Sulfur in Fertiliser: Why the % Mass of Sulfate?

[Stroodle]

Hi,

I'd just like to know why fertiliser producers refer to "the percentage by mass of sulfur present as sulfate" in their fertilisers?

Thanks!

 

[hamster143]

Because sulfur in fertilizers is typically present in the form of sulfates ... I'll guess that's because elemental sulfur is not soluble in water, and sulfites are too unstable.

 

[chemisttree]

It's possible that it is indeed present as sulfate but if it is time-released, it is usually present as zero valent sulfur or as a sulfur-containing polymer and perhaps both. Rather than speciate all the forms of sulfur present, the assay is given as if all were converted to sulfate.

 

[Cesium]

Phosphorous is listed as P2O5 though and clearly this is not the active form taken up by plants. I guess it's just a convenient metric, although for the chemist it makes things more complicated.

 

[chemisttree]

In the case as phosphorous, all of the P is converted to orthophosphate and the result is multiplied by a factor to express it as P2O5. A little more complicated but not by much.