Alternative Methods for Measuring Inorganic, Organic, and Total Dissolved Nitrogen in Soil

• There are numerous methods for measuring inorganic, dissolved organic, and microbial N in soils, although many of these are complex or require expensive equipment. We have modified methods for the measurement of NH(4)(+), NO(3)(-), total dissolved N (TDN), and soil microbial biomass N (SMBN) in soils. The methods are based on a microtiter plate format and are rapid and simple to perform. Ammonium is quantified by a colorimetric method based on the Berthelot reaction. Total dissolved N and SMBN (by CH(3)Cl fumigation-extraction) are quantified as NO(3)(-) after alkaline persulfate oxidation. Nitrate is estimated directly or after persulfate oxidation by reduction of NO(3)(-) to NO(2)(-) by VCl(3) and subsequent colorimetric determination of NO(2)(-) by acidic Griess reaction. The new suite of methods was compared with conventional methods such as high-performance anion-exchange chromatography for NO(3)(-) and high-temperature catalytic oxidation for TDN. Our methods produced comparable detection limits, linearities, and precisions compared with the conventional methods. Limits of quantification were 7 mu g NH(4)(+)-N L(-1), 55 mu g NO(3)(+)-N L(-1), and 0.275 mg TDN L(-1). The accuracy of the proposed methods was excellent, with recoveries of added NH(4)(+), NO(3)(-), and glycine ranging between 96 and 99%. Linearities of the respective calibrations were high (R(2) > 0.99), and precisions for NH(4)(+) (CV = 2.1%), NO(3)(-) (CV = 3.5%), and TDN (CV = 3.9%) were comparable to the reference methods. The simplicity, rapidity, and low cost of the proposed methods therefore allow an expansion of the scope and range of N cycle studies where sophisticated instrumentation is not available.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Markvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Soil Science (hsv//eng)

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