Integrated weed management in intensive cropping systems : towards reduction of herbicide input

Weed control in conventional cropping is commonly done using herbicides. Those, however, can have negative side-effects on the environment. The objective of this thesis is to investigate the potential of reducing herbicide input into cropping systems with a focus on two of the most important staple crops, maize and winter wheat. The thesis is divided into five main sections, dealing with different topics, i.e.: 1. Determination of herbicide efficacy 2. Efficacy of reduced herbicide dosages in maize 3. Efficacy of reduced herbicide dosages in winter wheat 4. Integrated weed management 5. Long-term effect of reduced herbicide dosages To examine herbicide efficacy at reduced dosages it is necessary to conduct a wide range of dose-reponse experiments. They are usually time and labour consuming and the assessment of herbicide efficacy is often not objective. To overcome these issues, a novel method for assessing herbicide efficacy using bi-spectral imaging was tested. The results show at the example of Bromus japonicus that weed coverage assessed with the bi-spectral camera system can serve as a non-destructive, rapid and objective method to assess herbicide efficacy. In field experiments the potential for reducing herbicide dosages in summer maize was investigated with several common herbicides and herbicide mixtures. These experiments show that it is possible to reduce herbicide dosages for weed control in maize without influencing weed control efficacy and crop yield. However, the extent to which dosages can be reduced without loss in efficacy is dependent on the herbicide used and the weed growth stage. One of the herbicide tested in the field (topramezone) is usually applied together with a methylated seed oil (MSO) adjuvant. Adjuvants play an important role for herbicide efficacy, but the mechanism for enhancing herbicide efficacy is often not clear, yet. To examine the mechanism of MSO in enhancing efficacy of topramezone, several experiments were conducted. Efficacy of topramzone was significantly increased by addition of MSO. The results show that MSO enhances the uptake and translocation of topramezone in the two tested weed species. Furthermore, physical properties of the spray solution were altered. More precisely, surface tension and thus the contact angle on the leaf was decreased. These results can explain why MSO adjuvant enhances topramezone efficacy. To investigate the potential of reducing herbicide dosages in winter wheat and its impact on weed seed production, experiments were conducted using A. fatua as weed. The results show, that dosages of the four tested herbicides could be tremendously reduced without loss in efficacy. However, A. fatua seed production was influenced by winter wheat competitiveness and herbicide mode of action and did not necessarily follow herbicide efficacy. These results on the one hand highlight the potential of herbicide dosage reduction for controlling A. fatua in winter wheat. But on the other hand, the results point out that decision on herbicide dosage reduction should not only be made on basis of herbicide efficacy data but also on its influence on weed seed production. Reduction of herbicide input cannot only be achieved by reducing herbicide dosages, but also by applying non-chemical weed control methods. These methods may not be able to fully replace herbicide usage, but they can serve as tool to reduce weed pressure and competitiveness. Field experiments were carried out to investigate the effect of adjusted winter wheat seeding rate and nitrogen fertilization on Calystegia hederacea abundance and herbicide control efficacy. The results show that increased seeding rate reduces density of this weed while enhancing herbicide efficacy. Lowering nitrogen fertilization rate towards Nmin based fertilization increased density of C. hederacea. This study points out how adjustment of agronomic parameters can influence weed competitiveness and can serve in enhancing weed control efficacy by herbicides. It had been shown in several studies that cover crops or undersown crops can effectively suppress weed growth. This suppression may not only be due to competition for resources, but also by chemical interaction via allelopathic active compounds. To examine the allelopathic effect of several cover crops, pot and laboratory experiments were carried out. These experiments show, that effects of the tested cover crops can be growth promoting or inhibiting, and are dependent on the species and extract concentration. Furthermore, cover crops can also affect growth of the crop. To discuss the long-term effect of reduced herbicide dosages on weed population development, a simulation model was set-up at the example of winter wheat and A. fatua. Different strategies for herbicide input reduction were simulated. This paper highlights the potential of reducing total herbicide input without population increase, while keeping grain yield and net return at high level. The presented articles work out the risks and potential for herbicide dosage reduction and point out the possibilities of using integrated weed management options for enhancing weed suppression.Im konventionellen Landbau werden Unkräuter in der Regel mit Herbiziden kontrolliert. Dies kann negative Auswirkungen auf die Umwelt haben. Ziel dieser Arbeit ist es Möglichkeiten zur Reduktion des Herbizideintrags in intensiven Anbausystemen zu untersuchen. Der Fokus liegt hierbei auf zwei der bedeutendsten Nutzpflanzen: Mais und Winterweizen, Die Arbeit ist in fünf Themenbereiche gegliedert, welche folgende Punkte abhandeln: 1. Bestimmung von Herbizidwirkung 2. Wirkung reduzierter Herbizidaufwandmengen in Mais 3. Wirkung reduzierter Herbizidaufwandmengen in Winterweizen 4. Integrierte Unkrautkontrolle 5. Langfristige Auswirkung reduzierter Herbizidaufwandmengen Um die Herbizidwikrung von reduzierten Aufwandmengen festzustellen, müssen breit angelegte Dosis-Wikrungsversuche durchgeführt werden. Diese sind in der Regal arbeits- und zeitintensiv und die Messung der Herbzidwirkung ist oftmals nicht objektiv. Um das Verfahren zur Herbizidmessung zu verbessern, wurde eine neue Methode getestet, welche die Herbizidwirkung anhand von bi-spektralen Bildaufnahmen bestimmt. Die Ergebnisse zeigen anhand von Bromus japonicus, dass der mit der bi-spektral Kamera gemessene Unkrautdeckungsgrad ein geeigneter Parameter ist, um Herbizidwirkung schnell, nicht desttruktiv sowie objektiv zu bestimmen. In Feldversuchen wurden unterschiedliche Herbizide einzeln und in Mischungen hinsichtlich ihres Potentials für Aufwandmengenreduktion in Mais getestet. Diese Versuche machen deutlich, dass eine Herbizidaufwandmengenreduktion zur Unkrautkontrolle in Mais möglich ist ohne dabei die Herbizidwirkung und den Maisertrag negativ zu beeinflussen. Inwieweit die Herbizidaufwandmenge ohne Wirkungsverlust reduziert werden kann hängt jedoch von dem jeweiligen Herbizid sowie des Wachstumsstadiums des Unkrauts ab. Eines der in Feldversuchen getesteten Herbizid (Topramzone) wird in Kombination mit einem Adjuvans appliziert. Adjuvantien spielen für die Herbizidwirkung eine wichtige Rolle. Die Mechanismen, mit denen Adjuvantien die Herbizidwirkung steigern können sind allerdings oftmals nicht bekannt. Um die Wirkunsgweise von methylierten Samenöl (MSO) auf die Wirkung von Topramezone zu untersuchen, wurden verschiedene Versuche durchgeführt. Die Ergebnisse ergaben, dass MSO die Aufnahme und Translokation von Topramezone in den zwei untersuchten Unkrautarten steigert. Zudem beinflusst es die physikalischen Eigenschaften der Applikationslösung. Die Ober_ächenspannung der Applikationslösung war herabgesetzt und dadurch verringerte sich der Kontaktwinkel der Applikationslösung auf dem Blatt. Die Ergebnisse können die Wirkungssteigerung von Topramezone durch Zugabe von MSO weitgehend erklären. Um das Potential zur Herbizidaufwandmengenreduktion in Winterweizen, sowie die Auswirkung auf Unkrautsamenproduktion zu untersuchen wurden Feldversuche mit Avena fatua durchgefgührt. Die Ergbenisse zeigen, dass die Aufwandmengen der vier getesteten Herbizide ohne Wirkungseinbußen stark vermindert werden können. Jedoch war die Samenprouktion von A. fatua abhängig von der Konkurrenzkraft des Winterweizens sowie des Wirkmechanismus der Herbizide und nicht zwangläufig abhängig von der Herbizidwirkung. Diese Ergbnisse verdeutlichen einerseits das Potential der Herbizidaufwandmengenreduktion zur Kontrolle von A. fatua in Winterweizen. Andereseits zeigen die Ergebnisse, dass eine Entscheidung zur Aufwandmengenreduktion nicht nur anhand der Herbizidwirkung getroffen werden sollte, sondern dass der Einfluss auf die Samenproduktion der Unkräuter für die Entscheidung berücksichtigt werden sollte. Der Herbizideintrag kann nicht nur durch Aufwandmengenreduktion vermindert werden, sondern auch durch Anwendung nicht-chemischer Unkrautkontrollmaßnahmen. Diese Maßnahmen mögen den Herbizideinsatz nicht vollständig ersetzen können, aber sie dienen als Instrument um Unkrautdruck und -konkurrenzkraft zu reduzieren. Feldversuche wurden durchgeführt, um den Einfluss von Winterweizensaatstärke und Stickstoffdüngung auf die Konkurrenzkraft von und die Herbizidwirkung auf Calystegia hederacea zu untersuchen. Die Ergbenisse zeigen, dass eine erhöhte Saatstärke die Konkurrenzkraft dieses Unkrauts verringert und gleichzeitig die Herbizidwirkung steigert. Eine Verminderung der applizierten Stickstoffmenge auf Nmin-basierte Stickstoffmengen förderte die Konkurrenzkraft von C. hederacea. Diese Versuche machen deutlich, inwieweit eine Anpassung von agronomischen Parametern die Konkurrenzkraft von Unkräutern beeinflussen kann und den Grad der Unkrautkontrolle durch Herbizide steigern kann. In einigen Arbeiten wurde gezeigt, dass Zwischenfrüchte und Untersaaten wirkungsvoll Unkraut unterdrücken können, wobei die Unterdrückung nicht nur durch Konkurrenz um Ressourcen hervorgerufen wird, sondern auch durch chemische Interaktionen über alleolpathisch wirksame Substanzen. Um die allelopathische Wirkung einiger Zwischenfrüchte zu untersuchen wurden Topf- und Laborversuche durchgeführt. Die Ergebnisse zeigen, dass die Wirkung von Zwischenfrüchten sowohl wuchsfördernd als auch wuchshemmend sein kann und dass die Wirkung artspezifisch ist sowie von der Konzentration der Stoffe abhängt. Außerdem können Zwischenfrüchte nicht nur das Wachstum der Unkräuter beeinflussen, sonder auch das der Kulturpflanze. Um den langfristigen Einfluss von reduzierten Herbizidaufwandmengen auf die Populationsentwicklung von Unkräutern am Beispiel von A. Fatua in Winterweizen zu untersuchen, wurde ein Simulationsmodell aufgestellt. Verschiedene Strategien zur Herbizidaufwandmengenreduktion wurden simuliert. Dieses Manuskript hebt das Potential hervor, Herbizidaufwandmengen bei gleichbleibendem Kornetrag und Erlös zu reduzieren, ohne dass die Unkrautpopulation ansteigt. Die in dieser Arbeit vorgestellten Manuskripte und Veröffentlichungen arbeiten die Risiken und Potentiale von Herbizidaufwandmengenreduktion aus und zeigen die Möglichkeiten auf, wie integrierte Unkrautkontrolle helfen kann, Unkräuter zu unterdrücken

Altered Nitrogen Availability in Pea-Barley Sole- and Intercrops Changes Dominance of Two Nitrophilic Weed Species

Effective and sustainable weed management in agricultural fields is a prerequisite for increasing crop yield without negatively impacting the environment. The aim of this study was to explore how varying nitrogen (N) availability in cropping arrangements of pea (Pisum sativum) and barley (Hordeum vulgare) grown as sole crops and intercrops at different fertilization levels and considering different N sources (soil mineralization, N fixation, N fertilizer) affects the response of weed species with differential N responsiveness. Crop and weed biomass were sampled at flowering and maturity. The total N content and N-15 isotope signatures were analyzed to differentiate between N sources and to estimate the amount of N available to weeds. The highly N-responsive weed (Chenopodium album) accumulated more N and biomass than the weed with reduced N responsiveness (Galeopsis spp.). Fertilizer supply favored Chenopodium album, but not the crops. Altered soil N availability caused a shift in the dominance of the nitrophilic weed species towards the highly N-responsive species. This shift in dominance could affect the long-term weed community composition and thus have implications for sustainable weed management

Sortval i ekologisk odling 2021 : sortförsök 2016–2020

Rapporten innehåller resultat från den ekologiska sortprovningen med spannmål, trindsäd och potatis under perioden 2016–2020. Resultaten är kommenterade med hänsyn till områden, årsmån och andra tillväxtbetingelser. Jämförelser är ibland även gjorda med den konventionella sortprovningen

Functional trait space in cereals and legumes grown in pure and mixed cultures is influenced more by cultivar identity than crop mixing

More efficient resource use, especially nitrogen (N) in agricultural fields could considerably reduce the losses and spillover effects on the environment. Cereal-legume mixtures can lead to more efficient uptake of growth-limiting resources, and increase and stabilize yields, due to the variation in functional traits that facilitate partitioning of niche space. Here we identify crop mixtures with functional traits that facilitate optimal N resource use in two selected cereal-legume mixtures by using the multi-dimensional trait space concept. Combinations of pea-barley and faba bean-wheat crops were grown in the field as pure cultures and mixtures in Central Sweden, during two years with contrasting weather. The ecological niche space was defined via the n-dimensional hypervolumes represented by N pool, tiller/branch number, shoot biomass, and grain yield functional traits. Regressions and correlations allowed quantifying the relations between functional traits and plant N pools. Differences in trait space were not a result of crop mixing per se, as similar hypervolumes were found in the pure culture and mixture-grown crops. Instead, the trait space differences depended on the cultivar identities admixed. Furthermore, cereals increased their efficiency for N uptake and therefore benefitted more than the legumes in the mixtures, in terms of accumulated N and grain yields. Tiller and shoot biomass production in cereals was positively correlated to N pool accumulation during the season. Resource acquisition through increased N uptake in the mixture was associated with a reduced overlap in niche-space in the mixtures, and initial seed N pools significantly contributed to within-season N accumulation, shoot and tiller production

Sortval i ekologisk odling 2022: sortförsök 2017-2021

Rapporten innehåller resultat från den ekologiska sortprovningen med spannmål, trindsäd och potatis under perioden 2017–2021. Resultaten är kommenterade med hänsyn till områden, årsmån och andra tillväxtbetingelser. Jämförelser är ibland även gjorda med den konventionella sortprovningen

Crop rotational diversity can mitigate climate-induced grain yield losses

Diversified crop rotations have been suggested to reduce grain yield losses from the adverse climatic conditions increasingly common under climate change. Nevertheless, the potential for climate change adaptation of different crop rotational diversity (CRD) remains undetermined. We quantified how climatic conditions affect small grain and maize yields under different CRDs in 32 long-term (10-63 years) field experiments across Europe and North America. Species-diverse and functionally rich rotations more than compensated yield losses from anomalous warm conditions, long and warm dry spells, as well as from anomalous wet (for small grains) or dry (for maize) conditions. Adding a single functional group or crop species to monocultures counteracted yield losses from substantial changes in climatic conditions. The benefits of a further increase in CRD are comparable with those of improved climatic conditions. For instance, the maize yield benefits of adding three crop species to monocultures under detrimental climatic conditions exceeded the average yield of monocultures by up to 553 kg/ha under non-detrimental climatic conditions. Increased crop functional richness improved yields under high temperature, irrespective of precipitation. Conversely, yield benefits peaked at between two and four crop species in the rotation, depending on climatic conditions and crop, and declined at higher species diversity. Thus, crop species diversity could be adjusted to maximize yield benefits. Diversifying rotations with functionally distinct crops is an adaptation of cropping systems to global warming and changes in precipitation.Industrial agriculture often relies on one or few crop species grown in monocultures or short crop rotations, making them vulnerable to changes in climatic conditions. Using data from several agricultural experiments in Europe and North America, we show that including more crop species or crop types in rotation can mitigate cereal yield losses caused by increasingly common shifts in climatic conditions, such as increasing temperatures and decreasing precipitation. Hence, increasing crop rotational diversity can support the climate adaptation of the way we produce our food.imag

Farmers’ intention towards intercropping adoption: the role of socioeconomic and behavioural drivers

The adoption of intercropping, a sustainable agricultural technology, is limited in Europe. This  paper  investigates factors driving the  intention to  intercrop in Sweden. Factors included in the analysis are participation in private certification schemes, interactions with  peers  and  agricultural advisors, attitude, knowledge, innovativeness, perceived intercropping attributes and  perceived behavioural control. The  first  two  reflect  potential socioeconomic determinants and  the  last four  are  possible behavioural drivers. For  the  first  time,  the  theory  of  planned behaviour (TPB) and diffusion of innovation theory were integrated to understand farmers’ adoption of  sustainable farming practices like  intercropping .  Structural equation modelling was applied to understand the behavioural drivers, whereas logit  regression was  employed to  identify the  socioeconomic determinant of adoption intention. The  paper  highlights the  important role  of  knowledge in fostering intercropping adoption. Knowledge was associated with innovativeness (B = 0.18,

Evidence for magnesium-phosphorus synergism and co-limitation of grain yield in wheat agriculture

Modern crop production is characterized by high nitrogen (N) application rates, which can influence the co-limitation of harvested yield by other nutrients. Using a multidimensional niche volume concept and scaling exponents frequently applied in plant ecological research, we report that increased N and phosphorus (P) uptake in a growing wheat crop along with enhanced grain biomass is associated with more than proportional increase of other nutrients. Furthermore, N conversion efficiency and grain yield are strongly affected by the magnesium (Mg) to P ratio in the growing crop. We analyzed a field trial in Central Sweden including nine wheat varieties grown during two years with contrasting weather, and found evidence for Mg co-limitation at lower grain yields and P co-limitation at higher yields. We argue that critical concentrations of single nutrients, which are often applied in agronomy, should be replaced by nutrient ratios. In addition, links between plant P and Mg contents and root traits were found; high root number enhanced the P:N ratio, whilst steep root angle, indicating deep roots, increased the Mg:N ratio. The results have significant implications on the management and breeding targets of agriculturally grown wheat, which is one of the most important food crops worldwide