Volcanic ash as soil amendment
Seek advice on the nature of and use of volcanic ash as a soil amendment. I have been a volunteer engineer in central Mexico for 16 years with a focus on rural water supply. All about are poverty stricken remote villages along with massive amounts of volcanic ash. I would like to create jobs for these people via the ash that is all about. My initial view was to manufacture light weight building blocks which I understand. Use as a soil amendment came in second, for which I have many questions - like what may be the criteria (grain size, pH, salt content, minerals most desired, ....) for selecting a type ash. I have 22 volcanoes nearby. By the way this area has the #2 best climate in the world.
Outside United States
Thank you for your question. This has not been extensively researched in American agricultural universities, but here is the one abstract of a study of the effects of the application of ash as a fertilizer.
The one Extension article I can find on volcanic ash' chemical content and application to soil is here. This second Hawaii Extension article which found that "Volcanic ash-derived soils: Soils formed in volcanic ash deposits characterized by non-crystalline clays with very high surface area. In areas with a wet climate (e.g., Hāmākua and Hāna), these soils are acidic and low in plant nutrients. In areas with seasonal rainfall, these soils are very fertile with near-neutral pH. Examples: mid-elevation Kona to Waimea (Hawai‘i Island); Kula (Maui)."
Another study of soils containing volcanic ash indicated that "On soils derived from volcanic ash parent material, the P [phosphorus] should be applied as a band application due to the high capacity of those soils to fix P." (Phosphorus fixing is described here.)
I wish I could find answers to your other questions about quality and makeup, but this is the best I could find. Good luck!
Many thanks for your kind reply.
We are trying to find sources of income for rural villages in central Mexico where very large masses of volcanic ash exists. The people here earn $8/day so are quite poor in a nation whose GDP equals that of France
We are thinking (1) soil amendment as noted, plus (2) light weight building blocks, additive to cement to stretch it, (3) use as a light weigh mortar on roofs,.......
Good luck in your challenging work!