Changing course of secondary succession in abandoned sandy fields

The vegetation of abandoned arable fields on dry sandy soils was investigated in 1986 and again in 2000. Comparison of the two data sets by ordination, calibration based on indicator values, and statistical modelling revealed that the vegetation in 2000 differed significantly from the vegetation in 1986. Part of this difference could be explained by field age, but significant difference remained after correction for age. The analysis showed that species indicating nutrient-rich and acidic conditions were more abundant in the 2000 samples than expected from the age of the fields. Possible causes for the observed differences are discussed, and the role of airborne nitrogen deposition and landscape changes is emphasised. Changing course of successional processes may place serious constraints on future habitat restoration.     

Alternative hosts for potato mop-top virus, genus Pomovirus and its vectorSpongospora subterranea f.sp. subterranea

Summary Seventeen weed species common in the potato fields in Denmark were grown in a hydroponic system infested with viruliferous zoospores ofSpongospora subterranea f.sp.subterranea carrying potato mop-top virus (PMTV). The plants were examined for infection with PMTV andS.s.s. using DAS-ELISA and based on visible symptoms. Only two weed species were found to be infected with PMTV,Chenopodium album andSolanum nigrum, whereas 13 became infected withS.s.s. C. album was infected with PMTV by mechanical inoculation were the infection became systemically and the leaves showed necrotic spots.S. nigrum became local infected with PMTV by mechanical inoculation. By inoculation with viruliferousS.s.s. the roots ofS. nigrum became infected but in three weeks PMTV had not spread into the top of the plants.Nicotiana benthamiana was used as a control susceptible toS.s.s. and PMTV.     

Formation of sandy anthropogenic soils in NW Europe: identification of inputs based on particle size distribution

Anthropogenic sandy soils in Scotland, Denmark and The Netherlands were studied to determine the extent to which they had been influenced by inputs of materials and current land management. Particle size distribution, pH, loss on ignition, ECEC, base saturation and total P were determined for eight profiles under different land uses (arable, meadow and woodland). Inputs of materials were identified by comparison of particle size distributions of the deepened cultivated horizons with those of parent materials. At all three sites turf derived from local sources was the main input though there were other mineral additions including an aeolian component. Overall, the anthropogenic soils are remarkably similar in field and some analytical properties, though land use has influenced pH, base saturation and total P.     

Photobacterium damselae subsp. damselae, an emerging pathogen in Danish rainbow trout, Oncorhynchus mykiss (Walbaum), mariculture

A selection of 16 field isolates of Photobacterium damselae from marine rainbow trout farms in Denmark was subjected to phenotypic and genotypic characterization and pathogenicity to fish. All isolates belonged to the subspecies damselae , being positive for haemolysis, motility and urease. There were considerable differences in haemolytic properties, some isolates presenting a broad zone of haemolysis and others only a narrow zone. Pulsed-field gel electrophoresis revealed a high diversity indicating that P. damselae subsp. damselae is an opportunistic, not clonal pathogen in Danish marine rainbow trout. Virulence of the strains to rainbow trout was highly variable with LD₅₀ values ranging from 3.9 × 10³ to 1.5 × 10⁸ cfu at 20 °C. The virulence was significantly higher at 20 °C than at 13 °C. The strains with the strongest haemolytic properties were the most virulent suggesting a strong involvement of haemolysin in the pathogenesis. The pathological changes were consistent with a bacterial septicaemia and the haemorrhages were more pronounced than for most other bacterial infections.     

Modelling climatic erosivity as a factor for soil erosion in Denmark: changes and temporal trends

Abstract. Daily measurements of precipitation and temperature at 82 locations in Denmark for periods of 10 to 43 years, were used for calculation of the impact energy and intensity of rain, climatic erosivity (hereafter called erosivity). The computed erosivity values were analysed for trends and variations in time and space. Analysis of 43 years of data from 6 locations showed a change in the annual distribution of intense (erosive) precipitation, with a tendency to bi-modality, increasing erosivity in September, and decreasing erosivity in August. Amounts of precipitation in autumn have generally increased, but the erosive power of rain has increased even more. The geographic location of high erosivity varied considerably from year to year. Using a simple crop model, the interaction between crop cover and erosivity was investigated. This suggested that changes in climate in combination with changes in cropping and management practice have increased risk of serious erosion over the period 1954 to 1996. We recommend that present and future cropping and management practices be evaluated for risk of adverse interaction with high erosivity events.     

丹麦的水貂养殖业现状

通过对丹麦水貂养殖业的历史、规模与经济效益以及饲养管理、繁殖、销售、人员培训和动物福利等进行阐述,指出了其目前存在的主要问题,并对未来的发展方向进行了展望。     

Using farmland prices to evaluate cost-efficiency of national versus regional reserve selection in Denmark

The current study focuses on the influence of geopolitical coordination of conservation strategies on cost and efficiency in terms of species representation when selecting network of protected areas. Conservation policies in the EU are implemented at many different administrative levels: from the European Union and national levels, to regional or/county levels within member countries. This arise the question what size of efficiency gains could be achieved if planning of conservation priorities could be coordinated between geopolitical units. Using data for the nationwide distribution of 763 species, representing all Danish species within eight taxa, we compared illustrative costs for the addition of new areas to the existing conservation network in order to ensure full coverage of all species. We found that the cost of independent regional planning is 20-fold higher than an inter-regional and nationally co-ordinated strategy. We also found that substituting land prices for a simple land-area measure in our analyses increased the expected conservation costs differential significantly, without increasing coverage of species representations. We suggest that in economic and biodiversity terms it can largely be a win-win situation to set a common goal, to develop priority-strategies, and to coordinate actions at higher rather than lower levels of administration.     

Exchangeable potassium in soil as indicator of potassium status in an organic crop rotation on loamy sand

Abstract. In organic agriculture, where K may be a limited resource, reliable tools are important in the assessment of K availability in the soil in order to avoid K deficiency. We investigated the effect of four organic farming systems on the exchangeable K in the plough layer of a six-course crop rotation from 1994 to 1997. The accumulated K balances over the four years varied between −49 and +120 kg K ha^–1and the corresponding exchangeable K (0–20 cm) in autumn 1997 was 7.1 and 9.6 mg K 100 g soil^–1, respectively, as an average of the crop rotation. The exchangeable K fraction responded to the K application in manure and to the crop in the rotation. In an additional experiment, no yield response to K was found, despite a low level of exchangeable K. The exchangeable K was a useful indicator of changes in the K status in the farming system with the largest positive K balance, but this K fraction was insufficient as an indicator in the other three farming systems. The considerable variation of exchangeable K through the crop rotation makes the soil test method most suitable at the crop rotation level where fluctuations caused by crop and management are smoothed out.     

Evaluation of World Reference Base for Soil Resources and FAO Soil Map of the World using nationwide grid soil data from Denmark

Abstract. Soil classification is a tool for stratifying and generalizing information on soil resources but most systems are tailored to handle only slightly disturbed soil. We tested the applicability of the legend of the FAO-Unesco Soil Map of the World and the new World Reference Base for Soil Resources by classifying at the highest order 831 profiles from a nationwide 7 km grid survey in Denmark, where soils are developed in Quaternary glacial and marine sediments and intensively farmed. Comparison of the variability of pH and % clay +% silt of the master horizons (A, E, B, and C) within and between the major well-drained soil groupings shows that liming, fertilizing and ploughing have produced significantly deeper A-horizons with higher pH, lower % humus and C:N ratios on the two-thirds of the country that is cultivated. ‘Anthropogenic’ mollic and umbric horizons are a common result but the liming causes a random final classification of these surface horizons and, hence, random allocation of the soils in both systems. It separates cultivated soils and their undisturbed equivalents, and results in considerable within-group variation in soil texture. Grouping of cultivated and undisturbed soils, on the other hand, results in wide within-horizon pH ranges for most groups, again compromising the advantage of making useful general statements on the basis of classification. We propose that anthropogenic mollic and umbric horizons should be allowed in any soil group and that ‘anthric properties’ should be used to distinguish between profoundly changed cultivated soils and largely undisturbed soils, hereby constructing a two-tier system within each highest-order soil group. We classified the soils according to this proposal. The results show generally narrower ranges for both pH and % clay +% silt. We evaluated the within-group homogeneity by multivariate analysis of variance of pH, % clay +% silt, % clay, % humus, C:N ratio, exchangeable cations, and CEC. The results (Wilks's Lamda) show a higher degree of group compactness compared to the original FAO and World Reference Base systems.     

The Use of Herbs in Pastures: An Interview Survey Among Bio-Dynamic and Organic Farmers with Dairy Cattle

Lack of knowledge about the effects of herbs in pastures and the frequency of their use by today's organic farmers has limited the development of new methods to improve animal health compatible with organic farming principles. Understanding farmers' agricultural practices is an early step in a participatory research process. With this in mind, we conducted a two-tiered, semi-structured survey of Danish organic farmers with dairy cattle to begin documenting their practices. Out of 350 farmers, 255 completed a mailed questionnaire – a response rate of 73%. Of these participating farmers, 66 (26%) confirmed their use of herbs in pastures. Caraway was sown at an average rate of 500 g of seed per hectare by 60 (91%). Of these, 32 used solely caraway, while 7 used it in combination with parsley. Twenty-one used caraway together with herbs other than parsley. Six used one or more herbs, not including caraway, such as chicory, chervil, dill, fenugreek, great burnet, and salad burnet. Further details concerning cultivation, convictions, observed effects, and information sources were obtained through telephone interviews. The results of this study would indicate that more research in this field is called for. Naja W. Smidt is a M.Sc. student in agricultural sciences at the Royal Veterinary and Agricultural University, Denmark. Leon Brimer is an Associate Professor of chemical food safety at the Royal Veterinary and Agricultural University, Denmark. His research focuses on the interface between chemistry and biology with special emphasis on aspects of cultivation, processing, and use of plants with physiologically active components (toxins).