Štefanić E., Kovačević V., Antunović S., Japundžić-Palenkić B., Zima D., Turalija A., Nestorović N.: Floristic biodiversity of weed communities in arable lands of Istria peninsula (from 2005 to 2017). This paper analyses the floristic biodiversity of weed communities in the arable lands of the Istrian peninsula during a twelve year period (2005−2017). A total of 50 fields were surveyed for each sampling time using the seven-degree Braun-Blanquet cover abundance scale in the following agricultural categories: a) permanent crops (vineyards/olive groves), b) alfalfa fields, c) cereals, d) row crops and e) ruderal areas. The taxonomic identification was performed during the full development of vegetation, for cereals in June and July, and for the rest -in August and September. A total of 175 weed species were determined during both study periods with Asteraceae and Poaceae families as the most abundant. Altogether, therophytes were dominant in both surveys, followed by hemycryptophytes and geophytes. Variations in species composition were visible in both study periods (2005 and 2017) as well as in the selected habitat types. Exclusive species were found in addition to those that were common for both surveys. Changes in species composition between 2005 and 2017 referred to the difference in row spacing in earlier period, and ruderal vs. agricultural habitats in the recent survey. The differences in phenological traits between the past and present surveys were greatest for germination season in permanent crops and row crops, flowering start for permanent crops, flowering period for ruderal area and weed height for permanent crops. Significant differences between the past and present survey for other plant traits did not occur.

Field margins are pollinator-friendly habitats and important refuges for many pollinators. As a valuable food resource throughout the vegetation season, not just when crop species are in flower, field margins need to be protect or restore in areas of intensive farming. This paper examines the floristic and functional structure of weed communities on field margins in the northeastern part of the Republic of Croatia. A phytocoenological survey was conducted during the summer period of 2017 and 2018. A total of 32 field margins was analyzed for species richness, abundance and their role for entomofauna. Floristically rich field margins consist of 72,6% plant species beneficial to pollinators. Foraging period can be stretching throughout the year, but stabile and high flowering period is from May to end of September. Among highest ranked honeybee plants, several invasive species with significant relative abundance are: Solidago gigantea, Asclepias syriaca and Amorpha fruticosa who pose a serious threat to plant biodiversity. Positive role of vegetation from field margins was not valuable for pollinators only, but they also serve as supply the substrates that provide a shelter and nesting sites.

Changes in floristic composition of weed flora were assessed comparing two phytocoenological surveys carried out during vegetation seasons in 2005 and in 2017 on the Istrian Peninsula. A total of 50 fields (row crops, cereals, alfalfa fields, orchards/vineyards and ruderal areas) were surveyed for each of the sampling time using Braun-Blanquet cover-abundance scale. Altogether 175 vascular plant species were recognized in both investigations. The most abundant species in 2005 were Avena fatua, Setaria verticilata, Lolium multiflorum and Veronica persica. In the recent survey these species became very rare or were even not detected in some habitats. In contrast, some species with very low relative abundance or not recorded in the earlier survey were found abundant in 2017. These are: Pastinaca sativa, Conyza canadensis, Picris echioides, Polygonum aviculare, and Heliotropium europaeum. The species richness was significantly higher in the earlier survey when 143 (82%) weeds were detected compared to only 97 species (55%) found in 2017. Only 64 species were found in both surveys, and these were considered frequent weeds. The comparison of weed communities from the earlier to the recent survey reflects the reduction of the weed flora at the regional scale, as well as at the field scale. The mean values of Shannon-Wiener diversity index were also higher in the earlier period and it decreased over time, particularly in row crops, cereals and ruderal habitats. This decrease was related to decline of species richness, and to the increase in inequality in the relative abundance of species. On the whole, canonical correspondence analysis indicated the major variations in species composition between different habitats.

In the decade from 2000 to 2009, the yield of maize grain in Croatia varied from 4.2 t ha−1 (2003) to 8.0 t ha−1 (2008). The yield variation was mainly caused by weather conditions unfavourable for maize production, meaning lack of precipitation, unevenly distributed during the vegetation season, and mean air temperatures above the long-term mean. Irrigation has become a justified and essential agrotechnical measure that minimizes the damage caused by water deficit during critical plant growth stages and ensures high yields with good quality. In this paper two vegetation seasons (2006 and 2007) with quite different weather conditions for maize production were analysed in order to examine the importance of irrigation in terms of yield increase, irrigation water use efficiency (IWUE), irrigation efficiency (IE) and irrigation water use index (IWUI) in years favourable (2006) or too dry (2007) for maize production. The yield surpluses achieved with irrigation ranged from 8.54 t ha−1 to 9.62 t ha−1 in the average crop year (2006) and from 8.43 t ha−1 to 10.7 t ha−1 in the dry year (2007), depending on the irrigation method. In the dry year the values of IWUE where higher than in the average year (6.16 and 13.75 kg ha−1/mm, respectively, averaged over the hybrids).

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