Visual Soil Assessment, a practical technique

Visual Soil Assessment, a practical technique for soil monitoring

By Bala Tikkisetty
Sustainable Agriculture Coordinator
Environment Waikato
Hamilton East

Protecting the physical properties of soil is vital to successful sustainable farming. This is because these physical properties control the movement of water and air through the soil, and the ease with which roots penetrate the soil.

Damage to the soil can change these properties and reduce plant growth, regardless of nutrient levels.

Loss of soil quality (soil degradation) can significantly affect the environmental sustainability of the soil, and the economic sustainability of farming.

And decline in soil physical properties takes considerable expense and many years to correct, and can increase the risk of soil erosion by water or wind.

So safeguarding the soil for present and future generations is a key task of land managers.

Generally, not enough attention is given to the basic role of soil quality in efficient and sustained production, and maintaining water quality and the effect of soil quality on the farm’s gross profit margin.

There is every need for farmers and land managers to be able to identify and predict the effects of their short and long term land management decisions on soil quality.

Therefore, reliable tools are needed to help make decisions that will lead to sustainable land management.

The Visual Soil Assessment (VSA), developed by well known soil scientist Graham Shepherd, has been a good tool in assessing soil quality at farmers' level and the results are easy to interpret and understand.

VSA also provides a useful educational and vocational training tool for those unfamiliar with soil science. It creates a better understanding of soil quality and its fundamental importance to sustainable resource and environmental management. In particular, VSA has developed a greater awareness of the importance of soil physical properties (such as soil aeration) in governing soil quality and on-farm production.

Many physical, biological and, to a lesser degree, chemical soil properties show up as visual characteristics. Changes in land use or land managements can markedly alter these.

Research in New Zealand and overseas shows many visual indicators are closely related to key quantitative (measurement-based) indicators of soil quality. Actually, these relationships have been used to develop VSA.

The VSA Field Guide helps land managers assess soil quality easily, quickly, reliably and cheaply on a paddock scale. It requires little equipment, training or technical skills. By assessing and monitoring soil quality on your farm with VSA, and following guidelines for prevention or recovery of soil degradation, farmers can improve their sustainable land management practices.

VSA presents visual assessment of key soil ‘state’ and plant ‘performance’ indicators of soil quality on a scorecard.

Soil quality is ranked by assessment of the soil indicators alone. It does not require knowledge of paddock history. Plant indicators, however, require knowledge of immediate crop and paddock history. Because of this, only those who have this information will be able to complete the plant indicator scorecard satisfactorily.

Each indicator is given a visual score of 0 (poor), 1 (moderate), or 2 (good), based on the soil quality observed when comparing the paddock sample with three photographs in the field guide manual.

The scoring is flexible, so if the sample you are assessing does not clearly align with any of the photographs but sits between two, a score in between can be given, for example 0.5 or 1.5. An explanation of the scoring criteria accompanies each set of photographs.

Because some soil factors or indicators are relatively more important for soil quality than others, VSA provides a weighting factor of 1, 2 or 3. For example, soil structure is a more important indicator (a factor of 3) than surface relief (a factor of 1).

The score you give each indicator is multiplied by the weighting factor to give a VS ranking.
The total of the VS rankings gives the overall ranking score for the sample you are assessing. Compare this with the score ranges at the bottom of the page to determine whether your soil has good, moderate or poor soil quality.

The VSA package has been recently updated by adding some more important indicators. The second edition of the VSA is a significant improvement on the first edition partly because it is better able to assess soil condition and plant performance as a result of a more balanced assessment of soil chemical, biological as well as physical properties. It is more strongly correlated to crop and pasture production and pasture quality, considers key aspects of the subsoil and better addresses the ecological footprint of organic carbon dynamics and environmental issues, including greenhouse gas emissions and nutrient loading (such as N and P) into water ways.

ENDS

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