I don't see anything in the pics that indicate N def.  However, the browning of the lower leaf margins is strongly suggestive of K def.   Sometimes P def also does this, and the plants have a dull greyish color, so P def is quite possible.  There may also be Mn, Zn, or Mg def lurking.  Need to figure out what the #1 problem is first, and the others may (partly) correct themselves.  S def cannot be ruled out either, but I suspect it isn't the main problem here.

The high amount of residue wouldn't be a problem unless the climate is very cold. However, excessively wet (and cold) soils do limit P & K uptake, as well as slowing mycorrhizal infection. 

There could also be issues with nutrient toxicities, since this is Australia -- B toxicity, for instance.  Or excess salt in the soils.

If there is slickening of the sidewall (where it was wetter during planting), or if straw is tucked into the furrow, there can be some slowing of the crown roots. 

This corn may grow out to be entirely normal.  However, I would strongly encourage you to take plant tissue samples and have everything analyzed (including moly, B, Cl, Na), along with soil tests from the same spots(s). And also b'cast K onto at least part of it and hope a rain will move it into the soil so you can see if you get a response.

Presumably you have also thought about herbicide injury and ruled that out.

cheers,

[Edited a few minutes after initial posting.]