Tag Archives: neutron probe

Soil Moisture Monitoring

20140214_neutronprobe

HydroServices continues to monitor our crops weekly using neutron probes to assess soil moisture status.

We use their measurements and reports to plan our irrigations.  We also consider predicted weather using MetService, Metvuw.com and HortPlus services. But we don’t always get it right.

For example, on 3rd November we irrigated our onion crop, aiming to get the irrigator around to the peas for the following day. At the time we were told of a 10% chance of significant rain. After filling our profile, we got a lot of rain and most was effectively wasted. You can see that in the HydroServices report here>.

Since November we’ve pretty much kept within the target range of full point to stress point with 15-18 mm irrigation events.

We are finding that 15-18 mm is around the most we want to apply for efficient irrigation. If we apply larger amounts we get surface run off to low spots. While we can prepare a budget that says we applied it, we are not able to account for the full amount in soil moisture readings.

Surface ponding onions
Surface ponding in onions crop following 20 mm irrigation application

The low spots in our onion paddock are easily seen in this image. We could help drainage from the wheel tracks by furrow dyking to hold water where it falls, and by ripping a slot to allow drainage through the compacted track. But we also observe increased run off from the beds to the wheel tracks when heavy applications are made.

In field crops such as vining peas and process sweetcorn we also see lower application efficiencies if we attempt deeper irrigation events. So it is not just wheel track compaction that is involved. We think our soil’s infiltration rate slows significantly once it gets wet. It just won’t let the extra soak in fast enough.