title: Development and Application of the Diffusive Gradients in Thin Films Technique for the Measurement of Nitrate in Soils.
abstract: 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. CDGTmeasurements 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.
authors.affiliation: Key Laboratory of Urban Environment and Health Institute of Urban Environment, Chinese Academy of Sciences , Xiamen 361021, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Cai
authors.affiliation: Key Laboratory of Urban Environment and Health Institute of Urban Environment, Chinese Academy of Sciences , Xiamen 361021, China.|Lancaster Environment Centre, Lancaster University , Lancaster LA1 4YQ, U.K.|Institute for Global Food Security, Queen's University Belfast , David Keir Building, Malone Road, Belfast BT9 5BN, Northern Ireland, U.K.
authors.forename: Paul N
authors.identifier: 0000-0002-0723-7997
authors.initials: PN
authors.lastname: Williams
authors.affiliation: Lancaster Environment Centre, Lancaster University , Lancaster LA1 4YQ, U.K.
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.affiliation: Lancaster Environment Centre, Lancaster University , Lancaster LA1 4YQ, U.K.
authors.forename: William
authors.initials: W
authors.lastname: Davison
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing, Jiangsu 210023, China.
authors.forename: Tian-Jiao
authors.initials: TJ
authors.lastname: Wei
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing, Jiangsu 210023, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Luo
authors.affiliation: Key Laboratory of Urban Environment and Health Institute of Urban Environment, Chinese Academy of Sciences , Xiamen 361021, China.
authors.forename: Yong-Guan
authors.initials: YG
authors.lastname: Zhu
authors.affiliation: Lancaster Environment Centre, Lancaster University , Lancaster LA1 4YQ, U.K.
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000327:Adsorption; D000383:Agriculture; D000837:Anion Exchange Resins / Q000737:chemistry*; D004058:Diffusion; D004784:Environmental Monitoring / Q000379:methods; D007700:Kinetics; D009566:Nitrates / Q000032:analysis*; D009994:Osmolar Concentration; D012685:Sepharose / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D020058:Styrene / Q000737:chemistry*; D014753:Vinyl Compounds / Q000737:chemistry*
chemical_list: D000837:Anion Exchange Resins; D009566:Nitrates; D012987:Soil; D014753:Vinyl Compounds; D020058:Styrene; D012685:Sepharose; C004985:divinyl benzene