Evapotranspiration of passionfruit and crop coefficient determined by energy balance and lysimeter hydraulic weighing. / Evapotranspiração e coeficiente de cultivo de maracujazeiros determinados pelo método do balanço de radiação e lisimetria de pesagem hidráulica.
Tonny José Araújo da Silva
DATA DE PUBLICAÇÃO
This work was carried out at the experimental irrigation farm of the Engineering Department - College of Agriculture Luiz de Queiroz - ESALQ/USP in Piracicaba, São Paulo, State. The 83-day-old passiflora seedlings (Passiflora edulis Sims f. flavicarpa Deg cv. IAC 275) were transplanted to experimental units with rows planted based on North- South and East-West directions. The Bowen ratio method was used to determine both sensible heat and latent heat fluxes. It was collected micrometeorological data from net radiation, soil flux heat, temperature and vapor pressure gradient with the aim to evaluate the energy available partition and evapotranspiration of trees planted under two row directions. The performance of a hydraulic load cells and a pressure transductor were evaluated by calibration of electronic load cells in laboratory and field conditions. In order to determine the evapotranspiration, it was used four similar hydraulic weighing lysimeters, being two in each direction of plant row. The daily evapotranspiration in liters per plant was adjusted to the leaf area present in each lysimeter, to hypothetically uniform the vegetative development and compare the values themselves. The net radiation was not influenced by row directions, and it was 60% of global radiation. The latent heat of evaporation was the major role on energy balance and the significant values happened immediately after a rainfall or irrigation. The use of intervals and exclusion analyzes model, when the Bowen ratio fails, improve the estimative of evapotranspiration. The triangular design of load cells promoted a good stability and distribution of forces. The establishment of an ideal fluid volume leaded a liner calibrations and better performances. Relationships between mass variation read in piezometer, electronic load cells and pressure transductor showed linear relation and high determination coefficient. The accumulative depth at 450 DAP for North-South unit was 1171 mm higher than 1083 mm for East-West. The average of extremes values for evapotranspiration was 5 L plant-1 day-1 for autumn and winter and 8 L plant-1 day-1 for summer period. No significant differences were found for ETc for units in months of lower energetic availability. The values for crop coefficient were 0.6 for apex vegetative growth, 0.9 for lateral vegetative growth, 1.2 for flowering and fruit development, 1.0 for fruit maturation and 0.8 for post-maturation period.
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