Antriebsdynamik von Multirotor VTOL's

Die Antriebe von Multirotor- VTOL’s (Vertical Take Off and Landings) bestehen heute aus mehreren Propellern mit Brushless- Motoren. Die Propeller sind dabei in fast allen Fällen starr mit den Motorachsen gekoppelt. Um die Systeme in der Luft zu navigieren und zu stabilisieren, ist es nötig, die Drehzahlen dynamisch zu verändern. Die Dynamik der ganzen Systeme ist dabei wesentlich von der Dynamik der Antriebe abhängig. Dieser Fachbeitrag beschäftigt sich mit der Simulation der Motor-/Propellerkombination und zeigt auch auf, worauf speziell geachtet werden muss, damit diese eine hohe Dynamik erreicht

Cover Crop Productivity in Contrasting Growing Conditions and Influence on the Subsequent Crop

In arable systems, cover crops provide multiple ecosystem services involved in soil protection and fertility. They can efficiently compete against weeds, control erosion or recycle nutrients. The supply of these services is however largely dependent on cover crop growth as most of the services are related to biomass production. The choice of a cover crop adapted to the growing conditions is thus essential. Growing mixtures instead of sole crops is expected to be a way to overcome variable growing conditions and to insure high biomass production.Different field trials have been conducted from 2013 to 2016 in Nyon, Switzerland to assess cover crop biomass production and stability, and their influence on the following crop. Indian mustard, field pea, black oat and phacelia were sown as sole crops and in mixtures with different diversity levels (2, 3 and 4 species). A mixture of 11 species (50% of legumes and 50% of other species) was also tested. Biomass production was assessed about three months after seeding, just before the seeding of the next main crop, in two 0.5 m × 0.5 m quadrats. For each cover crop, a risk of failure, e.g. the probability of producing less than 3 t/ha (minimal biomass allowing to provide the services expected from cover crops), was estimated. Weed pressure was appraised by weed biomass in quadrats. The yield of the following main crop, here winter wheat, was determined after harvesting with a combine harvester, at wheat maturity, in summer. Sole crops showed very contrasting performance according to the growing conditions. Pea was the most productive in low yielding conditions with 2 t/ha while other sole crops produced only 0.5 t/ha. Pea was barely more productive in high yielding conditions, reaching only 3 t/ha when cover crop average was 6 t/ha. By contrast, mustard and oat showed high production potential in these conditions, exceeding 7 t/ha. Pea should thus be favoured when the growing conditions are clearly identified as limiting (low N availability), while oat or mustard should be chosen in favourable conditions. However, in general, conditions are hardly predictable. Our results showed that mixtures should be preferred as they were adapted to a wider range of environments than sole crops, performing well regardless of the conditions and resulting in a lower risk of failure than sole crops. The 11-specie mixture revealed that generally 4 to 5 species are sufficient to insure a good performance regardless of the conditions. Regarding cover crop effect on the following crop, we evidenced the importance of high biomass production for efficient weed control and positive influence on crop yield in no till treatments.Our results showed that cover crop mixtures rather than sole crops should be chosen as they insure high biomass production and thus a good supply of ecosystem services. In addition, cover crop cultivation, even for a short period, proved to be paramount to the maintenance of grain yield and soil fertility on the long term, especially in reduced tillage systems

Cover Crops to Secure Low Herbicide Weed Control Strategies in Maize Grown with Reduced Tillage

As a key-element of conservation agriculture, the occasional or systematic suppression of full-inversion ploughing implies an adaptation of the cropping system. To assess the ability of cover crops to control weeds in a subsequent maize crop grown with reduced tillage, three annual experiments were implemented at the research station of Agroscope Changins, Nyon, Switzerland. Ten non-wintering cover crop (CC) species were sown in mid-summer and compared to a bare soil treatment in strip-plot experiments including different weeding strategies according to integrated weed management rules. In case of a predictable impasse for weed control, an alternative management option was chosen 1) at the end of winter: total herbicide application instead of no herbicide application, 2) at the beginning of May before maize sowing: minimum soil tillage instead of no tillage. The ability of cover crop species to control weed was evaluated at the stage 2-4 leaves of maize. The shoot dry matter yield of maize was measured at harvest at the end of August. At the beginning of November, mean CC dry shoot biomass varied between 1.2 and 11.1 t DM ha-1 depending on experimental year and CC species. On average over the three years, Asteraceae (Helianthusannuus and Guizotiaabyssinica) showed the highest shoot dry matter among the tested species (> 6.0 t DM ha-1). Legume species (Pisumsativum arvense, Trifolium alexandrinum and Vicia sativa) and Brassicaceae species (Brassicacampestrisoleifera and Raphanussativuslongipinnatus) presented the lowest 3-year mean shoot biomass (≤4.0 t DM ha-1) At the end of winter, the three legume species and Avenastrigosa showed the highest plant residue soil cover and Brassicaceae species the lowest one. CC residue soil cover at the end of winter was only slightly positively correlated with CC autumn shoot biomass. In three out of eight cases, the chosen weeding strategy was very efficient in terms of weed control at the stage 2-4 leaves of maize. In the remaining five cases, the weeding strategy did not succeed in preventing weed infestation at the beginning of maize development. A mean weed cover higher than 15% was observed when no total herbicide and/or no tillage was applied before maize sowing. In three out of these five cases, a significant CC effect on weed cover could be observed. CC species able to produce high amounts of biomass in autumn appeared to be useful in terms of weed control. The most efficient CC species varied from year to year: G. abyssinica in 2011, H. annuus in 2012 and A. strigosa in 2014. CC effect on maize yield was significant in a single case, but the effect of CC species tended to be positive compared to the control treatment without CC. Despite only partial efficacy, the use of cover crops is recommended for limiting weed incidence in cropping systems aimed at reducing soil tillage and herbicide use

Specific interactions leading to transgressive overyielding in cover crop mixtures

Growing mixtures of species instead of sole crops is expected to increase the ecosystem services provided by cover crops. This study aimed at understanding the interactions between species and investigating how they affect the performance of the mixture. Four species were combined in six bispecific mixtures in a field experiment. The performance of each species when grown in a mixture was compared to its performance as a sole crop at different sowing densities, to characterise the influence of intra- and interspecific competition for each species. Intra- and interspecific competition coefficients were quantified using a response surface design and the hyperbolic yield-density equation. Interactions between the four species ranged from facilitation to competition. Most of the mixtures exhibited transgressive overyielding. Without nitrogen (N) fertilisation, high complementarity between species allowed to achieve the highest biomass. With N fertilisation, high dominance of one mixture component should be avoided to achieve good performance. A revised approach in the use of the land equivalent ratio for the evaluation of cover crop mixtures is also proposed in this study. It allows to better identify transgressive overyielding in mixtures and to better characterise the effect of one species on the other within the mixture

Coexistence of specialist and generalist species is shaped by dispersal and environmental factors

Disentangling the mechanisms mediating the coexistence of habitat specialists and generalists has been a long-standing subject of investigation. However, the roles of species traits and environmental and spatial factors have not been assessed in a unifying theoretical framework. Theory suggests that specialist species are more competitive in natural communities. However, empirical work has shown that specialist species are declining worldwide due to habitat loss and fragmentation. We addressed the question of the coexistence of specialist and generalist species with a spatially explicit metacommunity model in continuous and heterogeneous environments. We characterized how species' dispersal abilities, the number of interacting species, environmental spatial autocorrelation, and disturbance impact community composition. Our results demonstrated that species' dispersal ability and the number of interacting species had a drastic influence on the composition of metacommunities. More specialized species coexisted when species had large dispersal abilities and when the number of interacting species was high. Disturbance selected against highly specialized species, whereas environmental spatial autocorrelation had a marginal impact. Interestingly, species richness and niche breadth were mainly positively correlated at the community scale but were negatively correlated at the metacommunity scale. Numerous diversely specialized species can thus coexist, but both species' intrinsic traits and environmental factors interact to shape the specialization signatures of communities at both the local and global scales