Friday, September 13, 2013

New paper finds Mediterranean cover crops are a net source of CO2 to the atmosphere

A new paper published in Science of the Total Environment finds cover crops in the Mediterranean act as a net source of CO2 to the atmosphere, and as a net sink of CH4 [methane]. The paper adds to several other peer-reviewed papers finding various agricultural and ocean sites act as net sources of CO2 rather than sinks as previously thought.

Do cover crops enhance N2O, CO2 or CH4 emissions from soil in Mediterranean arable systems?

  • a Technical University of Madrid, School of Agriculture, Avd. Complutense s/n, 28040 Madrid, Spain
  • b Dpt. Environmental Sciences (ELI-e), Earth and Life Institute, Université Catholique de Louvain, Croix du Sud 2 bte L7.05.02, 1348 Louvain-la-Neuve, Belgium


Differences in GHG emissions between CCs were only significant in the fallow period.
Vetch was the only CC significantly enhancing N2O losses.
There were CC specific effects over direct N2O emission.
Negative CH4 fluxes were measured in all incorporated CCs.
Planting CC may be a good strategy to decrease direct N2O losses in these rotations.


This study evaluates the effect of planting three cover crops (CCs) (barley, Hordeum vulgare L.; vetch, Vicia villosa L.; rape, Brassica napus L.) on the direct emission of N2O, CO2 and CH4 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 N2O and CO2 losses (75 and 47% increase compared with the control, respectively) in the fallow period. In all cases, fluxes of N2O 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 N2O compared with − Ba and − Rp. The direct emissions of N2O 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 NO3 pool due to highly denitrifying conditions and increased drainage. The fluxes of CO2 were in the range of other fertilized crops (i.e., 1118.71–1736.52 kg CO2–C ha− 1)  [positive values indicate a net source]. 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 CHfluxes were measured and displayed an overall sink effect for all incorporated CC (mean values of − 0.12 and − 0.10 kg CH4–C ha− 1 for plots with and without incorporated CCs, respectively).

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