• Authors:
    • Bakken ,L. R.
    • Dörsch,P.
    • Holtan-Hartwig, L.
  • Source: Soil Biology and Biochemistry
  • Volume: 34
  • Issue: 11
  • Year: 2002
  • Summary: Abstract: To explore the reason for reported high field fluxes of nitrous oxide (N2O) from temperate soils in winter and early spring, we investigated the temperature response of denitrifier N2O production and reduction in soil from three arable field sites along a temperature transect reaching from Finland over Sweden to Germany. Process rates were determined in anaerobic slurries with or without added NO3-, N2O and C2H2 at 0, 5, 10, 15, and 20C (and 30C in one experiment). The experiments were conducted immediately after the soils had become anaerobic, and after a long (48 h) anaerobic pre-incubation with excess of carbon and electron acceptors. All denitrifying enzymes were found to be active in the soil at onset of anaerobiosis. Significant levels of N2O production and reduction occurred at 0 8C, both at onset of anaerobiosis and after the 2 days anaerobic pre-incubation. Temperature response of N2O production and reduction could be fitted to an Arrhenius function in the range 5-20 °C, yielding apparent activation energies between 28 and 76 kJ mol -1. The estimated activation energy of the N2O reduction was found to be similar or lower than that for N2O production. High field N2O fluxes in winter and early spring could thus not be explained by the temperature sensitivity of the two processes. However, major deviations from the regular Arrhenius response were found for two soils at near freezing temperature. The rates measured at 0 °C were much lower than those predicted by the Arrhenius function based on data in the temperature range 5-20 °C. Low temperature may thus exert a particular challenge to denitrifying communities for some reason, and the effect was found to be most severe for the N2O reduction process. When such a breakdown affects N2O reductase to a greater extent than the N2O producing enzymes (NO3-, NO2-, and NO reductase), as was found in our soils, it will result in high N2O fluxes at low temperature. The temperature response of the estimated net N2O emission potential (based on measured N2O production and reduction rates) differed significantly between the three sites, indicating inherent differences between their microbial communities.
  • Authors:
    • Samu, F.
    • Sunderland, K.
  • Source: Entomologia Experimentalis Et Applicata
  • Volume: 95
  • Issue: 1
  • Year: 2000
  • Summary: A review of the literature showed that spider abundance was increased by diversification in 63% of studies. A comparison of diversification modes showed that spider abundance in the crop was increased in 33% of studies by `aggregated diversification' (e.g. intercropping and non-crop strips) and in 80% of studies by `interspersed diversification' (e.g., undersowing, partial weediness, mulching and reduced tillage). It is suggested that spiders tend to remain in diversified patches and that extending the diversification throughout the whole crop (as in interspersed diversification) offers the best prospects for improving pest control. There is little evidence that spiders walk in significant numbers into fields from uncultivated field edges, but diversification at the landscape level serves to foster large multi-species regional populations of spiders which are valuable as a source of aerial immigrants into newly planted crops. There are very few manipulative field studies where the impact of spiders on pests has been measured in diversified crops compared with undiversified controls. It is encouraging, however, that in those few studies an increased spider density resulted in improved pest control. Future work needs are identified.
  • Authors:
    • Soderstrom, M.
    • Rydberg, A.
  • Source: Proceedings of the 5th International Conference on Precision Agriculture, Bloomington, Minnesota, USA, 16-19 July, 2000
  • Year: 2000
  • Summary: This study investigates the potential of using SPOT multispectral images of agricultural fields to distinguish spatial variation in crop-growth patterns that can be used for site-specific agricultural management. Four years of SPOT data from 1995 to 1997 and 1999 are used in this study over south-western Sweden where satellite derived yield maps are compared to data from commercial yield mapping systems. The crops included rape, wheat, barley, meadow fescue [Festuca pratensis], oats, peas and rye. Our concept of crop growth maps is intended for use in areas where yield mapping, soil sampling and ground spectral measurements are not available. Maps of crop growth variability produced by clustering processes applied to images of the Normalized Difference Vegetation Index are compared to clustering of yield maps from the same years. Qualitative yield estimation is derived by dividing each field into several thematic classes, going from lowest to highest potential yield within a particular field. Qualitative comparisons are made within each field. For one year, the satellite data are also compared to three traditional yield maps derived from the same set of yield data. For a few fields where the time of image acquisition coincides with stages of optimum grain fill, high correlations were obtained between yield and NDVI. This study illustrates that satellite images can be a useful tool in precision agriculture management. The clusters created from the NDVI images show similar patterns as clusters created from the yield maps.
  • Authors:
    • Bertholdsson, N. O.
  • Source: Sveriges Utsädesförenings Tidskrift
  • Volume: 110
  • Issue: 4
  • Year: 2000
  • Summary: The use of hydroponic techniques to measure the response to stress by cereals is discussed with reference to studies on drought, low N inputs and crop weed competition with barley, wheat, oats, triticale and rape.
  • Authors:
    • Oenema, O.
    • Silvola, J.
    • Martikainen, P.
    • Berglund, K.
    • Klemedtsson, L.
    • Kasimir-Klemedtsson, Å.
  • Source: Soil Use and Management
  • Volume: 13
  • Issue: s4
  • Year: 1997
  • Summary: The large boreal peatland ecosystems sequester carbon and nitrogen from the atmosphere due to a low oxygen pressure in waterlogged peat. Consequently they are sinks for CO2 and strong emitters of CH4. Drainage and cultivation of peatlands allows oxygen to enter the soil, which initiates decomposition of the stored organic material, and in turn CO2 and N2O emissions increase while CH4 emissions decrease. Compared to undrained peat, draining of organic soils for agricultural purposes increases the emissions of greenhouse gases (CO2, CH4, and N2O) by roughly 1t CO2 equivalents/ha per year. Although farmed organic soils in most European countries represent a minor part of the total agricultural area, these soils contribute significantly to national greenhouse gas budgets. Consequently, farmed organic soils are potential targets for policy makers in search of socially acceptable and economically cost-efficient measures to mitigate climate gas emissions from agriculture. Despite a scarcity of knowledge about greenhouse gas emissions from these soils, this paper addresses the emissions and possible control of the three greenhouse gases by different managements of organic soils. More precise information is needed regarding the present trace gas fluxes from these soils, as well as predictions of future emissions under alternative management regimes, before any definite policies can be devised.