Instrumentação como suporte ao manejo racional da água na cultura da alface irrigada

Abstract

The demand for water exceeds its natural availability, notably in semi-arid regions, since it is a limited resource and such demand is increasing every day due to population and economic growth, with irrigated agriculture being the main consumer of the resource. Thus, improvements in water use efficiency become necessary, which can be achieved by monitoring soil moisture from low-cost and easy-to-handle systems. So, this research aims to employ microcontrollers associated with sensors of soil moisture, flow and water volume, for irrigation management in lettuce (Lactuca sativa L.) in the municipality of Nossa Senhora da Glória, region of semi-arid climate, in the State of Sergipe, as a support tool for optimizing the use of irrigated water in family farming. The system consists of a SCADA system, USB/RS-485 and RS-485/TTL converter modules, Arduino microcontroller, HD-38 humidity sensors, YF-S201 flow/volume sensor, Lm2596 step-down voltage regulator and cable 24AWG twisted pair network. The system was able to meet the objectives by monitoring the variables of soil moisture, accumulated volume and the operation of the network (scan) and, together with the SCADA system, allowed greater organization and treatment of data through analysis and graphical comparisons. Soil characteristics (texture and water retention curve) were analyzed to then proceed with the calibration of the sensors. For the calibration of the humidity sensor, the direct gravimetric method (stove standard) was adopted to determine the humidity, whose results were compared with those provided by the sensors. With the humidity data and the analog signal, calibration curves were constructed using linear interpolation. The quadratic models obtained to estimate soil moisture in the region were considered significant at the 95% probability level, adequately representing the relationship between the soil moisture variables and the resistive sensor response, in terms of analog output signal. The two cultivation cycles lasted 60 days, between sowing, transplanting and harvesting. The irrigation system used was located by gravity drip. Irrigation depths were applied using a striped experimental design. The lettuce culture responded significantly to all the blades applied in the first cycle, being the blade of 480 mm the one that presented the best results for the analyzed variables: plant fresh mass, aerial part fresh mass, lettuce head diameter, SPAD index, chlorophyll, root dry mass, shoot dry mass, stem diameter and number of leaves. There was greater water consumption in the second cycle, when irrigation was based on system information, however, there was a significant increase in the number of leaves per plant, an important commercial characteristic. Thus, the insertion of a system that monitors soil moisture and equipment that can generate information with accuracy and low cost, will help family farming to play a socioeconomic and cultural role, seeking to strengthen the interaction of man with the environment, adapting it to a sustainable model, with the application of disruptive technology in irrigation management.