Nice, very short article - doesn't take more than 5 minutes to read - addressing the general question of soil acidity and nutrient availability for plants. As many of you know, I am a big fan of soil acidity for plant culture but as the article clarifies, acidity is only beneficial down to a point, below which the availability of N, P, Ca, Mg and K drops off too much apparently.
Key here is that favorable pH for plants is in a RANGE from 5.9 to 7.0. Still, if you peruse the included graph closely you get the strong sense that optimum availability of most nutrients is at 5.9, especially the micronutrients iron, copper, manganese and zinc.
Many of our soils for berries in Salinas and Watsonville range from 6.5 to 7.5, so there are many above optimum (for many reasons, I know that). It would be an interesting avenue of research to pursue a soil that is at 5.9 and see how well a crop of berries does there.