Decomposition of plant residues of Lolium perenne in soils and induced priming effects under different land use

The decomposition of shoot and root residues of Lolium perenne was tested i n two grassland and two arable soils from the Kraichgau area (Baden-Wurttem berg, Germany) by incubation for three months under optimal conditions (20 degrees C, 60 % of mWK) in laboratory. The dynamics of (CO2)-C-14 and total CO2 efflux during the incubation and soil N-min before and after incubatio n were measured. Two periods with different rates of decomposition of shoots and roots of Lo lium were found. The slowly decomposable portion amounted to 86 %. The deco mposition rates of the easily decomposable portion of shoots amounted to 0. 2 day(-1). The decomposition rates of shoots are three times faster that th e decomposition rates of roots. The decomposition rates were independent fr om the soil management. Input of roots into grassland soil leads to intensive carbon immobilisation in soil. Input of shoots into soils induced the extra decomposition of soi l organic matter at the beginning. This can be interpreted as a positive pr iming effect. Carbon accumulation was observed in all variants of the exper iment after two weeks. The decomposition of shoots leads to the additional nitrogen mineralisation from soil organic matter-positive N priming effect of 15 to 53 kg N ha(-1) during three months. The decomposition of roots leads to N immobilisation of 0 to 42 kg N ha(-1).