Dear Sir. Concerning your issue about what the difference is between using KCl or CaCl2 or eventually H2O to extract NH4+ and NO3- from soils . Ammonium and nitrate are usually determined in the soil by extracting them by 1M KCl solution and measured by automated colorimetry (ammonium by salicylate; chlorine and nitrate by reduction, diazotisation and coupling with N-1-naphthylethylenediamine dihydrochloride). Soil nitrogen is usually calculated by commercial laboratories from the organic matter present. I think the following below links may help you in your analysis and answering more of your questions:

http://researchlibrary.agric.wa.gov.au/cgi/viewcontent.cgi?article=1308&context=rmtr http://www.cala.ca/sampling/20_manual-soil-sampling-analysis.pdf

http://igau.edu.in/pdf/pubdes42.pdf

http://www.niordc.ir/uploads%5C86_106_Binder1.pdf http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=3719&context=rtd

Thanks

Thank you !