Energy balance and latent heat flux partitioning in coffee hedgerows at different stages of canopy development

Abstract

The energy balance of drip-irrigated coffee ( Coffea arabica L. cv. Yellow Catuai) hedgerows was evaluated at different stages of canopy development using the Bowen ratio-energy balance technique. Simultaneous measurements of mass flow of water through the coffee stems using the heat balance method allowed total latent heat flux (λ E) to be partitioned between crop canopy (λ Ec) and soil and interrow vegetation (λ Es) components. The average Bowen ratio decreased from 0.92 at leaf area index ( L) of 1.4 to 0.36 at L = 6.7. Differences in the Bowen ratio between 2 consecutive years appeared to be related to stomatal response to leaf-to-air vapor pressure difference ( V) and variations in net radiation ( R r). Latent heat loss was the most important component of the energy balance at all stages of canopy development, while sensible heat flux ( H) remained relatively constant. Soil heat flux ( G) invariably declined as L increased. λ Ec was the major form of latent heat loss at all stages of canopy development except at L = 1.4, where λ Es accounted for 60% of λ E. However, the magnitude of λ Es declined with canopy development, with λ Ec accounting for nearly 100% of total λ E at L = 6.7. Withholding irrigation dramatically influenced the partitioning of energy, strongly reducing λ Es and increasing H. After irrigation was discontinued λ Ec dropped rapidly, and the contribution of λ Es to λ E became more important. After irrigation was resumed, a rapid recovery of all energy balance components to their previous values was observed. At low L, energy balance and latent heat partitioning of coffee hedgerows grown under wide spacing resembled the behavior of sparse row crops, but the development of a tall, dense canopy caused available energy to be partitioned in a way typically found in closed canopies such as those of forests.