Ammonium (NH4+) is one of the most important sources of nitrogen for plant nutrition and it is formed with the mineralization of decomposed organic matter.1 Research also has established that ammonium is the naturally preferred source of nitrogen for plant growth.2 With the increasing global demand for organic food products, farmers are resorting to the use of compost and manure. While ready-made ammonium fertilizers have defined concentrations of the cation and related compounds in them, it is important to analyze composts and manure for their accurate ammonium concentration. As the early phases of decomposition account for the loss of nitrogen as ammonia, and there is a natural loss of ammonium as the compost matures.3 Excess ammonium has also been reported to be toxic in higher plants.4
This application note details the photometric determination of ammonium in soils, using the indophenol blue method, after its extraction with calcium chloride solution. Post the sample extraction and in a strongly alkaline solution ammonium nitrogen is present almost entirely as ammonia, which reacts with hypochlorite ions to form monochloramine. This in turn reacts with a phenol compound to form a blue indophenol derivative that is determined photometrically.
For the measurement one of the following Spectroquant® test kits is necessary:
*not compatible with Move 100
For the measurement one of the following Spectroquant® photometers is necessary:
Optional Spectroquant® Prove Connect to LIMS software package (Y.11086) to transfer your data into an existing LIMS system.
Dissolve 3.68 g of calcium chloride dihydrate for analysis with 1 L of water to prepare a 0.025 mol/L calcium chloride solution.
Determine with the above-mentioned test kits.
Ammonium content in mg/kg NH4+ = analysis value in mg/L NH4+ x 2
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