19842015
  • 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:
    • Rogers, G. S.
    • Little, S. A.
    • Silcock, S. J.
    • Williams, L. F.
  • Source: Acta Horticulturae
  • Issue: 638
  • Year: 2004
  • Summary: A no-till system using permanent beds, permanent subsurface irrigation and organic mulches grown in situ was implemented as an alternative to conventional production in an experiment conducted in North Queensland, Australia. The system used a tropical legume, Centrosema pubescens 'Cavalcade', or the C 4 grasses Bothriochloa pertusa 'Keppel' or 'Hatch' as cover crops over summer and autumn. Cover crops were killed using glyphosate (1440 g a.i./ha) and residues were left on the soil surface. Vegetable seedlings were then planted through the mulch residues and grown using conventional agronomic techniques. Following harvest, crop residues were macerated and the following cover crop direct sown through the mulch residues. Soil from conventional production areas using polyethylene mulch had significantly lower aggregate stability than all other treatments. Soil aggregates taken from beneath cover crop mulches were more stable than aggregates under polyethylene mulch after one year under the no-till regime. Soil aggregates after three years of treatment showed similar statistical differences between the treatments. Bulk density in permanent beds under C. pubescens mulch was significantly lower than uncultivated bare soil and frequently cultivated polyethylene mulch. Soil under frequent cultivation was significantly more compacted than uncultivated bare soil. There were significantly more earthworms under C. pubescens and B. pertusa mulch than in uncultivated bare topsoil or under polyethylene mulch. No earthworms were found in any sample under polyethylene mulch. The yields of tomatoes after 5 harvests were not significantly different for conventional and no-till production.
  • Authors:
    • Chen, D.
    • White, R. E.
    • Chapman, D. F.
    • Eckard, R. J.
  • Source: Australian Journal of Dairy Technology
  • Volume: 59
  • Issue: 2
  • Year: 2004
  • Authors:
    • Kelly, K.
    • Edis, R. B.
    • Li, Y.
    • Chen, D.
    • Turner, D.
  • Source: SuperSoil: 3rd Australian New Zealand Soils Conference
  • Year: 2004
  • Authors:
    • Gibson, S. G.
    • Yarboro, W.
    • Hamrick, M.
    • Thompson, S.
    • King, R.
  • Source: Proceedings of the 26th Southern Conservation Tillage Conference for Sustainable Agriculture
  • Year: 2004
  • Summary: In addition to regular programming, County Agricultural Extension agents are asked many times to respond to questions, suggestions and concerns by their farmer clientele. In North Carolina as in other states an advisory leadership system is in place and farmers can formally and informally make suggestions and requests for on-farm demonstrational work. In many cases what the farmers are observing in their fields and/or things they have read "spark" the interactions with agents. Such has been the case in Cleveland County, NC. For example in the early continuous no-till era many area farmers were concerned about soil compaction. Measurements and simple demonstrations conducted by the Cleveland and Lincoln County agents and supported by the NCSU Soil Science Department and Cleveland County Government helped alleviate these concerns. Later as fields were in continuous no-till for 5 or more years, farmers began to notice a greater than expected development of their crops prior to major applications of fertilizer nitrogen. These observations led to a replicated test in wheat conducted by the Cleveland County Agricultural Extension agent comparing a field in a 2 year no-till wheat soybean rotation verses a nearby field in a 5 year continuous no-till wheat soybean rotation. Also a 6 year replicated test was initiated on Cleveland County owned land that had been in continuous no-till for 10 years. The test was set up as a continuous soybean corn rotation and in addition to the standard dryland portion, irrigation was used in part of the study to simulate a "good" corn year. Five nitrogen rates were used. The economics of the cost of fertilizer nitrogen was used to demonstrate that the Realistic Yield Expectation (RYE) method for determining nitrogen rates was very much applicable in continuous no-till. Both the wheat and corn tests indicated that residual soil nitrogen was indeed becoming a major factor in continuous no-till for these field crops and when farmers considered the realities of the weather very likely nitrogen rates can be reduced with confidence.
  • Authors:
    • Díaz, S.
    • Cabido, M.
    • Bonamici, I.
    • Pucheta, E.
  • Source: Austral Ecology
  • Volume: 29
  • Issue: 2
  • Year: 2004
  • Summary: We estimated the below-ground net plant productivity (BNPP) of different biomass components in an intensively and continuously 45-ha grazed site and in a neighbouring exclosure ungrazed for 16 years for a natural mountain grassland in central Argentina. We measured approximately twice as much dead below-ground biomass in the grazed site as in the ungrazed site, with a strong concentration of total below-ground biomass towards the upper 10 cm of the soil layer in both sites. The main contribution to total live biomass was accounted for by very fine (1 mm) in the grazed site. The seasonal variation of total live below-ground biomass mainly reflected climate, with the growing season being limited to the warmer and wetter portion of the year, but such variation was higher in the grazed site. Using different methods of estimation of BNPP, we estimated maximum values of 1241 and 723 g m-2 year-1 for the grazed and ungrazed sites, respectively. We estimated that very fine root productivity was almost twice as high at the grazed site as at the ungrazed one, despite the fact that both sites had similar total live biomass, and root turnover rate was twofold at the grazed site.
  • Authors:
    • Luo, J.
    • Hedley, C. B.
    • Bhandral, R.
    • Bolan, N. S.
    • Saggar, S.
  • Source: New Zealand Journal of Agricultural Research
  • Volume: 47
  • Issue: 4
  • Year: 2004
  • Summary: The agricultural sector in New Zealand is the major contributor to ammonia (NH3), nitrous oxide (N2O), and methane (CH4) emissions to the atmosphere. These gases cause environmental degradation through their effects on soil acidification, eutrophication, and stratospheric ozone depletion. With its strong agricultural base and relatively low level of heavy industrial activity, New Zealand is unique in having a greenhouse gas emissions inventory dominated by the agricultural trace gases, CH4 and N2O, instead of carbon dioxide which dominates in most other countries. About 96% of this anthropogenic CH4 is emitted by ruminant animals as a by-product during the process of enteric fermentation. Methane is also produced by anaerobic fermentation of animal manure and many other organic substrates.
  • 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:
    • Paustian, K.
    • Mosier, A. R.
    • Conant, R. T.
    • Breidt, F. J.
    • Ogle, S. M.
    • Six, J.
  • Source: Global Change Biology
  • Volume: 10
  • Issue: 2
  • Year: 2004
  • Summary: No-tillage (NT) management has been promoted as a practice capable of offsetting greenhouse gas (GHG) emissions because of its ability to sequester carbon in soils. However, true mitigation is only possible if the overall impact of NT adoption reduces the net global warming potential (GWP) determined by fluxes of the three major biogenic GHGs (i.e. CO2, N2O, and CH4). We compiled all available data of soil-derived GHG emission comparisons between conventional tilled (CT) and NT systems for humid and dry temperate climates. Newly converted NT systems increase GWP relative to CT practices, in both humid and dry climate regimes, and longer-term adoption (>10 years) only significantly reduces GWP in humid climates. Mean cumulative GWP over a 20-year period is also reduced under continuous NT in dry areas, but with a high degree of uncertainty. Emissions of N2O drive much of the trend in net GWP, suggesting improved nitrogen management is essential to realize the full benefit from carbon storage in the soil for purposes of global warming mitigation. Our results indicate a strong time dependency in the GHG mitigation potential of NT agriculture, demonstrating that GHG mitigation by adoption of NT is much more variable and complex than previously considered, and policy plans to reduce global warming through this land management practice need further scrutiny to ensure success.