311. Nitrous oxide emissions respond differently to mineral and organic Nitrogen sources in contrasting soil types.

• Authors:
  • Angers, D. A.
  • Rochette, P.
  • Chantigny, M. H.
  • Pelster, D. E.
  • Rieux, C.
  • Vanasse, A.
• Source: Journal of Environmental Quality
• Volume: 41
• Issue: 2
• Year: 2012
• Summary: The use of various animal manures for nitrogen (N) fertilization is often viewed as a viable replacement for mineral N fertilizers. However, the impacts of amendment type on N 2O production may vary. In this study, N 2O emissions were measured for 2 yr on two soil types with contrasting texture and carbon (C) content under a cool, humid climate. Treatments consisted of a no-N control, calcium ammonium nitrate, poultry manure, liquid cattle manure, or liquid swine manure. The N sources were surface applied and immediately incorporated at 90 kg N ha -1 before seeding of spring wheat ( Triticum aestivum L.). Cumulative N 2O-N emissions from the silty clay ranged from 2.2 to 8.3 kg ha -1 yr -1 and were slightly lower in the control than in the fertilized plots ( P=0.067). The 2-yr mean N 2O emission factors ranged from 2.0 to 4.4% of added N, with no difference among N sources. Emissions of N 2O from the sandy loam soil ranged from 0.3 to 2.2 kg N 2O-N ha -1 yr -1, with higher emissions with organic than mineral N sources ( P=0.015) and the greatest emissions with poultry manure ( P<0.001). The N 2O emission factor from plots amended with poultry manure was 1.8%, more than double that of the other treatments (0.3-0.9%), likely because of its high C content. On the silty clay, the yield-based N 2O emissions (g N 2O-N kg -1 grain yield N) were similar between treatments, whereas on the sandy loam, they were greatest when amended with poultry manure. Our findings suggest that, compared with mineral N sources, manure application only increases soil N 2O flux in soils with low C content.

312. Ammonia volatilization and yield response of energy crops after fertilization with biogas residues in a coastal marsh of Northern Germany.

• Authors:
  • Herrmann, A.
  • Techow, A.
  • Pacholski, A.
  • Quakernack, R.
  • Taube, F.
  • Kage, H.
• Source: Agriculture Ecosystems and Environment
• Volume: 160
• Year: 2012
• Summary: Anaerobic co-fermentation of animal slurries and crop silages leads to new types of biogas residues with an uncertain fertilizer value. Ammonia volatilization losses and crop productivity after supplying co-fermented biogas residues were investigated at a marshland site in Northern Germany. Due to the ecological risks of monocultures, maize ( Zea mays) in monoculture as the dominant biogas crop in the marsh was tested against a crop rotation (maize, wheat ( Triticum aestivum), Italian ryegrass ( Lolium multiflorum)) and perennial ryegrass ( Lolium perenne). Biogas residues, applied by trail hoses, and CAN (mineral fertilizer) were used as nitrogen fertilizers. Ammonia losses at all application dates were investigated by an approach including passive flux samplers and a calibrated dynamic chamber method. Simultaneously a micrometeorological technique was used as a reference. A comparison of methods showed a close correlation ( r2=0.92) between micromet and passive flux sampler techniques. Ammonia volatilization losses (on average 15% NH 4+-N applied) occurred mainly within the first 10 h. Concomitant with high ammonia losses, a significant yield depression of 5 t DM ha -1 for ryegrass fertilized by biogas residues compared to CAN was observed. Little or no affect of biogas was observed for maize and wheat. The crop rotation had yields (34 t DM ha -1 2 year -1) that were comparable with the maize monoculture (31 t DM ha -1 2 year -1).

313. Consistent effects of nitrogen amendments on soil microbial communities and processes across biomes.

• Authors:
  • Craine, J. M.
  • Ramirez, K. S.
  • Fierer, N.
• Source: Global Change Biology
• Volume: 18
• Issue: 6
• Year: 2012
• Summary: Ecosystems worldwide are receiving increasing amounts of reactive nitrogen (N) via anthropogenic activities with the added N having potentially important impacts on microbially mediated belowground carbon dynamics. However, a comprehensive understanding of how elevated N availability affects soil microbial processes and community dynamics remains incomplete. The mechanisms responsible for the observed responses are poorly resolved and we do not know if soil microbial communities respond in a similar manner across ecosystems. We collected 28 soils from a broad range of ecosystems in North America, amended soils with inorganic N, and incubated the soils under controlled conditions for 1 year. Consistent across nearly all soils, N addition decreased microbial respiration rates, with an average decrease of 11% over the year-long incubation, and decreased microbial biomass by 35%. High-throughput pyrosequencing showed that N addition consistently altered bacterial community composition, increasing the relative abundance of Actinobacteria and Firmicutes, and decreasing the relative abundance of Acidobacteria and Verrucomicrobia. Further, N-amended soils consistently had lower activities in a broad suite of extracellular enzymes and had decreased temperature sensitivity, suggesting a shift to the preferential decomposition of more labile C pools. The observed trends held across strong gradients in climate and soil characteristics, indicating that the soil microbial responses to N addition are likely controlled by similar wide-spread mechanisms. Our results support the hypothesis that N addition depresses soil microbial activity by shifting the metabolic capabilities of soil bacterial communities, yielding communities that are less capable of decomposing more recalcitrant soil carbon pools and leading to a potential increase in soil carbon sequestration rates.

314. Soil carbon lost from Mollisols of the North Central U.S.A. with 20 years of agricultural best management practices.

• Authors:
  • Hedtcke, J. L.
  • Kucharik, C. J.
  • Jackson, R. D.
  • Posner, J. L.
  • Sanford, G. R.
  • Lin, T. L.
• Source: Agriculture Ecosystems and Environment
• Volume: 162
• Year: 2012
• Summary: Soil organic carbon (SOC) is highly sensitive to agricultural land management, so there is a great deal of interest in managing cultivated soils to sequester atmospheric CO 2. In this study we evaluated the influence of six cropping systems on SOC at the Wisconsin Integrated Cropping System Trial (WICST) over a 20-year period. Analysis of SOC on either a concentration or mass per volume of soil basis indicated a significant decline across all of the systems at WICST. While the rotationally grazed pasture system sequestered carbon (C) in the surface 15 cm these gains were offset by losses at depth. Both no-till (NT) practices and inclusion of perennial crops reduced SOC loss, but neither resulted in C sequestration in the soil profile. Results from this study demonstrate the importance of (i) comparing current and initial soil samples when evaluating SOC sequestration and (ii) evaluating SOC changes throughout the soil profile. The losses of SOC at depths below the plow layer point to either a lack of C input from roots, increased oxidative loss at these depths or both.

315. Soil respiration under climate change: prolonged summer drought offsets soil warming effects.

• Authors:
  • Kitzler, B.
  • Borken, W.
  • Wunderlich, S.
  • Schindlbacher, A.
  • Zechmeister-Boltenstern, S.
  • Jandl, R.
• Source: Global Change Biology
• Volume: 18
• Issue: 7
• Year: 2012
• Summary: Climate change may considerably impact the carbon (C) dynamics and C stocks of forest soils. To assess the combined effects of warming and reduced precipitation on soil CO 2 efflux, we conducted a two-way factorial manipulation experiment (4°C soil warming+throughfall exclusion) in a temperate spruce forest from 2008 until 2010. Soil was warmed by heating cables throughout the growing seasons. Soil drought was simulated by throughfall exclusions with three 100 m 2 roofs during 25 days in July/August 2008 and 2009. Soil warming permanently increased the CO 2 efflux from soil, whereas throughfall exclusion led to a sharp decrease in soil CO 2 efflux (45% and 50% reduction during roof installation in 2008 and 2009, respectively). In 2008, CO 2 efflux did not recover after natural rewetting and remained lowered until autumn. In 2009, CO 2 efflux recovered shortly after rewetting, but relapsed again for several weeks. Drought offset the increase in soil CO 2 efflux by warming in 2008 (growing season CO 2 efflux in t C ha -1: control: 7.11.0; warmed: 9.51.7; warmed+roof: 7.40.3; roof: 5.90.4) and in 2009 (control: 7.60.8; warmed+roof: 8.31.0). Throughfall exclusion mainly affected the organic layer and the top 5 cm of the mineral soil. Radiocarbon data suggest that heterotrophic and autotrophic respiration were affected to the same extent by soil warming and drying. Microbial biomass in the mineral soil (0-5 cm) was not affected by the treatments. Our results suggest that warming causes significant C losses from the soil as long as precipitation patterns remain steady at our site. If summer droughts become more severe in the future, warming induced C losses will likely be offset by reduced soil CO 2 efflux during and after summer drought.

316. Consequences of declining snow accumulation for water balance of mid-latitude dry regions.

• Authors:
  • Lauenroth, W. K.
  • Schlaepfer, D. R.
  • Bradford, J. B.
• Source: Global Change Biology
• Volume: 18
• Issue: 6
• Year: 2012
• Summary: Widespread documentation of positive winter temperature anomalies, declining snowpack and earlier snow melt in the Northern Hemisphere have raised concerns about the consequences for regional water resources as well as wildfire. A topic that has not been addressed with respect to declining snowpack is effects on ecosystem water balance. Changes in water balance dynamics will be particularly pronounced at low elevations of mid-latitude dry regions because these areas will be the first to be affected by declining snow as a result of rising temperatures. As a model system, we used simulation experiments to investigate big sagebrush ecosystems that dominate a large fraction of the semiarid western United States. Our results suggest that effects on future ecosystem water balance will increase along a climatic gradient from dry, warm and snow-poor to wet, cold and snow-rich. Beyond a threshold within this climatic gradient, predicted consequences for vegetation switched from no change to increasing transpiration. Responses were sensitive to uncertainties in climatic prediction; particularly, a shift of precipitation to the colder season could reduce impacts of a warmer and snow-poorer future, depending on the degree to which ecosystem phenology tracks precipitation changes. Our results suggest that big sagebrush and other similar semiarid ecosystems could decrease in viability or disappear in dry to medium areas and likely increase only in the snow-richest areas, i.e. higher elevations and higher latitudes. Unlike cold locations at high elevations or in the arctic, ecosystems at low elevations respond in a different and complex way to future conditions because of opposing effects of increasing water-limitation and a longer snow-free season. Outcomes of such nonlinear interactions for future ecosystems will likely include changes in plant composition and productivity, dynamics of water balance, and availability of water resources.

317. Soil respiration is stimulated by elevated CO 2 and reduced by summer drought: three years of measurements in a multifactor ecosystem manipulation experiment in a temperate heathland (CLIMAITE).

• Authors:
  • Mikkelsen, T. N.
  • Pedersen, J. K.
  • Larsen, K. S.
  • Michelsen, A.
  • Ibrom, A.
  • Linden, L. van der
  • Selsted, M. B.
  • Pilegaard, K.
  • Beier, C.
  • Ambus, P.
• Source: Global Change Biology
• Volume: 18
• Issue: 4
• Year: 2012
• Summary: This study investigated the impact of predicted future climatic and atmospheric conditions on soil respiration ( RS ) in a Danish Calluna-Deschampsia-heathland. A fully factorial in situ experiment with treatments of elevated atmospheric CO 2 (+130 ppm), raised soil temperature (+0.4°C) and extended summer drought (5-8% precipitation exclusion) was established in 2005. The average RS , observed in the control over 3 years of measurements (1.7 mol CO 2 m -2 sec -1), increased 38% under elevated CO 2, irrespective of combination with the drought or temperature treatments. In contrast, extended summer drought decreased RS by 14%, while elevated soil temperature did not affect RS overall. A significant interaction between elevated temperature and drought resulted in further reduction of RS when these treatments were combined. A detailed analysis of short-term RS dynamics associated with drought periods showed that RS was reduced by ~50% and was strongly correlated with soil moisture during these events. Recovery of RS to pre-drought levels occurred within 2 weeks of rewetting; however, unexpected drought effects were observed several months after summer drought treatment in 2 of the 3 years, possibly due to reduced plant growth or changes in soil water holding capacity. An empirical model that predicts RS from soil temperature, soil moisture and plant biomass was developed and accounted for 55% of the observed variability in RS . The model predicted annual sums of RS in 2006 and 2007, in the control, were 672 and 719 g C m -2 y -1, respectively. For the full treatment combination, i.e. the future climate scenario, the model predicted that soil respiratory C losses would increase by ~21% (140-150 g C m -2 y -1). Therefore, in the future climate, stimulation of C storage in plant biomass and litter must be in excess of 21% for this ecosystem to not suffer a reduction in net ecosystem exchange.

318. Crop residue removal effects on soil carbon: measured and inter-model comparisons.

• Authors:
  • Desjardins, R. L.
  • McConkey, B. G.
  • Campbell, C. A.
  • Grant, B. B.
  • Smith, W. N.
  • Krobel, R.
  • Malhi, S. S.
• Source: Agriculture Ecosystems and Environment
• Volume: 161
• Year: 2012
• Summary: Crop residues can be a viable source for biofuel production and other industrial products; however, their removal from agricultural land may negatively impact productivity and environmental quality. In this study three process-based models (CENTURY, DAYCENT, and DNDC) and the CAMPBELL empirical model were used to simulate soil organic carbon (SOC) change and were compared to observations from 14 residue removal experiments within the temperate climate areas of Canada and the Midwestern USA. The experimental results indicated that residue removal effects on SOC were more likely to be observed (i) with greater rates of residue removal, (ii) after longer periods, and (iii) with greater rates of (N) fertilizer. All four models simulated the hypothesized decline in SOC when residues were removed. The average measured SOC change for residue removal across all experimental sites and durations was -235 g m -2 (i.e., 3.3% of SOC in top 20 cm) whereas the SOC change as estimated by the models were -423, -417, -201, and -218 g m -2 for the CENTURY, DAYCENT, DNDC, and CAMPBELL models, respectively. All model predictions were close or within the range of uncertainty of estimates derived from measurements.

319. Spatially explicit land-use and land-cover scenarios for the Great Plains of the United States.

• Authors:
  • Kanengieter, R. L.
  • Sleeter, R. R.
  • Bennett, S. L.
  • Reker, R. R.
  • Bouchard, M. A.
  • Sayler, K. L.
  • Sleeter, B. M.
  • Sohl, T. L.
  • Zhu, Z. L.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 153
• Year: 2012
• Summary: The Great Plains of the United States has undergone extensive land-use and land-cover change in the past 150 years, with much of the once vast native grasslands and wetlands converted to agricultural crops, and much of the unbroken prairie now heavily grazed. Future land-use change in the region could have dramatic impacts on ecological resources and processes. A scenario-based modeling framework is needed to support the analysis of potential land-use change in an uncertain future, and to mitigate potentially negative future impacts on ecosystem processes. We developed a scenario-based modeling framework to analyze potential future land-use change in the Great Plains. A unique scenario construction process, using an integrated modeling framework, historical data, workshops, and expert knowledge, was used to develop quantitative demand for future land-use change for four IPCC scenarios at the ecoregion level. The FORE-SCE model ingested the scenario information and produced spatially explicit land-use maps for the region at relatively fine spatial and thematic resolutions. Spatial modeling of the four scenarios provided spatial patterns of land-use change consistent with underlying assumptions and processes associated with each scenario. Economically oriented scenarios were characterized by significant loss of natural land covers and expansion of agricultural and urban land uses. Environmentally oriented scenarios experienced modest declines in natural land covers to slight increases. Model results were assessed for quantity and allocation disagreement between each scenario pair. In conjunction with the U.S. Geological Survey's Biological Carbon Sequestration project, the scenario-based modeling framework used for the Great Plains is now being applied to the entire United States.

320. Climatic and genetic controls of yields of switchgrass, a model bioenergy species.

• Authors:
  • Boe, A.
  • Wimberly, M. C.
  • Tulbure, M. G.
  • Owens, V. N.
• Source: Agriculture Ecosystems and Environment
• Volume: 146
• Issue: 1
• Year: 2012
• Summary: The U.S. Renewable Fuel Standard calls for 136 billion liters of renewable fuels production by 2022. Switchgrass (Panicum virgatum L.) has emerged as a leading candidate to be developed as a bioenergy feedstock. To reach biofuel production goals in a sustainable manner, more information is needed to characterize potential production rates of switchgrass. We used switchgrass yield data and general additive models (GAMs) to model lowland and upland switchgrass yield as nonlinear functions of climate and environmental variables. We used the GAMs and a 39-year climate dataset to assess the spatio-temporal variability in switchgrass yield due to climate variables alone. Variables associated with fertilizer application, genetics, precipitation, and management practices were the most important for explaining variability in switchgrass yield. The relationship of switchgrass yield with climate variables was different for upland than lowland cultivars. The spatio-temporal analysis showed that considerable variability in switchgrass yields can occur due to climate variables alone. The highest switchgrass yields with the lowest variability occurred primarily in the Corn Belt region, suggesting that prime cropland regions are the best suited for a constant and high switchgrass biomass yield. Given that much lignocellulosic feedstock production will likely occur in regions with less suitable climates for agriculture, interannual variability in yields should be expected and incorporated into operational planning.