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Development and application of the diffusive gradients in thin films technique for the measurement of nitrate in soils

Research output: Contribution to journalJournal articlepeer-review

<mark>Journal publication date</mark>17/01/2017
<mark>Journal</mark>Analytical Chemistry
Issue number2
Number of pages7
Pages (from-to)1178-1184
Publication StatusPublished
<mark>Original language</mark>English


Nitrate (NO3−N), the main plant/microbial nitrogen source, has a fast turnover in soil driven by species transformation (nitrification/denitrification) and phyto/microbiota assimilation. The technique of diffusive gradients in thin films (DGT) is capable of a robust, low disturbance measurement of NO3−N but has not been implemented due to the absence of a binding layer suitable for deployment in soils. In this study, a new styrene divinylbenzene-based absorbent with amine functional groups (SIR-100-HP) was cast into an agarose gel support. The NO3−N ion selectivity of the SIR-100-HP/ agarose binding layer was retained in the presence of high multivalent ion concentrations and was used successfully to acquire in situ NO3−N measurements in bulk soil. The kinetics of binding and the maximum binding capacity were determined. The total capacity of the DGT containing the SIR-100-HP/agarose binding phase was 667 μg of NO3−N. The performance of DGT was not affected by varying pH (3−8) or ionic strength (0−0.018 mol L−1), while anion competition effects at concentrations reflecting those in common agricultural soils were found to be negligible. Complete elution (100% efficiency) of NO3−N from the binding phase was achieved using a solution of 5% NaCl. This technique was validated in three contrasting soils. CDGT measurements were in excellent agreement with pore water NO3−N values. Two-dimensional NO3−N mapping of a profile of flooded rice paddy soil demonstrated the potential of this novel methodology for improved characterization of in situ N speciation for further understanding of bioavailability and biogeochemical processes of NO3−N in soils.