Image-based quantification of soil microbial dead zones induced by nitrogen fertilization

Area of Science:

• Soil Science
• Microbiology
• Environmental Science

Background:

• Microbial communities are vital for soil ecosystem services.
• Fertilization's impact on soil microbial health is not fully understood.
• Nitrogen (N) transport dynamics in soil are complex.

Purpose of the Study:

• To investigate spatial and temporal dynamics of nitrogen transport from fertilizer granules at the pore scale.
• To examine how soil structure and moisture influence nitrogen movement and microbial communities.
• To model nitrogen transport and reactions within the soil pore network.

Main Methods:

• Developed a pore-scale mathematical model for nitrogen transport and reactions.
• Used X-ray Computed Tomography to reconstruct soil pore geometry.
• Simulated nitrogen speciation (ammonium, nitrate, DON) and cycling under varying water saturations.
• Measured microbial activity at different nitrogen concentrations for validation.

Main Results:

• Nitrogen diffusion and concentration are critically dependent on soil moisture and species.
• Predicted high ammonium and nitrate concentrations near fertilizer pellets, especially under dry conditions.
• Modeled nitrogen concentrations can significantly inhibit microbial activity in the short term (0.9-3.8 mm zone).

Conclusions:

• Pore-scale processes are crucial in regulating nitrogen movement in soils.
• Fertilizer-induced nitrogen concentrations can disrupt soil microbiome functioning.
• Understanding pore-scale nitrogen dynamics is essential for sustainable agricultural practices.