Opportunities and future directions for visual soil evaluation methods in soil structure research

As the use of visual soil evaluation (VSE) methods has spread globally, they have been exposed to different climatic and pedological scenarios, resulting in the need to elucidate limitations, encourage refinements and open up new avenues of research. The main objective of this paper is to outline the potential of VSE methods to develop novel soil structure research and how this potential could be developed and integrated within existing research. We provide a brief overview of VSE methods in order to summarize the soil information that is obtained by VSE. More detailed VSE methods could be developed to provide spatial information for soil process models, e.g. compaction models. VSE could be combined with sensing techniques at the field or landscape scale for better management of fields in the context of precision farming. Further work should be done to integrate plant vigour, roots and soil fauna into VSE methods to provide general indicators of soil quality and for estimation of environmental risk factors related to soil C storage, GHG emissions and nutrient leaching, with particular reference to temporal changes. There is a great potential in combining (rather than comparing) VSE with measurements of soil structure, i.e. integrating VSE in soil structure and compaction research, as these methods provide spatial information that is difficult to obtain with other methods.