Carbon-to-nitrogen ratio

The C / N ratio describes the weight percentages of carbon ( C) and nitrogen (N), for example, of parts of plants or soil, and is a common indicator of the availability of nitrogen to plants and microorganisms.

Importance

The smaller the number, the tighter the C / N ratio and the more nitrogen is available.

Furthermore, the humification degree of organic matter can also be determined by this ratio. In the decomposition namely CO2 is released and installed N large part in the microbial biomass. This is the C / N ratio close, which in turn speaks for advanced humification. Also, the C / N ratio varies depending on the humus.

Background

The absolute amount of nitrogen is to determine a fuzzy measure to the availability of nitrogen for plants. Because microorganisms can absorb nitrogen better than plants because they mineralize organic parts, so sit right at the source, and a much greater surface area (and thus more uptake systems for nitrogen ) than plants. Since microorganisms are different from plants that obtain carbon and energy from the air depends on the carbon in the soil, their growth is limited by too little carbon and the disadvantaged in the nitrogen supply to plants are better to train.

Thus, for many plant species from a C / N ratio of less than 20 sufficient nitrogen is available. From a C / N ratio greater than 25 microbial activity as a result of nitrogen deficiency starts to slow down.

Determination

The C / N ratio is determined as follows:

  • The sample at 950 ° C is oxidized ( burned) → CO2 N2 ( after reduction of the catalyst )
  • Conditioning (calibration ) of the thermal conductivity detector ( TCD) with two dummy values ​​and two standard samples for the determination of the calibration factor
  • Measurement takes place in TCD after entering the sample weight and sample numbers
  • Output of the results of the C and N contents in mg / g Ctot and Ntot
  • Optionally, the sample is divided in carbonate samples:
  • Conversion and reporting of results in Corg / Ntot (in percent)
  • Estimated by multiplying C with 1.72 in the mineral soil and 2 in organic layers gives approximate humus content in the soil

Size information

  • Green waste 7-15 C / N, Moder at 20 C / N, raw humus between 25 and 40
  • Grassland about 11 C / N, Acker about 14 C / N, Forest about 21 C / N
  • Young grass 10-15 C / N, corn at 55 C / N, grains between 60 and 100 C / N
  • Elm forest about 28 C / N, Linde forest about 37 C / N, Buchwald about 51 C / N

Application

Just for agriculture can draw meaningful conclusions about the maintenance of soil fertility on the ratio of C and N. So should, for example, a cereal farmer fertilize after a harvest despite leaving the straw on the field the field or grow legumes to push the shifted C / N ratio again in the direction which increases the microbial activity.

Swell

  • Scheffer - SCHACHTSCHABEL: Textbook of soil science. 15th edition. Stuttgart 2002.
  • WERRES F.: Determination of the concentration of dissolved nitrogen in natural waters by thermal conductivity detection. In: water and soil. Vol 52, H. 3, S. 36-40. Berlin 2000.
  • H. WILD: Environmental Oriented Soil Science - An Introduction. Heidelberg 1995.
  • Soil fertility
Mineralization (biology) Fertility (soil)
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