Posted: 27/08/2016 at 12:43
Rock dust is very fine waste from scottish quarries, granite or volcanic basalt.
The theory goes that is is a good source of lots of micronutrients. The amount a plant can grow is limited by the nutrient level., not just NPK. Adding comfrey water adds micronutrients, the comfrey drags it up from the subsoil. It will be limited by the subsoil content. Rock is not soluble and plants cannot absorb it, so I initially thought it would be a total waste of time. Where it has been added to sandy soil in the wheat belts of Australia, it made absolutely no difference. No worms, no humus.
Where it is used as part of a humus rich environment with lots of worms, the plants grow larger and stronger.
Erosion of rock releases the contents into a soluble for, whether by being scraped by a glacier or silt from a river on a flood plain. Some of the most fertile soils in the world are flood plains and the sides of volcanoes.
Soils that have been grown on for 100 s of years have lost a lot of their micronutrients, and the nutrient values in our foods is less now than 100 years ago.I ordered a tonne bag to remineralise the veg plot, and with lots of FYM, turn sandy free draining soil ( my side) and heavy clay and shale(next door) into productive soil. That was three years ago, and I have found a big difference . Even flowers grown in the veg plot for the house look better, stronger stems on the sweet peas. I should point out that my side has seen 22 years of added mushroom compost, FYM and BFB, but it is a very free draining sand, and soon loses nutrients. Next doors clay has not had anything added in all the time I have been here, before I got my wellies on it.
If you want to try it, I think it is worms along with the humus that are essential. Being worked by the worms releases the nutrients in some way, into a soluble form. ( Acid and enzymes in the worm gut???)If your compost bins are on concrete, I would mix the dust in with the compost when you use it for mulch on the soil, or dig it in. The worms will then mix it. If you have no worms I do not think you will see much difference.There are a few sites for more information.
The Seer centre in Scotland http://www.seercentre.org.uk/
Remin rock dust http://www.reminscotland.com/
and an American site
Maybe we could do an experiment for people with allotments. Treat half of each patch with rock dust, and half exactly the same other stuff but no rock dust. No quick fixes, but after a couple of years a big difference.
I should add that it is not like a straight fertiliser. I found better effects in the second year. Again, after the worms have worked it into a soluble form. Only at molecular level can nutrients be absorbed by the plant roots.