• Authors:
    • Wise,M.
    • Hodson,E. L.
    • Mignone,B. K.
    • Clarke,L.
    • Waldhoff,S.
    • Luckow,P.
  • Source: Energy Economics
  • Volume: 50
  • Year: 2015
  • Summary: Accurately characterizing the emissions implications of bioenergy is increasingly important to the design of regional and global greenhouse gas mitigation policies. Market-based policies, in particular, often use information about carbon intensity to adjust relative deployment incentives for different energy sources. However, the carbon intensity of bioenergy is difficult to quantify because carbon emissions can occur when land use changes to expand production of bioenergy crops rather than simply when the fuel is consumed as for fossil fuels. Using a long-term, integrated assessment model, this paper develops an approach for computing the carbon intensity of bioenergy production that isolates the marginal impact of increasing production of a specific bioenergy crop in a specific region, taking into account economic competition among land uses. We explore several factors that affect emissions intensity and explain these results in the context of previous studies that use different approaches. Among the factors explored, our results suggest that the carbon intensity of bioenergy production from land use change (LUC) differs by a factor of two depending on the region in which the bioenergy crop is grown in the United States. Assumptions about international land use policies (such as those related to forest protection) and crop yields also significantly impact carbon intensity. Finally, we develop and demonstrate a generalized method for considering the varying time profile of LUC emissions from bioenergy production, taking into account the time path of future carbon prices, the discount rate and the time horizon. When evaluated in the context of power sector applications, we found electricity from bioenergy crops to be less carbon-intensive than conventional coal-fired electricity generation and often less carbon-intensive than natural-gas fired generation. © 2015 Elsevier B.V.
  • Authors:
    • Adewopo,J. B.
    • Silveira,M. L.
    • Xu,S.
    • Gerber,S.
    • Sollenberger,L. E.
    • Martin,T.
  • Source: Soil Science Society of America Journal
  • Volume: 79
  • Issue: 4
  • Year: 2015
  • Summary: Proper management of grassland ecosystems for improved productivity can enhance their potential to sequester atmospheric CO2 in the soil. However, the direction and extent of soil C changes in response to improved grassland management or land-use conversion varies depending on the ecoregion or management practice. The objectives of this study were to: (i) assess the long-term (>20-yr) impact of grassland management intensification on soil C fractions after conversion of native rangelands to silvopasture and sown pasture ecosystems; and (ii) determine the contribution of sown grass species to soil C sequestration in both the labile and more stable soil C fractions. Experimental sites consisted of a gradient of management intensities ranging from native rangeland (lowest), to silvopasture (intermediate), to sown pasture (highest). After 22 yr following land-use conversion from native rangeland to silvopasture or sown pasture, total soil C stocks (0-30-cm depth) were greater under silvopasture (69.2 Mg C ha-1) and sown pasture (62.0 Mg C ha-1) than native rangeland (40.9 Mg ha-1). Conversion to sown pasture increased particulate organic C concentration (10.6 g C kg-1) compared with native rangeland (6.3 g C kg-1), while silvopasture increased the mineral-associated C fraction (5.7 vs. 10 g C kg-1 for native rangeland and silvopasture, respectively). Isotopic analysis indicated that the C4 grass component contributed significantly to soil C accumulation within these ecosystems. Data also showed that grassland management intensification has the potential to promote soil C sequestration, and the use of strategic management practices such as integration of trees can improve soil C stability under similar subtropical conditions. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All rights reserved.
  • Authors:
    • Bagley,Justin E.
    • Miller,Jesse
    • Bernacchi,Carl J.
  • Source: Plant Cell Environment
  • Volume: 38
  • Issue: 9
  • Year: 2015
  • Summary: The potential impacts of climate change in the Midwest United States present unprecedented challenges to regional agriculture. In response to these challenges, a variety of climate-smart agricultural methodologies have been proposed to retain or improve crop yields, reduce agricultural greenhouse gas emissions, retain soil quality and increase climate resilience of agricultural systems. One component that is commonly neglected when assessing the environmental impacts of climate-smart agriculture is the biophysical impacts, where changes in ecosystem fluxes and storage of moisture and energy lead to perturbations in local climate and water availability. Using a combination of observational data and an agroecosystem model, a series of climate-smart agricultural scenarios were assessed to determine the biophysical impacts these techniques have in the Midwest United States. The first scenario extended the growing season for existing crops using future temperature and CO2 concentrations. The second scenario examined the biophysical impacts of no-till agriculture and the impacts of annually retaining crop debris. Finally, the third scenario evaluated the potential impacts that the adoption of perennial cultivars had on biophysical quantities. Each of these scenarios was found to have significant biophysical impacts. However, the timing and magnitude of the biophysical impacts differed between scenarios. This study assessed the biophysical impacts of several climate-smart agricultural practices in the Midwest United States. Specifically we investigated the biophysical impacts of adapting crops to extended growing season length, expanding no-till agriculture, and the adoption of perennial cultivars. We found that each of these practices had significant biophysical impacts, but the seasonality and extent of the impacts differed between scenarios.
  • Authors:
    • Baumhardt,R. L.
    • Mauget,S. A.
    • Gowda,P. H.
    • Brauer,D. K.
    • Marek,G. W.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 5
  • Year: 2015
  • Summary: Equatorial Pacific sea surface temperature anomalies can cause a systematic El Nino-Southern Oscillation (ENSO) coupling with the atmosphere to produce predictable weather patterns in much of North America. Adapting irrigation strategies for drought-tolerant crops like cotton ( Gossypium hirsutum L.) to exploit forecast climatic conditions represents one potential innovative technique for managing the declining Ogallala Aquifer beneath the US Southern High Plains. The crop simulation model GOSSYM was used with ENSO phase-specific weather records during 1959 to 2000 at Bushland, TX, to estimate lint yields of cotton emerging on three dates from soil at 50 or 75% available water content for all possible combinations of irrigation durations (0, 4, 6, 8, and 10 wk) and rates (2.5, 3.75, and 5.0 mm d -1). From those data, our objective was to compare partial center pivot deficit irrigation strategies that optimize calculated net cotton lint yield in relation to ENSO phase, initial soil water content, and emergence date. Although phase classification in June was inconsistent with maturing fall phases, the most accurately classified La Nina phase had limited rain that reduced lint yields compared with wetter Neutral and El Nino phases. During La Nina phase conditions, irrigation strategies that focused fixed water resources on smaller areas were better suited to increase net yield than spreading water across larger areas. Alternatively, during less predictable and wetter Neutral and El Nino phases, irrigation strategies that spread water increased net lint yield over focused applications except when both initial soil water and irrigation amount were limiting.
  • Authors:
    • Brookes,G.
    • Barfoot,P.
  • Source: GM Crops & Food
  • Volume: 7
  • Issue: 2
  • Year: 2015
  • Summary: This paper updates previous assessments of how crop biotechnology has changed the environmental impact of global agriculture. It focuses on the environmental impacts associated with changes in pesticide use and greenhouse gas emissions arising from the use of GM crops since their first widespread commercial use in the mid 1990s. The adoption of GM insect resistant and herbicide tolerant technology has reduced pesticide spraying by 553 million kg (-8.6%) and, as a result, decreased the environmental impact associated with herbicide and insecticide use on these crops (as measured by the indicator the Environmental Impact Quotient (EIQ)) by 19.1%. The technology has also facilitated important cuts in fuel use and tillage changes, resulting in a significant reduction in the release of greenhouse gas emissions from the GM cropping area. In 2013, this was equivalent to removing 12.4 million cars from the roads.
  • Authors:
    • Congreves,K. A.
    • Van Eerd,L. L.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 102
  • Issue: 3
  • Year: 2015
  • Summary: Vegetables are important horticultural commodities with high farm gate values and nutritional quality. For many vegetables, growers apply large amounts of N fertilizer (> 200 kg N ha(-1)) to increase yield and profits, but such high N fertilizer applications can pose a significant threat for N loss and environmental contamination via denitrification, volatilization, leaching, runoff, and erosion. Nitrogen losses can reduce air and water quality by contributing to greenhouse gas emissions, ground-level ozone and particulate matter production, ground and surface water contamination, and eutrophication. The processes governing N loss include a complex of biological, physical, and chemical factors, which are impacted by management practices, climatic conditions and soil properties. Therefore, we reviewed and evaluated various management practices for minimizing N loss in N-intensive vegetable production within a temperate climate. Most soil nutrient management practices have focused on reducing N loss throughout the growing season, but the risk for N loss is very high after harvesting vegetables with low N harvest indices, low C:N ratios, and high quantities of N in crop residues, such as most Brassica oleracea L. crops. Amending soil with organic C material may present a novel strategy for reducing N losses after harvest by 37 %, compared to the typical practice of incorporating N-rich vegetable crop residues. Research must focus on testing new and innovative methods of minimizing post-harvest N loss in intensive horticulture.
  • Authors:
    • Dare,Anne
  • Source: Journal of Soil and Water Conservation
  • Volume: 70
  • Issue: 4
  • Year: 2015
  • Authors:
    • Eleto Torres,Carlos M. M.
    • Kohmann,Marta M.
    • Fraisse,Clyde W.
  • Source: Agricultural Systems
  • Volume: 137
  • Year: 2015
  • Summary: Agriculture is an important source of greenhouse gases (GHG), especially from crop production practices and enteric fermentation by ruminant livestock. Improved production practices in agriculture and increase in terrestrial carbon sinks are alternatives for mitigating GHG emissions in agriculture. The objective of this study was to estimate GHG emissions from hypothetical farm enterprise combinations in the southeastern United States with a mix of cropland and livestock production and estimate the area of forest plantation necessary to offset these emissions. Four different farm enterprise combinations (Cotton; Maize; Peanut; Wheat + Livestock + Forest) with different production practices were considered in the study resulting in different emission scenarios. We assumed typical production practices of farm operations in the region with 100 ha of cropland area and a herd of 50 cows. GHG emissions were calculated regarding production, storage and transportation of agrochemicals (pre-farm) and farm activities such as fertilization, machinery operation and irrigation (on-farm). Simulated total farm GHG emissions for the different farm enterprise combinations and production practices ranged from 348.8 t CO(2)e year(-1) to 765.6 t CO(2)e year(-1). The estimated forest area required to neutralize these emissions ranged from 19 ha to 40 ha. In general, enterprise combinations with more intense production practices that include the use of irrigation resulted in higher total emissions but lower emissions per unit of commodity produced. (C) 2015 Elsevier Ltd. All rights reserved.
  • Authors:
    • Hao,B.
    • Xue,Q.
    • Marek,T. H.
    • Jessup,K. E.
    • Becker,J.
    • Hou,X.
    • Xu,W.
    • Bynum,E. D.
    • Bean,B. W.
    • Colaizzi,P. D.
    • Howell,T. A.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 5
  • Year: 2015
  • Summary: Drought is an important factor limiting corn ( Zea mays L.) yields in the Texas High Plains, and adoption of drought-tolerant (DT) hybrids could be a management tool under water shortage. We conducted a 3-yr field study to investigate yield, evapotranspiration (ET), and water use efficiency (WUE) in DT hybrids. One conventional (33D49) and 4 DT hybrids (P1151HR, P1324HR, P1498HR, and P1564HR) were grown at three water regimes (I 100, I 75, and I 50, referring to 100, 75, and 50% ET requirement) and three planting densities (PD) (5.9, 7.4, and 8.4 plants m -2). Yield (13.56 Mg ha -1) and ET (719 mm) were the greatest at I 100 but WUE (2.1 kg m -3) was the greatest at I 75. Although DT hybrids did not always have greater yield and WUE than 33D49 at I 100, hybrids P1151HR and P1564HR consistently had greater yield and WUE than 33D49 at I 75 and I 50. Compared to 33D49, P1151HR and P1564HR had 8.6 to 12.1% and 19.1% greater yield at I 75 and I 50, respectively. Correspondingly, WUE was 9.8 to 11.7% and 20.0% greater at I 75 and I 50, respectively. Greater PD resulted in greater yield and WUE at I 100 and I 75 but PD did not affect yield and WUE at I 50. Yield and WUE in greater PD (8.4 plants m -2) were 6.3 to 8.3% greater than those in smaller PD (5.9 plants m -2). The results of this study demonstrated that proper selection of DT hybrids can increase corn yield and WUE under water-limited conditions.
  • Authors:
    • Jacinthe,P. A.
    • Vidon,P.
    • Fisher,K.
    • Liu,X.
    • Baker,M. E.
  • Source: Journal of Environmental Quality
  • Volume: 44
  • Issue: 4
  • Year: 2015
  • Summary: Riparian buffers contribute to the mitigation of nutrient pollution in agricultural landscapes, but there is concern regarding their potential to be hot spots of greenhouse gas production. This study compared soil CO 2 and CH 4 fluxes in adjacent crop fields and riparian buffers (a flood-prone forest and a flood-protected grassland along an incised channel) and examined the impact of water table depth (WTD) and flood events on the variability of gas fluxes in riparian zones. Results showed significantly ( P22°C), but the effect of flooding was less pronounced in early spring (emission <1.06 mg CH 4-C m -2 d -1), probably due to low soil temperature. Although CH 4 flux direction alternated at all sites, overall the croplands and the flood-affected riparian forest were CH 4 sources, with annual emission averaging +0.040.17 and +0.921.6 kg CH 4-C ha -1, respectively. In the riparian forest, a topographic depression (<8% of the total area) accounted for 78% of the annual CH 4 emission, underscoring the significance of landscape heterogeneity on CH 4 dynamics in riparian buffers. The nonflooded riparian grassland, however, was a net CH 4 sink (-1.080.22 kg CH 4-C ha -1 yr -1), probably due to the presence of subsurface tile drains and a dredged/incised channel at that study site. Although these hydrological alterations may have contributed to improvement in the CH 4 sink strength of the riparian grassland, this must be weighed against the water quality maintenance functions and other ecological services provided by riparian buffers.