Wednesday, 8 April 2015

The best time to get your farm EM Surveyed

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