What is the difference between (dried) lives, twigs, branches etc turn in to compost and ....?

Question

same material turned in ash (by burning)?

I am talking about nutritanal and biological difference.

Why pHs of both end-products are different? And why we can use one very liberally (compost) and other (ash) sparingly?

Answer 1

Composting the leaves twigs and branches (usually broken down in small pieces) gives you all of the advantages of extra organic matter plus all of the minerals released over a slow period of time.  Burning to ash destroys all of the organic matter and supplies the minerals in a concentrated amount.  The ash is alkaline and can make the soil less acid.  Which in most cases is a good thing.  As you say the ash is concentrated so it must be used sparingly to avoid burning your plants and changing the pH of the soil too much.  With compost, usually the more you apply the better, because it improves soil texture and water holding capacity.  Since it releases the minerals slowly there is no chance of plant burn.

Answer 2

Vegetable matter typically contains only a few percent of inorganic material that is left as ash after burning.  To answer your last question first, the ash is therefore much more concentrated than compost would be; and the ash has also undergone a chemical change during burning (typically, forming a sodium, calcium or potassium rich alkaline material),  and the ash might have a harmful effect on some growing plants, if present in the soil in too high a proportion.

Composting, on the other hand is a biological process, effected by microorganisms , worms, etc on the organic content of the vegetation, and there is no chemical reaction with the mineral content.  Composting requires water for the microorganisms to grow and feed, and hence, in the absence of water, the vegetation will dry out (desiccate), without undergoing a biologically induced organic change.

Answer 3

Ash is just the mineral left behind from the burning process which is really a chemical process. What is left behind are very strong oxides, salts and hydroxides that are a lot more soluble than minerals they would replace. When material is burned as opposed to composted, the one thing readily noticed as missing will be all the nitrogen components as well as the bulk.

If leaves, twigs and the chipped wood (in small amounts) products are composted, there are a lot of biological processes that happen, both microscopically as well as macroscopically, and should be encouraged. The proper balance of green and brown material composted aerobically and in the presence of animals like worms and insects as well as fungi and bacteria are the basis for soil (when mixed with the parent rock material) and it is that niche in the environment that plants have adapted to. Though the actual bulk of the pre-composted material is larger, the reduced material is changed, with nitrogen compounds (as well as other minerals) readily available, and quite live and active, still slowly releasing organic solutes into the soil solution for plant uptake. The ash though is a good way to make changes in the pH of the soil and soil solution but this tool needs to be used with care as it will damage the soil environment and make it sterile and even unable to support plants if overdone.

Answer 4

The ash is combusted into a product with very little organic nutrients left but does have the potash chemical. The compost still retains nutrients that can be used to provide all of the major requirements for plant growth (nitrogen, phosphorus, and potassium).

Since the compost is not completely broken down into chemicals it does not provide strongly concentrated chemical food and can be used liberally to eventually release those nutrients. The ashes are strong enough chemicals that they can  be used only in lesser quantities to avoid burning the plant roots.

Answer 5

stuff composts better when damp.

ash is a good source of potash (potassium)