• Energy Research

Agriculture significantly contributes to global soil nitrous oxide (N2O) emissions. Crop rotation diversification and cover cropping are feasible agronomic strategies to reduce nitrogen losses to the environment. However, input of cover crop residues could potentially increase soil N2O emissions. Dual nitrification and urease inhibitors (NUI) administered after cover crop termination at the time of nitrogen fertiliser addition could reduce emissions, but this has not been widely evaluated in field studies. A 4-year crop rotation study was conducted to determine the effect of crop diversification and use of NUI on N2O emissions, crop yield and N2O intensity. Nitrous oxide flux was measured year-round using a micrometeorological method deployed on four 4-ha fields. Two fields were managed with a conventional crop rotation (CONV) (corn – soybean – soybean) and two fields were managed with a diverse crop rotation (DIV) (corn – soybean – winter-wheat plus cover crops either as 2-species mixture under seeded to corn or 4-species mixture after winter-wheat harvest). The effect of a NUI [N(-n-Butyl) thiophosphoric triamide and Pronitridine] was tested in corn in the fourth year. The DIV rotation resulted in 43 % lower annual N2O emissions when winter wheat was grown instead of soybean and 18–26 % increase in annual N2O emissions for corn. The DIV rotation increased N2O intensity by 15 % in Year 1 and 36 % in Year 4 compared to corn in the CONV rotation. The use of NUI in DIV rotation resulted in 15 % lower total N2O emissions over 3 years of the rotation cycle. The application of NUI resulted in a 19 % reduction in N2O intensity within the DIV rotation, with no observable effect on corn yield. Further research should focus on optimising the N application rates according to NUI use, considering available nitrogen from crop residues and cover crops when integrated into the crop rotation.

Abstract Soil freeze-thaw (FT) and dry-wet (DW) cycles are brief transitory biophysical changes, but these events have important implications in determining the timing and magnitude of N2O emissions and may represent a significant proportion of annual N2O emissions from agricultural systems. It is often assumed that FT and DW cycles influence the processes of N2O production and emission in a similar manner, however, research has yet to systematically identify the similarities and differences in the mechanisms which lead to potentially higher N2O fluxes during FT compared to DW cycles. Herein, we present the first review to do so; in addition, we identify strategic research areas required for improving the understanding of FT and DW processes leading to N2O emissions. There are key differences between the mechanisms that contribute to N2O fluxes during FT and DW cycles, centered on the duration and spatial extent of anaerobiosis, temperature sensitivity of microbial activity, relative gas diffusivity, and soil water dynamics. These differences might increase the risk of N2O emissions during FT cycles relative to soil DW cycles. Current research gaps include (i) the identification of organic substrates made available due to FT and DW cycles, and their contribution to ensuing N2O fluxes, (ii) an understanding of how cryosuction dynamics potentially influence N2O production and emission, (iii) understanding and predicting the air-entry potential of soil as it relates to N2O fluxes, (iv) identifying the relative significance of dissolved N2O in soil water and its solubility changes during FT and DW phases, and (v) determining microbial community and functional changes across soil spatial and temporal scales. Advances in these areas are recommended for improving process descriptions in biogeochemical models in order to more accurately predict N2O emissions from soils prone to FT and DW cycles.

This review examined methane (CH4) and nitrous oxide (N2O) mitigation strategies for Canadian dairy farms. The primary focus was research conducted in Canada and cold climatic regions with similar dairy systems. Meta-analyses were conducted to assess the impact of a given strategy when sufficient data were available. Results indicated that options to reduce enteric CH4from dairy cows were increasing the dietary starch content and dietary lipid supplementation. Replacing barley or alfalfa silage with corn silage with higher starch content decreased enteric CH4per unit of milk by 6%. Increasing dietary lipids from 3% to 6% of dry matter (DM) reduced enteric CH4yield by 9%. Strategies such as nitrate supplementation and 3-nitrooxypropanol additive indicated potential for reducing enteric CH4by about 30% but require extensive research on toxicology and consumer acceptance. Strategies to reduce emissions from manure are anaerobic digestion, composting, solid–liquid separation, covering slurry storage and flaring CH4, and reducing methanogen inoculum by complete emptying of slurry storage at spring application. These strategies have potential to reduce emissions from manure by up to 50%. An integrated approach of combining strategies through diet and manure management is necessary for significant GHG mitigation and lowering carbon footprint of milk produced in Canada.

Abstract Integrated Systems (IS) have been identified as an efficient land-management strategy for restoring degraded areas worldwide, increasing crops and beef yields and providing technical potential for carbon (C) sequestration in soil and trees as an option for offsetting CH 4 and N 2 O emissions from cattle production. The aim of our study is to estimate the greenhouse gas (GHG) balance and the C footprint of beef cattle (fattening cycle) in three contrasting production scenarios on the Brachiaria pasture in Brazil—1) degraded pasture (DP), 2) managed pasture (MP), and 3) the crop-livestock-forest integrated system (CLFIS)—presenting new alternatives of land use as a GHG mitigation strategy. Area-scaled total GHG emissions were highest in MP (84,541 kg CO 2 eq ha −1 ), followed by CLFIS (64,519 kg CO 2 eq ha −1 ) and DP (8004 kg CO 2 eq ha −1 ) over a 10-yr period. Our results note that the highest C footprint of beef cattle was in the DP, 18.5 kg CO 2 eq per kg LW (live weight), followed by 12.6 kg CO 2 eq per kg LW in the CLFIS and 9.4 kg CO 2 eq per kg LW in the MP, without taking into account the technical potential for C sequestration in MP (soil C) and CLFIS (soil and Eucalyptus C). Considering the potential for soil C sequestration in the MP and CLFIS, the C footprint of beef cattle could be reduced to 7.6 and −28.1 kg CO 2 eq per kg LW in the MP and CLFIS, respectively. The conversion of the degraded pasture to a well-managed pasture and the introduction of CLFIS can reduce their associated GHG emissions in terms of kg CO 2 eq emitted per kg of cattle LW produced, increasing the production of meat, grains and timber. This reduction is primarily due to pasture improvement and increases in cattle yields and the provision of technical potential for C sinks in soil and biomass to offset cattle-related emissions.