This thesis focuses on the diversity of weed vegetation and possibilities of its evaluati-on. The survey was carried out on fields of Mendel Univesity in Žabčice. Species di-versity was determined in the growth of opium poppy in 2013 and spring barley in 2014. Index of diversity were calculated according to the collected data. Spatial preference of individual weed species was designed by statistical analysis DCA (Detrended Corre-spondence Analysis) and RDA (Redundancy Analysis), processed on the basis of obtai-ned results. A total amount of 27 species was identified in opium poppy and 24 weed species were determined in spring barley. However, the vegetation consisted mostly by individuals of dominant species Echinochloa crus-galli, Chemopodium album and Lamium amplexicaule, in both monitored areas. It was found, that higher species richness are monitored on the edges of the fields, than their midpoints. Diversity of opium poppy was 0.17 and 0.36 of spring barely on experimental fields.

This theses summarizes results obtained from studying of one-year experimental pot of permanent grassland which was established in Vítězná - Záboří in 2015. There has been observed 4 levels of nitrogen fertilization on the meadow plot (without fertilizing, 30 kg N.ha-1, 60 kg N.ha-1 and 90 survey was influence of nitrogen on the change in species richness by using weight share representation of individual agrobotanical groups in the stand (grasses, legumes, other forbs). Results of this experiment were considerable affected by unfavourable weather events in the observed year. We should bear in mind the short time of this experiment. Positive unofficial effect of nitrogen on higher yield of above-ground biomass was recorded, especially by using 30 kg N.ha-1 and 60 kg N.ha-1. There is an exception at using 90 kg N.ha-1 with yield off balance. From the perspective of infuence of nitrogen on changes of species richness the increasing of doses of fertilizing has shown especially in increase proportion of grasses while present retreating herbs in the species composition of the reference stand. However results of experiment are not statistically different. We can not confirm studies which state decrease proportion of legumes in the grassland due to nitrogen fertilization from results of this experiment.

The aim of this diploma thesis is to evaluate species structure of vegetation in a chosen city. Three different localities (road, park and neighbourhood) were chosen in territory of Trnava. The evaluation of species structure was done by phytosociological relevés (20 m2). All found plant species were determined and their coverage was estimated. The evaluation was done in two months (june and august) in 2015. Acquired data was statistically evaluated by DCA and RDA analysis. Overall number of found species is 35. The most common plant species in neighbourhood were: Lolium perenne, Convolvulus arvensis, Trifolium repens, Hordeum murinum a Plantago lanceolata. The most common species in the park were: Lolium perenne, Trifolium repens, Acer platanoides, Plantago major, P. lanceolata. The most common species by road were: Elytrigia repens, Lolium perenne, Reseda lutea, Tripleurospermum inodoratum.

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