• Authors:
    • Drinkwater, L. E.
    • Puget, P.
  • Source: Soil Science Society of America Journal
  • Volume: 65
  • Issue: 3
  • Year: 2001
  • Summary: Although roots are an important source of soil organic matter (SOM) and are thought to be the major constituent of the particulate organic matter (POM) fraction, few studies have documented the fate of belowground C inputs in situ. The main purpose of this experiment was to determine the fate of root-derived C vs. shoot-derived C and to identify factors contributing to any differences in the retention of aboveground vs. belowground C inputs. We labeled hairy vetch (Vicia villosa Roth subsp. villosa) in situ with 13CO2 and followed both root- and shoot-derived C in total soil organic C (SOC) and labile C pools for the first growing season following hairy vetch incorporation. At the end of the growing season, nearly one-half of the root-derived C was still present in the soil, whereas only 13% of shoot-derived C remained. A greater proportion of root-derived C was found as occluded POM and associated with the clay and silt fraction. Greater root-derived C also was retained as chloroform-extractable microbial biomass. We suggest that three different mechanisms contributed to the increased retention of root-derived C: (i) the greater biochemical recalcitrance of root litter, (ii) increased physical protection of root-derived POM within aggregates, and (iii) the continuous nature of root C inputs from exudates and fine root turnover. We conclude that shoot residues are broken down rapidly and serve as the source of N for the following cash crop, whereas the root litter is probably largely responsible for the short-term soil structural improvements associated with the use of green manures. Furthermore, on the basis of these findings, we hypothesize that the greater retention of root-derived C in the first 6 mo of decomposition will increase the persistence of this C in SOM in the long term.
  • Authors:
    • Stuedemann, J. A.
    • Franzluebbers,A. J.
    • Sanderson, M. A.
    • Stout, W. L.
    • Schnabel, R. R.
  • Source: The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect
  • Year: 2001
  • Authors:
    • Follett, R. F.
  • Source: The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect
  • Year: 2001
  • Summary: This book chapter examines the organic carbon pools in grazing land soils.
  • Authors:
    • Lal, R.
    • Kimble, J. M.
    • Follett, R. F.
  • Year: 2001
  • Summary: Grazing lands represent the largest and most diverse land resource-taking up over half the earth's land surface. The large area grazing land occupies, its diversity of climates and soils, and the potential to improve its use and productivity all contribute to its importance for sequestering C and mitigating the greenhouse effect and other conditions brought about by climate change. The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect gives you an in-depth look at this possibility.
  • Authors:
    • Travis, G. R.
    • Larney, F. J.
    • Chang, C.
    • Hao, X.
  • Source: Journal of Environmental Quality
  • Volume: 30
  • Issue: 2
  • Year: 2001
  • Summary: The emission of greenhouse gases (GHG) during feedlot manure composting reduces the agronomic value of the final compost and increases the greenhouse effect A study was conducted to determine whether GHG emissions are affected by composting method. Feedlot cattle manure was composted with two aeration methods-passive (no turning) and active (turned six times). Carbon lost in the forms of CO2 and CH4 was 73.8 and 6.3 kg C Mg-1 manure for the passive aeration treatment and 168.0 and 8.1 kg C Mg-1 manure for the active treatment. The N loss in the form of N2O was 0.11 and 0.19 kg N Mg-1 manure for the passive and active treatments. Fuel consumption to turn and maintain the windrow added a further 4.4 kg C Mg-1 manure for the active aeration treatment. Since CH4 and N2O are 21 and 310 times more harmful than CO2 in their global warming effect, the total GHG emission expressed as CO2-C equivalent was 240.2 and 401.4 kg C Mg-1 manure for passive and active aeration. The lower emission associated with the passive treatment was mainly due to the incomplete decomposition of manure and a lower gas diffusion rate. In addition, turning affected N transformation and transport in the windrow profile, which contributed to higher N2O emissions for the active aeration treatment. Gas diffusion is an important factor controlling GHG emissions. Higher GHG concentrations in compost windrows do not necessarily mean higher production or emission rates.
  • Authors:
    • Williams, S.
    • Schuler, J.
    • Killian, K.
    • Kautza, T.
    • Elliott, T.
    • Easter, M.
    • Cipra, J.
    • Bluhm, G.
    • Paustian, K.
    • Brenner, J.
  • Year: 2001
  • Summary: Land managers have long known the importance of soil organic matter in maintaining the productivity and sustainability of agricultural land. More recently, interest has developed in the potential for using agricultural soils to sequester C and mitigate increasing atmospheric carbon- dioxide by adopting practices that increase standing stocks of carbon in soil organic matter and vegetation. Practices that increase the amount of CO2 taken up by plants (through photosynthesis), which then enter the soil as plant residues, tend to increase soil C stocks. Likewise, management practices that reduce the rate of decay or turnover of organic matter in soils will also tend to increase carbon stocks.
  • Authors:
    • Paustian, K. H.
    • Elliott, E. T.
    • Mooney, S.
    • Capalbo, S. M.
    • Antle, J. M.
  • Source: Journal of Agricultural and Resource Economics
  • Volume: 26
  • Issue: 2
  • Year: 2001
  • Summary: This study develops an integrated assessment approach for analysis of the economic potential for carbon sequestration in agricultural soils. By linking a site-specific economic simulation model of agricultural production to a crop ecosystem model, the approach shows the economic efficiency of soil carbon (C) sequestration depends on site-specific opportunity costs of changing production practices and rates of soil C sequestration. An application is made to the dryland grain production systems of the U.S. Northern Plains which illustrates the sensitivity of the sequestration costs to policy design. The marginal cost of soil C ranges from $12 to $500 per metric ton depending upon the type of contract or payment mechanism used, the amount of carbon sequestered, and the site-specific characteristics of the areas.
  • Authors:
    • Wu, J. J.
  • Source: American Journal of Agricultural Economics
  • Volume: 82
  • Issue: 4
  • Year: 2000
  • Summary: Each year, billions of dollars of public funds are expended to purchase conservation easements on farmland. One unintended impact of these programs is that they may bring non-cropland into crop production. Such a slippage effect can be caused by increased output prices and by substitution effects. This article shows that for each one hundred acres of cropland retired under the Conservation Reserve Program (CRP) in the central United States, twenty acres of non-cropland were converted to cropland. offsetting 9% and 14% of CRP water and wind erosion reduction benefits, respectively. Implications of these results for the design of conservation programs are discussed.
  • Authors:
    • Kwon, K. C.
    • Post, W. M.
  • Source: Global Change Biology
  • Volume: 6
  • Issue: 3
  • Year: 2000
  • Summary: When agricultural land is no longer used for cultivation and allowed to revert to natural vegetation or replanted to perennial vegetation, soil organic carbon can accumulate. This accumulation process essentially reverses some of the effects responsible for soil organic carbon losses from when the land was converted from perennial vegetation. We discuss the essential elements of what is known about soil organic matter dynamics that may result in enhanced soil carbon sequestration with changes in land-use and soil management. We review literature that reports changes in soil organic carbon after changes in land-use that favour carbon accumulation. This data summary provides a guide to approximate rates of SOC sequestration that are possible with management, and indicates the relative importance of some factors that influence the rates of organic carbon sequestration in soil. There is a large variation in the length of time for and the rate at which carbon may accumulate in soil, related to the productivity of the recovering vegetation, physical and biological conditions in the soil, and the past history of soil organic carbon inputs and physical disturbance. Maximum rates of C accumulation during the early aggrading stage of perennial vegetation growth, while substantial, are usually much less than 100 g C m-2 y-1. Average rates of accumulation are similar for forest or grassland establishment: 33.8 g C m-2 y-1 and 33.2 g C m-2 y-1, respectively. These observed rates of soil organic C accumulation, when combined with the small amount of land area involved, are insufficient to account for a significant fraction of the missing C in the global carbon cycle as accumulating in the soils of formerly agricultural land.
  • Authors:
    • Rossoni-Longnecker, L.
    • Janke, R. R.
    • Drinkwater, L. E.
  • Source: Plant and Soil
  • Volume: 227
  • Issue: 1
  • Year: 2000
  • Summary: Abstract In 1988 an experiment was established at the Rodale Institute Experimental Farm to study weed control and nitrogen (N) management in rotations with grain crops and N-fixing green manures under reduced tillage without the use of herbicides. Tillage intensities ranging from moldboard plow (MP) to continuous no-till (NT) were compared. We present results for maize production in 1994, the seventh year of the experiment. Our goal was to further investigate reduced tillage regimes that alternated no-till with different forms of primary tillage in legume-based systems. In the chisel-disc (CD) and MP treatments comparable yields were achieved under so-called organic (weeds controlled with cultivation and green manure N source) and conventional management (weeds controlled with herbicides and mineral N fertilizer applied). Weed competition in these treatments was minimal and the N status of maize plants was essentially the same regardless of the N source (fertilizer or green manure). Of the four organic no-till maize treatments, only the mixed-tillage system with cultivation for weed control (CD-NTc) produced yields comparable to conventional NT maize. The fate of vetch N as well as temporal N dynamics were largely determined by tillage intensity and the handling of the vetch residues at maize planting. Treatments with primary tillage (CD and MP) had extremely high levels of mineral N early in the season and had greater average net N-mineralization, even though N content of hairy vetch in these treatments was equal to or lower than that in treatments with mow-killed vetch. In terms of soil mineral N concentrations, the CD-NTc treatment was similar to the other mow-killed vetch/no-till maize treatments. However, N availability in this treatment was greater, probably due to more complete decomposition of green manure residues. Cultivation for weeds not only helped control weeds but also increased mineralization of the vetch residues, which in turn increased the N supply during the period of maximum N demand by the maize. Carefully designed rotations combining tillage reductions with the use of leguminous N sources can have multiple benefits, including improved timing of N availability, reduced herbicide applications, and improved soil quality in the long term.