>> But does it lose anything from being burned at the high temps?
I doubt if you're getting any "organic material" in the sense composters use the term. Any carbon compounds like cellulose are almost certainly burned away. If the remains are burned to ash. you're only getting minerals. Are the cremains like fine ash, or gritty?
I can't think of any nitrogen compounds that would not burn away. But phosphorus and potassium salts should remain, along with calcium and iron. I'm just guessing, from general chemistry.
Maybe (MAYBE) the ashes are pretty basic (meaning high pH). They might be caustic or rasie the soil pH too much if too much was used in one spot.
If some plants reacted very favorably, they needed something like the phosphorus, or maybe calcium, or MAYBE the raised pH.
If you can check the soil pH, maybe they would also appreciate some form of lime. If you add soluble fertilizers, some of those can be on the acid side. HOWEVER, from what I read, both tomatoes and peppers prefer slightly acid soil: like pH 6.0 to 6.8. So don't add too much lime!
