Evaluation of the different soil organic matter (SOM) pools stability in long-term field experiments of germany by physical fractionation*

Abstract

Samples of Ap horizons of different soil types with different clay content selected from nil plot and different fertilized plots of the long-term field experiments Thyrow, Groß Kreutz, Seehausen, Methau, Bad Lauchstädt, Straußfurt located in closely related climatic conditions had been analyzed by method of granulo-densimetric fractionation developed in Dokuchaev Soil Science Institute (Moscow). For comparison mountainous soil from long-term experiment Lauterbach located in more moist and cold conditions had been studied. Three groups of functional significant SOM fractions had been isolated: (1) light fraction (d < 2g·cm-3), clay fraction (< 1 μm) and fraction rest. The partition of C and N accumulated in these fractions related to the level of soil fertilization and clay content had been estimated. Light fraction is the least stable: it is sensitive to the level and forms of fertilizers as well as to the changing ecological conditions. SOM interacting with clay minerals is a main factor of soil carbon level stabilization. Light fraction is responsible for decomposable SOM pool dynamics and may be appropriate criteria of its estimation.