Map-based Technologies for Soil Maps

Soil maps provide information such as soil type, nutrient levels, moisture and topography (eg slope and elevation)[1]. They can be used to divide fields into homogenous zones for management, important when deciding on strategies for planting (density or type of crop), fertiliser application or irrigation.

Example of a soil moisture map using electroconductivity scans. Contains modified Copernicus Sentinel data 2020 and basemap from the Polish geoportal. ©SatAgro

Soil maps can be generated in a variety of ways [1]:

• The electrical conductivity can be measured using ‘on-the-go’ hand-held or mobile sensors and provides information about soil pH. (For more detail on how to measure Soil Electrical Conductivity, there’s a USDA guide listed in ‘See Also’ at the end of this Step).

Gator Veris Iscan measuring soil EC. © John Deere

This video from Precision Decisions, shows how soil is sampled and scanned. (Please note, there is no audio on this video.)

• Remote sensing using satellite imagery can be used to determine soil moisture content [4]. There’s an example of this in the case study below.
• Soil samples can be collected and sent for lab analysis to determine characteristics such as nutrient content. If sampling by hand, it’s important to ensure that the samples taken are representative of the heterogeneous nature of a field. Samples should be taken from different areas that represent aspects such as variations in crop management, erosion, poor yields, topographical features (such as low lying or higher areas) and drainage. Samples should also be taken at both the bottom and top of a slope so any washing away of organic matter and soil nutrients can be noted. (For more detail on soil sampling, there are some helpful links listed in the ‘See Also’ section at the end of this Step.)

These data are combined with accurate geo-referencing, using GPS for example, to create maps.

The maps provide information about:

• Texture (eg sandy, clay)
• pH
• Nutrient content
• Moisture levels
• Organic matter content [2,3]

This video shows how various different sensor technologies can be mounted on machinery carrying out normal farming operations to provide data about a wide variety of soil features and detailed maps.

Soil maps have been produced for whole counties, such as the National soil map of England and Wales and the International Soil Reference and Information Centre provides a catalogue of digital soil resources.

Why Use Soil Maps?

Mapping the soil can support a range of farming and precision farming techniques and technologies. Soil maps can help to determine management zones in a field, enabling VRA (variable rate application) of seeds or fertiliser [1, 6]. They could also support variable or precision irrigation using, for example, soil moisture sensors [7] and combining this with vegetation indices (such as NDMI) to highlight areas of water stress. Linking together soil moisture sensors with irrigation systems also has the potential to set up automated precision irrigation systems [8].

Combining soil maps with other techniques and technologies such as vegetation indices and yield maps can also support decisions to change land use. This may result in growing an alternative crop [5], changing seeding density [6] or not growing a crop at all in areas with consistently low yields.