Overview

Electromagnetic (EM) mapping is a method for mapping the relative conductivity of soils in a field. Conductivity of soils is affected by soil properties including but not limited to soil moisture, clay content, compaction, salinity, cation exchange capacity and temperature.

By creating an EM Map of a field being irrigated, we get a good insight into the variability of the field and this is a great starting point for creating a plan for Variable Rate Irrigation.

Precision Irrigation and Wheresmycows.com Farm Mapping provide EM Mapping services in New Zealand and in association with Landcare Research New Zealand Ltd, can create an Available Water holding Capacity (AWC) map to load into a VRI map or any other GIS software.

EM to AWC Map

After a well carried out EM survey, an accurate EM Map will show the spatial differences in soil conductivity. With local knowledge of field characteristics and by doing some ground truthing by digging up samples and lab testing, the EM map can be interpreted and used as a basis for making decisions on how to best utilise VRI.

Landcare Research New Zealand Ltd offer a service whereby they will take an EM Map created by Precision Irrigation, carry out a ground-truthing procedure on-site, and then extrapolate the ground truthing results using the EM Map to create an Available Water-Holding Capacity (AWC) map. Combined with soil moisture monitoring, an AWC is a very useful tool for determining how much irrigation should be applied to different areas of the field.

As a simple guide, you can often expect:

• 10% water saving where AWC varies by 50mm
• 15% water saving where soil AWC varies by 100mm
• >15% where soil AWC varies by >100mm

Sample maps

Raw EM Map of an areas beneath pivots showing distinct differences in soil properties.

VRI treatment zones identified from an AWC map generated by Landcare Research.

Quote

If you would like a quote for an EM Map of your farm, please fill out the quote reqest form on http://www.gpsfarmmap.com/en/pages/free_quote/ and enter in the comments section that you would like an EM map of your farm.