Effect of fertilization on respiration from different sources in a sandy soil of an agricultural long-term experiment

Annual changes in stocks of soil organic carbon may be detected by measurement of heterotrophic respiration, but field studies of heterotrophic respiration in longterm 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 aCO2-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 Nm72 year 71. This study used d13C 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 Cm72 year 71). 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 m72 year 71) indicated the MSI treatment (approximately -190) as a stronger source compared with the FYM treatment (*730)