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.

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.

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.

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 http://www.hydroservices.co.nz/index.php?option=com_content&view=featured&Itemid=308 for more details.