You’re definitely getting it, I’ll try to answer best I can, I only know so much. I was taught a grow room is a large system full of smaller sub-systems (media, plant tissue, water, etc).
Let’s take a hydro-reservoir RDWC setup vs your ocean example. The larger the volume, the higher the mass, the higher thepositive pressure, so the bottom of the ocean is basically a crushing + push force from the water’s mass.
Now the reservoir, a small mass, we can guess a res would range +1 to + 3 without a pump on, estimate it using density, mass volume & area, or measure it with an instrument. But let’s assume +2. Now we turn the pump on, and once again guessing, let’s say the moving, vacuumized water is now -15 as it is now being sucked into the pump.
The negative pressure in a room is -5000 or lower (-7000 and below) with a HVAC system.
-15 is a much higher value than -5000.
So the water is being sucked by the immense negative pressure into the environment. The value of negative pressure in your grow area is HVAC’ed so high that it will dictate the negative pressure within the plant. This occurs first at the leaf/stomata surfaces (guessing -80) which puts pressure on leaf vein cell walls of its xylem and phloem (the plant’s ‘arteries/veins’, guessing -60) after leaf veins, the axillary branches (-40) down the trunk, (-25) all the way down to the base of the plant (-20) and finally the root zone (-15). In this way, water travels from high (roots -15) to low (-5000 grow room air). It is very similar to a humans blood pressure, in that systolic pressure is strongest at the systemic artery, only we don’t breath out blood lol. We don’t rely on air pressure to pump our fluids until things get crazy, like your ocean example, where even at safe depths sudden depth changes pressure and can cause air bubbles in our blood. So hydro water is negative, but just not as negative as the environment. So water gets sucked into the plant readily. Having a negative pressure in the water only completes the cycle, as a positive water pressure would still keep plants alive, but with a slower rate of growth, no oxygen, and bacteria growth, etc. They wouldn’t live long because of all the detrimental effects of stagnant water, but theoretically could still live if it were to be filtered/cleansed daily. Like a fish tank. But that would be gross and way more difficult to oxygenate with hydrogen peroxide, fun to consider though. It’s amazing how all systems play together. In theory, you could perfectly balance this environment vs pump pressure to have the perfect rate of nutrient application to your plants, which could vary even by! Field capacity is assumed -15 based on -5000 average outside air pressure. Remember the environment is the ultimate, negative (low) pressured vacuum.
So now apply this to a coco pot, that dumping of water is a push, or + pressure. This forces the water and old salts to drain, as now the pot is pressurized. This only lasts as the mass of the water in the pot drains away, out the bottom, and the immense negative pressure of the environment acts the whole time, once again sucking water from the pot and plant/roots from +30 to 0 bar, over time water is sucked out of the soil surface and plants until the media reaches -0.1, then with more suction-time -15 media bar is reached, the pressure know as field capacity. Field capacity (-15) is the perfect low media pressure where the root zone is optimally oxygenated by free’ed up pore space, as well as fully ‘drinking’ water with filled pore space. This is assuming -5000 outside air, remember, the environments negative pressure is the ultimate vacuum drawing water out of your plants and into the air. The media itself is made of micro pores (fine grain) and macro pores (large grain). Putting large grain under fine further enhances pot drainage, like perlite at the bottom. This drainage can return your media to field capacity even faster, allowing you to get more nutrient cycles. In the case of hydro, you could theoretically balance the pump to -15 water pressure and aim for -5000 in the environment, at which point you could operate at field capacity
Pressure!!! -30-35 is known as the wilting point for most species of plants, where in the mass of the water has become way too low. Also theoretically, you can easily run hydro at wilt point, where the environment is way too strong of an HVAC, and water is being sucked from the plants too fast, causing less nutrient absorption. A hydro field capacity might actually be -30! No idea If there’s data On that! Just Remember the general science rule, matter/energy travels in the direction of (high)—>(low) and you’ll be good.
