Visual Soil Assessment Field Guides (VSA)

The Visual Soil Assessment (VSA) approach is based on the visual appraisal of key soil ‘state’ and plant performance indicators of soil quality, presented on a scorecard. The rationale for this approach is that many physical, biological and, to a lesser degree, chemical soil properties show up as visual characteristics, and that changes in land use or land management can markedly alter these. Moreover research has shown that many visual indicators are closely related to key quantitative indicators of soil quality.

VSA guides have been developed for general land cover categories (annual crops, pastures, orchard) sand some specific crops (maize, olive orchards, vineyards, wheat).

VSA allows land managers to assess soil quality easily, quickly, reliably and cheaply on a plot scale. It requires little equipment, training or technical skills.

The VSA tool kit is basic, comprising a spade, a plastic basin, a hard square board, a heavy-duty plastic bag, a knife, a water bottle, a tape measure, a VSA field guide, and a pad of scorecards.

The soil indicators are texture, structure, porosity, colour, number and colour of soil mottles, presence of earthworms, potential rooting depth and presence of a hardpan, surface ponding, surface crusting and surface cover, soil erosion and soil management of the particular crop or land cover. With the exception of soil texture, the soil indicators are dynamic indicators, i.e. capable of changing under different management regimes and land-use pressures. They can cheaply and rapidly be measured in the field, and, being sensitive to change, are useful early warning indicators of changes in soil condition and therefore

Each indicator is given a visual score (VS) of 0 (poor), 1 (moderate), or 2 (good), based on the soil quality observed when comparing the soil sample with three photographs in the field guide manual. The scoring is flexible, so if the sample one is assessing does not align clearly with anyone of the photographs but sits between two, an in-between score can be given, i.e. 0.5 or 1.5. Because some soil indicators are relatively more important in the assessment of soil quality than others, VSA provides a weighting factor of 1, 2 and 3. The total of the VSA rankings gives the overall Soil Quality Index score for the evaluated sample. Comparing this with the rating scale at the bottom of the scorecard allows to determine whether the soil is in good, moderate or poor condition.