EM Soil Surveys

By: Agri Optics New Zealand  06-Dec-2011
Keywords: Surveying Services

EM Soil Surveys

Agri Optics New Zealand Ltd now provides Electromagnetic (EM) soil surveying services to clients throughout the South Island.

Agri Optics undertaking EM Soil Survey at AMI Stadium, Christchurch following the Fedruary 2011 Earthquake

Soils vary across farms and within paddocks but the practice has been to manage these as though variations did not exist – applying a consistent rate of fertiliser across a paddock being an example.

This method of management is being questioned as farmers strive to cut costs and improve production efficiencies.

They are keen to find out where the high and low yielding areas are, and the causes of the variations. Sometimes it is possible and practical to treat low yielding areas and make them more productive. If it is not then why waste inputs such as seed, fertiliser or chemicals, for little or no gain? Interest in electromagnetic surveying is increasing as farmers look for tools that enable them to capture more information at low expense and to more effectively manage areas with a high degree of local area knowledge.

Invest in our service because

  • We work direct with you the farmer and with your agronomist/ farm advisor
  • Data is collected at 12metre intervals
  • We use RTK foraccuate repeatable positioning
  • Full colour zone maps are provided
  • We give you your raw data
  • We help you import this into your mapping system
  • We can provided mapping software as required
  • We zone areas based on all your information
  • We collect data every metre we travel across your paddock
  • Our EM scanner is factory and in-field calibrated
  • Non-invasive,low impact EM scanner

What is an electromagnetic (EM) survey?

An EM conductivity survey is used to establish the bulk electrical conductivity of an area. The survey allows spatial differences in soil characteristics to be mapped. The electrical conductivity of a soil profile is governed by a combination of properties, including:

  • Soil texture
  • Soil moisture
  • Soil temperature
  • Bulk density
  • Salinity (very few soils in New Zealand are influenced by this characteristic)
  • Cation exchange capacity

The EM38-MK2:

Ground conductivity meters such as the EM38-MK2 provide (frequency domain) measurement of subsurface conductivity and magnetic susceptibility for spatial site characterisation and detection of structural anomalies, both natural (e.g. bedrock fractures) and man-made (e.g. storage tanks).

The EM38-MK2 provides measurement of both quad-phase (conductivity) and in-phase (magnetic susceptibility) components, within two distinct depth ranges, all simultaneously, without any requirement for soil-to-instrument contact. With a maximum effective depth of exploration of 1.5m, the EM38-MK2 will be of value to those with an interest in the very near surface: applications in agriculture, archaeology and general soil science are common.

The standard EM38-MK2 includes two receiver coils, each in the vertical dipole orientation, separated by 1m and 0.5m from the transmitter, simultaneously providing data within depth ranges of 1.5m and 0.75m respectively: the instrument can be rotated such that both coils are in the horizontal dipole orientation, with effective depth ranges then of 0.75m and 0.375m respectively.

The EM measures apparent conductivity in millisiemens per meter (mS/m) while the instrument operates at 14.5kHz.

EM in New Zealand:

In New Zealand, most differences in EC that we see in maps generated by an EM Survey are the result of differences in soil type, moisture content and compaction. With local knowledge of particular areas and some ground-truthing, we can correlate EM survey findings to other characteristics such as available water-holding capacity (AWC) which allows us to create prescriptions for variable rate irrigation scheduling.

Finer textured soils have higher EC values than coarse textured soils, due to better conducting pathways. Similarly, wetter soils have higher EC values than drier soils. It is this interaction of soil EC, soil texture and soil moisture that enables soil EC to be used as a surrogate measure of soil available water-holding capacity.

EM mapping for zone management:

A land owner will often know of particular fields that give significantly variable yields, and wants to know why. The important question is can these variable yields be managed by:

1.       Changing management to improve yields in the low yielding area, or

2.       Reducing inputs to the low yielding area, because these areas will always be low-yielding.

 For more information onEM Soil Surveys

Ph: Jemma  Mackenzie 021796095

Keywords: Surveying Services

Contact Agri Optics New Zealand


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