one simple modification to the calibration process

[M.Meron]

I would suggest one simple modification to the calibration process, where 
climate conditions permit:

Instead of sacrifing two tubes (one dry and one wet) for paired 
calibration, insert one tube in dry soil - for instance by closing 
irrigation for a while in small spots in the field - collect dry soil 
samples from the insertion hole in depth increments while boring it, read 
density and neutrone probes in the accsess tube and oven dry the samples.

Apply ample irrigation, let it drain freely and repeat the procedure in 
reverse:

Read density and neutrone probes, and by sacrifing the site, take soil 
samples around the access tubes.

In our summer conditions (winter rains only) we have very good experience 
with this calibration process.

[M.Meron]