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Part circle pivots and K-Lines - how do I schedule my irrigation?

These are some common questions that come up in our irrigation scheduling workshops.

How do I best schedule irrigation under my part circle pivots?

The challenge with part circles pivots is overwatering near the stops, i.e., the same amount of water is applied within a very short space of time as the pivot comes into the stop and bounces out again. As it is often not practical to run the machine back dry, the best solution to minimise this is to apply the desired irrigation depth on one pass and on the return halve this.

How do I best to schedule irrigation under long lines and k-line?

Unfortunately, soil moisture monitoring under these systems is often not accurate because they have poor uniformity. Hand-held sensors can be used (in soils with no stones), but for this multiple samples need to be taken in a repeatable sampling pattern. A rule of thumb approach can also work well. For this you need to know how much water the soil holds, rainfall, and monthly plant water use. For example, for Mid Canterbury plant water use in September is typically 2 mm/day, October 3 mm/day, November 4 mm/day, December through January 4.5 mm/day, February 4mm/day, March 2.5 mm/day and April 1.5 mm/day. If you get 20 mm rainfall in October the rule of thumb would be to turn the irrigation off for 6 days, whereas 20mm in January means turn it off for 4 days.

When should my sprinkler pack be replaced?

Sprinkler manufacturers state that sprinkler packs are good for 10,000 hours, however, depending on water quality they can wear out before this (high sediment loads) or last longer (clean water). A good indicator that the sprinkler pack is on the way out is the regulators start failing, i.e., streams of water can be observed coming from the regulator body.

How do I ensure my soil moisture trace full point is set up correctly?

The best way to check the full point is set correctly is go back to a period when you know it was wet (winter is good for this) and compare where your full point line is set in relation to the trace. Otherwise give Primary Insight a call!


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