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The assessment of the weed infestation effect on biomass yield of Miscanthus × giganteus in the first year of its commercial yield was conducted on two types of soil with different productive ability – Luvic Chernozem and Calcic Gleysol. The formed mass of weeds was higher on Luvic Chernozem and the infestation had grown according to the stages of Miscanthus growth. The biomass of weeds depended on the planting density of Miscanthus as well as on the weather conditions during the studied years. Weed infestation of crops very significantly influenced the formation of aboveground biomass of Miscanthus, so that the yields in the first year of commercial harvesting in the control where the weeds were removed manually were significantly higher compared to the crops in which weeds were not removed. The obtained results showed that weeds significantly affect the initial growth and development of Miscanthus plants that are, in general, slow, especially in the year of the crop establishment. The study evaluates the impact of a manual method of suppression and weed infestation of crops on the commercial yield of Miscanthus.

The critical time for weed removal (CTWR) is a period in the crop growth cycle when weed control must be initiated to prevent yield losses. Knowing the CTWR is useful for making decisions about the timing of weed control and in achieving efficient herbicide use from both biological and economic perspectives. Field studies were conducted in 2008 and 2009 at three locations in Serbia and one location in the USA to determine the CTWR in imidazolinone (IMI)-resistant sunflower grown with and without application of pre-emergence (PRE) herbicide. A four-parameter log-logistic model was fitted to data relating relative crop yield to increasing duration of weed presence. The CTWR without PRE herbicide treatment ranged from 14 to 26 d after emergence (DAE) corresponding to the V3 (three leaves) to V4 stages compared to 25 to 37 DAE, which corresponded to the V6 to V8 stages with PRE herbicide. The CTWR in IMI-resistant sunflower grown with PRE herbicide can be delayed by an additional 6 to 12 d compared to the crop grown without PRE herbicide under the present experimental conditions. The practical implication of this study is that the use of PRE herbicide could extend post-herbicide treatments by another 6 to 12 d with respect to the critical time required for weed removal without PRE herbicide in IMI-resistant sunflower.

A three-year trial (2003-2005) was conducted under agro ecological conditions of Timočka Krajina (the experiment farm of Technological Research Center in Zaječar). Research object were six malting barley genotypes, which were top-dressed with the following amounts of nitrogen in the course of growing season: 40, 60, 80 and 100 kg ha-1. A non-fertilized variant served as a control. The obtained results indicated that the tested genotypes reacted to increased amounts of nitrogen by changing their morphological and biological characteristics as well as the technological values of grain. The effectiveness of the applied nitrogen depended significantly on the distribution of rainfall in periods of highest water uptake by malting barley