Visualizing NH emission and the local O and pH microenvironment of soil upon manure application using optical sensors.

The application of fertilizers and manure on fields is the largest source of ammonia (NH) in the atmosphere.·NH emission from agriculture has negative environmental consequences and is largely controlled by the chemical microenvironment and the respective biological activity of the soil. While gas phase and bulk measurements can describe the emission on a large scale, those measurements fail to unravel the local processes and spatial heterogeneity at the soil air interface. We report a two dimensional (2D) imaging approach capable of visualizing three of the most important chemical parameters associated with NH emission from soil. Besides the released NH itself also O and pH microenvironments are imaged using reversible optodes in real-time with a spatial resolution of <100 µm. This combined optode approach utilizes a specifically developed NH optode with a limit of detection of 2.11 ppm and a large working range (0-1800 ppm) ideally suited for studying NH volatilization from soil. This NH optode will contribute to a better understanding of the driving factors for NH emission on a microscale and has the potential to become a valuable tool in studying NH dynamics.