Comparing Two Methods for Soil Carbon and Nitrogen Determination Using Selected Brazilian Soils

Abstract

Considering the increasing need for reliable soil carbon (C) and nitrogen (N) determinations, 19 Brazilian soil samples were selected to compare the results of two methods (a) a modified dichromate wet digestion and Kjeldahl that has been in use by Embrapa in most of Brazilian soil surveys (Embrapa's method), and (b) an automated technique based on dry combustion (PerkinElmer 2.400 Series II-CHN Mode). Considering that the last method is very much influenced by sample size, two weights were tested (10 and 100 mg). The influence of two particle sizes for both 295 ORDER REPRINTS methods (crushed and sieved to pass a 0.177-mm mesh) was also tested. A simple linear regression with the confidence limits for the intercept and slope were used to compare methods. Precision was evaluated by the coefficient of variation (C.V.). The results showed that simple crushing is inadequate for performance analysis by dry combustion mainly for small samples (10 mg), where the precision is also low (19.77% for N and 9.41% for C). The dry combustion method is significantly affected by the use of small samples (10 mg), mainly for N analysis. For finely ground samples (Ͻ0.177 mm), a comparison of the results obtained by dry combustion (100 mg weight sample) and by Embrapa's method showed a significant 1 : 1 relation. Thus the use of correction factor is not necessary.

Organic carbon determination in histosols and soil horizons with high organic matter content from Brazil

“…A comparison between organic carbon content, measured through C-Embrapa and C-CHN methods, from 19 highly weathered Brazilian soils, resulted in a linear regression (Pérez et al, 2001) Table 3 Figure 1); regression coefficients were 0.489 and 0.499, respectively. The discrepancy of results according to methods emphasizes the need for distinguishing mineral soil materials from soils with high organic matter content, such as the Histosols, when analyzing organic carbon.…”

Pedo-Transfer Functions for Estimating Soil Bulk Density in Central Amazonia

“…This device employs the dry combustion technique, which is the conversion of elements in the samples to simple gases such as CO 2 and N 2 . The resulting gases are mixed and maintained under standard conditions of pressure, temperature and volume, and are then depressurized in a column where they are detected, identified and separated based on their thermal conductivity (Pérez et al, 2001). …”

Nutrient flux associated with the emergence of Quesada gigas Olivier (Hemiptera: Cicadidae) in an urban ecosystem

“…While some of the reviewed studies were based on the Dumas combustion method for nitrogen quanti ication, the differences found in the concentrations of nitrogen were unlikely to have resulted from the choice of method (Dumas or Kjeldahl), since the results were suf iciently similar to allow for comparisons regardless the method adopted (Perez et al 2001, Watson & Galliher 2001. The relatively low level of nitrogen found in tissues of Q. gigas may stem from the low availability of nitrogen in their food source, since insects feeding on nitrogen-de icient matter usually have low nitrogen content in their tissues (Fagan et al 2002).…”