Ward N. Smith

ESTIMATED N2O AND CO2 EMISSIONS AS INFLUENCED BY AGRICULTURAL PRACTICES IN CANADA

The Denitrification-Decompostion (DNDC) model was used to estimate the impact of change in management practices on N2O emissions in seven major soil regions in Canada, for the period 1970 to 2029. Conversion of cultivated land to permanent grassland would result in the greatest reduction in N2O emissions, particularly in eastern Canada wherethe model estimated about 60% less N2O emissions for thisconversion. About 33% less N2O emissions were predicted for a changefrom conventional tillage to no-tillage in western Canada, however, a slight increase in N2O emissions was predicted for eastern Canada. GreaterN2O emissions in eastern Canada associated with the adoption of no-tillage were attributed to higher soil moisture causing denitrification, whereas the lower emissions in western Canada were attributed to less decomposition of soil organic matter in no-till versus conventional tilled soil. Elimination of summer fallow in a crop rotation resulted in a 9% decrease in N2O emissions, with substantial emissions occurringduring the wetter fallow years when N had accumulated. Increasing N-fertilizer application rates by 50% increased average emissions by 32%,while a 50% decrease of N-fertilizer application decreased emissions by16%. In general, a small increase in N2O emissions was predicted when N-fertilizer was applied in the fall rather than in the spring. Previous research on CO2 emissions with the CENTURY model (Smith et al.,2001) allowed the quantification of the combined change in N2O andCO2 emissions in CO2 equivalents for a wide range of managementpractices in the seven major soil regions in Canada. The management practices that have the greatest potential to reduce the combined N2O andCO2 emissions are conversion from conventional tillage to permanent grassland, reduced tillage, and reduction of summer fallow. The estimated net greenhouse gas (GHG) emission reduction when changing from cultivated land to permanent grassland ranged from 0.97 (Brown Chernozem) to 4.24 MgCO2 equiv. ha−1 y−1 (BlackChernozem) for the seven soil regions examined. When changing from conventional tillage to no-tillage the net GHG emission reduction ranged from 0.33 (Brown Chernozem) to 0.80 Mg CO2 equiv. ha−1 y−1 (Dark GrayLuvisol). Elimination of fallow in the crop rotation lead to an estimated net GHG emission reduction of 0.43 (Brown Chernozem) to 0.80 Mg CO2 equiv.ha−1 y−1 (Dark Brown Chernozem). The addition of 50% more or 50% less N-fertilizer both resulted in slight increases in combined CO2 and N2O emissions. There was a tradeoff in GHG flux with greaterN2O emissions and a comparable increase in carbon storage when 50% more N-fertilizer was added. The results from this work indicate that conversion of cultivated land to grassland, the conversion from conventional tillage to no-tillage, and the reduction of summerallow in crop rotations could substantially increase C sequestration and decrease net GHG emissions. Based on these results a simple scaling-up scenario to derive the possible impacts on Canadas Kyoto commitment has been calculated.

Testing the DNDC model using N2O emissions at two experimental sites in Canada

Measured data from two experimental sites in Canada were used to test the ability of the DeNitrification and DeComposition model (DNDC) to predict N2O emissions from agricultural soils. The two sites, one from eastern Canada, and one from western Canada, provided a variety of crops, management practices, soils, and climates for testing the model. At the site in eastern Canada, the magnitude of total seasonal N2O flux from the seven treatments was accurately predicted with a slight average over-prediction (ARE) of 3% and a coefficient of variation of 41%. Nitrous oxide emissions based on International Panel for Climate Change (IPCC) methodology had a relative error of 62% for the seven treatments. The DNDC estimates of total yearly emissions of N2O from the field site in western Canada showed an underestimation of 8% for the footslope landscape position and an overestimation of 46% for the shoulder position. The data input for the DNDC model were not of sufficient detail to characterize the moisture differ...

Estimates of the interannual variations of N2O emissions from agricultural soils in Canada

The DNDC model was used to estimate direct N2O emissions from agricultural soils in Canada from 1970 to 1999. Simulations were carried out for three soil textures in seven soil groups, with two to four crop rotations within each soil group. Over the 30-year period, the average annual N2O emission from agricultural soils in Canada was found to be 39.9 Gg N2O–N, with a range from 20.0 to 77.0 Gg N2O–N, and a general trend towards increasing N2O emissions over time. The larger emissions are attributed to an increase in N-fertilizer application and perhaps to a trend in higher daily minimum temperatures. Annual estimates of N2O emissions were variable, depending on timing of rainfall events and timing and duration of spring thaw events. We estimate, using DNDC, that emissions of N2O in eastern Canada (Atlantic Provinces, Quebec, Ontario) were approximately 36% of the total emissions in Canada, though the area cropped represents 19% of the total. Over the 30-year period, the eastern Gleysolic soils had the largest average annual emissions of 2.47 kg N2O–N ha−1 y−1 and soils of the dryer western Brown Chernozem had the smallest average emission of 0.54 kg N2O–N ha−1 y−1. On average, for the seven soil groups, N2O emissions during spring thaw were approximately 30% of total annual emissions. The average N2O emissions estimates from 1990 to 1999 compared well with estimates for 1996 using the IPCC methodology, but unlike the IPCC methodology our modeling approach provides annual variations in N2O emissions based on climatic differences.

Evaluation of two process-based models to estimate soil N2O emissions in Eastern Canada

Process-based models play an important role in the estimation of soil N2O emissions from regions with contrasting soil and climatic conditions. A study was performed to evaluate the ability of two process-based models, DAYCENT and DNDC, to estimate N2O emissions, soil nitrate- and ammonium-N levels, as well as soil temperature and water content. The measurement sites included a maize crop fertilized with pig slurry (Quebec) and a wheat-maize-soybean rotation as part of a tillage-fertilizer experiment (Ontario). At the Quebec site, both models accurately simulated soil temperature with an average relative error (ARE) ranging from 0 to 2%. The models underpredicted soil temperature at the Ontario site with ARE from −5 to −7% for DNDC and from −5 to −13% for DAYCENT. Both models underestimated soil water content particularly during the growing season. The DNDC model accurately predicted average seasonal N2O emissions across treatments at both sites whereas the DAYCENT model underpredicted N2O emissions by 32...

Management Strategies to Sequester Carbon in Agricultural Soils and to Mitigate Greenhouse Gas Emissions

Carbon sequestration in agricultural soils is frequently promoted as a practical solution for slowing down the rate of increase of CO2 in the atmosphere. Consequently, there is a need to improve our understanding of how land management practices may affect the net removal of greenhouse gases (GHG) from the atmosphere. In this paper we examine the role of agriculture in influencing the GHG budget and briefly discuss the potential for carbon mitigation by agriculture. We also examine the opportunities that exist for increasing soil C sequestration using management practices such as reduced tillage, reduced frequency of summer fallowing, introduction of forage crops into crop rotations, conversion of cropland to grassland and nutrient addition via fertilization. In order to provide information on the impact of such management practices on the net GHG budget we ran simulations using CENTURY (a C model) and DNDC (a N model) for five locations across Canada, for a 30-yr time period. These simulations provide information on the potential trade-off between C sequestration and increased N2O emissions. Our model output suggests that conversion of cropland to grassland will result in the largest reduction in net GHG emissions, while nutrient additions via fertilizers will result in a small increase in GHG emissions. Simulations with the CENTURY model also indicated that favorable growing conditions during the last 15 yr could account for an increase of 6% in the soil C at a site in Lethbridge, Alberta.

Estimated changes in soil carbon associated with agricultural practices in Canada

The Century model was used to estimate the influence of changing agricultural practices on C levels in seven major soil groups in Canada for the years from 2000 to 2010. Conversion of arable land to permanent cover, and inclusion of forages in crop rotations would result in the greatest sequestration of C, averaging 0.62 and 0.44 Mg C ha–1 yr–1, respectively. The increase in soil C when conventional-tillage is converted to no-tillage management was estimated to average about 0.13 Mg C ha–1 yr–1. Reduction of summerfallow (wheat-fallow to wheat-wheat-fallow) in the arid and semi-arid chernozems of Western Canada would reduce C losses by about 0.03 Mg C ha–1 yr–1. If fertilizer use efficiency was increased by 50%, 0.04 Mg C ha–1 yr–1 would be sequestered, whereas a decrease of 50% in fertilizer use efficiency would result in a loss of 0.05 Mg C ha–1 yr–1. Timing of N application (fall vs. spring) had little effect on C change. This study indicates that there are several feasible techniques that could be ado...

The rate of carbon change in agricultural soils in Canada at the landscape level

The Century model [a computer simulation of the dynamics of soil organic carbon (SOC)] was used to estimate the rate of SOC change in agricultural soil in Canada. The analysis was carried out on 180 Soil Landscapes of Canada (SLC) polygons, representing 15% of the SLC polygons within agricultural regions. The analysis was stratified into soil zones and into soil textural classes. For each sampled polygon, Century was run for 1 to 5 types of crop rotations under conventional-tillage as well as no-tillage, providing that no-till was used on at least 5% of the land. From the Century simulations, it was estimated that the overall rate of SOC loss from agricultural soils in Canada for 1990 was 39.1 kg ha−1 yr−1 This implies that 1.93 Mt of SOC (7.08 Mt of CO2) was lost from agricultural soils in Canada. Compared to 1990, the SOC loss was estimated to have been greater by 11.9 kg ha−1 yr−1 in 1980 and 9.1 kg ha−1 yr−1 in 1985. The lower loss in 1990 was primarily due to the incorporation of no-till practices an...

Canadian greenhouse gas mitigation options in agriculture

In 1991, on farm management practices contributed 57.6 Tg CO2 equivalent in greenhouse gas emissions, that is, about 10% of the anthropogenic GHG emissions in Canada. Approximately 11% of these emissions were in the form of CO2, 36% in the form of CH4 and 53% in the form of N2O. The CO2 emissions were from soils; CH4 emissions were from enteric fermentation and manure, and N2O emissions were primarily a function of cropping practices and manure management. With the emissions from all other agricultural practices included, such as the emissions from fossil fuels used for transportation, manufacturing, food processing etc., the agricultural sectors contributions were about 15% of Canadas emissions. In this publication, several options are examined as to their potential for reducing greenhouse gas emissions. These involve soil and crop management, soil nutrient management, improved feeding strategies, and carbon storage in industrial by-products. The Canadian Economic Emissions Model for Agriculture (CEEMA) was used to predict the greenhouse gas emissions for the year 2010, as well as the impact of mitigation options on greenhouse gas emissions from the agricultural sector. This model incorporates the Canadian Regional Agricultural sub-Model (CRAM), which predicts the activities related to agriculture in Canada up to 2010, as well as a Greenhouse Gas Emissions sub-Model (GGEM), which estimates the greenhouse gas emissions associated with the various agricultural activities. The greenhouse gas emissions from all agricultural sources were 90.5 Tg CO2 equivalent in 1991. Estimates based on CEEMA for the year 2010 indicate emissions are expected to be 98.0 Tg CO2 equivalent under a business as usual scenario, which assumes that the present trends in management practices will continue. The agricultural sector will then need to reduce its emissions by about 12.9 Tg CO2 equivalent below 2010 forecasted emissions, if it is to attain its part of the Canadian government commitment made in Kyoto. Technologies focusing on increasing the soil carbon sink, reducing greenhouse gas emissions and improving the overall farming efficiency, need to be refined and developed as best management practices. The soils carbon sink can be increased through reduced tillage, reduced summer fallowing, increased use of grasslands and forage crops, etc. Key areas for the possible reduction of greenhouse gas emissions are improved soil nutrient management, improved manure storage and handling, better livestock grazing and feeding strategies, etc. The overall impact of these options is dependent on the adoption rate. Agricultures greenhouse gas reduction commitment could probably be met if soils are recognized as a carbon sink under the Kyoto Accord and if a wide range of management practices are adopted on a large scale. None of these options can currently be recommended as measures because their socio-economic aspects have not been fully evaluated and there are still too many uncertainties in the emission estimates.

Impact of management strategies on the global warming potential at the cropping system level

Estimating the greenhouse gas (GHG) emissions from agricultural systems is important in order to assess the impact of agriculture on climate change. In this study experimental data supplemented with results from a biophysical model (DNDC) were combined with life cycle assessment (LCA) to investigate the impact of management strategies on global warming potential of long-term cropping systems at two locations (Breton and Ellerslie) in Alberta, Canada. The aim was to estimate the difference in global warming potential (GWP) of cropping systems due to N fertilizer reduction and residue removal. Reducing the nitrogen fertilizer rate from 75 to 50 kg N ha(-1) decreased on average the emissions of N2O by 39%, NO by 59% and ammonia volatilisation by 57%. No clear trend for soil CO2 emissions was determined among cropping systems. When evaluated on a per hectare basis, cropping systems with residue removal required 6% more energy and had a little change in GWP. Conversely, when evaluated on the basis of gigajoules of harvestable biomass, residue removal resulted in 28% less energy requirement and 33% lower GWP. Reducing nitrogen fertilizer rate resulted in 18% less GWP on average for both functional units at Breton and 39% less GWP at Ellerslie. Nitrous oxide emissions contributed on average 67% to the overall GWP per ha. This study demonstrated that small changes in N fertilizer have a minimal impact on the productivity of the cropping systems but can still have a substantial environmental impact.

Quantifying carbon sequestration in a minimum tillage crop rotation study in semiarid southwestern Saskatchewan

Scientists and the agricultural community require methods of quantifying C sequestration in soils. This is important in assessing the impact of crop management practices on emission of greenhouse gases and for “C trading”. Using simulation models may be a more effective method of quantification as compared with in situ measurements. A 17-yr crop rotation experiment being conducted on a medium-textured Orthic Brown Chernozem at Swift Current, Saskatchewan, in which soil organic C (SOC) was being monitored periodically, was used to assess the effect on C sequestration of cropping frequency, wheat class, legume green manure (LGM), flexible cropping based on available water, and regrassing of crop land. Prior to the study, the experimental site had been cropped to fallow-wheat (F-W) for the previous 60 yr. Crop management in this experiment involved minimum tillage, snow trapping, and N + P fertilization based on soil tests. Three models [Century, the Introductory C Balance model (ICBM), and the Campbell mode...