Energy Fluxes and Evapotranspiration in a Rubber Agroecosystem of the Southern Thailand

Abstract

Evapotranspiration (ET) plays an important role in land surface atmosphere interaction which significantly drives hydrological cycle, vegetation functioning resulting to agricultural production. In this study, observations of energy fluxes, energy partitioning, and evapotranspiration (ET) were conducted on a monoclonal stand of rubber trees (Hevea brasiliensis) plot (clone RRIM 600) in 2017. The forestry population was 17 years old and had been tapped continuously over 10 years for latex harvesting at the Rubber Estate Organization station in Na Bon district, Nakhon Si Thammarat province in Thailand. The ET rate and associated energy fluxes were determined by means of eddy covariance (EC) method and complemented by micrometeorological measurements at 25 m tall tower. Tree stands were spaced on plots of 3.0×7.0 m2 with mean canopy height of 22 m. Data were collected during January 1 to September 27, 2017. Results found that the energy balance closure of the rubber agroecosystem was approximately 78 %. Overall, the latent heat (LE) flux was the main term of energy exchange (58 - 60 %) due to its dominance across the growing season. The ratios of the latent heat (LE) and sensible heat (H) to net radiation were 0.58 and 0.24 throughout the period of study, respectively. Moreover, the daily mean of evapotranspiration (ET) was 7.16 mm.d-1 over the whole period of this study. However, a slightly higher rate of daily mean ET (7.35 mm.d-1) was indicated during the foliage period than during the leaf senescence period due to sufficient soil moisture associated with high rate of seasonal precipitation. It is concluded, that ET is an extremely sensitive variable to understand in energy flow in this ecosystems as well as a precursor for presetting condition for droughts prognosis (forecast) in a rubber ecosystem.