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Effects of application of crop residues with different chemical composition on soil N and N2O/CO2 emissions

Ernfors, Maria; Laville, P.; Lashermes, G.; Janz, B.; Bleken, M.A.; Rittl, T.; Recous, S.; Havermann, F.; Nadeem, S.; Butterbach-Bahl, K.


Crop residues contribute to sustaining or enhancing soil carbon (C) stocks, thus promoting soil health and potentially mitigating climate change. Emissions of N2O can to some degree offset C sequestration after residue addition to soil, but the effects of crop type and residue chemical composition on N2O emissions are not well quantified. To assess the effects of residue chemical properties on N2O emissions and soil respiration, we incubated a wide range of residues, including cover crop, ley, intercrop and root residues, using four different soils, under controlled laboratory conditions. We demonstrated that the amount of residue N per area or the residue C:N ratio are not sufficient to explain the variation in N2O emissions. At C:N ratios below 25, the soluble C content of the residue was an important driver for N2O emissions. The emissions induced by belowground residues were only studied for grassland species and should be studied further, but the results indicated a very low impact on the total N2O emission, regardless of the chemical composition of the residues. We concluded that the crop species and its physiological maturity at the time of incorporation or addition to the soil could be used as a proxy for short-term N2O emissions - at least when fertilizer is not added, which is generally the case in autumn. Aboveground residues with C:N ratios above 25 could be assumed to induce low N2O emissions, at least during the first two months. For residues that have C:N ratios below 25, which is often the case for fresh green residues and cover crops, a high concentration of easily degradable C should be regarded as a risk factor for N2O emissions. Degradable C is not a commonly measured variable, but crop species and crop maturity stage may be good enough indicators. The very low emissions from the belowground residues of ley, regardless of their chemical composition, suggest that the current inventory methodology may be overestimating the contribution of belowground residues to total N2O emissions.

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Publisher: ResidueGas