Effects of humic acid on growth and leaf photosynthesis in longan

In this research, the effects of humic acid at different concentrations on new shoot growth and leaf photosynthesis in longan were investigated.
One-year-old sand-cultured ‘Daw’ longan trees were studied at the Agricultural Technology Research Institute of Thailand.
The experiment was designed based on a CRD consisting of 4 concentration levels of humic acid: 0 (control), 50, 100, and 150 mg L^‑1. The longan trees were grown in 25-L plastic pots.
The results showed that humic acid had no effect on plant height or canopy width, while 100, and 150 mg L^‑1 decreased stem diameter.
The negative impacts on chlorophyll fluorescence at 12 am was observed in the treatment with the highest humic acid concentration (150 mg L^‑1). The stomata conductance, transpiration rate, and CO₂ assimilation rate of all treatments showed diurnal trends that increased from 6 am to 10 am and dropped from 10 am to 6 pm The new shoot growth was comparable among treatments.
However, the 150 mg L^‑1 treatment decreased stomata conductance, transpiration rate, CO₂ assimilation rate, and leaf greenness index.

VII International Symposium on Lychee, Longan and Other Sapindaceae Fruits

C. Sritontip, P. Sritontip

humic acid, CO₂ assimilation rate, physiological change

https://doi.org/10.17660/ActaHortic.2026.1447.15