Are you adding any other sulfates, nitrates or carbonates (including bicarbonate) to your plants? Or, are your soils high in nitrate or carbonate? or your water high in carbonates?

It takes a lot of energy to knock off 4 oxygens from the sulfur in a sulfate (SO4). aka “reducing sulfate” If you’re already taxing your plants with other sulfates like gypsum(CaSO4) and epsom salt(MgSO4), and/or nitrates (NO3), or carbonates (CO3…possibly in your water or soil)…then the plant may prioritize reducing the nitrate or carbonate before reducing sulfate, because it needs carbon and/or nitrogen more than it needs sulfur.

I think the sap analysis doesn’t give a good picture of carbon deficiencies. And can lead you on a fools errand to increase the uptake of something like sulfur before increasing the uptake of carbon. If your plants aren’t glossy/shiny (don’t have good lipid production) then your plants are carbon/energy deficient. And they don’t have enough carbon/energy available to produce more complex organic compounds.

I suspect if your plants had enough carbon/energy then it would have no problem reducing that sulfate and putting sulfur in the sap…making it available for amino acid assimilation.

The reason why there are so many sulfates, carbonates, and nitrates available in the earth’s crust for mining, is because almost no organism wants to eat it, (which makes them cheap fertilizers). So they sit around for millions of years, till some human comes along and figures out that he can make a profit by convincing farmers that their plants need it. But, if there’s any other form of the same essential nutrient available, then most of the time the plant will always prefer to take up the other form.

…my theory anyway…