Application of a visual soil examination and evaluation technique at site and farm level

Visual soil examination and evaluation (VSEE) techniques are semi-quantitative methods that provide rapid and cost-effective information on soil quality. These are mostly applied at site or field level, but there is an increased need for soil quality indicators at farm level to allow integration with other sustainability indicators. The objectives of this study were to develop and apply a protocol for application of a VSEE technique at site level, to assess the VSEE observations against standardized laboratory analyses and to aggregate VSEE observations to farm level using an appropriate sampling design. The study was conducted at ten dairy farms in a reclaimed polder in the Netherlands with clay and organic soils. A stratified random sampling design was used to account for spatial variability in land use and soil series. VSEE was carried out using the Visual Soil Assessment approach. Results show that 81% of sites were assessed as good and the remainder as moderate to poor. For the clay soils, field observations of soil structure were significantly correlated with pH, bulk density, soil organic matter (SOM) and mean weight diameter of aggregates, whereas for organic soils, soil structure significantly correlated with pH, bulk density, organic C and SOM. The range in overall scores calculated at farm level was smaller than at site level, and most farms were assessed as good.