Effects of Cocopeat–rice Husk Biochar Growing Media on Growth, Yield, Phenolic Content, and Nitrogen Uptake of Mint (Mentha spp.) under Drip Hydroponics

Abstract

Mint (Mentha spp.) is a high-value medicinal and aromatic crop whose productivity and quality are influenced by growing media under hydroponic cultivation. This study evaluated the effects of cocopeat–rice husk biochar growing media on the growth, yield, phenolic content, and nitrogen uptake of three mint varieties cultivated in a drip hydroponic system. The experiment was conducted in a greenhouse using a two-factor completely randomised design (CRD) with six replications. The first factor consisted of three mint varieties (Spearmint, Chocolate Mint, and Apple Mint), while the second factor comprised four cocopeat–rice husk biochar ratios (80% cocopeat : 20% rice husk biochar, 60% cocopeat : 40% rice husk biochar, 40% cocopeat : 60% rice husk biochar, and 20% cocopeat : 80% rice husk biochar, v/v). Data were analysed by analysis of variance (ANOVA), followed by the Least Significant Difference (LSD) test at the 5% significance level. Mint variety significantly affected most growth, yield, and quality traits, whereas growing medium composition significantly influenced stem diameter, while the interaction between growing medium composition and variety affected fresh and dry root and leaf weights. Total phenolic content ranged from 8.87 to 9.17 ppm, while leaf nitrogen content varied from 0.22% to 0.24%. Apple Mint exhibited superior shoot productivity, producing the largest stem diameter and highest leaf dry weight, whereas Chocolate Mint produced the greatest root biomass and the highest phenolic content (9 mg/L); Spearmint showed the highest leaf nitrogen content (0.24%). Overall, media enriched with rice husk biochar enhanced plant productivity and quality, indicating that cocopeat–rice husk biochar mixtures are suitable hydroponic growing media for mint cultivation.