• Authors:
    • Potter, K. N.
  • Source: Journal of Soil and Water Conservation
  • Volume: 61
  • Issue: 6
  • Year: 2006
  • Summary: Management's effects on soil physical properties can be difficult to determine because there is often no fixed starting point. Soil organic carbon was determined for central Texas Vertisols (Udic Haplusterts) on archived samples from 1949 and samples taken in 2004. Management records were used to interpret the data. Five fields were sampled, representing an untilled native pasture, two previously titled soils which had been planted to Bermuda grass (Cynodon dactylon (L.) Pets.) for 55 and 39 years before the 2004 sampling period, and two fields which had been continuously cropped for nearly the entire 55 year time interval. Soil organic carbon was determined for depth increments of 0 to 15, 15 to 30, 30 to 60, 60 to 90 and 90 to 105 cm (cl to 6, 6 to 12, 12 to 24, 24 to 36 and 36 to 42 in). The titled soils had been seriously degraded of organic carbon by agricultural activities prior to 1949 compared to the native pasture soil. Soil carbon concentration in croplands had decreased from greater than five percent near the surface of native grasslands to less than one percent in croplands. Agricultural practices since 1949 have increased soil carbon concentration in the surface 15 cm (6 in) to 1.45 percent in croplands and 2.09 percent in restored grasslands. Returning the soils to grass production increased soil surface carbon contents at a faster rate than the conventional agricultural practices. Having archived samples greatly aided in interpreting the effects on management on the soil. It appears that previous estimates of carbon sequestration rates for the Vertisols may have been under estimated by comparative studies of no-tilt and conventional tillage practices.
  • Authors:
    • Derner, J. D.
    • Potter, K. N.
  • Source: Journal of Soil and Water Conservation
  • Volume: 61
  • Issue: 3
  • Year: 2006
  • Summary: Establishment of perennial grasses on degraded soils has been suggested as a means to improve soil quality and sequester carbon in the soil. Particulate organic carbon may be an important component in the increased soil carbon content. We measured particulate organic carbon [defined as organic carbon in the 53 to 2000 PM (0.002 to o.o8 in) size fraction] and mineral associated organic carbon (defined as the less than 53 PM (0.002 in) size fraction) at three locations in central Texas. Each location had a never-tilled native grassland site, a long-term agricultural site and a restored grassland on a previously tilled site. Organic carbon pool sizes varied in the surface 40 cm (16 in) of native grassland, restored grasslands and agricultural soils. The native grasslands contained the largest amounts of total organic carbon, while the restored grasslands and agricultural soils contained similar amounts of total organic carbon. Both particulate organic carbon and mineral associated carbon pools were reduced beyond the depth of tillage in the restored grass and agricultural soils compared to the native grassland soils. The restored grassland soils had a larger particulate organic carbon content than the agricultural soils, but the increase in particulate organic carbon was limited to the surface 5 cm (2 in) of soil. Trends in particulate organic carbon accumulation over time from nine to 30 years were not significant in this study.
  • Authors:
    • Kimble, J. M.
    • McCarty, G. W.
    • Follett, R. F.
    • Reeves, J. B.
  • Source: Communications in Soil Science and Plant Analysis
  • Volume: 37
  • Issue: 15-20
  • Year: 2006
  • Summary: The objective of this study was to compare mid-infrared (MIR) an near-infrared (NIR) spectroscopy (MIRS and NIRS, respectively) not only to measure soil carbon content, but also to measure key soil organic C (SOC) fractions and the delta13C in a highly diverse set of soils while also assessing the feasibility of establishing regional diffuse reflectance calibrations for these fractions. Two hundred and thirty-seven soil samples were collected from 14 sites in 10 western states (CO, IA, MN, MO, MT, ND, NE, NM, OK, TX). Two subsets of these were examined for a variety of C measures by conventional assays and NIRS and MIRS. Biomass C and N, soil inorganic C (SIC), SOC, total C, identifiable plant material (IPM) (20x magnifying glass), the ratio of SOC to the silt+clay content, and total N were available for 185 samples. Mineral-associated C fraction, delta13C of the mineral associated C, delta13C of SOC, percentage C in the mineral-associated C fraction, particulate organic matter, and percentage C in the particulate organic matter were available for 114 samples. NIR spectra (64 co-added scans) from 400 to 2498 nm (10-nm resolution with data collected every 2 nm) were obtained using a rotating sample cup and an NIRSystems model 6500 scanning monochromator. MIR diffuse reflectance spectra from 4000 to 400 cm-1 (2500 to 25,000 nm) were obtained on non-KBr diluted samples using a custom-made sample transport and a Digilab FTS-60 Fourier transform spectrometer (4-cm-1 resolution with 64 co-added scans). Partial least squares regression was used with a one-out cross validation to develop calibrations for the various analytes using NIR and MIR spectra. Results demonstrated that accurate calibrations for a wide variety of soil C measures, including measures of delta13C, are feasible using MIR spectra. Similar efforts using NIR spectra indicated that although NIR spectrometers may be capable of scanning larger amounts of samples, the results are generally not as good as achieved using MIR spectra.
  • Authors:
    • Parrish, D. J.
    • Ebinger, M. H.
    • Lal, R.
    • Sartori, F.
  • Source: Critical Reviews in Plant Sciences
  • Volume: 25
  • Issue: 5
  • Year: 2006
  • Summary: Energy crops are fast-growing species whose biomass yields are dedicated to the production of more immediately usable energy forms, such as liquid fuels or electricity. Biomass-based energy sources can offset, or displace, some amount of fossil-fuel use. Energy derived from biomass provides 2 to 3% of the energy used in the U.S.A.; but, with the exception of corn-(Zea mays L.)-to-ethanol, very little energy is currently derived from dedicated energy crops. In addition to the fossil-fuel offset, energy cropping might also mitigate an accentuated greenhouse gas effect by causing a net sequestration of atmospheric C into soil organic C (SOC). Energy plantations of short-rotation woody crops (SRWC) or herbaceous crops (HC) can potentially be managed to favor SOC sequestration. This review is focused primarily on the potential to mitigate atmospheric CO2 emissions by fostering SOC sequestration in energy cropping systems deployed across the landscape in the United States. We know that land use affects the dynamics of the SOC pool, but data about spatial and temporal variability in the SOC pool under SRWC and HC are scanty due to lack of well-designed, long-term studies. The conventional methods of studying SOC fluxes involve paired-plot designs and chronosequences, but isotopic techniques may also be feasible in understanding temporal changes in SOC. The rate of accumulation of SOC depends on land-use history, soil type, vegetation type, harvesting cycle, and other management practices. The SOC pool tends to be enhanced more under deep-rooted grasses, N-fixers, and deciduous species. Carbon sequestration into recalcitrant forms in the SOC pool can be enhanced with some management practices (e.g., conservation tillage, fertilization, irrigation); but those practices can carry a fossil-C cost. Reported rates of SOC sequestration range from 0 to 1.6 Mg C ha(-1) yr(-1) under SRWC and 0 to 3 Mg C ha(-1) yr(-1) under HC. Production of 5 EJ of electricity from energy crops-a perhaps reasonable scenario for the U.S.A.-would require about 60 Mha. That amount of land is potentially available for conversion to energy plantations in the U.S.A. The land so managed could mitigate C emissions (through fossil C not emitted and SOC sequestered) by about 5.4 Mg C ha(-1) yr(-1). On 60 Mha, that would represent 324 Tg C yr(-1)-a 20% reduction from current fossil-fuel CO2 emissions. Advances in productivity of fast-growing SRWC and HC species suggest that deployment of energy cropping systems could be an effective strategy to reduce climate-altering effects of anthropogenic CO2 emissions and to meet global policy commitments.
  • Authors:
    • Deregibus, V. A.
    • Bartoloni, N.
    • Rodriguez, A. M.
    • Jacobo, E. J.
  • Source: Rangeland Ecology & Management
  • Volume: 59
  • Issue: 3
  • Year: 2006
  • Summary: We evaluated the adequacy of rotational grazing to improve rangeland condition in the Flooding Pampa region, eastern Argentina, comparing the floristic composition dynamic of the 2 main plant communities under rotational and continuous grazing over a study period of 4 years (1993-1996). The experiment was conducted in commercial farms located in 4 sites of the Flooding Pampa region. In each site, a couple of farms, one managed under rotational grazing (implemented in 1989) and an adjacent one managed under continuous grazing at a similar stocking rate (1 AU(.)ha(-1)), constituted the replications of the experiment. Basal cover of species, litter, and bare soil were monitored in midslope and lowland grassland communities on each farm. Total plant basal cover in midslope and in lowland communities remained unchanged over the whole experimental period under both grazing methods. Under rotational grazing, litter cover was higher in both communities while the amount of bare soil showed a significant reduction in lowlands and a tendency to be lower in midslope. Basal cover of legumes, C-3 annual and C-3 perennial grasses was higher, while cover of C-4 prostrate grasses was lower under rotational grazing in the midslope community. In the lowland community, rotational grazing effects were evident only in the drier years, when higher cover of hydrophytic grasses and legumes and lower cover of forbs occurred. Plant species diversity did not change in response to grazing. In conclusion, rotational grazing promoted functional groups composed of high forage value species and reduced bare soil through the accumulation of litter. These changes indicate an improvement in rangeland condition and in carrying capacity. As the stocking rate was approximately 60% higher than the average stocking rate of the Flooding Pampa region, we believe that productivity and sustainability may be compatible by replacing continuous with rotational grazing.
  • Authors:
    • Perez, A.
    • Ali, M.
    • Pollack, S.
    • Lucier, G.
  • Year: 2006
  • Summary: The U.S. fruit and vegetable industry accounts for nearly a third of U.S. crop cash receipts and a fifth of U.S. agricultural exports. A variety of challenges face this complex and diverse industry in both domestic and international markets, ranging from immigration reform and its effect on labor availability to international competitiveness. The national debate on diet and health frequently focuses on the nutritional role of fruit and vegetables, and a continued emphasis on the benefits of eating produce may provide opportunities to the industry. In the domestic market, Americans are eating more fruit and vegetables than they did 20 years ago, but consumption remains below recommended levels. In terms of per capita consumption expressed on a fresh-weight basis, the top five vegetables are potatoes, tomatoes, lettuce, sweet corn, and onions while the top five fruit include oranges, grapes (including wine grapes), apples, bananas, and pineapples. The industry also faces a variety of trade-related issues, including competition with imports. During 2002-04, imports accounted for 21 percent of domestic consumption of all fresh and processed fruit and vegetables, up from 16 percent during 1992-94.
  • Authors:
    • Giardini, L.
    • Berti, A.
    • Lugato, E.
  • Source: Geoderma
  • Volume: 135
  • Year: 2006
  • Summary: Crop residue incorporation is recognised as a simple way to increase C input into the soil, with positive effects on C sequestration from the atmosphere. However, in some long-term experiments, a lack of response to soil C input levels has been observed as a consequence of saturation phenomena and/or interactions between C input and fertilisation. This paper analyses the outcomes of a long-term experiment in north-eastern Italy that started in 1966 and is still ongoing, where residue incorporation is compared with residue removal, over a range of mineral N fertilisations. A general decrease of SOC content was observed in the first 10 years of the experiment, followed by an approach to a steady state. However, SOC content differed markedly according to residue management and, in plots with residue incorporation, to N fertilisation. Considering 20 years as a compromise period for reaching a new equilibrium after a land-use change, the sequestration rate of residue incorporation in comparison with removal resulted as 0.17 t ha-1 of C per year. The measured data were then simulated with Century, a model based on first-order decomposition kinetic, to evaluate if the data could be interpreted by this kind of decomposition process. Model performances were good in most cases, but overestimated SOC decomposition in the more limiting situations for C and N inputs. A possible explanation is given for this behaviour, involving a feed-back effect of the microbial community.
  • Authors:
    • Wander, M.
    • Marriott, E. E.
  • Source: Soil Biology and Biochemistry
  • Volume: 38
  • Issue: 7
  • Year: 2006
  • Authors:
    • McLauchlan, K.
  • Source: Ecosystems
  • Volume: 9
  • Issue: 8
  • Year: 2006
  • Summary: Since the domestication of plant and animal species around 10,000 years ago, cultivation and animal husbandry have been major components of global change. Agricultural activities such as tillage, fertilization, and biomass alteration lead to fundamental changes in the pools and fluxes of carbon (C), nitrogen (N), and phosphorus (P) that originally existed in native ecosystems. Land is often taken out of agricultural production for economic, social, or biological reasons, and the ability to predict the biogeochemical trajectory of this land is important to our understanding of ecosystem development and our projections of food security for the future. Tillage generally decreases soil organic matter (SOM) due to erosion and disruption of the physical, biochemical, and chemical mechanisms of SOM stabilization, but SOM can generally reaccumulate after the cessation of cultivation. The use of organic amendments causes increases in SOM on agricultural fields that can last for centuries to millennia after the termination of applications, although the locations that provide the organic amendments are concurrently depleted. The legacy of agriculture is therefore highly variable on decadal to millennial time scales and depends on the specific management practices that are followed during the agricultural period. State factors such as climate and parent material (particularly clay content and mineralogy) modify ecosystem processes such that they may be useful predictors of rates of postagricultural biogeochemical change. In addition to accurate biogeochemical budgets of postagricultural systems, ecosystem models that more explicitly incorporate mechanisms of SOM loss and formation with agricultural practices will be helpful. Developing this predictive capacity will aid in ecological restoration efforts and improve the management of modern agroecosystems as demands on agriculture become more pressing.
  • Authors:
    • Young, G.
    • Stuth, J.
    • Rauzi, S.
    • Peterson, T.
    • Pawar, R.
    • Kobos, P.
    • Mankin, C.
    • Leppin, D.
    • Lee, R.
    • Kim, E.
    • Hughes, R.
    • Guthrie, G.
    • Cappa, J.
    • Brown, J.
    • Biediger, B.
    • Allis, R.
    • McPherson, B.
  • Year: 2006
  • Summary: The Southwest Partnership on Carbon Sequestration completed its Phase I program in December 2005. The main objective of the Southwest Partnership Phase I project was to evaluate and demonstrate the means for achieving an 18% reduction in carbon intensity by 2012. Many other goals were accomplished on the way to this objective, including (1) analysis of CO2 storage options in the region, including characterization of storage capacities and transportation options, (2) analysis and summary of CO2 sources, (3) analysis and summary of CO2 separation and capture technologies employed in the region, (4) evaluation and ranking of the most appropriate sequestration technologies for capture and storage of CO2 in the Southwest Region, (5) dissemination of existing regulatory/permitting requirements, and (6) assessing and initiating public knowledge and acceptance of possible sequestration approaches. Results of the Southwest Partnership's Phase I evaluation suggested that the most convenient and practical "first opportunities" for sequestration would lie along existing CO2 pipelines in the region. Action plans for six Phase II validation tests in the region were developed, with a portfolio that includes four geologic pilot tests distributed among Utah, New Mexico, and Texas. The Partnership will also conduct a regional terrestrial sequestration pilot program focusing on improved terrestrial MMV methods and reporting approaches specific for the Southwest region. The sixth and final validation test consists of a local-scale terrestrial pilot involving restoration of riparian lands for sequestration purposes. The validation test will use desalinated waters produced from one of the geologic pilot tests. The Southwest Regional Partnership comprises a large, diverse group of expert organizations and individuals specializing in carbon sequestration science and engineering, as well as public policy and outreach. These partners include 21 state government agencies and universities, five major electric utility companies, seven oil, gas and coal companies, three federal agencies, the Navajo Nation, several NGOs, and the Western Governors Association. This group is continuing its work in the Phase II Validation Program, slated to conclude in 2009.