Agricultural nitrogen (N) application to soils is the main source of atmospheric ammonia (NH3). Ammonia
negatively impacts the environment on a large scale. However, emissions of NH3 are affected by
spatiotemporal heterogeneities of soil parameters on a microscale. Some key parameters controlling
processes of the N cycle are soil oxygen (O 2) and pH. To better understand biogeochemical soil
processes, NH3 emissions and the interconnection of the ecospheres, we propose the application of
optical chemical sensors (optodes) in and above soils. The use of optodes in soil science is in its infancy.
In this laboratory-based study, we investigated the possibilities and challenges of using optodes in non-
waterlogged soils with the extended application of a recently developed NH3 optode along with pH and
O2 optodes in two different soils and with different fertilisers. Our intention is to help expand the use of
optodes in soil science. Our results demonstrated the possibility to visualise reductions of NH 3
concentrations by 76% and 87% from the incorporation of sludge compared to the surface application of
sludge. We showed from 2D measurements how soil pH and fertiliser composition correlate with NH3
volatilisation. Our measurements demonstrated that pH optodes can have advantages over conventional
methods when measuring pH in soils in situ but are challenged by the limited dynamic range (typically 3
pH units) compared to pH electrodes. Finally, we investigated the spatiotemporal dynamics of O2 at
different soil water contents and discuss potential challenges, which can lead to measuring artifacts.