Perspectives and methodological challenges of imaging soil hotspots and coupling soil images of different origin in multi-imaging approach

Soil imaging visualizes and quantifies processes in soil hotspots across space and time involving microorganisms, roots and carbon and nutrient sources, thereby helping to elucidate mechanisms. A wide range of individual approaches exists to determine spatial distributions of soil pH (optodes), root exudation and pesticides (14C phosphor imaging), fertilizers (33P phosphor imaging), nutrient fluxes (DGT), etc.Since processes and mechanisms are clearly multi-factorial, combining individual approaches is key for any real understanding of soil processes. Multi-imaging comes with a set of challenges as firstly, scales need to be bridged as imaging methods operate at different spatial scales from cm to nm. Secondly, their time scales vary from minutes to days. Thirdly, the sequence of method application needs careful consideration as some methods leave behind chemicals, which may interfere with other measurements.Imaging methods were initially developed for laboratory-controlled conditions, and only several were already adapted for field conditions. We will present the challenges for application soil imaging techniques in the field and problems related to sequential application. We will suggest a workflow for multi-imaging, which includes suggestions on coupling methods to study defined soil process, the sequence of the methods application, image alignment, hotspot thresholding and analysis, co-localization of images and quantitative image analysis. The perspectives, advantages and challenges of multi-imaging approaches will be comprehensively discussed.