Soil Mapping with Electromagnetic Induction Scanning

Last year we completed a substantial assignment for a large cotton grower in Azerbaijan. Having acquired over 6000 hectares of undeveloped territory in an area with a high water table and issues with salinity, they were aware that a properly designed drainage system would be needed to enable leaching of salts out of the soil and into drains. Over time this will render the soils less saline, improve plant productivity, and allow for more salt-sensitive crops than cotton to be grown as rotation crops. There was also interest in what crops should be grown where, and what fertiliser regimes would be needed to meet certain yield targets.

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The classical approach to soil surveying for such a task is to divide the property up into a grid, and sample soil and groundwater at the grid square intersections, like so.

autogrid

Fig. 1: Preplotting soil test sites using a grid generator (PAM software)

The technology for assessing soil type/characteristics without digging holes has advanced to the stage whereby using an Electromagnetic Induction (EMI) probe towed behind a vehicle, a basic map of electrical conductivity can be developed. Soil samples can then be taken from within areas of certain EM characteristics as needed, instead of at regular intervals, potentially saving a great deal of time and money on soil testing of fields with very regular soils, and identifying otherwise undetected variation within a field, down to an accuracy of a few centimetres.

Depending on probe design, scanning may be done at more than one depth; 4 depths is common (e.g. 20,40,60 and 80 cm).

Because electrical conductivity is correlated with many soil parameters of practical importance, such as soil texture, nutrient content, salinity, field capacity/wilting point, Cation Exchange Capacity and so on, we can pre-plot soil sample sites after scanning, and cross-reference soil test results with the EM data to develop quite accurate maps of key soil characteristics. Concurrently, we can map elevation of each square metre of the field.

Northern Farm_DEM

Fig. 3 Elevation

 

Northern Farm_Composition

Fig. 4 Soil Texture

 

Northern Farm Field Capacity

Fig 5: Field Capacity (Available Moisture at 1/3 Bar)

Field Capacity

Northern Farm Soluble Salts

Fig. 6 Soluble Salts

 

The practical applications of this are:

  • Capacity to design and install a precision irrigation system, to ensure that water is applied according to plant need and underlying soil type in various management zones. Water usage and pumping costs per tonne of product can be brought down accordingly.
  • Determine which soil type zones are suitable for which types of crop.
  • Determine exactly where soil amendments like gypsum should be applied to remediate salinity, with clear demarcations between areas requiring such intervention.
  • Target future annual pre-season soil tests and mid-season tissue tests within clearly demarcated zones based on underlying soil type.
  • Modify seeding rates according to soil type zones, to reduce seed cost/tonne of product harvested.
  • Modify fertiliser application rates according to clearly demarcated soil type zones, to reduce fertiliser cost/tonne of product harvested.

These datasets may be used to develop variable rate seeding or variable rate fertiliser application plans for in-cab computer systems, allowing the operator to have the computer automatically adjusting dosage according to need without manual adjustment.

Northern Farm_Cotton_Nitrogen_March 2017

Fig 7. Nitrogen Application recommendation, cotton

Northern Farm_Cotton_Phosphate_Mar2017

Fig 8. Phosphate application recommendations

They may also be used in precision irrigation systems to divide fields up into irrigation management zones based on underlying soil type, and to use data from soil moisture sensors to apply exactly the desired amount of water to each small irrigation zone, even under one pivot.

EM Screen Shots.pptx

Fig. 9 , Variable Rate Irrigation Zone Control (from Valley Irrigation)

 

This has application for drip systems in vineyards and orchards also. The following diagrams were part of a 2016 presentation delivered by Luis Sanchez from major US wine company E. & J. Gallo Winery

Soil Vineyard

Fig. 11: Soil Composition of Vineyard; s= sand sl = sandy loam ls = loamy sand

 

 

Yield Map

Legend Yield

Fig 12: Yield/acre

VRI 2nd Gen.jpeg

Fig 13: Variable Rate Irrigation Design; 96 irrigation zones, 30x30m each, 24.4 acres, Includes Variable Rate fertilisation

 

For more information on how we can map your property and save you money on seed, fertiliser and water pumping costs, and how we can optimise your yield/quality balance in your vineyards to enhance your profits, contact us here