Influence of clover species in mixtures with grasses on fatty acid composition of mixtures

White clover (WC, Trifolium repens L.) or red clover (RC, Trifolium pratense L.) was grown in mixture with grasses. Samples of the mixtures and pure clovers were taken during three cuts, and the fatty acids (FA) compositions were determined. The clover species had no significant effect on the individual FA contents of the leys (g kg-1 dry matter (DM)), nor on the total FA content. Pure clovers had lower content of all individual FA (8.2 vs. 12.4 g kg-1 DM) than mixtures; the contents of all FA decreased with increasing percentage of clover in the mixture, but the decrease was weaker for C18:3n-3 than for the other FA. Although pure WC and RC had similar FA contents, the relative proportions (percentage of total FA content) of C16:0 and C18:3n-3 differed; RC had a higher proportion of C18:3n-3 and a lower proportion of C16:0. These results are partly in contradiction with previously reported

Effect of green manure management on barley yields and N-recovery

Mulching of GM herbage can increase cereal yields compared to its removal. However, the same GM herbage removed for biogas production will provide biogas residue that can be used as spring fertilizer to cereals. This will improve N-recovery and reduce the risk for N pollution. Cooperation with existing biogas plants will be more efficient, as building small biogas plants are costly and challenging

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 strat- egy; 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 re- gimes. 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 be- fore ploughing. We observed substantial N2O fluxes after ploughing, with peaks during a relatively warm wet period after freezing and higher peaks during diurnal snowmelt over frozen soil. Average N2Ofluxes 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 minerali- zation and nitrification, thus resulting in N2Omitigation

A review and meta-analysis ofmitigation measures for nitrous oxide emissions from crop residues

Crop residues are of crucial importance to maintain or even increase soil carbon stocks and fertility, and thereby to ad- dress the global challenge of climate change mitigation. However, crop residues can also potentially stimulate emis- sions of the greenhouse gas nitrous oxide (N2O) from soils. A better understanding of how to mitigate N2O emissions due to crop residue management while promoting positive effects on soil carbon is needed to reconcile the opposing effects of crop residues on the greenhouse gas balance of agroecosystems. Here, we combine a literature review and a meta-analysis to identify and assess measures for mitigating N2O emissions due to crop residue applica- tion to agricultural fields. Our study shows that crop residue removal, shallow incorporation, incorporation ofresidues with C:N ratio > 30 and avoiding incorporation of residues from crops terminated at an immature physiological stage, are measures leading to significantly lower N2O emissions. Other practices such as incorporation timing and interac- tions with fertilisers are less conclusive. Several of the evaluated N2O mitigation measures implied negative side- effects on yield, soil organic carbon storage, nitrate leaching and/or ammonia volatilization. We identified additional strategies with potential to reduce crop residue N2O emissions without strong negative side-effects, which require fur- ther research. These are: a) treatment ofcrop residues before field application, e.g., conversion ofresidues into biochar or anaerobic digestate, b) co-application with nitrification inhibitors or N-immobilizing materials such as compost with a high C:N ratio, paper waste or sawdust, and c) use ofresidues obtained from crop mixtures. Our study provides a scientific basis to be developed over the coming years on how to increase the sustainability of agroecosystems though adequate crop residue management