Equipment digitally measures water infiltrated into the soil

A partnership between Embrapa Soils (RJ) and the Brazilian Center for Physics Research (also in Rio de Janeiro)CBPF) developed an innovative solution for automating data collection in the field, more specifically on infiltration and water flow in the soil. It is a new permeameter - the most used equipment in the world to evaluate water conduction in soil - capable of collecting this data digitally, using a low-cost microcomputer. This reduces the time and costs of evaluating hydraulic parameters, which makes it possible to understand the process of water absorption by the earth. Institutions are now looking for a partner to produce the equipment on a large scale and place it on the market.

Measuring water infiltrated into the soil is essential to optimize irrigation, reducing water waste and erosion; and to estimate the collapse of slopes, helping to prevent and create more effective alarms and evaluate the behavior of land for the construction of roads or dams. 

However, the evaluation of soil hydraulic parameters has always been a challenge for researchers, basically for two reasons: the need for a technician trained in data collection and evaluation, which is time-consuming and expensive in terms of financial resources and time. Thus, one of the advantages of approaching the problem in an interdisciplinary way was articulating the expertise and experience of those who understand the soil problem (Embrapa Solos) with the application of intelligent sensors, digital control and signal conditioning tools (CBPF).

The new permeameter: digitalization in soil water measurement The most used equipment in the world to evaluate water conduction in saturated soils are well permeameters and, among these, one of the most popular is the Guelph Permeameter. It requires a professional to manually collect water flow data, which makes it possible to calculate the hydraulic conductivity of the soil. “The partnership between Embrapa and CBPF developed a new permeameter that makes this collection automated. With this device, the technician, who spent hours recording flow values, is freed up to carry out other assessments and collections, increasing the yield and efficiency of work in rural areas. Furthermore, the equipment has a reading accuracy of millimeters and a time record of tenths of a second, which increases the precision of the data collected”, says the researcher from Embrapa Solos Wenceslau Teixeira.  The Guelph is an analogue device with complex operation. The data is obtained by visually reading the variation in the level of a water column, using a millimeter scale and a stopwatch. The data is recorded manually in a notebook. This operation is carried out in the field, under the sun, and can take a long time. The operator is an expensive professional who needs qualifications to acquire the measurements and the results are later analyzed using spreadsheets. The progress of the new device comes from the fact that the measurements are obtained digitally, using a low-cost microcomputer. “In addition to measuring the variation in volume and time more precisely, recording it on a memory card and transmitting this data to a cell phone or tablet (via Bluetooth), the system calculates the magnitude immediately. If there is any inconsistency in the measurements, it is possible to identify them on site and do them again, without the need for a new, and costly, trip. The device simplifies the measurement operation, allowing its use by operators with less training, in addition to alerting to certain errors due to sudden temperature variations that were not considered in the traditional method”, reveals Geraldo Cernicchiaro, from CBPF.  It is worth remembering that CBPF has extensive experience in creating measurement sensors, especially those that are not yet available on the market.

The new permeameter: digitalization in soil water measurement

The most used equipment in the world to evaluate water conduction in saturated soils are well permeameters and, among these, one of the most popular is the Guelph Permeameter. It requires a professional to manually collect water flow data, which makes it possible to calculate the hydraulic conductivity of the soil. “The partnership between Embrapa and CBPF developed a new permeameter that makes this collection automated. With this device, the technician, who spent hours recording flow values, is freed up to carry out other assessments and collections, increasing the yield and efficiency of work in rural areas. Furthermore, the equipment has a reading accuracy of millimeters and a time record of tenths of a second, which increases the precision of the data collected”, says the researcher from Embrapa Solos Wenceslau Teixeira. 

The Guelph is an analogue device with complex operation. The data is obtained by visually reading the variation in the level of a water column, using a millimeter scale and a stopwatch. The data is recorded manually in a notebook. This operation is carried out in the field, under the sun, and can take a long time. The operator is an expensive professional who needs qualifications to acquire the measurements and the results are later analyzed using spreadsheets. The progress of the new device comes from the fact that the measurements are obtained digitally, using a low-cost microcomputer.

“In addition to measuring the variation in volume and time more precisely, recording it on a memory card and transmitting this data to a cell phone or tablet (via Bluetooth), the system calculates the magnitude immediately. If there is any inconsistency in the measurements, it is possible to identify them on site and do them again, without the need for a new, and costly, trip. The device simplifies the measurement operation, allowing its use by operators with less training, in addition to alerting to certain errors due to sudden temperature variations that were not considered in the traditional method”, reveals Geraldo Cernicchiaro, from CBPF. 

It is worth remembering that CBPF has extensive experience in creating measurement sensors, especially those that are not yet available on the market.

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An innovative approach

The challenge of digitizing this process was precisely identifying how to automate data collection. The Guelph methodology is based on digging a small well in the ground and vertically tipping a long closed cylinder of transparent polyurethane with water inside. The tendency of the water is to flow from the tube, due to gravity, and fill the well until the level covers the mouth of the tube. This causes a certain vacuum inside the tube, whose technical name is Mariotte reservoir. At a certain moment, the atmospheric pressure equals that resulting from the height of the water column and the vacuum inside the reservoir, and thus the water stops flowing. Due to the penetration of water into the ground, the water level in the well changes. Small air bubbles enter the reservoir, changing the pressure, and the liquid drops. Until you restore balance. In the manual method, a millimeter scale allows you to determine the variation in water level, and consequently its volume.

“Our approach was to include a pressure and temperature gauge, with the necessary precision to monitor the variation in vacuum in the Mariotte reservoir. This approach made process automation possible and our field and laboratory tests demonstrated its accuracy. From digitized data, we have access to a wide range of technological resources. A small microcontroller receives this information, an internal clock records the variations between the measurements and the moment of reading, and a program allows us to process, calculate, record and present the result on a display”, says Cernicchiaro, detailing the process.  

Field tests excite scientists After some tests with prototypes in the CBPF and Embrapa laboratories and grounds, the device was validated in the field, in two locations: São Luís (MA) and Lençóis Paulista (SP). “The results were excellent, which motivated us to publish an article in Journal of Hydrology reporting this achievement”, highlights Teixeira. The locations were chosen because they have different types of soil, which impacts water absorption. For example, in sandy soil, it is absorbed quickly. In clayey soil, absorption is slower and may even form puddles. Simply put, this means that different soils exhibit different behaviors regarding the liquid absorption process, and that these behaviors can be quantified.  One of the parameters associated with this behavior is saturated hydraulic conductivity. This parameter, characteristic of each soil, is the ratio between the volume of water absorbed per unit of time, when the soil is wet or, in technical terms, saturated.

Field tests excite scientists

After some tests with prototypes in the CBPF and Embrapa laboratories and grounds, the device was validated in the field, in two locations: São Luís (MA) and Lençóis Paulista (SP). “The results were excellent, which motivated us to publish an article in Journal of Hydrology reporting this achievement”, highlights Teixeira.

The locations were chosen because they have different types of soil, which impacts water absorption. For example, in sandy soil, it is absorbed quickly. In clayey soil, absorption is slower and may even form puddles. Simply put, this means that different soils exhibit different behaviors regarding the liquid absorption process, and that these behaviors can be quantified. 

One of the parameters associated with this behavior is saturated hydraulic conductivity. This parameter, characteristic of each soil, is the ratio between the volume of water absorbed per unit of time, when the soil is wet or, in technical terms, saturated. 

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The Embrapa/CBPF partnership is also involved in other challenges, such as the development of automated soil water potential sensors and the automatic collection of data in infiltrometers and evaporation tanks.