Tolerance of four spring barley (Hordeum vulgare) varieties to weed harrowing

We investigated the tolerance to weed harrowing of four spring barley varieties and examined the possible interactions between varietal weed suppressive ability and two nutrient levels. Tolerance was defined as the combined effect of crop resistance (ability to resist soil covering) and crop recovery (the ability to recover in terms of yield). The weed harrowing strategy was a combination of one pre‐ and one post‐emergence weed harrowing. In terms of yield, the four varieties responded significantly differently to weed harrowing and the response depended on nutrient level. At the lower nutrient level, weed harrowing caused an increase in yield of 4.4 hkg ha⁻¹ for a strong competitor (cv. Otira), while there was no effect on yield at the higher nutrient level. For a weaker competitor (cv. Brazil), weed harrowing caused no change in yield at the lower nutrient level, whereas yield decreased by 6.0 hkg ha⁻¹ at the higher nutrient level. There were marked differences between the weed suppressive ability of the four varieties when not harrowed, with less pronounced but significant differences when harrowed. Weed harrowing did not change the weed suppressive ability of a variety. Varieties that are tall at post‐emergence harrowing and have increased density after pre‐emergence harrowing, are the ones that benefit most from weed harrowing.     

Reduction of brown trout, Salmo trutta L., salmon, S. salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), smolt bycatches in eel pound nets

Two types of bycatch reduction devices (BRDs) were tested in the Randers Fjord, Denmark, aimed at deflecting the surface-oriented smolts of brown trout, Salmo trutta L., salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), before they became trapped, while retaining the catches of eel, Anguilla anguilla (L.). The methods tested were: a) placing a floating guard net between the wings; and b) submerging the pot net (i.e. last enclosure before fyke net) 55–100 cm below mean sea level. After each haul the pound net-setups were changed from the control to one of the types of BRD, and vice versa. Both methods significantly reduced the bycatch of brown trout smolts, while catches of legal-sized eels were not affected. Submerging the pot net reduced smolt catches of all species; mean reductions were 91.1% for brown trout, 74.5% for rainbow trout, and 86.1% for salmon.     

Testing harrows for mechanical control of annual weeds in agricultural crops

Selectivity, defined as the ratio between weed control and crop burial in soil as a result of harrowing, has been used to test different implements according to their degree of selective operation. For this purpose a concept considering qualitative and quantitative aspects of selectivity has been proposed. This makes it possible to determine whether differences in selective mode of operation were caused by construction or by application of implements. Analysis of covariance was used to make this separation. Only if implements affected parameters in a model describing the relationship between crop soil cover and weed control were they suggested to operate with different selectivities. Crop soil cover was assessed by visual score as percentage of crop leaf area covered by soil as a result of harrowing. Using this method it was shown that none of the five harrows tested could be separated on the basis of their selective mode of operation. Selectivity was shown to be influenced by day of treatment, composition of the weed flora, site characteristics and degree of weed control. Harrowing at late crop growth stages was more selective than expected. Essai de hersage pour lutter mecaniquement contre les mauvaises herbes annuelles dans les cultures La sélectivité, définie comme le ratio entre la destruction des mauvaises herbes et l'en fouissement de la culture dans le sol après un hersage, a été utilisée pour tester différents matériels en regard de leur degré d'opération sélective. Pour cela, un concept prenant en compte les aspects qualitatifs et quantitatifs de la sélectivité a été proposé. Celui-ci permet de déterminer si les différences de sélectivité viennent de la construction ou de la mise en oeuvre des matériels. Une analyse de covar-iance a été utilisée pour opérer cette séparation. Seulement si les matériels affectaient les paramètres dans un modèle décrivant la relation entre la couverture de la culture par le sol et le deshérbage, il était envisagé d'opérer avec différentes sélectivités. La couverture de la culture par le sol a étéévaluée par une estimation visuelle du pourcentage de surface foliaire recouverte par le sol après un hersage. Par cette méthode il a été montré qu'aucun des 5 hersages testés ne pouvait être séparé sur la base de leur mode d'opération sélective. La sélectivité a été montrée comme étant influencée par le jour de traitement, la composition de la flore adventice, les caractéristiques du site et le taux de desherbage. Un hersage aux stades tardifs de la culture a été plus sélectif que ce que l'on attendait. Wirksamkeit verschiedener Eggen zur mechanischen Bekämpfung einjähriger Unkräuter in landwirtschaftlichen Kulturen Es wurden verschiedene Geräte nach ihrer selektiven Wirksamkeit beurteilt, wobei die Selektivität als Verhältnis zwischen der Bekämpfung der Unkräuter und dem Verschütten der Kulturpflanzen definiert wurde. Hierfür wurde ein Konzept vorgeschlagen, das die qualitativen und quantitativen Aspekte der Selektivität berücksichtigt. Dadurch konnte bestimmt werden, ob Selektivitätsunterschiede durch die Konstruktion oder durch die Anwendung eines Geräts bedingt waren. Die Unterscheidung erfolgte mittels Kovarianz Analyse. Nur wenn Geräte die Parameter eines Modells über die Beziehung zwischen dem Verschütten der Kulturpflanzen und der Unkrautbekämpfung beeinflußten, wurden ver-schiedene Selektivität angenommen. Das Verschutten der Kulturpflanzen wurde als prozentuale Bedeckung der Blattflächen mit Boden bonitiert. Danach ergab sich, daß die 5 getesteten Eggen in ihrer selektiven Wirkung nicht unterschieden werden konnten. Die Selektivitität wurde vom Tag der Behandlung, der Zusammensetzung der Unkrautflora, den Eigenschaften des Standorts und dem Grad der Unkrautbekämpfung beeinflußt. Das Eggen in fortgeschrittenen Entwicklungsstadien der Kulturpflanzen war selektiver als erwartet.     

Cardiovascular effects of intravenous administration of tetracycline in cattle

Tetracycline chloride dissolved in saline was injected intravenously to seven cows. Two doses of tetracycline were used: 5 and 10 mg/kg b.wt, and the injections were given over a period of either 10, 60 or 300 sec.
A number of the cows collapsed shortly after the injection was completed, usually when the 10 mg dosage was given in 60 sec. When the same dose was given over a period of 5 min none of the cows collapsed. A more or less pronounced drop in blood pressure could be detected during or shortly after the injection; in those cows which collapsed the blood pressure fell almost to zero. The predominant change in pulse rate in connection with the tetracycline administration was a decrease which could be quite marked, pulse rates falling as low as 10–20 per min. Simultaneously with these changes in blood pressure and pulse rate severe abnormalities in ECG could be observed. Pre-treatment with a normal therapeutic dose of calcium borogluconate intravenously prevented collapse in the cows and diminished the drop in blood pressure associated with an ensuing tetracycline injection.
It is concluded that intravenous injection of tetracycline is hazardous, but that collapse can be avoided by giving the injection very slowly over a period of no less than 5 min.     

Investigating the selectivity of weed harrowing with new methods

In six field experiments on post‐emergence weed harrowing in spring barley, the effects of row spacing, timing, direction and orientation on crop/weed selectivity were investigated. The efficacies of increasing intensities of harrowing generated either by increasing number of passes or increasing driving speed were also tested. Selectivity was defined as the relationship between crop burial in soil immediately after treatment and weed control. To estimate crop burial, digital image analysis was used in order to make objective estimations. The study showed that narrow row spacing decreased selectivity in a late crop growth stage, whereas row spacing in the range 5.3–24 cm had no effects at an early growth stage. Harrowing across rows decreased selectivity in one out of two experiments. Whether repeated passes with the harrow were carried out in the same orientation along the rows or in alternative orientations forth and back was unimportant. There were indications that a high harrowing intensity produced by a single pass at high speed gave a lower selectivity than a similar intensity produced by several passes at a low speed. Impacts on selectivity, however, were small and only significant at high degrees of weed control. Timing had no significant impact on selectivity.     

Fission–fusion dynamics of a pelagic delphinid in the arctic: the white-beaked dolphin (Lagenorhynchus albirostris)

Delphinids exhibit great variability in their social structures. It is therefore important to document lesser known species, in extreme changing habitats, to compare and contrast mechanisms driving sociality. Here, we describe the first long-term assessment of social structure of white-beaked dolphins (Lagenorhynchus albirostris) using a compiled version of SOCPROG 2.8 and an 11-year photo-identification dataset (2002–2013) collected from whale-watching vessels at 2 sites (Faxaflói and Skjálfandi bays) off Iceland. We identified a total of 487 dolphins which are suggested to be part of an open population as shown by the discovery curve obtained analyzing photo-id data. The social analyses were restricted to 35 adults which were sighted on ≥5 different days. The mean residency time of white-beaked dolphins in our 2 study areas was of 95 days (SE = 35.63; 95% CI: 23–171), with the “migration-full interchange” model best describing movements of dolphins in and out of our 2 study sites. Social differentiation in this population was high (Likelihood: S = 0.87, SE = 0.04; r = 0.31, SE = 0.03) indicating diverse, non-random social relationships. Temporal associations best fit the model of “casual acquaintances” against the standardized lagged association rates with the majority of white-beaked dolphin associations being short-term, but with a few long-term across years. Testing for preferred companionship, long-term associations are favored over short-term. In this study, associations among white-beaked dolphins are short-term but with desirably long-term associations fitting into a society with fission–fusion dynamics. This information expands the latitudinal range for which social structure has been described for oceanic dolphin species.     

A model for prediction of yield response in weed harrowing

A model is presented to describe crop yield response in weed harrowing. The selectivity of harrowing, crop yield response to soil covering, and the competitive strength of the weeds are all variables in the model, which is derived from the hyperbolic yield-density relationship, and therefore accounts for the effects of weed density. An advantage of the modelling approach is that the yield response can be separated into two parts, one derived from the positive weed-killing effect of harrowing, and the other derived from the negative crop-covering effect. Simulation runs based on experimental data showed that crop damage, when it occurs, cannot be ignored, and may sometimes even dominate the positive weed-killing effect. Possible scientific and practical applications of the model are discussed.