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Water retention properties of wood fiber based growing media and their impact on irrigation strategy
(2024)
Distribution of water and air in growing media during ebb-and-flow irrigation depends on water storage properties (water retention curve) and water transport properties (hydraulic conductivity) of the materials. Growing media with their high number of coarse pores are known to exhibit strong hysteresis, i.e., differences in the water retention properties during drying and wetting cycles. To account for potential ecological disadvantages of peat, wood fibers are commonly used as substitutes for peat in growing media. However, the wood fibers generally have higher air capacities and hydraulic conductivities and lower water capacities compared to peat which may results in necessary adaptions of the irrigation strategy. Tools to optimize irrigation systems are physically based water transport models, such as HYDRUS-1D, which is commonly used to describe water transport in soils, but not often for growing media. In this study, white peat and pure wood fibers were used to describe differences in their water retention behavior. Water retention curves (drying cycles) and hydraulic conductivities were measured with standard analytical procedures. Hysteresis of the water retention curves was analytically determined based on their capillary rise properties. The results were used with a modified HYDRUS-1D model to test model quality against measured water contents during ebb-and-flow irrigation cycles and to optimize the irrigation strategy for the different materials. The results showed that the model quality was sufficiently good only if the strong hysteresis of the water retention curves was considered during the simulation process. Different strategies were tested to modify ebb-and-flow irrigation (irrigation frequency, irrigation duration and irrigation height) in that way that the water suction in the root zone was similar to that of the peat material. Simulation results showed that significant improvements could only be reached by increasing the flooding depth in ebb-and-flow systems to ensure an optimum water supply of plants in the wood fiber based growing media.
Wood fibers can contribute to replacing peat in growing media and thus help to protect peatlands. As domestic, renewable raw materials, they represent a sustainable option for this purpose. To date, however, wood fibers are usually used as a peat substitute at a maxi-mum of 30% (v/v). A main reason for this limitation is the insufficient microbial stability of wood fibers, which favors nitrogen immobilization and can thus impair nitrogen supply of plants. To address this drawback, in this study wood fibers were subjected to different thermal or thermal-hydrolytic treatments. Seedling tests with napa cabbage were conducted to determine whether treated wood fibers were free of phytotoxic substances. Mixtures with 50% (v/v) wood fiber and white peat each were used. In addition, three wood fiber varieties were evaluated in the cultivation of petunia. Two wood fiber proportions (30 and 60% v/v) and two nitrogen fertilization rates (common and increased supply) were included in each case. In the seedling trial with napa cabbage, no phytotoxic effects were detectable in any of the wood fiber variants investigated. However, when cultivating petunias, both shoot mass growth and number of flowers decreased with increasing wood fiber content. In substrates with a wood fiber content of 60% (v/v), plant development was inhibited so severely that the petunias no longer achieved marketable quality. Increased nitrogen fertilization was able to compensate for this negative effect only in few cases. This suggests that other factors than nitrogen limited plant growth in wood fiber-rich substrates. Among others, physical proper-ties such as the lower water capacity of wood fibers may be a cause. More in-depth investigations are still required in this regard.
Enhancing the nutritional value of pears through agronomic biofortification with iodine (Abstract)
(2024)
Mehr direkte Demokratie wagen : Volksentscheid und Bürgerentscheid: Geschichte - Praxis - Vorschläge
(2024)
Die Wahlbeteiligung sinkt, die Parteien haben immer weniger Mitglieder. Viele Bürgerinnen und Bürger kehren der Politik den Rücken zu - ein wesentlicher Grund dafür: Ob Klimaschutz oder Migration, Steuern oder Schuldenbremse, Kranken- oder Rentenversicherung ... Ständig treffen Politikerinnen und Politiker in Deutschland und Europa grundlegende Weichenstellungen, ohne dass die Bürgerinnen und Bürger darüber selbst entscheiden können. Dies soll anders werden: 42 Autorinnen und Autoren - darunter Wissenschaftlerinnen und Wissenschaftler, Politikerinnen und Politiker und Vertrauensleute von Volksbegehren in den Bundesländern - analysieren und berichten über direkte Demokratie. Insgesamt ergibt sich ein Bild, das für die Öffnung des Grundgesetzes spricht. Die Arbeit des Parlaments und der Parteien bleibt unentbehrlich - aber ergänzend sollen die Bürgerinnen und Bürger die Möglichkeit haben, durch Volksbegehren und Volksentscheid einzugreifen und punktuell politische Fragen selbst zu beantworten. Was in der Schweiz und vielen anderen europäischen Staaten, in vielen US-Gliedstaaten und in den deutschen Bundesländern und Gemeinden funktioniert, könnte auch auf Bundes- und Europaebene gegen Politikverdrossenheit helfen und Lust auf mehr politisches Engagement machen.
Die Maschine ist in der Lage faserverstärkte thermoplastische Kunststoffrohre herzustellen. Entwickelt und konstruiert wurde die Maschine als Open Source Hardware Projekt. Das bedeutet die Baupläne und Zeichnungen werden frei zur Verfügung gestellt. Heimwerker und andere Interessierte sollen dadurch die Möglichkeit bekommen faserverstärkte Rohre eigenständig und günstig herzustellen. Die Entwicklung und Konstruktion der Wickelmaschine ist das Ergebnis einer Masterarbeit an der Hochschule Osnabrück.