312 SOIL NITRATE AND EXTRACTABLE AMMONIUM BY FLOW INJECTION ANALYZER METHOD
Fertility: NO3-N, NH4-N
Equilibrium extraction of soil for nitrate and ammonium with potassium chloride and subsequent determination by flow-injection analyzer.
Summary: This method involves the quantitative extraction of nitrate (NO3-N) from soils using an equilibrium extraction with 2.0 N KCl solution. Nitrate is determined by reduction to nitrite via a copperized cadmium column. The nitrite is then determined by diazotizing with sulfanilamide followed by coupling with N-(1-naphthyl)ethlyenediaminie dihydrochloride. The absorbance of the product is measured at 520 nm. This method is also semi-quantitative for ammonium (NH4-N) in soils. Ammonia is heated with salicylate and hypochlorite in an alkaline phosphate buffer. The presence of EDTA prevents precipitation of calcium and magnesium and sodium nitroprusside is added to enhance sensitivity. The absorbance of the reaction product is measured at 660 nm and is directly proportional to the original ammonia concentration. Extracts can be stored for up to three weeks at low temperature (<4°C). For long term storage, toluene or thymol may be added to the sample to prevent microbial growth. The method has detection limit of approximately 0.1 mg/kg (on a soil basis) and is generally reproducible within 7%.
Hofer, S. 2003. Determination of Ammonia (Salicylate) in 2M KCl soil extracts by Flow Injection Analysis. QuikChem Method 12-107-06-2-A. Lachat Instruments, Loveland, CO.o:p>
Knepel, K. 2003. Determination of Nitrate in 2M KCl soil extracts by Flow Injection Analysis. QuikChem Method 12-107-04-1-B. Lachat Instruments, Loveland, CO.