On-the-go tropical soil sensing for pH determination using ion-selective electrodes

Abstract

The objective of this work was to assess the performance of an antimony ion-selective electrode (ISE) sensor system, using manual and automatic operating modes, for measuring the potential of hydrogen (pH), in real time, in Oxisols with different characteristics. Samples were manually collected and sent to a laboratory for determination of pH in water and calcium chloride, whose values were used as references. Another set of samples was also automatically collected using a commercial equipment, and readings were performed in manual mode. The performance parameters of the sensor system were calculated and evaluated. Part of the soil samples was used to assess the degree of influence of moisture in determining pH. Calibration lines were constructed. The statistical analysis revealed better results for the manual mode. Both modes of operation had errors superior to those accepted as a limit in laboratory techniques, however, with the possibility of high data density and with positive and promising results. Soil moisture interfered with the result of the readings. The sensor system yields a sampling density of 45 data per hectare, which represents a great contribution to the intensification of data for a better spatial evaluation of soil information.

Sensor Systems for Mapping Soil Fertility Attributes: Challenges, Advances, and Perspectives in Brazilian Tropical Soils

“…In Brazilian soils, electrochemical sensors for pH prediction were evaluated by Silva and Molin (2018) and Eitelwein et al (2016), who both used the pH Manager equipment. These authors applied different methodologies to compare the ISE performance and the results found by both were divergent and ranged from good (R² > 0.8) to weak (R² < 0.1) predictions.…”

Precision Agriculture in Brazil: The Trajectory of 25 Years of Scientific Research

“…Starting in the 2000s, many studies have been conducted in Brazilian soils to evaluate proximal and remote sensing techniques to characterize agricultural fields with a high spatial density of information [57,58]. Studies evaluating proximal soil sensing techniques have mainly covered apparent electrical conductivity (ECa) sensors [59], with few studies evaluating on-the-go applications of ion-selective electrodes (ISE) [60] and the diffuse reflectance spectrometers that work in the visible and near infrared (Vis-NIR) regions [61]. Most studies have evaluated the predictive performance of these sensors for determining soil attributes of agronomic interest.…”

The effect of soil moisture content and soil texture on fast in situ pH measurements with two types of robust ion-selective electrodes

“…Furthermore, they observed a strongly increased dispersion of the pH measurements at low SMC. Another study on Oxisoles in São Paulo (Brazil) by de Souza Silva and Molin (2018) reported that SMC interferes with the readings of antimony pH ISEs in the manner that pH values proportionally increased with increasing SMC by about 0.9 units. Thus, they concluded that SMC should be considered an issue when measuring pH in situ.…”

“…Previous studies have investigated the effect of varying SMC on the pH measurement on different soils (Schaller and Fischer, 1981;Adamchuk et al, 1999;Kahlert et al, 2004;Oliviera et al, 2018;de Souza Silva and Molin, 2018;Patil et al, 2019). However, most of the studies have been carried out with glass electrodes and detailed evaluation of antimony electrode performance at low moisture regimes in different soil textures is lacking.…”