Energy balance in irrigated wheat in the cerrados region of Central Brazil

Abstract

To evaluate the water requirements for irrigated wheat, a micrometeorological study was conducted during the dry seasons of 1982 and 1983 at the Cerrados Agricultural Research Center, Brasilia-DF, Brazil The crop was irrigated when the soil water potential at 5 cm rached -60 to -70J/Kg.Bowen ratio measurements were made on an hourly basis during the entire crop season. Total amount of water evapotranspired during the crop cycle and the energy balance terms varied year to year due to regional advection; In 1982, a less advective year, the total amount of water evapotranspired was 345 mm, with approximately 80% of the net radiation dissipated as latent heat, 13% as a sensible heat and 7% as soil heat after the crop obtained a Leaf Area Index (LAI) of 1.5. In 1983, when advection was greater than 1982, total water evapotranspired increased to 385 mm. The partitioning of energy was similar to 1982 during periods of little or no advection. However, during periods of intense advection, latent heat was greater hi net radiation partitioning. Although regional advection increased the water used by the crop, irrigation scheduling based on soil tensiometers was considered adequate and efficient due to the low values of the Bowen ratio obtained.