• Authors:
    • Paustian,Keith
    • Cole,C. Vernon
    • Sauerbeck,Dieter
    • Sampson,Neil
    • Peairs,F. B.
    • Bean,B.
    • Gossen,B. D.
  • Source: Agronomy Journal
  • Volume: 97
  • Issue: 2
  • Year: 2005
  • Summary: The intensification of traditional wheat (Triticum aestivum L.)-fallow production systems may have important consequences for management of insects, pathogens, and weeds in Great Plains dryland production systems. Assessment of these consequences is difficult due to the diversity of production systems, environmental conditions, and pests found in the region. Certain pest groups, such as weeds, traditionally controlled during the fallow period, may be favored by intensified cropping while others, such as those specializing on wheat, should be disadvantaged. Changes in pest and disease complexes will likely be evolutionary rather than revolutionary, as has been the case with other significant changes in production practices. Preventive practices in dryland production systems currently emphasize the control of grassy weeds while intensified systems may have less emphasis on the control of volunteer wheat. Crop rotation will remain a key avoidance strategy for pathogens and will help broaden herbicide options. Pest monitoring provides essential information on pest activity and environmental conditions and will become more complex as production systems are intensified. Important suppressive practices for dryland production systems include conservation biological control, tillage, and chemical controls. Chemical control, in particular, is expected to become more complicated due to drift concerns, rotational restrictions, the possible need for herbicide-tolerant crops, and the development of weed populations resistant to glyphosate. Pest management requirements should be considered during cropping system design and establishment.
  • Authors:
    • Traxler, G.
    • Qaim, M.
  • Source: Agricultural Economics
  • Volume: 32
  • Issue: 1
  • Year: 2005
  • Authors:
    • Ahuja, L. R.
    • Westfall, D. G.
    • Peterson, G. A.
    • Sherrod, L. A.
  • Source: Soil Science Society of America Journal
  • Volume: 69
  • Issue: 5
  • Year: 2005
  • Summary: Previous studies of no-till management in the Great Plains have shown that increased cropping intensity increased soil organic carbon (SOC). The objectives of this study were to (i) determine which soil C pools (active, slow, and passive) were impacted by cropping intensity after 12 yr of no-till across potential evapotranspiration (PET) and slope position gradients; (ii) relate C pool sizes to the levels found in total SOC; and (iii) determine C pool sizes relative to C levels found in a grass treatment (G). Cropping systems were wheat (Triticum aestivum)-fallow (WIT), wheat-corn (Zea mays L.)-fallow (WCF), wheat-corn-millet (Panicum miliaceum)-fallow (WCMF), and continuous cropping (CC) at three PET sites in Colorado. Active C (Soil microbial biomass C [SMBC]); and slow pool C (particulate organic matter C; POM-C) increased as cropping intensity increased, dependent on PET. Passive C (mineral associated organic C [MAOC]) was strongly influenced by a site-by-slope position interaction but not by cropping system. Toeslope soils had 35% higher POM-C compared with summits and sideslopes. All C pools were strongly correlated with total SOC, with the variability decreasing as C pool turnover time increased. Carbon pool sizes in cropping systems relative to levels found in G were independently influenced by cropping system. The highest were found in the CC system, which had 91, 78, and 90% of the amounts of C found in the perennial G system in the active, slow, and passive C pools, respectively.
  • Authors:
    • Burke, I. C.
    • McCulley, R. L.
    • Kaye, J. P.
  • Source: Global Change Biology
  • Volume: 11
  • Issue: 4
  • Year: 2005
  • Summary: Urban ecosystems are expanding globally, and assessing the ecological consequences of urbanization is critical to understanding the biology of local and global change related to land use. We measured carbon (C) fluxes, nitrogen (N) cycling, and soil microbial community structure in a replicated (n=3) field experiment comparing urban lawns to corn, wheat-fallow, and unmanaged shortgrass steppe ecosystems in northern Colorado. The urban and corn sites were irrigated and fertilized. Wheat and shortgrass steppe sites were not fertilized or irrigated. Aboveground net primary productivity (ANPP) in urban ecosystems (383 +/- 11 C m(-2) yr(-1)) was four to five times greater than wheat or shortgrass steppe but significantly less than corn (537 +/- 44 C m(-2) yr(-1)). Soil respiration (2777 +/- 273 g C m(-2) yr(-1)) and total belowground C allocation (2602 +/- 269 g C m(-2) yr(-1)) in urban ecosystems were both 2.5 to five times greater than any other land-use type. We estimate that for a large (1578 km(2)) portion of Larimer County, Colorado, urban lawns occupying 6.4% of the land area account for up to 30% of regional ANPP and 24% of regional soil respiration from land-use types that we sampled. The rate of N cycling from urban lawn mower clippings to the soil surface was comparable with the rate of N export in harvested corn (both similar to 12-15 g N m(-2) yr(-1)). A one-time measurement of microbial community structure via phospholipid fatty acid analysis suggested that land-use type had a large impact on microbial biomass and a small impact on the relative abundance of broad taxonomic groups of microorganisms. Our data are consistent with several other studies suggesting that urbanization of arid and semiarid ecosystems leads to enhanced C cycling rates that alter regional C budgets.
  • Authors:
    • Schuman, G. E.
    • Gollany, H. T.
    • Ellert, B. H.
    • Reeder, J. D.
    • Morgan, J. A.
    • Liebig, M. A.
  • Source: Soil & Tillage Research
  • Volume: 83
  • Issue: 1
  • Year: 2005
  • Summary: Concern over human impact on the global environment has generated increased interest in quantifying agricultural contributions to greenhouse gas fluxes. As part of a research effort called GRACEnet (Greenhouse Gas Reduction through Agricultural Carbon Enhancement Network), this paper summarizes available information concerning management effects on soil organic carbon (SOC) and carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) fluxes in cropland and rangeland in northwestern USA and western Canada, a region characterized by its inherently productive soils and highly variable climate. Continuous cropping under no-tillage in the region increased SOC by 0.27 ± 0.19 Mg C ha-1 yr-1, which is similar to the Intergovernmental Panel on Climate Change (IPCC) estimate for net annual change in C stocks from improved cropland management. Soil organic C sequestration potential for rangelands was highly variable due to the diversity of plant communities, soils, and landscapes, underscoring the need for additional long-term C cycling research on rangeland. Despite high variability, grazing increased SOC by 0.16 ± 0.12 Mg C ha-1 yr-1 and converting cropland or reclaimed mineland to grass increased SOC by 0.94 ± 0.86 Mg C ha-1 yr-1. Although there was generally poor geographical coverage throughout the region with respect to estimates of N2O and CH4 flux, emission of N2O was greatest in irrigated cropland, followed by non-irrigated cropland, and rangeland. Rangeland and non-irrigated cropland appeared to be a sink for atmospheric CH4, but the size of this sink was difficult to determine given the few studies conducted. Researchers in the region are challenged to fill the large voids of knowledge regarding CO2, N2O, and CH4 flux from cropland and rangeland in the northwestern USA and western Canada, as well as integrate such data to determine the net effect of agricultural management on radiative forcing of the atmosphere.
  • Authors:
    • Martin, R. C.
    • Patterson, G.
    • Fredeen, A.
    • Cohen, R. D. H.
    • Lynch, D. H.
  • Source: Canadian Journal of Soil Science
  • Volume: 85
  • Issue: 2
  • Year: 2005
  • Summary: The GrassGro model (a computer simulation of management-induced changes in range and pasture forage and livestock productivity) was combined with spreadsheet analyses to estimate the influence of improved grazing practices on soil organic carbon (SOC), and farm profitability, across native rangelands and tame pastures of the southern Canadian Prairies. Improved practices included complementary grazing (CG) and reduced stocking density (RSD) on rangeland; and N fertilization (FERT), seeded grass/legumes grazed continuously (GLGC) or rotationally (GLGR), and RSD on tame pastures. The analysis was stratified into three ecoregions on the basis of similarities in climate and soil type. Averaged over 30 yr and ecoregions, SOC rates of gain through improved management were 5 (RSD) to 26 (CG) kg C ha(-1) yr(-1) for rangelands, and 86 (RSD), 75 (GLGC), 62 (GLGR) and 222 (FERT) kg C ha(-1) yr(-1) for tame pastures. Gains with FERT were considered largely negated by associated energy (C) costs, N2O emissions, and shifts in grassland species. The CG system alone improved net returns to the producer. The estimated potential combined SOC gain on prairie grazinglands (11.5 Mha) was 1.63 MMT CO2 yr(-1) (or 0.465 MMT C yr(-1)), slightly less than the 1.70 MMT CO2 yr(-1) currently emitted from agricultural soils in Canada.
  • Authors:
    • Johnson, D. W.
    • Moeltner, K.
    • van Kooten, G. C.
    • Manley, J.
  • Source: Climatic Change
  • Volume: 68
  • Issue: 1-2
  • Year: 2005
  • Summary: Carbon terrestrial sinks are often seen as a low-cost alternative to fuel switching and reduced fossil fuel use for lowering atmospheric CO2. To determine whether this is true for agriculture, one meta-regression analysis (52 studies, 536 observations) examines the costs of switching from conventional tillage to no-till, while another (51 studies, 374 observations) compares carbon accumulation under the two practices. Costs per ton of carbon uptake are determined by combining the two results. The viability of agricultural carbon sinks is found to vary by region and crop, with no-till representing a low-cost option in some regions (costs of less than $10 per tC), but a high-cost option in others (costs of $100-$400 per tC). A particularly important finding is that no-till cultivation may store no carbon at all if measurements are taken at sufficient depth. In some circumstances no-till cultivation may yield a triple dividend of carbon storage, increased returns and reduced soil erosion, but in many others creating carbon offset credits in agricultural soils is not cost effective because reduced tillage practices store little or no carbon.
  • Authors:
    • Johnsen, T. N.
    • McLain, J. E. T.
    • Emmerich, W.
    • Martens, D. A.
  • Source: Soil & Tillage Research
  • Volume: 83
  • Issue: 1
  • Year: 2005
  • Summary: Agriculture in the southwestern USA is limited by water supply due to high evaporation and limited seasonal precipitation. Where water is available, irrigation allows for production of a variety of agricultural and horticultural crops. This review assesses the impacts of agriculture on greenhouse gas emission and sequestration of atmospheric C in soils of the hot, dry region of the southwestern USA. In Texas, conservation tillage increased soil organic C by 0.28 Mg C ha(-1) year(-1) compared with more intensive tillage. Conversion of tilled row crops to the conservation reserve program or permanent pastures increased soil organic C by 0.32 +/- 0.50 Mg C ha(-1) year(-1). Soil organic C sequestration was dependent on rotation, previous cropping, and type of conservation tillage employed. Relatively few studies have interfaced management and C cycling to investigate the impacts of grazing management on soil organic C, and therefore, no estimate of C balance was available. Irrigated crop and pasture land in Idaho had soil organic C content 10-40 Mg C ha(-1) greater than in dryland, native grassland. Soil salinity must be controlled in cropland as soil organic C content was lower with increasing salinity. Despite 75% of the region's soils being classified as calcic, the potential for sequestration of C as soil carbonate has been only scantly investigated. The region may be a significant sink for atmospheric methane, although in general, trace gas flux from semiarid soils lacks adequate characterization. Agricultural impacts on C cycling will have to be better understood in order for effective C sequestration strategies to emerge. Published by Elsevier B.V.
  • Authors:
    • Milbrandt, A.
  • Source: Technical Report
  • Year: 2005
  • Authors:
    • Sherrod, L.
    • Robertson, G. P.
    • Peterson, G. A.
    • Halvorson, A. D.
    • Mosier, A. R.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 72
  • Issue: 1
  • Year: 2005
  • Summary: When appraising the impact of food and fiber production systems on the composition of the Earth's atmosphere and the 'greenhouse' effect, the entire suite of biogenic greenhouse gases - carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) - needs to be considered. Storage of atmospheric CO2 into stable organic carbon pools in the soil can sequester CO2 while common crop production practices can produce CO2, generate N2O, and decrease the soil sink for atmospheric CH4. The overall balance between the net exchange of these gases constitutes the net global warming potential (GWP) of a crop production system. Trace gas flux and soil organic carbon (SOC) storage data from long-term studies, a rainfed site in Michigan that contrasts conventional tillage (CT) and no-till (NT) cropping, a rainfed site in northeastern Colorado that compares cropping systems in NT, and an irrigated site in Colorado that compares tillage and crop rotations, are used to estimate net GWP from crop production systems. Nitrous oxide emissions comprised 40-44% of the GWP from both rain-fed sites and contributed 16-33% of GWP in the irrigated system. The energy used for irrigation was the dominant GWP source in the irrigated system. Whether a system is a sink or source of CO2, i.e. net GWP, was controlled by the rate of SOC storage in all sites. SOC accumulation in the surface 7.5 cm of both rainfed continuous cropping systems was approximately 1100 kg CO2 equivalents ha-1 y-1. Carbon accrual rates were about three times higher in the irrigated system. The rainfed systems had been in NT for >10 years while the irrigated system had been converted to NT 3 years before the start of this study. It remains to be seen if the C accrual rates decline with time in the irrigated system or if N2O emission rates decline or increase with time after conversion to NT.