I’ve been growing and consulting on southern and northern highbush blueberries, both organic and conventional, for 20 years in California and the Pacific Northwest. We have never, nor has anyone I’ve ever worked with (other than someone growing in substrate media in pots), used EC measurements as a guide for growing. We rather have used pH monitoring (and want to get into eH now) and our now pretty solid understanding of the nutritional requirements of blueberries. John Kempf has a blog on blueberries too, discussing redox and manganese and iron availability. To me, everything comes down to that, and nitrate vs ammonium management. The only thing about EC that we watch is we want to make sure it doesn’t get too high. Since we have a lot of saline groundwater being used in California, that is one major area of observation, but not trying to get precise to the tenth or hundredth of a point on the EC scale at different times. I would love to hear more about why this is practiced in soil grown blueberries and how well it works. With our system we routinely grow 30,000 lbs per acre crops that are high quality. We are also using sap analysis now, along with a strong biological program that we use to release nutrients, rather than try to feed them as in a chemical or hydroponic systems approach.