Calibração de sensores de umidade do solo de baixo custo

Abstract

The monitoring of soil moisture is of extreme importance for the correct management of agricultural activities, such as irrigation. There are several methods to perform this monitoring: direct methods and indirect methods. These methods have advantages and disadvantages with respect to each other, for example, the direct (gravimetric) method, or standard method has the advantage of being a cheap method, however it has the disadvantage of being a destructive and slow method in the acquisition of the data. Indirect methods, which enable instantaneous and accurate readings, have the disadvantage of the high cost of purchasing such equipment. In this way, there is a need for a soil moisture monitoring system using low cost sensors and equipment, which can be accurate and read in a short period of time. Therefore, the present work had the objective of calibrating soil moisture sensors of low cost in soils of different textures. For this, soil samples were collected and submitted to particle size analysis. In order to obtain samples with different textures. A soil with high organic matter content and hydrophobic character were also used to evaluate the effect of hydrophobicity on the functioning of the sensors. After that, calibration tests were carried out on 06 units of low cost sensors model HL-69. The calibration tests consisted of determining the soil moisture directly (gravimetric method) and at the same time the sensors were read for different soil water contents. After the calibration tests, the data were tabulated and processed in electronic spreadsheets, where from the means of the readings of the 06 sensors, equations of adjustments were obtained for each type of soil. The percentage errors of each sensor were also calculated with respect to the mean of each sensor for each texture. It was observed that, independently of soil texture, the sensors presented a stabilization of the reading when submitted to humidity above the field capacity of each soil. It was also noted that for soils of the same texture and at the same moisture level, each sensor presented a different reading, indicating the need for individual calibration of the same. In relation to soil with a high content of organic matter (hydrophobic), it was verified that the sensor readings were different from the soils without this characteristic. Thus, it is concluded that low-cost sensors have good sensitivity within the range of available soil water, and can be used for irrigation management. However, they require specific calibrations for each type of soil and also for each sensor, this need increases even more when dealing with soils with high levels of organic matter.