• 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:
    • Cerri, C. C.
    • Victoria, R.
    • Bernoux, M.
    • Jenkinson, D. S.
    • Coleman, K.
    • Cerri, C. E. P.
  • Source: Soil Science Society of America Journal
  • Volume: 67
  • Issue: 6
  • Year: 2003
  • Summary: Conversion of tropical forest to agricultural management has important implications for C storage in soils and global climate change. The Nova Vida Ranch in the Western Brazilian Amazon basin provided a unique opportunity to study the conversion of tropical forests to pastures established in 1989, 1987, 1983, 1979, 1972, 1951, and 1911, in comparison with uncleared forest. Soils were analyzed for organic C, bulk density, total N, pH, clay content, and biomass C. The forest soil contained 34 Mg C ha(-1) in the 0- to 30-cm layer: modeling clearance and conversion to pasture caused an initial fall in the C stock, followed by a slow rise. After 88 yr, the pasture soil contained 53% more C than the forest soil. The increase in total N on conversion to pasture was less marked, which led to C/N ratios in the pasture soils being higher than in the forest soil. The Rothamsted C turnover model (RothC-26.3) was used to simulate changes in the 0- to 10- and 0- to 30-cm layer of soils when forest was converted to pasture. The model predicted that conversion to pasture would cause a 54% increase in the stock of organic C in the top 30 cm of soil in 100 yr. The modeled input of plant C to the 0- to 30-cm layer of soil under pasture was assumed to be 8.28 Mg C ha(-1) yr(-1). The model provided a reasonable estimate of the microbial biomass (BIO) C in the 0- to 10-cm soil layer. This was an independent test of model performance, because no adjustments were made to the model to generate output.
  • Authors:
    • Ruiz-Suárez, L. G.
    • González-Avalos, E.
  • Source: Bioresource Technology
  • Volume: 80
  • Issue: 1
  • Year: 2001
  • Authors:
    • Snelder, D. J.
  • Source: Agroforestry Systems
  • Volume: 52
  • Issue: 3
  • Year: 2001
  • Summary: Frequent burning and grazing and cultivation of cash crops increasingly threaten forest patches in hilly grassland in Northeast Luzon, yet their importance as a resource with multiple environmental functions and forest products persists. The aim of this study is to identify different types of forest patches, and their condition under present land-use intensification, and discuss prospects for their integration into sustainable local farming systems. Five types of forest patches are distinguished, both natural and planted ones, including rows of trees, woody patches, gallery forests, hill-slope forests and homegarden conglomerations. Natural woody patches and gallery forests in Imperata grassland are subject to degradation and land-use conversion under conditions of agricultural intensification. Woody patches in grassland affected by frequent burning and grazing cover small areas (66% below 50 m(2) as opposed to 28% in protected grassland) and contain relatively few woody plant species (25 woody species in total as opposed to 82 where protected). Yet where well managed, they may provide a variety of products for sale and subsistence, covering emergency needs and giving off-season cash income to rural communities. Moreover they serve like the gallery forest various ecological functions, carrying valuable indigenous tree species, retaining soil base nutrients, providing a continuous supply of organic matter and intercepting fine earth soil particles removed from bare surfaces. It is suggested that forest- patch management systems may be developed, taking into account both patch diversity and the diverse needs of rural communities, and to strengthen existing and undervalued functions of forest patches as permanent elements in an agricultural landscape.
  • Authors:
    • Fernandes, S. V.
    • Martin-Neto, L.
    • Amado, T. J. C.
    • Mielniczuk, J.
    • Bayer, C.
  • Source: Soil & Tillage Research
  • Volume: 54
  • Issue: 1-2
  • Year: 2000
  • Summary: Soil organic matter decline and associated degradation of soil and environmental conditions under conventional tillage in tropical and subtropical regions underline the need to develop sustainable soil management systems. This study aimed first to evaluate the long-term effect (9 years) of two soil-tillage systems (conventional tillage: CT, and no-tillage: NT) and two cropping systems (oat (Avena strigosa Schreb)/maize (Zea mays L.): O/M; and oat+common vetch (Vicia sativa L.)/ maize+cowpea (Vigna unguiculata (L.) Walp): O+V/M+C without N fertilization on total organic carbon (TOC) and total nitrogen (TN) concentrations in a sandy clay loam Acrisol in southern Brazil. The second objective was to assess soil potential for acting as an atmospheric CO2 sink. Under NT an increase of soil TOC and TN concentrations occurred, in both cropping systems, when compared with CT. However, this increase was restricted to soil surface layers and it was higher for O+V/M+C than for O/M, The O+V/M+C under NT, which probably results in the lowest soil organic matter losses (due to erosion and oxidation) and highest addition of crop residues, had 12 Mg ha(-1) more TOC and 0.9 Mg ha(-1) more TN in the 0-30.0 cm depth soil layer, compared with O/M under CT which exhibits highest soil organic matter losses and lowest crop residue additions to the soil. These increments represent TOC and TN accumulation rates of 1.33 and 0.10 Mg ha(-1) per year, respectively. Compared with CT and O/M, this TOC increase under NT and O+V/M+C means a net carbon dioxide removal of about 44 Mg ha(-1) from the atmosphere in 9 years. NT can therefore be considered, as it is in temperate climates, an important management strategy for increasing soil organic matter. In the tropicals and subtropicals, where climatic conditions cause intense biological activity, in order to maintain or increase soil organic matter, improve soil quality and contribute to mitigation of CO2 emissions, NT should be associated with cropping systems resulting in high annual crop residue additions to soil surface. (C) 2000 Elsevier Science B.V. All rights reserved.
  • Authors:
    • Van Noordwijk, M.
    • Sitompul, S. M.
    • Rodrigues, V.
    • Ricse, A.
    • Parton, W. J.
    • Njomgang, R.
    • Murdiyarso, D.
    • Moukam, A.
    • Mendes, A.
    • Kotto-Same, J.
    • Hairiah, K.
    • Feigl, B.
    • Cordeiro, D. G.
    • Castilla, C.
    • Arevalo, L.
    • Alegre, J.
    • Woomer, P. L.
    • Palm, C. A.
  • Source: ASB Climate Change Working Group Final Report, Phase II
  • Year: 1999
  • Summary: The overall objectives of the Climate Change Working Group during Phase II of the Alternatives to Slash-and-Burn Programme (ASB) were to determine those land-use systems that sequester more carbon and reduce trace gas emissions. The research consisted of three activities: 1 Collect strategic information on changes in carbon stocks and land use, 2 Develop a database on trace gas fluxes from different land-use systems, and 3 Assess land rehabilitation techniques for increasing carbon sequestration.
  • Authors:
    • Johnson, D. E.
    • Minami, K.
    • Heinemeyer, O.
    • Freney, J. R.
    • Duxbury, J. M.
    • Mosier, A. R.
  • Source: Climatic Change
  • Volume: 40
  • Issue: 1
  • Year: 1998
  • Summary: Agricultural crop and animal production systems are important sources and sinks for atmospheric methane (CH4). The major CH4 sources from this sector are ruminant animals, flooded rice fields, animal waste and biomass burning which total about one third of all global emissions. This paper discusses the factors that influence CH4 production and emission from these sources and the aerobic soil sink for atmospheric CH4 and assesses the magnitude of each source. Potential methods of mitigating CH4 emissions from the major sources could lead to improved crop and animal productivity. The global impact of using the mitigation options suggested could potentially decrease agricultural CH4 emissions by about 30%.
  • Authors:
    • Silburn, D. M.
    • Dimes, J. P.
    • Nelson, R. A.
    • Paningbatan, E. P.
    • Cramb, R. A.
  • Source: Agricultural Systems
  • Volume: 58
  • Issue: 2
  • Year: 1998
  • Summary: A version of the Agricultural Production Systems Simulator (APSIM) capable of simulating the key agronomic aspects of intercropping maize between legume shrub hedgerows was described and parameterised in the first paper of this series (Nelson et al., this issue). In this paper, APSIM is used to simulate maize yields and soil erosion from traditional open-field farming and hedgerow intercropping in the Philippine uplands. Two variants of open-field farming were simulated using APSIM, continuous and fallow, for comparison with intercropping maize between leguminous shrub hedgerows. Continuous open-field maize farming was predicted to be unsustainable in the long term, while fallow open-field farming was predicted to slow productivity decline by spreading the effect of erosion over a larger cropping area. Hedgerow intercropping was predicted to reduce erosion by maintaining soil surface cover during periods of intense rainfall, contributing to sustainable production of maize in the long term. In the third paper in this series, Nelson et al. (this issue) use cost-benefit analysis to compare the economic viability of hedgerow intercropping relative to traditional open-field farming of maize in relatively inaccessible upland areas. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • Authors:
    • Cassel, D. K.
    • Alegre, J. C.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 58
  • Issue: 1
  • Year: 1996
  • Summary: A change from slash-and-burn to continuously cropped agricultural systems is occurring in heavily populated areas in the humid tropics. Well managed alternative systems to slash-and-burn can reduce soil structure deterioration, maintain soil fertility, and promote long-term. productivity. The objectives of this paper are to describe the dynamics of soil physical properties under slash-and-burn and some alternative systems, Different land-clearing methods and post land-clearing management systems were evaluated on Typic Paleudults at Yurimaguas, Peru, for their effects on soil physical properties such as: bulk density, soil water characteristic, infiltration rate, aggregate stability, and penetrometer cone resistance. Mechanical clearing reduced the infiltration rate from 420 mm h(-1) before clearing to 35 mm h(-1) for the straight blade and 95 mm h(-1) for the shear-blade bulldozing. Straight-blade clearing damaged soil structure the most as indicated by a decrease in the percentage of larger soil aggregates. The practice of planting on raised beds prevented foot compaction of soil near the plants; bulk density was 1.14 and 1.29 Mg ha(-1) for bedded and flat planted soil, respectively. Of the various agroforestry systems evaluated (multistrata, peach palm production, shifting agriculture low input and high input continuous cropping) bulk density was lower after 4 years for the systems with trees or cover crops. Mean annual soil loss for alley cropping on sloping soils was 0.2 Mg ha(-1) year(-1) compared with 53 Mg ha(-1) year(-1) for two annual crops per year. The infiltration rate after 5 years of intensive grazing on five associations of legumes with grasses was reduced from 127 to 41 mm h(-1). Overgrazing caused severe soil compaction and reduced earthworm biomass, Research indicates that the greatest change in soil physical properties occurs during mechanical land clearing, Agroforestry systems improved soil physical properties when cover crops and trees were included in the system.
  • Authors:
    • Partoharjono, S.
    • Hairiah, K.
    • Van Noordwijk, M.
    • Labios, R. V.
    • Garrity, D. P.
  • Source: Agroforestry Systems
  • Volume: 36
  • Issue: 1-3
  • Summary: Purely annual crop-based production systems have limited scope to be sustainable under upland conditions prone to infestation by Imperata cylindrica if animal or mechanical tillage is not available. Farmers who must rely on manual cultivation of grassland soils can achieve some success in suppressing Imperata for a number of years using intensive relay and intercropping systems that maintain a dense soil cover throughout the year, especially where leguminous cover crops are included in the crop cycle. However, tabour investment increases and returns to tabour tend to decrease in successive years as weed pressure intensifies and soil quality declines. Continuous crop production has been sustained in many Imperata-infested areas where farmers have access to animal or tractor draft power. Imperata control is not a major problem in such situations. Draft power drastically reduces the tabour requirements in weed control. Sustained crop production is then dependent more solely upon soil fertility management. Mixed farming systems that include cattle may also benefit from manure application to the cropped area, and the use of non-cropped fallow areas for grazing. In extensive systems where Imperata infestation is tolerated, cassava or sugarcane are often the crops with the longest period of viable production as the land degrades. On sloping Imperata lands, conservation farming practices are necessary to sustain annual cropping. Pruned tree hedgerows have often been recommended for these situations. On soils that are not strongly acidic they may consistently improve yields. But tabour is the scarcest resource on small farms and tree-pruning is usually too tabour-intensive to be practical. Buffer strip systems that provide excellent soil conservation but minimize tabour have proven much more popular with farmers. Prominent among these are natural vegetative strips, or strips of introduced fodder grasses. The value of Imperata to restore soil fertility is low, particularly compared with woody secondary growth or Compositae species such as Chromolaena odorata or Tithonia diversifolia. Therefore, fallow-rotation systems where farmers can intervene to shift the fallow vegetation toward such naturally-occurring species, or can manage introduced cover crop species such as Mucuna utilis cv. cochinchinensis, enable substantial gains in yields and sustainability. Tree fallows are used successfully to achieve sustained cropping by some upland communities. A variation of this is rotational hedgerow intercropping, where a period of cropping is followed by one or more years of tree growth to generate nutrient-rich biomass, rehabilitate the soil, and suppress Imperata. These options, which suit farmers in quite resource-poor situations, should receive more attention.