EM Surveying - other uses for the data

Today it's our final blog for the 4-part series on EM Surveying that we've run you through over the last month. To date we've covered off:

• Part 1 - the process
• Part 2 - what the data is telling you
• Part 3 - the main uses

Today Chris is going to take you on a run-through of what some of the other uses are for your EM Survey data are & how they can be applied on farm...

...I touched on probe placement at the end of the last post, so will continue where I left off. The EM layers are very useful for making sure you have your moisture probe in the most indicative soil type if you only put one probe in under a pivot for example, or if you have several soil types it ensures you can put probes under the lightest, heaviest and average soils, to make more informed management decisions on irrigation application. The topography information collected at the time of survey can also be used for determining soil moisture probe locations. 

Figure 1: Shallow EM Map with 3 probe locations in the different soil types. 

Where the land is undulating we can bring the elevation data into the equation for probe placement to find a flat area in each of the different soil types. We can also use a moisture probe in a dry land situation for adjusting inputs to the season (such as fertiliser, re-grassing & de-stocking).

When conduiting the EM survey we are using RTK GPS to log the EM data, this topography data and its derivatives are very powerful information layers. We can create water flow maps so you can see potential areas there may be issues for your Farm Environment plans, contour maps, and water flow animated videos as shown below. The Water Shed model mimics a large rainfall event, then over time shows where the water moves from quickly and where it hangs around longer. 

These Water Shed models highlight potential avoidance areas for planting, especially for nurseries and high value crops, in areas prone to heavy rainfall.

As you can see there are many ways people are using their EM survey data, and there are many other uses tailored to the individual client’s requirements. It is generally best to discuss with you your issues then we can work together on using the data to achieve the best solutions for you.

For any more information or to discuss your requirements give me a call.

Chris Smith

Operations Manager @ Agri Optics NZ Ltd 

EM Surveying - The Uses

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.

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.

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%.

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.

EM Values - What the data is telling you

Today we've got the second part of a 4 part series on EM Surveying and all it's uses. This week we've been into the EM Surveying over on the West Coast (check out our Facebook page if you want to see more) and it's certainly an important part of the job being out there doing the survey and seeing the physical aspects of the job to help make sense of the data and what it's telling you. Today we look at what the EM data does tell you...

An electro-magnetic (EM) sensor generates a constant electro-magnetic field that penetrates into the soil profile. It measures the bulk electrical conductivity of the soil profile. As we conduct an EM survey the sensor is taking readings at two different depths simultaneously. These two depths are known as the ‘Shallow EM’ and the ‘Deep EM’. The depths the DualEM reads depends on the height the machine is off the ground. With our EM setup we are reading the soil profile depth of 0-50cm for the shallow EM and the deep EM at a soil profile of 0-125cm. So the deep EM values are the same as the shallow plus another 75cm deeper. This is why the deep EM readings are always higher than the shallow as it is reading that extra 5cm.

Figure 1: Shallow EM survey values varying from 2-20 EM units (mS/m)

Figure 2: Deep EM of the same area with values ranging from 14-30 EM units (mS/m)

In this survey the same features are showing in the shallow EM and deep EM results, however sometimes this is not always the case the deeper profile can have a different underlying soil type that the shallow EM doesn’t pick up but the extra 85cm of deeper soil does and it changes the overall structure.

Generally speaking and depending on what part of the country you are in and the time of year the survey is carried out amongst other things, we would class a range in EM in the shallow profile of 1-3 units as low variability, 4-8 units as moderate variability and over 8 units range as high variability in the shallow layer/soil profile. In the deep EM/soil profile layer a range of 1-6 would be low variability, 6-15 moderate variability and over that high. It is often dangerous to generalise like that, but it gives you an idea of the type of ranges we look at, and as previously stated there are a lot of other factories that determine if the readings are low, medium or high variability. You also have to look at the distribution of the values as well, if the majority of the values are within a certain range and a few rogue values outside that but on a minimal area of the total, then the range in variation may not be as much as it first looks. How much the variability is costing you in terms of blanket irrigation applications compared to variable rate irrigation applications be it water, seed or fertilizer is a subject for another day!

For more information on EM Surveying please contact us at Agri Optics NZ Ltd.

Chris Smith.facebook

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. 

Regulatory Update

Below is a quick update on where things have gotten too from a regulatory perspective. 

Canterbury

2017 saw Environment Canterbury (ECan) introduce Good Management Practices (GMP) into its Land and Water Plan framework.  This is known as Plan Change 5.  Plan Change 5 also introduced the Waitaki specific nutrient management rules.  The decisions on the plan were appealed by a number of parties, particularly in relation to how the irrigation and fertiliser GMP’s were being treated in the Farm Portal (the online tool developed to determine exactly what GMP is at a farm level).  Appeals are still yet to be resolved, and therefore, it is likely to be mid-2018 before this plan is made operative.

Plan Change 2, which is specific to the Hinds Plains region, is also still under appeal, however, Plan Change 3, which is specific to the South Canterbury Coastal Streams area, had all its appeals resolved in November 2017, and is now fully operative.

ECan has also been doing a big push in the areas where a consent to farm is required, to encourage those who need one to go through the process.  There has been a good response to this (contrary to the opinion of Dr. Mike Joy) as the process is new to many, and requires professional help and a change in mindset for many. 

Otago

Otago’s nutrient management rules are now two years away from kicking in (the date is 1 April 2020).  Otago Regional Council has been encouraging farmers to get their Overseer done.  They have also taken the initiative in the more sensitive catchments such as the Kakanui, and have been providing resources and funding to assist with this.

 

Southland

Southland’s Land and Water Plan is nearing the completion of hearings.  Council gave its reply report and recommendations (a summary of all the information and submissions presented to the hearings panel, and answers to all questions from the panel during the hearing) in November 2017.  Watch this space.

Horizons

Horizons One Plan struck a major hurdle in early 2017, with the Environment Court deciding that the way in which the Council was implementing its plan was not what the plan actually said.  This has left the council with a plan that effectively doesn’t practically work as it was written, and wondering what to do now.  Implementing the plan as written creates a massive cost to farmers and other consent holders, and doesn’t necessarily achieve the desired water quality outcomes.  Given this, in August 2017, the council voted to investigate the possibility of a partial plan change.  However, this will not be a quick or easy process as it is both a legal and public process.

Hawkes Bay

Irrigators in the Tukituki catchment are left high and dry (literally) after the Ruataniwha Dam project is put on the shelf indefinitely.  The Tukutuki River minimum flow is still going up, and without the dam to augment and flush the river, the increase in minimum flow will mean the possibility of severe restrictions for irrigators in this catchment.  Effectively, the raise in minimum flow was coupled with the dam, but the impacts of de-coupling are now about to be realised.

Gisborne

Gisborne’s Freshwater Plan decision was released in August 2017, and was subsequently appealed.  The appeals are still to be worked through and there is no timeframe at this stage on when appeals are likely to be resolved.  Gisborne’s Freshwater Plan was actually pretty kind from a nutrient management perspective when compared to Canterbury for example.  There is no requirement for on farm limits using Overseer, and they have adopted a Farm Environment Plan approach to managing water quality.  However, it does have some issues with water quantity.  As horticulture, and kiwifruit in particular, look set to increase, those looking in the Gisborne area for plots to develop are soon realising that there is basically no water available for allocation unless you are prepared to take high flow water and store it.  Therefore, this is limiting the potential for the Gisborne region.

Overall

As well as all that is going on the regions, we have a new government who looks set to wind up funding irrigation scheme development, has already taken a stand on climate change, and will undoubtedly want to stamp its feet on the water issues.  2018 will be an interesting year…

By Keri Johnston, Irricon Resource Solutions

Phone 0272 202 425 or email keri@irricon.co.nz

www.irricon.co.nz