Influence of sowing seasons and irrigation levels on surface energy balance, radiation utilization and water use efficiency of sunflower in an eastern Indian watershed

Surface energy balance, water use efficiency and radiation utilization efficiency of sunflower were studied under different sowing dates and irrigation regimes in Bahasuni watershed, Dhenkanal, Odisha. The latent heat flux of the crop varied with the photo-thermal environments and values ranged between 8.64 to 18.77 MJ m⁻² day⁻¹ under different treatments. It was revealed that during mid-growth stage when canopy was fully developed and water did not limit transpiration (wet soil), latent heat flux consumed most of the energy from net radiation. As the soil dried towards maturity, water became less available for evapotranspiration and the energy was used mostly for heating the soil (soil heat flux) or heating the air (sensible heat flux). Supplemental irrigations had significant effects on crop growth and radiation utilization efficiency (RUE) of the crop in dry season. Mean values of RUE were 1.44, 1.63 and 1.73 g MJ ⁻¹ with three, four and five irrigations, respectively. The water use efficiency (WUE) of the crop also varied with sowing dates and irrigations. Averaged over years and irrigations, winter season crops registered high WUE with the values being 3.16 and 3.28 kg ha⁻¹ mm⁻¹ for second (October-February) and third sown (June-November) crops, respectively.