EM surveying - Knowledge is Power... (and Potential profit!)

An Electromagnetic Survey is one of the key layers required on the precision farming journey. Precise location and understanding of soil types is a key piece of information in driving decisions around water use and nutrient placement. Not only can an EM survey be used to reduce water inputs it can form the basis of other decisions related to plant health, production and nutrient uptake. Turning the pretty maps into useful data requires some powerful software. That is where VA Gateway comes in. Gateway allows for in depth analysis of multiple layers, including Yield and EM. All Agri Optics customers have access to VA Gateway and AgCloud the online version.

With the software we create reports on the various layers of data collected. Clients get information on two EM soil profiles, one measuring the conductivity in the top 0-50 cm of soil and the other looking at changes in the top 0-125cm of your soil profile. Our report explains our findings on each layer with an explanation of what you are seeing. Depending on the variability arising from the survey, we then create different management zones based on the range in EM units. These zoned maps can then be imported into your variable rate irrigation (VRI) software if they are used for irrigation or into your VR seed drilling control box if you are using it for variable rate seeding based on your soils.

Figure 1. Top left is a shallow EM map and to the right of it a zoned map of that layer. Below is the same but for the deeper EM (0-125cm).

We also report on topography features. As we log the EM data at 2cm accuracy we are also mapping these features. This data set in its own right is very useful and gives you the surface characteristics of the area surveyed in the form of six additional maps, slope, elevation, landscape change, aspect, any depressions and witness index (which way water will move in a rain or irrigation event). This data can be a powerful management tool. The water movement models can help highlight potential areas of issue, so they can be addressed, be it nutrient movement or run off.

Figure 2. Gateway software generates water movement models based on the topography data.

The elevation data can also be used to create contour maps that can be used in the design stage of your centre pivot system, e.g. when calculating tower spacing's or to help with budgeting for any required earth works.

Figure 3. Gateway software can be used to create 3D contour maps.

We can also create moisture probe placement maps based on your EM and elevation data to find your optimum site within each management zone. These sites can also be used as ground-truthing sites with HydroServices neutron probe to put actual specific values to the different zones water holding capacities and then convert the EM map into a water holding capacity map.

A further report can be created to gauge the likely payback time from the installation of VRI based on your soil variability, the crop you are growing, its value per unit and the cost of your VRI system. This is proving very helpful for those who are unsure as to whether they have enough variability in the surveyed area to warrant VRI.

All our data is collected using strict protocols, with the highest standards in continuity and quality every time. This ensures our clients have powerful, solution-focused information. For more details check out our website www.agrioptics.co.nz.

Post credit to Chris Smith.

Why my soil moisture sensor might be lying to me?

After choosing the type of moisture sensor you are going to invest in, the most crucial thing is to get the installation correct. It goes back to the old adage; rubbish in rubbish out, if you don’t get the installation correct everything that follows will at best be very marginal data.

Most probes are measuring a very small volume of soil within 10-20mm of the sensor itself, so good soil contact is imperative as well as a crop cover around the probe that is representative of the rest of the field being monitored.

If you are looking at installing a probe for next season or looking at maintenance on an existing probe then read on! These few basic does and don’ts will be of good use!

Don’t!

• Don't leave the excess cables on the ground – it is an accident waiting to happen!
• Don’t leave exposed cables for wildlife that want to see how tasty it is!
• Don’t site the probe on a ridge or in a hollow!
• Don’t site the probe in bare soil. Is there a crop growing over the probe site to give you a true representation of what is happening in the rest of the field? 
• Don’t site under the fence line

Don't leave cables on the ground

Do!

• Ensure you use good consistency of slurry around the probe to ensure good soil contact.
• Ensure you know the soil type your moisture sensor is located in and how that compares to the rest of the area you are monitoring.
• Make sure any tramlines or irrigation tracks miss the probe site by metres rather than millimetres!
• If your probe is near an electric fence, do ensure any metalwork is earthed.
• Do install the probe as early in the season as you can, so it has time to bed in and the crop over the top of it time to establish like the rest of the field.
• Do ensure a competent and trained person installs the probe with the right equipment to do so!
• If checking an old installation make sure there are no cracks around the probe site, the soil around the probe hasn’t sunk and the wires are in good order.

AquaLINK telemetry unit, away from AquaCheck probe out in the paddock

If you have any doubts about the site or installation of your probe, by installing it as early in the season as you can means that it can be moved and still have the winter to bed in again.

AquaCheck WEB, induvial sensor graph responding to irrigation and rain events.

Monitor your probe data and its response to rain or irrigation events, the beauty of the capacitance probes is that moving them is not an issue.

This article contains information from a post previously written by HydroServices but has been updated to include the experience from the Agri Optics team installing AquaCheck probes.

Improving Irrigation Efficiency for Only $50 cont.

Here is the much anticipated second installment from the Improving Irrigation Efficiency field day run by The Waihao Wainono Group and Morven Glenavy Irrigation. Dr Anthony Davoren, renowned Irrigation Consultant with Hydroservices, shares how drainage through the soil profile can be measured. With this key piece of information we can improve our irrigation management, and know when to turn the irrigator on (or off) to ensure all irrigation that is being applied is going to benefit the grass or crops we are growing.

Thank you to Dr Anthony Davoren, Waihao Wainono Group and Morven Glenavy Irrigation.

Improving Irrigation Efficiency for Only $50

Dr Anthony Davoren is renowned as one of New Zealand’s leading irrigation consultants, establishing Hydroservices in 1983. If you have a question about irrigation management, soil and soil water assessment or surface and groundwater water resources then Tony will have the answer. What sets Tony apart is his practical, hands-on approach and the way he communicates information in a way that farmers can easily understand and relate to… I mean how many other speakers will you find presenting from a hole in the ground!

The Waihao Wainono Group and Morven Glenavy Irrigation recently hosted a field day focusing on improving irrigation efficiency. H2Grow is lucky enough to be able to share with you some short videos from this day. In the first in this series Tony explains how the root depth of the pasture or crop you are growing should be considered when deciding on the most appropriate soil moisture measuring equipment for your property.

Considering Root Depth when Measuring your Soil Moisture Levels

Keep a look out for the next video in this series where Tony explains how to measure drainage so that you can better manage your irrigation and prevent irrigation water, and nutrients, draining through the soil... and his top tips of how to greatly improve your systems irrigation efficiency for as little as $50!

Thank you to Dr Anthony Davoren, Waihao Wainono Group and Morven Glenavy Irrigation.

Inaugural PAANZ Conference - Summary

Precision Ag in New Zealand is finally starting to gain a bit of traction in NZ & this was seen last Friday by:

1)      the fact that the Precision Ag Association of NZ (PAANZ - www.precisionagriculture.org.nz) ran their first conference

2)      the  number of attendees that came from far and wide to attend & learn

Firstly, I’d like to congratulate the PAANZ committee on organising a well-run event with some thought provoking topics and speakers. I’m going to run through a bit of a summary of the day in terms of what was covered and some ideas to ponder.

Andy Macfarlane from Macfarlane Rural Business kicked the conference off to a start with a general overview of NZ ag and where we’re at in terms of water, nutrients and farming within limits. One of the key points from his presentation was that “Good Management Practice (GMP) is a given – everyone needs to get there NOW!” GMP will evolve and is not a fixed point. ‘Good’ will also not be good enough, farmers will need to be ‘great’ to keep ahead of the game and ensure long term farm viability. Precision Ag is going to be integral going forward to achieving this.

Some Key Principles for mitigating N leaching

1. Measure before you apply – need to know what you’re dealing with so you can make the right input decision.
2. Use nitrogen (& water) interceptors – roots, different crops etc
3. Smaller and often applications are better than large amounts and less often
4. Do not put nutrients where you don’t need them (use targeted application technology – Precision Ag)
5. Apply less urine or less nitrogen concentration in urine
6. Increase nitrogen utilisation in gut to decrease output of nitrogen
7. Less water drained = less nitrogen leached
8. Integrated farm systems approach required to achieve long term desired outcome
9. Validation of science needed both at research level and on farm

Keith Cameron, Professor of Soil Science at LincolnUniversity also posed a sound point that irrigation, even though it might be controversial in some areas and need better management allows increased N uptake as the plants are actively growing and not under stress, therefore less leaching of nitrogen results. Is there a case for environmental irrigation? Especially in summer dry areas? He also pointed out that we need to look at plant uptake as a mitigation strategy for decreasing nitrogen leaching. Catch crops following/during winter grazing is likely a good way to achieve this and studies have shown that this can be by between 20-40%.

While we all know that nitrogen itself is a key part to the nitrogen leaching discussion, in irrigated Canterbury and other parts of the South Island managing soil moisture is key to effective nitrogen management. Dr Tony Davoren from HydroServices spoke on this topic and highlighted the following:

• Measuring and understanding your soil moisture is key to good irrigation management and reduced leaching
• No drainage throughout the growing season from pivots if managed well – the same can’t be said of other irrigation systems with high application rates in particular
• You need to measure soil moisture at and below the root zone. Firstly to understand your plants requirements, and secondly to know and be able to prove that you aren't leaching and wasting water
• It’s also important to measure soil temperature as this is also a factor when scheduling irrigation and brings in the ‘farm systems approach’ that Andy talked about by looking at multiple factors.

As the focus of the day was mostly looking at how nitrogen leaching could be reduced using Precision Ag (PA) techniques there wasn't a lot of emphasis on other areas, however some were slightly touched on. These included Ian Yule (Massey University) talking about the economic impact of poor spreading pattern and that it could cost a farmer on average $45/ha if his spreading CV was at 20%, however CV was likely to be nearer 30% when out in the field. At costs like this we obviously need to get our spread pattern accurate before we start doing variable rate fert. Accuracy is key to everything in Precision Ag. The benefits of ‘All Paddock Soil Testing’ was highlighted for reducing paddock to paddock nutrient variation and pushing pasture yield along on dairy farms.

There were a vast array of topics covered during the day, stretching further than just nitrogen leaching and it was truly encouraging to see such a good turn-out of interested people to this inaugural event as well as the robust debates and discussion that went along with it. It’s truly heartening to see NZ farmers and industry pushing the boundaries and meeting NZ farming targets using tools and technologies that are already out there today. The future is very bright for NZ ag and coupled with all of the emerging technologies and the science to back these up I feel very encouraged about the position of the New Zealand farmer. Now to get everyone dabbling their toe in the water of Precision Ag…

~ Jemma

ANNUAL VOLUMES NEED TO BE USED JUDICIOUSLY

In an El Niño spring and summer water for irrigation is a precious commodity.  As expected irrigation started earlyish – like September - and with current predictions is likely to continue through to April.  That means irrigation will be required on a regular (aka daily) basis and will likely result in two potential issues for irrigating farmers:

a)     Groundwater users could have self-limiting bores.  This occurs when water levels drop to the point where cavitation (sucking air) occurs and/or the head required to lift water to the surface falls outside the optimum for the pump.  Both circumstances result in a reduction in L/s that can be pumped.

b)     Of greater concern is that the season is likely to be greater than the 9/10 (or 90-percentile) demand season and annual volume could be exceeded.  Therefore it is essential every effort is made to use water judiciously.

Judicious use does not include irrigating hard surfaces (aka roads).  I thought we had left the “cleaning of roads” behind – it is such an obvious waste of water and is a misdemeanour, in some cases “fineable”.  All in all not a bright use of water!

My first example is an old one and is thanks to a colleague in Hawkes Bay.  It dates back to early 2000’s, maybe 2006ish.  We have used this photo endless time to emphasise this is not the wisest use of water, and in this case a dangerous use of water.  Can you imagine riding a motorcycle and being hit by the stream of water from the high pressure gun!!  It will wash your windscreen though you could run off the road by the time you recover from the shock of the water hitting the windscreen and the wipers have been able to clear 25L/s of water.

My second example is very recent – November 2015.  No doubt the lane closest to the hedge has been well washed.  While this irrigator is less likely to result in a deluge of water on a windscreen or affect a motorcyclist as badly. It is nonetheless a waste of irrigation water.

The volume of water irrigated onto the roads is relatively small in the scheme of things.  But in a season where every drop will undoubtedly be worth $$$ in return, cleaning roads is not an effective way to make the water pay.  Quite the contrary, in both examples the water has been pumped from bores (a lost cost) and has not added any value to crop intended.

Dr Anthony Davoren, http://www.hydroservices.co.nz

WHO SAID IRRIGATING WAS EASY?

Being an Irrigating Farmer has many benefits with increased land value and production to less reliance on rainfall events being at the top of the list.

But with these benefits comes responsibilities and duties to ensure success at being an irrigating farmer.  So, what is involved?

1. Regular System Maintenance

1.       Irrigation System checks should be undertaken pre-season and at least twice over the irrigation season.  This involves doing pressure tests, checking sprinklers and nozzles, cleaning out filters, checking and fixing leaks.  Click on the link below for checklists and guides.

http://irrigationnz.co.nz/news-resources/irrigation-resources/irrigation-system-checklist/

2. Irrigation Evalulations

Irrigation Systems need to be evaluated much like getting a vehicle Warrant of Fitness.  Evaluating your system allows you to check that it is working to the design specifications and performing as you would expect.  High distribution uniformity (how evenly the system applies water) is the key to achieving an efficient and effective irrigation system.  

Ideally, irrigation systems should be ‘farmer’ evaluated annually using the ‘Irrig8lite’ guide - http://www.pagebloomer.co.nz/resources/irrigation-calibration/irrig8lite/.  

Should your system show low performance, a full system evaluation should be undertaken by a qualified evaluator: http://www.hydroservices.co.nz/index.php?option=com_content&view=featured&Itemid=271.

3. Measuring Soil Moisture

Measuring your soil moisture is the BEST way to manage and schedule your irrigation efficiently.  If you don’t know what your soil moisture content is, it is likely you are either under irrigating or over irrigating which can be detrimental to your crop and/or the environment.  There are a number of options when it comes to measuring soil moisture whether it be an on farm service or telemetered continuous soil moisture sensors.  

Find out more at: http://www.hydroservices.co.nz/index.php?option=com_content&view=featured&Itemid=268.

The Irrigation Season has already arrived for some and is fast approaching for others.  If you haven’t completed your pre-season system maintenance checks already, now is the time to do it!

EM Surveying and Water Holding Capacity

In recent weeks we’ve been through the calendar of EMSurveying, A day in the life of an EM Surveyor and The value in ground-truthing your EM Survey in amongst other informative posts from Lindsay NZ and HydroServices. This week we’re going to shed some light on how an EM Survey by Agri Optics can be used to evaluate water-holding capacity of the surveyed area.

Predominately our clients ask us to conduct an EM survey for them to determine the differences in their soils with a view to varying their irrigation depths on the different soil types; however we can adapt the EM Surveys for many different uses, one of these being to evaluate water-holding capacity variation.

The DualEM sensor works by emitting an electro-magnetic field into the soil and measuring the returning conductivity of the soil. The conductivity of the soil in New Zealand is affected mostly by soil texture and the amount of water the different soil textures can hold (the more water the soil can hold the more conductive it is). The readings can also be influenced by salinity, however other than a few isolated areas in NZ we don’t have an issue with salinity affecting the readings. 

Figure 1: DualEM sensor being trailed behind our light weight Polaris

To fully relate the EM readings to water holding capacity (WHC), ground-truthing is needed to quantify the actual WHC at different locations as the EM Survey only measures relative difference of one area compared to another. As we have mentioned in previous blogs we create a map of EM zones and within that locate sample sites for each zone to be ground-truthed. The ground-truthing is then carried out by typically HydroServices using their neutron probe and our agreed protocols. They then provide us with the water-holding capacities for each different depth. From this we then create a map of WHC variation across the surveyed and provide a report back to the client of these additional maps with description on correlations of WHC and EM and recommendations on how these maps would be used to implement more efficient irrigation.  

In addition to getting accurate WHC maps and the associated report back the client can also use the ground-truthing sites to help site soil moisture probes and if the probes are installed before the ground-truthing is completed, the ground-truthing reading can also be used as one of the field calibration readings for the soil moisture probes.  

Figure 2: Water-holding capacity map created from an EM map

All of this information helps the client get the most of their EM data and make efficient use of their water by matching the water to the different zones and then monitoring moisture levels with their moisture probes. If the 2015/16 season is going to be as dry as forecast then making every drop count will be crucial. We not only conduct the EM surveying we can now also provide our clients with AquaCheck soil moisture probes to help manage your irrigation as efficiently as possible. Visit our website or give Jemma or Chris a call to discuss any of the above.  

Temperature – How cold is too cold?

Following on the theme of soil (moisture) sensors, this blog is concentrating on soil temperature.  At this time of the year (mid-August) soil temperature is or has become the most important factor influencing irrigation (and to a lesser degree fertiliser application).  Just like soil moisture, if you don’t get the installation or measurement point this right you will never get any decent data and never be able to utilise the soil temperature measurements with any confidence.  There are three key requirements for soil temperature measurement:

a)     Ensure any sensor is centred at 10cm depth or the measurement is taken at 10cm;

b)     Ensure the sensor or measurement taken is under the crop/pasture (not in a bare patch for example); and

c)     Temperature is measured at 9am (and not 9am daylight saving time).

Why is 10cm depth and 9am so important?  Crop production models use the 9am 10cm soil temperature as a key input parameter.  If the soil temperature is not above the base temperature at 9am then production will be affected.

It is imperative you measure soil temperature on your farm and in the paddocks of interest.  As at mid-August there is a wide range in soil temperature.  On the east coast of both islands the temperature gradient is large – warm enough for pasture growth in the North Island and too cold in the South Island.

In the northern east coast of the North Island (Gisborne area) temperatures have already peaked above the base temperature for pasture at 15°C and have been above 10°C for 6 days in August.

In the South Island (in the example mid Canterbury) temperatures have not even approached the 10°C base temperature.

So whether you have soil moisture sensors installed that also measure soil temperature or you use a $50 manual gauge, measure soil temperature from now to assist and guide the need to irrigate.

For more information on anything in this blog please contact HydroServices 

How to get the best out of your soil moisture sensors Part 2 (DO)

Following on the theme of what not to do with your soil moisture sensors, below are some gems about the best way we have found to install sensors in the event you need to do it yourself, or need to move a sensor.  Remember most of the sensors that are installed are sampling small volumes and only a few cm from the sensor itself and require “perfect” contact with the soil and must be measuring the crop in question.

DO #1

• Separate topsoil from subsoil so it can be replaced the same way
• Put soil on tarpaulin so easier and tidier when put back
• Measure, install, AND RECORD depths of sensor. In this case 10cm to 30cm (root zone)

DO #2

• Install sensor vertically, i.e. on its edge
• Where possible into undisturbed soil. In this occasion we made a slot for the sensor to be pushed into. 

DO #3

• Mark and RECORD where the sensor is located. Marking can be with tiles as shown or something metal buried at 10cm to be found with a metal detector if necessary.
• The ground will settle over time, so ensure all soil removed is replaced, even if it appears to be too much.
• Ensure above ground 'bits' are protected from stock (still to be done here) 

In a subsequent blog we will show that the time taken to install your soil moisture sensor properly will produce quicker and more reliable results. For more information on how Hydroservices can help with your soil moisture sensors you can find more information on our website or you can contact us directly. Cheers, Phil

The Value in Ground Truthing your EM Survey

We’ve talked about water holding capacity (WHC) previously, and following on from Nicole’s blog about visual soil assessments (VSA),  I’m wanting to shed a bit more light on how we go about putting water holding capacity values to your EM soil survey.

An EM survey shows you the differences in the EM value across the site where it is conducted. The values are relative to the rest of the values on the map and are not a specific water holding capacity. To get that you must ground truth the different EM zones and put values to the EM variation.

As a general rule we find that for every EM unit of change in your report, excluding the extremes at each end, the EM unit range is around 7-10mm of WHC difference in the top 700mm of the soil profile. I have to emphasise that this is a general rule and we have seen surveys where 1 mS/m (EM unit) has been worth 30mm of WHC difference over a map and others where the value is a lot less.

To find out the actual variation in WHC for your EM survey, Agri Optics select ground truthing sites and work alongside HydroServices who then go to the site with a neutron probe to ascertain the actual values at the given points. The objectives of this exercise are to:

1. Confirm the EM mapping reflects the differences in the soil moisture content.
2. Provide WHC assessments at key locations in key EM zones.
3. Confirm the EM map can be converted to a WHC zonal map for variable rate irrigation (VRI).

Agri Optics sends an EM map to HydroServices along with the GPS coordinate files so they know where to take the samples.

A shallow EM map with geo-referenced ground truthing sampling points marked.

Agri Optics also gives HydroServices the actual two soil profile depths (cm) and a spreadsheet with the EM values at the point locations.

Point #	Id	Lon	Lat	Zone Value	Shallow EM	Deep EM
1	Orange	175.xxx	-41.xxx	14.37	13.2	40.34
2	Orange	175.xxx	-41.xxx	14.37	12.95	35.73
3	Orange	175.xxx	-41.xxx	14.37	11.44	35.82
4	Yellow	175.xxx	-41.xxx	18.28	17.38	43.73
5	Yellow	175.xxx	-41.xxx	18.28	17.85	46.56
6	Yellow	175.xxx	-41.xxx	18.28	18.2	45.73
7	Green	175.xxx	-41.xxx	21.95	21.84	54.19
8	Green	175.xxx	-41.xxx	21.95	22.66	54.59
9	Green	175.xxx	-41.xxx	21.95	20.31	51.41
10	Blue	175.xxx	-41.xxx	25.81	27.01	62.05

With this data HydroServices then measure the soil moisture, calculate the full point, the stress point and the WHC at each site. This is then compared to the EM values in the different profiles and the correlations drawn up. HydroServices then write a report on their results for the client.

Graph showing the relationship between the soil moisture results and EM data.

From the data HydroServices collects Agri Optics can then generate a WHC map.

Normal EM zone maps can and are used in the majority of situations with great success for VRI, but by ground truthing the zones and generating a WHC zone map, the client is given an extra  level of information and certainty.

Ground truthing sites can also be used for moisture probe placement sites, as these sites have effectively been field calibrated by HydroServices for moisture probes. Agri Optics can provide you with AquaCheck soil moisture probes . I’ll go into more detail on this in a future blog, but more information is available now at www.agrioptics.co.nz/portfolio/aquacheck.

For more information on ground truthing contact Agri Optics or HydroServices.

Blog post written by Chris Smith from Agri Optics NZ Ltd. To find out more about EM mapping or any of the topics discussed in this blog call Chris directly, 021 796876.