Hi SoilScience community.

Anyone knows a methodology adapted for the determination of N,P,K in Soil Extracts Using Microplate Techniques?

Are needed fresh/frozen samples or can be used air-dried soil samples, like a chemical assays with Olsen extraction or Kjeldahl digestion?

And more important, with typical reagents from a soil laboratory?

I saw these two methodologies for P https://www.tandfonline.com/doi/abs/10.1081/CSS-120029731?scroll=top&needAccess=true&journalCode=lcss20 and N-species Article Determination of N-species in soil extracts using microplate...