- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
Microdialysis fluxes of inorganic nitrogen differ from extractable nitrogen by minimising disturbance of mineral-associated sources
Buckley, Scott; Allen, Diane; Brackin, Richard; Schmidt, Susanne
Measuring soil nitrogen (N) provides important information for ecosystem productivity and improving N use efficiency in agricultural systems. Conventional means of sampling N using soil extractions disturb soil structure and function, and likely distort accurate quantification. In situ microdialysis is a novel sampling method that generates differing N profiles compared to soil extractions. Here we test the hypothesis that differences observed between sampling methods are due to the minimal disturbance and sampling of a mobile N fraction when using microdialysis, with discernible patterns expected across soils with distinct clay and organic matter contents. In a short-term laboratory microcosm experiment with 21 sugarcane cropping soils, we compared salt (potassium chloride; KCl) or aqueous (H2O) extractants and microdialysis. KCl-extractable ammonium (NH4+) was highly correlated with the content of clay, total N and carbon, indicative of bound N being solubilised. In contrast, NH4 (+) contributed significantly less to microdialysis fluxes and was not correlated with the measured soil properties, which we attribute to minimal disturbance of bound N center dot H2O extracts sampled proportionally more NH4 (+) than microdialysis but were significantly correlated with fluxes. This suggests that while microdialysis and H2O extraction sample from a dissolved N pool, H2O extracts sample from an additional pool of loosely-bound NH4+. Nitrate (NO3) measures were correlated between methods, but shared no relationship with the measured soil properties, indicating that NO3 sampling is less affected by the disturbance introduced by extractions. We conclude that sampling inorganic N is biased by the degree to which soil sampling methods disturb adsorbed N sources with implications for interpreting soil N measurements.
Inorganic nitrogen; Microdialysis; Soil extractions; Nitrogen sampling; Nitrogen measurement
2023, Volume: 435, article number: 116510
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