Liming halved N2O emissions following plowing of grass-clover mixtures in an acidic soil

Summary in the original language of the document

Introduction
Leguminous in ley mixtures and green cover crops in rotation with cash crops are means to increase nitrogen use efficiency and/or reduce N losses. However, their benefits can be offset by increased N2O emissions following termination by tillage. Liming of low pH soils can reduce N2O from denitrification1), but the effect on total N2O emissions from incorporation of nitrogen rich green residues1) is uncertain, as it can also enhance mineralization and nitrification.
Methods
We measured field N2O emissions following ploughing of several ley mixtures. Treatments were repeated in control (pHaq ~5.5) and limed (pHaq ~6.0) plots which were wholly
randomized in a silty clay loam at Ås, Norway. Liming took place shortly before establishing the leys, 4 years before ploughing.
Results
N2O emissions increased with increasing ley yields in the previous years, which indicates a linear relationship with residue amounts. However, at any level of previous biomass yield, N2O emissions in limed treatments were only half of those in low pH treatments. In this experiment the biomass yield dependent on species composition and N fertilization, not on soil pH, and was higher in red clover-grass than in grass only or white clover-grass mixtures. Liming significantly raised the total mineral N content in the soil, but the increase was small (typically around 3 mg N kg-1).
Conclusion
Maintaining a sub-neutral pH can effectively mitigate N2O emissions following incorporation of nitrogen rich green residue. Whether this applies also in the case of large incorporation of fresh herbage deserves further studies