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Background: Although cover crops provide many agronomic and environmental benefits, they may also increase nitrous oxide (N2O) emissions after termination. The N2O emissions from decomposing biomass of cover crops largely depends on the type of cover and maturity level at termination. Aim: The objective of this study was to quantify N2O emissions following soil incorporation of a non‐legume (oat; Avena sativa L.) and a legume (grass pea; Lathyrus sphaericus Retz.) cover crop residues at two different maturity levels. Methods: Oat and grass pea were terminated at vegetative (early‐termination) and reproductive (late‐termination) stages, and stored fresh before soil incorporation (2.5 Mg dry matter ha−1) together in late‐May. A treatment with no cover crop was included as the control. The experiment was laid out as completely randomized block design with three replicated plots (2 m × 2 m) in each treatment combination. Finger millet [Eleusine coracana (L.) Gaertn] seedlings were transplanted as a summer crop. The N2O fluxes were measured with a closed chamber with a portable gas analyzer on 25 dates over an experimental period of 98 days. Results: In general, fluxes of N2O increased after rainfall or irrigation events and approximated zero during dry periods. Cumulative N2O emissions during the 98 days study period were higher (p < 0.01) from all cover crops treatments than the control. Effects of maturity level at termination on cumulative N2O emissions were significant (p < 0.05) as 30–35% higher emissions were recorded from both cover crops terminated at the reproductive stage than the vegetative stage. Yields of finger millet biomass from oat incorporated plots were 15–19% greater (p < 0.05) than grass pea incorporated plots, while the yields from control plots were not significantly different from plots receiving cover crop residues. Conclusions: Stage of maturity at termination alone was not a strong predictor of total cumulative N2O emissions from decomposing cover crop residues, as maturity level interacted with environment variables (e.g., timing of rainfall events). [ABSTRACT FROM AUTHOR]

In this study, we measured nitrous oxide (N2O) emissions from plots of fall-planted hairy vetch (HV, Vicia villosa) grown as a green nitrogen (N) source for following summer forage crabgrass (Digitaria sanguinalis). Two treatments were compared: (i) HV grown solely as green manure where all biomass was incorporated by tillage, and (ii) harvesting of aboveground HV biomass prior to planting of crabgrass. Fluxes of N2O were measured with closed chamber systems on 27 dates during a 2-month growth period of crabgrass after the termination of HV in early May. At termination, the average aboveground biomass yield of HV was 4.6 Mg ha−1 with 146 kg N ha−1 content. The N2O emissions were as high as 66 g N2O-N ha−1 day−1 on day 1 after HV incorporation, but reached close to zero within a week. Emissions of N2O increased with subsequent rainfall and irrigation events from both treatments but emission peaks were not observed during the rapid growth of crabgrass. Two-month cumulative emission of N2O (mean ± s.e., n = 4) from HV incorporated plots (921 ± 120 g N2O-N ha−1) was three times (P < 0.05) of HV harvested plots (326 ± 30 g N2O-N ha−1). However, crabgrass biomass yields, N concentrations and total biomass N uptake were decreased significantly by harvesting HV. In conclusion, the results suggested that whereas removal of HV biomass for use as forage may significantly reduce N2O emissions, quantity and quality of the following recipient crops may be constrained. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare the effects of cowpea green manure and inorganic nitrogen (N) fertilizers on yields of winter wheat and soil emissions of nitrous oxide (N2O). The comparisons included cowpea grown solely as green manure where all biomass was terminated at maturity by tillage, summer fallow treatments with 90 kg N ha−1 as urea (90-N), and no fertilization (control) at planting of winter wheat. Fluxes of N2O were measured by closed chamber methods after soil incorporation of cowpea in autumn (October–November) and harvesting of winter wheat in summer (June–August). Growth and yields of winter wheat and N concentrations in grain and straw were also measured. Cowpea produced 9.5 Mg ha−1 shoot biomass with 253 kg N ha−1 at termination. Although soil moisture was favorable for denitrification after soil incorporation of cowpea biomass, low concentrations of soil mineral N restricted emissions of N2O from cowpea treatment. However, increased concentrations of soil mineral N and large rainfall-induced emissions were recorded from the cowpea treatment during summer. Growth of winter wheat, yield, and grain N concentrations were lowest in response to cowpea treatment and highest in 90-N treatment. In conclusion, late terminated cowpea may reduce yield of winter wheat and increase emissions of N2O outside of wheat growing seasons due to poor synchronization of N mineralization from cowpea biomass with N-demand of winter wheat. [ABSTRACT FROM AUTHOR]

Rewetted peatlands are weak to negligible sources of the greenhouse gas nitrous oxide (N2O). However, rewetted peatlands in use for paludiculture may require nitrogen (N) fertilization potentially creating hot moments for denitrification and N2O emissions. In this study, we measured N2O emissions from an N-rich riparian fen for two consecutive years using static chambers. The field experiment included side-by-side plots cultivated with reed canary grass (Phalaris arundinacea L.) under different degrees of manipulated rewetting. The treatments were defined as control, semi-flooded and flooded conditions corresponding to 2-year weighted mean groundwater table (GWT) depths of 9, 3 and 1 cm below soil surface, respectively. The crop was fertilized and harvested twice a year (160 kg N ha−1 year−1 in two equal splits). Large N2O emissions were observed from all treatments after each fertilization event, which contributed to cumulative annual emissions of 3.2–6.0 kg N2O–N ha−1 in the first year and 1.8–4.2 kg N2O–N ha−1 in the second year. Emissions outside the fertilization periods were negligible. Annual N2O emissions were similar (P > 0.05) among the treatments in the first year whereas control treatments had the lowest emissions in the second year. Nitrogen removal in harvested biomass (197–218 kg N ha−1 year−1) exceeded the fertilizer N in all treatments, indicating that the cultivated biomass utilized substantial amounts of mineralized N from the peat soil. Overall, the results indicate that fertilizer-induced N2O emissions can be high although background soil emissions are low when high GWT is maintained on N-rich riparian peatland. [ABSTRACT FROM AUTHOR]

Cultivation of bioenergy crops has been suggested as a promising option for reduction of greenhouse gas ( GHG) emissions from arable organic soils (Histosols). Here, we report the annual net ecosystem exchange ( NEE) fluxes of CO2 as measured with a dynamic closed chamber method at a drained fen peatland grown with reed canary grass ( RCG) and spring barley ( SB) in a plot experiment ( n = 3 for each cropping system). The CO2 flux was partitioned into gross photosynthesis ( GP) and ecosystem respiration ( RE). For the data analysis, simple yet useful GP and RE models were developed which introduce plot-scale ratio vegetation index as an active vegetation proxy. The GP model captures the effect of temperature and vegetation status, and the RE model estimates the proportion of foliar biomass dependent respiration ( Rfb) in the total RE. Annual RE was 1887 ± 7 (mean ± standard error, n = 3) and 1288 ± 19 g CO2-C m−2 in RCG and SB plots, respectively, with Rfb accounting for 32 and 22% respectively. Total estimated annual GP was −1818 ± 42 and −1329 ± 66 g CO2-C m−2 in RCG and SB plots leading to a NEE of 69 ± 36 g CO2-C m−2 yr−1 in RCG plots (i.e., a weak net source) and −41 ± 47 g CO2-C m−2 yr−1 in SB plots (i.e., a weak net sink). Standard errors related to spatial variation were small (as shown above), but more significant uncertainties were related to the modelling approach for establishment of annual budgets. In conclusion, the bioenergy cropping system was not more favourable than the food cropping system when looking at the atmospheric CO2 emissions during cultivation. However, in a broader GHG life-cycle perspective, the lower fertilizer N input and the higher biomass yield in bioenergy cropping systems could be beneficial. [ABSTRACT FROM AUTHOR]

Cultivated peatlands under drainage practices contribute significant carbon losses from agricultural sector in the Nordic countries. In this research, we developed the BASGRA-BGC model coupled with hydrological, soil carbon decomposition and methane modules to simulate the dynamic of water table level (WTL), carbon dioxide (CO 2 ) and methane (CH 4 ) emissions for cultivated peatlands. The field measurements from four experimental sites in Finland, Denmark and Norway were used to validate the predictive skills of this novel model under different WTL management practices, climatic conditions and soil properties. Compared with daily observations, the model performed well in terms of RMSE (Root Mean Square Error; 0.06-0.11 m, 1.22-2.43 gC/m 2 /day, and 0.002-0.330 kgC/ha/day for WTL, CO 2 and CH 4 , respectively), NRMSE (Normalized Root Mean Square Error; 10.3-18.3%, 13.0-18.6%, 15.3-21.9%) and Pearson's r (Pearson correlation coefficient; 0.60-0.91, 0.76-0.88, 0.33-0.80). The daily/seasonal variabilities were therefore captured and the aggregated results corresponded well with annual estimations. We further provided an example on the model's potential use in improving the WTL management to mitigate CO 2 and CH 4 emissions while maintaining grass production. At all study sites, the simulated WTLs and carbon decomposition rates showed a significant negative correlation. Therefore, controlling WTL could effectively reduce carbon losses. However, given the highly diverse carbon decomposition rates within individual WTLs, adding indicators (e.g. soil moisture and peat quality) would improve our capacity to assess the effectiveness of specific mitigation practices such as WTL control and rewetting., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.)