• 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:
    • Ayuk, E. T.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 61
  • Issue: 1-2
  • Year: 2001
  • Summary: In recent years and in some situations the status of soil organic matter (SOM) has deteriorated considerably due to long periods of continuous cultivation and limited external inputs in the form of mineral fertilizers. Deterioration of SOM varies by agro-ecological zones, by soil types and by cropping patterns. It is more intense in East Africa, followed by coastal West Africa and Southern Africa and least intensive in the Sahel and Central Africa. It is also more serious in areas under low-input agriculture irrespective of the prevailing cropping system. The major consequence of the decrease in SOM in the tropics is lower agricultural productivity with a direct negative effect on food security. While biophysical dynamics of SOM have been extensively covered in the literature, social considerations have not received similar attention. This paper examines the social, economic and policy factors associated with the management of tropical soil organic matter. Empirical data from a range of environments in Africa show that SOM improvement options yield a positive return to land as well as labour. However, there are a number of constraints. Social constraints are related to the large quantities of organic matter that are required (case of farmyard manure), the competitive uses for the material (case of crop residues), land and labour requirements, and gender-related issues. From a policy stand point, unsecured tenure rights together with price distortions and other market failures may be important constraints. Challenges for sustainable management of SOM are identified. These include management conflicts, land tenure arrangements, the divergence in goals between individuals and society, land and labour requirements, inadequate support systems for land users, profitability issues, the role of subsidies, and the absence of national action plans. A number of opportunities are identified that could enhance the improvement or maintenance of SOM. These include: exploring the need and potential role of community-based SOM management practices; development of an integrated plant nutrient management strategy involving both organic and inorganic inputs; and development of concrete national action plans. It is argued that because externalities of SOM improvement or maintenance extend beyond the farmer's fields, SOM investment may require cost sharing between individuals and the society. Policies on subsidies need to be reconsidered. Research priorities are identified that require closer collaboration between scientists from a variety of disciplines.
  • 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:
    • Hall, D. O.
    • Scurlock, J. M. O.
  • Source: Global Change Biology
  • Volume: 4
  • Issue: 2
  • Year: 1998
  • Summary: The challenge to identify the biospheric sinks for about half the total carbon emissions from fossil fuels must include a consideration of below-ground ecosystem processes as well as those more easily measured above-ground. Recent studies suggest that tropical grasslands and savannas may contribute more to the 'missing sink' than was previously appreciated, perhaps as much as 0.5 Pg (= 0.5 Gt) carbon per annum. The rapid increase in availability of productivity data facilitated by the Internet will be important for future scaling-up of global change responses, to establish independent lines of evidence about the location and size of carbon sinks.
  • 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:
    • Schad, P.
  • Source: Forstwissenschaftliches Centralblatt vereinigt mit Tharandter forstliches Jahrbuch
  • Volume: 117
  • Issue: 3
  • Year: 1998
  • Summary: This paper discusses the agricultural system in the Charazani region in the Bolivian Eastern Cordillera. The zone from 2800 m to 4300 m asl is intensively used by Indian people and a small Mestizo group. Their traditional agriculture reflects both Indian and Spanish (16th century) traditions. Such traditional systems have been subject to rather contrary myths: some call them primitive, others ecologically adapted. Studying key variables of soil fertility (concentrations and contents (pools) of organic carbon and utilizable water storage capacities) we will investigate the degree of ecological adaptation of the soil-use system in the Charazani region. These parameters, studied in 110 field sequences covering 0-30 cm soil depth, are discussed according to their absolute levels, differences between semi-natural and agriculturally used areas, and (only for organic carbon contents) actual changes during continuous management. The results show that land-use on the dry, wind-exposed and nor irrigated sites is often insufficiently ecologically adapted. Here, intensive crop farming and sheep pasture without protection against wind erosion result in low and even decreasing soil fertility. Good ecological adaptation according to the investigated parameters is to be found, by contrast, on the more humid and better wind-protected sites as well as on the irrigated areas.
  • 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:
    • De Jong, B. H. G.
    • Montoya-Gómez, G.
    • Nelson, K.
    • Soto-Pinto, L.
    • Taylor, J.
    • Tipper, R.
  • Source: Interciencia
  • Volume: 20
  • Issue: 6
  • Year: 1995
  • Summary: Although forestry and agroforestry are recognized as promising land-use alternatives for reducing the increasing levels of global atmospheric carbon, the viability of carbon sequestration projects at the land-user level has rarely been evaluated. We present the results of a feasibility study to: (1) evaluate the interest of local communities in a carbon sequestration project and how they would organize themselves for the proposed forestry project; (2) identify the carbon sequestration potential of the agroforestry/forestry systems that are both ecologically viable and preferred by local farmers (3) determine the social constraints of and potential for, such projects,- and (4) assess the economic potential of the carbon offsets estimated for such systems. This project was carried out by an interdisciplinary team of scientists and farmers in two ecological regions: the Tojolabal and Tzeltal zones of Chiapas, Mexico. Five systems with high carbon sequestration potential were considered technically and socially viable for each region. Initially, all participants will plant trees on an individual basis in their coffee plantation, fallow, and pasture lands, or in their maize fields. The estimated amount of carbon sequestered ranged from 46 7 to 236 7 tons of carbon per hectare (tC/ha). Net income benefits due to converting fields from maize cultivation to farm forestry ranged from $500-1000/ha depending on the value assigned to the sequestered carbon.1 Forests and farm woodlands that are sustainably managed have substantial economic and carbon sequestration potential. The principal barrier to communal forest management appears to be sociopolitical rather than economic. Because forest management requires long-term investments, good planning is essential and includes community control of projects, selection of appropriate tree species, and management techniques that are specific to the ecological and social conditions of the area. 1 All references to dollars in this report refer to U.S. dollars ($US).
  • Authors:
    • Schroeder, P. E.
    • Lee, J. J.
    • Andrasko, K. J.
    • Winjum, J. K.
    • Dixon, R. K.
  • Source: Climatic Change
  • Volume: 27
  • Issue: 1
  • Year: 1994
  • Summary: Degraded or sub-standard soils and marginal lands occupy a significant proportion of boreal, temperate and tropical biomes. Management of these lands with a wide range of existing, site-specific, integrated, agroforest systems represents a significant global opportunity to reduce the accumulation of greenhouse gases in the atmosphere. Establishment of extensive agricultural, agroforest, and alternative land-use systems on marginal or degraded lands could sequester 0.82-2.2 Pg carbon (C) per year, globally, over a 50-year time-frame. Moreover, slowing soil degradation by alternative grassland management and by impeding desertification could conserve up to 0.5-1.5 Pg C annually, A global analysis of biologic and economic data from 94 nations representing diverse climatic and edaphic conditions reveals a range of integrated land-use systems which could be used to establish and manage vegetation on marginal or degraded lands. Promising land-use systems and practices identified to conserve and temporarily store C include agroforestry systems, fuelwood and fiber plantations, bioreserves, intercropping systems, and shelterbelts/windbreaks. For example, successful establishment of low-intensity agroforestry systems can store up to 70 Mg C/ha in boreal, temperate and tropical ecoregions. The mean initial cost of soil rehabilitation and revegetation ranges from $500-3,000/ha for the 94 nations surveyed. Natural regeneration of woody vegetation or agro-afforestation establishment costs were less than $1000/ha in temperate and tropical regions. The costs of C sequestration in soil and vegetation systems range from $1-69/Mg C, which compares favorably with other options to reduce greenhouse gas emissions to the atmosphere. Although agroforestry system projects were recently established to conserve and sequester C in Guatemala and Malaysia, constraints to wide-spread implementation include social conditions (demographic factors, land tenure issues, market conditions, lack of infrastructure), economic obstacles (difficulty of demonstrating benefits of alternative systems, capital requirements, lack of financial incentives) and, ecologic considerations (limited knowledge of impacts and sustainability of some systems).