Time‐resolved in‐situ pH measurement in differently treated, saturated and unsaturated soils

Abstract

The pH-value is of utmost relevance for soil properties and functioning. Hence, a time-resolved in-situ measurement is mandatory but lacking. As an alternative, a two-probe pH electrode with gel-covered reference electrode was newly constructed and tested for a continuous, in-situ pH recording in saturated and unsaturated soil. This was done using samples from a set of 14 soils with different composition and pH CaCl 2 ranging from 3.5 to 7.5 in batch and repacked soil column experiments. In the latter, changes in pH and redox potential were monitored upon transport of citrate-phosphate buffer and pig slurry through the soil columns. The pH measurements were largely stable even upon substantial shifts in soil moisture content down to air-dry conditions. The results of the pH measurements agreed with standard methods using settled soil suspensions in electrolyte solutions and the conventional combination (single-probe) pH electrode. Testing the suspension effect, it was found that measuring pH directly in the soil is recommended. The pH measured in-situ was closest to pH values determined in 0.01 M CaCl 2 suspensions according to DIN ISO 10390 (DIN, 2005). The transport of citrate buffer and pig slurry as pH active substances through soil induced strong effects on the pH and in part on the redox potential; the reversible effects lasted over days, which may affect the mobility and speciation of nutrients and pollutants as well as microbial processes.

Pesticide contamination of the upper Elbe River and an adjacent floodplain area

“…The soil was determined to an Arenic Fluvisol (WRB 2015). The pHvalue of the soil was measured according to Thiele-Bruhn et al (2015) in the supernatant of a settled soil suspension with a soil/solution ratio 1:2.5 (water used as solute), which was stirred two times during 1 h measurement using a WTW pH 330i probe (Weilheim, Germany). The total organic carbon content (TOC) was analyzed using a Vario Max C instrument (Elementar, Langselbold, Germany).…”

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

“…In contrast, in the field, the measurement conditions are affected by spatially and temporally fluctuating soil moisture content (SMC), which is highly influenced by soil texture and topographic position. In addition to the mechanical stress and variable moisture conditions, in situ measurements can create problems due to losses of the inner aqueous electrolyte solution to the unsaturated soil, drying of the glass membrane and the suspension effect (Thiele-Bruhn et al, 2015). The suspension effect is named after the observation that pH readings are different from clear solutions of soil extracts (filtrates or the clear supernatant solution of suspensions) as compared to measurements in the sediments of a soil suspension (Essington, 2015).…”

A Comparison of Analytical Methods for the Determination of Soil pH: Case Study on Burned Soils in Northern Portugal

“…The literature describes a variety of techniques, including a robust methodology for obtaining the pH with modified glass sensors [19], one based on PVC for flow injection analysis [20] and antimony oxide [21,22], among others. Despite this variety of methods, the most used protocols are based on potentiometric measurement performed by glass or reference electrode.…”