Tecnologia do Irrigâmetro aplicada em minilisímetro e lisímetro com lençol freático constante para determinação da evapotranspiração de referência / Technology of Irrigâmetro applied in minilysimeters and lysimeters with constant groundwater table for the determination of the reference evapotranspiration

Franklin José Valbuena Materán

This investigation was carried out in the unit of research and development of the modified Irrigâmetro, belonging to the Department of Agricultural Engineering of the Federal University of Viçosa, in Viçosa, state of Minas Gerais, Brazil, located at 20 45 S and 42 45 W , in the period from July to December of 2005. Two experiments were conducted with the grass-batatais (Paspalum notatum Flugge), with one using minilysimeters and the other with lysimeters both with constant groundwater table, filled sand substrate, fed with nutritive solution and operating with modified Irrigâmetro. The treatments comprised of four constant groundwater tables (15, 20, 25 and 30 cm of dept), established in the minilysimeters (M15. M20, M25 and M30), with four repetitions. In the experiment with the lysimeters, the same treatments were applied (L15. L20, L25 and L30), with three repetitions. In both experiments the research design was entirely randomized. The grass-batatais was also cultivated in three draining lysimeters filled with red-yellow latossoil. The purposes of this investigation were: to determine the reference evapotranspiration (ETo), by means of the lysimeters and minilysimeters, both with constant groundwater table and operating with modified Irrigametro, as well as to study the effects of the groundwater levels of 15, 20, 25 and 30 cm on the ETo and to evaluate their performance in relation to the modified Penman, Radiation, Hargreaves-Samani, Pan and draining lysimeter methods. With the Penman-Monteith FAO 56 method being considered the standard method. To compare the performance of minilysimeter in the determination of the ETo in relation to the constant level lysimeter, both operating with modified Irrigâmetro. To evaluate the effects of the different groundwater table on the productivity of dry matter and EUA of the grassbatatais cultivated in constant level minilysimeters and lysimeters operating with modified Irrigâmetro. To compare the productivity of dry matter and EUA of the grass-batatais obtained in the minilysimeters and lysimeters with constant groundwater table in relation to the productivity of the draining lysimeter (standard). The methods of L15, L20, M30, Radiation, draining lysimeter and Pan exhibited a good performance in the determination of the ETo. The methods that exhibited the worst performance was the Hargreaves-Samani and the minilysimeters M15, M20, M25, not being recommended their use for the estimate of the ETo, under conditions similar to those studied in this investigation, due to their low precision and accuracy. The external cylinder used as borders in the minilysimeters as buffer-area were not sufficient to avoid the clothesline effect, leading to a higher consumption of water in comparison to the ones verified in the groundwater table lysimeters and the draining lysimeter. The highest consumption of water occurred in the 15 cm groundwater table, decreasing with depth, with this effect being most pronounced in the minilysimeters. The groundwater table in the different methods studied did not affect significantly the productivity of dry matter of the grass-batatais cultivated in the lysimeters and minilysimeters. The average productivity of dry matter of the grass-batatais cultivated in the minilysimeters did not differ significantly from the one observed for the constant level lysimeters operating with modified Irrigâmetro, in the groundwater table of 15, 20 and 20 cm of depth. The dry matter productivity of the grass-batatais obtained with the constant level lysimeter maintained at 20 cm of depth surpassed statistically the productivity obtained with draining lysimeter. The efficiency of the use of water by the grass-batatais obtained in the lysimeters and minilysimeters with constant groundwater table did not vary significantly in the different ground water levels investigated. The efficiency of the use of water by the grass-batatais cultivated in the minilysimeters did not differ statistically from the one obtained in the lysimeters with constant groundwater table operating with modified Irrigâmetro, at the different freatic levels investigated. The efficiency of the use of water of the grass-batatais obtained in the lysimeters and minilysimeters with constant groundwater table, operating with modified Irrigâmetro, did not vary significantly from the one obtained in the drainage lysimeter.

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