Estimation of available nitrogen content in upland soil by a boiling decoction method
2008
Yamaki, A.(Chiba-ken. Agriculture Research Center (Japan))
Organic nitrogen in boiling upland soil decoctions was decomposed with potassium peroxodisulfate to form nitrate nitrogen. The amount of the nitrate nitrogen was used to estimate available nitrogen content. 1. Each of the upland soil decoctions was sealed with potassium peroxodisulfate in a pressure-resistant glass bottle and placed in a thermostatic convection dryer for decomposition at 120degC for three hours. The procedure converted as much organic nitrogen to nitrate nitrogen as a conventional method did. 2. An andosol, a brown lowland soil, a brown forest soil a farmer used as a plow layer, and a test soil continuously given compost were heated to 100degC for six hours for decoction. A highly positive correlation was found between the organic nitrogen content and available nitrogen content of the decoctions. A correlation equation of y=0.58x-0.98, R**2=0.68, could be used to estimate the available nitrogen content from the organic nitrogen content. 3. A small reflection photometer, instead of the method of naphthylethylene diamine with copper-cadmium reduction, was used to measure nitrate nitrogen. The organic nitrogen content was found correlated with the available nitrogen content by an equation of y=0.51x-0.23, R**2=0.54. Although the standard deviation was somewhat larger, the method could be easily used to estimate available nitrogen content.
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