Risk evaluation of mechanical, chemical and combined mechanical-chemical weed control in sugar beet

Feldversuche mit Zuckerrüben wurden an zwei Standorten in Niedersachsen durchgeführt, um die Effizienz und die Risiken mechanischer (Hacke), chemischer (Herbizidspritzung) und kombinierter mechanisch-chemischer Unkrautbekämpfung zu vergleichen. Die Unkrautbekämpfungstechniken wurden in vier Wiederholungen an zwei Standorten getestet. Hier werden Ergebnisse zur Wirksamkeit gegenüber Verunkrautung und zur Auswirkung auf Mulchbedeckung und Bodenerosion durch Wasser berichtet. Nach der Durchführung aller Nachauflaufbehandlungen wurden in den Parzellen mit rein mechanischen und rein chemischer Unkrautbekämpfung Regensimulationen durchgeführt, um den Oberflächenabfluss und den Bodenabtrag zu messen. Der kumulative Bodenabtrag war zwei Mal größer bei der mechanischen als bei der chemischen Unkrautregulierung in Sieboldshausen (p-Wert=0,03), aber 8 Mal höher bei der chemischen als bei der mechanischen Unkrautregulierung in Obernjesa (p-Wert=0,004). Der kumulative Wasserabfluss war nicht signifikant verschieden zwischen den beiden Unkrautbekämpfungstechniken in Sieboldshausen, aber wiederum signifikant höher für die chemisch als für mechanisch behandelten Flächen in Obernjesa. Der Wirkungsgrad der chemischen Unkrautregulierung war nur bei der zweiten Nachauflaufbehandlung am Standort 1 signifikant höher als der der mechanischen Unkrautregulierung. Bei der zweiten Nachauflaufbehandlung wurde die Mulchbedeckung an beiden Standorten durch das Hacken signifikant stärker reduziert als in der Herbizidvariante.Sugar beet field trials were conducted at two sites in Southern Lower Saxony to compare mechanical (hoeing), chemical (herbicide spraying) and combined mechanical-chemical weed control operations in their weed control efficacy, and in their effect on mulch coverage and soil erosion by water. Three treatments were tested in four replications at both sites. To measure runoff and soil erosion, rainfall simulations were carried out for mechanical and chemical treatments after completion of the last weed control operation. The cumulative soil loss was twice higher in mechanical than in chemical treatment in Sieboldshausen (p-value=0.03) but was eight times lower in mechanical than in chemical treatment in Obernjesa (p-value=0.004). The cumulative runoff was not significantly different between treatments in Sieboldshausen but was again significantly lower for hoeing than for spraying in Obernjesa. Also the effect on weed control efficacy by second weed control operation (2-4-leaf-stage) was site-specific, with no effect in Sieboldshausen and significantly reduced efficacy of mechanical weed control in Obernjesa. Mulch coverage loss due to the second weed control operation was significantly higher for mechanical than for chemical treatment at both sites

Toward homochiral protocells in noncatalytic peptide systems

The activation-polymerization-epimerization-depolymerization (APED) model of Plasson et al. has recently been proposed as a mechanism for the evolution of homochirality on prebiotic Earth. The dynamics of the APED model in two-dimensional spatially-extended systems is investigated for various realistic reaction parameters. It is found that the APED system allows for the formation of isolated homochiral proto-domains surrounded by a racemate. A diffusive slowdown of the APED network such as induced through tidal motion or evaporating pools and lagoons leads to the stabilization of homochiral bounded structures as expected in the first self-assembled protocells.Comment: 10 pages, 5 figure

Universal Sequence Replication, Reversible Polymerization and Early Functional Biopolymers: A Model for the Initiation of Prebiotic Sequence Evolution

Many models for the origin of life have focused on understanding how evolution can drive the refinement of a preexisting enzyme, such as the evolution of efficient replicase activity. Here we present a model for what was, arguably, an even earlier stage of chemical evolution, when polymer sequence diversity was generated and sustained before, and during, the onset of functional selection. The model includes regular environmental cycles (e.g. hydration-dehydration cycles) that drive polymers between times of replication and functional activity, which coincide with times of different monomer and polymer diffusivity. Template-directed replication of informational polymers, which takes place during the dehydration stage of each cycle, is considered to be sequence-independent. New sequences are generated by spontaneous polymer formation, and all sequences compete for a finite monomer resource that is recycled via reversible polymerization. Kinetic Monte Carlo simulations demonstrate that this proposed prebiotic scenario provides a robust mechanism for the exploration of sequence space. Introduction of a polymer sequence with monomer synthetase activity illustrates that functional sequences can become established in a preexisting pool of otherwise non-functional sequences. Functional selection does not dominate system dynamics and sequence diversity remains high, permitting the emergence and spread of more than one functional sequence. It is also observed that polymers spontaneously form clusters in simulations where polymers diffuse more slowly than monomers, a feature that is reminiscent of a previous proposal that the earliest stages of life could have been defined by the collective evolution of a system-wide cooperation of polymer aggregates. Overall, the results presented demonstrate the merits of considering plausible prebiotic polymer chemistries and environments that would have allowed for the rapid turnover of monomer resources and for regularly varying monomer/polymer diffusivities

Natural colloid mobilization and leaching in wettable and water repellent soil under saturated condition

The coupled transport of pollutants that are adsorbed to colloidal particles has always been a major topic for environmental sciences due to many unfavorable effects on soils and groundwater. This laboratory column study was conducted under saturated moisture conditions to compare the hydrophobic character of the suspended and mobilized colloids in the percolates released from a wettable subsoil and a water repellent topsoil. Both soils with different organic matter content were analyzed for wettability changes before and after leaching using sessile drop contact angles as well as water and ethanol sorptivity curves, summarized as repellency index. Hydrophobicity of the effluent suspensions was assessed using the C18 adsorption method. Water repellency level of the repellent soil decreased after leaching but remained on a lower level of water repellency, while, the wettable soil remained wettable. The leached colloids from the repellent soil were predominantly hydrophilic and the percentage of the hydrophobic colloid fraction in the effluent did not systematically changed with time. Total colloid release depended on soil carbon stock but not on soil wettability. Our results suggest that due to the respective character of transported colloids a similar co-transport mechanism for pollutants may occur which does not depend explicitly on soil wettability of the releasing horizon, but could be more affected by total SOM content. Further studies with a wider range of soils are necessary to determine if the dominant hydrophilic character of leached colloids is typical. Due to the mostly hydrophilic colloid character we conclude also that changes in wettability status, i.e. of wettable subsoil horizons due to the leachate, may not necessarily occur very fast, even when the overlaying topsoil is a repellent soil horizon with a high organic matter content

Natural colloid mobilization and leaching in wettable and water repellent soil under saturated condition

The coupled transport of pollutants that are adsorbed to colloidal particles has always been a major topic for environmental sciences due to many unfavorable effects on soils and groundwater. This laboratory column study was conducted under saturated moisture conditions to compare the hydrophobic character of the suspended and mobilized colloids in the percolates released from a wettable subsoil and a water repellent topsoil. Both soils with different organic matter content were analyzed for wettability changes before and after leaching using sessile drop contact angles as well as water and ethanol sorptivity curves, summarized as repellency index. Hydrophobicity of the effluent suspensions was assessed using the C18 adsorption method. Water repellency level of the repellent soil decreased after leaching but remained on a lower level of water repellency, while, the wettable soil remained wettable. The leached colloids from the repellent soil were predominantly hydrophilic and the percentage of the hydrophobic colloid fraction in the effluent did not systematically changed with time. Total colloid release depended on soil carbon stock but not on soil wettability. Our results suggest that due to the respective character of transported colloids a similar co-transport mechanism for pollutants may occur which does not depend explicitly on soil wettability of the releasing horizon, but could be more affected by total SOM content. Further studies with a wider range of soils are necessary to determine if the dominant hydrophilic character of leached colloids is typical. Due to the mostly hydrophilic colloid character we conclude also that changes in wettability status, i.e. of wettable subsoil horizons due to the leachate, may not necessarily occur very fast, even when the overlaying topsoil is a repellent soil horizon with a high organic matter content

Natural colloid mobilization and leaching in wettable and water repellent soil under saturated condition

We thank Andreas Kolb and Michael Wachten for their helps with preparing staff and soil sampling, and the German Academic Exchange Service (DAAD) for partial financial support of this project. We appreciate the valuable manuscript reviews provided by Professor Mark Coyne from the University of Kentucky, USA.Peer reviewe

Standortspezifische Risikobewertung von Verfahren mechanischer und chemischer Unkrautbekämpfung in Reihenkulturen als Baustein eines nachhaltigen Pflanzenschutzes (Verbundvorhaben)

Die F2F-Strategie der EU zielt auf eine Reduktion des Pestizideinsatzes ab. In der Unkrautkontrolle sollen dazu mechanische Maßnahmen chemische ersetzen. Eine mehrdimensionale Bewertung mechanischer Verfahren auf ökologische, ökonomische und verfahrenstechnische Parameter liegt jedoch bislang nicht vor. Ziel des Projekts war es daher, Kenngrößen mechanischer und chemischer Unkrautbekämpfung in Zuckerrüben als Modellfrucht zu erfassen und zu bewerten. Zu diesem Zweck wurden 3 methodische Ansätze verwendet: (i) Feldversuche wurden in 3 Jahren auf 5-7 Feldern bei Göttingen durchgeführt, um die Auswirkungen des Hackens zur Unkrautkontrolle auf Regenwürmer, Insekten und Spinnen, Wassererosion sowie Unkrautwirkungsgrad und Zuckerrübenertrag zu erfassen; (ii) Das ökotoxikologische Risiko von 5 Unkrautbekämpfungs-verfahren wurde mit SYNOPS-GIS modelliert; (iii) Ressourcenverbrauch, Treibhausgas(THG)-Emissionen und Wirtschaftlichkeit wurden für 11 Unkrautbekämpfungsverfahren mittels Literatur und Webanwendungen berechnet. Die Gesamtbetrachtung der mehrdimensionalen Risiken verschiedener konventioneller und neuer Verfahren zeigt, dass derzeit keine Methode als uneingeschränkt umweltfreundlich bezeichnet werden kann. Die toxikologische Risikobewertung mit SYNOPS-GIS zeigt, dass die Flächenspritzung von praxisüblichen Herbiziden in den meisten Boden-Klima-Räumen (BKR) und Jahren mit einem niedrigen toxikologischen Risiko verbunden. Die Flächenspritzung mit einem Herbizid wie Conviso One ist zwar vorteilhaft für Energieverbrauch, Klimawirkung und Toxizität für Bodenorganismen, weist aber die höchste akute Toxizität auf. Herkömmliche mechanische Verfahren sind toxikologisch zwar unbedenklich, im Vergleich zum ganzflächigen Herbizideinsatz aber mit 100-150 % höheren THG-Emissionen verbunden. Insgesamt hat ein Kleinroboter kombiniert mit Punktspritzung Vorteile. Diese Technik weist einen geringeren Ressourcen- und Energieverbrauch als die konventionelle Flächenspritzung sowie ca. 30 % geringere THG-Emissionen auf und hat ein um 87 % niedrigeres toxikologisches Risiko. Bodenerosion, Abundanz von Regenwürmern, Insekten und Spinnen sowie Zuckerrübenertrag unterschieden sich nicht zwischen den Unkrautbekämpfungs-verfahren