Friday 21 August 2015

A guide to S-Map

What is S-Map?
S-Map is a map containing information of the soils across the country. It is being developed by Landcare Research and information is continually being added to it. The project was started to collaborate and update information on New Zealand’s soils into one easily accessible map of the whole country with different layers of information for different applications and to support land management at different scales.

Anyone can access the information freely. Mapping is carried out by Landcare scientists who either use old soil maps or go to the area and undertake traditional soil surveying. This is where soil core samples are taken to determine the soil type and this information, alongside the history of the area, is used to present what they think the pattern of soils will look like. The most detailed information available is currently on the lowlands while the uplands of the country are being mapped using digital modelling based on the soils having similar characteristics to other known soil types.

How to use it
In the previous blog (identifying soil textures) you see how the content of sand, silt and clay determines soil physical properties such as WHC, porosity and bulk density and how there are different horizons in a soil profile with different quantities of these three particle sizes. S-Map also uses soil horizons to determine soil characteristics.

You can search for your location on S-Map and select to see polygon layers to view the soil types present on your farm as shown below for Methven, Canterbury.

S-Map Online is freely accessible for anyone;
You can then select the ‘Soil information’ tab at the top of the screen and click on a point on the map. S-Map will show you the percentage of each soil type present around this point and you can select to view the factsheet of the dominant soil type (and the other soil types present). In the figure below the Greenvale farm near Methven is shown by S-Map to have three dominant soil types: 50% is a shallow, well drained Eyre, 25% is a shallow Darnley and the final 25% is a moderately deep Mayfield.

The soil will have been given a series of names using the New Zealand Soil Classification System however don’t worry about this too much, the information contained further down in the factsheet has more practical applications. The fact sheet tells you:
  • ·         How stony the soil is which relates to its drainage class
  • ·         The amount of water expected to be held at different depth increments
  • ·         The clay content
  • ·         Potential rooting depth
  • ·         Soil phosphorus retention
  • ·         Water management such as the potential for waterlogging and drought
  • ·         Nutrient management such as nitrogen and phosphorus leaching vulnerability. 

Page 1 of an S-Map report for an Eyre soil, downloaded from
You can also select different layers to view on the map, on the left hand side of the screen: soil drainage, depth to hard soil/ gravel/ rock and soil moisture. The map will then update using the colour scheme from the legend for this layer which is shown on the right hand side of the screen. The figure below shows that for the Greenvale farm the soil drainage depth layer has been selected and on the right hand side the legend explains what each drainage class means.

S-Map brings all information on NZ soils into one database that can be easily accessed and used by all land users and interested parties. It is the largest national resources on soils that NZ has and it contains a range of information that is relevant and useful for all scales of management. However there are also aspects to S-Map that limit its usefulness, especially to farmers.

According to S-Map the Greenvale farm, shown in the S-Map figures above is a mix of mainly three soil types. However an Electromagnetic map carried out alongside soil sampling showed that there was, in fact, a much more complex pattern of soils present on the farm. The picture below and top is the Electromagnetic map of the property and the different colours represent different textures while the picture below and bottom uses the patterns from the EM map alongside soil sampling to identify the pattern of soil types (families) on the property. 

Top, EM map by Agri Optics Ltd. Bottom map of soil types developed from soil sampling.

These maps provide a substantial amount more information than the map of the farm from S-Map (discussed above). The soil information used by Overseer to determine nitrate leaching is supplied by S-Map and this can result in inaccuracies in N leaching figures when S-Map believes the soil pattern on a farm is more simple or different than it actually is. Furthermore using soil information from S-Map for irrigation scheduling could mean over or under irrigating areas which can decrease yields as well as creating inefficiencies in water and power use.