Fruit, Veg or Composting?

[salome2001]

ooh, won't you need an EU pesticides licence for that???

[veggiechicken]

Feral definitely won't need anything EU licensed!!

[snohare]

<Dons anorak>
I was never formally educated in chemistry at school (their one and only computer screwed up the timetable for the Chemistry classes for me at a crucial period), but my understanding is as follows:
Acids are molecules - a molecule is any collection of atoms, sometimes more than one different type of atom. (An element is made of just one type of atom.) Any chemical whose formula begins with "H" is usually an acid; e.g., H2SO4.
They are acids because they react with other chemicals called bases, and in the process break down into salts and spare protons (bitties of atoms). In water they conduct electricity, which makes them electrolytes - very useful energy to power chemical reactions. So they are inclined to transfer/modify to other chemicals relatively easily, and this is why (slightly) acid soil is better for growing most plants in - you have lots of chemical changes already going on, and the roots can more easily grab the available protons/chemicals/electrical charge that are around, rather than having to start the process from scratch. Most nutrients (as well as pollutants) occur in the soil as salts, and this is why plants take them up.
Different acids vary in how they behave because although they have similar structures (electrolytes in water, and those spare ions/protons) which gives them some things in common, the bases which they are made of have different properties. That's why when oxalic acid meets calcium, they bind to make a chemical that won't let the calcium interact with other things very easily. (Did you know the calcium in milk is like that ? Bit of a fib by the Milk Marketing Board. )
So:

are they still acidic enough to affect the soil?

Only until the first chemical reaction takes place. You have to flood the soil with lots of extra acid to change the pH. Water does this best, if the soil has salts.

what acid makes soil acidic?

Loads of 'em. Strong acids and weak acids (which is which depends on the base atoms).

If "acid" is just a generic term for any acid, you could alter the acidity of soil by say, watering it with vinegar - but nobody does this (or do they?)

Yes, you could alter the acidity with any acid; but sometimes you'd poison the soil (and plants) because of the base of which the acid is made, or how it would react with other things once broken down.

So, if rhubarb leaves were used around blueberry bushes would their decomposition be beneficial, have an adverse effect or have no effect whatsoever?

I think you need particular bases - for example iron - in ericaceous soil, for the right acids to power those particular plants atypical root chemical reactions; so oxalic acid probably wouldn't make much difference, unless it grabbing calcium helps. Try it and see, let us know...
Don't ask me about alkalis...something about metals that blow up.
<Doffs anorak>

If you have a functioning compost heap, it's basically a bioreactor with thousands of chemical reactions going on, it will munch on oxalates for brekky with nary a hiccup. Anything that breathes...different matter.
Any human with a malfunctioning kidney, or gout - beware of oxalates !

[Jeanied]

Maybe I'll tell the weeds inspector I'm planning to do that next, his brains will probably explode if I do.

Bladdy 'ell - you have weeds inspectors????

[Bigmallly]

Cheers Sno, very educational.......by the way, the Anorak suited you.......

[Kaiya]

Acids are molecules - a molecule is any collection of atoms, sometimes more than one different type of atom. (An element is made of just one type of atom.) Any chemical whose formula begins with "H" is usually an acid; e.g., H2SO4.
They are acids because they react with other chemicals called bases, and in the process break down into salts and spare protons (bitties of atoms). In water they conduct electricity, which makes them electrolytes - very useful energy to power chemical reactions. So they are inclined to transfer/modify to other chemicals relatively easily, and this is why (slightly) acid soil is better for growing most plants in - you have lots of chemical changes already going on, and the roots can more easily grab the available protons/chemicals/electrical charge that are around, rather than having to start the process from scratch. Most nutrients (as well as pollutants) occur in the soil as salts, and this is why plants take them up.

Just to clarify (sorry!) Acids are molecules that, when put into water dissociate (split) into H+ and other-bit. So HCl (hydrocloric acid) becomes H+ and Cl- floating about in water - these charged particles are called ions and the solution is acidic. Bases are molecules that when put into water dissociate into OH- and other-bit and forms an alkaline solution. So NaOH (sodium hydroxide) becomes Na+ and OH-. When you measure pH you are very literally measuring the number of H+ and OH- ions floating about in water. Thus you can't measure the pH of a solid. Other things like NaCl (sodium chloride, i.e. table salt) also dissociate in water to become ions (Na+ and Cl-) but as neither of those are H+ or OH- they don't affect the pH. When an acid and alkali are mixed, the H+ and OH- combine to make water (H2O) and the other-bits combine to make a salt. e.g. if you mix the acidic HCl and the alkaline NaOH as described above in equal parts , you get H2O and NaCl - salt water

Water conducts electricity on its own. The link between electricity and acid is if you put two different metal poles into an acidic solution, one will be reduced (gains electrons) and the other oxidised (loses electrons), and the flow of electrons from one metal pole to the other is electricity. The lead-acid car battery is an example of this.

I don't think plants preferences to acid or alkali is related to the 'energy' of acids and alkalis, otherwise no plant would ever like neutral soil. From what I've learnt it's more related to the optimal working conditions for the plant's enzymes and other proteins. Enzymes are proteins with a shape that functions best at a particular temperature and a particular pH. Too acidic, too alkali, too hot or two cold, and the enzyme changes shape, rendering it less effective or totally non-functional. Some enzymes are tough and operate well over a range of conditions, and some are very delicate and require strict conditions. Organisms (plants, animals, whatever) all have enzymes and proteins that have been evolved to deal with the environment they find themselves in - so the enzymes and proteins in a blueberry plant are fussy and work best in acidic environments and malfunction if put in too neutral or alkaline an environment. Conversely, the enzymes in dandelions are unfortunately more tolerant and take a wide range of conditions before starting to malfunction.

[eirish]

Also, plants get the energy they need to power chemical reactions from sunlight, not from the soil. Roots take up water and essential substances like nitrogen, phosphorus, and potassium (the NPK in fertilisers). Plant 'food' is actually more like our vitamin tablets - plants make their own food from sunlight, water, and carbon dioxide.

[Bigmallly]

So where does that leave my rhubarb leaves?...............

[MojoJojo]

I imagine the acid content is very low compared to the amount bacteria make while composting.
Also, (if it's like brewing anyway), the bacteria will make it more acidic until it's too acidic for them - so adding more acid at the start just means they reach that point sooner.

So I doubt it makes any difference, although experimenting would say for sure. Also, I imagine many plants have acid/bases in them, but we don't hear about it because they aren't poisonous or we weren't planning to eat them anyway.
(googling for acids in plants seems to support the view that plants have lots of different acids in)

[snohare]

PM me your address Kaiya, I think you are a much more worthy wearer of the anorak than I am !
Beautifully explained, lucidly explicated, joyously educational...at long last it feels like I know How It Works in this instance. Truly, I am unworthy !

[Kaiya]

Sorry - I'm science OCD!

I've no idea about rhubarb though. You could try it - maybe compost them with an amount of normal brown matter (since I assume neat rhubarb leaves would be too green on their own?) and then test the pH in comparison to normal compost. I imagine like MojoJojo says it probably undergoes too many processes for the acid level to remain related to the material you put in in the first place.

[Bigmallly]

Sorry - I'm science OCD!

I've no idea about rhubarb though. You could try it - maybe compost them with an amount of normal brown matter (since I assume neat rhubarb leaves would be too green on their own?) and then test the pH in comparison to normal compost. I imagine like MojoJojo says it probably undergoes too many processes for the acid level to remain related to the material you put in in the first place.

Cheers, that was my plan. I have a dustbin full of leaves with some brown matter so watch this space as they say in the movies..........

Makes note: Don't ask any questions relating to acid..........

[snohare]

Don't ask any questions relating to acid

If you have any burning questions about leaves, feel free...

[eirish]

Ah, now I've re-read the original post I think I actually understand the question!

Rhubarb leaves are poisonous because of the *oxalic* acid content. So it may not be that they have a particularly low pH overall, but rather that the acid they do contain has a large percentage of a specific type of acid that has toxic effects.

If you've got a soil pH tester or some litmus paper maybe you could puree some rhubarb leaves and compare against, say, lettuce or cabbage leaves to see if they're substantially more acidic?

taking off my mad scientist lab coat now...

[Fred Perry]

Steep leaves in container and use smelly water for brassicas, Cabbage White Butterflies go elsewhere as they dont like the smell. Reapply coating after heavy rain as it will wash the smelly coating off. Just as a point of interest my cats stayed well away from a acccidental spill area for ages, so now use it to surround newly planted plants in border as it masks the smell of turned earth.
All the best to all,
Fred P