• Authors:
    • Pookpakdi, A.
    • Juntakool, S.
    • Suwanketnikom, R.
    • Chinawong, S.
    • Woldetsadik, G.
  • Source: Kasetsart Journal: Natural Science
  • Volume: 39
  • Issue: 1
  • Year: 2005
  • Summary: A field experiment was conducted during the rainy season of 2003 to study the effects of nitrogen rates (0, 10, 20 and 30 kg/ha) and moisture conservation practices (flat bed, ridge furrow, flat bed + mulching and ridge furrow + mulching) on the soil, soil water, yield and yield components of maize ( Zea mays) grown in a rift valley in central Ethiopia. Grain yield was affected by nitrogen fertilizer levels but 1000-grain weight, total biomass, straw yield, soil temperature, soil moisture content, and infiltration rate were not affected by the nitrogen rates. Significant effects in harvest index and water use efficiency of nitrogen rates were observed only at Dera and Melkassa, respectively. Moisture conservation practices improved grain and straw yields, harvest index, and total biomass compared to the use of flat beds due to the availability of moisture. Bulk density, infiltration rate, water use efficiency, and soil moisture content were also affected by moisture conservation practices. Mulching reduced soil temperature prior to maize maturity.
  • Authors:
    • Plaixats, J.
    • Bartolome, J.
    • Fanlo, R.
    • Boada, M.
  • Source: Biological Conservation
  • Volume: 122
  • Issue: 1
  • Year: 2005
  • Summary: In the Mediterranean region, cycles of controlled burning combined with continuous grazing appear to have been an effective tool for maintaining isolated Calluna vulgaris heathlands in the form in which they occur in many places in the Atlantic region. Changes in land use and management of the mosaic of extensively exploited heathland and associated grassland over recent decades, such as bringing land into cultivation followed by its abandonment and the prohibition of fires has resulted in a process of transformation into new shrub communities with lower biodiversity. In the Mediterranean region, these changes are similar to those described in the Atlantic area, but encroachment occurs faster and could lead ultimately to afforestation by Mediterranean woodland. In a study area of 300 ha of heathland in the Spanish Mediterranean basin (specifically, in the Montseny Natural Park and Biosphere Reserve), comparison of present and former vegetation showed that shrub cover increased from 15% in 1967 to 32% in 2000. Broom (Cytisus scoparius) was the main invasive species in abandoned crop fields, whereas Mediterranean holm oak forest (Quercus ilex) increased by 18%. The surface area of fernlands doubled and C. vulgaris heathlands decreased from 35% to just 9% during the same period. Intermixed grasslands also decreased moderately and progressively from 4% to 3%. It seems probable that cycles of fires are more important in terms of shrub control and biodiversity conservation than continuous grazing alone, even at a high rate of stocking (four small ruminants per hectare per year). This encroachment process throws into relief the role that isolated habitats can play as a monitor of land use changes. (C) 2004 Elsevier Ltd. All rights reserved.
  • Authors:
    • Weise, D. R.
    • Schreuder, M. D.
    • Wiitala, M. A.
    • Schaaf, M. D.
  • Source: Proceedings of the Second International Symposium on Fire Economics, Planning, and Policy: A Global View
  • Year: 2004
  • Summary: In this study, the Fire Effects Tradeoff Model (FETM) was used to evaluate the economic tradeoffs between fuels treatment and fire suppression on the Angeles National Forest located in southern California of the United States. FETM uses historical weather data, fire history data, current vegetation maps, prescribed-fire planning data, fuels treatment and wildfire costs and benefits, and surface and stand composition data to simulate the future annual wildland fire area burned, landscape composition, smoke emissions, and the present net value of fire suppression and fuels treatment over any time period. Five fire suppression and fuels treatment alternatives were evaluated, combining one of two fire suppression program options with five prescribed-fire intensities ranging from 0 to 52 percent of the available chaparral area per decade. Our results show that maintaining a larger suppression program with a low level of fuels treatment substantially reduces the wildfire area burned. However, the increased costs associated with this program are not met with a commensurate reduction in resource loss and suppression costs. Similarly, our results show that a smaller fire suppression program coupled with an aggressive prescribed-fire treatment option substantially reduces the wildfire area burned, but the increased costs of treatment are likewise not met with a commensurate reduction in resource loss and suppression costs. We found instead that a smaller and less costly fire suppression program, matched with a moderate intensity fuels treatment program targeting only the highest loading classes of chaparral, provides the most cost-beneficial fire protection strategy for the study area.
  • Authors:
    • Ismail, S.
    • Sharrow, S. H.
  • Source: Agroforestry Systems
  • Volume: 60
  • Issue: 2
  • Year: 2004
  • Summary: Pastures store over 90% of their carbon and nitrogen below-ground as soil organic matter. In contrast, temperate conifer forests often store large amounts of organic matter above-ground in woody plant tissue and fibrous litter. Silvopastures, which combine managed pastures with forest trees, should accrete more carbon and nitrogen than pastures or timber plantations because they may produce more total annual biomass and have both forest and grassland nutrient cycling patterns active. This hypothesis was investigated by conducting carbon and nitrogen inventories on three replications of 11 year-old Douglas-fir (Pseudotsuga menziesii)/perennial ryegrass (Lolium perenne)/subclover (Trifolium subterraneum) agroforests, ryegrasss/subclover pastures, and Douglas-fir timber plantations near Corvallis, Oregon in August 2000. Over the 11 years since planting, agroforests accumulated approximately 740 kg ha^-1 year^-1 more C than forests and 520 kg ha^-1 year^-1 more C than pastures. Agroforests stored approximately 12% of C and 2% of N aboveground compared to 9% of C and 1% of N above ground in plantations and less than 1% of N and C aboveground in pastures. Total N content of agroforests and pastures, both of which included a nitrogen-fixing legume, were approximately 530 and 1200 kg ha^-1 greater than plantations, respectively. These results support the proposition that agroforests, such as silvopastures, may be more efficient at accreting C than plantations or pasture monocultures. However, pastures may accrete more N than agroforests or plantations. This apparent separation of response in obviously interrelated agroecosystem processes, points out the difficulty in using forest plantation or pasture research results to predict outcomes for mixed systems such as agroforests.
  • Authors:
    • Vine, E.
  • Source: Mitigation and Adaptation Strategies for Global Change
  • Volume: 9
  • Issue: 1
  • Year: 2004
  • Summary: Carbon C sequestration in terrestrial ecosystems and geologic formations provides a significant opportunity for California to address global climate change. The physical size of its resources (e.g., forests, agriculture, soils, rangeland, and geologic formations) and the expertise in California provides a substantial foundation for developing C sequestration activities. Furthermore, the co-benefits c sequestration - such as improved soil and water quality, restoration of degraded ecosystems, increased plant and crop productivity, and enhanced oil recovery - are significant. In fact, C sequestration often represents a "no regrets" strategy - implementing C sequestration provides multiple benefits, even without the advent of global climate change. Nevertheless, researchers need to address several issues to determine more accurately the potential, benefits, and costs of sequestering C in California's terrestrial ecosystems and geologic formations, as well as to identify the most promising sequestration methods and their optimal implementation. One key issue is the type of regulatory constraints facing developers of C sequestration projects: what permits are needed for developing these projects? The permitting process may impede the penetration of sequestration technologies into the market if the costs (including transaction costs) of obtaining the permits are too burdensome and costly. For example, at least nine federal regulations and seven state regulations will potentially influence C sequestration projects in California. This paper also provides an example of the types of permits needed for developing a C sequestration project, using California as an example. It is possible that a C sequestration project may have to obtain a total of 15 permits (3 federal, 6 state, 6 local), before it even starts to operate. In the concluding section, we offer some suggested areas for research and activities for policy makers.
  • Authors:
    • Dale, B. E.
    • Kim, S.
  • Source: Biomass and Bioenergy
  • Volume: 26
  • Issue: 4
  • Year: 2004
  • Summary: The global annual potential bioethanol production from the major crops, corn, barley, oat, rice, wheat, sorghum, and sugar cane, is estimated. To avoid conflicts between human food use and industrial use of crops, only the wasted crop, which is defined as crop lost in distribution, is considered as feedstock. Lignocellulosic biomass such as crop residues and sugar cane bagasse are included in feedstock for producing bioethanol as well. There are about 73:9 Tg of dry wasted crops in the world that could potentially produce 49:1 GL year-1 of bioethanol. About 1:5 Pg year-1 of dry lignocellulosic biomass from these seven crops is also available for conversion to bioethanol. Lignocellulosic biomass could produce up to 442 GL year-1 of bioethanol. Thus, the total potential bioethanol production from crop residues and wasted crops is 491 GL year-1, about 16 times higher than the current world ethanol production. The potential bioethanol production could replace 353 GL of gasoline (32% of the global gasoline consumption) when bioethanol is used in E85 fuel for a midsize passenger vehicle. Furthermore, lignin-rich fermentation residue, which is the coproduct of bioethanol made from crop residues and sugar cane bagasse, can potentially generate both 458 TWh of electricity (about 3.6% of world electricity production) and 2:6EJ of steam. Asia is the largest potential producer of bioethanol from crop residues and wasted crops, and could produce up to 291 GL year -1 of bioethanol. Rice straw, wheat straw, and corn stover are the most favorable bioethanol feedstocks in Asia. The next highest potential region is Europe (69:2 GL ofbioethanol), in which most bioethanol comes from wheat straw. Corn stover is the main feedstock in North America, from which about 38:4 GL year -1 of bioethanol can potentially be produced. Globally rice straw can produce 205 GL of bioethanol, which is the largest amount from single biomass feedstock. The next highest potential feedstock is wheat straw, which can produce 104 GL of bioethanol. This paper is intended to give some perspective on the size ofthe bioethanol feedstock resource, globally and by region, and to summarize relevant data that we believe others will 0nd useful, for example, those who are interested in producing biobased products such as lactic acid, rather than ethanol, from crops and wastes. The paper does not attempt to indicate how much, if any, of this waste material could actually be converted to bioethanol.
  • Authors:
    • Paustian, K.
    • Eve, M.
    • Sperow, M.
  • Source: Climatic Change
  • Volume: 57
  • Issue: 3
  • Year: 2003
  • Summary: Soil carbon sequestration has been suggested as a means to help mitigate atmospheric CO2 increases, however there is limited knowledge aboutthe magnitude of the mitigation potential. Field studies across the U.S. provide information on soil C stock changes that result from changes in agricultural management. However, data from such studies are not readily extrapolated to changes at a national scale because soils, climate, and management regimes vary locally and regionally. We used a modified version of the Intergovernmental Panel on Climate Change (IPCC) soil organic C inventory method, together with the National Resources Inventory (NRI) and other data, to estimate agricultural soil C sequestration potential in the conterminous U.S. The IPCC method estimates soil C stock changes associated with changes in land use and/or land management practices. In the U.S., the NRI provides a detailed record of land use and management activities on agricultural land that can be used to implement the IPCC method. We analyzed potential soil C storage from increased adoption of no-till, decreased fallow operations, conversion of highly erodible land to grassland, and increased use of cover crops in annual cropping systems. The results represent potentials that do not explicitly consider the economic feasibility of proposed agricultural production changes, but provide an indication of the biophysical potential of soil C sequestration as a guide to policy makers. Our analysis suggests that U.S. cropland soils have the potential to increase sequestered soil C by an additional 60–70 Tg (1012g) C yr-1, over present rates of 17 Tg C yr-1 (estimated using the IPCC method), with widespread adoption of soil C sequestering management practices. Adoption of no-till on all currently annually cropped area (129 Mha) would increase soil C sequestration by 47 Tg C yr-1. Alternatively, use of no-till on 50% of annual cropland, with reduced tillage practices on the other 50%, would sequester less – about 37 Tg C yr-1. Elimination of summer fallow practices and conversion of highly erodible cropland to perennial grass cover could sequester around 20 and 28 Tg C yr-1, respectively. The soil C sequestration potential from including a winter cover crop on annual cropping systems was estimated at 40 Tg C yr-1. All rates were estimated for a fifteen-year projection period, and annual rates of soil C accumulations would be expected to decrease substantially over longer time periods. The total sequestration potential we have estimated for the projection period (83 Tg C yr-1) represents about 5% of 1999 total U.S. CO2 emissions or nearly double estimated CO2 emissions from agricultural production (43 Tg C yr-1). For purposes of stabilizing or reducing CO2 emissions, e.g., by 7% of 1990 levels asoriginally called for in the Kyoto Protocol, total potential soil C sequestration would represent 15% of that reduction level from projected 2008 emissions (2008 total greenhouse gas emissions less 93% of 1990 greenhouse gasemissions). Thus, our analysis suggests that agricultural soil C sequestration could play a meaningful, but not predominant, role in helping mitigate greenhouse gas increases.
  • Authors:
    • Yang, H.
    • Walters, D. T.
    • Dobermann, A.
    • Cassman, K. G.
  • Source: Annual Review of Environment and Resources
  • Volume: 28
  • Issue: 1
  • Year: 2003
  • Summary: Agriculture is a resource-intensive enterprise. The manner in which food production systems utilize resources has a large influence on environmental quality. To evaluate prospects for conserving natural resources while meeting increased demand for cereals, we interpret recent trends and future trajectories in crop yields, land and nitrogen fertilizer use, carbon sequestration, and greenhouse gas emissions to identify key issues and challenges. Based on this assessment, we conclude that avoiding expansion of cultivation into natural ecosystems, increased nitrogen use efficiency, and improved soil quality are pivotal components of a sustainable agriculture that meets human needs and protects natural resources. To achieve this outcome will depend on raising the yield potential and closing existing yield gaps of the major cereal crops to avoid yield stagnation in some of the world's most productive systems. Recent trends suggest, however, that increasing crop yield potential is a formidable scientific challenge that has proven to be an elusive goal.
  • Authors:
    • Paustian, K.
    • Smith, G. R.
    • Conant, R. T.
  • Source: Journal of Environmental Quality
  • Volume: 32
  • Issue: 1
  • Year: 2003
  • Summary: The potential to sequester atmospheric carbon in agricultural and forest soils to offset greenhouse gas emissions has generated interest in measuring changes in soil carbon resulting from changes in land management. However, inherent spatial variability of soil carbon limits the precision of measurement of changes in soil carbon and hence, the ability to detect changes. We analyzed variability of soil carbon by intensively sampling sites under different land management as a step toward developing efficient soil sampling designs. Sites were tilled crop-land and a mixed deciduous forest in Tennessee, and old-growth and second-growth coniferous forest in western Washington, USA. Six soil cores within each of three microplots were taken as an initial sample and an additional six cores were taken to simulate resampling. Soil C variability was greater in Washington than in Tennessee, and greater in less disturbed than in more disturbed sites. Using this protocol, our data suggest that differences on the order of 2.0 Mg C ha(-1) could be detected by collection and analysis of cores from at least five (tilled) or two (forest) microplots in Tennessee. More spatial variability in the forested sites in Washington increased the minimum detectable difference, but these systems, consisting of low C content sandy soil with irregularly distributed pockets of organic C in buried logs, are likely to rank among the most spatially heterogeneous of systems. Our results clearly indicate that consistent intramicroplot differences at all sites will enable detection of much more modest changes if the same microplots are resampled.
  • Authors:
    • Jackson, LE
    • Burger, M.
  • Source: Soil Biology and Biochemistry
  • Volume: 35
  • Issue: 1
  • Year: 2003
  • Summary: Agricultural systems that receive high or low organic matter (OM) inputs would be expected to differ in soil nitrogen (N) transformation rates and fates of ammonium (NH4+) and nitrate (NO3-). To compare NH4+ availability, competition between nitrifiers and heterotrophic microorganisms for NH4+ and microbial NO3- assimilation in an organic vs. a conventional irrigated cropping system in the California Central Valley, chemical and biological soil assays, N-15 isotope pool dilution and N-15 tracer techniques were used. Potentially mineralizable N (PMN) and hot minus cold KCl-extracted NH4+ as indicators of soil N supplying capacity were measured five times during the tomato growing season. At mid-season, rates of gross ammonification and gross nitrification after rewetting dry soil were measured in microcosms. Microbial immobilization of NO3- and NH4+ was estimated based on the uptake of N-15 and gross consumption rates. Gross ammonification, PMN, and hot minus cold KCl-extracted NH4+ were approximately twice as high in the organically than the conventionally managed soil. Net estimated microbial NO3- assimilation rates were between 32 and 35% of gross nitrification rates in the conventional and between 37 and 46% in the organic system. In both soils, microbes assimilated more NO3- than NH4+. Heterotrophic microbes assimilated less NH4+ than No-3(-) probably because NH4+ concentrations were low and competition by nitrifiers was 'apparently strong. The high OM input organic system released NH4+ in a gradual manner and, compared to the low OM input conventional system, supported a more active microbial biomass with greater N demand that was met mainly by NO3- immobilization. (C) 2003 Elsevier Science Ltd. All rights reserved.