Core Exposures and C1/2

[JMOL3]

Noticed in section 10.2.7, the advice against <50mm cores being primarily focused on their lack of ability to sample below the topsoil.
I'm assuming this is soil diameter/core tube inner diameter.
Over the ditch, Christie handheld petrol driven corers with 38 or 42 mm cutting tip inner diameter are probably amongst the most common cores taken, and can pretty reliably get down to 1m +.
Is the depth restriction in the C1 category more associated with push probe cores, or do the 38/42s struggle because of gravels/texture differences in NZ?

What are the common sampling tools across NZ these days?

Not suggesting that 38 or 42 mm cores are appropriate for mapping, they probably have similar issues to augured samples, giving less information on structure, making mottles and multiple matrix colours harder to identify, etc.

[lauren-obrien]

Ah, you've actually spotted a regression - I had a similar conversation a few months ago and we agreed to drop it back to 40mm so that standard corers like the Christie driver weren't caught up. NFI why I put it back up, probably a deep subconscious desire for nice round numbers 🙃.

We use Christie corers here quite a bit. They do have some limitations around where/when you can use them and what you can realistically describe given the 'observation window', but they certainly have their place.

What I'm actually trying to single out as 'less good' are these punch-probe type samplers:

• https://www.soilsamplers.com/collections/soil-probes
• https://nzsti.co.nz/product/20mm-soil-sampler/
• https://www.royaleijkelkamp.com/products/augers-samplers/soil-samplers/grass-plot-samplers/

They're fine for e.g. bulk sampling over a paddock, but you can't really do any description stuff beyond colour and texture on what they extract. They also have a fixed depth limitation, usually 10-40cm.

Pulling the diameter cutoff back to maybe 30mm might be better, and/or adding some commentary about 'fixed depth samplers'?