Question; Does the polyfill wick water to keep the roots moist, or do you have to maintain the moisture level by top watering??
Because as you explained below neither dry nor waterlogged roots absorb O2 well.
Only things I count on in zone B is darkness,condensation retension,passive airflow between surface,and drain hole,for comfy roots..As the plants pumps from the res,the roots that are in a comfy state keep themselves moist.Though not very effecient,and more stressfull,the larger the container,I feel one can Hempy with only gravel.Zone B will enjoy a flooding from time to time.An over flowing feed,or a thumb plugged drain hole feed now and then mimics what Cannabis loves in nature.
Great explanation on the root zone in the bucket.
I've always tried to get a full light spectrum during the flower cycle. I've used hps only one run between my LED phase and current CMH phase. I wish I'd payed more attention to the roots when I broke down those hps buckets.
I run 50/50 Spectrum with floros in flower.I get more res penetration with the Polyfil,than with Hydroton.Not that the Hydroton stops the feeder roots,but the roots feel more comfort in the less dense Hydroton.This is at the expense of danger of collapse for a larger plant.Imho some 6500K in flower helps with resin production,and aids in an allready low priority at this stage root development.
So in your style of growin' and jella's do you think that the change in mediums at the rez limits the root penetration?? Where with a common medium through zones B & C the roots have no problems in the transition.
I feel as long roots are dipping in res they will find there comfy state on what they are given,and what they can do built in.If the medium in zone C has enough water retension,combined with a comfy state then they will hang,for the feeder roots needs are met.
Concrete does not stop a weed,so neither should let's say Coco as a medium.
I'm not convinced on jella's idea that the extra chunky perlite is creating an air pruning situation. Mainly because the air in the zone will be extremely moist. And as in the 2L root shot I posted I used fresh size #4 perlite which is mainly 1/2" chunks, and those roots went hard to the bottom. I've always believed that letting the rez completely dry forced the roots to head for the bottom. Where as you mentioned that the roots will get cozy if the water source is always available at one level.
Air pruning,or woody/callous roots in zone B would be a result of an inbalance of the comfy state for that specific zone.If I was doing driveway gravel Hempy?That would be exceptible,and I still would get a harvest.It would only mean that zone B is running with some degree of collapse even though it is physically not.
I can theorise that the Gold's Gym style workout for the roots of letting the res run dry can cause an osmotic snap back.Picture drinking milk with a straw.When you reach the bottom you lose suction,and some milk flows back.Now does this flow back trigger the roots to use the flow back juices,and grow deeper into what it needs the most at that moment?I prefer a Jack LaLanne workout of allowing some PH drift,and giving it what it needs when it needs it.
I've got more pondering to do on this topic, sounds like a job for a big fatty.