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