Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2006
Sammendrag
Light is a common component of forecasting models for downy mildews because its presence is assumed to suppress sporulation. Our objectives were to evaluate the effects of light intensity and quality, temperature, and diurnal periodicity on sporulation of Bremia lactucae, the causal agent of lettuce downy mildew. We found that the suppressive effect of light on sporulation was strongly dependent upon temperature; there was little suppression of sporulation by light at " 10 ºC. At temperatures where light suppressed sporulation, light in the range from 450-500 nm had the most suppressive effect, although a lesser effect of the wavebands from 450-500 nm was detected. At 15 ºC, a diurnal pattern of sporulation was observed independent of light and darkness. In current forecasting models, the time of sunrise and sunset are used to delimit the dark period when leaf wetness and high RH can induce sporulation. In Nordic countries the effects of short nights and extended twilight conditions should be incorporated into forecasting models. Also, since sporulation may be greatly reduced by light at temperatures above 15-20 ºC, this should be used to modify model predictions of sporulation during the time of day when sporulation can occur. The diurnal rhythm could interact with light and temperature to confound the results of controlled environment studies, and may be the controlling factor in timing of sporulation at low temperatures.
Forfattere
Tor Gunnar Vågen Markus G Walsh Keith D. ShepherdSammendrag
The impacts of human land use in the highlands of Madagascar are often equated with land degradation and decreasing soil fertility. The practice most often focused on is deforestation through slash-and-burn cultivation (tavy), and shifting cultivators are often portrayed as being ignorant, poverty-stricken peasants felling trees for fields and food. However, there is uncertainty whether soil degradation is related to recent tavy or earlier forest clearance, and whether some highland areas were ever forested. In this paper we use stable isotopes (!13C) and diffuse reflectance spectroscopy (DRS) to study the impacts of deforestation and various other land use changes on ecosystem properties, soil organic carbon (SOC) dynamics and soil quality (fertility) in the highlands of Madagascar. Land cover transitions (between C3 and C4 systems) are defined and quantified in the study area. Historical land use had greater effect on soil organic carbon concentrations than current land use, with cultivated areas previously under C3 and C4 systems having 37.3 and 14.8 g SOC kg"1, respectively. Grasslands previously under C3 had approximately 124% more SOC than grasslands previously under C4, while SOC concentrations were 65.3 and 54.9 g C kg"1 under natural forest and in mixed fallow systems, respectively. A soil fertility index developed for the study area based on diagnostic soil spectra was compared with findings related to SOC dynamics and land use change.
Sammendrag
Increasing levels of Fusarium mycotoxins have been recorded in Norwegian cereals during the last few years. In 2004, unusual high levels of deoxynivalenol (DON) were recorded, in particular in oats (e.g. 25-30 000 ppb) and some alarming levels of T-2 and HT-2 were recorded in 2005, also in oats. Due to the lack of effective control measures, FHB and mycotoxin contamination poses a significant threat to the yield and quality of cereals. Today only a very limited number of check samples of grains used for food and fodder are tested for mycotoxin content. To reduce the risk of contaminated cereals entering the food and feed processing chain, a four-year project (2006-2009) has been started, with the aim to develop a strategy for identification and discarding of unsuitable grain lots. Because there will be impracticable to analyse every lot the basis for a three-step screening system will be established: 1 - Development of prediction models based on information about effects of agronomic/cultivation practice and climatic conditions, for selection of putative `high-risk" fields/lots; 2 " Selection of a suitable and rapid testing method with capacity to screen a large number of samples for relevant mycotoxins at low costs, for testing of `high-risk" lots; 3 " Chemical toxin analyses of grain lots found to be highly contaminated in step 2. Fusarium avenaceum , F. culmorum, F. poae and F. tricinctum have been the most frequently recorded Fusarium species on cereals in Norway for many years. However, more recently also F. graminearum has occurred more frequently and F. langsethia has been detected especially in oats. Investigations will be carried out to see if there has been a change in the composition of Fusarium species.
Sammendrag
The aim of this study was to investigate the possible influence of surface topographical features on the spatial variability of glyphosate degradation and some microbial characteristics in sandy loam soil. Soil samples were taken from the ploughed layer across an agricultural field after seedbed preparation for grain (Grue site), and down to 1 m depth under a ridge tilled field (Målselv site), both sites having similar soil textural characteristics (sandy loam soil). Laboratory experiments were performed looking at glyphosate mineralization and soil microbial activity at the Grue site, as well as microbial biomass, activity and substrate utilization patterns at the Målselv site. Microbial biomass and activity decreased, and substrate utilization patterns changed with increasing soil depth, reflecting naturally occurring changes in quantity and quality of soil organic carbon. Further, our results show that considerable spatial heterogeneity in the degradation rate of glyphosate and general carbon utilization exists even across small areas within a single agricultural field. This horizontal variability was observed over several spatial scales, and could not be clearly explained. It evidently arose from differences in environmental factors affecting microbial activity and growth, and topographical features controlling redistribution of water and matter flow patterns were correlated to the investigated soil microbial variables.
Sammendrag
Three continuous production experiments and three short term cross over experiments were carried out in Northern Norway to investigate different feeding strategies for dairy cows in organic farming. This paper focuses on the effects on sensoric milk quality. Half of the 32 Norwegian red dairy cows in the production experiments were fed 40% (HC) concentrates (on energy basis per year) and the other half 10% (LC). Twelve cows (HC) participated in the short term cross over experiments. The experimental factors in the continuous production experiments were barley preservation method (P1), grass silage maturity (P2) and type of protein supplement (P3), and in the short term cross over experiments barley preservation method (C1), type of protein supplement (C2) and time for fishmeal feeding (C3). In all experiments the cows were offered grass silage ad libitum, restricted amounts of cereals and protein feeds, and mineral and vitamin supplements. The sensoric quality of milk was in general high. In the production experiments, milk from cows in HC had slightly higher quality than from cows in LC (significant in P2, p = 0.04). Neither the preservation method of barley (dried or ensiled with molasses), maturity of grass silage or type of protein supplement (fishmeal or peameal) influenced the sensoric milk quality significantly. Also in the cross over experiments no effect of the studied factors was found in milk flavour and odour. Early harvested grass silage gave significantly lower FFA contents than grass silage cut at normal time (P2) and FM gave significantly lower FFA concentrations than peameal (P3). These results indicate that organic farmers with different feeding regimes can produce milk of first class sensoric quality. Also the content of FFA has been low in all experiments (except C1). However, feeding regimes containing low levels of concentrates may reduce milk taste slightly.
Forfattere
Hege Hvattum Divon Carmit Ziv Olga Davydov Oded Yarden Robert Fluhr Hege DivonSammendrag
Fusarium oxysporum is a soil-borne pathogen that infects plants through the roots and uses the vascular system for host ingress. Specialized for this route of infection, F. oxysporum is able to adapt to the scarce nutrient environment in the xylem vessels. Here we report the cloning of the F. oxysporum global nitrogen regulator, Fnr1, and show that it is one of the determinants for fungal fitness during in planta growth. The Fnr1 gene has a single conserved GATA-type zinc finger domain and is 96% and 48% identical to AREA-GF from Gibberella fujikuroi, and NIT2 from Neurospora crassa, respectively. Fnr1 cDNA, expressed under a constitutive promoter, was able to complement functionally an N. crassa nit-2(RIP) mutant, restoring the ability of the mutant to utilize nitrate. Fnr1 disruption mutants showed high tolerance to chlorate and reduced ability to utilize several secondary nitrogen sources such as amino acids, hypoxanthine and uric acid, whereas growth on favourable nitrogen sources was not affected. Fnr1 disruption also abolished in vitro expression of nutrition genes, normally induced during the early phase of infection. In an infection assay on tomato seedlings, infection rate of disruption mutants was significantly delayed in comparison with the parental strain. Our results indicate that FNR1 mediates adaptation to nitrogen-poor conditions in planta through the regulation of secondary nitrogen acquisition, and as such acts as a determinant for fungal fitness during infection.
Forfattere
Christian UhligSammendrag
Reindeer husbandry has lead to consecutive landscape changes in Finnmark, Northern Norway, during the last 30 years. Vegetational changes, particularly the degradation of fruticose lichen winter pastures, are well documented. Impacts on other landscape components such as soils are less known. The aim of this paper is I) to document changes in soil properties due to reindeer grazing and II) to specify potential implications for future landscape changes and management. In general, reported pattern for impacts of reindeer grazing on lichen pastures are rather similar, but opposite to those found for the post-fire succession of many lichen dominated boreal and arctic ecosystems, which floristically are characterized by the succession of cryptogams. Based on this assumption four degradation/ succession stages (DS) ranging from an average fruticose lichen (FL) carpet exceeding 4 cm in depth (DS I) to the total disappearance of FL and dominance of crustose lichens and bare mineral soil (DS IV) were characterised. Results showed a significant decrease in humus mass per area from approximately 4800 g/m2 (DS I) to 4100 g/m2 (DS II) and 3600 g/m2 (DS III). Furthermore, total calculated amounts of the essential plant nutrients N, P, Ca, Mg, and K stored in the upper organic horizon at DS III were about 30 to 45 % lower than those of DS I. Findings clearly indicate that degradation of fruticose lichen carpets by reindeers also negatively influence on soil organic matter quantity and quality. At Finnmarksvidda the organic layer can be considered the key factor for soil fertility, and thus landscape stability. The sustainable management of soil resources may therefore be of vital importance to avoid further degradation of reindeer pastures on Finnmarksvidda.
Sammendrag
Winter conditions with seasonally frozen soils may have profound effects on soil structure and erodibility, and consequently for runoff and erosion. Such effects on aggregate stability are poorly documented for Nordic winter conditions. The purpose of this study was to quantify the effect of variable freeze-thaw cycles and soil moisture conditions on aggregate stability of three soils (silt, structured clay loam-clay A and levelled silty clay loam-clay B), which are representative of two erosion prone areas in southeastern Norway. A second purpose was to compare aggregate stabilities measured by the Norwegian standard procedure (rainfall simulator) and the more widely used wet-sieving procedure. Surface soil was sampled in autumn. Field moist soil was sieved into the fraction 1-4 mm and packed into cylinders. The water content of the soil was adjusted, corresponding to matric potentials of -0.75, -2 and -10 kPa. The soil cores were insulated and covered, and subjected to 0, 1, 3 or 6 freeze -thaw cycles: freezing at -15 °C for 24 h and thawing at 9 °C for 48 h. Aggregate stability was measured in a rainfall simulator (all soils) and a wet-sieving apparatus (silt and clay B). The rainfall stability of silt was found to be significantly lower than of clay A and clay B. Clay A and clay B had similar rainfall stabilities, even though it was expected that the artificially levelled clay B would have lower stability. Freezing and thawing decreased the rainfall stability of all soils, but the effect was more severe on the silt soil. There was no evident effect of water content on the stability, probably due to experimental limitations. The same effects were observed for wet-sieved soil, but the wet-sieving resulted in less aggregate breakdown than the rainfall simulator. Rainfall impact seemed to be more detrimental than wet-sieving on more unstable soil, that is, on silt soil and soil subjected to many freeze-thaw cycles. Such conditions are expected to occur frequently during field conditions in unstable winters.
Foredrag – Thresholds for seed borne diseases in organic cereal seed
Guro Brodal, Birgitte Henriksen
Sammendrag
To avoid problems with seed borne diseases in organic cereal production, seed health testing should be compulsory in certification of organic seed. In general, significantly lower infection frequencies of seed borne diseases are recorded on seedlings than on seed. Thresholds for the amount of seed borne inoculum that can be accepted for organic production are therefore needed. The aim of the work presented is to compare transmission rates of Drechslera on barley and oats under organic and conventional conditions, to be able to decide if existing thresholds used to assess the need of chemical seed treatment, can be applied for acceptance of organic seed lots, or for recommendation of alternative treatments. Field experiments were carried out in 2005 in conventional and organic fields situated close to each other at each of three locations (south/east-Norway, east-Norway and mid-Norway). 10 seed lots of barley and 10 lots of oats, with a range of seed infections (barley: 0-94 % Drechslera teres, average 23,7 %; oats: 0-66 % Drechslera avenae, average 22,0 %) were planted in rows of 100 seeds with 8 replicates in each location/`growing system". Percent emergence and seedlings with primary infections were recorded at BBCH 12-13. In average of the three locations 2,5 % and 2.1 % barley seedlings were infected when grown in conventional and organic fields, respectively. In oats, 2,0 % and 0,8 % infected seedlings were recorded in conventional and organic fields, respectively. Similar experiments will be carried out in 2006 and results from this will also be presented.
Sammendrag
During snowmelt Oslo airport has on repeated occations experienced the formation of large meltwater ponds due to impermeable ice forming below the snowcover. The airport is situated on a large glacial outwash plane with coarse sandy gravely sediments, hence the area normaly has a high infiltration capacity. Focussed infiltration can cause fast transport of contaminants to the groundwater, hence improved understanding of the processes determining where and how the focussed infiltration takes place is important. Previously the melting process has been monitored successfully on a small scale (4 m2) using a two dimensional grid of permanently installed electrodes (French and Binley, 2004). In the present work snowmelt infiltration was monitored by time-lapse measurements of electrical resistivity using grounded electrodes on 4 and 20 m2 plots and a capacitively coupled resistivity system (Ohmmapper, Geometrics) on a larger scale. While the smaller scale systems provide 3D images the capacitively coupled system was used to monitor changes in two dimensional vertical sections in a retention pond adjacent to one of the runways. The area covered by 4 lines was 170 m by 340 m. The initial data were collected late in the spring (2006) during the final stages of the snowmelt. The lines were repeated later in the year when the soil profile was dryer. The lines show good consistency in the description of the general geology of the subsurface and the time-lapse changes describe the infiltration pattern that occurred during snowmelt and subsequent drainage. The surveys provide useful information about the differences in spatial distribution of snowmelt infiltration at different scales. And there are good indications that capacitively coupled resistivity surveys can be used to describe infiltration processes at relatively large spacio-temporal scales. References French, H. and A. Binley, 2004, Snowmelt infiltration: monitoring temporal and spatial variability using time-lapse geophysics, J. Hydrology, 297, 174-186