Yes, aim for pH 6.5 to 6.8 for optimum nutrient availability. If you are already at the high end of Ca base saturation (i.e. >65-75%), then look to elemental Sulfur. Available at ag/coop centers. Golf courses here are starting to use a form of slow-release S. I use a product called Steric S. And you are also on the right track with humic acid - temporarily increase the cation exchange. Also, anything to improve the soil's biology, such as compost topdressing or liquid biology amendments will help break down nutrients. Think of this whole process as stepping on the gas pedal for a period of time.
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