Mitteilungen der Gesellschaft für Pflanzenbauwissenschaften Band 23

Mitt. Ges. Pflanzenbauwiss. 23: 201 (2011)
Carbon and nitrogen mineralization kinetics in various soils
amended with wheat straw and biochars
Muhammad Farooq Qayyum 1 , Diedrich Steffens 1 , Hans Peter Reisenauer 2 and Sven
Schubert 1
1 Institute of Plant Nutrition, Justus Liebig University, Gießen; 2 Institute of Organic Chemistry, Justus
Liebig University, Gießen. E-mail: farooq.qayyum@ernaehrung.uni-giessen.de
Introduction
Carbon (C) sequestration in soils by applying carbonized compounds (biochars) can
be an important step towards soil organic matter (SOM) stabilization and
conservation. With the discovery of Terra Preta it is evident that charcoal can be
used to increase SOM (Glaser 2002). The objectives of our research were to study C
and N mineralization kinetics of biochars in comparison to wheat straw in three soils
and to study their contribution to C stabilization.
Materials and Methods
Three soils (Ferralsol, Luvisol topsoil and Luvisol subsoil) were incubated with wheat
straw, charcoal, hydrothermal carbonization coal (HTC), low-temperature conversion
coal (LTC), and a control (un-amended soil). The characterization of biochar
materials was performed by chemical analysis and Fourier transformation infrared
spectroscopy (FTIR). The soils were amended with the C compounds with an amount
equivalent to the C content of 50 t charcoal ha -1 . Carbon mineralization was
measured in a long-term incubation by capturing CO2 released in KOH at regular
intervals over a time scale of 635 d. Soil samples were taken after 5 d and 365 d of
incubation and analyzed for 0.01 M CaCl2-extractable Corg, NO3-N and NH4-N.
Results and Discussion
The results show higher C mineralization and a lower half-life of straw C as
compared to all biochars. The HTC was next to wheat straw which showed higher C
mineralization and lower half-life. Overall, C mineralization was the lowest in charcoal
and LTC treatments and these treatments showed higher half-lives. In Ferralsol,
charcoal-C had longer half-life whereas in Luvisol topsoil and subsoil, LTC showed
longer half-lives. At the start of the incubation experiment, the total N supply
(application of mineral N in form of NH4NO3 + N coming from C compounds) was
adjusted to the same level in all treatments. Incubation of the Ferralsol with straw for
a period of 365 d strongly reduced both NO3-N and NH4-N. In the LTC treatment, a
slight increase of NO3-N was recorded but no significant change of NO3-N and NH4-N
was found in any other treatment. In Luvisol topsoil and Luvisol subsoil, there was a
significant increase of NO3-N in all treatments except straw. The concentration of
NH4-N was significantly decreased in all treatments after 365 d of incubation. It is
concluded that the various biochars have different stabilization behavior in soils and it
is the soil mineral and organic contents that affect the stabilization of biochar-C. It is
also concluded that, as the biochar C is stable in soil, it prevents the immobilization
of N in soil.
References
Glaser, B., J. Lehmann, W. Zech 2002: Biol. Fert. Soil. 35:219-23.