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Weeds in conservation agriculture. Biology, emergence dynamics and modelling to improve their control
Full text linkThe increasing attention of public opinion towards the environmental impact of production activities has made it imperative to reduce the aggressiveness of productive systems on the environment. Also the agricultural sector, considered one of the principal strengths of transformation of the territory, is asked to predispose eco-compatible programmes of production. The institutions and national and international organisms encourage the adoption of techniques of conservative agriculture as a tool for guaranteeing, on the one hand the necessary crop production to face the demand for food of the growing population and, on the other the safeguarding and improvement of the quality of natural resources. Conservative agriculture is born with the intent to reduce or eliminate the intense tillage of cultivated lands that has caused impoverishment, degradation and loss of soil in favour of a more eco-friendly management of different agroecosystem components. Nevertheless weed management, the complexity of which is a deterrent for the adoption of this type of agronomic system, represents one of the main problems. Weeds are the main cause of economic losses in agriculture worldwide, both as crop yield reduction and control costs. In a conventional farming system weeds are controlled by herbicides and mechanical operations that together are able to maintain the infestation level beneath the threshold of economic damage. In a conservative system, to obtain the same level of crop defence, it is necessary to increase the chemical control with the consequent increased costs for farmers, health risks and environmental impacts. In this scenario, Integrated Weed Management plays a key role in order to achieve environmental, social and economic sustainability of crop production. Particularly, weed emergence and weed-crop competition models can provide useful indications about timing, type and cost-effectiveness of control measures.
This research has the goal of providing wider and deeper knowledge of what is involved for the weed science sector in the implementation of conservation agriculture protocols. The main objective, common to all the studies presented in this thesis, is the calibration of a prediction model to optimize the timing for the weed control in a no-tillage soil. The model under study is AlertInf, a model created for tilled soils that is based on the concept of hydrothermal time. According to this approach the emergence dynamics is determined by two main factors: temperature and water potential of the soil. Seeds in the soil accumulate hydrothermal time for their germination according to temperature threshold values and a water potential typical for each species. Chapter 1 describes the experiments for the estimation of temperature thresholds for four no-tillage soil weed species: Taraxacum officinale, Sonchus oleraceus, Senecio vulgaris, Conyza spp, comparing different methods for the estimation of this parameter. Chapter 2 highlights the importance of soil microclimate information acquisition (such as temperature and water potential) in the seed germination area. A field experiment was designed to assess the extent of changes in temperature and soil moisture resulting from no-tillage. In particular, a system of sensors, which allows the measurement of temperature and water potential in the upper soil layers, was tested as the soil surface is involved in the germination processes and weed growth in a conservative system. For modelling purposes, the emergence dynamics of the some weed species were studied and whether and how the dynamics of these species change in a different agronomic management was verified. A study was therefore conducted in a controlled environment to test the effect of the seed burial depth and tillage on the amount of emerging plants and the emergence dynamics (Chapter 3). Seasonal weed surveys were done on three experimental farms in Veneto region from 2011 to 2013 in conventional and conservative management fields to verify the species present in the two different systems and the emergence dynamics (Chapter 4). The last chapter (Chapter 5) shows the transferability of AlertInf model from maize to soybean in conventional management. A result that advances the hypothesis of the transferability also in a conservative environment.
With this thesis the bases have been established for the construction of a predictive model of weed emergences in conservation agriculture, but model construction necessitates in-depth knowledge of all the factors involved in the phenomenon determination and accurate inputs, therefore it has been underlined that many problems still have to be solved and further researches are neede
Is emergence pattern of Sonchus oleraceous affected by soil tillage system? A study conducted on bare soil, maize and soybean.
No full textSoil tillage modifi es weed seedling emergence by acting on the vertical seed distribution in
the soil profi le. Seed burial depth has the potential to change quantitatively and qualitatively
weed emergence. Sonchus oleraceus is a dominant weed increasing in prevalence in
conservation tillage managed fi elds. It seems that reduced tillage creates optimal conditions
for its establishment over the years. To better understand the emergence pattern of this
species for management decisions, an experiment was conducted to study the response in
terms of emergence magnitude and dynamics to diff erent soil tillage systems in northeast
Italy.
The research consisted in comparing weed emergence patterns in tilled and no-tilled
systems in bare soil (under simulated conditions), and in fi eld with maize and soybean. In
bare soil, two treatments were performed to simulate conditions in arable (seeds buried in
the soil and mixed in 5 cm–deep soil) and no-till managements (seeds on soil surface without
disturbance). Emerged seedlings were counted and removed weekly from spring till August.
Moreover, fi eld experiments were conducted in 2011 in maize and 2013 in soybean. In each
year, two fi elds were monitored, a conventionally tilled fi eld (autumn mouldboard ploughing
and spring harrowing) and a conservation tillage fi eld (sod seeding with the previous crop
residues on the soil surface). Emergence was sampled weekly by destructive counts in 11
fi xed 0.3x0.3 m2 quadrats per fi eld.
From comparison of the emergence patterns in conventional and conservation system,
no diff erence was observed in dynamics expressed as percentage both in bare soil and
in the two crops, even if density was diff erent between tillage systems in particular in
maize: 8 plants/m2 in conventional and 152 plants/m2 in no-tilled system. These fi ndings
are important for a future emergence modelling for this species, the same algorithm can be
used both in tilled and no-tilled system
Modeling weed emergence of Polygonum lapathifolium L. and Solanum nigrum L. in maize
No full textThe agronomic importance of knowing weed emergence patterns has been recognized for many years and several studies have been conducted on weed emergence dynamics with various approaches. Predictive weed emergence models can estimate, in a given moment, the percentage of weeds that have already emerged and the successive seedling emergence dynamics. Therefore they may be useful to achieve well-timed and efficient weed control, both chemical and mechanical. There is no universal best approach to create an accurate model, since it depends on many factors, such as climatic characteristics of the area, cultivation practices, etc. A commonly used approach is the hydrothermal time concept, based on the idea that seeds need a certain amount of hydrothermal time to germinate. The aim of the this research was to model weed emergence of Polygonum lapathifolium L. and Solanum nigrum L. to enrich and improve the information provided by the predictive emergence model AlertInf. Base temperature required for the hydrothermal time calculation of these weed species was calculated with an innovative method using alternating temperatures. Base water potential was empirically derived from field data using an iterative process. Emergence dynamics were modelled using data of seedling emergence collected from 2005 to 2012 in maize fields at two sites located in northeastern Italy. Simulating emergence dynamics based on hydrothermal time of species which germinate only with alternating temperature is fundamental to increase number of species predicted by AlertInf and consequently the richness of information provided by the model for more effectively timed weed management
Development of a decision support system for integrated weed management
No full textIn the last years only a few new action mechanisms have been introduced in the chemical weed control sector. Consequently, when product innovation slows down, process innovation becomes the only possible solution to reduce dependence on chemical herbicides. To rationalize weed control is a priority in this process. Developing and spreading via the Internet a DSS that can advise farmers about weed management, suggesting the correct timing and appropriate mixture of active ingredients for each situation, may represent a key step for this. The combination of two existing models, GESTINF and AlertInf, makes possible the realization of this complete DSS. GESTINF is an existing DSS that evaluates the cost effectiveness of weed control, providing users with a ranking of possible technical alternatives, i.e. herbicide mixtures, according to their specific economic return and the environmental risk of ground and surface water contamination by leaching and runoff. AlertInf has recently been created to predict weed emergence dynamics of several weeds in maize fields. AlertInf provides the percentage of emergence reached by a given weed species in real time using meteorological data, such as soil temperature and soil water potential. The major cause of poor post-emergence weed control is improper application timing, which can be either too early or too late. AlertInf, estimating daily the percentage of weeds that have already emerged and the successive seedling emergence dynamics, allows to make appropriate evaluation on the timing for post-emergence applications to achieve efficient weed control. The two models are integrated in a unified DSS that is able to indicate to the users the date for the single scouting to be carried out in the field to know the quali-quantitative characteristics of the infestation and estimate the density of each weed species for the rest of the season. The predicted daily density of each species is used by the DSS as input without any further survey. The single time survey method for indicating the survey date and estimating the density for the rest of the season, uses the cumulated emergence estimated by AlertInf; the method is described in Masin et al. (2011). The DSS gives indications on post-emergence treatments in traditional tillage maize and soybean and no-tillage maize in terms of herbicide to use ranked according to economic net return. The output of the combined DSS is a more complete information about if, when and how control weeds in their specific situation. This combination of models has the objective to overcome the constraints that have so far hindered the use of DSS, such as GESTINF, by farmers. Furthermore the combined DSS available on-line should encourage farmers to adopt the criteria and methods of IWM
Estimation of temperature thresholds of three weed specie in maize in central-northern Italy.
No full textWeed emergence under simulated arable and no-till conditions: first year results
No full textNo-till management leads to beneficial effects on soil fertility preservation, erosion mitigation and cost reduction. However, weed management strategies should be adapted to no-till field conditions. A field experiment was set up on November 2011 to compare emergence behavior of three weed species (Abutilon theophrasti Medik., Sonchus oleraceus L. and Sorghum halepense L. Pers.) and to evaluate if a single model could be adopted to predict their emergence in arable and no-till managements. Two treatments were performed to simulate conditions of weed seeds in arable (seeds overwinter buried in the soil and are affected by soil disturbance due to spring seedbed preparation) and no-till managements (seeds overwinter on soil surface without any further disturbance). Four 100-seeds replicates were included for each treatment. Seedlings were counted weekly from March 2012. Mean percentages of emerged seedlings were calculated for each species, treatment and their combinations. Emergence dynamics was modeled using a logistic function from which time of 50% relative emergence (t50) was estimated. Factorial ANOVA (P<0.05) identified significant effects of species, treatment and their interaction on percentage and t50 of emergence. Regarding emergence percentage, significant differences were found between treatments for A. theophrasti and S. halepense, but not for S. oleraceus. Moreover, the two treatments of each species presented identical emergence dynamics without any significant difference for emergence t50. These findings may suggest that a single model could be adopted to predict seedling emergence for the three species in arable and no-till systems. However, this experiment has to be replicated to confirm these results under different environmental conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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