Thursday 26 April 2018

EM Surveying - it's that time of year again!

With all the early season rainfall we've had the EM Surveying season has started a lot earlier than most years. It's great in a couple of respects: 1) we can get across the ground before it all gets really wet (if that happens) and the potential to make a mess increases and 2) it gives you more time to analyse and incorporate the data into your decision making over the winter months. 

As we're already into it this year, we thought it was time to give you a reminder about EM Surveying and how it all works. Today you'll get the first of a two part blog looking at the process, what you get from an EM Survey and what it can all be used for. 

EM Survey – Part 1 - the process.

When we conduct an EM survey we are measuring the electrically conductivity within the soil profile, the values have close links to the soil texture properties, where clay gives a higher reading than silt that in turn gives a higher reading than sand. So, by driving over a block of land you pick up the differences in the soil texture at two different depths 0-50cm and 0-125cm. Other factors have varying degrees of influence on the readings such as soil bulk density and moisture within the profile at the time of the survey. High salinity readings can have a huge influence on readings, but this is only in specific areas of New Zealand. The EM data is logged using 2cm accurate RTK GPS, so not only do we map the relative changes in soil texture, we are also collecting valuable topography data at the same time.

Agri Optics' EM Survey setup with soil profile shown. The measurements penetrate 1.25m into the ground. 

We drive most commonly at 12m swaths across the area, but closer resolution can be used for more intensive situations such as viticulture. Once the survey has been conducted we write a report about the findings from the two different EM layers, we then zone the EM data up into different management areas and run topography generated maps. Once you have had time to read through the report we arrange a meeting to then run through the report with you in person if you so desire. We also supply the client with software to view the data on their own computers and look at the different layers plus make your own management zones if required. From this point we can then focus on the areas of interest for your requirements.

The survey data has many uses, depending on the farming type and location and includes but is not limited to the following;  being the basis of variable rate irrigation application maps, moisture probe placement, used in zonal soil sampling, in dryland farming areas knowing where to put your effluent, to varying your nitrogen use depending on the underling soil types and used for flood modelling. It can also be used in conjunction with other layers of data such as yield maps, biomass maps and as happens frequency used with the topography data. Over the next few blogs I can drill into more detail on these different uses.

The EM season runs form the end of irrigation in the autumn through to Spring, but from now onwards is the ideal timing. For more information on EM surveying or to book one in for this season, please contact one of the Agri Optics team. Cheers, Chris.