Measurement of Water Matriial Potential in the Soil Through Instrumented Tensiometers with Pressure Sensors and Puncture Device
Authors: De Queiroz Tadeu Miranda , De Matos Rigoberto Moreira , Seabra Júnior Santino , Vieira Carlos Luiz , Fagundes Minéia Cappellari 
Published: August 2023

Objective: The search for a practical and accessible solution for measuring water tension in the soil using tensiometers is fundamental for irrigation management, efficient use of water and increased profitability of irrigated crops. The objective of this study was to propose a technique based on the instrumentation of a tensiometer with a pressure sensor and a device for reading the sensor's response.

Theoretical Frame: This study used the following main quotes as a theoretical basis: Freescale and NPX Semiconductors manufacturers of pressure sensors, Azevedo & Silva for the soil water tension correction methodology and Van Genuchten to describe the relationship between soil water content and suction.

Method: Pressure transducers with a range of 0-50 and 0-100 kPa were used, with an analog signal varying between 200 and 4700 mV, whose response was measured by a digital multimeter with the scale adjusted to V or mV. The transducer was adapted by attaching a hypodermic needle Nº 7/30 to the vacuum measurement inlet, leaving the other inlet free for the atmosphere. The transducer was powered by a 9 Vcc battery with rectified voltage to 5 Vcc through a specific integrated circuit for this function. The conversion of the transducer response signal in mV to voltage in kPa was performed using the response function informed by the manufacturer, reversing the order of the variables so that the voltage could be measured as a function of the output signal in mV. The system was used to measure the water tension in the soil of tensiometers installed in an area cultivated with tomatoes in a greenhouse during a complete cycle, functioning satisfactorily.

Results and conclusions: During the experimental period, the water tension in the soil observed with the new tensiometer with pressure sensor and sensor response reading device ranged from 0.00 kPa (minimum tension) to 53.33 kPa (maximum tension) in the two soil layers. analyzed soil, while the average tension was 23.64 kPa in the 0-20 cm soil layer and 21.38 kPa in the 20-40 cm layer. Soil moisture obtained from soil water tension and soil water retention curve ranged from 0.11 (minimum) to 0.50 m3 m-3 (maximum) in both studied soil layers, while that the average soil moisture in the depth from 0 to 20 cm was 0.21 m3 m-3 and from 20 to 40 cm was 0.20 m3 m-3. The instrumented tensiometer with pressure sensor and sensor response reading device makes it possible to satisfactorily determine the matrix potential of water in the soil. The matriial tension data obtained with the new pressure sensor are consistent with reports in the literature as adequate to provide higher yields in tomato cultivation. The technique and instrumentation proposed in this study allows measuring the water tension in the soil, knowing the soil moisture and carrying out irrigation management, applying an irrigation depth according to the needs of the plants, making a more efficient use of water and providing water and electricity savings.

Implications of the research: This study qualifies as being of great relevance for the purposes of the Department of Agronomic Engineering at the Universidade do Estado de Mato Grosso, Nova Mutum Campus, as well as for the entire academic and scientific community and rural producers interested in tensiometers to carry out a management of water from the soil and farm sustainably.

Originality and value: The study sought to present to the academic, scientific and rural producers community a practical and accessible solution for measuring the water tension in the soil through tensiometers, thus providing current information on a new instrument for irrigation management, which makes it possible to carry out a more efficient use of water and increase the profitability of irrigated crops.