Abstract
The objective of this study was to evaluate the effects of topdressing controlled-release fertilizer (CRF) over rice hull mulch on nutrient release and ornamental plant quality over time. Two ornamental species, Robyn coleus (
Plectranthus scutellarioides
‘Robyn’) and chaste tree (
Vitex agnus-castus
), were grown under combinations of three rice hull mulch depths (0, 2.5, and 5 cm) and two CRF placements (topdressed or incorporated). Leachate was collected weekly to determine nutrient leaching in response to mulch depth and fertilizer placement. The plant growth index was measured at 2, 4, 8, and 12 weeks after potting (WAP), and shoot dry weight was recorded at the conclusion of the trial (12 WAP). For both species, CRF incorporation produced larger plants and greater shoot dry weight than topdressing. Compared with incorporation, topdressing reduced shoot dry weight of Robyn coleus by 24% and that of chaste tree by 10%. The incorporation of CRF also reduced NH
4
-N leaching by up to 85% at 12 WAP compared with topdressing, while NO
3
-N leaching decreased over time across all treatments, likely because of increased plant uptake and reduced fertilizer release rates. Overall, the results indicate that CRF incorporation in combination with rice hull mulch (2.5–5 cm) enhances plant growth and minimizes nutrient losses without adversely affecting substrate chemistry. This integrated approach provides a practical and sustainable strategy for improving nutrient management and environmental performance in containerized ornamental plant production.