Abstract
Soil nitrate–nitrogen (NO3−-N) is one of the primary factors used to control nitrogen topdressing application during the crop growth period. The ion-selective electrode (ISE) is a promising method for rapid lower-cost in-field detection. Due to the simplification of sample preparation, the accuracy and stability of ISE-based in-field detection is doubted. In this paper, a self-designed prototype system for on-site soil NO3−-N detection was developed. The procedure of spinning centrifugation was used to avoid interference from soil slurry suspension. A modified Nernstian prediction model was quantitatively characterized with outputs from both the ISE and the soil moisture sensor. The measurement accuracy of the sensor fusion model was comparable with the laboratory ISE detections with standard sample pretreatment. Compared with the standard spectrometric method, the average absolute error (AE) and root-mean-square error (RMSE) were found to be less than 4.7 and 6.1 mg/L, respectively. The on-site soil testing efficiency was 4–5 min/sample, which reduced the operation time by 60% compared with manual sample preparation. The on-site soil NO3−-N status was dynamically monitored for 42 consecutive days. The declining peak of NO3−-N was observed. In all, the designed ISE-based detection system demonstrated a promising capability for the dynamic on-site monitoring of soil macronutrients.
Highlights
The ion-selective electrode (ISE) transfers the ionic activity of the target ion dissolved in testing solutions into electromotive force (EMF)
The measured EMF is related to the logarithm of the ionic activity according to the Nernst equation
Both the NO3 − ISE and soil moisture sensor were employed as the sensing unit
Summary
The ion-selective electrode (ISE) transfers the ionic activity (or concentration) of the target ion dissolved in testing solutions into electromotive force (EMF). ISE based laboratory soil NO3 − -N detection demonstrated good accuracy with standard deviations ranging from 8.04 to. The testing error, produced by “soil particle suspension disturbance”, reached a magnitude of 26.6 mg/kg with an average relative error of 50% according to our preliminary laboratory validation of ISE-based NO3 − -N detection with 15 soil samples [12]. For the purpose of improving the accuracy of on-site soil NO3 − -N detection, a self-designed prototype system was designed by making use of the sensor fusion method Both the NO3 − ISE and soil moisture sensor were employed as the sensing unit. The specific objectives were, first, to integrate necessary soil pretreatment steps, e.g., sample weighting and extractant spinning centrifugation into an on-site testing bench.
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