Scharpenseel et al. 1986c

Scharpenseel, H.-W., Tsutsuki, K., Becker-Heidmann, P., Freytag, J. (1986): Studies with radioactive and stable isotopes regarding organic matter dynamics in Vertisols and loessic Mollisols; soil management consequences. – In: Malang (Hg.): Report on the International Conference on the Management and Fertilization of Upland Soils (ICMFUS) in the Tropics and Subtropics



Organic matter dynamic, as controlled by radioactive (14C) and stable (13C) isotope measurements, is undoubtedly not uniform in soils with morphological and clay mineralogical features of Vertisols. Homogenizing peloturbation processes and organic matter stability/decomposition vary between soil profiles and soil provinces considerably. δ13C variations in two Vertisols from the Gezira (Sudan) reveal however due to surface-near 13C-dilution from δ13C of C3 cotton plant with -25‰ and 13C enrichment below in full cracking depth by δ13C of C4 durra with -10‰, that the homogenizing trend by peloturbation truly exists.
Bioturbation in Mollisols is not leading to homogeneity of carbon species. All tested profiles show distinct 14C-age gradients towards depth. Also, the organic matter stability varies greatly between different Mollisol profiles as well as depth layers. Earthworm body-C from different depth layers is all completely recent bomb-C, contrary to C of humus in these layers being up to several 1000 years of age. Earthworms therefore feed exclusively on modern vegetal relics. Some concentration of youngest material is found also in body-C from the deepest end of escape tracks. Humus skins of crotovins and uninhabited worm tracks however were all fossil and had a radiocarbon age higher than that of the humus of corresponding soil depth. Among texture fractions middle clay and in one case fine clay showed highest 14C-age.
Carbon compartments from greater soil depth decomposed slower than those, closer to the surface.
Soil management consequences for preservation and stabilisation of organic matter in Vertisols and Mollisols are discussed.

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