The use of double-cropping in combination with no-tillage and optimized nitrogen fertilization reduces soil N2O emissions under irrigation

Measurement of nitrous oxide soil fluxes using sorbent-stabilized sampling of flux chambers

A new chamber-based method to measure nitrous oxide soil gas fluxes using an N2O sorbent is presented. The Greenhouse Gas Reduction through Agricultural Carbon Enhancement network (GRACEnet) protocols require grab samples (typically 25 mL ea.) obtained at multiple intervals throughout chamber deployment (i.e., 0, 15, and 30 min) and linear and nonlinear options to process the raw concentrations, based on goodness-of-fit tests. The new method uses a single, sorbent-stabilized large volume (400 mL) gas sample collected at the end of each chamber deployment (30 min) and assumes a linear concentration increase. Both methods estimate the initial (time 0) gas flux using chamber concentration changes and deployment time. This report presents a side-by-side field test in experimental plots. Samples were independently analyzed by gas chromatography and thermal desorption/gas chromatography for the standard and new method, respectively. Gas concentrations measured by both methods at the end of the chamber deployment and calculated soil gas fluxes were in close agreement (R2 = 0.92 and R2 = 0.91, respectively). Additionally, four 100 mL samples taken from multiple chambers at the end of the deployment were pooled into a single cartridge to explore the sorbent's potential to further reduce the number of samples. Pooled sample results from four locations correlated well with average chamber deployments (R2 = 0.92 and R2 = 0.95 for concentrations and soil gas fluxes, respectively). These results suggest sorbent-based sampling can yield soil gas flux data of similar magnitude to interval grab sampling methods. Further testing is required to study the advantages and limitations of the new method.

Alternatives to maize monocropping in Mediterranean irrigated conditions to reduce greenhouse gas emissions

Winter legume cover crops or double-cropping in high N-fertilizer maize-based sprinkler-irrigated systems enhance agroecosystem diversity and potentially increase yields. However, the effects on direct N2O emissions and global warming potential (GWP) have not been fully established. For two years, in the Ebro Valley (Spain), four maize-based systems consisted of: long-season maize (Zea mays) with winter fallow period (F-LSM) the reference system; or after a leguminous cover crop (common vetch, Vicia sativa) (CC-LSM); and short-season maize after a cereal crop (barley, Hordeum vulgare) (B-SSM) or after a leguminous crop (pea, Pisum sativum) (P-SSM). They were assessed in terms of productivity, direct greenhouse gasses emissions (GHG: N2O, CH4, CO2), and global warming potential (GWP). Direct GHG emissions were measured using the static chamber technique, while soil parameters were monitored. Crop yields and nitrogen uptake were also quantified. GHG emissions linked to management and inputs were calculated to obtain GWP and greenhouse gas intensity (GHGI). The most productive system (B-SSM) obtained the highest direct (79 %, 35 %, and 30 % higher than the F-LSM, P-SSM, and CC-SSM, respectively) and scaled N2O emissions. The P-SSM system had similar N-uptake-scaled emissions to the monocropping (MC) systems. Irrigation, fertilizer, and farm operations accounted for the 26 %, 31 %, and 27 % of the total indirect emissions, respectively. Fertilizer production-related emissions in B-SSM and F-LSM systems were 172 % and 45 % higher than the average emissions in the systems with legumes (461 kg CO2eq. ha-1). Diversified systems lead to slightly higher GHGI values than the reference system (F-LSM). However, no differences were found between the F-LSM and P-SSM systems in GWP (4521 and 5512 kg CO2-eq. ha-1, respectively) or GHGI (144 and 158 kg CO2-eq. ha-1, respectively). The P-SSM system may be a potential alternative for increasing the diversification of maize-based irrigated agrosystems without increasing GHG emissions.

A global meta-analysis of yield-scaled N2 O emissions and its mitigation efforts for maize, wheat, and rice

Maintaining or even increasing crop yields while reducing nitrous oxide (N2 O) emissions is necessary to reconcile food security and climate change, while the metric of yield-scaled N2 O emission (i.e., N2 O emissions per unit of crop yield) is at present poorly understood. Here we conducted a global meta-analysis with more than 6000 observations to explore the variation patterns and controlling factors of yield-scaled N2 O emissions for maize, wheat and rice and associated potential mitigation options. Our results showed that the average yield-scaled N2 O emissions across all available data followed the order wheat (322 g N Mg-1 , with the 95% confidence interval [CI]: 301-346) > maize (211 g N Mg-1 , CI: 198-225) > rice (153 g N Mg-1 , CI: 144-163). Yield-scaled N2 O emissions for individual crops were generally higher in tropical or subtropical zones than in temperate zones, and also showed a trend towards lower intensities from low to high latitudes. This global variation was better explained by climatic and edaphic factors than by N fertilizer management, while their combined effect predicted more than 70% of the variance. Furthermore, our analysis showed a significant decrease in yield-scaled N2 O emissions with increasing N use efficiency or in N2 O emissions for production systems with cereal yields >10 Mg ha-1 (maize), 6.6 Mg ha-1 (wheat) or 6.8 Mg ha-1 (rice), respectively. This highlights that N use efficiency indicators can be used as valuable proxies for reconciling trade-offs between crop production and N2 O mitigation. For all three major staple crops, reducing N fertilization by up to 30%, optimizing the timing and placement of fertilizer application or using enhanced-efficiency N fertilizers significantly reduced yield-scaled N2 O emissions at similar or even higher cereal yields. Our data-driven assessment provides some key guidance for developing effective and targeted mitigation and adaptation strategies for the sustainable intensification of cereal production.