• Authors:
    • McFee, W. W.
    • Kladivko, E. J.
    • Michéli, E.
    • Vyn, T. J.
    • Gál, A.
  • Source: Soil & Tillage Research
  • Volume: 96
  • Issue: 1-2
  • Year: 2007
  • Summary: Numerous investigators of tillage system impacts on soil organic carbon (OC) or total nitrogen (N) have limited their soil sampling to depths either at or just below the deepest tillage treatment in their experiments. This has resulted in an over-emphasis on OC and N changes in the near-surface zones and limited knowledge of crop and tillage system impacts below the maximum depth of soil disturbance by tillage implements. The objective of this study was to assess impacts of long-term (28 years) tillage and crop rotation on OC and N content and depth distribution together with bulk density and pH on a dark-colored Chalmers silty clay loam in Indiana. Soil samples were taken to 1 m depth in six depth increments from moldboard plow and no-till treatments in continuous corn and soybean-corn rotation. Rotation systems had little impact on the measured soil properties; OC content under continuous corn was not superior to the soybean-corn rotation in either no-till or moldboard plow systems. The increase in OC (on a mass per unit area basis) with no-till relative to moldboard plow averaged 23 t ha(-1) to a constant 30 cm sampling depth, but only 10 t ha(-1) to a constant 1.0 m sampling depth. Similarly, the increase in N with no-till was 1.9 t ha(-1) to a constant 30 cm sampling depth, but only 1.4 t ha(-1) to a constant 1.0 m sampling depth. Tillage treatments also had significant effects on soil bulk density and pH. Distribution of OC and N with soil depth differed dramatically under the different tillage systems. While no-till clearly resulted in more OC and N accumulation in the surface 15 cm than moldboard plow, the relative no-till advantage declined sharply with depth. Indeed, moldboard plowing resulted in substantially more OC and N, relative to no-till, in the 30-50 cm depth interval despite moldboard plowing consistently to less than a 25 cm depth. Our results suggest that conclusions about OC or N gains under long-term no-till are highly dependent on sampling depth and, therefore, tillage comparisons should be based on samples taken well beyond the deepest tillage depth. (c) 2007 Elsevier B.V. All rights reserved.
  • Authors:
    • Robertson, G. P.
    • Grandy, A. S.
  • Source: Ecosystems
  • Volume: 10
  • Issue: 1
  • Year: 2007
  • Summary: Restoring soil C pools by reducing land use intensity is a potentially high impact, rapidly deployable strategy for partially offsetting atmospheric CO2 increases. However, rates of C accumulation and underlying mechanisms have rarely been determined for a range of managed and successional ecosystems on the same soil type. We determined soil organic matter (SOM) fractions with the highest potential for sequestering C in ten ecosystems on the same soil series using both density- and incubation-based fractionation methods. Ecosystems included four annual row-crop systems (conventional, low input, organic and no-till), two perennial cropping systems (alfalfa and poplar), and four native ecosystems (early successional, midsuccessional historically tilled, midsuccessional never-tilled, and late successional forest). Enhanced C storage to 5 cm relative to conventional agriculture ranged from 8.9 g C m(-2) y(-1) in low input row crops to 31.6 g C m(-2) y(-1) in the early successional ecosystem. Carbon sequestration across all ecosystems occurred in aggregate-associated pools larger than 53 mu m. The density-based fractionation scheme identified heavy-fraction C pools (SOM > 1.6 g cm(-3) plus SOM 250 mu m), as having the highest potential C accumulation rates, ranging from 8.79 g C m(-2) y(-1) in low input row crops to 29.22 g C m(-2) y(-1) in the alfalfa ecosystem. Intra-aggregate light fraction pools accumulated C at slower rates, but generally faster than in inter-aggregate LF pools. Incubation-based methods that fractionated soil into active, slow and passive pools showed that C accumulated primarily in slow and resistant pools. However, crushing aggregates in a manner that simulates tillage resulted in a substantial transfer of C from slow pools with field mean residence times of decades to active pools with mean residence times of only weeks. Our results demonstrate that soil C accumulates almost entirely in soil aggregates, mostly in macroaggregates, following reductions in land use intensity. The potentially rapid destruction of macroaggregates following tillage, however, raises concerns about the long-term persistence of these C pools.
  • Authors:
    • Hao,X.
    • Kravchenko,A. N.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 1
  • Year: 2007
  • Summary: Management practice and soil texture are known to affect soil C. Relatively little information exists, however, on interactions between textural and management effects. The objective of this study was to evaluate management effects on soil total C along a textural gradient in well-drained Typic Hapludalfs in southwest Michigan. Three management practices considered in this study were conventional tillage (CT) and no-till (NT) both with conventional chemical inputs, and conventional tillage with leguminous cover crops and no chemical inputs (CT-cover). Four replicate plots were sampled for each practice, with approximately 100 soil samples taken at the 0- to 5-cm depth in each plot. In all management practices, the relationships of total C and N with clay + silt varied depending on the range of clay + silt values, with regression slopes at clay + silt 570 g kg-1. Total C in the CT-cover and NT treatments was higher than that in the CT treatment across the whole range of studied textures; however, a greater difference in total C between NT and CT occurred at greater clay + silt contents. Total C in the CT-cover and NT treatments were not different when clay + silt was 600 g kg-1. The results indicate that the potential for C accumulation in surface soils via NT treatment depends on soil texture.
  • Authors:
    • Qi, J.
    • Thelen, K.
    • Kravchenko, A.
    • Senthilkumar, S.
    • Huang, X.
  • Source: Geoderma
  • Volume: 141
  • Issue: 1-2
  • Year: 2007
  • Summary: Accurate mapping of total soil carbon is important for reliable assessment of carbon sequestration potential from a field to regional scales. Highly variable soil and topographical attributes of glacial till terrain cause difficulties in mapping soil carbon based only on a limited number of soil samples. The objectives of this study were to demonstrate the feasibility of mapping total soil carbon using newly developed on-the-go near-infrared spectroscopy (NIRS) measurements and Landsat Enhanced Thematic Mapper (ETM) image reflectance in glacial till soils with and without additional topographical information. The studied field was about 50 ha in size and located in Kalamazoo County of Michigan. The predominant soil is Kalamazoo loam (fine-loamy, mixed, mesic Typic Hapludalfs). NIRS spectra were collected along 22 north-south transects separated by a distance of 25 m and the distance between the measurements within a transect was equal to 5 m. The field was bare of vegetation and relatively dry during soil sampling. Landsat ETM imagery during soil sampling period was obtained. Eighty-five soil samples were collected on the NIRS transects from 0-10 cm depth. Principal component regression was used to relate NIRS spectra and ETM data to measured soil carbon. Regression coefficients between measured and predicted carbon values were equal to 0.70 and 0.46 using NIRS data and ETM imagery, respectively. When topographical attributes, such as elevation and terrain curvature were included into the regression model along with NIRS and ETM data, the regression coefficients improved to 0.81 and 0.62, respectively. The results indicated that combination of the NIRS and ETM measurements with topography is a valuable tool for accurate total carbon mapping in glacial till soils. Field soil moisture and texture were found to be helpful in explaining carbon variation and improving its prediction for ETM imagery data, but were not useful when added to NIRS measurements.
  • Authors:
    • Desjardins, R. L.
    • Campbell, C. A.
    • Hutchinson, J. J.
  • Source: Agricultural and Forest Meteorology
  • Volume: 142
  • Issue: 2-4
  • Year: 2007
  • Summary: One of the main options for greenhouse gas (GHG) mitigation identified by the IPCC is the sequestration of carbon in soils. Since the breaking of agricultural land in most regions, the carbon stocks have been depleted to such an extent, that they now represent a potential sink for CO, removal from the atmosphere. Improved management will however, be required to increase the inputs of organic matter in the top soil and/or decrease decomposition rates. In this paper we use data from selected regions to explore the global potential for carbon sequestration in arable soils. While realising that C sequestration is not limited to the selected regions, we have, however, focussed our review on two regions: (i) Canadian Prairies and (ii) The Tropics. In temperate regions, management changes for an increase in C involve increase in cropping frequency (reducing bare fallow), increasing use of forages in crop rotations, reducing tillage intensity and frequency, better crop residue management, and adopting agroforestry. In the tropics, agroforestry remains the primary method by which sequestration rates may be significantly increased. Increases in soil C may be achieved through improved fertility of cropland/pasture; on extensive systems with shifting cultivation cropped fallows and cover crops may be beneficial, and adopting agro forestry or foresting marginal cropland is also an alternative. In addition, in the tropics it is imperative to reduce the clearing of forests for conversion to cropland. Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized North America where the majority of research pertaining to C sequestration has been carried out. More research is needed, especially for the Tropics, to more accurately capture the impact of region-specific interactions between climate, soil, and management of resources on C sequestration, which are lost in global level assessments. By itself, C sequestration in agricultural soils can make only modest contributions (3-6% of fossil fuel contributions) to mitigation of overall greenhouse gas emissions. However, effective mitigation policies will not be based on any single 'magic bullet' solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option. (c) 2006 Elsevier B.V. All rights reserved.
  • Authors:
    • Chicago Climate Exchange
  • Year: 2007
  • Summary: Chicago Climate Exchange (CCX) is the world's first and North America's only active voluntary, legally binding integrated trading system to reduce emissions of all six greenhouse gases (GHGs), with Offset Projects worldwide. CCX employs independent verification and has been trading GHG emission reductions since 2003. CCX Members that cannot reduce their own emissions can purchase credits from those who make extra emission cuts or from verified Offset Projects. CCX issues tradable Carbon Financial Instrument (CFI) contracts to owners or aggregators of eligible projects on the basis of sequestration, destruction or displacement of GHG emissions. Eligible projects include: agricultural methane, landfill methane, coal mine methane, agricultural and rangeland soil carbon, forestry and renewable energy.
  • Authors:
    • Groffman, Peter M.
    • Gold, A. J.
    • Nowicki, B. L.
    • Kellogg, D. Q.
    • Addy, K.
    • Clough, T. J.
  • Source: Global Change Biology
  • Volume: 13
  • Issue: 7
  • Year: 2007
  • Summary: Few data are available to validate the Intergovernmental Panel on Climate Change's (IPCC) emission factors for indirect emissions of nitrous oxide (N2O). In particular the N2O emissions resulting from nitrogen leaching and the associated groundwater and surface drainage (EF5-g) are particularly poorly characterized. In situ push-pull methods have been used to identify the fate of NO3 in the groundwater. In this study, we adapted a previously published in situ denitrification push-pull method to examine the fate of 15N2O introduced into the subsoil-groundwater matrix. Enriched 15 N2O was manufactured, added to groundwater via a closed system in the laboratory, and then introduced into the groundwater-subsoil matrix in an upland-marsh transition zone of a salt marsh and a forested alluvial riparian zone. Conservative tracers (SF6 and Br ) and 15N2O were injected into the groundwater and left for 1-4 h after which the groundwater was sampled. Added 15N2O behaved in a conservative manner at one site while the other site showed variability with some injections showing significant consumption (38 [micro]g N2O-15 Nkg-1 soil day-1) of 15N2O. Our results show that the fate and dynamics of N2O in groundwater are complex and variable and that these dynamics should be considered in the development of improved IPCC inventory calculations.
  • Authors:
    • Alberta Agriculture and Food
  • Year: 2007
  • Authors:
    • Guzman, J.
    • Al-Kaisi, M.
  • Source: Integrated Crop Management
  • Volume: IC-498
  • Issue: 7
  • Year: 2007
  • Authors:
    • Griffin, T. S.
    • Larkin, R. P.
  • Source: Crop Protection
  • Volume: 26
  • Issue: 7
  • Year: 2007
  • Summary: Brassica crops used in crop rotations and as green manures have been associated with reductions in soilborne pests and pathogens. These reductions have been attributed to the production of volatile sulfur compounds through a process known as biofumigation, and to changes in soil microbial community structure. In this study, selected Brassica crops, including canola, rapeseed, radish, turnip, yellow mustard, and Indian mustard, were evaluated for control of various soilborne potato pathogens and diseases in culture, in greenhouse trials, and in field trials on commercial potato farms. In in vitro assays, volatiles released from chopped leaf material of Brassica crops and barley inhibited growth of a variety of soilborne pathogens of potato, including Rhizoctonia solani, Phytophthora erythroseptica, Pythium ultimum, Sclerotinia sclerotiorum, and Fusarium sambucinam, with Indian mustard resulting in nearly complete inhibition (80-100%). All Brassica crops and barley reduced inoculum levels of R. solani (20-56% reduction) in greenhouse tests, and radish, rapeseed, and Indian mustard reduced subsequent potato seedling disease by 40-83%. In an on-farm field trial at a site with a substantial powdery scab problem, Indian mustard, rapeseed, canola, and ryegrass grown as green manure rotation crops reduced powdery scab in the subsequent potato crop by 15-40%, and canola and rapeseed reduced black scurf by 70-80% relative to a standard oats rotation. At another field site where common scab was the primary disease problem, an Indian mustard green manure reduced common scab by 25%, and rapeseed, yellow mustard, and 'Lemtal' ryegrass also reduced black scurf relative to a standard ryegrass rotation. Disease reductions were not always associated with higher glucosinolate-producing crops, and were also observed with non- Brassica crops (barley and ryegrass), indicating other mechanisms and interactions are important, particularly for control of R. solani. Overall, Indian mustard was most effective for reducing powdery scab and common scab diseases, whereas rapeseed and canola were most effective in reducing Rhizoctonia diseases. These results indicate that Brassica crops have potential for use as green manures for the control of multiple soilborne disease problems.