Growing Media Affects Biomass-Water Use Efficiency Trade-Off in Sub-Surface Irrigated Pak Choi (Brassica rapa L. subsp. chinensis)
Abstract
Efficient water use is crucial for the sustainable production of leafy vegetables under limited water resources. This study evaluated the trade-off between biomass production and water use efficiency (WUE) in pak choi (Brassica rapa L. subsp. chinensis) grown under a sub-surface capillary irrigation system across three growing media: rice husk charcoal (RHC), sand (SPM), and cocopeat (CPT). A completely randomised design with three replications was used over a 24-day growth period. Results showed that while CPT produced the highest total biomass (108.8 g/plant) and canopy area (472.8 cm²), these vegetative parameters were not significantly different across media (p > 0.05). In contrast, water relations varied significantly; SPM achieved the highest water productivity (87.8 kg/m³), representing a 34.4% improvement over CPT (p < 0.05). Root biomass and length also varied significantly among media. No significant linear correlation was found between vapour pressure deficit (VPD) and daily evapotranspiration (ETc) for any growing medium (|r| ≤ 0.101, p > 0.05). These findings highlight a trade-off between biomass yield and water efficiency. For water-limited systems, SPM is recommended; for balanced performance, RHC is suitable. The hypothesis that a mixture of CPT and SPM could optimise both biomass yield and water conservation requires direct testing in future studies.
© 2026 Ahmad Tusi, M. Reihan Andri H, Elhamida Rezkia Amien, Winda Rahmawati, published by National Agricultural and Food Centre
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