Browsing by Subject "Greenhouse gas"
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Item Corn production and environmental implications under varying nitrogen and management practices(2013-12) Maharjan, BijeshEconomic and environmental issues combined have increased the need for better understanding of the fate of nitrogen (N) applied to crop production systems. The objectives of this dissertation were to evaluate the effects of different N sources including conventional urea (CU), polymer-coated urea (PCU), stabilized urea with chemical inhibitors (IU), and anhydrous ammonia (AA) on N losses and yield. Besides N sources, their interaction with placement (deep- versus shallow-banded; broadcast/incorporation versus subsurface banding), tillage management (conventional tillage versus no tillage) and irrigation management (irrigated versus rain fed) were also studied. In the first experiment, split-applied CU increased yield and N uptake compared with preplant applied PCU or IU and decreased nitrate (NO3-) leaching compared with PCU in a sandy loam soil. Direct soil-to-atmosphere nitrous oxide (N2O) emissions were significantly less with IU or split-U than with PCU and there was a trend for greater emissions with split-U than with IU (P =0.08). Irrigation significantly increased NO3- leaching during the growing season, but had no effect on direct N2O emissions in the same experiment. Indirect emissions due to NO3- leaching were estimated to be 79-117% of direct emissions using the default value of EF5, thus signifying the potential importance of indirect emissions in evaluating management effects on N2O emissions. In the second experiment, no-till significantly increased N2O emissions in fertilized treatments in a dry year and decreased crop yield in the control treatment in a silt loam soil. There were no significant differences in N2O emissions, grain yield or NO3- leaching potential with AA placement depth. In the third experiment, mid-row banding (MRB) significantly increased N2O emissions compared to broadcast/incorporation (BI) for PCU and CU in silt loam soils. Nitrous oxide emissions were correlated to a greater extent with soil nitrite (NO2-) intensity than with nitrate (NO3-) intensity; N intensity being a measure of integrated N concentrations over time. Compared to BI, MRB reduced NH3 volatilization loss and the CU treatment had greater NH3 loss than PCU or IU had. All these experiments highlighted the significant roles that N and other management practices can play in mitigating N losses.Item Impacts of agricultural management and landscape factors on soil carbon and nitrogen(2011-12) Van Vleck, Harriet E.Agricultural management has altered soil carbon (C) and nitrogen (N) inputs, losses, and turnover rates. Understanding how management interacts with landscape factors to regulate soil C and N losses is essential to addressing climate change. Through research conducted in agricultural systems in Minnesota I investigated: (1) how the loss of corn root-derived C as carbon dioxide (CO2), and N as nitrous oxide (N2O) differed among five management systems, and (2) how hillslope position and soil moisture affected the size and turnover of soil C pools. In a field study using stable isotope techniques, I found that the fraction of root-derived C and N emitted as CO2 and N2O, the C and N emission factors, were 35% and less than 1% respectively. Individually, each emission factor was lower in systems with increased rotation diversity. Conversely, the relationship between C and N emission factors differed with tillage and fertilization intensity, not with rotation diversity. The magnitude of root-derived C and N emission factors has agricultural policy implications. Currently an emission factor of 1% is used for all N inputs to agricultural systems. My research suggests that a lower emission factor would better reflect N2O emissions from belowground N sources.In a laboratory study, both position and soil moisture significantly impacted the size and mean residence time of soil C pools along a low slope hillslope. Intact core sections of the upper four horizons from three hillslope positions were incubated at 50, 75, 90 and 100% water-filled pore space (WFPS) for 355 days. Total soil C (TC), N, and the resistant fraction of TC (64%) increased downslope. Under saturated conditions, 100% WFPS treatment, the size and mean residence time of the labile C fraction (<1% of TC) increased. Increased moisture, between 50% and 90% WFPS, also lengthened the mean residence time of slow C. In this low slope landscape I found effects of both position and moisture on C pool dynamics; soil moisture had the most significant impacts on labile C pool size and the slow C pool mean residence time.Item Minnesota Low Carbon Fuels Standard Study(2011-06) Taff, Steven J.; Apland, Jeffrey; Kittelson, David B.; Smith, Timothy M.Under a Minnesota Department of Commerce, Office of Energy Security contract, the University of Minnesota investigated and developed modeling and analytical frameworks with available data in order to compare the greenhouse gas, economic, and environmental implications of various low carbon fuel standards (LCFS) policies for vehicles operated on Minnesota public roads. This report provides findings of work performed under this contract. A low carbon fuels standard (LCFS) would require any person producing, refining, blending, or importing transportation fuels in Minnesota to reduce these fuels' average carbon intensity (AFCI), measured across the full fuel cycle: feedstock extraction, production, transport, storage, and use. An LCFS is expected to lower overall emissions from the transportation fleet. The framework was used in part to analyze a performance-based LCFS that measures progress in reducing greenhouse gas emissions on a lifecycle basis and the economic and environmental impacts on each transportation fuel and production pathway as compared to the state's current policies to replace gasoline consumption with 20 percent ethanol by 2013, and to replace diesel consumption with 20 percent biodiesel by 2015.