPS and HA) positively affected the biomass accumulation of perilla and mint. The combination of the highest doses of MPS and HA (20 % and 6 %, respectively) resulted in an accumulation of total fresh weight and total dry weight several times (the total fresh and dry weight of perilla was 2.70 and 2.37 times, the total fresh and dry weight of mint was 1.47 and 1.51 times, respectively) greater than that of the control. Furthermore, the addition of MPS and HA could improve the secondary metabolite synthesis of mint and perilla and this synthesis was related to the hydrologic-physical and biochemical properties of growing substrates. Unexpectedly but reasonably, perilla was more sensitive to the addition of MPS while there was no significant (p < 0.05) correlation between the addition of MPS or HA for mint and the addition of HA for perilla. Notably, the best effective components of both herbs were achieved when perilla grown in GWC modified by 20 % MPS and 3 % HA and mint grown in GWC modified by 10 % MPS and 6 % HA. Overall, the quality of GWC could be effectively modified by the addition of MPS and HA and the modified GWC could be used as an environmentally and friendly substrate to improve the effective components of mint and perilla.