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Background: Agricultural residues could potentially be converted to bioenergy, but the sustainable harvest rate is unclear. Results: Residue removal increases soil loss at rates that vary with topography, crop rotation and management; decreases yields (100-year mean yields changed -0.07 to -0.08% for every percent of residue mass removed); decreases soil carbon (approximately 40–90 kg C ha-1 year-1 per Mg of residue harvested); and decreases soil nitrogen (∼3 kg N ha-1 year-1 per Mg residue harvested). Conclusion: Even where soil loss is within tolerable limits, harvesting residue is a question of trade-offs in terms of reduction of yield and loss of soil nutrients. The effects of increased residue harvest are highly variable, depending on local climate and soil erodibility and it is thus problematic to apply a single harvest rate globally. However, on flat land under conservation management, the majority of residue could be sustainably harvested for bioenergy.

Used as cover crops, clover species may differ in their ability to suppress weed growth. Field trials were conducted in Alberta, Canada to measure the growth of brown mustard [Brassica juncea (L.) Czern.], in mowed and nonmowed production, as influenced by alsike (Trifolium hybridum L.), balansa [T. michelianum Savi var. balansae (Boiss.) Azn.], berseem (T. alexandrinum L.), crimson [T. incarnatum (Boiss.) Azn.], berseem (T. alexandrinum L.), crimson (T. incarnatum L.), Persian (T. resupinatum L.), red (T. pratense L.), and white Dutch (T. repens L.) clover and fall rye (Secale cereale L.). In 1997, clovers reduced mustard biomass in nonmowed treatments by 29% on a high- fertility soil (Typic Cryoboroll) at Edmonton and by 57% on a low- fertility soil (Typic Cryoboralf) at Breton. At Edmonton, nonmowed mustard biomass was reduced by alsike and berseem clover in 1996 and by alsike, balansa, berseem, and crimson clover in 1997. At Breton, all seven clover species suppressed weed biomass. A negative correlation was noted among clover and mustard biomass at Edmonton but not at Breton. The effects of mowing varied with location, timing, and species. Mowing was beneficial to crop/weed proportion at Edmonton but not at Breton. Mowing at early flowering of mustardmore » large-seeded legumes and sweetclover (Melilotus offici) produced greater benefit than mowing at late flowering. With early mowing, all clover species suppressed mustard growth at Edmonton. Clovers reduced mustard regrowth (g plant21 ) and the number of mustard plants producing regrowth. The characteristics of berseem clover (upright growth, long stems, high biomass, and late flowering) would support its use as a cover crop or forage in north-central Alberta.« less

Soil dry aggregate size distribution (DASD) and surface roughness are important factors affecting wind erodibility. This study monitored overwinter changes in DASD and surface roughness and identified relationships with climatic variables in the chinook-dominated region of southern Alberta. A different site was monitored in each of three winters (18 Sept. 1992 to 12 May 1993; 26 Oct. 1993 to 29 Apr. 1994; 30 Aug. 1994 to 24 May 1995) on Dark Brown Chernozemic clay loams (fine-loamy, mixed, Typic Haploborolls). The DASD was expressed as geometric mean diameter (GMD) and wind erodible fraction (EF). The GMD ranged from 1.88 to 0.08 mm in 1992-1993, from 9.05 to 1.17 mm in 1993-1994, and from 4.71 to 0.80 mm in 1994-1995. The EF ranged from 38.9 to 74.0% in 1992-1993, from 12.6 to 43.7% in 1993-1994, and 31.3 to 55.0% in 1994-1995. Surface roughness was measured parallel (C par ) to tillage direction on two of the sites. Using the chain method, C par ranged from 15.1 to 3.7% in 1993-1994 and from 14.4 to 3.3% in 1994-1995. Regression analysis with time revealed significant exponential decay for GMD (R 2 = 0.57 in 1992-1993, 0.97 in 1993-1994, and 0.78 in 1994-1995) and C par (R 2 = 0.98 in 1993-1994, 0.91 in 1994-1995) and a positive linear fit for EF (R 2 = 0.57 in 1992-1993, 0.91 in 1993-1994, and 0.62 in 1994-1995). Three overwinter periods, differentiated by the timing and form of precipitation and designated as fall rainlsnow, winter snow, and spring snowl rain, were used to assess the changes in EF using cumulative freeze-thaw cycles, precipitation, and snow cover variables. Results indicated that precipitation, which directly influences soil water content, is necessary for freeze-thaw cycles to be effective in disrupting soil aggregates. Snowmelt and spring rainfall appear capable of reducing wind erodibility on these clay loam soils by promoting soil crusting. Our study showed that overwinter soil properties affecting wind erodibility are highly transitory and that the timing and form of precipitation played a major role in determining wind erosion risk in southern Alberta.

Freeze-drying has been implicated as a factor causing soil aggregate breakdown on the Canadian Prairies and northern Great Plains. Aggregates of a Dark Brown Chernozemic clay loam soil sampled in October 1993 and January and April 1994 were subjected to repeated cycles of wetting (to 0.1, 0.2 and 0.3 kg kg−1 water contents) freezing, and freeze-drying under laboratory conditions. The October 1993 samples showed less disruption when initially exposed to freeze-drying cycles compared to samples taken in January and April 1994. Using regression analysis, we predicted that 31 freeze-dry cycles were required for the 0.1 kg kg−1 water content aggregates to reach 60% erodible fraction (EF, % aggregates −1 aggregates and 2 for 0.3 kg kg−1 aggregates. In a field study, conducted over the 1994–1995 winter on a similar clay loam soil, we estimated the number of freeze-drying cycles using large vapour pressure (VPL) and small vapour pressure (VPS) gradients between the soil surface (which had a mean winter water content of ~0.1 kg kg−1) and the atmosphere. With solar energy adjustments, we predicted that the number of freeze-dry cycles required for the soil to reach 60% EF was 60 for VPL and 37 for VPS conditions. The latter number was similar to the 31 cycles predicted in the laboratory study of aggregates at 0.1 water content. Our results demonstrate that freeze-drying is an important overwinter process in the breakdown of soil aggregates and hence wind erosion risk in the Canadian prairie region. Key words: Freeze-drying, wind erosion, erodible fraction

The Agricultural Policy Environmental eXtender (APEX) model was developed by the Blacklands Research and Extension Center in Temple, Texas. APEX is a flexible and dynamic tool that is capable of simulating a wide array of management practices, cropping systems, and other land use across a broad range of agricultural landscapes, including whole farms and small watersheds. The model can be configured for novel land management strategies, such as filter strip impacts on pollutant losses from upslope cropfields, intensive rotational grazing scenarios depicting movement of cows between paddocks, vegetated grassed waterways in combination with filter strip impacts, and land application of manure removal from livestock feedlots or waste storage ponds. A description of the APEX model is provided, including an overview of all the major components in the model. Applications of the model are then reviewed, starting with livestock manure and other management scenarios performed for Livestock and the Environment: A National Pilot Project (NPP), and then continuing with feedlot, pesticide, forestry, buffer strip, conservation practice, and other management or land use scenarios performed at the plot, field, watershed, or regional scale. The application descriptions include a summary of calibration and/or validation results obtained for the different NPP assessments as well as for other APEX simulation studies. Available APEX Geographic Information System–based or Windows-based interfaces are also described, as are forthcoming future improvements and additional research needs for the model.

Computer models are important tools for assessing regional carbon sequestration and other environmental impacts of agricultural management practices. The Environmental Policy Integrated Climate (EPIC) model is a very flexible model that has been used to make a wide range of field- and regional-scale environmental assessments. Large regional-scale applications of EPIC and similar models can require thousands of runs, resulting in a huge data management task. To address this problem, the Center for Agricultural and Rural Development (CARD) has developed an interactive EPIC (i_EPIC) software package that provides an automated approach to executing large sets of EPIC simulations. Overviews of both the latest EPIC version and the i_EPIC software package are presented. We also present examples of regional applications using both EPIC and i_EPIC conducted by the Resource and Environmental Policy Division of CARD, by the Joint Global Change Research Institute of the University of Maryland and the Pacific Northwest National Laboratory, and by the Resource Assessment Division of the Natural Resources Conservation Service, U.S. Department of Agriculture.

This report summarizes the major findings of a study in which an integrated agro-ecological economic modeling system was constructed around Agriculture Canada's Canadian Regional Agriculture Model (CRAM) to analyze the economic and environmental impacts of proposed agricultural policies. The discussion covers the integrated modeling system and the policy analysis results, and presents future recommendations that emphasize how the current system can be improved.

Described in this report is the application of an integrated agro-ecological modeling system that has been constructed around Agriculture Canada's Canadian Regional Agriculture Model (CRAM) to analyze the economic and environmental impacts of proposed agricultural policies for Alberta, Saskatchewan, and Manitoba. This integrated modeling system consists of an agricultural decision component and an environmental component.

The Breton Plots research site is owned and operated by the University of Alberta located at latitude 53° 07′ N and longitude 114° 28′ W near the town of Breton (Alberta, Canada). The research site currently holds five long-term crop rotations and tillage experiments. The oldest plots, the Breton Classical Plots, were initiated in 1930 with the objective of finding “systems of farming suitable for the wooded soil belt” (Wyatt et al., 1936).

This report describes the interface between RS-CRAM (resource sensitive Canadian Regional Agriculture Model) and the environmental components of the integrated modeling system for crops, crop sequences, and management systems representative of western Canadian agriculture. An experimentally designed set of EPIC (Erosion Productivity Impact Calculator) simulations were performed to generate erosion output that was then used to construct wind and water erosion metamodels (response functions) for several Canadian provinces.

The trade-off between agricultural production stability and environmental sustainability is a growing concern. The two major Canadian farm income stabilization programs of 1991, GRIP (Gross Revenue Insurance Plan) and NISA (Net Income Stabilization Account), are being considered for their resource neutrality impacts. This report presents a conceptual framework designed to evaluate the environmental impacts of GRIP and NISA, focusing on land use, technology, and soil degradation shifts. The approach involves a multidisciplinary effort to create a system that permits evaluation of important relationships between policy, agricultural production and the environment. The focus is on development of an integrated agro-ecological economic system built around Agriculture Canada's Regional Agricultural Model (CRAM) and the Erosion Productivity Impact Calculator (EPIC) model. CRAM, a risk-neutral, aggregate resource allocation model, is modified to include a more detailed technology specification and producer risk due to production and net return variability. Environmental impact indicator functions are developed using EPIC simulations based on experimental design and metamodeling techniques. The integrated system will be used to evaluate the economic and environmental impacts of alternative policies.