Automated elemental analysis: A rapid and reliable but expensive measurement of total carbon and nitrogen in plant and soil samples uri icon

abstract

  • The performance of a commercial automated CHN elemental analyzer was evaluated by comparison with classical wet methods and with another commercial analyzer. With proper standardization, calibration, and sample preparation, the Perkin-Elmer 2400 CHN elemental analyzer was shown to give reliable carbon (C) and nitrogen (N) analyses of plant and soil materials. Precision was demonstrated by the consistent reference rice straw C and N results obtained (1.6 to 2.8% CV for N, and 0.3 to 0.7% CV for C) when 11 samples were analyzed consecutively within a day or on other days. A simple linear regression analysis showed generally higher plant N values measured by the CH-N analyzer than the Kjeldahl method. Predicted analyzer plant N values were only slightly lower than Kjeldahl N, with plant materials containing less than 1% N. Recovery of different amounts of nitrate-N (NO3-N) added to rice straw samples was better with the CHN analyzer than with both the common and the salicylic acid-modified Kjeldahl method. A very good 1:1 relationship between analyzer soil N values and the permanganate-reduced iron modified Kjeldahl N values was also shown at the range measured (0.005-0.200% N). However, the soil C values determined by the analyzer were generally lower than the Walkley-Black C values. Based on precision, analyzer soil C results with 0.4 to 5% CV appear to be more reliable than the Walkley-Black C results with 0.3 to 18% CV. In spite of its reliability, speed of analysis, and low manpower requirement, studies showed the high cost of analyzing samples (minimum of US$2.38 per plant and US$3.83 per soil sample) with the CHN analyzer and of maintaining such a sensitive equipment.

publication date

  • 1993
  • 1993
  • 1993