Abstract

Background and aim:The diffusion of inorganic nitrogen (N) in soils is strongly affected by their physical characteristics and hydraulic gradients, which enable them to store and transport nutrients over time and space. The objective of this research was to use the microdialysis technique to continuously monitor the diffusive fluxes of inorganic N from the physical N store towards root surfaces in two volcanic soils after soil rewetting. Methods:Undisturbed soil samples were collected in metallic cylinders (230 cm(3)) at four depths (0-20, 20-40, 40-70, 70-100 cm) in two distinct volcanic soils (Andisol and Ultisol) that are used in agriculture. Diffusive N fluxes were determined during continuous drying and rewetting cycles (0 to 100 kPa) of intact undisturbed soil cores. Soil water content (SWC) at each water potential was calculated. Results and Conclusions:DiffusiveNO3-fluxes increased significantly (p< 0.001) after rewetting in both soils: 16-fold in the Andisol, from 32.7 +/- 12.1 to 541.5 +/- 306.5 nmol N cm(-2)h(-1)(34 to 62% SWC) and 66-fold in the Ultisol, from 65.6 +/- 25.8 to 4298.7 +/- 1289.9 nmol N cm(-2)h(-1)(31 to 58% SWC) in the upper 20 cm of the soils. In addition, diffusiveNO3-fluxes decreased with depth in both soils. We found that the residence time of availableNO3-in these soils strongly depended upon actual SWC and thereby the functionality of the pores in the system. We propose that the ability of the porous system to transport water throughout the soil profile is a relevant parameter within N diffusion, since it allows us to estimate the increase or decrease of diffusiveNO3-fluxes as a function of the soil water content during continuous drying and rewetting cycles.