• Authors:
    • Grace, P. R.
    • Post, W. M.
    • Hennessy, K.
  • Source: Carbon Balance and Management
  • Volume: 1
  • Year: 2006
  • Authors:
    • Chapman, D.
    • Johnson, I.
    • Eckard, R.
  • Source: International Congress Series
  • Volume: 1293
  • Year: 2006
  • Authors:
    • Valdes, G. S. B.
    • Lee, H. C.
    • Cook, H. F.
  • Source: Soil & Tillage Research
  • Volume: 91
  • Issue: 1-2
  • Year: 2006
  • Summary: Application of organic amendment to the soil surface is widely used in order to ameliorate topsoil physical conditions, especially with respect to temperature, evaporation and water content. Water intercepted by mulch and crop canopy involves loss through evaporation that never replenishes the soil water. In this study, hydrological and temperature conditions beneath mulches of manufactured materials, organic waste, wheat straw ( Triticum aestivum L.) and soybean straw ( Glycine max L. Merrill) applied at different thickness were investigated in glasshouse and field conditions in southern England. Interception loss by a maize ( Zea mays L.) canopy and mulch modified the soil water balance by adversely affecting soil water content beneath thicker application. Mulching had a beneficial effect on soil water and temperature regimes. These findings are important for identifying mulching practices for dryland agriculture and under scenarios of climatic change that predict lower rainfall and higher temperatures in summer.
  • 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:
    • 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:
    • Zwart, K.
    • Smit, A.
    • van der Hoek, K. W.
    • Kuikman, P. J.
  • Year: 2006
  • Summary: Emissions of nitrous oxide (N2O) in the Netherlands are reported to the UNFCCC on the basis of a country specific methodology. In this study we have identified and anlysed the values for emission facotrs in measurement from in the Netherlands in the period 1993 - 2003. The overall averaged emission factor extracted from over 86 series of one year measurements on nitrous oxide emission from agricultural fields in the Netherlands is 1.1% and a weighed average for soil types is 1.01%. The average for mineral soils is 0.88%. The calculated emissions factors are lower than the value suggested by the IPCC for EF1 for fertilizer and animal manure of 1.25%. We recommend to use a value of 1.0% for EF1 and to use corrections of EF1 in reporting the use of fertilizers without nitrate (0.5%), for subsurface application of manure (1.5%) and for fertilizer, manure and urine on organic soils (2.0%).
  • Authors:
    • Rolston, D. E.
    • van Kessel, C.
    • King, A. P.
    • Six, J.
    • Lee, J.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Issue: 3
  • Year: 2006
  • Summary: There is a lack of understanding of how associations among soil properties and management-induced changes control the variability of greenhouse gas (GHG) emissions from soil. We performed a laboratory investigation to quantify relationships between GHG emissions and soil indicators in an irrigated agricultural field under standard tillage (ST) and a field recently converted (2 yr) to no-tillage (NT). Soil cores (15-cm depth) were incubated at 25{degrees}C at field moisture content and 75% water holding capacity. Principal component analysis (PCA) identified that most of the variation of the measured soil properties was related to differences in soil C and N and soil water conditions under ST, but soil texture and bulk density under NT. This trend became more apparent after irrigation. However, principal component regression (PCR) suggested that soil physical properties or total C and N were less important in controlling GHG emissions across tillage systems. The CO2 flux was more strongly determined by microbial biomass under ST and inorganic N content under NT than soil physical properties. Similarly, N2O and CH4 fluxes were predominantly controlled by NO3- content and labile C and N availability in both ST and NT soils at field moisture content, and NH4+ content after irrigation. Our study indicates that the field-scale variability of GHG emissions is controlled primarily by biochemical parameters rather than physical parameters. Differences in the availability and type of C and N sources for microbial activity as affected by tillage and irrigation develop different levels and combinations of field-scale controls on GHG emissions.
  • Authors:
    • O'Mara, F. P.
    • Dillon, P.
    • Shalloo, L.
    • Lovett, D. K.
  • Source: Agricultural Systems
  • Volume: 88
  • Issue: 2-3
  • Year: 2006
  • Summary: A model was developed to determine what effect management practices would have on the production of the greenhouse gases (GHG) within pastorally based dairy production systems typical of those practiced in Ireland. The model simulates two levels of GHG emissions, firstly the on-farm GHG emissions of methane, nitrous oxide and carbon dioxide for example from the pastorally spreading of slurry and secondly, off-farm GHG emissions associated with both inputs brought onto the farm to maintain productivity (for example emissions arising from manufacture of concentrate feeds and fertiliser) as well as from indirect GHG emissions associated with nitrate leaching and ammonia. The aim of this work was to allow the development of effective GHG mitigation strategies at the farm level capable of reducing GHG emissions per litre of milk. Greenhouse gas emissions were modelled for nine farming systems differing in the level of concentrate supplementation (376, 810 and 1540 kg per cow per lactation) and genotype for milk production as assessed by their pedigree index (<100, 100-200 and 200-300 kg) of milk production. A three-year study to evaluate the influence of cow genetic potential for milk production and concentrate supplementation level on profitability of pasture-based systems of milk production was used to drive the Moorepark Dairy Systems Model (MDSM). Output from this model then described farm size, feed budgets, animal numbers and farm profitability when annual milk quota was set to 468,000 kg of milk year. Relating GHG emissions to annual milk sales revealed that for these pastorally based systems increasing concentrate usage reduced both on-farm and off-farm emissions, but that increasing the genotype of the dairy cow (i.e., the genetic capacity of the animal to produce milk) will increase both on-farm and off-farm GHG emissions. Lowest GHG emissions per kilogram of milk were achieved for an intermediate genotype type cow fed within a high concentrate system whilst the highest emissions were associated with high genotype cows fed within a low concentrate system. Maximum profitability was obtained when either a high concentrate feeding regime was combined with high genotype cows or where low concentrate systems were fed to low genotype cows. Relating farm profitability to GHG emissions allowed the identification of scenarios where changing from one management systems to another would achieve a simultaneous reduction in GHG emissions whilst improving farm profitability. By implementing this approach of assessing management induced change on both GHG emissions arising from the farm together with farm profitability, individual whole farm GHG mitigation strategies could be developed with a high degree of acceptability to the producer.
  • 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.