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Dynamics of the distribution of weeds and the possibilities of their control in cereals in crop rotations in Vidzeme. Summary of the Doctoral thesis for the scientific degree Dr.agr.  [2010]

Vanaga, I., Latvia Univ. of Agriculture, Jelgava (Latvia) Latvia Univ. of Agriculture, Jelgava (Latvia) [Corporate Author]

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Research involving annual counts of weeds in the actual flora and the weed seedbank was carried out in the Vidzeme region in monitoring areas in five districts (Riga, Cesis, Valka, Valmiera and Limbazi), to determine the abundance of weed species and their groups in Latvia and the dynamics of their occurrence from 1994 to 2002. Field trials to examine the relationship between grain yield and level of weed infestation in cereals as well as to examine the effects of applying herbicides were carried out in 2000 – 2002 in the Riga district in Adazi parish. The aim of the research was to evaluate the changes in weed infestations in cereals in the monitoring areas, making an assessment of the factors influencing crop and soil infestation with weeds, including the crop and weed management measures in the crop rotations, and to clarify the relationships between grain yields and weed infestations in spring barley and winter wheat. The tasks of the investigations: - to investigate the changes in the numbers of weeds in crops and seeds in soil in five monitoring areas in the Vidzeme region under the conditions of practical crop production; - to determine the relationships between weed infestation in winter wheat and spring barley and grain yield, including its major components; - to assess the changes in weed biodiversity and in the risk to production in spring barley under the conditions of herbicide application. Based on the topical needs, the research aims and tas
ks are defined, the research novelty is estimated and the publications based on this work and presentations by the author in conferences, symposiums and congresses are listed. Literature survey is arranged in four sub-chapters, in which information about research on weed distribution dynamics in Latvia and neighbouring countries is reviewed with the emphasis on the harm caused by weeds and the possibilities of control of the weed distribution in cereals. The conditions of research and methods in Vidzeme region monitoring areas and the field trials are characterised, the agro–meteorological conditions are analyzed, and the mathematical methods of data analysis for the professional interpretation of the conclusions and for justification of the validation of the findings are described. This chapter takes 51% from the total scope of the work and is arranged in four sub-chapters. The evaluation of weed distribution dynamics in crop sowings and soil and the conditions which could have affected them in the Vidzeme region monitoring areas are supplied by the author as well as the changes in occurrence of individual species in period from 1947. The effects of weed infestation on grain yield and its major components in winter wheat and spring barley were determined. The biodiversity and risk of the production were evaluated in the conditions by using different application doses of herbicides in spring barley.