You know Nullis...I'm not sure whose side you're on. And when I said "I don't suppose it matters..." I was being sarcastic to pSi007.
Back on topic (so I don't get my hand slapped) On the subject of organic vs inorganic: I will cite the venerable AlB Fuct, the plant can only use nutrients in their chemical form. So you add compost...but the plant selects NPK to absorb (plus a host of micro-nutrients) So really, I guess it doesn't matter from a certain perspective.
JD
As far as sulfuric acid goes, I agree with you that it is not carcinogenic in solution, and not in diluted solutions, and is probably just fine for use as pH down in hydroponics. Sulfuric acid is carcinogenic when inhaled. Nobody who grows hydroponically should be using fuming sulfuric acid, and saying that people who use diluted solutions of it for growing are "adding carcinogens" is a stretch by any sense of the word.
However, there is something really big you're missing with the "plants can only use nutrients in their chemical form" perspective. There is another reason for adding compost/earthworm castings besides providing nutrients. Plant roots absorb [most] nutrients as simple ions or charged particles: cations are positively charged, anions are negatively charged. They are "inorganic" in the sense that the particles themselves are carbon free.
Nitrogen is the only nutrient that can come as either a cation (NH[SUB]4[/SUB][SUP]+[/SUP]) or an anion (NO[SUB][SUP]3[/SUP][/SUB][SUP]-[/SUP]). Many are available as cations: Ca[SUP]2+[/SUP], Mg[SUP]2+[/SUP], K[SUP]+[/SUP], Fe[SUP]2/3+[/SUP], Zn[SUP]2+[/SUP], Mn[SUP]2+[/SUP],Na[SUP]+[/SUP], Cu[SUP]2+[/SUP]. Others are anions: Cl-, S[SUP]2-[/SUP],
MoO[SUB]4[/SUB][SUP]2-[/SUP] (molybdate), H[SUB]2[/SUB]
PO[SUB]4[/SUB][SUP]-[/SUP] and H
PO[SUB]4[/SUB][SUP]2-[/SUP] (ortho-phosphates primarily), H[SUB]2[/SUB]
BO[SUB]3[/SUB][SUP]-[/SUP] (borate), etc. In soil ammonium is readily converted to nitrate by microbes. Other elements have their own peculiarities, for example P has a tendency to form complexes with other things in the soil that result in it becoming unavailable. They may also displace or interact or compete with each other.
Ion charge is an important consideration because humus/compost/soil, clay as well as sphagnum and coco coir (used in potting mix) actually have a tendency to hold onto the cations (cation exchange capacity). Soil, or humus/clay particles possess a net negative charge, which allows them to hold onto cations such that they will not leach out of the soil, but remain plant available. Those anions which do not precipitate or complex with organic matter have a tendency to leach out of the soil, and concentrations of them can be low in the soil solution.
Luckily, plants didn't evolve alone, and soil is not an inert material by any means. Forest soil\humus is alive with thousands of different species of bacteria/archaea and fungi as well as other microbes and beneficial organisms. Plants establish mutually beneficial (symbiotic) relationships with a variety of micro-organisms, which the plant helps to support via plant root exudates, including carbohydrates. One of the most notable relationships is between the plant root and several species of fungi which are referred to as mycorrhizal fungi. This kind of fungi forms an intimate relationship with plant roots, either penetrating the root cells or forming a sheath around them, and they go out in search of minerals (particularly phosphorous) and water to bring back to the plant. The way hyphae grow they are able to branch out and increase their surface area much more efficiently than plant roots, they can go places the roots can't get to and fungi have enzymes that allow them to digest and dissolve materials to convert them to plant available form.
A primary role of bacteria and fungi is to decompose organic matter, resulting in plant available nutrients; while other microbes eat the bacteria and fungi and each other, resulting in even
more plant available nutrients. But this whole process results in more than
just plant available nutrients. Humus is the end result of composting/leaf litter and vegetative decomposition. It has micro-organisms and plant usable nutrients, but also humates, humic substances and humic/fulvic acids. Humic and fulvic acids are natural chelating agents. They form plant available complexes with certain metals and micro-nutrients, assisting with nutrient availability and transport. Certain kinds of bacteria/archae can even take the nitrogen gas from the atmosphere and turn it into ammonium (NH[SUB]4[/SUB]+), while others can further change it into nitrate.
Microbes in organic soil do even more than make nutrients available, protecting the plants from predators, regulating pH in the rhizosphere, producing antimicrobial compounds and even plant growth regulators/hormones. Really, the plant is selecting which microbes to stimulate for greatest benefit to itself.
