Site selection

These comments are mainly concerned with neutron probes, but the principles will be similar with other measuring methods.

It will be argued that it is not possible to schedule an entire field with data from a single measurement - soils and crops are much too variable.

What is the area that can have an independantly controlled amount of water applied ? An irrigation unit can have more than one monitoring point, but in the end the measurements have to be combined to produce just one schedule.

Multiple monitoring points in the same irrigation unit could be used to investigate variability across the unit - but if it is found to be significant then the water supply system will have to be changed to allow smaller irrigation units.

Separate irrigation units could be scheduled from a single monitoring point if the soil types and crops are similar.

The monitoring point needs to be where changes are occurring
- Not at a dripper, where it will be permanently wet
- Not mid-way between drippers where it will be permanently dry
- In an active root zone to measure crop water use
Need to monitor to below the rooting depth
- To measure through-drainage
- To measure depth of root extraction
Use the average of three tubes to give spatial representation.
The average of three tubes is going to give an estimate of the water content of a large volume of soil.
If the soil varies across the total site, position each tube in different representative soil types.
If the slope varies across the total site, position a tube at the top, middle and bottom of the slope.