Data of biomass and N in grass and clover roots, stubbles, and herbage and associated N2O and CO2 emissions, inclusive soil air composition, following autumn ploughing - A field study.

This article presents the detailed data of the soil characteristics, field management, amount and N content of below- (roots +crown) and aboveground (stubble and herbage) grass mixture, red clover and red clover grass swards at the end of the 3rd production year, together with fluxes of greenhouse gas emissions (N2O, CO2, CH4) and soil air composition (CO2, N2O, CH4, N2 and O2) of a field experiment in Norway. These data supplement the findings presented in the research article " Roots and other residues from ley with or without red clover: quality and effects on N2O Emission Factor in a partly frozen soil following autumn ploughing"(Bleken et al. 2022). For understanding of the effects of incorporating ley above- and belowground residues on cumulative greenhouse emissions refer to article from this research.

Roots and other residues from leys with or without red clover: Quality and effects on N2O emission factors in a partly frozen soil following autumn ploughing.

Revised IPCC guidelines assume that a constant share of N in decomposing crop residues is directly emitted as N2O (emission factor: EFN2O), and calculate the amount of nitrogen (N) in non-removable residues of temporary grasslands proportionally to the average annual herbage yield. However, EFN2O depends on the intrinsic quality of the residues and their interactions with environmental conditions. Only a few field studies on N2O emissions from grassland renewal are available, and none have simultaneously quantified the N amount and quality of non-removable residues (roots and stubble). To gain insight into the effect of non-removable residue quality on EFN2O, we studied the amount and quality of roots and stubble and their effect on EFN2O following the ploughing of three-year-old swards. The measured amount of N in non-removable residues was approximately 20, 25, and 31 kg N per 1 Mg average annual dry matter yield in grass, red clover-grass, and red clover, and 70-83% of it was below ground. However, the EFN2O of non-removable residues measured over 252 days was lower (0.24%, SE = 14% for grass and red clover-grass) than the IPCC default value (0.6%, CV: 50%) for wet regions, although within the uncertainty margin, and was significantly lower than the EFN2O of incorporated herbage, which was related to differences in EFCO2. We advocate for more specific studies that separate the effects of belowground and aboveground residues (AGR), considering the possibility of simplifying the accounting of N2O emissions from belowground residues while improving that of non-removable AGR from temporary grasslands and other green crops. We observed the accumulation of N2O in the frozen soil under snow, which was released during diurnal percolation of meltwater. N2O emissions from frozen soil accounted for 30% or more of the total emissions.

Soil pH-increase strongly mitigated N2O emissions following ploughing of grass and clover swards in autumn: A winter field study.

Emissions from crop residues contribute largely to the total estimated N2O emissions from agriculture. Since low soil pH increases N2O production by impairing the last denitrification step, liming has been suggested as a mitigation strategy; however, it may also increase N2O emissions by enhancing mineralization and nitrification. To gain field-based empirical knowledge, we measured N2O fluxes with an autonomous field-flux robot in limed and control plots before and after autumn ploughing of 3-year-old grass, clover grass or red clover swards under different N fertilization regimes. Dolomite applied before establishing the swards raised soil pHCaCl2 from ~4.8 to ~5.8 in limed plots. Higher pH halved emissions from ploughed leys despite higher soil mineral N contents. It also reduced emissions before ploughing. We observed substantial N2O fluxes after ploughing, with peaks during a relatively warm wet period after freezing and higher peaks during diurnal snow melt over frozen soil. Average N2O fluxes were strongly positively correlated with high herbage yields in the preceding growing seasons rather than with the presence of clover. The yield-scaled average N2O fluxes were strongest in low pH soils at all yield levels; this was a true effect of soil pH on N2O, as herbage yields were not increased by liming. Here, yield-scaled flux was defined as the average N2O flux after ploughing divided by the dry matter. Fluxes in red clover plots were similar to those in grass plots, despite the lower C/N ratio and higher total amount of N in clover residues. However, clover in mixtures with grass increased yields and N2O emissions. This suggests that higher ley production enhanced microbial activity, including nitrifiers and denitrifiers, and that the pH effect on facilitating complete denitrification to N2 overrode any effect on mineralization and nitrification, thus resulting in N2O mitigation.

High nitrogen costs of dairy production in Europe: worsened by intensification.

Intensification of agriculture has been proposed as one way of minimizing emissions per unit of product, apparently legitimizing the ongoing structural changes in agriculture. We have investigated the relationship between the farming intensity and the nitrogen (N) dissipation by calculating the overall N emission factor (E: total N surplus per unit of N in the produce) from several studies of dairy farms, covering a wide range of environments and production intensities. Fundamental steps were (1) the distinction between trophic levels, mineral, plant and animal N; and (2) the inclusion of N losses related to bought feed. The results show that E increases significantly with the production intensity of the dairy farm. The tradition for separate optimization of the animal and crop sectors may be a reason. We suggest that the N pollution can be mitigated by more extensive farming, both by re-coupling crop and animal production side by side, and by keeping land under cultivation when production is reduced.