Okay. So, you’ve decided to EM survey an area of your farm,
but aren’t sure when is the best time to do it. Not only at what time of year
but also in relation to the planning of your irrigation development.
The first decision, what time of year, is relatively easy to
determine. Here at Agri Optics NZ we recommend conducting a survey outside the
irrigation season - before you start or after you finish irrigating, ideally
when the paddocks are naturally nearer their peak water holding capacity. This
ensures that any man-made influence from your irrigation system is not showing
through in the survey results. By waiting until the ground has had a couple of good
rain events this will bring the soil back to its natural state.
The image below shows
on the left an EM survey conducted at the right time of year (top map being the
0-50cm profile and the bottom one the 0-125cm soil profile) conducted in 2013,
while the image on the right show the same paddock with EM survey conducted in
February 2015, undertaken as an experiment. This highlights why Agri Optics do not
recommend conducting EM surveys in the summer when land is being irrigated.
 |
| Comparison between EM Surveying conducted in winter (left) and summer (right) and different survey depths. |
As you can see the influence of the pivot irrigation on the
two maps on the right-hand side (especially the top map showing the shallow
profile) is masking the true characteristics of the soil, not only on the dry
red areas around the edge but also in the blue areas where there was run off
and ponding.
The second timing decision lies around at what stage in your
project development planning to do the survey. Should it be in the early
planning stages or before or after building the pivot?
If you EM survey while still in the planning stages but before
work starts then the elevation data recorded as part of the survey can be used
to help with pivot design and help budgeting for any potential earth works,
especially on hilly ground. This can help your pivot designers enormously, and
also at this early stage give a good indication on how much savings can be made
by varying your water to the soil’s requirements under the pivot footprint. A
note of caution though, if you plan on doing major earth works then be aware
that you will be removing the soil the EM survey has based upon and this can
alter how relevant the EM map will be to your final soil profile.
If the EM survey is conducted after the pivot is up and
running, but before the Variable Rate Irrigation (VRI) system is purchased, the
Information from the survey can be used to see what the gains are from varying
water application across your different soil zones. By using Agri Optics VA Gateway software we
can show you the payback time of implementing VRI based on the initial
variability and what a return on investment is likely to be for your specific
situation.
An EM survey can also be undertaken after VRI is already
fitted, where it’s existing use is for the management of avoidance zones such
as lanes and waterways. With the data from an EM survey you can then tweak your
applications to match the soil types within your current setup. By going down
this route you will already be familiar with the VRI software before
introducing the application maps from your EM data and making the step up to
site specific management.
Here at Agri Optics we’re happy to give you our independent
advice, helping you make the right decision for your farm and business,
providing you with a truly sustainable solution – sustainable for your land and
for your business. You can find our contact details here