Assessing Soil Nitrogen Availability using Microdialysis‐Derived Diffusive Flux Measurements

Abstract

Microdialysis‐based soil sampling offers a potential alternative to traditional soil core extractions that better informs about the availability of nitrogen (N) for plant nutrition. This study compared soil N status, as estimated using 0.5 M K2SO4 and distilled water extractions, with microdialysis‐derived diffusive flux measurements in eight grassland soils up an altitudinal gradient. Soil extracts and microdialysis samples were analyzed for plant‐available N: total free amino acids, NH4+, and NO3−. In terms of the percentage contribution that amino acids, NH4+, and NO3− made to total plant‐available N, the microdialysis‐derived diffusive flux measurements were most similar to distilled water extractions. However, the relative magnitude of the diffusive flux measurements did not always reflect the pool sizes as estimated by the soil extractions, which suggests that the availability of N to plants, via diffusion, may be decoupled from concentration in these soils. The potential and limitations of microdialysis sampling and the implications of the results for soil N management are discussed.