• Authors:
    • Hadatsch, S.
    • Milestad, R.
  • Source: Conservation Ecology
  • Volume: 8
  • Issue: 1
  • Year: 2003
  • Summary: Farming in the Austrian Alps is small in scale and involves a high degree of manual labor. In the face of structural changes in agriculture, alpine farms are finding it increasingly difficult to remain economically viable. Organic farming presents a promising alternative for alpine farmers because it receives considerable financial support under the Common Agricultural Policy of the European Union. Recent years have seen an increase in the number of organic farms in Austria in general, and in alpine areas in particular. Using data from an empirical study carried out in the alpine area of Solktaler, Austria, this paper examines the issues of how closely the regulations and principles of organic farming match farmers' perspectives on sustainable agriculture and whether or not organic farming is capable of building social-ecological resilience for local farms. Qualitative interviews and a series of workshops were used to learn about farmers' "desired system state" with regard to their region, disturbances to this system, and their perspectives on organic farming. The desired system in Solktaler as formulated by the farmers depicts a vivid farming community that manages a diverse traditional agricultural landscape and performs a number of ecological services. The desired system and the principles of organic farming have several aspects in common, and many management practices and features of the social system support social-ecological resilience. The vulnerability of farms increases, however, when farmers must deal with structural changes in agriculture, the erosion of traditional ecological knowledge, and societal transformation. In conclusion, organic farming is a tool that can be used to build social-ecological resilience for Solktaler farms, because it secures economic funding for the area and makes it possible to sustain environmentally benign practices. What remains is the question of whether the farming community is capable of reorganizing the social system under the pressures of modernization so that the desired system state can be reached.
  • Authors:
    • Pu, X. P.
    • Kang, M. Y.
    • Hu, Z. Z.
    • Long, R. J.
    • Dong, S. K.
  • Source: Grass and Forage Science
  • Volume: 58
  • Issue: 3
  • Year: 2003
  • Summary: Abstract The productivity and nutritive value of some cultivated perennial grasses, Bromus inermis (B), Elymus sibricus (S), E. nutans (N), Agropyron cristatum (A), Poa crymophila (P) and mixtures B + N, S + A, B + S + A, S + B + N, N + S + A, B + S + N + A, B + N + A + P, B + S +A + P and S + N + A + P, in the alpine region of the Tibetan Plateau were investigated. Elymus nutans and E. sibricus and the mixtures, B + S + N + A, B + S +A + P and S + N + A + P, were most productive with yields of dry matter (DM) of between 11 000 and 14 000 kg-1 of biomass annually in the second harvest year. Acid-detergent fibre (ADF) concentrations increased (P < 0·05), and crude protein (CP) concentrations and in sacco DM degradability values decreased (P < 0·05) with the maturity of the cultivated grasses. Swards, based on these species and mixtures, have the potential to be the main choices for cultivation in the Tibetan Plateau because they produce more nutrients than other grass species and mixtures. Late August (flowering stage of dominant grasses) is the optimum time for harvesting as the yield of rumen-degradable CP is highest that of DM relatively high and the DM degradability is satisfactory.
  • Authors:
    • Liu, A.
    • Hamel, C.
    • Madramootoo, C.
    • Elmi, A.
  • Source: Biology and Fertility of Soils
  • Volume: 38
  • Issue: 6
  • Year: 2003
  • Summary: There is a growing interest in the adoption of conservation tillage systems [no-till (NT) and reduced tillage (RT)] as alternatives to conventional tillage (CT) systems. A 2-year study was conducted to investigate possible environmental consequences of three tillage systems on a 2.4-ha field located at Macdonald Research Farm, McGill University, Montreal. The soil was a sandy loam (0.5 m depth) underlain by a clay layer. Treatments consisted of a factorial combination of CT, RT, and NT with the presence or absence of crop residue. Soil NO 3 --N concentrations tended to be lower in RT than NT and CT tillage treatments. Denitrification and N 2O emissions were similar among tillage systems. Contrary to the popular assumption that denitrification is limited to the uppermost soil layer (0–0.15 m), large rates of N 2O production were measured in the subsurface (0.15–0.45 m) soil, suggesting that a significant portion of produced N 2O may be missed if only soil surface gas flux measurements are made. The N 2O mole fraction (N 2O:N 2O+N 2) was higher in the drier season of 1999 under CT than in 2000, with the ratio occasionally exceeding 1.0 in some soil layers. Dissolved organic C concentrations remained high in all soil depths sampled, but were not affected by tillage system .
  • Authors:
    • Saliendra, N. Z.
    • Johnson, D. A.
    • Gilmanov, T. G.
  • Source: Basic and Applied Ecology
  • Volume: 4
  • Issue: 2
  • Year: 2003
  • Summary: The sagebrush-steppe ecosystem covers more than 36 million ha and could play an important role in the global carbon cycle; however, quantitative estimates of CO2 fluxes on these extensive ecosystems are not available. The Bowen ratio/energy balance technique (BREB) was used to continuously monitor CO2 fluxes during the 1996 to 1999 growing seasons at a sagebrush-steppe site near Dubois, Idaho, USA. The daytime and night-time CO2 fluxes were modeled to provide estimates of occasionally missing or aberrant data points so that daily (24-h) integrals across the entire growing season could be quantified. Depending on the particular time of the season, daytime fluxes were best described by a rectangular hyberbolic, nonrectangular hyperbolic, or hysteresis-type functions that included radiation, relative humidity, and soil temperature. Night-time CO2 fluxes exhibited greater variability than daytime fluxes and were not closely correlated with any single meteorological characteristic. Night-time fluxes were predicted using a nonlinear parameter identification technique that estimated values of daytime respiration, which were significantly correlated with night-time fluxes. For the four growing seasons of our study, the integrated seasonal fluxes ranged from 284 to 1,103 g CO2 m-2 with an overall average of 635 g CO2 m-2. Respiratory losses during the non-growing season were estimated to be about 1.5 g CO2 m-2 day-1 or a total of 270 g CO2 m-2. This gives an annual net positive flux (carbon sequestration) estimate of 365 g CO2 m-2 (or 1.0 t C ha-1). These results suggest that the combination of BREB measurements and modeling techniques can be used to provide estimates of CO2 fluxes on important rangeland ecosystems.
  • Authors:
    • Volk, T. A.
    • Keoleian, G. A.
    • Heller, M. C.
  • Source: Biomass and Bioenergy
  • Volume: 25
  • Issue: 2
  • Year: 2003
  • Summary: The environmental performance of willow biomass crop production systems in New York (NY) is analyzed using life cycle assessment (LCA) methodology. The base-case, which represents current practices in NY, produces 55 units of biomass energy per unit of fossil energy consumed over the biomass crop's 23-year lifetime. Inorganic nitrogen fertilizer inputs have a strong influence on overall system performance, accounting for 37% of the non-renewable fossil energy input into the system. Net energy ratio varies from 58 to below 40 as a function of fertilizer application rate, but application rate also has implications on the system nutrient balance. Substituting inorganic N fertilizer with sewage sludge biosolids increases the net energy ratio of the willow biomass crop production system by more than 40%. While CO2 emitted in combusting dedicated biomass is balanced by CO2 adsorbed in the growing biomass, production processes contribute to the system's net global warming potential. Taking into account direct and indirect fuel use, N2O emissions from applied fertilizer and leaf litter, and carbon sequestration in below ground biomass and soil carbon, the net greenhouse gas emissions total 0.68 g CO2 eq. MJ(biomass produced)(-1). Site specific parameters such as soil carbon sequestration could easily offset these emissions resulting in a net reduction of greenhouse gases. Assuming reasonable biomass transportation distance and energy conversion efficiencies, this study implies that generating electricity from willow biomass crops could produce 11 units of electricity per unit of fossil energy consumed. Results from the LCA support the assertion that willow biomass crops are sustainable from an energy balance perspective and contribute additional environmental benefits.
  • 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:
    • Paustian, K.
    • Smith, G. R.
    • Conant, R. T.
  • Source: Journal of Environmental Quality
  • Volume: 32
  • Issue: 1
  • Year: 2003
  • Summary: The potential to sequester atmospheric carbon in agricultural and forest soils to offset greenhouse gas emissions has generated interest in measuring changes in soil carbon resulting from changes in land management. However, inherent spatial variability of soil carbon limits the precision of measurement of changes in soil carbon and hence, the ability to detect changes. We analyzed variability of soil carbon by intensively sampling sites under different land management as a step toward developing efficient soil sampling designs. Sites were tilled crop-land and a mixed deciduous forest in Tennessee, and old-growth and second-growth coniferous forest in western Washington, USA. Six soil cores within each of three microplots were taken as an initial sample and an additional six cores were taken to simulate resampling. Soil C variability was greater in Washington than in Tennessee, and greater in less disturbed than in more disturbed sites. Using this protocol, our data suggest that differences on the order of 2.0 Mg C ha(-1) could be detected by collection and analysis of cores from at least five (tilled) or two (forest) microplots in Tennessee. More spatial variability in the forested sites in Washington increased the minimum detectable difference, but these systems, consisting of low C content sandy soil with irregularly distributed pockets of organic C in buried logs, are likely to rank among the most spatially heterogeneous of systems. Our results clearly indicate that consistent intramicroplot differences at all sites will enable detection of much more modest changes if the same microplots are resampled.
  • Authors:
    • Paustian, K.
    • Elliott, E.
    • Mooney, S.
    • Capalbo, S. M.
    • Antle, J. M.
  • Source: Journal of Environmental Economics and Management
  • Volume: 46
  • Issue: 2
  • Year: 2003
  • Summary: In this paper we develop methods to investigate the efficiency of alternative contracts for Carbon (C) sequestration in cropland soils, taking into account the spatial heterogeneity of agricultural production systems and the costs of implementing more efficient contracts. We describe contracts being proposed for implementation in the United States and other countries that would pay farmers for adoption of specified practices (per-hectare contracts). We also describe more efficient contracts that would pay farmers per tonne of soil C sequestered, and we show how to estimate the costs of implementing these more efficient contracts. In a case study of a major agricultural region in the United States, we confirm that the relative inefficiency of per-hectare contracts varies spatially and increases with the degree of spatial heterogeneity. The results also show that per-hectare contracts are as much as five times more costly than per-tonne contracts--a degree of inefficiency similar to that found in assessments of command-and-control industrial emissions regulations. Measurement costs to implement the per-tonne contracts are found to be positively related to spatial heterogeneity but are estimated to be at least an order of magnitude smaller than the efficiency losses of the per-hectare contract for reasonable error levels. This finding implies that contracting parties could afford to bear a significant cost to implement per-tonne contracts and achieve a lower total cost than would be possible with the less efficient per-hectare contracts.
  • Authors:
    • Cadisch, G.
    • Hartwig, U. A.
    • Richter, M.
    • Baggs, E. M.
  • Source: Global Change Biology
  • Volume: 9
  • Issue: 8
  • Year: 2003
  • Summary: Emissions of N2O were measured during the growth season over a year from grass swards under ambient (360 [micro]L L-1) and elevated (600 [micro]L L-1) CO2 partial pressures at the Free Air Carbon dioxide Enrichment (FACE) experiment, Eschikon, Switzerland. Measurements were made following high (56 g N m-2 yr-1) and low (14 g N m-2 yr-1) rates of fertilizer application, split over 5 re-growth periods, to Lolium perenne, Trifolium repens and mixed Lolium/Trifolium swards. Elevated pCO2 increased annual emissions of N2O from the high fertilized Lolium and mixed Lolium/Trifolium swards resulting in increases in GWP (N2O emissions) of 179 and 111 g CO2 equivalents m-2, respectively, compared with the GWP of ambient pCO2 swards, but had no significant effect on annual emissions from Trifolium monoculture swards. The greater emissions from the high fertilized elevated pCO2 Lolium swards were attributed to greater below-ground C allocation under elevated pCO2 providing the energy for denitrification in the presence of excess mineral N. An annual emission of 959 mg N2O-N m-2 yr-1 (1.7% of fertilizer N applied) was measured from the high fertilized Lolium sward under elevated pCO2. The magnitude of emissions varied throughout the year with 84% of the total emission from the elevated pCO2 Lolium swards measured during the first two re-growths (April-June 2001). This was associated with higher rainfall and soil water contents at this time of year. Trends in emissions varied between the first two re-growths (April-June 2001) and the third, fourth and fifth re-growths (late June-October 2000), with available soil NO3- and rainfall explaining 70%, and soil water content explaining 72% of the variability in N2O in these periods, respectively. Caution is therefore required when extrapolating from short-term measurements to predict long-term responses to global climate change. Our findings are of global significance as increases in atmospheric concentrations of CO2 may, depending on sward composition and fertilizer management, increase greenhouse gas emissions of N2O, thereby exacerbating the forcing effect of elevated CO2 on global climate. Our results suggest that when applying high rates of N fertilizer to grassland systems, Trifolium repens swards, or a greater component of Trifolium in mixed swards, may minimize the negative effect of continued increasing atmospheric CO2 concentrations on global warming.
  • Authors:
    • Wang, H.
    • Brandt, S.
    • Lafond, G.
    • Moulin, A.
    • Campbell, C.
    • Curtin, D.
    • Schoenau, J.
    • McConkey, B.
    • Liang, B.
  • Source: Canadian Journal of Soil Science
  • Volume: 83
  • Issue: 1
  • Year: 2003
  • Summary: Light fraction of soil organic C (LFOC) represents a major portion of labile soil organic C (SOC) and is a key attribute of soil quality. Soil respiration (C min) is an important index depicting the potential activity of the labile SOC. Six field experiments, varying in duration (8 to 25 years), in location (brown [aridic Kastanozem], dark brown [typic Kastanozem] and black chernozemic soil zones of Saskatchewan, Canada; all soils were classified as Chernozems) and soil texture, were conducted to evaluate the impact of tillage and crop rotations on crop production and soil quality. We sampled the 0-7.5 cm depth of soil in these experiments to determine the treatment effects on LFOC, the proportion of LFOC in the SOC (LFOC:SOC) and C min. The crops in the rotation were spring wheat, flax, winter wheat, peas and rape. Increasing the frequency of summer fallow in cropping systems decreased the LFOC in all soil zones; it also decreased the proportion of LFOC in SOC and C min. Tillage had little impact on LFOC in the brown and dark brown chernozemic soil zones, although it significantly decreased LFOC in the black chernozemic soil zone. Thus, crop rotation had a greater impact on LFOC than tillage. Tillage did not influence C min in any soil zone. Because adoption of no-till management increased SOC in all soil zones, we concluded that LFOC was not a sensitive indicator of the impact of tillage on this soil quality attribute for these chernozemic soils in Saskatchewan. We also found that LFOC:SOC is directly proportional to sand content. This relationship may assist us in partitioning SOC pools with differing turnover times when modelling SOC dynamics.