Carbon footprint of South Dakota dairy production system and assessment of mitigation options.

Livestock production contributes to greenhouse gas (GHG) emissions. However, there is a considerable variability in the carbon footprint associated with livestock production. Site specific estimates of GHG emissions are needed to accurately focus GHG emission reduction efforts. A holistic approach must be taken to assess the environmental impact of livestock production using appropriate geographical scale. The objective of this study was to determine baseline GHG emissions from dairy production in South Dakota using a life cycle assessment (LCA) approach. A cradle-to-farm gate LCA was used to estimate the GHG emissions to produce 1 kg of fat and protein corrected milk (FPCM) in South Dakota. The system boundary was divided into feed production, farm management, enteric methane, and manure management as these activities are the main contributors to the overall GHG emissions. The production of 1 kg FPCM in South Dakota dairies was estimated to emit 1.23 kg CO2 equivalents. The major contributors were enteric methane (46%) and manure management (32.7%). Feed production and farm management made up 14.1 and 7.2%, respectively. The estimate is similar to the national average but slightly higher than the California dairy system. The source of corn used in the dairies influences the footprint. For example, South Dakota corn had fewer GHG emissions than grain produced and transported in from Iowa. Therefore, locally and more sustainably sourced feed input will contribute to further reducing the environmental impacts. Improvements in efficiency of milk production through better genetics, nutrition animal welfare and feed production are expected to further reduce the carbon footprint of South Dakota dairies. Furthermore, anaerobic digesters will reduce emissions from manure sources.

Life cycle assessment of wheat production and wheat-based crop rotations.

In the northern Great Plains (NGP), wheat is the primary grain commodity. There is a need for the NGP to have a detailed analysis of environmental impacts for wheat-based agricultural production systems to better understand regional agroecosystems. This article provides a cradle-to-field gate life cycle assessment (LCA) for NGP dryland wheat (Triticum aestivum L.) production. The environmental impacts for winter wheat production using crop rotation and agricultural intensification are quantified. Fourteen no-till crop rotations ranging in duration from 2 to 6 yr were evaluated and compared using data from a historical 13-yr replicated rotation study (>300 observations). Midpoint LCA categories chosen for this comparison are energy, agricultural land use, climate change potential, freshwater eutrophication, and freshwater ecotoxicity due to their direct links with agricultural management practices. The NGP farmers commonly use a fallow period every other year due to moisture limitations. This specific agricultural practice and allocations within rotations are critical considerations within agricultural LCAs. Two aspects of fallow considerations and a sensitivity analysis were also performed. The allocated midpoint impacts between crops in rotational studies averaged 0.31, 0.79, 0.62, and 0.63 kg CO2 eq. per unit of winter wheat when energy, economic, mass, and cereal unit allocations were used, respectively. Economic analysis of the studied experimental crop was performed; results demonstrated that crop insurance policies improved diversification economics by 20%. Agricultural diversification benefits and burdens were better represented by endpoint damage assessments than by midpoint impact analysis.

Eco-Efficiency Model for Evaluating Feedlot Rations in the Great Plains, United States.

Environmental impacts attributable to beef feedlot production provide an opportunity for economically linked efficiency optimization. Eco-efficiency models are used to optimize production and processes by connecting and quantifying environmental and economic impacts. An adaptable, objective eco-efficiency model was developed to assess the impacts of dietary rations on beef feedlot environmental and fiscal cost. The hybridized model used California Net Energy System modeling, life cycle assessment, principal component analyses (PCA), and economic analyses. The model approach was based on 38 potential feedlot rations and four transportation scenarios for the US Great Plains for each ration to determine the appropriate weight of each impact. All 152 scenarios were then assessed through a nested PCA to determine the relative contributing weight of each impact and environmental category to the overall system. The PCA output was evaluated using an eco-efficiency model. Results suggest that water, ecosystem, and human health emissions were the primary impact category drivers for feedlot eco-efficiency scoring. Enteric CH emissions were the greatest individual contributor to environmental performance (5.7% of the overall assessment), whereas terrestrial ecotoxicity had the lowest overall contribution (0.2% of the overall assessment). A well-balanced ration with mid-range dietary and processing energy requirements yielded the most eco- and environmentally efficient system. Using these results, it is possible to design a beef feed ration that is more economical and environmentally friendly. This methodology can be used to evaluate eco-efficiency and to reduce researcher bias of other complex systems.

Life-Cycle Assessment of Oilseeds for Biojet Production Using Localized Cold-Press Extraction.

As nonfood oilseed varieties are being rapidly developed, new varieties may affect agricultural production efficiency and life-cycle assessment results. Current, detailed feedstock production information is necessary to accurately assess impacts of the biofuel life-cycle. The life-cycle impacts of four nonfood oilseeds (carinata [ L. Braun], camelina [ L. Crantz], canola or rapeseed [ L.], and sunflower [ L.]) were modeled using Argonne National Laboratory's GREET model to compare feedstocks for renewable biojet production using cold-press oil extraction. Only feedstock-related inputs were varied, allowing isolation of feedstock influence. Carinata and camelina performed slightly better than other oilseed crops at most product stages and impact categories as a result of current, low-input agricultural information and new feedstock varieties. Between 40 to 50% of SO and NO emissions, ∼25% of greenhouse gas (GHG) emissions, and ∼40% of total energy consumption for the biojet production impact occurred during feedstock production. Within the first standard deviation, total well-to-tank emissions varied between ∼13% (GHG) and ∼35% (SO) for all feedstocks emphasizing the importance of accurate agricultural production information. Nonfood oilseed feedstock properties (e.g., oil content, density) and agricultural management (e.g., fertilization, yield) affect life-cycle assessment results. Using biofuels in feedstock production and focusing on low-impact management would assist producers in improving overall product sustainability.

Meta-Analysis of Soybean-based Biodiesel.

Biofuel policy changes in the United States have renewed interest in soybean [ (L.) Merr.] biodiesel. Past studies with varying methodologies and functional units can provide valuable information for future work. A meta-analysis of nine peer-reviewed soybean life cycle analysis (LCA) biodiesel studies was conducted on the northern Great Plains in the United States. Results of LCA studies were assimilated into a standardized system boundary and functional units for global warming (GWP), eutrophication (EP), and acidification (AP) potentials using biodiesel conversions from peer-reviewed and government documents. Factors not fully standardized included variations in NO accounting, mid- or end-point impacts, land use change, allocation, and statistical sampling pools. A state-by-state comparison of GWP lower and higher heating values (LHV, HHV) showed differences attributable to variations in spatial sampling and agricultural practices (e.g., tillage, irrigation). The mean GWP of LHV was 21.1 g·CO-eq MJ including outliers, and median EP LHV and AP LHV was 0.019 g·PO-eq MJ and 0.17 g·SO-eq MJ, respectively, using the limited data available. An LCA case study of South Dakota soybean-based biodiesel production resulted in GWP estimates (29 or 31 g·CO-eq MJ; 100% mono alkyl esters [first generation] biodiesel or 100% fatty acid methyl ester [second generation] biodiesel) similar to meta-analysis results (30.1 g·CO-eq MJ). Meta-analysis mean results, including outliers, resemble the California Low Carbon Fuel Standard for soybean biodiesel default value without land use change of 21.25 g·CO-eq MJ. Results were influenced by resource investment differences in water, fertilizer (e.g., type, application), and tillage. Future biofuel LCA studies should include these important factors to better define reasonable energy variations in regional agricultural management practices.

Life Cycle Assessment modelling of stormwater treatment systems.

Stormwater treatment technologies to manage runoff during rain events are primarily designed to reduce flood risks, settle suspended solids and concurrently immobilise metals and nutrients. Life Cycle Assessment (LCA) is scarcely documented for stormwater systems despite their ubiquitous implementation. LCA modelling quantified the environmental impacts associated with the materials, construction, transport, operation and maintenance of different stormwater treatment systems. A pre-fabricated concrete vortex unit, a sub-surface sandfilter and a raingarden, all sized to treat a functional unit of 35 m(3) of stormwater runoff per event, were evaluated. Eighteen environmental mid-point metrics and three end-point 'damage assessment' metrics were quantified for each system's lifecycle. Climate change (kg CO2 eq.) dominated net environmental impacts, with smaller contributions from human toxicity (kg 1,4-DB eq.), particulate matter formation (kg PM10 eq.) and fossil depletion (kg oil eq.). The concrete unit had the highest environmental impact of which 45% was attributed to its maintenance while impacts from the sandfilters and raingardens were dominated by their bulky materials (57%) and transport (57%), respectively. On-site infiltrative raingardens, a component of green infrastructure (GI), had the lowest environmental impacts because they incurred lower maintenance and did not have any concrete which is high in embodied CO2. Smaller sized raingardens affording the same level of stormwater treatment had the lowest overall impacts reinforcing the principle that using fewer resources reduces environmental impacts. LCA modelling can serve as a guiding tool for practitioners making environmentally sustainable solutions for stormwater treatment.