Water vapor flux in tropical lowland rice.

A field experiment was conducted at Indian Council of Agricultural Research-National Rice Research Institute, Cuttack, Odisha, India in the dry seasons of 2015 and 2016 to assess the water vapor flux (FH2O) and its relationship with other climatic variables. The FH2O and climatic variables were measured by an eddy covariance system and a micrometeorological observatory. Daily mean FH2O during the dry seasons of 2015 and 2016 were 0.009-0.092 g m-2 s-1 and 0.014-0.101 g m-2 s-1, respectively. Seasonal average FH2O was 14.6% higher in 2016 than that in 2015. Diurnal variation for FH2O showed a bell-shaped curve with its peak at 13:30-14:00 Indian Standard Time (IST) in both the years. Carbon dioxide flux was found higher with rise in FH2O. This relationship was stronger at higher vapor pressure deficit (VPD) (20 ≤ VPD ≤ 40 and VPD > 40 hPa). The FH2O showed significant positive correlation with latent heat flux, net radiation flux, photosynthatically active radiation, air, water and soil temperatures, shortwave down and upwell radiations, maximum and minimum temperatures, evaporation, and relative humidity in both the years. Principal component analysis showed that FH2O was very close to latent heat flux in both the years (Pearson correlation coefficient close to 1). The two-dimensional observation map of the principal component F1 and F2 showed the observations taken during the vegetative stage and panicle initiation stage, and flowering stage and maturity stage were closer to each other. It can be concluded that the most important climatic variables controlling the FH2O were latent heat of vaporization, net radiation, air temperature, soil temperatures, and water temperature.