Do cover crops enhance N_2O, CO_2 or CH_4 emissions from soil in Mediterranean arable systems?

摘要

This study evaluates the effect of planting three cover crops (CCs) (barley, Hordeum vulgare L; vetch, Vitia villosa L; rape, Brassica napus L) on the direct emission of N_2O, CO_2 and CH_4 in the intercrop period and the impact of incorporating these CCs on the emission of greenhouse gas (GHG) from the forthcoming irrigated maize (Zea mays L.) crop. Vetch and barley were the CCs with the highest N_2O and CO_2 losses (75 and 47% increase compared with the control, respectively) in the fallow period. In all cases, fluxes of N_2O were increased through N fertilization and the incorporation of barley and rape residues (40 and 17% increase, respectively). The combination of a high C:N ratio with the addition of an external source of mineral N increased the fluxes of N_2O compared with - Ba and - Rp. The direct emissions of N_2O were lower than expected for a fertilized crop (0.10% emission factor, EF) compared with other studies and the IPCC EF. These results are believed to be associated with a decreased NOf pool due to highly denitrifying conditions and increased drainage. The fluxes of CO_2 were in the range of other fertilized crops (i.e., 1118.71-1736.52 kg CO_2-C ha~(-1)). The incorporation of CC residues enhanced soil respiration in the range of 21-28% for barley and rape although no significant differences between treatments were detected. Negative CH_4 fluxes were measured and displayed an overall sink effect for all incorporated CC (mean values of -0.12 and -0.10 kg CH_4-C ha~(-1) for plots with and without incorporated CCs, respectively).