• Authors:
    • Moreira, A.
    • Martins, G.
    • Mccann, J.
    • German, L.
    • Kern, D.
    • Lehmann, J.
  • Source: Amazonian Dark Earths
  • Volume: Part 2
  • Year: 2004
  • 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:
    • Silva, E. M. da
    • Rauber, J. C.
    • Azevedo, J. A. de
    • Reatto, A.
  • Source: Boletim de Pesquisa e Desenvolvimento - Embrapa Cerrados
  • Issue: 101
  • Year: 2003
  • Summary: The no-till system have positive impacts in soil and water conservation. This work aims to evaluate the main modifications on the soil physical properties caused by no-till system, carried out during 3, 6, and 12 years under rainfed conditions. The cases of direct drilling for five years under irrigated condition, a conventional tillage system, and a soil condition under natural Biome Cerrado were also evaluated in the Ampessan farm, Cabeceiras, Goias, Brazil. The soil physical characteristics were evaluated by samples taken from the following layers: 0-5, 2.5-7.5, 5-10, 10-15, 20-25, 42.5-47.5 and 72.5-77.5 cm. The infiltration characteristics were evaluated at 12 and 80 cm soil depth, using the Guelph permeameter to determine the field saturated hydraulic conductivity. The results showed that the intense soil mechanization on irrigated condition favoured a significant decrease in the field saturated hydraulic conductivity in the layers near to the soil surface. There was a tendency for higher water availability in the cultivated soils, in relation to that under natural soil environment, up to 22.5 cm soil depth.
  • Authors:
    • Nunes, R. P.
    • Pinho, J. L. N.
    • Silva, J. B. F.
    • Pitombeira, J. B.
    • Cavalcante Junior, A. T.
  • Source: Planta Daninha
  • Volume: 21
  • Issue: 1
  • Year: 2003
  • Summary: A study was conducted from September to December 1997, in Pentecoste, Ceara, Brazil, to determine the effectiveness of the herbicides glyphosate (1800 g ha -1) and paraquat (800 g ha -1), applied as desiccants before sowing, and fenoxaprop-P-ethyl [fenoxaprop-P] (0, 40, 80 and 120 g ha -1) and imazamox (0, 21, 42 and 63 g ha -1), applied in post-emergence conditions, in controlling the weeds and to evaluate the phytotoxicity of the herbicides to cowpea plants ( Vigna unguiculata cv. Epace 10) under a no-tillage system with furrow irrigation. The treatments with glyphosate associated with imazamox or fenoxaprop-P-ethyl was more efficient in controlling the weeds, showing reduced weed shoot dry biomass production, when compared to paraquat combined with the post-emergence herbicides. Fenoxaprop-P-ethyl and imazamox did not cause visual phytotoxicity symptoms to the cowpea plants. The best post-emergence weed control was provided by fenoxaprop-P-ethyl at the rate of 80 g ha -1, associated with glyphosate (1800 g ha 1). Fenoxaprop-P-ethyl was effective against the grass weeds, but not against Cenchrus echinatus and Digitaria horizontalis. Imazamox was not effective in controlling the broadleaf weeds Chamaesyce hirta and Euphorbia heterophylla at the studied rates.
  • Authors:
    • Lal, R.
  • Source: Critical Reviews in Plant Sciences
  • Volume: 22
  • Issue: 2
  • Year: 2003
  • Summary: An increase in atmospheric concentration of CO2 from 280 ppmv in 1750 to 367 ppmv in 1999 is attributed to emissions from fossil fuel combustion estimated at 270 +/- 30 Pg C and land use change at 136 +/- 55 Pg. Of the emissions from land use change, 78 +/- 12 Pg is estimated from depletion of soil organic carbon (SOC) pool. Most agricultural soils have lost 50 to 70% of their original SOC pool, and the depletion is exacerbated by further soil degradation and desertification. The restoration of degraded soils, conversion of agriculturally marginal lands to appropriate land use, and the adoption of recommended management practices on agricultural soils can reverse degradative trends and lead to SOC sequestration. Technological options for SOC sequestration on agricultural soils include adoption of conservation tillage, use of manures, and compost as per integrated nutrient management and precision fanning strategies, conversion of monoculture to complex diverse cropping systems, meadow-based rotations and winter cover crops, and establishing perennial vegetation on contours and steep slopes. The global potential of SOC sequestration and restoration of degraded/desertified soils is estimated at 0.6 to 1.2 Pg C/y for about 50 years with a cumulative sink capacity of 30 to 60 Pg. The SOC sequestration is a cost-effective strategy of mitigating the climate change during the first 2 to 3 decades of the 21(st) century. While improving soil quality, biomass productivity and enhanced environment quality, the strategy of SOC sequestration also buys us time during which the non-carbon fuel alternatives can take effect.
  • 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:
    • Merrill, S.
    • Tanaka, D.
    • Anderson, R.
  • Source: Agricultural Water Management
  • Volume: 58
  • Issue: 3
  • Year: 2003
  • Summary: The predominate crops grown in the northern Great Plains of the United States are cereal grains, which are well adapted to the region's semiarid climate and short growing season. However, rotations are changing because minimum- and no-till production systems improve precipitation-use-efficiency. Therefore, producers are seeking diversity in crop choices to improve the design of their rotations. Our objective with this study was to examine water relations and agronomic performance of seven broadleaf crops that may be suitable for a semiarid climate. Dry pea ( Pisum sativum L.), dry bean ( Phaseolus vulgaris L.), and sunflower ( Helianthus annuus L.) were the most favorable for this region considering crop yield and water-use-efficiency (WUE). Soybean ( Glycine max L.), crambe ( Crambe abyssinica Hochst), canola ( Brassica rapa L.), and safflower ( Carthamus tinctorius L.) were less successful. Water use for grain production ranged from 23 to 37 cm among crops whereas water-use-efficiency varied three-fold. Soil water extraction patterns differed between sunflower and dry pea, with sunflower extracting more water as well as accessing water deeper in the soil profile. Integrating oilseed and legume crops with cereal grains in a cycle-of-four rotation will aid producers in managing diseases and weeds, as well as improve grain yield due to the rotation effect.
  • Authors:
    • Thornton, P. K.
    • Jones, P. G.
  • Source: Conservation Ecology
  • Volume: 5
  • Issue: 2
  • Year: 2003
  • Summary: Making decisions in natural resource management involves an understanding of the risk and uncertainty of the outcomes, such as crop failure or cattle starvation, and of the normal spread of the expected production. Hedging against poor outcomes often means lack of investment and slow adoption of new methods. At the household level, production instability can have serious effects on income and food security. At the national level, it can have social and economic impacts that may affect all sectors of society. Crop models such as CERES-Maize are excellent tools for assessing weather-related production variability. WATBAL is a water balance model that can provide robust estimates of the potential growing days for a pasture. These models require large quantities of daily weather data that are rarely available. MarkSim is an application for generating synthetic daily weather files by estimating the third-order Markov model parameters from interpolated climate surfaces. The models can then be run for each distinct point on the map. This paper examines the growth of maize and pasture in dryland agriculture in southern Africa (includes the southern part of Tanzania, Malawi, much of Mozambique, and all of Zimbabwe, and extends west from the Indian Ocean to include Zambia, the southeastern part of the Democratic Republic of Congo and small portions of Angola). Weather simulators produce independent estimates for each point on the map; however, we know that a spatial coherence of weather exists. We investigated a method of incorporating spatial coherence into MarkSim and show that it increases the variance of production. This means that all of the farmers in a coherent area share poor yields, with important consequences for food security, markets, transport, and shared grazing lands. The long-term aspects of risk are associated with global climate change. We used the results of a global circulation model to extrapolate to the year 2055. We found that low maize yields would become more likely in the marginal areas, whereas they may actually increase in some areas. The same trend was found with pasture growth. We outline areas where further work is required before these tools and methods can address natural resource management problems in a comprehensive manner at local community and policy levels.