Below from here.
“Julia Gaskin, a Land Application Specialist for the University of Georgia Extension Service who recently updated their wood ash information article. She explains that ash from good quality hardwoods contains a very nice amount of potassium; at least 3% by weight.”
“Good quality hardwood ashes contain about half to two-thirds the”calcium carbonate equivalency” of lime, so you’d use one and a half to twice as much ash (by weight) to follow your soil test recommendations. In other words, if you’re told to spread ten pounds of lime, you can achieve the same goals with 15 to 20 pounds of hardwood ash. But I suggest being cautious and applying the same amount of ash as lime was called for—you’ll still be moving the pH in the right direction and adding those wonderful nutrients, but avoiding possible alkalinity problems. “