Visual soil evaluation: a summary of some applications and potential developments for agriculture

Visual soil evaluation techniques have gained popularity and are increasingly used in agriculture and soil science for research, consultancy and teaching purposes. We describe recent applications, developments, opportunities and limitations, mainly of the Visual Evaluation of Soil Structure (for topsoil (VESS) and for subsoil (SubVESS)), and of the Visual Soil Assessment (VSA). Data are taken from experiments on compaction and from assessments made in farmer's fields in the UK, Brazil and New Zealand. The methods are widely used to detect compaction and are well-suited for monitoring changes in compaction status, particularly in relation to weather extremes. VESS proved useful in distinguishing grazing vs wheel compaction in the UK and Brazil by permitting detection of layers at different depths within the topsoil zone. The depths of compact layers are important for scoring management decisions for soil improvement. However the use of scores as limiting thresholds in different soil types needs the back up of further soil measurements and/or additional visual assessments of soil and crop. VSA and VESS were also used to estimate the risk of significant soil emissions of nitrous oxide where compaction damage was present and rates of mineral N fertiliser were high. Visual assessments also have the potential to assess the risk of surface water runoff and nutrient loss. The potential role of soil colour was shown for the further development of visual evaluation techniques for a soil carbon storage index. Visual soil evaluation techniques also provide a useful visual aid for improving soil awareness in groups of stakeholders, helping the exchange of knowledge and ideas for innovation in agriculture.