Monday 21 December 2015

A trick to combat rust on your irrigator

Many of us have seen brown or orange irrigators out in the field. If the spans, truss rods, v-jacks and towers are all orange or brown, that’s a sure sign that there is a lot of iron in the water that is being irrigated and in the scheme of things it isn’t generally a big concern. 

Discoloration caused by iron in water supply

What you should be concerned about though is all the moving components that can rust, especially if your irrigator is in a coastal area where the salt in the wind causes rapid corrosion. In these areas some of the first signs and parts to cause problems will be hinges and tower alignment components.
Tower alignment components are vital to keeping your irrigator straight and if any of these parts seize, they can break and the corresponding pivot tower could either get stuck in a moving or still state, or if you are lucky, just safety out the machine before anything bad happens.
Likewise, any hinges that seize will either stop you getting into panels, or simply corrode and snap off. 

We’ve found that fish oil products like the one pictured here are fantastic for preventing rust (or at least slowing it down), making your components last much longer. The frequency that you need to apply it will depend on the climate you are in, but keeping a tin of fish oil based product in the shed and applying it frequently to moving and rust-susceptible parts will go a long way to help extend the life of your system.

Monday 14 December 2015


In an El NiƱo 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,

Monday 7 December 2015

The 2015 EM Season has come to a close

As we fast approach the end of 2015 it is good to look back at the EM surveying season we have just had. Due to the very dry summer we didn’t get going until nearly the end of April which is about 3-4 weeks later than the season before. Stewart Darling join the team this year and many of you would of met him if we conducted any survey work for you. As Stu’s from Scotland he found the colder winter weather easier to handle than this already hot summer! We also changed our side by side Polaris for a larger capacity machine for greater capability in the field and improved downhill descent which comes in very handy at times in Otago!   We did a lot of testing with the new set up to make sure it was performing well before the season kicked off.

Field testing the EM rig on the new Polaris back in February 2015.
Like every season we have faced new challenges and found solutions and developed our protocols to take them into consideration. So next season we will be another step ahead of the previous year! We have met some varied and interesting new clients as well as continuing to work with our existing clients, helping all to achieve their goals with precision ag. through our services.
With the introduction of our AquaCheck soil  moisture probes this season we have been able to add another dimension to the service we offer, not only surveying  your soil’s variability and moisture holding characteristics but now also providing the means to monitor them very effectively.

Travelling past Mount Cook on one of many trips through the central South Island.

Moving forward to 2016 we will start surveying as soon as conditions allow; that is usually when irrigation has finished and we have had a couple of large rain events to negate the man-made influences of that seasons irrigation on the soil. This is usually anytime from late March to April depending on the year.  Our main concern is that our clients get the best data possible. This only happens when the conditions are right so please bare this in mind. If you want to book a survey in for a particular month to fit in with your on-farm management that is fine or if you just want to complete the  survey as soon as possible just let us know so we can keep in touch and start as soon as we’re able. For all enquiries be it for just more information on our services or a full quote please contact us at Agri Optics.

Wishing you all a fruitful and productive summer for what looks to be a very challenging time ahead. And hopefully you have the tools in place to help manage your water resource as efficiently as possible! Have a Merry Christmas and all the best for 2016 from the team at Agri Optics.
Chris Smith

Agri Optics 2015/16 Xmas Hours:
Closed Wednesday 23rd December  & re-opening on Tuesday the 5th of January. For any urgent matters over this time please call Jemma Mulvihill on 021796124. 

Monday 30 November 2015

Is your irrigator going to perform for you this season?

Most of the country's irrigators should be well into gear by now, so it's a good time to ensure that your system is going to get you through the season with as little hassle possible.

Giving your irrigator a mid-winter service is generally the best way to prevent mechanical breakdowns the following season. A mid-winter service generally involves things like lubricating joints, replacing oil in gearboxes, looking for signs of fatigue, etc. Addressing these points will go a long way in setting you up for a happy irrigation season to come.

Avoid scenes like this!

If you have or have not given your irrigator a winter service, there are several crucial things that you should check at the beginning and throughout the irrigation season. Some of the simple things to check include:
  • Riser pipe is greased and well lubricated
  • Tower box components are free and not corroded. Depending on the type of alignment your pivot has, there may be points to lubricate. If joints corrode, seize, and fail this will cause your machine to safety out.
  • Alignment is good – when the pivot is running the spans naturally have a bow one way or the other depending on whether it is in forward or reverse. If this bow is always one way, that is a sign that the alignment needs adjustment and excess pressure is being put on spans, towers and the centre point. This can also lead to excessive wheel rutting.
  • No electrical components are exposed. Loose cable glands can let moisture in to electrical components and lead to premature failure.
  • Tyre condition – this one should be pretty obvious
  •  No obvious leaks – leaks should be treated early as can often be fixed by simply tightening components. For example, if a flange joint between span-pipes is leaking, that is a sign to immediately get up and check that the nuts and bolts are all tight – a simple way to avoid a disaster!
  • Visual inspection – anything that doesn’t look right probably isn’t.

Signs of fatigue such as the crack in this base beam bracket should sound alarm-bells!

If you are not comfortable with repairing any of the issues you find with your machine yourself, it is going to be much cheaper to get a service technician to come out and repair it now than it is going to be when it causes your machine to stop working, causes more damage, and affects whatever crop you are irrigating.

Monday 16 November 2015

EM values - What the data is telling 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 0-40cm 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 85cm deeper. This is why the deep EM readings are always higher than the shallow as it is reading that extra 85cm.

Figure 1: Shallow EM of the same area with values from 1.6-27 EM units (mS/m)

Figure 2: Deep EM survey values varying from 16-43 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 factors 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!

Also of note as an aside; is that with all our readings legend red is the lowest value and dark blue the highest. This does not mean that red is bad and blue is good, there are a number of factors that determine that, and there is also a climatic influence on what is good or bad, in a dry year the heavier EM areas would be better where you don’t have VRI, and in wet years the lighter areas with more free draining soils would be more favourable. Likewise in peaty acidic soils with high organic matter they would show through as the high blue EM areas and clay soils would show up as the lighter red soils on the map. So it is always worth taking samples as you conduct the survey to see what is affecting the readings.

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

Chris Smith.

Monday 9 November 2015

Irrigator Maintenance – Sand

A little while ago I wrote about Sand Traps and how they should be inspected and cleaned regularly. This week we’ll look at the effect sand has on your irrigation system.

In general terms, sand inside an irrigation system = bad!

Sprinkler spray pattern

Just like sand-paper or sand blasting, sand suspended in water inside your irrigator is abrasive and will cause expedited wear on your system. This wear occurs anywhere exposed to the sand. It will start at the pump, causing impellors to wear faster, go through your mainline and headworks. If you have a mechanical flow meter, this will suffer. The sand then gets into the riser and makes its way along your span-pipes causing wear on the galvanising all the way along. Some of the sand will make its way up into the goosenecks and then down into your regulators and sprinkler nozzles, then onto the sprinkler plates. And guess what – it’s still abrasive and causing wear on these components too!

The main two problems caused by sand wear are
1.       Decreased life expectancy
2.       Decreased performance

As components like regulators and nozzles experience wear, they will start letting more and more water through, the more water that is going through, the greater the wear and the cycle continues. Your nicely calibrated system at the beginning of its life will soon start to over-apply water and as it is doing this it is also causing more wear on the sprinkler plate which will distort the sprinkler’s application pattern.

If you have a lot of sand in your system, other than emptying the sand trap frequently, you should also be aware that your system will need checking and re-calibrating more frequently to account for the wearing effect.

In order to mitigate some of the bad effects caused, you might want to consider a sand separation system such as the lakos sand separator filter pictured below. This type of filter will remove 98% of sand-like particle matter down to 200 mesh (74 micron) with low and steady pressure loss of only 0.137 to 0.413 bar.

Lakos sand separation system

For more information about sand filtration systems, contact your local Lindsay dealer.

Wednesday 4 November 2015

My Soil Moisture Sensors Are Spot On – Yeah Right!

There is a misconception that all soil (moisture) sensors are precise and tell you the exact soil moisture content.  Not so.  HydroServices runs a trial site where a number of soil moisture sensors are installed for comparison – for both the “calibrated” soil moisture content and any long term trends.  A boring looking trial site because the sensors are installed toward the small gap in the trees.  In all there are 8 sensors – neutron probe, Decagon 5TM and GS1, Acclima, AquaCheck and two (2) Aquaflex.  The Decagon 5TM, GS1 and Acclima sensors are installed at 10cm, the shallow Aquaflex on a slope from 10-25cm, and the neutron probe and AquaCheck can measure at 15 and 10cm respectively.

Sensors are provided with a factory calibration, usually one for silt loam, clay loam and sandy loam soil types.  These are generic and may or may not truly measure the soil moisture content at your location because (for example):
a)    Your soil is unlikely to be the same as the generic soil type;
b)    The sensor is poorly installed (especially if there is not perfect contact between the sensor and the soil); and
c)    The soil is loose (cultivated) and perfect contact is not possible

While the traces of soil moisture content are sort of similar, none (with their generic calibration) read the same soil moisture content, as shown in the plot of all sensors.  (Note the GS1 Sensor is a recent addition and no data is available for the dates compared).

The only sensor that has been calibrated against true soil moisture content (gravimetric laboratory analysis) is the neutron probe.  Knowing that Field Capacity at this location and soil type should be about 40%; only the neutron probe and Aquaflex measure soil moisture content at this level.  The other three sensors measure field capacity 10% less than the true field capacity. Disconcertedly two sensors measure soil moisture content between irrigation events (the vertical rise in the traces) at or very close to wilting point – approximately 17-18%.  This is not the case; the pasture never died nor showed any sign of being close to wilting point.

What is to be taken home from the comparison?  If you want sensible and realistic soil moisture measurements the sensors must be field calibrated.  The simplest and easiest way to field calibrate is by neutron probe – click on for more details.

Monday 19 October 2015

Irrigator Maintenance - Sand Trap

Have you ever removed your sand trap or flushed your pivot?
It may surprise you, but this is a question we often ask when people are having trouble with sprinklers on overhangs and we are questioned in return “What is the sand trap?”

Sand trap location shown by red arrow

Every centre pivot and lateral irrigator should have a sand trap just after the last tower and immediately before the overhang. You’ll often find it directly below the boost pump for the end gun.

During normal operation, any sand and fine particles that make their way into the irrigator will travel through the spans and then settle in the sand trap. For this reason, the sand trap is designed with a ring-lock mechanism so that it can be quickly and easily removed, inspected, emptied and replaced.

Components that make up the sand trap

How much sand and fine debris is pumped through your irrigator will determine how often you will need to empty the sand trap. How quickly the sand trap fills is something you will learn from experience. Note that the amount of sand pumped out of a well can change over time and may be affected by events such as earthquakes. You should never let your sand trap fill completely as this will mean sand will go past your sand trap and continue to go down into the overhang.

If you’ve got an exceptionally sandy water-source, or you’ve neglected to empty your sand trap for some time, your overhang may be filling with sand. This adds weight to your irrigator increasing mechanical stress and in extreme cases blocks entirely and stops water from coming out of the sprinklers on the overhang. If your overhang has a build-up of sand, you can remove the plate on the end of the overhang and pump a small amount of water through your irrigator to flush the sand out.

Of course, proper maintenance and emptying of the sand trap will avoid having to flush your machine. Sand also does all sorts of other damage to irrigators. We’ll look at what sort of damage it does and how to mitigate this in a future post.

Stu Bradbury

Tuesday 13 October 2015

Good Old Spring Weather

In the past seven days we have had a bit of everything, 10 to 29 degree days, 100km per hour NW winds, rain through to hail and bitterly cold southerly winds reminding us that spring is upon us!

Whilst forecasters don’t always get the rainfall amounts correct, they are pretty accurate when it comes to predicting strong winds.  After the wind on Sunday, it only took two minutes after leaving home to see some damage caused by the strong NW winds.

With a long dry irrigation season predicted, a broken irrigator can take a long time to fix leading to reduced yields in crops and lost dry matter in pastures. This can be avoided by having a simple plan in place for windy conditions, whether it be securing pivots to a heavy roller or parking a Rotorainer in a sheltered position on the farm.

Measuring and recording rainfall through the season is also key, rain gauges are cheap and may help save valuable water, especially in the shoulder seasons.  Turning irrigators off for a couple of days here and there may not seem like it making a big difference at the time, but those days all count at the end of the season if water allocations are getting tight.

Weather forecasts
The forecasters are predicting cold and wet weather on Tuesday this week, perhaps an opportunity to save a round or two with the pivot if they are correct.

Happy Irrigating!

Mark Fitzgibbon

Monday 5 October 2015

Variation in Electro-magnetic (EM) Readings

When talking to clients about Electromagnetic (EM) surveying of soil’s conductivity, I often get asked what a low or high EM variability is. This is quite a hard question to answer, as there are so many factors that you need to take into account. These include:

1.       The region of the country where the land to be surveyed is located.

For example, as a general rule there is a big difference between the readings we get in Otago compared to the Canterbury Plains. However within each of those regions we can also get big variations from the stony soils to the areas of heavy clay. So it is definitely site dependant within a certain range of values. In areas like Seddon and Ranfurly we have also come across salinity issues that take the EM readings to a different level all together. 

Figure 1: A vineyard in Otago on sloping ground.

Figure 2: The relatively flat, stony river bed soils on the Canterbury plains.

Figure 3: Salinity issues near Ranfurly can be visibly seen to effect crop growth and can dramatically increase EM readings.

2.       Geography and topography features.
These features can also influence factors affecting the soil depositions and therefore the EM readings. We often find that weathering and water movement over many years can create areas of higher EM readings. Topography data from an EM survey also backs up this finding. We use the VA Gateway software platform to analyse these different layers side by side, bringing all the different data together.

3.       The time of year the survey is conducted.
We take this in to consideration in our EM reports. At Agri Optics we don’t start our surveying season until the Autumn and then not until the ground has had enough rain to bring it nearer to field capacity, eliminating the effects from that summer’s irrigation. In previous blogs we have shown why surveying in Summer does not provide good data and I would be extremely cautious of the quality of data provided by anyone offering to conduct a survey for you in the summertime. The EM readings in Autumn are slightly less than you would get in the Winter and early Spring. Winter generally is the season that gives the higher readings followed by Spring. Our main concern in Winter is that the ground can be travelled on safely without damaging the crop and without getting our light weight EM buggy stuck. We continue to get very good data Spring, but as we get into further into Spring the EM season is draws to an end as farmers start  up their irrigators. At this stage we stop EM surveying, as we start to pick up the influence of the irrigation applications on the soil maps. So if anyone is still thinking about having a EM survey conducted this year, you should get on to it straight away, as time is slipping away.

When we carry out an EM survey the sensor is measuring the soils conductivity at two depths simultaneously, the shallow EM and deep EM. In a pastoral situation we recommend using the shallow EM layer to base decisions off as the crops roots are predominantly within this shallower profile. In an arable scenario where you have crops roots going deeper into the soil profile we would recommend using the deep EM layer to make your management decisions from. These readings are generally higher than the shallow EM readings as they measure deeper into the soil profile.
In the next few blogs I will go into more detail on how historic management practices and historic boundaries can sometimes come through on an EM survey and how the EM survey can be used to identify salinity issues. For more information on EM surveying or if you have any questions please contact us at Agri Optics.

~ Chris Smith

Wednesday 23 September 2015


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.

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 -  

Should your system show low performance, a full system evaluation should be undertaken by a qualified evaluator:

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.  

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!

Tuesday 15 September 2015

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.  

Tuesday 8 September 2015

Variable Rate Irrigation Pioneers

Ashburton cropping farmers Eric and Maxine Watson (Rangitata Holdings) were the South Island’s original Precision VRI pioneers. Ordering four VRI systems in 2008, after only two systems had been built and tested less than twelve months earlier, Eric and Maxine took a lot of trust and belief that the system would achieve what Precision Irrigation claimed.

This 3 News clip has been bought out of the archives from 2008. Eric and Maxine Watson along with Stu Bradbury, one of the engineers who developed the technology, showcasing the first system up and running in the South Island. And the results exceeded their expectations. The Watsons now have seven out of their nine lateral-move irrigators fitted with Precision VRI. 

The Watsons farm 490 hectares on the Canterbury Plains, with annual rainfall of 600mm, growing a wide range of crops on different soil types. In 2005 Rangitata Holdings water right restricted their annual and daily water take, so they started looking for ways to stretch their available irrigation water. With an annual water volume of 1,183,500m³, 3.7mm per hectare per day and 5ha of irrigator overlaps, VRI was considered as the solution to save water where it was being wasted. An unlooked-for advantage was the negated need for turning taps off and on when watering in pivot mode.
At least partly as a result of maximising water efficiency, and being able to prove minimal wastage, ECan raised the Watsons’ annual water volume to 1,420,000m³, 4.1mm per hectare per day. This consent only permits pumping 270 litres per second across all pumps. When one irrigator is watering in an over-lap situation or using different rates over different crops, they are able to use the saved water to turn on another smaller irrigator elsewhere on the property, thus ensuring soil moisture levels are maintained at critical times.

“It’s a great system with a big future... Now that I have VRI, I wouldn’t want to run the machines without it.”

Caption: Eric and Maxine say that the Growsmart Precision VRI system exceeded their expectations allowing them to maximise the use of their limited annual water volume allocation.

The couple’s dedication to efficient water use has seen them recognised with numerous awards including the 2011 Canterbury Ballance Farm Environment Award and the Environment Canterbury Water Efficiency Award. The Watsons say they were just doing what was needed to get the best out of their limited water take. Once they identified the greater efficiency with Growsmart Precision VRI, the opportunities snowballed. 

Eric and Maxine had the property electro-magnetically (EM) mapped and the soil water holding capacities quantified. Soil moisture sensors were installed to measure the actual moisture content of the soil. This allows the Watsons to schedule the correct amount of irrigation to individual zones which is then applied by the intelligent Growsmart Precision VRI system. This results in the crops getting the exact quantity of moisture required and no water is wasted. Resulting in a considerable saving of 15% of water that can then be used elsewhere.

"Being able to match application rates to the exact amount of water needed to ensure the soil has enough moisture is important to water efficiency and means that over-watering of crops is eliminated."

For More information contact your local Zimmatic by Lindsay irrigation dealer or visit

Wednesday 26 August 2015

The EM Surveying Calendar

We have had another successful EM year so far and our clients have used their surveys for many different uses. I will go into that in more detail in a future blog. Today I will cover the EM and the four seasons. I often get asked when the best time to conduct a survey is, the answer is any time from late autumn through winter into the spring right up to late November.

For an autumn survey, natural moisture is our deciding factor on start dates.  Once the irrigation on farm has finished and we have had at least a good 50mm of rain to balance out any irrigation affects, we can start EM surveying. This year we held off until the end of April and in some areas south of Oamaru and north of Canterbury later still, as we didn’t get the 50mm+ for quite a while. So we concentrated on the areas that once they got too wet we knew we would not be able to get on again! Getting this sort of information from our client’s knowledge of the land is very useful to help with the logistics and completing the survey with as little fuss as possible. Once on site we are self-sufficient and conduct the survey without the client having to get involved, but we rely on good information on the conditions to manage the logistics before we arrive!

Getting ready to start a survey in Ellesmere, early May.

Winter is ideal for surveying and the concerns here are not getting stuck and being able to get along without making a mess especially in cropping situations. We can juggle between all grassland projects and cropping regimes as the weather fluctuates between torrential rain and drying enough so we can travel on it! It involves shifting jobs around depending on the conditions to ensure we get all the projects conducted in a timely manner, not making a mess or damaging crops and without too much to-ing and fro-ing, to ensure all data is collected as efficiently as possible. On some farms we have to leave a few paddocks if they have winter feed crops in or crops in the ground still to be harvested, in that situation we can come back in the spring and drive some transects over the rest of the project and tie all the data in together. Ponded surface water is not an issue and does not interfere with the EM readings and results. If there is a big rain event between starting and finishing a project we can tie the data together be driving transects and using our robust protocols to ensure data quality is not compromised. The only weather that stops us is snow! Mainly because we can’t see the ground and any potential hazards are covered up, as well as getting to and from the site can be tricky, we had a few close calls getting in and out of regions this winter but we managed to keep ahead of the snow!

Surveying near Staveley in July once the snow had thawed.

In the spring we also get good results, the temperature is a little warmer and we can get along very well in most cases, the only issue comes in the cropping situation when the crops start to get too tall. Generally we are fine in a cereal crop until stem elongation. Again it is a matter of logistics and knowing the clients requirements, timing limitations and concerns, as long as there is good communication this is not an issue. We can and have EM surveyed right through to early December before in dryland situations where there has not been any irrigation and good natural moisture. Once clients start irrigating the influence of the irrigation pattern will start to show through in the data. In the summer itself the ground is too dry, the variation in your soil textures is still there but the low moisture levels means the range in EM units is reduced and the EM profile compressed so outside influences start to creep in and have more of an effect on the readings so reducing the quality of data – which is the main reason we make a conscious decision to stop as quality data is of paramount importance. In situations where we are just looking to gauge salinity issues then we can go later as the very high EM values (150-600 mS/m) are not affected by moisture, but for general EM work we stop and concentrate on the other areas of precision agriculture until the following autumn. 

Surveying in late August on a freshly drilled spring barley paddock near Blenheim.

Now we are getting to the end of August if you are still interested in getting a survey conducted this year please let us know as soon as possible otherwise you may have to wait until next autumn.

Chris Smith
Field Manager Agri Optics NZ Ltd

Friday 21 August 2015

A guide to S-Map

What is S-Map?
S-Map is a map containing information of the soils across the country. It is being developed by Landcare Research and information is continually being added to it. The project was started to collaborate and update information on New Zealand’s soils into one easily accessible map of the whole country with different layers of information for different applications and to support land management at different scales.

Anyone can access the information freely. Mapping is carried out by Landcare scientists who either use old soil maps or go to the area and undertake traditional soil surveying. This is where soil core samples are taken to determine the soil type and this information, alongside the history of the area, is used to present what they think the pattern of soils will look like. The most detailed information available is currently on the lowlands while the uplands of the country are being mapped using digital modelling based on the soils having similar characteristics to other known soil types.

How to use it
In the previous blog (identifying soil textures) you see how the content of sand, silt and clay determines soil physical properties such as WHC, porosity and bulk density and how there are different horizons in a soil profile with different quantities of these three particle sizes. S-Map also uses soil horizons to determine soil characteristics.

You can search for your location on S-Map and select to see polygon layers to view the soil types present on your farm as shown below for Methven, Canterbury.

S-Map Online is freely accessible for anyone;
You can then select the ‘Soil information’ tab at the top of the screen and click on a point on the map. S-Map will show you the percentage of each soil type present around this point and you can select to view the factsheet of the dominant soil type (and the other soil types present). In the figure below the Greenvale farm near Methven is shown by S-Map to have three dominant soil types: 50% is a shallow, well drained Eyre, 25% is a shallow Darnley and the final 25% is a moderately deep Mayfield.

The soil will have been given a series of names using the New Zealand Soil Classification System however don’t worry about this too much, the information contained further down in the factsheet has more practical applications. The fact sheet tells you:
  • ·         How stony the soil is which relates to its drainage class
  • ·         The amount of water expected to be held at different depth increments
  • ·         The clay content
  • ·         Potential rooting depth
  • ·         Soil phosphorus retention
  • ·         Water management such as the potential for waterlogging and drought
  • ·         Nutrient management such as nitrogen and phosphorus leaching vulnerability. 

Page 1 of an S-Map report for an Eyre soil, downloaded from
You can also select different layers to view on the map, on the left hand side of the screen: soil drainage, depth to hard soil/ gravel/ rock and soil moisture. The map will then update using the colour scheme from the legend for this layer which is shown on the right hand side of the screen. The figure below shows that for the Greenvale farm the soil drainage depth layer has been selected and on the right hand side the legend explains what each drainage class means.

S-Map brings all information on NZ soils into one database that can be easily accessed and used by all land users and interested parties. It is the largest national resources on soils that NZ has and it contains a range of information that is relevant and useful for all scales of management. However there are also aspects to S-Map that limit its usefulness, especially to farmers.

According to S-Map the Greenvale farm, shown in the S-Map figures above is a mix of mainly three soil types. However an Electromagnetic map carried out alongside soil sampling showed that there was, in fact, a much more complex pattern of soils present on the farm. The picture below and top is the Electromagnetic map of the property and the different colours represent different textures while the picture below and bottom uses the patterns from the EM map alongside soil sampling to identify the pattern of soil types (families) on the property. 

Top, EM map by Agri Optics Ltd. Bottom map of soil types developed from soil sampling.

These maps provide a substantial amount more information than the map of the farm from S-Map (discussed above). The soil information used by Overseer to determine nitrate leaching is supplied by S-Map and this can result in inaccuracies in N leaching figures when S-Map believes the soil pattern on a farm is more simple or different than it actually is. Furthermore using soil information from S-Map for irrigation scheduling could mean over or under irrigating areas which can decrease yields as well as creating inefficiencies in water and power use.