• Authors:
    • Jones, P. G.
    • Atieno, F.
    • Kruska, R. L.
    • McCrabb, G.
    • Thornton, P. K.
    • Reid, R. S.
  • Source: Environment, Development and Sustainability
  • Volume: 6
  • Issue: 1-2
  • Year: 2004
  • Summary: Climate change science has been discussed and synthesized by the world's best minds at unprecedented scales. Now that the Kyoto Protocol may become a reality, it is time to be realistic about the likelihood of success of mitigation activities. Pastoral lands in the tropics hold tremendous sequestration potential but also strong challenges to potential mitigation efforts. Here we present new analyses of the global distribution of pastoral systems in the tropics and the changes they will likely undergo in the next 50 years. We then briefly summarize current mitigation options for these lands. We then conclude by attempting a pragmatic look at the realities of mitigation. Mitigation activities have the greatest chance of success if they build on traditional pastoral institutions and knowledge (excellent communication, strong understanding of ecosystem goods and services) and provide pastoral people with food security benefits at the same time.
  • 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:
    • Moreira, A.
    • Martins, G.
    • Mccann, J.
    • German, L.
    • Kern, D.
    • Lehmann, J.
  • Source: Amazonian Dark Earths
  • Volume: Part 2
  • Year: 2004
  • Authors:
    • Palm, C.
    • King, J.
    • Verchot, L.
    • Wassmann, R.
    • Mosier, A.
  • Source: Environment, Development and Sustainability
  • Volume: 6
  • Issue: 1-2
  • Year: 2004
  • Summary: Tropical soils are important sources and sinks of atmospheric methane (CH4) and major sources of oxides of nitrogen gases, nitrous oxide (N2O) and NOx (NO+NO2). These gases are present in the atmosphere in trace amounts and are important to atmospheric chemistry and earth's radiative balance. Although nitric oxide (NO) does not directly contribute to the greenhouse effect by absorbing infrared radiation, it contributes to climate forcing through its role in photochemistry of hydroxyl radicals and ozone (O3) and plays a key role in air quality issues. Agricultural soils are a primary source of anthropogenic trace gas emissions, and the tropics and subtropics contribute greatly, particularly since 51% of world soils are in these climate zones. The soil microbial processes responsible for the production and consumption of CH4 and production of N-oxides are the same in all parts of the globe, regardless of climate. Because of the ubiquitous nature of the basic enzymatic processes in the soil, the biological processes responsible for the production of NO, N2O and CH4, nitrification/denitrification and methanogenesis/methanotropy are discussed in general terms. Soil water content and nutrient availability are key controls for production, consumption and emission of these gases. Intensive studies of CH4 exchange in rice production systems made during the past decade reveal new insight. At the same time, there have been relatively few measurements of CH4, N2O or NOx fluxes in upland tropical crop production systems. There are even fewer studies in which simultaneous measurements of these gases are reported. Such measurements are necessary for determining total greenhouse gas emission budgets. While intensive agricultural systems are important global sources of N2O and CH4 recent studies are revealing that the impact of tropical land use change on trace gas emissions is not as great as first reports suggested. It is becoming apparent that although conversion of forests to grazing lands initially induces higher N-oxide emissions than observed from the primary forest, within a few years emissions of NO and N2O generally fall below those from the primary forest. On the other hand, CH4 oxidation is typically greatly reduced and grazing lands may even become net sources in situations where soil compaction from cattle traffic limits gas diffusion. Establishment of tree-based systems following slash-and-burn agriculture enhances N2O and NO emissions during and immediately following burning. These emissions soon decline to rates similar to those observed in secondary forest while CH4 consumption rates are slightly reduced. Conversion to intensive cropping systems, on the other hand, results in significant increases in N2O emissions, a loss of the CH4 sink, and a substantial increase in the global warming potential compared to the forest and tree-based systems. The increasing intensification of crop production in the tropics, in which N fertilization must increase for many crops to sustain production, will most certainly increase N-oxide emissions. The increase, however, may be on the same order as that expected in temperate crop production, thus smaller than some have predicted. In addition, increased attention to management of fertilizer and water may reduce trace gas emissions and simultaneously increase fertilizer use efficiency.
  • Authors:
    • Thomas, R. J.
    • Fisher, M. J.
  • Source: Environment, Development and Sustainability
  • Volume: 6
  • Issue: 1-2
  • Year: 2004
  • Summary: Three of the nine physiographic regions that comprise the 8.2 million km2 (Mkm2) of the central lowlands of tropical South America have undergone substantial conversion from the native vegetation in the last 30 years, a good deal of it to introduced pastures. The converted lands were either formerly treeless grasslands of the Brazilian Shield and the Orinoco Basin, or semi-evergreen seasonal forest mainly in the east and southwest of the Amazon Basin in Brazil. There are about 0.44Mkm2 of introduced Brachiaria pastures in the former grasslands and we estimate that there are 0.096Mkm2 of introduced pastures in the Amazon Basin, mostly Brachiaria species. Based on extensive descriptions of the land systems of the central lowlands by Cochrane et al. (1985) we extrapolated data of carbon (C) accumulation in the soil under introduced pastures on the eastern plains of Colombia (about 3 t Cha-1 yr-1), which are treeless grasslands of the Orinoco Basin, to estimate the probable change in C stocks as a result of conversion to pasture elsewhere. Losses of above-ground C on conversion of the former grasslands is negligible, while in contrast the forests probably lose about 115 t C for each ha converted. We estimated the mean time since conversion started and allowed for the degradation of the pastures that commonly occurs. We concluded that introduced pastures on the former grasslands have been a net sink for about 900 million t (Mt) C, while conversion of the forest has been a net source of about 980 Mt C, leading to a net source of about 80 Mt C for the central lowlands as a whole. We identify a number of issues and possible methodologies that would improve precision of the estimates of the changes in C stocks on conversion of native vegetation to pasture.
  • Authors:
    • Feller, C.
    • Oliver, R.
    • Lesaint, S.
    • Villenave, C.
    • Girardin, C.
    • Blanchart, E.
    • Azontonde, A.
    • Barthès, B.
  • Source: Soil Use and Management
  • Volume: 20
  • Issue: 2
  • Year: 2004
  • Summary: Long term fallow is no longer possible in densely populated tropical areas, but legume cover crops can help maintain soil fertility. Our work aimed to study changes in soil carbon in a sandy loam Ultisol in Benin, which involved a 12-year experiment on three maize cropping systems under manual tillage: traditional no-input cultivation (T), mineral fertilized cultivation (NPK), and association with Mucuna pruriens (M). The origin of soil carbon was also determined through the natural abundance of soil and biomass 13C. In T, NPK and M changes in soil carbon at 0±40 cm were ±0.2, +0.2 and +1.3 tC ha±1 yr±1, with residue carbon amounting to 3.5, 6.4 and 10.0 tC ha±1 yr±1, respectively. After 12 years of experimentation, carbon originating from maize in litter-plus-soil (0±40 cm) represented less than 4% of both total carbon and overall maize residue carbon. In contrast, carbon originating from mucuna in litter-plus-soil represented more than 50% of both total carbon and overall mucuna residue carbon in M, possibly due to accelerated mineralization of native soil carbon (priming effect) and slow mulch decomposition. Carbon originating from weeds in litter-plus-soil represented c. 10% of both total carbon and overall weed residue carbon in T and NPK. Thus mucuna mulch was very effective in promoting carbon sequestration in the soil studied.
  • Authors:
    • Sharma, R. D.
    • Corrêa, J. C.
  • Source: Pesquisa Agropecuária Brasileira
  • Volume: 39
  • Issue: 1
  • Year: 2004
  • Summary: An experiment was carried out on a heavy red yellow latosol to evaluate crop rotation on herbaceous cotton ( Gossypium hirsutum) yields in no-till system under rainfed Savannah conditions. The treatments were: soyabean-millet ( Pennisetum glaucum)-soyabean-millet-cotton; soyabean-amaranth ( Amaranthus hypochondriacus)-soyabean-forage radish-soyabean-cotton; soyabean-grain sorghum ( Sorghum vulgare [ S. bicolor])-soyabean-grain sorghum-cotton; soyabean-black rye ( Avena strigosa [ A. nuda])-soyabean-black rye-cotton and soyabean-soyabean-cotton. The highest cotton seed yield and best weed control were recorded in the sequence soyabean-millet-soyabean-millet-cotton.
  • Authors:
    • Shively, G. E.
    • Zelek, C. A.
  • Source: Land Economics
  • Volume: 79
  • Issue: 3
  • Year: 2003
  • Summary: We present a method for measuring the opportunity cost of sequestering carbon on tropical farms. We derive the rates of carbon sequestration for timber and agroforestry systems and compute incentive compatible compensating payment schedules for farmers who sequester carbon. The method is applied to data for an agricultural watershed in the Philippines. Area- and land quality-adjusted total costs are estimated. The present value of the opportunity cost of carbon storage via land modification falls between $3.30 and $62.50 per ton. Carbon storage through agroforestry is found to be less costly than via a pure tree-based system.
  • Authors:
    • Glaser, B.
    • Zech, W.
    • Nehls, T.
    • Steiner, C.
    • Pereira da Silva, J.
    • Lehmann, J.
  • Source: Plant and Soil
  • Volume: 249
  • Issue: 2
  • Year: 2003
  • 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.