Comparative investigation on soil nitrate-nitrogen and available potassium measurement capability by using solid-state and PVC ISE

• Novel graphene-based bilayer solid-state nitrate and potassium ISEs were evaluated.
• Comparative studies on solid-state and PVC ISEs were conducted in soil extracts.
• The working settings for each ISE were identified in soil measurement.

Soil macronutrient monitoring is of crucial importance for fertilizer recommendation and site-specific fertilization. Compared to the conventional methods, ion-selective electrode (ISE) shows advantages on its rapid response, inexpensive cost and simple operation. In this study, two kinds of novel solid-state ISEs (S-ISEs) were manufactured and evaluated. In standard solution measurement, quasi-ideal Nernstian performances were observed on both of the monolayer and bilayer S-ISEs. Besides, S-ISEs demonstrated the faster response time of less than 30 s, which was 60% time reduction of the conventional PVC polymeric ISE (PVC-ISE). The bilayer S-ISE illustrated more stable potential responses than the monolayer S-ISE in the continuous 500 s detection. In soil extract measurement, the nitrate bilayer S-ISE provided the smallest absolute error(AE) of 6.8 mg L−1 among the tested three ISEs. The potassium bilayer S-ISE generated the similar testing ability as the monolayer S-ISE and PVC-ISE. In soil slurry measurement, obvious disturbance was placed on all of the tested ISEs. Thus, the filtration was an necessary operation of soil pretreatment for the ISE-based soil detection. More soil samples of a broader geographical area should be tested for the validation of the applicability of S-ISEs.