You could potentially get a permanent drop, assuming that you are able to a) remove all calcium carbonate (or salts in the case of high pH caused by salts) and b) mitigate any circumstances that cause the pH to rise (eg, high pH water).
When I started mulching the orchard, I had the same thought -- that I wouldn't need any inputs other than mulch. And I held to that ideal for years, continuously applying mulch at the rate of a few hundred cubic yards per year. But, over the years, I noticed something -- the chlorosis was actually getting worse, and the fruit quality was declining (lower measured brix, poor flesh quality, etc).
After some research and with the help of Har, I figured out what was happening. Organic matter actually locks up some nutrients and makes them less available. For example, if you have too much copper in your soil, the way to correct it is to add organic matter (which then locks up the excess copper). Same applies to many other micronutrients.
However, there is a good side to mulch: it acts as a "storage bin" for nutrients -- like biochar. So, once you apply minor elements, the compost will absorb and slowly release them. Currently, my trees are dark green and beautiful -- even when I don't fertilize them, because the compost has stored the nutrients I laid down.
And for best fruit quality (high brix, firm flesh, etc), you want a calcium to potassium ratio somewhere north of 10 to 1. But unfortunately, compost normally contains ca and k in a ratio closer to 1 to 1. In order to correct this imbalance, you need to add calcium (eg, gypsum) -- which greatly improves fruit quality. (Here's an article explaining this:
https://www.highbrixgardens.com/victory-gardens/putting-compost-in-its-place.html)
Great info, Jeff
I had wondered how long sulfur’s effects would last. Unfortunately I guess I had a fairytale idea that it would be permanent. Do you have “free calcium” in the underlying soil?
I’m a bit puzzled that you say you have to add specific inputs even though you have effectively been “sheet mulching” for all this time. What I’ve read (limited, for sure) I thought your type of composting in place was the gold standard for permaculture and required no other inputs (outside of perhaps a major deficiency in the underlying soil).
Or is it that your mulch was one-dimensional, so to speak?
Just trying to get some learnin’