Irrigation controller mechanically actuated by soil-water tension: II--Field evaluations/Controlador de irrigacao mecanico acionado pela tensao da agua no solo: II--Avaliacoes em campo

In this study, a field evaluation of the performance of an irrigation controller mechanically actuated by soil-water tension (SWT) was performed. The controller employs a tensiometer used as a sensor of SWT to directly control a mechanically actuated hydraulic valve. Six controllers were installed in an orchard to control the irrigation for six rows of plants over 64 days. Each controller controlled the irrigation of one lateral drip line. The drip irrigation system was gravity-fed from a water source placed 7 m above the soil surface. The SWT and the pressure in each lateral line were measured to evaluate the performance of the controllers. All the controllers tested in the field autonomously initiated and terminated the irrigation during the evaluation. Irrigation events were initiated when values close to the set soil-tension values were reached and were terminated at lower soil-tension values. As the SWT in the root zone was maintained close to the setup threshold plus 20% tolerance for at least 90% of the evaluation period, the performance of the controllers was considered satisfactory. The proposed controller was shown to be functional and was operated effectively for an SWT range of up to 30 kPa, which is commonly encountered under high -frequency irrigation conditions. Key words: irrigation scheduling technological innovation tensiometer automation O objetivo deste trabalho foi avaliar, em campo, o desempenho de um controlador de irrigacao acionado mecanicamente pela tensao de agua no solo. O controlador utiliza um tensiometro como sensor da tensao de agua do solo para controlar diretamente uma valvula hidraulica acionada mecanicamente. Seis controladores foram instalados em um pomar para controlar a irrigacao de seis linhas de plantas durante 64 dias. Cada equipamento controlou a irrigacao de uma linha lateral. O sistema de gotejamento foi pressurizado por gravidade devido a uma fonte de agua localizada sete metros acima da superficie do solo. Todos os controladores testados no campo acionaram e desligaram a irrigacao autonomamente durante o periodo de avaliacao. Os eventos de irrigacao foram iniciados quando as tensoes de agua no solo atingiram valores estabelecidos e terminaram em baixos valores de tensao. O desempenho foi considerado satisfatorio, pois as tensoes de agua no solo foram mantidas dentro das faixas estabelecidas considerando-se uma tolerancia de 20% para pelo menos 90% do tempo. O controlador proposto mostrou-se funcional e operou