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Shelterbelts sequester and store atmospheric carbon as a direct result of the growth of trees and thus present an opportunity for climate change mitigation. The objectives of this paper were to quantify the growth characteristics and to estimate the carbon stocks of six common shelterbelt species in Saskatchewan: hybrid poplar, Manitoba maple, Scots pine, white spruce, green ash, and caragana. Growth curves (3PG) and carbon dynamics (CBM-CFS3) modelling approaches were used to simulate shelterbelt growth and to estimate the carbon stocks in 50 439 km shelterbelts containing the six species. Shelterbelt width ranged from 6.3 to 14.0 m, age ranged from 5 to 100 yr, and tree density ranged from 356 to 791 trees ha −1. The r 2 of the growth curve equations ranged from 28% to 97%, with <50% root-mean-square error and <30% bias. The total ecosystem carbon stocks of all shelterbelts of the six species in Saskatchewan were 10.8 Tg C (1 Tg C = 1 million Mg C), of which 3.77 Tg C was sequestered in the soil and shelterbelt biomass since 1990. The climate mitigation potential of the six shelterbelt species, ranging from 1.78 to 6.54 Mg C km −1 yr −1 , emphasized the important role that trees can have on the agricultural landscape to mitigate greenhouse gases (GHGs). Planting shelterbelt trees and shrubs on agricultural landscapes is an important strategy for mitigating GHGs.

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, T. 2008. Soil carbon change factors for the Canadian agriculture national greenhouse gas inventory. Can. J. Soil Sci. 88: 671Á680. Canada annually reports on all of its annual greenhouse gas emissions to the United Nations Framework Convention on Climate Change (UNFCCC), including estimates of CO 2 emissions and removals from cropland management. Soil carbon (C) change in cropland resulting from management is estimated by using C change factors multiplied by the area of cropland subjected to a management change. In this paper we compare soil C change factors in Canadian cropland obtained using a C modelling approach (Century model) to both empirical estimates obtained from the scientific literature, and to default Intergovernmental Panel on Climate Change (IPCC) estimates. Factors were estimated for land management changes from annual to perennial cropping, tillage to no-tillage and from summer fallow to continuous cropping. Empirical data comparing C change between conventional tillage (CT) and no-tillage (NT) were highly variable, but the modelled factors were still within the range derived from the empirical data. Factors for changes from CT to NT varied from 0.06 to 0.16 Mg C ha(1 yr (1 across the country. When considering the change from annual to perennial cropping, the modelled factors ranged from 0.46 to 0.56 Mg C ha(1 yr(1 , which is in the range of empirical values, and were slightly greater in the eastern than the western soil regions. For conversion of crop-fallow to continuous cropping, the modelled rate of C storage (0.33 Mg C ha(1 yr (1 ) was more than double the average rate of 0.1590.06 Mg C ha (1 yr (1 derived from two independent assessments of the literature. For each of the management changes considered, the modelled factors were generally lower than IPCC estimates, and this is partly attributable to differences in calculation methods and to the fact that C changes likely occur more slowly in the cold climate of Canada. Generally, the results show that the modelling approach used at present to derive C change factors for use in Canada's inventory is adequate. However, soil C change factors for cropland soils in Canada would be greatly improved by a reduction in the high variability usually associated with empirical data, and by improved simulation of the Century model under varying management conditions.

Purpose This paper presents an improved methodological approach for studying life cycle impacts (especially global warming) from changes in crop production practices. The paper seeks to improve the quantitative assessment via better tools and it seeks to break down results in categories that are logically separate and thereby easy to explain to farmers and other relevant stakeholder groups. The methodological framework is illustrated by a concrete study of a phosphate inoculant introduced in US corn production. Methods The framework considers a shift from an initial agricultural practice (reference system) to an alternative practice (alternative system) on an area of cropland A. To ensure system equivalence (same functional output), the alternative system is expanded with displaced or induced crop production elsewhere to level out potential changes in crop output from the area A. Upstream effects are analyzed in terms of changes in agricultural inputs to the area A. The yield effect is quantified by assessing the impacts from changes in crop production elsewhere. The field effect from potential changes in direct emissions from the field is quantified via biogeochemical modeling. Downstream effects are assessed as impacts from potential changes in post-harvest treatment, e.g., changes in drying requirements (if crop moisture changes). Results and discussion An inoculant with the soil fungus Penicillium bilaiae has been shown to increase corn yields in Minnesota by 0.44 Mg ha−1 (~ 4%). For global warming, the upstream effect (inoculant production) was 0.4 kg CO2e per hectare treated. The field effect (estimated via the biogeochemical model DayCent) was − 250 kg CO2e ha−1 (increased soil carbon and reduced N2O emissions) and the yield effect (estimated by simple system expansion) was − 140 kg CO2e ha−1 (corn production displaced elsewhere). There were no downstream effects. The total change per Mg dried corn produced was − 36 kg CO2e corresponding to a 14% decrease in global warming impacts. Combining more advanced methods indicates that results may vary from − 27 to − 40 kg CO2e per Mg corn. Conclusion and recommendations The present paper illustrates how environmental impacts from changes in agricultural practices can be logically categorized according to where in the life cycle they occur. The paper also illustrates how changes in emissions directly from the field (the field effect) can be assessed by biogeochemical modeling, thereby improving life cycle inventory modeling and addressing concerns in the literature. It is recommended to use the presented approach in any LCA of changes in agricultural practices.