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Abstract
Annual changes in stocks of soil organic carbon may be detected by measurement of heterotrophic respiration, but field studies of heterotrophic respiration in long-term fertilization experiments on sandy soils are scarce. Our objectives were to: (1)investigate the influence of fertilizer type on mineralization of soil organic carbon and crop residue, and (2) show how fertilization treatments affect the annual C balance (net ecosystem carbon balance, NECB; negative values indicate a CO2-source) in the sandy soil of the Darmstadt experiment. Treatments were long-term mineral fertilization with cereal straw incorporation (MSI) and application of rotted farmyard manure (FYM), both treatments receiving 14 g N m−2 year−1. This study used δ13C natural abundance after introduction of a C4 crop to distinguish between different sources of respiration. Mineralization derived from C3 sources was similar for MSI and FYM treatments (∼270 g C m−2 year−1). The rate of residue mineralization in MSI treatments was higher, resulting in a mineralization of 49 and 37% of initial residue C in the soil of MSI and FYM treatments, respectively. The NECB (g C m−2 year−1) indicated the MSI treatment (approximately −190) as a stronger source compared with the FYM treatment (∼−30).
Acknowledgements
This research was funded by the Deutsche Forschungsgemeinschaft (DFG) in the frame of the Research Training Group ‘Regulation of soil organic matter and nutrient turnover in organic agriculture’ (GRK 1397/1). The work of Meike Oltmanns and Lorenz Dobiaschowski on thefield experiment is highly appreciated. Isotopic composition was measured by the Centre for Stable Isotope Research and Analysis, Göttingen, Germany. We are thankful to two anonymous reviewers for their useful comments.
