Organic Soil Management: Impacts on Yields, Soil Quality and Economics

Understanding organic management practices is a key in developing sustainable organic farming systems. We report the results of four different organic fertilization strategies in a field trial on yields, soil quality and economic performance. We found highest yields and economic performance in two direct plant feeding strategies. One of these strategies, a newly developed strategy based on biowaste compost (GFT) and an additional fertilizer performed well in terms of yields but looks also very promising in terms of soil quality and biodiversity. The economic perspective of this strategy renders it promising in regions with little animal manures

Organic fertilisers of the mac trial and their impact on soil quality, environment and climate change

After 8 years, the MAC field trial in Lelystad, the Netherlands, shows the effects of different fertiliser strategies, ranging from animal manure to plant compost to mineral fertiliser. The impact on yield, soil quality, soil health, environment and climate change is discussed. The trial is unique in monitoring the effect of so many types of fertilisers over so many year

Dutch research on organic agriculture: approaches and characteristics

Dutch research on organic agriculture began in the late 1970s. Key characteristics of this research were the systems approach and the strong participation of farmers and stakeholders. The ambitions for a fully sustainable organic agriculture as formulated by the Dutch organic sector set the research agend

Integrating all-optical switching with spintronics

All-optical switching (AOS) of magnetic materials describes the reversal of the magnetization using short (femtosecond) laser pulses, and has been observed in a variety of materials. In the past decade it received extensive attention due to its high potential for fast and energy-efficient data writing in future spintronic memory applications. Unfortunately, the AOS mechanism in the ferromagnetic multilayers commonly used in spintronics needs multiple pulses for the magnetization reversal, losing its speed and energy efficiency. Here, we experimentally demonstrate `on-the-fly' single-pulse AOS in combination with spin Hall effect (SHE) driven motion of magnetic domains in Pt/Co/Gd synthetic-ferrimagnetic racetracks. Moreover, using field-driven-SHE-assisted domain wall (DW) motion measurements, both the SHE efficiency in the racetrack is determined and the chirality of the optically written DW's is verified. Our experiments demonstrate that Pt/Co/Gd racetracks facilitate both single-pulse AOS as well as efficient SHE induced domain wall motion, which might ultimately pave the way towards integrated photonic memory devices

Gravitational Lens Time Delays in CDM

In standard CDM halo models, the time delay of a gravitational lens is determined by the cold baryon mass fraction, f, of the visible galaxy relative to the overall halo. The observed time delays in PG1115+080, SBS1520+530, B1600+434 and HE2149-2745 give Hubble constants consistent with the HST Key Project value of H0=72+/-8 km/s Mpc only if f>0.2 (1-sided 68% confidence), which is larger than the upper bound of fmax=Omega_b/Omega_0=0.15+/-0.05 estimated from the CMB. If all available baryons cool and f=fmax then the time delays imply H0=65+/-6 km/s Mpc (95% confidence). If local inventories of cold baryons, f=0.013/h70, are correct, then H0=52+/-6 km/s Mpc and the halo parameters closely match isothermal mass models. Isothermal models are also consistent with strong and weak lens studies, stellar dynamics and X-ray observations on these scales, while significantly more centrally concentrated models are not. There is a a conflict between gravitational lens time delays, the local distance scale and standard CDM halo models.Comment: Submitted to ApJ. 22 pages, 7 figure

Growth and metabolism of sponges

Sponges (phylum Porifera) are multi cellular filter-feeding invertebrate animals living attached to a substratum in mostly marine but also in freshwater habitats. The interest in sponges has increased rapidly since the discovery of potential new pharmaceutical compounds produced by many sponges. An enormous amount of different chemical structures have been found. Thus far no sustainable production technique has been developed for these marine natural products, because not sufficient knowledge is present about the needs of sponges for both growth and bioactive compound production. The aim of this thesis was to get a better understanding of the growth and metabolism of sponges and of their nutritional needs. Aquaculture is thus far the best method to produce these compounds, although also this technique is not fully developed. To gain more insight in the nutritional needs for growth, we studied the growth rate of Haliclona oculata in its natural environment, Oosterschelde, the Netherlands, and monitored environmental parameters in parallel (Chapter 2). A stereo photogrammetry approach was used for measuring growth rates. Stereo pictures were taken and used to measure volumetric changes monthly during 1 year. The volumetric growth rate of Haliclona oculata showed a seasonal trend with the highest average specific growth rate measured in May: 0.012±0.004 day−1. In our study a strong positive correlation (p In order to produce drugs by culturing sponges their growth must be improved. To improve growth, basic knowledge about how food sources are used by the sponge is needed. To find the exact relation between food retained and food converted to sponge biomass we need to be able to distinguish between feed components and sponge biomass, which means we need biomarkers for the feed and for the sponge. The fatty acid (FA) composition of organisms is specific and can therefore be used as biomarkers. We identified and compared fatty acid profiles of five different sponges in three habitats with those in the suspended particulate matter (SPM) in the surrounding water (Chapter 4). Haliclona oculata and Haliclona xena from the Oosterschelde, Haliclona xena and Halichondria panicea from Lake Veere, both in The Netherlands and Dysidea avara and Aplysina aerophoba from the Mediterranean were studied. In the SPM we found comparable FAs to the FAs of sponges up to chain lengths of 28 C-atoms. Different species of sponges showed similarities, but also very different FA profiles, while they were collected from the same habitat at the same moment. The biomarkers for diatoms and dinoflagellates were abundantly found in all sponges except A. aerophoba as this sponge relies mostly on bacterial food sources based on the many bacterial FAs found in this sponge. In all species, except A. aerophoba, C26:3(5,9,19) and C26:2(5,9) were very abundantly present. These FAs were also abundant in the SPM, while it was stated in literature that these compounds are very typical for sponges. Several FA biomarkers were found for the different sponges. Fatty acid composition is dependent on different factors like food availability and temperature and thus the composition will change in the different seasons. We have studied fatty acid composition and stable isotope 13C natural abundance of suspended particulate matter (SPM) from seawater and sponges in different seasons in the same locations as in chapter 4 (Chapter 5). 13C natural abundance can be used to find the origin of compounds, as the 13C values of compounds are similar to the values from their original producers. The FA concentration variation in sponges was related to changes in fatty acid concentration in SPM. 13C natural abundance in sponge specific FAs showed very limited seasonal variation at all sites. Algal FAs in sponges were mainly acquired from the SPM through active filtration in all seasons. Sponge specific FAs had similar 13C ratios as algal FAs in May at the two Dutch sites, suggesting that sponges were mainly growing during spring and probably summer. During autumn and winter, they were still actively filtering, but the food collected during this period had little effect on sponge 13C values suggesting limited growth. The bacterial sponge A. aerophoba relies mostly on the symbiotic bacteria. In all sponges we found that the ω7 longer chain FAs, C24:1(17) and C26:3(5,9,19) could be traced back to be of bacterial origin. Using a 13C pulse-chase approach metabolic rate can be studied inside organisms. The carbon metabolism of two marine sponges, Haliclona oculata from the Oosterschelde (The Netherlands) and Dysidea avara from the Mediterranean (Spain), has been studied (Chapter 6). The sponges were fed 13C labelled diatom (Skeletonema costatum) for 8 hours in a closed system during which they took up between 75 and 85 % of the diatoms added. At different times whole sponges were sampled for total 13C enrichment, fatty acid composition and 13C enrichment in these fatty acids. During the first day the level of 13C label inside the sponges stayed the same after which the 13C label was metabolized and excreted. Algal biomarkers present in the sponges were highly labeled after feeding and their labeling levels decreased from the second day until no label was left 10 days after enrichment. The sponge specific long chain C26 fatty acids incorporated 13C label already during the first day and the amount of 13C label inside these FAs kept increasing until 3 weeks after labeling. Thus, the algae fed to the sponges were taken up by the sponges within 8 hrs and first conversion started during the first day. Conversion of label occurred at least until at least 3 weeks after feeding. In different studies it was shown that sponges grow slow, but are able to regenerate damaged tissue fast. Moreover, it has been found that damaged tissue coincides with higher secondary metabolite production. Therefore, we were interested in carbon metabolic rate changes after damaging sponge tissue. We have examined the change of carbon metabolic rate of fatty acid synthesis due to mechanical damage of sponge tissue in Haliclona oculata and Dysidea avara (Chapter 7). Metabolic studies were performed by feeding sponges with 13C labeled biomass of diatom, Pheaodactylum tricornutum, either after or before damaging and tracing back the 13C content in the damaged and healthy tissue. Filtration and respiration rate in both sponges responded quickly to damage. For the finger-sponge H. oculata the rate of respiration was reduced immediately after damage. 6 Hours after damage the filtration rate increased to a level that was higher than the starting value, while the respiration rate returned to the initial value before damage. For the encrusting sponge D. avara the filtration rate also decreased directly after damage, but in this case it did not return to the value before damage after one day. Respiration was not measured for D. avara. The 13C data revealed that H. oculata has a higher metabolic rate in the tips where growth occurs compared to the rest of the tissue and that the metabolic rate is increased after damage of the tissue. For D. avara no differences were found between damaged and non damaged tissue. Thus far it is still not fully understood why, when, where and how bioactive metabolites are produced in sponges. For the near future sea-based sponge culture seems to be the best production method. However, for controlled production in a defined system it is better to develop in vitro production methods. This could be in vitro sponge culture or sponge cell culture, culture methods for symbionts or transfer production routes into another host. We still have insufficient information about the background of metabolite production in sponges. Before culture methods are developed we should focus on factors that induce metabolite production, which could be done in the natural habitat by studying the relation between stress factors (such as predation) and the production of bioactive metabolites. Next, the biosynthetic pathway of metabolite production should be unraveled, as well as the genes involved. The location of production within the sponge should be identified in order to choose between sponge cell culture and symbiont culture. Alternatively the biosynthetic pathways could be introduced into hosts that can be easily cultured in bioreactors. Chapter 8 discusses the current state of sponge metabolite production and the steps that need to be taken to develop commercial production techniques. The different possible production techniques are also discussed. <br/

Absorption and generation of femtosecond laser-pulse excited spin currents in non-collinear magnetic bilayers

Spin currents can be generated on an ultrafast timescale by excitation of a ferromagnetic (FM) thin film with a femtosecond laser-pulse. Recently, it has been demonstrated that these ultrafast spin currents can transport angular momentum to neighbouring FM layers, being able to change both the magnitude and orientation of the magnetization in the adjacent layer. In this work, both the generation and absorption of these optically excited spin currents are investigated. This is done using non-collinear magnetic bilayers, i.e. two FM layers separated by a conductive spacer. Spin currents are generated in a Co/Ni multilayer with out-of-plane (OOP) anisotropy, and absorbed by a Co layer with an in-plane (IP) anisotropy. This behaviour is confirmed by careful analysis of the laser-pulse induced magnetization dynamics, whereafter it is demonstrated that the transverse spin current is absorbed very locally near the injection interface of the IP layer (90% within the first approx. 2 nm). Moreover, it will also be shown that this local absorption results in the excitation of THz standing spin waves within the IP layer. The dispersion measured for these high frequency spin waves shows a discrepancy with respect to the theoretical predictions, for which a first explanation involving intermixed interface regions is proposed. Lastly, the spin current generation is investigated using different number of repeats for the Co/Ni multilayer, which proves to be of great relevance for identifying the optical spin current generation mechanism

Controlling skyrmion bubble confinement by dipolar interactions

Large skyrmion bubbles in confined geometries of various sizes and shapes are investigated, typically in the range of several micrometers. Two fundamentally different cases are studied to address the role of dipole-dipole interactions: (I) when there is no magnetic material present outside the small geometries and (II) when the geometries are embedded in films with a uniform magnetization. It is found that the preferential position of the skyrmion bubbles can be controlled by the geometrical shape, which turns out to be a stronger influence than local variations in material parameters. In addition, independent switching of the direction of the magnetization outside the small geometries can be used to further manipulate these preferential positions, in particular with respect to the edges. We show by numerical calculations that the observed interactions between the skyrmion bubbles and structure edge including the overall positioning of the bubbles are fully controlled by dipole-dipole interactions

Preganglionic innervation of the pancreas islet cells in the rat

The position and number of preganglionic somata innervating the insulin-secreting β-cells of the endocrine pancreas were investigated in Wistar rats. This question was approached by comparing the innervation of the pancreas of normal rats with the innervation of the pancreas in alloxan-induced diabetic animals. The presumption was made that alloxan treatment destroys the β-cells of the islet of Langerhans and results in a selective degeneration of the β-cells innervation. Cell bodies of preganglionic fibers innervating the pancreas were identified by retrograde transport of horseradish peroxidase following pancreas injections. It was found that 25% of the cells innervating the pancreas in the left dorsal vagal motor nucleus, 50% of the cells in the ambiguus nucleus and 50% of the cells innervating the pancreas, that originate in segments C3-C4 of the spinal cord, fail to become labeled after alloxan treatment. The position and distribution of these cell groups are described in detail and are assumed to be involved in preganglionic β-cell innervation. A second cell population in the ventral horn and intermediolateral column of the segments T3-L2 of the cord also was labeled in normal rats and was not affected by the alloxan treatment. These thoracic cell groups are thus considered as sympathetic preganglionic somata that maintain direct connections to the pancreas. Additional preliminary information is presented dealing with the general aspects of sympathetic and parasympathetic organization of the pancreas innervation.

Tunable chiral spin texture in magnetic domain-walls

Magnetic domain-walls (DWs) with a preferred chirality exhibit very efficient current-driven motion. Since structural inversion asymmetry (SIA) is required for their stability, the observation of chiral domain walls in highly symmetric Pt/Co/Pt is intriguing. Here, we tune the layer asymmetry in this system and observe, by current-assisted DW depinning experiments, a small chiral field which sensitively changes. Moreover, we convincingly link the observed efficiency of DW motion to the DW texture, using DW resistance as a direct probe for the internal orientation of the DW under the influence of in-plane fields. The very delicate effect of capping layer thickness on the chiral field allows for its accurate control, which is important in designing novel materials for optimal spin-orbit-torque-driven DW motion.Comment: 12 pages, 5 figure