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. C_DGT 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.