• Authors:
    • Zhu, X. D.
    • Zhuang, Q. L.
    • Qin, Z. C.
  • Source: GLOBAL CHANGE BIOLOGY BIOENERGY Volume: 7 Issue: 1 Pages: 25-39 DOI:
  • Volume: 7
  • Issue: 1
  • Year: 2015
  • Summary: This study estimated the potential emissions of greenhouse gases (GHG) from bioenergy ecosystems with a biogeochemical model AgTEM, assuming maize ( Zea mays L.), switchgrass ( Panicum virgatum L.), and Miscanthus ( Miscanthus * giganteus) will be grown on the current maize-producing areas in the conterminous United States. We found that the maize ecosystem acts as a mild net carbon source while cellulosic ecosystems (i.e., switchgrass and Miscanthus) act as mild sinks. Nitrogen fertilizer use is an important factor affecting biomass production and N 2O emissions, especially in the maize ecosystem. To maintain high biomass productivity, the maize ecosystem emits much more GHG, including CO 2 and N 2O, than switchgrass and Miscanthus ecosystems, when high-rate nitrogen fertilizers are applied. For maize, the global warming potential (GWP) amounts to 1-2 Mg CO 2eq ha -1 yr -1, with a dominant contribution of over 90% from N 2O emissions. Cellulosic crops contribute to the GWP of less than 0.3 Mg CO 2eq ha -1 yr -1. Among all three bioenergy crops, Miscanthus is the most biofuel productive and the least GHG intensive at a given cropland. Regional model simulations suggested that substituting Miscanthus for maize to produce biofuel could potentially save land and reduce GHG emissions.
  • Authors:
    • Suh, Sangwon
    • Yang, Yi
  • Source: INTERNATIONAL JOURNAL OF LIFE CYCLE ASSESSMENT
  • Volume: 20
  • Issue: 2
  • Year: 2015
  • Summary: Purpose Rising corn prices in the USA due partly to increasing ethanol demands have led to a significant expansion of corn areas displacing natural vegetation and crops including cotton. From 2005 to 2009, cotton area harvested in the USA nearly halved with a reduction of 2.5 million hectares, while that of corn increased by 1.8 million hectares. However, environmental impacts of land shifts from cotton and corn have been largely neglected in literature. Methods In this study, we evaluate the environmental properties of US corn and cotton production and implications of land cover change from cotton to corn using state-specific data and life cycle impact assessment. Focusing on regional environmental issues, we cover both on-farm direct emissions such as different types of volatile organic compounds and pesticides and indirect emissions embodied in input materials such as fertilizers. TRACI 2.0 is used to evaluate the environmental impacts of these emissions. Results and discussion The results show that US cotton and corn productions per hectare on average generate roughly similar impacts for most impact categories such as eutrophication and smog formation. For water use and freshwater ecotoxicity, corn shows a smaller impact. When land shifts from cotton to corn in cotton-growing states, however, the process may aggravate most of the regional environmental impacts while relieving freshwater ecotoxicity impact. The differences in the two estimates are due mainly to underlying regional disparities in crop suitability that affects input structure and environmental emissions. Conclusions Our results highlight the importance of potential, unintended environmental impacts that cannot be adequately captured when average data are employed. Understanding the actual mechanisms under which certain policy induces marginal changes at a regional and local level is crucial for evaluating its net impact. Further, our study calls for an attention to biofuel-induced land cover change between crops and associated regional environmental impacts.
  • Authors:
    • Li, Z. P.
    • Sohl, T.
    • Sleeter, B.
    • Wein, A.
    • Bliss, N.
    • Ratliff, J.
    • Byrd, K.
  • Source: MITIGATION AND ADAPTATION STRATEGIES FOR GLOBAL CHANGE
  • Volume: 20
  • Issue: 3
  • Year: 2015
  • Summary: We examined opportunities for avoided loss of wetland carbon stocks in the Great Plains of the United States in the context of future agricultural expansion through analysis of land-use land-cover (LULC) change scenarios, baseline carbon datasets and biogeochemical model outputs. A wetland map that classifies wetlands according to carbon pools was created to describe future patterns of carbon loss and potential carbon savings. Wetland avoided loss scenarios, superimposed upon LULC change scenarios, quantified carbon stocks preserved under criteria of carbon densities or land value plus cropland suitability. Up to 3420 km(2) of wetlands may be lost in the region by 2050, mainly due to conversion of herbaceous wetlands in the Temperate Prairies where soil organic carbon (SOC) is highest. SOC loss would be approximately 0.20 +/- 0.15 megagrams of carbon per hectare per year (MgC ha(-1) yr(-1)), depending upon tillage practices on converted wetlands, and total ecosystem carbon loss in woody wetlands would be approximately 0.81 +/- 0.41 MgC ha(-1) yr(-1), based on biogeochemical model results. Among wetlands vulnerable to conversion, wetlands in the Northern Glaciated Plains and Lake Agassiz Plains ecoregions exhibit very high mean SOC and on average, relatively low land values, potentially creating economically competitive opportunities for avoided carbon loss. This mitigation scenarios approach may be adapted by managers using their own preferred criteria to select sites that best meet their objectives. Results can help prioritize field-based assessments, where site-level investigations of carbon stocks, land value, and consideration of local priorities for climate change mitigation programs are needed.
  • Authors:
    • Delucia, E. H.
    • Parton, W.
    • Davis, S. C.
    • Hudiburg, T. W.
  • Source: GLOBAL CHANGE BIOLOGY BIOENERGY
  • Volume: 7
  • Issue: 2
  • Year: 2015
  • Summary: Perennial grasses have been proposed as viable bioenergy crops because of their potential to yield harvestable biomass on marginal lands annually without displacing food and to contribute to greenhouse gas (GHG) reduction by storing carbon in soil. Switchgrass, miscanthus, and restored native prairie are among the crops being considered in the corn and agricultural regions of the Midwest and eastern United States. In this study, we used an extensive dataset of site observations for each of these crops to evaluate and improve the DayCent biogeochemical model and make predictions about how both yield and GHG fluxes would respond to different management practices compared to a traditional corn-soy rotation. Using this model-data integration approach, we found 30-75% improvement in our predictions over previous studies and a subsequent evaluation with a synthesis of sites across the region revealed good model-data agreement of harvested yields (r(2) > 0.62 for all crops). We found that replacement of corn-soy rotations would result in a net GHG reduction of 0.5, 1.0, and 2.0 Mg C ha(-1) yr(-1) with average annual yields of 3.6, 9.2, and 17.2 Mg of dry biomass per year for native prairie, switchgrass, and miscanthus respectively. Both the yield and GHG balance of switchgrass and miscanthus were affected by harvest date with highest yields occurring near onset of senescence and highest GHG reductions occurring in early spring before the new crops emergence. Addition of a moderate length rotation (10-15 years) caused less than a 15% change to yield and GHG balance. For policy incentives aimed at GHG reduction through onsite management practices and improvement of soil quality, post-senescence harvests are a more effective means than maximizing yield potential.
  • Authors:
    • Verfaillie, J.
    • Koteen, L.
    • Matthes, J. H.
    • Sturtevant, C.
    • Knox, S. H.
    • Baldocchi, D.
  • Source: GLOBAL CHANGE BIOLOGY
  • Volume: 21
  • Issue: 2
  • Year: 2015
  • Summary: Agricultural drainage of organic soils has resulted in vast soil subsidence and contributed to increased atmospheric carbon dioxide (CO 2) concentrations. The Sacramento-San Joaquin Δ in California was drained over a century ago for agriculture and human settlement and has since experienced subsidence rates that are among the highest in the world. It is recognized that drained agriculture in the Delta is unsustainable in the long-term, and to help reverse subsidence and capture carbon (C) there is an interest in restoring drained agricultural land-use types to flooded conditions. However, flooding may increase methane (CH 4) emissions. We conducted a full year of simultaneous eddy covariance measurements at two conventional drained agricultural peatlands (a pasture and a corn field) and three flooded land-use types (a rice paddy and two restored wetlands) to assess the impact of drained to flooded land-use change on CO 2 and CH 4 fluxes in the Delta. We found that the drained sites were net C and greenhouse gas (GHG) sources, releasing up to 341 g C m -2 yr -1 as CO 2 and 11.4 g C m -2 yr -1 as CH 4. Conversely, the restored wetlands were net sinks of atmospheric CO 2, sequestering up to 397 g C m -2 yr -1. However, they were large sources of CH 4, with emissions ranging from 39 to 53 g C m -2 yr -1. In terms of the full GHG budget, the restored wetlands could be either GHG sources or sinks. Although the rice paddy was a small atmospheric CO 2 sink, when considering harvest and CH 4 emissions, it acted as both a C and GHG source. Annual photosynthesis was similar between sites, but flooding at the restored sites inhibited ecosystem respiration, making them net CO 2 sinks. This study suggests that converting drained agricultural peat soils to flooded land-use types can help reduce or reverse soil subsidence and reduce GHG emissions.
  • Authors:
    • Brye, K. R.
    • McMullen, R. L.
    • Gbur, E. E.
  • Source: JOURNAL OF ENVIRONMENTAL QUALITY
  • Volume: 44
  • Issue: 1
  • Year: 2015
  • Summary: The United States produced 8.4 billion broiler chickens (Gallus gallus) and an estimated 10.1 to 14.3 million Mg of broiler litter (BL) in 2012. Arkansas' production of 1 billion broilers in 2012 produced an estimated 1.2 to 1.7 million Mg of BL, most of which was concentrated in the Ozark Highlands region of northwest Arkansas. Increased CO 2 release from soils associated with agricultural practices has generated concerns regarding the contribution of certain agricultural management practices to global warming. The objectives of this study were to evaluate the effects of long-term (>6 yr) BL application to a Udult on soil respiration and annual C emissions and to determine the predictability of soil respiration based on soil temperature and moisture in the Ozark Highlands region of northwest Arkansas. Soil respiration was measured routinely between May 2009 and May 2012 in response to annual BL application rates of 0, 5.6, and 11.2 Mg dry litter ha -1 that began in 2003. Soil respiration varied (P0.05) by BL application rate but differed (P<0.01) among study years. Multiple regression indicated that soil respiration could be reasonably predicted using 2-cm-depth soil temperature (T 2cm) and the product of T 2cm and VWC as predictors (R2=0.52; P<0.01). Results indicate that organic amendments, such as BL, can stimulate release of CO 2 from the soil to the atmosphere, potentially negatively affecting atmospheric greenhouse gas concentrations; thus, there may be application rates above which the benefits of organic amendments may be diminished by adverse environmental effects. Improved BL management strategies are needed to lessen the loss of CO 2 from BL-amended soils.
  • Authors:
    • Jabro, J. D.
    • Benjamin, J. G.
    • Hergert, G. W.
    • Mikha, M. M.
    • Nielsen, R. A.
  • Source: SOIL SCIENCE SOCIETY OF AMERICA JOURNAL
  • Volume: 79
  • Issue: 2
  • Year: 2015
  • Summary: Long-term studies document that soil properties influenced by management practices occur slowly. The objectives of this study were to evaluate 70 yr of manure (M) and commercial fertilizer (F) additions and moldboard plowing on soil organic C (SOC), soil total N (STN), water-stable aggregates (WSA), and aggregate-associated C and N. The Knorr-Holden plots have been in furrow irrigated continuous corn (Zea mays L.) since 1912 on a Tripp sandy loam (coarse-silty, mixed, superactive, mesic Aridic Haplustoll). Soil samples were collected from the 0- to 5-, 5- to 10-, 10- to 15-, and 15- to 30-cm depths in 2011. Soils were fractionated by wet sieving into four aggregate-size classes (>1000, 500-1000, 250-500, and 53-250 mm). Continuous M amendment increased the SOC in the 0- to 30-cm depth approximately 1.7-fold compared with the F treatment. The combination of F + M further increased SOC in the 0- to 15-cm depth by approximately 36% for the M treatment receiving 90 kg N ha-1 of F (90 + M) and by 16% for the M treatment receiving 180 kg N ha-1 of F (180 + M) compared with the 15- to 30-cm depth. Macroaggregates increased with M and F + M when compared with F with the corresponding increase in microaggregate quantities associated with the F and no-N treatment. In the 0- to 30-cm depth, microaggregates were approximately 1.8 to 4.9 times greater than the macroaggregates. Aggregate-associated C masses were greater in microaggregates than in macroaggregates, which reflects greater amounts of microaggregates present in the soil. A significant, positive correlation was observed between SOC and aggregate-associated C. Overall, the addition of manure-based amendments, with or without F, increased SOC and enhanced aggregate stability.
  • Authors:
    • Guinan, P. E.
    • Vories, E. D.
    • Drummond, S. T.
    • Sudduth, K. A.
    • Sadler, E. J.
  • Source: JOURNAL OF ENVIRONMENTAL QUALITY
  • Volume: 44
  • Issue: 1
  • Year: 2015
  • Summary: Knowledge of weather, particularly precipitation, is fundamental to interpreting watershed and hydrologic processes. The long-term weather record in the Goodwater Creek Experimental Watershed (GCEW) complements hydrologic and water quality data in the region. The GCEW also is the core of the Central Mississippi River Basin (CMRB) node of the Long-Term Agroecosystem Research network. Our objectives are to (i) describe the climatological context of the GCEW and CMRB settings, (ii) document instrumentation and the data collection, quality assurance, and reduction processes; (iii) provide examples of the data obtained and descriptive statistics; and (iv) document the availability of and access methods to obtain the data from the web-based data access portal at http://www.nrrig.mwa.ars.usda.gov/stewards/stewards.html. These objectives support an overall goal to make these long-term data available to the public for use in further analyses and modeling in support of research and public policy on watershed management.
  • Authors:
    • Hickie, K. A.
    • James, T. A.
    • Robinson, J. L.
    • Moffitt, D. C.
    • Hays, P. D.
    • DeFauw, S. L.
    • Van Brahana, J.
    • Skinner, J. V.
    • Brauer, D. K.
    • Brye, K. R.
    • Thomas, A. L.
    • Coblentz, W. K.
    • Sauer, T. J.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 101
  • Issue: 2
  • Year: 2015
  • Summary: Optimal utilization of animal manures as a plant nutrient source should also prevent adverse impacts on water quality. The objective of this study was to evaluate long-term poultry litter and N fertilizer application on nutrient cycling following establishment of an alley cropping system with eastern black walnut (Juglans nigra L.), pecan [Carya illinoensis (Wangenh.) K. Koch], and northern red oak (Quercus rubra L.) trees and orchardgrass (Dactylis glomerata L.). One half of a 4.25-ha site in northwestern Arkansas USA received broadcast applications of 3.9-6.7 Mg ha(-1) fresh poultry litter and the other half 50-76 kg ha(-1) N as NH4NO3 fertilizer each spring from 2001 to 2008. Macronutrient (N, P, K, Ca, Mg, and S) and micronutrient (Na, Fe, Mn, Zn, and Cu) concentrations in soil, forage, and tree leaf tissue were monitored along with NO3-N in soil water and groundwater. Poultry litter application resulted in significantly increased concentrations of each macronutrient except S with increases from 6.3 (N) to 121 % (P). Nitrogen fertilizer application resulted in decreased concentrations from 2.1 (N) to 60.9 % (S) for all macronutrients except Ca. Patterns of nutrient content in forage and tree leaf tissue did not generally follow patterns of soil nutrient concentrations suggesting nutrient sufficiency in most years and that climate and plant growth had a greater effect on nutrient uptake. Soil P with litter application increased 41.3 mg kg(-1) over 7 years (from 34.1 to 75.4), which may necessitate a lower litter application rate to avoid excessive P runoff.
  • Authors:
    • Erskine, R. H.
    • Sherrod, L. A.
    • Green, T. R.
  • Source: SOIL SCIENCE SOCIETY OF AMERICA JOURNAL
  • Volume: 79
  • Issue: 2
  • Year: 2015
  • Summary: Soil erosion and deposition impact the sustainability of agricultural lands within the semiarid Great Plains in the United States. Temporal differences between high-resolution digital elevation maps provide physical estimates of spatial erosion or deposition, and the depth to a calcic horizon is a chemical indicator. We hypothesized that soil surface layer CaCO3 concentration is inversely correlated with the change in surface elevation (Δz). We studied a 109-ha field in northeastern Colorado under winter wheat (Triticum aestivum L.)-fallow rotation in alternating strips perpendicular to the prevailing wind. Soil samples (top 30 cm) collected from 185 landscape positions in 2001 and 2012 were analyzed for CaCO3 using a modified pressure-calcimeter method. The change in CaCO3 (ΔC) was significantly correlated with large-scale erosional and depositional areas (west and east blocks, respectively) and with soil units, whereas Δz was correlated with management strips and blocks. The west block had an average ΔC of 3.2 g kg-1 with 2.0 cm of erosion, whereas the east block decreased by 4.4 g kg-1 with 4.2 cm of deposition. Summit positions had the highest CaCO3, and toeslope positions had the lowest. We found inverse relationships between Δz and ΔC in summit and toeslope positions at both erosional (Δz 5 cm) areas, but Δz was not correlated significantly with ΔC overall. High values of CaCO3 (>100 g kg-1) decreased with time. A high-resolution map of Δz showed complex spatial patterns across scales, which inferred water and wind erosion and deposition affected by terrain and management.