Balanço de energia e evapotranspiração de cafezal adensado em crescimento sob irrigação localizada. / Energy balance and evapotranspiration in a high density young coffee under located irrigation.
AUTOR(ES)
Evandro Zanini Righi
DATA DE PUBLICAÇÃO
2005
RESUMO
The objectives of this study were to evaluate the magnitude of global evapotranspiration (ETc) in a high density young coffee crop (3.5mx0.9m) under drip irrigation, the ETc partition considering hedgerows and interrows, and the partition of the available radiant energy between sensible and latent heat fluxes. The experiments were conducted from September 2002 to September 2003, in Piracicaba, SP, Brazil. ETc was determined by the Energy balanceBowen ratio (BRM) and aerodynamic (AM) methods. Hedgerows evapotranspiration was measured by weighing lysimeters and coffee transpiration by the sap flow using the stem heat balance method. When AM was used, several problems were observed. One of them was the zero plane displacement (d) normalized by the crop height, which showed an earlier small increase, followed by an unexplained decrease when plant height increased, besides of a huge variation of the roughness length (zo), which depended on interrows cover conditions and wind direction and speed. Also, the effect of these former was noticed on d. Probably, the major source of error in AM was the use of turbulent transport coefficients determined with empirical functions, using the Richardson number, valid for homogeneous surfaces, and measurements taken on the inertial atmospheric sublayer. This procedure proved to be inadequate for the heterogeneous coffee crop surface, resulting in unrealistic ETc values. The BRM estimates of ETc were more appropriate, as a consequence of the good similarity between potential temperature and vapor pressure profiles, indicating that the ratio between the turbulent transport coefficients for sensible and latent heat was close to unity. During the dry season, in the majority of the days with measurements, ETc estimates were less effective due the small vapor pressure gradients and the errors caused by the psychrometer sensors. The ratio between global latent heat flux and available surface energy was higher than 80% in the wet season, decreasing to 64% when the interrows were drying. The global crop coefficient (Kc), representing the ratio between ETc and reference evapotranspiration (ETo) ranged from 1.04 to 1.30, being highly dependent on soil moisture conditions. In the latest period of measurements, Kc was about 0.86, which must be analyzed with care due problems in the coffee crop management. The hedgerows evapotranspiration coefficient, which means the ratio between hedgerows evapotranspiration (evaporation of continuous soil area under hedgerows plus the crop transpiration) and ETo, ranged from 0.22 to 0.43, being influenced by soil moisture, especially by the soil surface area wetted by the drip irrigation and by the increase of leaf area. The basal crop coefficient (ratio between transpiration and ETo) ranged from 0.03 to 0.20. During the dry season, effect of advection on the measurements was observed; so, some criteria were used to select days in which this effect was considered to be null or having a minimum degree, in order to calculate the mean values of the above described coefficients.
ASSUNTO(S)
micrometeorology evapotranspiração evapotranspiration energy balance located irrigation micrometeorologia balanço de energia irrigação localizada café coffee
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