I’m working with volcano soil. Farm #1 has soil made from long term degraded vegetable matter and volcanic ash. Farm #2 has soil that is degraded volcanic ash. Each farm has its challenges, but the best results I have seen with both is lightly tilling in compost between each crop (I till the top 3 to 4 inches) while also tilling in last crop’s mulch. I apply a 2 to 3 inch mulch layer to each crop, which by harvest time, is down to 1/2 to 1 inch. So my answer is shallow light tilling in of fresh homemade compost between each crop and using mulch.
I have some of the garden area developed where it does ok using no-till, but it took perhaps 10 years to get to that point. I maintain a constant mulch on this soil, a mulch that includes compost. And only certain crops will produce well using no-till. After 5 years of no-till, I see that the soil is getting rather dense in spite of the worms, microbes, etc, and the veggie plants are not all that robust anymore. So I believe it is time to introduce the tiller and add a generous amount of compost again. I plan to till down 6 inches and let the soil re-establish itself again.
By the way, I get a lot of rain on Farm #1. The past two years have been over 80 inches annually, and we get a light rain practically every night. So leaching is a definite issue. But Farm #2 is just opposite, getting little rain and seldom has leaching issues except occasionally (every 3 years) when heavy extended rain occurs. On both farms, nitrogen loss has to be watched. So I use applications of homemade fish emulsion and/or manure tea whenever the plants show signs of needing a nitrogen boost.
By the way, contrary to what I hear people often say, volcanic soil is not all that "rich". If one is growing pasture or non-fruiting trees, you don’t have to do much to it. But if you want to produce all your own food, then one needs to add nutrients to the soil.
By the way #2…. The compost I use is homemade. I put everything into it, and I mean everything as long as it organic compostable material, along with lava sand, heat treated coral and bones that have broken up using a hammer or running over the pile with my pickup truck (hammer vs truck depends upon how big the pile is). So it has a broad range of nutrients. And by using fresh grass clippings, animal manures, and dead animals, it has a goodly amount of nitrogen. No, I don’t age my compost 6 to 12 months before using. It loses too much nitrogen that way. I coarsely sift it at about 3-4 months, tossing the chunks back into the next compost bin. I love my compost!