ph doesnt affect molybdenum only under 5.5 so im reaching for temps and aluminum content. thats nuts.
here is a read.
The most telling sign of aluminum toxicity in plants themselves is diminished root growth. Generally, the growth of roots is reduced to about half of what is normal, but this varies from crop to crop.
Reduced root mass and length means reduced uptake of virtually every other nutrient, as well as the capacity to take in enough water. Additionally, vital plant nutrients like sulfur and phosphorus tend to bond with available aluminum.
Due to these two factors, excess aluminum in the soil can lead to the appearance of other nutrient deficiencies: pale or faded color, wilted or stunted growth, thin or weak stems, and necrotic spots.
Aluminum is also more available to plants in acidic soils (soils with a very low pH), and thus acid-loving crops like blueberries and cranberries are among the more aluminum tolerant selections.
A soil with pH below 6 (and especially below 5) is much more likely to have an excess of soluble aluminum, and thus contain levels that are toxic to most crops: however the cause of such a low pH can only truly be ascertained with the right soil tests.
The threshold at which available or soluble aluminum (Al+++) in soil can begin to do damage is about 0.5 ppm, with few commercial crops tolerating more than 1.0 ppm.
