• Authors:
    • Kohmann, M. M.
    • Torres, C. M. M. E.
    • Fraisse, C. W.
  • Source: Agricultural Journal
  • 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 CO2e year-1 to 765.6 t CO2e 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. © 2015 Elsevier Ltd.
  • Authors:
    • Shonnard, D.
    • Archer, D.
    • Beck, E.
    • Ukaew, S.
  • Source: Journal
  • Volume: 20
  • Issue: 5
  • Year: 2015
  • Summary: Rapeseed is being considered as a potential feedstock for hydrotreated renewable jet (HRJ) fuel in the USA through its cultivation in rotation with wheat. The goal of this research was to determine the impact of soil C changes, induced through replacing the fallow period with rapeseed in rotation with wheat, and the effects it would have on emission of greenhouse gases (GHG) of rapeseed HRJ. The Intergovernmental Panel on Climate Change (IPCC) (Tier 1) method was used with modifications to determine the changes in soil C of wheat-wheat-rapeseed (WWR) relative to the reference wheat-wheat-fallow (WWF) rotation for 20 years of cultivation. The 27 case scenarios were conducted to study the impacts of changes in management practices (tillage practice and residue input) on changes in soil C for WWR rotation in multiple locations in 10 US states. The CO2 emissions resulting from soil C changes were incorporated into the rapeseed HRJ pathway in order to evaluate the GHG emissions. Introducing rapeseed to replace the fallow period with wheat could either increase or decrease changes in soil C, depending on management practices. Soil C is predicted to increase with increased residue input and reduced tillage. The greatest gain of soil C was found when using high residue input for wheat and rapeseed under no tillage, resulting in the best management practice. Conversely, adding low residue input to both crops with full tillage created the highest loss of soil C, referring to as the worst management practice. Soil C changes varied across locations from -0.22 to 0.32 Mg C ha(-1) year(-1). Consequently, the GHG emissions of rapeseed HRJ ranged from 4 to 70 g CO2 eq./MJ, comparing to 46 g CO2 eq./MJ for excluding soil C change. The rapeseed HRJ exhibited the GHG savings of 65-96 % for the best practice and 20-42 % for the worst practice when compared to petroleum jet fuel. Based on results using the modified IPCC method, adoption of high residue input with no tillage for the rotation cropping of rapeseed with wheat had the potential to increase soil C. However, the method has limitations for predicting soil C changes regarding crop management practices. Biogeochemical-based models that have a potential to capture processes of C and N dynamics in soil and yield may be better suited to quantify regional variations in soil C changes for the rotation cropping of rapeseed with wheat.
  • Authors:
    • Lobell, D.
    • Schlenker, W.
    • Roberts, M.
    • Urban, D.
  • Source: Journal
  • Volume: 130
  • Issue: 2
  • Year: 2015
  • Summary: Short durations of very high spring soil moisture can influence crop yields in many ways, including delaying planting and damaging young crops. The central United States has seen a significant upward trend in the frequency and intensity of extreme precipitation in the 20th century, potentially leading to more frequent occurrences of saturated or nearly saturated fields during the planting season, yet the impacts of these changes on crop yields are not known. Here we investigate the yield response to excess spring moisture for both maize and soybean in the U.S. states of Illinois, Iowa, and Indiana, and the impacts of historical trends for 1950-2011. We find that simple measures of extreme spring soil moisture, derived from fine-scale daily moisture data from the Variable Infiltration Capacity (VIC) hydrologic model, lead to significant improvements in statistical models of yields for both crops. Individual counties experience up to 10 % loss in years with extremely wet springs. However, losses due to historical trends in excess spring moisture measures have generally been small, with 1-3 % yield loss over the 62 year study period.
  • Authors:
    • Coulter, J. A.
    • Venterea, R. T.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 1
  • Year: 2015
  • Summary: Modification of N fertilizer application timing within the growing season has the potential to reduce soil nitrous oxide (N 2O) emissions but limited data are available to assess its effects. We compared cumulative growing season nitrous oxide emissions (cN 2O) following urea applied to corn ( Zea mays L.) in a single application (SA) at planting or in three split applications (SpA) over the growing season. For both SA and SpA, granular urea was broadcast and incorporated at six fertilizer N rates in the corn phase of a corn-soybean [ Glycine max (L.) Merr.] rotation and in a continuous corn system over two growing seasons. Daily N 2O flux was measured using chambers on 35 dates in 2012 and 40 dates in 2013 and soil nitrate-N concentration was measured weekly. Split application did not affect grain yield and did not reduce cN 2O. Across N rates and rotations, cN 2O was 55% greater with SpA compared with SA in 2012. Increased cN 2O with SpA in 2012 likely resulted from a prolonged dry period before the second split application followed by large rainfall events following the third split application. Across years and rotations, SpA increased cN 2O by 57% compared with SA when the maximum N rate was applied. Exponential relationships between cN 2O and fertilizer N rate explained 62 to 74% of the variance in area-based cN 2O and 54% of the variance in yield-based cN 2O. Applying urea to coincide with periods of high crop N demand does not necessarily reduce and may increase N 2O emissions.
  • Authors:
    • Suh, S. W.
    • Yang, Y.
  • Source: Article
  • Volume: 20
  • Issue: 2
  • Year: 2015
  • Summary: Purpose: Previous estimates of carbon payback time (CPT) of corn ethanol expansion assumed that marginal yields of newly converted lands are the same as the average corn yield, whereas reported marginal yields are generally lower than the average yield (47-83% of average yield). Furthermore, these estimates assumed that the productivity of corn ethanol system and climate change impacts per unit greenhouse gas (GHG) emissions remain the same over decades to a century. The objective of this study is to re-examine CPT of corn ethanol expansion considering three aspects: (1) yields of newly converted lands (i.e., marginal yield), (2) technology improvements over time within the corn ethanol system, and (3) temporal sensitivity of climate change impacts. Methods: A new approach to CPT calculation is proposed, where changes in productivity of ethanol conversion process and corn yield are taken into account. The approach also allows the use of dynamic characterization approach to GHGs emitted in different times, as an option. Data are collected to derive historical trends of bioethanol conversion efficiency and corn yield, which inform the development of the scenarios for future biofuel conversion efficiency and corn yield. Corn ethanol's CPTs are estimated and compared for various marginal-to-average (MtA) yield ratios with and without considering technology improvements and time-dependent climate change impacts. Results and discussion: The results show that CPT estimates are highly sensitive to both MtA yield ratio and productivity of ethanol system. Without technological advances, our CPT estimates for corn ethanol from newly converted Conservation Reserve Program (CRP) land exceed 100 years for all MtA yield ratios tested except for the case where MtA yield ratio is 100%. When the productivity improvements within corn ethanol systems since previous CPT estimates and their future projections are considered, our CPT estimates fall into the range of 15 years (100% MtA yield ratio) to 56 years (50% MtA yield ratio), assuming land conversion takes place in early 2000s. Incorporating diminishing sensitivity of GHG emissions to future emissions year by year, however, increases the CPT estimates by 57 to 13% (from 17 years for 100% MtA yield ratio to 88 years for 50% MtA yield ratio). For 60 MtA yield ratio, CPT is estimated to be 43 years, which is relatively close to previous CPT estimates (i.e., 40 to 48 years) but with very different underlying reasons. Conclusions: This study highlights the importance of considering technological advances in understanding the climate change implications of land conversion for corn ethanol. Without the productivity improvements in corn ethanol system, the prospect of paying off carbon debts from land conversion within 100 years becomes unlikely. Even with the ongoing productivity improvements, the yield of newly converted land can significantly affect the CPT. The results reinforce the importance of considering marginal technologies and technology change in prospective life cycle assessment.
  • Authors:
    • Lynch, J. P.
    • Zhan, A.
  • Source: Article
  • Volume: 66
  • Issue: 7
  • Year: 2015
  • Summary: Suboptimal nitrogen (N) availability is a primary constraint for crop production in developing countries, while in developed countries, intensive N fertilization is a primary economic, energy, and environmental cost for crop production. We tested the hypothesis that under low-N conditions, maize ( Zea mays) lines with few but long (FL) lateral roots would have greater axial root elongation, deeper rooting, and greater N acquisition than lines with many but short (MS) lateral roots. Maize recombinant inbred lines contrasting in lateral root number and length were grown with adequate and suboptimal N in greenhouse mesocosms and in the field in the USA and South Africa (SA). In low-N mesocosms, the FLphenotype had substantially reduced root respiration and greater rooting depth than the MS phenotype. In low-N fields in the USA and SA, the FLphenotype had greater rooting depth, shoot N content, leaf photosynthesis, and shoot biomass than the MS phenotype. The FLphenotype yielded 31.5% more than the MS phenotype under low N in the USA. Our results are consistent with the hypothesis that sparse but long lateral roots improve N capture from low-N soils. These results with maize probably pertain to other species. The FLlateral root phenotype merits consideration as a selection target for greater crop N efficiency.
  • Authors:
    • Grosso, S. J.
    • Spatari, S.
    • Pourhashem, G.
    • Mitchell, J. G.
    • Adler, P. R.
    • Parton, W. J.
  • Source: Research Article
  • Volume: 25
  • Issue: 4
  • Year: 2015
  • Summary: Crop residues are potentially significant sources of feedstock for biofuel production in the United States. However, there are concerns with maintaining the environmental functions of these residues while also serving as a feedstock for biofuel production. Maintaining soil organic carbon (SOC) along with its functional benefits is considered a greater constraint than maintaining soil erosion losses to an acceptable level. We used the biogeochemical model DayCent to evaluate the effect of residue removal, corn stover, and wheat and barley straw in three diverse locations in the USA. We evaluated residue removal with and without N replacement, along with application of a high-lignin fermentation byproduct (HLFB), the residue by-product comprised of lignin and small quantities of nutrients from cellulosic ethanol production. SOC always decreased with residue harvest, but the decrease was greater in colder climates when expressed on a life cycle basis. The effect of residue harvest on soil N 2O emissions varied with N addition and climate. With N addition, N 2O emissions always increased, but the increase was greater in colder climates. Without N addition, N 2O emissions increased in Iowa, but decreased in Maryland and North Carolina with crop residue harvest. Although SOC was lower with residue harvest when HLFB was used for power production instead of being applied to land, the avoidance of fossil fuel emissions to the atmosphere by utilizing the cellulose and hemicellulose fractions of crop residue to produce ethanol (offsets) reduced the overall greenhouse gas (GHG) emissions because most of this residue carbon would normally be lost during microbial respiration. Losses of SOC and reduced N mineralization could both be mitigated with the application of HLFB to the land. Therefore, by returning the high-lignin fraction of crop residue to the land after production of ethanol at the biorefinery, soil carbon levels could be maintained along with the functional benefit of increased mineralized N, and more GHG emissions could be offset compared to leaving the crop residues on the land.
  • Authors:
    • Congreves, K. A.
    • Eerd, L. L.
  • Source: Journal Article
  • 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 Brassicaoleracea 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. © 2015 Springer Science+Business Media Dordrecht
  • Authors:
    • Daigh,A. L.
    • Sauer,T.
    • Xiao,X. H.
    • Horton,R.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 3
  • Year: 2015
  • Summary: Models of instantaneous soil-surface CO 2 efflux (SCE ins) are critical for understanding the potential drivers of soil C loss. Several simple SCE ins models have been reported in the literature. Our objective was to compare and validate selected soil temperature ( Ts)- and water content (theta v)-based equations for modeling SCE ins among a variety of cropping systems and land management practices. Soil-surface CO 2 effluxes were measured and modeled for grain-harvested corn ( Zea mays L.)-soybean [ Glycine max (L.) Merr.] rotations, grain- and stover-harvested continuous corn systems with and without a cover crop, and reconstructed prairies with and without N fertilization on soils with subsurface drainage. Soil-surface CO 2 effluxes, Ts, and theta v were measured from 2008 to 2011. Models calibrated with weekly measured SCE ins, Ts, and theta v throughout the growing season produced lower root mean squared error (RMSE) than models calibrated with several weeks of hourly measured data. Model selection significantly affected SCE ins estimations, with models that use only Ts parameters having lower RMSE than models that use both Ts and theta v. However, the model that produced the lowest RMSE during validation estimated growing-season SCE that did not significantly differ from numerical integration of weekly measured SCE ins. All models had similar residual errors with autocorrelated trends at monthly, weekly, and hourly scales. Autoregressive moving average functions were able to precisely describe the temporal errors. To accurately model SCE ins and scale across time, improvement of temporal errors in Ts- and theta v-based SCE ins models is needed to obtain accurate and precise closure of C balances for managed and natural ecosystems.
  • Authors:
    • Fan,T. -T
    • Wang,Y. -J
    • Li,C. -B
    • Zhou,D. -M
    • Friedman,S. P.
  • Source: Soil Science Society of America Journal
  • Volume: 79
  • Issue: 3
  • Year: 2015
  • Summary: Wien effect measurements were used to study the effect of organic matter on the interactions between divalent cations and soil clay particles of two black soil samples containing organic matter (OM) at 54.4 and 12.3 g kg-1 in the top (0-20-cm) and bottom (100-120-cm) horizons, respectively, and a sample of OM-free black soil, all saturated with Cd2+, Cu2+, Pb2+, and with Ca2+ as a reference cation. The weak-field electrical conductivities of suspensions of the top and bottom horizons and OM-free black soil samples were 0.021 to 0.033, 0.011 to 0.021, and 0.0065 to 0.0082 mS cm-1, respectively. The mean free binding energies of the cations in the same soil sample suspensions were 5.5 to 7.3, 7.3 to 9.3, and 9.6 to 10 kJ mol-1, respectively. The mean free adsorption energies of all cations increased with field strength and were in the order OM-free > bottom horizon > top horizon. At field strengths >100 kV cm-1, in the top-horizon soil, the adsorption energies of Ca were 0.21 to 0.72 kJ mol-1, those of Cd and Cu were similar to one another at 0.01 to 0.25 kJ mol-1, and those of Pb were close to zero, while in the bottom horizon soil, the adsorption energies of the various cations were in descending order: Ca > Cd > Pb > Cu, and in the OM-free soil the order of the adsorption energies of the various cations were Cd ˜ Cu ˜ Ca > Pb. The humus basically increased the negative electrokinetic potentials of the clay-size-fraction particles of the three black soil samples saturated with Ca, Cd, Cu, or Pb. © Soil Science Society of America, 5585 Guilford Rd., Madison Wl 53711 USA.