Cover crops play an increasingly important role in improving soil quality, reducing agricultural inputs and improving environmental sustainability. The main objectives of this critical global review and systematic analysis were to assess cover crop practices in the context of their impacts on nitrogen leaching, net greenhouse gas balances (NGHGB) and crop productivity. Only studies that investigated the impacts of cover crops and measured one or a combination of nitrogen leaching, soil organic carbon (SOC), nitrous oxide (N2O), grain yield and nitrogen in grain of primary crop, and had a control treatment were included in the analysis. Long‐term studies were uncommon, with most data coming from studies lasting 2–3 years. The literature search resulted in 106 studies carried out at 372 sites and covering different countries, climatic zones and management. Our analysis demonstrates that cover crops significantly (p < 0.001) decreased N leaching and significantly (p < 0.001) increased SOC sequestration without having significant (p > 0.05) effects on direct N2O emissions. Cover crops could mitigate the NGHGB by 2.06 ± 2.10 Mg CO2‐eq ha−1 year−1. One of the potential disadvantages of cover crops identified was the reduction in grain yield of the primary crop by ≈4%, compared to the control treatment. This drawback could be avoided by selecting mixed cover crops with a range of legumes and non‐legumes, which increased the yield by ≈13%. These advantages of cover crops justify their widespread adoption. However, management practices in relation to cover crops will need to be adapted to specific soil, management and regional climatic conditions.

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HighlightsThe impact of grazing on SOC is climate-dependent.Grazing increases SOC for C4 but decreases it for C3 and C3-C4 mixed grasslands.Grazing increases TN and BD but has no effect on soil pH.

Northern peatlands constitute a significant source of atmospheric methane (CH 4). However, management of undisturbed peatlands, as well as the restoration of disturbed peatlands, will alter the exchange of CH 4 with the atmosphere. The aim of this systematic review and meta‐analysis was to collate and analyze published studies to improve our understanding of the factors that control CH 4 emissions and the impacts of management on the gas flux from northern (latitude 40° to 70°N) peatlands. The analysis includes a total of 87 studies reporting measurements of CH 4 emissions taken at 186 sites covering different countries, peatland types, and management systems. Results show that CH 4 emissions from natural northern peatlands are highly variable with a 95% CI of 7.6–15.7 g C m−2 year−1 for the mean and 3.3–6.3 g C m−2 year−1 for the median. The overall annual average (mean ± SD) is 12 ± 21 g C m−2 year−1 with the highest emissions from fen ecosystems. Methane emissions from natural peatlands are mainly controlled by water table (WT) depth, plant community composition, and soil pH. Although mean annual air temperature is not a good predictor of CH 4 emissions by itself, the interaction between temperature, plant community cover, WT depth, and soil pH is important. According to short‐term forecasts of climate change, these complex interactions will be the main determinant of CH 4 emissions from northern peatlands. Drainage significantly (p < .05) reduces CH 4 emissions to the atmosphere, on average by 84%. Restoration of drained peatlands by rewetting or vegetation/rewetting increases CH 4 emissions on average by 46% compared to the original premanagement CH 4 fluxes. However, to fully evaluate the net effect of management practice on the greenhouse gas balance from high latitude peatlands, both net ecosystem exchange (NEE) and carbon exports need to be considered.

Conservation tillage (CT) is an umbrella term encompassing many types of tillage and residue management systems that aim to achieve sustainable and profitable agriculture. Through a global review of CT research, the objective of this paper was to investigate the impacts of CT on greenhouse gas (GHG) emissions. Based on the analysis presented, CT should be developed within the context of specific climates and soils. A number of potential disadvantages in adopting CT practices were identified, relating mainly to enhanced nitrous oxide emissions, together with a number of advantages that would justify its wider adoption. Almost all studies examined showed that the adoption of CT practices reduced carbon dioxide emissions, while also contributing to increases in soil organic carbon and improvements in soil structure.

12Simulation models are one of the approaches used to investigate greenhouse 13 gas emissions and potential effects of global warming on terrestrial ecosystems. 14 DayCent which is the daily time-step version of the CENTURY biogeochemical 15 cumulative N 2 O flux under climate change and baseline conditions. However, above-7 ground grass biomass was significantly increased from the baseline of 33 t ha -1 to 45 8 (+34%) and 50 (+48%) t dry matter ha -1 for the low and high temperature sensitivity 9 scenario respectively. The increase in above-ground grass biomass was mainly due to 10 the overall effects of high precipitation, temperature and CO 2 concentration. Our 11 results indicate that because of high N demand by the vigorously growing grass, 12 cumulative N 2 O flux is not projected to increase significantly under climate change, 13 unless more N is applied. This was observed for both the high and low temperature 14 sensitivity scenarios. 15

Models are increasingly used to examine the potential impacts of management and climate change in agriculture. Our aim in this paper was to assess the applicability of the field-DeNitrification DeComposition (DNDC) model in Irish agriculture. This study provides the results of that evaluation, which is a prerequisite for using the model for assessing management impacts in the future. The DNDC model was tested against seasonal and annual data sets of nitrous oxide flux from a spring barley field and a cut and grazed pasture at the Teagasc Oak Park Research Centre, Co. Carlow, Ireland. In the case of the arable field, predicted fluxes of N 2 O agreed well with measured fluxes for medium to high fertilizer input (70-160 kg N ha − 1 ) but poorly described those fluxes from zero fertilizer treatments. In terms of cumulative flux values, the relative deviation of the predicted fluxes from the measured values was a maximum of 6% for the highest N fertilizer inputs but increased to 30% for the medium N and more than 100% for the zero N fertilizer treatments. There is a linear correlation of predicted against measured flux values for all fertilizer treatments (r 2 = 0.85) but the model underestimated the seasonal flux by 24%. Incorporation of literature values from a range of different studies on arable and pasture land did not significantly improve the regression. The description by DNDC for measured fluxes of N 2 O from reduced tillage plots was poor with underestimation of up to 55%. For the cut and grazed pasture the relative deviations of predicted to measured fluxes were 150 and 360% for fertilized and unfertilized plots. A sensitivity analysis suggests that the poor model fit is due to DNDC overestimating WFPS and the effect of initial soil organic carbon (SOC) on N 2 O flux. As the arable and grassland soils differed only in SOC content, reducing SOC of the grassland field to that of the arable field value significantly improved the fit of the model to measured data such that the relative deviations decreased to 9 and 5% respectively. Sensitivity analysis highlighted air temperature as the main determinant of N 2 O flux, an increase in mean daily air temperature of 1.5°C resulting in almost a 65% increase in the annual cumulative flux. This is interesting as with future global warming, N 2 O flux from the soil will have a strong positive feedback. It can be concluded that DNDC is unsuitable for predicting N 2 O from Irish grassland due to its overestimation of WFPS and effect of SOC on the flux.

Table 1 Spring barley grain yields, cumulative N 2 ON emitted and emission factors for the conventional and reduced tillage plots in 2004/2005 Treatment Grain yields (t ha-1), cumulative N 2 O emissions (kg N 2 ON ha-1) and EF (%) Conventional tillage Reduced tillage 2004 140 kg N ha-1 7.73 0.79 ± 0.08 0.63 ± 0.06 7.58 0.98 ± 0.21 0.63 ± 0.20 70 kg N ha-1 6.34 0.26 ± 0.26 0.42 ± 0.41 6.43 0.49 ± 0.28 0.65 ± 0.45 0 kg N ha-1 3.41 0.01 ± 0.13-3.20 0.09 ± 0.03-2005 159 kg N ha-1 6.55 0.87 ± 0.04 0.61 ± 0.03 6.17 0.94 ± 0.20 0.65 ± 0.14 79 kg N ha-1 5.92 0.39 ± 0.10 0.54 ± 0.13 4.93 0.42 ± 0.02 0.59 ± 0.03 0 kg N ha-1 2.91 0.16 ± 0.03-2.64 0.13 ± 0.09-Each value represents the mean ± SE of four replicate values 123