• Authors:
    • Paustian, K.
    • Capalbo, S. M.
    • Antle, J. M.
    • Mooney, S.
  • Source: Environmental Management
  • Volume: 33
  • Issue: Supplement 1
  • Year: 2004
  • Summary: A large body of research suggests that US crop-land soils can also sequester significant amounts of C and are a promising source of C credits. This paper presents a framework for assessing the transactions costs associated with per-hectare and per-credit contract types and addresses the potential magnitude of transactions costs associated with measuring soil C credits under a per-credit contract within the dry-land crop region of Montana, USA. In the empirical analysis, we estimate the total measurement costs for soil C credits and investigate how changes in contract (and region) size as well as increases in C credit variability affect total measurement costs. The empirical analyses suggest that increasing the size of the contract and aggregating credits over a larger number of producers can lower measurement costs associated with the per-credit contract, even in the face of increasing C variability. Thus contracts for large quantities of soil credits increase the likelihood that the per-credit contract remains more efficient than the per-hectare contract. However, these empirical results reflect the specific data and conditions present within the case study region. The theoretical expectation is that sample size and measurement costs can either increase or decrease as the population to be sampled increases. Thus the measurement costs associated with a per-credit contract could respond differently from this analysis across the spatial extent of the US.
  • Authors:
    • Tan, C. S.
    • Reynolds, W. D.
    • Yang, X. M.
    • Drury, C. F.
  • Source: Soil & Tillage Research
  • Volume: 79
  • Issue: 1
  • Year: 2004
  • Summary: The influence of soil and crop management practices on soil aggregation is well documented; however very little information is available on the impact of aggregation on biological processes such as greenhouse gas emissions. Soils (Ap horizon of a Brookston clay loam) were sampled in the spring of 2002 from two treatments in a long-term study (established in 1959). The treatments included continuous corn (Zea mays L.) and the corn phase of a 4-year crop rotation which included corn-oats (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa. The continuous corn (CC) treatment was plowed every fall whereas the rotation corn (RC) treatment was plowed 2 out of the 4 years (in the fall following second year alfalfa and following corn). The objectives were to determine the impact of crop rotation and continuous corn on aggregate size distribution, and the influence of aggregate size on CO2 and N2O production through denitrification. The soil samples were separated into six aggregate size fractions (<0.25, 0.25-0.50, 0.50-1.0, 1.0-2.0, 2.0-4.0, and 4.0-8.0mm diameter) using a dry sieving procedure. Each aggregate size fraction was separated into two subsamples with one subsample left intact and the other ground to <0.15mm (100-mesh sieve). The intact and ground aggregates from each size fraction were incubated anaerobically using the acetylene inhibition technique and carbon dioxide (CO2) and nitrous oxide (N2O) production (denitrification) were determined. Nitrate was added and thus not limiting in the incubations. In both cropping treatments, the 2–4mm aggregate size was the dominant size fraction (~35-45% of the soil by weight) followed by the 1-2mm size fraction (~20-25% of the soil by weight). Crop rotation increased both CO2 and N2O production (denitrification) and the proportion of <2mm diameter aggregates compared to continuous corn. For intact aggregates, CO2 production decreased with increasing aggregate size, while N2O production (denitrification) increased with increasing aggregate size. When the aggregates were ground, CO2 production was independent of the original aggregate size, while N2O production (denitrification) decreased as the size of the original aggregates increased. This study demonstrates that both the size distribution of natural soil aggregates and soil grinding can have substantial impacts on the CO2 and N2O production through denitrification.
  • Authors:
    • Gassman, P. W.
    • Kling, C. L.
    • Feng, H.
  • Source: Choices
  • Year: 2004
  • Summary: Capturing and storing carbon in biomass and soils in the agriculture and forest sector has gained widespread acceptance as a potential greenhouse gas mitigation strategy. Scientists increasingly understand the mechanisms by which various land-use practices can sequester carbon. Such practices include the introduction of cover crops on fallow land, the conversion of conventional tillage to conservation tillage, and the retirement of land from active production to a grass cover or trees. However, the policy design for implementing carbon sequestration activities is still being developed, and significant uncertainties remain concerning the cost effectiveness of carbon sequestration relative to other climate-change mitigation strategies.
  • Authors:
    • Frank, A. B.
  • Source: Environmental Management
  • Volume: 33
  • Issue: Supplement 1
  • Year: 2004
  • Summary: The large area occupied by temperate grassland ecosystems makes it important to determine their strength as a carbon sink. The Bowen ratio/energy balance (BREB) technique was used to determine CO 2 fluxes over a moderately grazed mixed-grass prairie at Mandan, North Dakota, USA, over a 6-year period from 1996 to 2001. Above-ground biomass and leaf area index (LAI) were measured about every 21 days throughout the growing period. Root biomass was determined to 1.1 m depth in mid-July each year. Peak above-ground biomass typically occurred between mid-July to early August and ranged from 782 kg/ha in 1998 to 2173 kg/ha in 1999. Maximum LAI ranged from 0.4 in 1998 to 0.9 in 1999. Root biomass ranged from 11.8 Mg/ha in 1997 to 17.4 Mg/ha in 1996. Maximum daily CO 2 fluxes generally coincided with periods of maximum LAI and above-ground green biomass. The average time period for CO 2 uptake was 5 May to 3 October. Annual CO 2 fluxes ranged from a low of 13 g CO 2/m 2 in 1998 to a high of 247 g CO 2/m 2 in 2001, nearly a 20-fold difference, and averaged 108 g CO 2/m 2. The cumulative annual flux over all 6 years was 646 g CO 2/m 2 or 176 g CO 2-C/m 2. These results indicate that the strength of the carbon sink for this moderately grazed prairie site is about 30 g CO 2-C/m 2/yr, which is quite small, but considering that the site was grazed and still remains a sink for carbon, it is significant.
  • Authors:
    • Li, C.
    • Lemke, R. L.
    • Desjardins, R. L.
    • Smith, W. N.
    • Grant, B.
  • Source: Climatic Change
  • Volume: 65
  • Issue: 3
  • Year: 2004
  • Summary: The Denitrification-Decompostion (DNDC) model was used to estimate the impact of change in management practices on N2O emissions in seven major soil regions in Canada, for the period 1970 to 2029. Conversion of cultivated land to permanent grassland would result in the greatest reduction in N2O emissions, particularly in eastern Canada where the model estimated about 60% less N2O emissions for this conversion. About 33% less N2O emissions were predicted for a change from conventional tillage to no-tillage in western Canada, however, a slight increase in N2O emissions was predicted for eastern Canada. Greater N2O emissions in eastern Canada associated with the adoption of no-tillage were attributed to higher soil moisture causing denitrification, whereas the lower emissions in western Canada were attributed to less decomposition of soil organic matter in no-till versus conventional tilled soil. Elimination of summer fallow in a crop rotation resulted in a 9% decrease in N2O emissions, with substantial emissions occurring during the wetter fallow years when N had accumulated. Increasing N-fertilizer application rates by 50% increased average emissions by 32%,while a 50% decrease of N-fertilizer application decreased emissions by16%. In general, a small increase in N2O emissions was predicted when N-fertilizer was applied in the fall rather than in the spring. Previous research on CO2 emissions with the CENTURY model (Smith et al.,2001) allowed the quantification of the combined change in N2O andCO2 emissions in CO2 equivalents for a wide range of management practices in the seven major soil regions in Canada. The management practices that have the greatest potential to reduce the combined N2O and CO2 emissions are conversion from conventional tillage to permanent grassland, reduced tillage, and reduction of summer fallow. The estimated net greenhouse gas (GHG) emission reduction when changing from cultivated land to permanent grassland ranged from 0.97 (Brown Chernozem) to 4.24 MgCO2 equiv. ha-1 y-1 (Black Chernozem) for the seven soil regions examined. When changing from conventional tillage to no-tillage the net GHG emission reduction ranged from 0.33 (Brown Chernozem) to 0.80 Mg CO2 equiv. ha-1 y-1 (Dark Gray Luvisol). Elimination of fallow in the crop rotation lead to an estimated net GHG emission reduction of 0.43 (Brown Chernozem) to 0.80 Mg CO2 equiv.ha-1 y-1 (Dark Brown Chernozem). The addition of 50% more or 50% less N-fertilizer both resulted in slight increases in combined CO2 and N2O emissions. There was a tradeoff in GHG flux with greater N2O emissions and a comparable increase in carbon storage when 50% more N-fertilizer was added. The results from this work indicate that conversion of cultivated land to grassland, the conversion from conventional tillage to no-tillage, and the reduction of summerfallow in crop rotations could substantially increase C sequestration and decrease net GHG emissions. Based on these results a simple scaling-up scenario to derive the possible impacts on Canada's Kyoto commitment has been calculated.
  • Authors:
    • Campbell,Sara
    • Mooney,Siân
    • Hewlett,John P.
    • Menkhaus,Dale J.
    • Vance,George F.
  • Source: Rangelands
  • Volume: 26
  • Issue: 4
  • Year: 2004
  • Summary: Carbon credits can be created on rangelands at costs that are competitive with credits from cropland and forestry, revealing that ranchers could play a role in reducing climate change.
  • Authors:
    • Tolbert, V. R.
    • Tolsted, D. N.
    • Isebrands, J. G.
    • Coleman, M. D.
  • Source: Environmental Management
  • Volume: 33
  • Issue: Supplement 1
  • Year: 2004
  • Summary: We collected soil samples from 27 study sites across North Central United States to compare the soil carbon of short rotation poplar plantations to adjacent agricultural crops and woodlots. Soil organic carbon (SOC) ranged from 20 to more than 160 Mg/ha across the sampled sites. Lowest SOC levels were found in uplands and highest levels in riparian soils. We attributed differences in bulk density and SOC among cover types to the inclusion of woodlot soils in the analysis. Paired comparison found few differences between poplar and agricultural crops. Sites with significant comparisons varied in magnitude and direction. Relatively greater SOC was often observed in poplar when native soil carbon was low, but there were important exceptions. Woodlots consistently contained greater SOC than the other crops, especially at depth. We observed little difference between paired poplar and switchgrass, both promising bioenergy crops. There was no evidence of changes in poplar SOC relative to adjacent agricultural soils when considered for stand ages up to 12 years. Highly variable native SOC levels and subtle changes over time make verification of soil carbon sequestration among land cover types difficult. In addition to soil carbon storage potential, it is therefore important to consider opportunities offered by long-term sequestration of carbon in solid wood products and carbon-offset through production of bioenergy crops. Furthermore, short rotation poplars and switchgrass offer additional carbon sequestration and other environmental benefits such as soil erosion control, runoff abatement, and wildlife habitat improvement.
  • Authors:
    • USDA-ARS
    • Clapp, C. E.
    • Linden, D. R.
    • Allmaras, R. R.
  • Source: Soil Science Society of America Journal
  • Volume: 68
  • Issue: 4
  • Year: 2004
  • Summary: Soil organic carbon (SOC) is sensitive to management of tillage, residue (stover) harvest, and N fertilization in corn (Zea mays L.), but little is known about associated root biomass including rhizodeposition. Natural C isotope abundance ({delta}13C) and total C content, measured in paired plots of stover harvest and return were used to estimate corn-derived SOC (cdSOC) and the contribution of nonharvestable biomass (crown, roots, and rhizodeposits) to the SOC pool. Rhizodeposition was estimated for each treatment in a factorial of three tillage treatments (moldboard, MB; chisel, CH; and no-till, NT), two N fertilizer rates (200 and 0 kg N ha-1), and two corn residue managements. Treatments influenced cdSOC across a wide range (6.8-17.8 Mg C ha-1). Nitrogen fertilization increased stover C by 20%, cdSOC by only 1.9 Mg C ha-1, and increased rhizodeposition by at least 110% compared with that with no N fertilizer. Stover harvest vs. stover return reduced total source carbon (SC) by 20%, cdSOC by 35%, and total SOC. The amount of stover source carbon (SSC) responded to tillage (MB > CH > NT), but tillage affected the amount of cdSOC differently (NT > CH > MB). Total SOC was maintained only by both N fertilization and stover return during the 13-yr period. The ratio of SC in the nonharvestable biomass to SSC ranged from 1.01 to 3.49; a ratio of 0.6 conforms to a root-to-shoot ratio of 0.4 when the root biomass includes 50% rhizodeposits. Tillage controlled the fraction of SC retained as cdSOC (i.e., humified; 0.26 for NT and 0.11 for MB and CH), even though N fertilization, stover harvest, and tillage all significantly influenced SC. Decomposition of labile rhizodeposits was a major component of the nonhumified fraction. Rhizodeposition was as much as three times greater than suggested by laboratory and other controlled studies. To understand and manage the entire C cycle, roots and rhizodeposition must be included in the analysis at the field level.
  • Authors:
    • Lindwall, W.
    • Kulshreshtha, S.
    • Desjardins, R.
    • Junkins, B.
    • Boehm, M.
  • Source: Climatic Change
  • Volume: 65
  • Issue: 3
  • Year: 2004
  • Summary: Net greenhouse gas (GHG) emissions from Canadian crop and livestock production were estimated for 1990, 1996 and 2001 and projected to 2008. Net emissions were also estimated for three scenarios (low (L), medium (M) and high (H)) of adoption of sink enhancing practices above the projected 2008 level. Carbon sequestration estimates were based on four sink-enhancing activities: conversion from conventional to zero tillage (ZT), reduced frequency of summerfallow (SF), the conversion of cropland to permanent cover crops (PC), and improved grazing land management (GM). GHG emissions were estimated with the Canadian Economic and Emissions Model for Agriculture (CEEMA). CEEMA estimates levels of production activities within the Canadian agriculture sector and calculates the emissions and removals associated with those levels of activities. The estimates indicate a decline in net emissions from 54 Tg CO2-Eq yr-1 in1990 to 52 Tg CO2-Eq yr-1 in 2008. Adoption of thesink-enhancing practices above the level projected for 2008 resulted in further declines in emissions to 48 Tg CO2-Eq yr-1 (L), 42 TgCO2-Eq yr-1 (M) or 36 Tg CO2-Eq yr-1 (H). Among the sink-enhancing practices, the conversion from conventional tillage to ZT provided the largest C sequestration potential and net reduction in GHG emissions among the scenarios. Although rates of C sequestration were generally higher for conversion of cropland to PC and adoption of improved GM, those scenarios involved smaller areas of land and therefore less C sequestration. Also, increased areas of PC were associated with an increase in livestock numbers and CH4 and N2O emissions from enteric fermentation andmanure, which partially offset the carbon sink. The CEEMA estimates indicate that soil C sinks are a viable option for achieving the UNFCCC objective of protecting and enhancing GHG sinks and reservoirs as a means of reducing GHG emissions (UNFCCC, 1992).
  • Authors:
    • Schoenau, J.
    • Mohr, R.
    • McLaren, D.
    • Irvine, R.
    • Derksen, D.
    • Monreal, M.
    • Grant, C.
  • Source: Better Crops with Plant Food
  • Volume: 88
  • Issue: 2
  • Year: 2004
  • Summary: Field experiments were conducted at the Research Centre and the Zero-Till Farm, Manitoba, Canada, during 1999-2000, 2000-01 and 2001-01, wherein rape and spring wheat were sown using conventional tillage (CT) and no-till (NT) in the first year of study. The crops were supplemented with 0, 22 or 44 lb P 2O 5/acre, side-banded at sowing. After rape and spring wheat harvest, the stubble in the CT plots was tilled. In the second year, flax was sown into both stubbled and tilled plots, and supplemented with P fertilizer side-banded at 0 or 44 lb P 2O 5/acre. The roots were evaluated for mycorrhizal association at 5 weeks of growth and seed yield was collected at crop maturity. The P nutrition of flax was most influenced by the preceding crop in rotation, while tillage system and P fertilizer management had minor impact on flax. Comparative data on the effect of P fertilizer application to current year flax, previous crop type and P fertilizer management, and tillage system on mycorrhiza incidence and flax seed yield are tabulated.