Burnt dead plants as fertilizer

Question

Just wondering if anyone has tried using burnt dead or discarded plants as fertilizer for new plants, and how much of the nutrients you can recycle if you reuse the waste from the previous harvest. My idea was simply to burn the plant matter, possibly in an oxygen rich environment, to be left with only ashes, and then either do some more chemical separation or just use the ash as it was. From my limited understanding all the Carbon and Hydrogen should just be turned into CO2 and H2O and I should be left with the nutrients (ideally I would conserve the CO2 so I can have a CO2 rich environment to speed up the growth).

Has anyone here done something similar?

EDIT: I was rather tired when I asked the question it seems :/ I meant to ask specifically about burning the plants, not composting (I want to extract energy while burning them)

Answer 1

People do use dead or discarded plants as a source of nutrients for the soil (rather than for plants directly) AFTER they've been composted - in other words, the best use of soft plant material is on or in a compost pile or heap. The resulting compost, once its ready, is a great soil conditioner, and frequent applications of such material increases soil bio diversity; in this way, a better growing environment is created, for the soil is the most important element in growing plants.

Woody parts of plants rendered into ash may contain a reasonably high amount of potassium, a small amount of phosphorus plus low levels of trace elements, but no nitrogen - this burns off into the atmosphere. Wood ash can be used in small amounts on more acidic soils, though is best not used on alkaline soils; again, ash is more a treatment for the soil than for plants directly. Further info on wood ash here https://homeguides.sfgate.com/soil-ash-burn-pile-good-gardens-77889.html

Answer 2

Comfrey makes a great fertilizer. I wouldn't burn the leaves, they will rotten easily in water and this creates a liquid fertilizer. See here: https://www.thespruce.com/comfrey-plants-make-great-free-fertilizer-1402191

Answer 3

Burning does not leave much to put in the ground. Primarily ashes ( wood) will have potassium compounds which are relatively alkaline so should be spread thinly.

Answer 4

The mantra in gardening is that we feed the soil so that the soil can feed the plants. Feeding the plants directly is of course possible using direct chemical approach but we recognize that adding composted material contributes to soil microorganisms which are beneficial to plant growth as part of a healthy environment.

There are occasions when burning is important and perhaps the only solution, but the reasons must be extremely persuasive to outweigh the benefits of compost. A couple of examples that come to mind are extremely fibrous plants that are selected for their resistance to rot such as flax and hemp and crops which accumulate diseases in their top growth that persist when simply composted or plowed into the soil.

Flax and hemp are known for their tendency to plug up equipment when attempting to deal with post harvest residues. Harvesting has to remove as much of the growth as possible. Flax is pulled, not cut at soil level. If you try to run a mower or plough through flax residue you will be unplugging the machine on a regular basis.