Desenvolvimento dum sistema de rega automático, autónomo e adaptativo – estudo comparativo de cinco métodos para o cálculo da ETo

Para efeitos de desenvolvimento dum sistema de rega automático, são estudados e calibrados cinco métodos de cálculo de Evapotranspiração de referência (Priestley-Taylor, Makkink, Hargreaves, Turc, Jensen-Haise) utilizando apenas os parâmetros climáticos temperatura, T, e radiação solar, Rs. O estudo envolve o cálculo da Evapotranspiração para todos os dias do ano hidrológico 2005/06 e a sua comparação com o método de Penman-Monteith. A estação escolhida para o estudo é a estação de Divor. Nas condições do estudo (Sul da Península Ibérica) os melhores resultados são obtidos com os métodos de Priestley-Taylor e Jensen-Haise. São apresentados os coeficientes de calibração para todos os cinco métodos para a zona do estudo, por forma a aproximar ao máximo os resultados aos obtidos pelo método de referência.In order to develop an automatic irrigation system, a set of five different methods for calculating reference evapotranspiration are studied and calibrated (Priestley-Taylor, Makkink, Hargreaves, Turc, Jensen-Haise). These methods use temperature, T, and solar radiation, Rs, to calculate evapotranspiration. Evapotranspiration is calculated for all the days of the 2005/06 hidrological year at the Divor meteorological station. The results are compared to, and calibrated against, the Penman-Monteith method. The best results are obtained by the Priestley-Taylor and Jensen-Haise methods. Calibration coefficients are also calculated for all five methods, so that the results can be as close as possible to those produced by the Penman-Monteith method

Drip irrigation using a PLC based adaptive irrigation system

Most of the water used by man goes to irrigation. A major part of this water is used to irrigate small plots where it is not feasible to implement full-scale Evapotranspiration based irrigation controllers. During the growth season crop water needs do not remain constant and varies depending on the canopy, growth stage and climate conditions such as temperature, wind, relative humidity and solar radiation. Thus, it is necessary to find an economic irrigation controller that can adapt the daily water application to the plant needs. The dramatic development of Programmable Logic Controllers, PLCs, and their rather affordable price has made it possible to use them as stand-alone irrigation controllers. In this paper a PLC is used to adapt the daily irrigation amount to actual ETc, using a Hargreaves-Samani type equation. This equation only requires temperature values to calculate Evapotranspiration. Once the ETc is calculated, then the PLC manages the irrigation according to the characteristics of the field, the irrigation equipment and the growth stage of the crop. First year results are very encouraging and indicate a 12% saving in irrigation water. It was also found that heat flux form the soil can influence canopy temperature.The development of this study was funded by the Fundação para a Ciência e a Tecnologia (FCT) research project PTDC/AGR-AAM/81271/2006: “Desenvolvimento dum controlador de rega adaptativo, autónomo e automático”

Water saving with a PLC based adaptive irrigation system

Irrigation is presently the main user of world´s fresh water. Most of it goes to irrigating small plots where it is not feasible to implement full-scale Evapotranspiration based irrigation controllers. The dramatic development of Programmable Logic Controllers, PLCs, and their rather affordable price has made it possible to use them as stand-alone irrigation controllers. In this paper a PLC is used to adapt the daily irrigation amount to actual ETc, using a Hargreaves-Samani type equation. Once the ETc is calculated, then the PLC manages the irrigation according to the specifications given by the farmer. First year results indicate an 8% saving in irrigation water

Optimizing rain harvesting for Mediterranean climate

Most of the urban landscaped areas are watered with drinking water from the city utility. This represents a waste of energy used to pump the water all the way into urban areas, as well as a waste of chemicals and energy used to purify the water for human consumption. This paper analysis the feasibility of harvesting rainwater over buildings in Mediterranean climate, and storing them, for use in irrigation. The results indicate that a typical house can annually save between 3000 and 11000 l of water through rain harvesting. A simulation model is elaborated that can calculate optimize the relation between catchment area, irrigated area and tank size, based on daily rainfall and evapotranspiration of a five year period