• Authors:
    • Ding, H.
    • Edis, R.
    • Zhang, Y.
    • Chen, D.
    • Li, Y.
  • Source: Global Biogeochemical Cycles
  • Volume: 19
  • Year: 2005
  • Authors:
    • Castellanos, J. Z.
    • Buenger, E. D.
    • Follett, R. F.
  • Source: Soil & Tillage Research
  • Volume: 83
  • Issue: 1
  • Year: 2005
  • Summary: Conservation tillage could enhance soil organic carbon (SOC) sequestration, but is rarely used in cropping systems in Mexico, especially under irrigation. A study was conducted on a clayey, smectitic, isothermic Udic Pellustert to evaluate the use of traditional-deep and no-tillage systems on SOC dynamics for wheat (Triticum aestivum L.)-corn (Zea mays L.) and wheat-bean (Phaseolus vulgaris L.) cropping systems. Experimental design was a randomized block of five tillage/crop-rotation (two crops per year) systems with four replications: (WC-CTb) wheat-corn, burning the residues of both crops, plowing and disking twice (WC-CT) wheat-corn under conventional tillage (plowing and disking twice to incorporate crop residues following the harvest of each crop), (WC-NT) wheat-corn under no-till, (WB-CT) wheat-bean under conventional tillage, and (WB-NT) wheat-bean under no-till. Each crop in the sequence received one of three fertilizer-N rates broadcast as urea: (a) 0, 150, and 300 kg N ha(-1) for corn; (b) 0, 40, and 80 kg N ha(-1) for bean; and (c) 0, 125, and 250 kg N ha(-1) for wheat. The baseline year was 1994, and relative changes were measured from 1994 to 1999 for grain yield and residue production, crop residue C and delta(13)C, SOC, soil C/N ratio, and change in soil delta(13)C. Interaction of cropping system x fertilizer-N rate was highly important to grain yield and crop residue production and amount of crop-residue C produced. High N rates increased SOC sequestration and decreased soil C/N ratios. In WC systems, more negative delta(13)C was associated with higher N rates, indicating increased contribution of wheat (a C(3) plant) residue C relative to corn (a C(4) plant). In WB, N-rate and tillage had no effect on SOC sequestration. Highest rate of SOC sequestration was under WC-NT and when increases in SOC from 1994 to 1999 were annualized was 1.0 and 1.9 Mg SOC yr(-1) in the 0-15- and 15-30-cm depths, respectively. Corresponding SOC in 0-15- and 15-30-cm depths in the WC-CT treatment was 0.2 and 0.6 Mg yr(-1) and amounts in all other treatments were equal or lower than those observed for WC-CT. There was a significant correlation between aboveground crop-residue C produced and amount of SOC sequestered. Results from this study indicate no-till on N-fertilized WC systems can potentially increase SOC sequestration on large areas of irrigated Vertisols in Central Mexico while maintaining high crop yields.
  • Authors:
    • Ginting, D.
    • Eghball, B.
  • Source: Soil Science Society of America Journal
  • Volume: 69
  • Issue: 3
  • Year: 2005
  • Summary: Field experiments were conducted to determine optimal time during the day for N 2O flux determination and to evaluate the effects of wheel traffic and soil parameters on N 2O fluxes following urea ammonium nitrate (UAN) injection and summer UAN fertigations. The experiments were located on silty clay loam soils under no-till irrigated continuous corn of eastern Nebraska. Three approaches were used. First, near-continuous N 2O flux measurements were made in non-wheel-tracked (NWT) interrows in four 24-h periods during the growing season of 2002. Second, point measurements of N 2O flux were made in the wheel-tracked (WT) and NWT interrows at five dates during the growing season of 2002. Third, point measurements of N 2O fluxes and soils (nitrate, ammonium, moisture, and temperature) were made in the NWT interrows from 2001 to 2004. The differences between point vs. continuous flux measurements (<8 g N 2O-N ha -1 d -1) and between the WT vs. the NWT (<3.7 g N 2O-N ha -1 d -1) were not significant. The means of N 2O daily flux within 60 d after injection (period of high soil N) in the first, second, and third year were 26.8, 21.2, and 28.0 g N 2O-N ha -1 d -1, respectively. The means during low soil N were 9.24, 4.05, and 7.50 g N 2O-N ha -1 d -1, respectively. Summer fertigations did not increase N 2O flux. Under the conditions of this study, optimal point measurement for N 2O daily flux can be made any time during the day at the NWT interrows. Among the soil parameters, soil nitrate dynamics in the injection zone correlates best with N 2O fluxes.
  • Authors:
    • Verchot, L.
    • Palm, C.
    • Albrecht, A.
    • Cadisch, G.
    • Mutuo, P.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 71
  • Issue: 1
  • Year: 2005
  • Summary: Losses of carbon (C) stocks in terrestrial ecosystems and increasing concentrations of greenhouse gases in the atmosphere are challenges that scientists and policy makers have been facing in the recent past. Intensified agricultural practices lead to a reduction in ecosystem carbon stocks, mainly due to removal of aboveground biomass as harvest and loss of carbon as CO2 through burning and/or decomposition. Evidence is emerging that agroforestry systems are promising management practices to increase aboveground and soil C stocks and reduce soil degradation, as well as to mitigate greenhouse gas emissions. In the humid tropics, the potential of agroforestry (tree-based) systems to sequester C in vegetation can be over 70 Mg C ha-1, and up to 25 Mg ha-1 in the top 20 cm of soil. In degraded soils of the sub-humid tropics, improved fallow agroforestry practices have been found to increase top soil C stocks up to 1.6 Mg C ha-1 yr-1 above continuous maize cropping. Soil C accretion is linked to the structural development of the soil, in particular to increasing C in water stable aggregates (WSA). A review of agroforestry practices in the humid tropics showed that these systems were able to mitigate N2O and CO2 emissions from soils and increase the CH4 sink strength compared to cropping systems. The increase in N2O and CO2 emissions after addition of legume residues in improved fallow systems in the sub-humid tropics indicates the importance of using lower quality organic inputs and increasing nutrient use efficiency to derive more direct and indirect benefits from the system. In summary, these examples provide evidence of several pathways by which agroforestry systems can increase C sequestration and reduce greenhouse gas emissions.
  • Authors:
    • Rykiel, E. J. Jr.
    • Vaughan, B. E.
    • Oliveira, M. E. D. D.
  • Source: BioScience
  • Volume: 55
  • Issue: 7
  • Year: 2005
  • Summary: The major contributor to global warming is considered to be the high levels of greenhouse gas emissions, especially carbon dioxide (CO2), caused by the burning of fossil fuel. Thus, to mitigate CO2 emissions, renewable energy sources such as ethanol have been seen as a promising alternative to fossil fuel consumption. Brazil was the world's first nation to run a large-scale program for using ethanol as fuel. Eventually, the United States also developed large-scale production of ethanol. In this study, we compare the benefits and environmental impacts of ethanol fuel, in Brazil and in the United States, using the ecological footprint tool developed by Wackernagel and Rees. We applied the STELLA model to gauge possible outcomes as a function of variations in the ethanol production scenario.
  • Authors:
    • Patzek, T. W.
    • Pimentel, D.
  • Source: Natural Resources Research
  • Volume: 14
  • Issue: 1
  • Year: 2005
  • Summary: Energy outputs from ethanol produced using corn, switchgrass, and wood biomass were each less than the respective fossil energy inputs. The same was true for producing biodiesel using soybeans and sunflower, however, the energy cost for producing soybean biodiesel was only slightly negative compared with ethanol production. Findings in terms of energy outputs compared with the energy inputs were: * Ethanol production using corn grain required 29% more fossil energy than the ethanol fuel produced. * Ethanol production using switchgrass required 50% more fossil energy than the ethanol fuel produced. * Ethanol production using wood biomass required 57% more fossil energy than the ethanol fuel produced. * Biodiesel production using soybean required 27% more fossil energy than the biodiesel fuel produced (Note, the energy yield from soy oil per hectare is far lower than the ethanol yield from corn). * Biodiesel production using sunflower required 118% more fossil energy than the biodiesel fuel produced.
  • Authors:
    • Seidel, R.
    • Douds, D.
    • Hanson, J.
    • Hepperly, P.
    • Pimentel, D.
  • Source: BioScience
  • Volume: 55
  • Issue: 7
  • Year: 2005
  • Summary: Various organic technologies have been utilized for about 6000 years to make agriculture sustainable while conserving soil, water, energy, and biological resources. Among the benefits of organic technologies are higher soil organic matter and nitrogen, lower fossil energy inputs, yields similar to those of conventional systems, and conservation of soil moisture and water resources (especially advantageous under drought conditions). Conventional agriculture can be made more sustainable and ecologically sound by adopting some traditional organic farming technologies.
  • Authors:
    • Powers, S.
  • Source: Technical Report NREL/TP-510-37500
  • Year: 2005
  • Summary: Corn, soybeans and corn stover are all valuable feedstocks for conversion of biomass into consumer goods. Utilizing these agricultural products and residues creates a potential for both environmental benefits and deleterious impacts. The national use of these products could have a disproportionate negative impact in the Midwestern states on the soil and water resources, while having positive impacts on air quality and global climate change over a wider geographic scale. Many studies completed to date that have quantified the environmental impacts of bio-based products have focused on the air quality and greenhouse gas (GHG) benefits (Wang, 1999; Sheehan et al., 2002 Heller et al., 2003). There are clear benefits to using bio-based materials, especially in terms of greenhouse gas generation. Plant growth consumes atmospheric carbon dioxide is transformed to plant matter. Eventually, the carbon is released back to the environment at the end-of-life stage of a bio-based product or fuel. However, that release results in a near zero net GHG emission. In comparison, combustion of fossil fuels cause carbon sequestered in the subsurface for millennia to be added to our atmospheric carbon dioxide load.
  • Authors:
    • Lal, R.
    • Puget, P.
  • Source: Soil & Tillage Research
  • Volume: 80
  • Issue: 1-2
  • Year: 2005
  • Summary: Minimum tillage practices are known for increasing soil organic carbon (SOC). However, not all environmental situations may manifest this potential change. The SOC and N stocks were assessed on a Mollisol in central Ohio in an 8-year-old tillage experiment as well as under two relatively undisturbed land uses; a secondary forest and a pasture, on the same soil type. Cropped systems had 51 +/- 4 (equiv. mass) Mg ha(-1) lower SOC and lower 3.5 +/- 0.3 (equiv. mass)Mg ha(-1) N in the top 30cm soil layer than Linder forest. Being a secondary forest, the loss in SOC and N stocks by cultivation may have been even more than these reported herein. No differences among systems were detected below this depth. The SOC stock in the pasture treatment was 29 +/- 3 Mg ha(-1), greater in the top 10 cm layer than in cultivated soils. but was similar to those tinder forest and no-till (NT). Among tillage practices (plow, chisel and NT) only the 0-5 cm soil layer under NT exhibited higher SOC and N concentrations. An analysis of the literature of NT effect on SOC stocks. using meta-analysis, suggested that NT would have an overall positive effect on SOC sequestration rate but with a greater variability of what was previously reported. The average sequestration rate of NT was 330 kg SOC ha(-1) year(-1) with a 95%, confidence interval ranging from 47 to 620 kg SOC ha(-1) year(-1). There was no effect of soil texture or crop rotation on the SOC sequestration rate that could year explain this variability. The conversion factor for SOC stock changes from plow to NT was equal to 1.04. This suggests that the complex mechanisms and pathways of SOC accrual warrant a cautious approach when generalizing the beneficial changes of NT on SOC stocks. (C) 2004 Elsevier B.V. All rights reserved.
  • Authors:
    • Traxler, G.
    • Qaim, M.
  • Source: Agricultural Economics
  • Volume: 32
  • Issue: 1
  • Year: 2005