Hydraulic weighing lysimeters have been widely used and improved to minimize operational problems, and provide good accuracy for detection of changes in soil water content under field conditions. The objectives of this study were to construct, install and calibrate a hydraulic weighing lysimeter with a hydrostatic pressure sensor for automation of readings, and analyze its performance as compared to the traditional reading system with mercury Lima, et. al. 541Irriga, Botucatu, v. 18, n. 3, p. 540-557, julho-setembro, 2013 piston. The lysimeter consisted of a tank with internal glass fiber, circular edge area of 1.32 m² and volume of 1 m³, and a weighing system with three hydraulic flexible pillow of butyl nylon 100 mm in diameter. Calibration was conducted in known mass containers, which represented a range of mass variation of 50 mm. The results showed high linearity between mass variation and the sensor and manometer readings. Accuracy of 0.135 mm ETo recorded by the pressure gauge and up to 0.061 mm ETo by the sensor showed that the pressure sensor is more sensitive to mass variations than the lysimeter. Errors associated with hysteresis, estimates of mass variation and the average positional error were higher in the manometric system.

A B S T R A C TThis study aimed to evaluate the effect of salt stress on production and antioxidative defense metabolism of two bell pepper cultivars (Capsicum annuum L.) grown hydroponically. The experimental design was in randomized blocks, with treatments arranged in a 5 x 2 factorial scheme with five replicates. The treatments consisted of five salinity levels of the nutrient solution (2.0, 3.5, 4.5, 5.5 and 6.5 dS m -1 ) with two bell pepper cultivars, 'Bruno' and 'Rúbia' . Biomass and yield were reduced with increasing salinity. The contents of chlorophyll a, b and total decreased with increasing salinity. There was an increase in proline content and activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), showing the activation of the antioxidant defense mechanism. The higher yield in the cv. 'Rúbia' , as well as the greater activity of the APX and the lower levels of chlorophyll content, reflect the best acclimatization of this cultivar to saline stress. The estimated yield of the cv. 'Rúbia' , 39.9 t ha -1 when grown with ECs of up to 3.5 dS m -1, indicates the feasibility of its commercial cultivation in hydroponic conditions. Produção e metabolismo antioxidativo em pimentão cultivado com água salina em sistema hidropônico R E S U M O Este trabalho foi realizado com o objetivo de avaliar o efeito do estresse salino sobre a produção e o metabolismo de defesa antioxidativa de duas cultivares de pimentão (Capsicum annuum L.), cultivadas em sistema hidropônico. O delineamento experimental foi em blocos casualizados, com os tratamentos arranjados em esquema fatorial 5 x 2, com cinco repetições. Os tratamentos consistiram da combinação de cinco níveis de salinidade da solução nutritiva (2,0; 3,5; 4,5; 5,5 e 6,5 dS m -1 ) com duas cultivares de pimentão (Bruno e Rúbia). A biomassa e a produção foram reduzidas com o incremento da salinidade. Os teores de clorofila a, b e total, diminuíram com o aumento da salinidade. Houve aumento no teor de prolina e na atividade das enzimas superóxido dismutase (SOD), catalase (CAT) e ascorbato peroxidase (APX), evidenciando a ativação do mecanismo de defesa antioxidativo. A maior produção de frutos na cv. Rúbia, bem como a maior atividade da APX e os menores teores de clorofilas refletem a melhor aclimatação desta cultivar ao estresse salino. A produtividade estimada da cv. Rúbia, 39,8 t ha , indica a viabilidade de seu cultivo comercial em condições hidropônicas.

Irrigation with brackish water is common in the semiarid region of the Brazilian Northeast, potentiating the process of salinization of the soil in these areas. The hydroponic system stands out as an important strategy for crop management in semiarid regions, since crops show greater tolerance to the salt stress under hydroponic conditions, which minimize the effects of soil salinization. Thus, the objective of this work was to evaluate the effects of salt stress on the growth, fruit yield and mineral nutrition of sweet pepper in hydroponic system, using brackish water and coconut fiber substrate. The experiment was conducted in Recife, State of Pernambuco, Brazil (8°3'15''S, 34°52'53''W). A randomized block experimental design in a 5x2 factorial arrangement with five replications was used, consisting of five water salinity levels of the nutrient solution (2.0; 3.5; 4.5; 5.5 and 6.5 dS m-1) and two sweet pepper cultivars (Bruno and Rubia). The increasing salinity level of the nutrient solution decreased the fruit yield of the cultivars evaluated, reduced the potassium, phosphorus and sulfur, and increased the sodium and chlorine contents in the leaf tissues. The Ca contents of the cultivar Bruno decreased with increasing salinity, and increased in the cultivar Rubia. The cultivar Rubia stood out with the highest fruit yield and ionic selectivity, accumulating high amounts of potassium and calcium and maintaining low Na and Cl contents. The fruit yield of the cultivar Rubia (39.9 t ha-1) grown under solution with electrical conductivity of up to 3.5 dS m-1, denotes the potential viability of growing this cultivar under hydroponic conditions.

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DESEMPENHO DE UM LISÍMETRO DE PESAGEM HIDRÁULICA COM DIFERENTES SISTEMAS DE LEITURA  ANTÔNIO HENRIQUE CARDOSO DO NASCIMENTO1; SUZANA MARIA GICO LIMA MONTENEGRO2; JOÃO AUDIFAX CÉSAR DE ALBUQUERQUE FILHO3; ÊNIO FARIAS DE FRANÇA E SILVA3 E NADIELAN DA SILVA LIMA3 1Unidade Acadêmica de Serra Talhada – UAST. Avenida Gregório Ferraz Nogueira, S/N Bairro: José Tomé de Souza Ramos CEP: 56909-535 - Serra Talhada / PE. E-mail: tonyagronomia@gmail.com2Departamento de Engenharia Civil/UFPE, Av. Acadêmico Hélio Ramos, s/n. Cidade Universitária. CEP 50.740-530. Recife, PE. Fone: (81) 2126 7216. E-mail: suzanam@ufpe.br3Departamento de Engenharia Agrícola/UFRPE. R. Dom Manoel de Medeiros, s/n, Dois Irmãos, CEP 52.171-900, Recife, PE. Fone: (81) 3320-6264. E-mails: jaudifax@dtr.ufrpe.br; enio.silva@pq.cnpq.br; nadielanlima@hotmail.com  1 RESUMO A lisimetria de pesagem é reconhecidamente a melhor técnica para determinar a evapotranspiração das culturas, sendo adotada como metodologia padrão para servir de referência na avaliação de outros métodos e para calibrar modelos de estimativa da evapotranspiração em diferentes culturas. Neste sentido, objetivou-se com o trabalho analisar o desempenho de lisímetro de pesagem hidráulica por meio de calibrações ao longo de um ano e através de estimativas de erros de medidas utilizando dois sistemas de pesagem: um sistema automatizado e o outro com sistema de leitura manual. O trabalho foi conduzido em Recife, no campus da Universidade Federal Rural de Pernambuco, no litoral de Pernambuco. A metodologia empregada na instalação e na calibração do lisímetro foi adequada, com coeficiente de determinação de 0,99 na equação de calibração. A relação entre a variação de massa e resposta na voltagem da célula de carga e/ou leitura no manômetro do lisímetro é descrita adequadamente por modelo linear com mínima histerese. O lisímetro de pesagem hidráulica, independente do sistema de leitura, obteve excelente estabilidade, sensibilidade, resolução e exatidão, ao longo de um ano, detectando variações de massa devido à chuva, irrigações e evapotranspiração nos momentos de calibração e durante o ano, mostrando-se adequado para a estimativa de demanda hídrica. Palavras-chave: evapotranspiração de referência, leitura manual, leitura automática.  NASCIMENTO, A. H. C; MONTENEGRO, S. M. G. L.; ALBUQUERQUE FILHO, J. A. C.; SILVA, E. F. F.; LIMA, N. S.ANNUAL PERFORMANCE OF A weighing lysimeter HYDRAULIC SYSTEMS WITH DIFFERENT READING  2 ABSTRACT The weighing lysimeter is recognized as the best technique to estimate evapotranspiration of crops, being adopted as standard reference method in the evaluation of other methods and to calibrate models to estimate evapotranspiration from different crops. In this sense, the objective of the present work is to analyze lysimeter performance through calibrations over a year and through estimates of measurement errors using hydraulic weighing lysimeters with two weighing systems: an automated system and another system with manual reading. The work was conducted in Recife, in the Federal Rural University of Pernambuco ( 8°01'05" south latitude, 34°56'48" west longitude, at an altitude of 6,4m).The methodology used in the lysimeter installation and calibration was adequate, resulting in a coefficient of determination of 0.99 in the calibration equation. The relationship between weight change and response to the load voltage and / or reading on the lysimeter cell gauge  is adequately described by a linear model with minimal hysteresis. The hydraulic weighing lysimeter, independent of the reading system showed excellent stability, sensitivity , resolution and accuracy over a year having detected variations in mass due to rain, irrigation and evapotranspiration , being suitable for the estimation of water demand. Keywords: reference evapotranspiration, manual reading, automatic reading.