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Update for key soil tool

Last updated 05:00 12/01/2014
Bala Tikkisetty carries out a visual soil analysis that will give him a better understanding of soil quality.
Fairfax NZ
LOOKS GOOD: Bala Tikkisetty carries out a visual soil analysis that will give him a better understanding of soil quality.

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As we begin another new year, with its inevitable challenges, it's always good to remember that - whatever the season - maintaining the condition of soils is a key to successful sustainable farming.

So I'm pleased to report that a strong tool for helping farmers do just that - the visual soil assessment or VSA - has been updated with some important new indicators. Understanding VSA and what it can tell us is a very good investment for farmers. A decline in soil's physical properties can take considerable expense and many years to correct, and can increase the risk of soil erosion by water or wind.

VSA's results are easy to interpret and create a better understanding of soil quality and its fundamental importance to sustainable resource and environmental management.

The updated VSA adds to that by improving assessments of soil condition and plant performance. It does this through a more balanced assessment of soil's chemical, biological and physical properties.

For example, VSA now helps consider key aspects of the subsoil. Also, it better addresses the ecological footprint of organic carbon dynamics and environmental issues, including nutrient loadings - such as nitrogen and phosphorus - getting into waterways.

One of the reasons I personally promote VSA is that I think not enough attention is given to the basic role of soil quality in efficient and sustained production and water quality, and its effect on the farm's gross profit margin.

It's based on scorecard-based assessments of key soil "state" and plant "performance" indicators.

Soil quality is ranked by assessment of the soil indicators alone. It does not require knowledge of paddock history. However, filling in the plant indicator scorecard satisfactorily requires knowledge of immediate crop and paddock history.

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. If the sample being assessed 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.

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).

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The score given to each indicator is multiplied by the weighting factor to give a "visual score ranking". The total of the rankings gives the overall ranking score for the sample being assessed. This is compared with score ranges to determine whether soil has good, moderate or poor qualities.

VSA can be used at any time of year, but is best carried out when the soils are moist and suitable for grazing or cultivation.

* Bala Tikkisetty is a sustainable agriculture co-ordinator at Waikato Regional Council.

- Waikato Times

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