Interactions between pre- and post-emergence weed harrowing in spring cereals

Pre- and post-emergence weed harrowing were studied in spring cereals in different environments and with two types of harrows in Norway during 2004–2006. The objectives were to investigate interactions between pre and post-emergence weed harrowing and the importance of harrow type. We hypothesised that pre- and post-emergence harrowing interact positively, that a combination gives more stable weed control effects than pre- and post-emergence weed harrowing used alone, and that a harrow type with bent tines is more aggressive and suitable on hard-packed soils than a harrow with strait tines. The results only supported the last of these hypotheses. Post-emergence weed harrowing controlled a certain percentage of the present weeds, and this percentage was not dependent on pre-emergence weed harrowing. On average, pre-emergence harrowing reduced weed density by 26% and weed biomass by 22%, while the average effect of postemergence harrowing was 47% on weed density and 41% on weed biomass. The combined effect of pre- and post-emergence weed harrowing was 61% on weed density and 54% on weed biomass. The combination did not give more stable weed control effects than preand post-emergence weed harrowing used alone. Preemergence harrowing increased the average crop yield by 6.2%, post-emergence harrowing by 4.0% and the combined effect was 10%. Crop yield was mainly increased on hard-packed soils. Weed and crop responses varied strongly among experiments, but the efficacy of pre- and post-emergence weed harrowing was positively correlated across experiments. Weed species composition was of minor importance regarding weed control. The study indicates that one aggressive postemergence cultivation may be as good as one preemergence and one less aggressive post-emergence cultivation. However, little is known about the interactions between cultivation at different crop and weed growth stage

Change of the weed seed bank during the first four years of a five-course crop rotation with organic vegetables

In a five-course rotation with organic vegetables (white cabbage, carrot and onion) the weed seed bank was reduced the year after two continuous years with red clover, mainly because of mowing of the second year red clover. The year after the weedy ribbed meliot the weed seed bank increased

Control of perennial weeds based on weed biology and environmental considerations

Timing, type and duration of tillage operations and cropping practices are of importance for reducing the regeneration of perennial weeds and also for minimizing the environmental impacts of such operations. In the present work and with reference to previous publications we find that, based on the knowledge gained on growth patterns, sensitivity to competition, growth potential of roots and mechanical and management measures it is possible to coordinate control of perennial weeds with considerations of yield and reduced environmental impact

Programming in Mathematics Education: An Intermediary between the Real-World and the Mathematical Model

In realistic mathematics education students expand their common sense through guided reinvention, aiming to prevent the dichotomy between what the students experience as real and the associated mathematical model. The mathematics curriculum is, however, often comprehensive and ambitious, and many students will find it challenging to develop the required skills and knowledge. In order to solve the complicated problems required at exams, students and teachers will yield to memorizing formulas and procedures, letting large parts of mathematics education reside in the formal mathematical model. In this paper we propose to utilize programming as an intermediary between the realworld problems and formal mathematics, not merely as a tool to solve the problems or find approximate solutions, but to increase understanding and to guide the student’s mathematical reinvention

Integrated programming and mathematics in schools - A solid fundation for a future engineering education?

The interest in programming in schools has the last decade increased, and many countries have introduced programming as part of the school curriculum. Teaching of programming to students in primary and secondary school is often focused on the computer sciences aspect of programming. The current study is a part of the recently initiated research project “Programming for understanding mathematics” which has a different emphasis; the project investigates how the mathematical competence of the students are affected by actively using programming in mathematics lessons. In this paper, a recognized analytical framework for analysing the cognitive demand of mathematical tasks is presented. We extend the framework to include the analysis of tasks that utilize programming, allowing us to distinguish between tasks that are demanding due to the mathematical content, but the programming aspect of the task is trivial, and tasks that are cognitive demanding due to complex programming, but the mathematics is simple. We use the extended framework to analyse tasks in four mathematics textbooks written for 16-17 year old students by two major publishers in Norway. The results show that the tasks provided in the textbooks mainly focus on elementary programming skills, and the tasks give limited experiences with cognitive demanding programming tasks

Optimale randbetingelser for det diskrete Laplace-problemet

In this master's thesis an optimization problem in relation to a partial differential equation (PDE) called the discrete Laplace problem with Dirichlet boundary conditions is studied. The solution of the optimization problem will provide optimal Dirichlet boundary conditions that allow solution of the discrete Laplace problem giving a best possible approximation to a given finite subset. Moreover, a number of methods that make use of various optimization tools to solve the aforementioned optimization problem are presented. Significant effort is also given to studies of various properties of the solution of the discrete Laplace problem. Theory of partial differential equations and linear optimization are combined, and the reader is expected to have basic knowledge in these subjects. In addition, some knowledge of linear algebra will be beneficial

Regrowth of Cirsium arvense from intact roots and root fragments at different soil depths

In the present work we measured the shoot rate from intact roots and from root fragments of Cirsium arvense at different digging depths and the number of leaves were used as estimate of minimum regenerative capacity. The experiments were performed on four sites with three or four repetitions of each treatment. On each site plot, the soil was removed down to a given depth within a 1 x 1 m square. All plant parts was excavated from the soil and the soil was either replaced without any root material, or roots of C. arvense was cut into 10 cm long fragments and replaced into the source hole. Shoot number, aboveground biomass and number of leaves were measured. Digging depth and time explained 50% - 60% of the variation in biomass (P<0.001). Replacement of root fragments increased the shoot number in one out of four treatments but did not affect biomass produced compared to production from undisturbed root systems. Number of leaves showed that shoots from all digging depths passed the level of minimum regenerative capacity. We conclude that the intact root system from all depths was able to regenerate within one season and it has a high contribution to the produced biomass compared with root fragments in the upper soil layers.Keywords: Biomass, compensation point, number of leaves, root systemAufwuchs von Cirsium arvense aus intakten Wurzeln und Rhizom-Fragmenten aus verschiedener BodentiefeZusammenfassungIn der vorliegenden Arbeit wurde die Sprossbildung aus intaktem Wurzelsystem und aus Wurzelfragmenten von Cirsium arvense bei verschiedenen Bodentiefen gemessen. Die Anzahl der Blätter diente zur Schätzung der minimalen Regenerationsfähigkeit. Die Experimente wurden an vier Standorten mit drei oder vier Wiederholungen der einzelnen Behandlungen durchgeführt. Auf jeder Versuchsparzelle wurde der Boden bis zu einer bestimmten Tiefe in einem 1 x 1 m-Quadrat entfernt. Alle Pflanzenteile wurden aus dem Boden entfernt, und der Boden wurde entweder ohne Wurzel oder mit 10 cm langen Wurzelteilen von C. arvense in den Boden zurückgegeben. Die Anzahl der Sprosse, die oberirdische Biomasse und die Anzahl der Blätter wurden gemessen. 50-60 % der Variationen der Biomasse erklärten sich aus Bodentiefe und Zeit (P < 0,001). Beim Einbringen der Wurzelfragmente stieg die Sprossdichte in einer von vier Behandlungen an, hatte aber keine Auswirkungen auf die Biomasse im Vergleich zur Produktion aus ungestörtem Wurzelsystem. Anhand der Anzahl der Blätter zeigte sich, dass Sprosse aus allen Bodentiefen die regenerative Mindestkapazität überstiegen. Wir schließen daraus, dass sich das intakte Wurzelsystem aus allen Bodentiefen innerhalb einer Saison regenerieren konnte und in hohem Maße zur produzierten Biomasse im Vergleich mit der aus Wurzelfragmenten in den oberen Bodenschichten beiträgt.Stichwörter: Anzahl der Blätter, Biomasse, Kompensationspunkt, Wurzelsyste

Ugrasharving i korn

Denne undersøkelsen har som målsetning å finne klarere kriterier om det skal harves, når det skal harves, hvordan harva skal stilles inn og hvilke harvtyper og tindetyper som er optimale på forskjellige jordtyper. Videre skal en se på hvordan underkultur kan tilpasses ugrasharving. Resultatene første år er interessante, men det er for tidlig å trekke konklusjoner

Activities of the NJF working group on Perennial Weeds - Comparison of seasonal sprouting readiness of three perennial weeds

The NJF working group on Perennial Weeds was launched in 2001 to facilitate communication and collaboration among the research scientists working with perennial weeds. The working group belongs to the Section of Plant Protection of the NJF (Nordic Association of Agricultural Scientist)