Desenvolvimento de plataforma de coleta de dados de sonda térmica utilizando o método Granier

Abstract

In irrigation, in order to achieve high efficiency of water application, besides having an adequate system the conditions of culture, climatic and socio-environmental, the irrigant must have a good management plan. Determining when and how much to irrigate is a factor that has been studied by the academic community during the last decades, developing new methods and equipment. Among the methods used, the measurement of transpiration in plants to determine the amount of water to be replenaged by irrigation has gained prominence since the twentieth century. The method proposed by Granier (1985) that uses thermal dissipation probes to measure the flow of sap and indirectly the transpiration flow of plants, stands out because it is easy to construct and application. This work has as general objective the development of a platform for data collection of thermal probe, as specific objectives: to construct thermal probes in a platform for data acquisition, storage and transmission; calculate the sap flow index; evaluate this index for meteorological and physiological factors. The construction of the probes consisted of hypodermic needles and K-type thermocouples, inside, and filled with thermal paste. In the heated probe, a constantan wire was used as resistance to promote its heating. This heating originated from a constant electrical power. The hardware consisted of an Arduino Mega, 5V power supply circuits and current limiter. The software was developed in the Arduino IDE. In the evaluation of the index in relation to meteorological factors, the air temperature influenced the temperature of the probes, however, had low influence on the difference between the heated and reference probes. The rain caused noise in the values obtained in the thermal probes, due to the flow in the stem cause a reduction in temperature in the heated probe, eliminating the heating. The sap flow index showed a strong correlation between global radiation and reference evapotranspiration. In the evaluation of the index in relation to leaf water potential, a good correlation was found between the variables evaluated, with greater similarity in the early morning (8 am to 10 am) and in the late afternoon (4 pm to 6 pm). It was possible to calculate the sap flow index from the data from the thermal probes and according to the results of its evaluation with the meteorological and physiological factors it is possible to conclude that the probes have a high potential in the use as sap flow sensor and, consequently, in the estimation of water consumption by the plant and its hydric stress.