In the previous EM survey blog, I ran through the process of
conducting the survey, this time I will go through some of the uses.
The data from an EM survey is very useful for irrigation in
many ways. The topography data can be used for planning the pivot design itself
with your irrigation provider for example working out tower spacing and pivot
positioning. The angle of slope can be used to see if the pivot stays within
design parameters for insurance purposes as well as design planning.
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| Figure 1: Contour map on top of elevation map |
After the initial pivot or irrigation design plans, we can
then look at the EM data itself to determine the amount of variability within
the surveyed area. Within the PCT Gateway software we can look at the value and
amount of the crop being grown on the area and the cost of installing variable
rate irrigation (VRI). The software needs to know the average yield and value
of the crop. That way using algorithms it calculates that by not over watering
the heavier soli types or under watering the lighter areas you bring the crop
yield on those areas up to the average. It looks at the reduction in
variability by using VRI as opposed to a blanket application. In the example
below the variability from using VRI drops from 30.4% to 4.68%. So, by using
the average yield and the price we can see the payback vs the cost of putting
VRI on your pivot.
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| Figure 2: Illustrating the payback from VRI, using an EM map. |
This model just looks at the costs vs savings of VRI from a
production prospective. It doesn’t take into consideration savings from reduced
water use, power savings, reduced track repairs etc, which will be in addition
to this.
The next stage is to make VRI maps up for the pivot, using
the different soil zones, predominately we use the shallow EM results. If the
area has a lot of variation in topography we can also combine the elevation
layers with the EM map to make an application map for the pivot. We can also
use other elevation layers to achieve the best solution used for each specific
survey, as required.
The map below, shows a three zone EM map, where red is the lightest soil, green the medium
textured soil and blue the heaviest soil. This has been combined with the slope
map, where the darker tone indicates a slope of 0-5% and the brighter tone of
colour areas where the slope is above 5%.
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| Figure 3: An EM map and slope map combined to make a VRI application map. Brighter red, green and blue indicate slope for the different soil zones. |
The EM zone maps can also be used for irrigation pod
placement, as well as moisture probe placement. If you only have one probe
under an irrigation management zone, you want to make sure its under the right
area. I will discuss this in more detail in the next blog. In the meantime, if
you have any questions about EM surveying please get in touch.
Chris Smith
Operations Manager Agri Optics NZ Ltd.
