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LITHUANIAN UNIVERSITY OF AGRICULTURE                                      
     Regina Romaneckien ė        WEED SPRING BARLEY COMPETITION AND ADAPTATION TO -DIFFERENT ENVIRONMENTAL CONDITIONS     Summary of doctoral dissertation  Biomedical sciences (B000), Agronomy (06 B)
       Akademija 2007
 The dissertation was prepared at the Lithuanian University of Agriculture during 2003-2007. Scientific supervisor:  Assoc. prof. dr. Vytautas Pilipavi č ius (Lithuanian University of Agriculture, biomedical sciences, agronomy  06 B).  The dissertation will be defended in the Council of Agronomy Sciences at the Lithuanian University of Agriculture:  Chairperson: Prof. habil. dr. Petras Lazauskas (Lithuanian University of Agriculture, biomedical sciences, agronomy  06 B). Members: Dr. Albinas Aukalnis (Lithuanian Institute of Agriculture, biomedical sciences, agronomy  06 B). Dr. (H.P.) Kerpauskas (Lithuanian University of Agriculture,  technological sciences, environmental Engineering and Landscape Management, 04T). Dr. Audrius Sasnauskas (Lithuanian Institute of Horticulture, biomedical sciences, agronomy  06 B). Habil. dr. Gvidas idlauskas (UAB Agrochema, biomedical sciences, agronomy  06 B).  Opponents:  Prof. habil. dr. Steponas Č iuberkis (Lithuanian Institute of Agriculture, biomedical sciences, agronomy  06 B). Dr. Danguol ė Raklevi č ien ė (Institute of Botany, biomedical sciences, biology  04 B).  Defence of the doctoral dissertation will take place at the public meeting of the Council of Agronomy Science on the 23 th  of November 2007 at 11 a.m. in the room 261, Central building of the Lithuanian University of Agriculture.   Address: Lithuanian University of Agriculture, Studentu st. 11, Lt-53067 Akademija, Kaunas, Lithuania. Phone/Fax.: (8-37) 752 211, (37) 397 500, e-mail: The summary of the doctoral dissertation was distributed on the 22 th  of Oktober, 2007. The doctoral dissertation is available in the libraries of the Lithuanian University of Agriculture and the Lithuanian Institute of Agriculture.
LIETUVOS EM Ė S Ū KIO UNIVERSITETAS                                      
      Regina Romaneckien ė        PIKTOLI Ų IR VASARINI Ų MIEI Ų KONKURENCIJA IR ADAPTACIJA SKIRTINGOMIS APLINKOS S Ą LYGOMIS   Daktaro disertacijos santrauka  Biomedicinos mokslai (B000), Agronomija (06 B)  
         Akademija 2007
Disertacija parengta 2003-2007 m. Lietuvos em ė s ū kio universitete  Mokslinis vadovas:  Doc. dr. Vytautas Pilipavi č ius (Lietuvos em ė s ū kio universitetas, biomedicinos mokslai, agronomija  06 B).  Disertacija ginama Lietuvos em ė s ū kio universiteto Agronomijos mokslo krypties taryboje: Pirmininkas: Prof. habil. dr. Petras Lazauskas (Lietuvos em ė s ū kio universitetas, biomedicinos mokslai, agronomija  06 B)  Nariai:   Dr. Albinas Aukalnis (Lietuvos emdirbyst ė s institutas, biomedicinos mokslai, agronomija  06 B). Dr. habil. proced ū ra Kerpauskas (Lietuvos em ė s ū kio universitetas, technologijos mokslai, aplinkos ininerija, kratotvarka  04 T). Dr. Audrius Sasnauskas (Lietuvos sodininkyst ė s ir darininkyst ė s institutas, biomedicinos mokslai, agronomija  06 B).  Habil. dr. Gvidas idlauskas (UAB Agrochema, biomedicinos mokslai, agronomija  06 B).  Oponentai: Prof. habil. dr. Steponas Č iuberkis (Lietuvos emdirbyst ė s institutas, Biomedicinos mokslai, Agronomija  06 B).   Dr. Danguol ė Raklevi č ien ė (Botanikos institutas, biomedicinos mokslai, botanika  04 B).  Disertacija bus ginama vieame Agronomijos mokslo krypties tarybos pos ė dyje 2007 m. lapkri č io m ė n. 23 d. 11 val. Lietuvos em ė s ū kio universiteto Centrini ų r ū m ų 261 auditorijoje. Adresas: Lietuvos em ė s ū kio universitetas, Student ų  g. 11, 53067 Akademija, Kauno r. Lietuva. Tel./Faks.: (37) 752 254, (37) 397 500.  Disertacijos santrauka isiuntin ė ta 2007 m. spalio 22 d. Disertacij ą  galima peri ū r ė ti Lietuvos em ė s ū kio universiteto ir Lietuvos emdirbyst ė s instituto bibliotekose.   
INTRODUCTION Relevance of the subject . The constant competition for light between agricultural plants and weeds exerts a great effect on agricultural plants growth and development. The competition effects biological mass production, quality and dependence on adjacently growing plants (Röhrig & Stützel, 1999). As a result, one of the most economical weed control methods is suppression of weeds by exploiting plant competitive qualities and increasing plant population density in cereal stands (ekonien ė , 2002). In denser agricultural crops due to the shortage of light for weeds (Ivaschenko, 1996; Dau et al., 2004), while competing with weeds, agricultural crops suppress them naturally. Climate change and environmental pollution have become the significant factors determining plant growth, development and productivity (Hoffmann & Persons, 1997; Duchovskis, 1998). These factors generate plant stress affecting physiological processes according to plant species, variety, duration of influence time and its intensity (Vassilev, 2002; Alexieva et al ., 2003). Anthropogenic factors are continuously changing our environment. Emission of CO 2  gasses is increasing the temperature of the environment, which is likely to have reached 5.5 o C by the end of the 21 st century (Houghton et al ., 2001). This can result in the global climate change. Plants respond to the increased concentration of CO 2 , therefore, this can trigger the processes of plant biomass accumulation (Rogers et al ., 1994). Such change can have an impact on microbiological variation of rhizosphere as well (Niklaus, 1996). The shorter are the waves of the radiation, the greater is the effect of the ultraviolet radiation on living organisms. The thickness of the ozone layer has the greatest impact on the flow of the UV-B radiation, therefore, in the case of the ozone layer depletion the major threat to vegetation is caused by this part of ultraviolet radiation spectrum (Helsper et al., 2003; Krizek, 2004). Greater than normal radiation causes damage to plant cells (Hollosy, 2002). The competition between cultivated crops and weeds occurs in agroecosystems and its outcome is determined by their resistance to abiotic factors. Although weeds are adapted to the various environmental conditions, their spread is controlled by the limiting factors, pH being one of them. Acid soils are toxic to plants not only because of deficiency or surplus of some chemical elements but also because of disorder of nutritious matter complex: decreased availability of phosphorus for plants; toxicity of Al, Mn and H + (Carver & Ownby, 1995). Varying sensitivity and adaptation of different plant species to intensified anthropogenic factors can determine their distribution and relation in agrosystems. Therefore, it is expedient to investigate the ability of not only cultivated crops but also weeds to adapt and grow under the influence of various environmental stressors. Germination of weed seed as affected by various environmental factors has been investigated for many years. Weed seed ability to sprout and grow under different conditions of lighting, temperature, humidity and osmotic potential (Hartmann, Mollwo, 2000; Grundy et al., 2003) or display of different diseases and pests (Kazinczi et al ., 2000) etc. has been evaluated. Experimental hypothesis . The competition between agricultural crops and weeds constantly occurs in agrophytocenoses. Increasing of crop stand density would result in enhanced competitive ability of spring barley, effective utilization of PAR and UV-B radiation as well as in a decline in weed emergence and in increasing weed death during the growing season. The competitive ability of a crop is affected by different sensitivity of a plant species and adaptivity to intensifying anthropogenic factors. It is foreseen that under simulated climate and environmental conditions (phyto-chamber), increasing intensity of exposure to anthropogenic factors - pH and acids (H 2 SO 4 ), carbon dioxide , ozone, UV-B, cadmium, temperatures as well as their complex effect would encourage weed growth (weeds would adapt) at low concentrations and would significantly inhibit weed growth (weeds would not be able to adapt) at increasing concentrations.   To verify the hypothesis, precision field trials were conducted during the period 2004-2006 at the Lithuanian University of Agriculture Experimental Station and laboratorypot trials were done at LUAs Laboratory of Agrobiotechnology and Lithuanian Institute of Horticulture Phytothrone.  The aim and objectives of the research . 1 .  Under natural (field trials) climate and environment conditions to investigate the changes in the between species and within species competitive ability of different weed and agricultural crops species during the growing period, as well as to study the diversity of weeds in spring barley crops, weed emergence and death, abundance of weed seed in the soil and the
effect of weed incidence on spring barley yield, 1000 grain weight as influenced by different stand density. 2. Under simulated climate and environment conditions (phyto-chambers) to identify the effects of background environment changes (pH, Cd, Ozone, UV-B radiation, CO 2 ) and a complex effect of their various combinations on weed growth.  Originality of the research work . For the first time in Lithuania we have studied the use of PAR and UV-B radiation in the crops of spring barley differing in density, as well as the dynamics of weed death. The novel theoretical knowledge was obtained about weed adaptivity under the conditions of changing climate and as effected by the anthropogenic factors: pH and acids (H 2 SO 4 ), CO 2 , ozone, UV-B, cadmium, temperatures and their complex effects. Theoretical and practical value of the results obtained . All over the world, the greatest attention is being devoted to the reduction of weed incidence in agricultural crops. Research evidence on plant competition is rather scarce, although it is one of the factors which contributes to yield increasing, since crops like natural communities are characterised by the between species and within species, competition for light, soil nutrients and moisture. As a result, it is important to study the competition between weeds and agricultural crops, which is determined by the growth and development peculiarities of the plants. With increasing levels of anthropogenic pollution, changes occur in climate and environment conditions. This change in atmosphere and environment pollution is one of the factors determining the change in agricultural crop and weed species or even their disappearance. Weeds are characterised by higher plasticity to various abiotic factors, therefore research into weed adaptation to the changing climate and environment conditions is becoming a relevant research task for reducing weed incidence in cereals (spring barley). Approval and publication of the dissertation work. The main results of the dissertation work were published in: Scientific Works of Estonian University of Life Sciences Agronomy Research (2006 ISI Master list); the Lithuanian University of Agricultures scientific journal Vagos (2006); the Lithuanian Institute of Agriculture and the Lithuanian University of Agricultures scientific journal: emdirbyst ė (2006); the Lithuanian Institute of of Horticulture and the Lithuanian University of Agricultures scientific journal: Sodininkyst ė ir darininkyst ė  (2006); the Latvian journal of agronomy Agronomijas vestis, (2005); in the international EWRS scienftific conference: Colloque International sur la Biologie des Mauvaises herbes (2004). Volume of work. The dissertation is written in Lithuanian. It consists of an introduction, review of literature, experimental materials and methods, experimental analysis and discussion, conclusions, list of publications on the subject of the dissertation, list of references. The dissertation comprises 119 pages, 27 tables and 25 figures, 292 literature references.  EXPERIMENTAL MATERIAL AND METHODS Experimental materials.  Spring barley  Hordeum vulgare  L. Aura. The seeds of the investigated weed species scentless mayweed Tripleurospermum perforatum  (L.), white goosefoot  Chenopodium album L., curly dock Rumex crispus L. and creeping thistle Cirsium arvense (L.) Scop. Field experiment site and soil type. Field  experiments were conducted during the period 2004-2006 at the Lithuanian University of Agriculture, Experimental station, on a medium-heavy loam in Noreikik ė s, Kaunas district. The soil of the site is LWg-n-w-cc-Endocalc(ar)i Endohypogleyic Luvisol  drained clay loam on sandy light loam. The soil pH was 7.02-7.13, humus content 2.23-2.50 %, P 2 O 5  123.96-294.95 mg kg -1 , K 2 O 144.28-197.31 mg kg -1 . Experimental design (Field). The analysis of spring barley and weed competition was made during 2004-2006, according to the following design: 1. Factor A . Different seed rates: 1)120 kg ha -1 ; 2) 200 kg ha -1 ; 3) 280 kg ha -1 ; 4) 0 kg ha -1 ; 2. Factor B:  The assessment dynamics of spring barley and weeds, according to growth and development stages (decimal code according to Meier (1997). 1)Beginning of tillering 25*; 22**; end of tillering 29*;** ;***; bootingt 39*; 37**; 39*** ; heading 51*;**; 52*** ; milk maturity 73*; 71**; 75*** ; hard maturity 92*; 97**; 92*** . (Note *-2004; **-2005; ***2006 ).  Experimental methods (Field). The amount of plant intercepted PAR and UV-B in the spring barley crop  in  2004 was measured at 5 crop heights corresponding to weed morphological classification in
cereals, and in 2005 and 2006 at four crop heights due to the shorter spring barley height. Assessments were done at spring barley booting, heading, milk and hard maturity stages. Dynamics of weed emergence and death. During each assessment emerged weeds were marked by different colour labels. Death weeds were determined by collecting and counting the needles with labels next to the dead weeds. The aim of the experiment was to establish weed emergence and death dynamics in the crop of spring barley. The assessment of weed death was carried out every 10-14 days in the fields. Dynamics of weed occurrence in the crop was determined in the experimental plots having set up six permanent weed emergence count sites arranged randomly. Weed assessments were done at six development stages according to spring barley growth stages (according to the experimental design). The sixth assessment of weed incidence was carried out before harvesting by quantitative-weight method ( Досп exo в ., 1987). Weeds were divided into species according to biological-agronomic classification. Weeds of each species were counted and weighed separately. Spring barley stems were counted and weighed. The amount of weeds and spring barley was expressed by number m -2 , and their dry matter weight by g m -2 (quantitative-weight method) (Stancevi č ius, 1979). The amount of weeds in the soil. Soil samples from the 0-20 cm soil layer were taken from 20 places. Weed seeds were extracted by using heavy solution method (Arvasas et al., 1999). The yield . Spring barley yield was determined in the plots 138 m 2 in size, in each treatments four replications and was recalculated into kg ha -1 . Grain yield was adjusted to 14 % moisture content and expressed in absolutely clean mass. Grain moisture was determined by drying in a thermostat at 105°C to a constant weight. 1000 grain weight . Three samples of 500 grain each were taken from the mean sample and weighed. Chemical composition of spring barley grain and soil. Spring barley grain and soil agrochemical  properties were estimated at the outset of the experiments and upon completion. Soil as well grain chemical composition was established at the LUA Experimental Station with Infrared rays PSCCO/ISI IBM  PC 4250 system (Rimkevi č ien ė , 2000). Chemical composition of weeds. Contents of dry matter, crude protein, crude fat, crude fibre, and crude ash were determined in prepared samples for analyses. Drying plant samples at 103°C for 4 hours, we established the content of dry matter and burning at 550°C for 3.5 hours in muffle-furnace, we established the content of crude ash. Crude protein was established by the Kjeldahl method and crude fat by direct extraction with petrolether for 6 hours in Sokslet device. The concentration of crude fibre was established by plant samples boiling with adequate concentration of sulphuric acid and potassium alkali, filtered, separated, washed, dried, weighed and burned at 500°C for 3 hours in a muffle-furnace (Naumann et al., 1993). Vegetative and Laboratory tests. Laboratory and vegetative pot experiments were carried out at the of the LUA Agrobiotechnology laboratory and  Phytotron Lithuanian Institute of Horticulture during the period 2004-2006. The laboratory experiment factor was environment of contrasting acidity (pH) . Seven levels of pH: 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5 were tested in the laboratory experiments and five levels of pH: 4.5, 5.5, 6.5, 7.5, 8.5 in the experiments.  Weed germination, initial growth properties and evaluation.  Germination of the T. perforatum ,  C. album , R. crispus  and C. arvense  seeds was investigated in the laboratory experiment. 30 seeds of a chosen weed species were placed into each covered Petri dishes of 10 cm diameter (4 replication) and watered with 10 mL of pH solutions. Photoperiod of 16 h and temperatures of 22/18°C were used for 7-10 days. Germinated weed seeds were counted after 7, 8, 9 and 10 days. In the experiment weed seedling growth (height of roots and sprouts and mass accumulation) was studied. In vegetative experiment the plastic pots (capacity of 1 L) substratum of quartz sand was used and watered three times a week with 50 mL of nutritional solution (CaHPO 4. 2H 2 O  0.42 g L -1 ; K 2 HPO 4   0.131 g L -1 ; CaCl 2. 6H 2 O  0.42 g L -1 ; MgSO 4   0.06 g L -1 ; NH 4 NO 3   0.30 g L -1  and ferro-citrate  0.01 g L -1 ). Emerged weeds were thinned out leaving 25 seedlings per pot. Results were evaluated after 21 days from weed emergence.  General conditions of pot trials. The emerged weeds were thinned out leaving 25 seedlings per pot. A photoperiod of 14 h was used. Length of roots and sprouts was measured (mm) and weed mass (g per pot) was established oven-dried at 105°C. The experiment was conducted in three replications. At the end of the experiment over-ground weed mass and its length were evaluated. For the evaluation of  pH  influence on the initial growth of C. album  seedlings an experiment was conducted. Substratum of turf
was used in the plastic pots (capacity of 5 L). For the achieving different turf substratum pH acidity sulphur acid was used. Two days before the experiment substratum of turf was watered by the 3 L sulphur acid solution of 0.5; 1; 2; 4; 6 and 8 mL L -1  concentration. Till weed emergence and one week after emergence the pots were kept in a greenhouse for two weeks (14 days) and then were transferred to the phytotron. For the evaluation of Cadmium (Cd )  influence on the initial growth of album  seedlings we conducted a pot  greenhouse experiment like for the pH evaluation. Only for the achievement of different cadmium concentration in the substratum for each pot 3 L of cadmium saline (CdSO 4 ·8H 2 O) was used. Temperature regime 21/17°C was used. Six levels of Cadmium : 0.01mM, 0.05mM, 0.1mM, 0.5mM, 1mM and 3mM. UVB radiation .  To generate the chosen UVB radiation medical lamps Philips TL 40W/12 RS UVB were used. Six levels of UVB radiation: 0 kJ m -2 , 1 kJ -2 , 3 kJ m -2 , 5 m kJ m -2 , 7 kJ m -2 , 9 kJ m -2  and two levels of temperature regimes: 21/14°C and 25/16°C, per day were tested. Ozone. The selected ozone concentration was achieved using the ozone generator OSR-8 (Ozone Solutions, Inc.) 5 days per week, 7 hours per day. Ozone concentration was measured by the mobile ozone measuring instrument OMC-1108 (Ozone Solutions, Inc.).  Four levels of ozone concentrations: 0 µg m -3 (control treatment), 120 µg m -3 , 240 µg m -3 , 360 µg m -3  (temperature regimes: 21/17°C) were investigated, and 40 µg m -3 (control treatment), 80 µg m -3 , 160 µg m -3 , temperature regimes: 21/14°C and 25/16°C, were tested. UV–B radiation  and ozone concentration combinations  influence on two levels of ozone concentrations 120 µg m -3 and 360 µg m -3 with two levels of UVB radiation: 3 kJ m -2 and 9 kJ m -2  (temperature regime: 21/17°C) were tested. Carbon dioxide  (CO 2 ). The experimental factor was the environment of contrasting carbon dioxide (CO 2 ) concentrations and temperature levels combinations. Concentration of CO 2 was controlled using CO 2 cylinder-reservoir controlled by CO 2 measurer CO 2 RT-5 (produced by Regin, Sweden). Photoperiod was achieved using high-pressure sodium (HPS) lamps SON-T Agro (Philips). The level of background radiation (PAR) made up 170 micro-mol m -2  s -1 . Four levels of CO 2  concentration: 700 µg m -3  (control treatment), 1400 µg m -3 , 3000 µg m -3 , 6000 µg m -3  (temperature regime 21/17°C) were investigated, and two levels of CO 2 and temperature regime: 700 µg m -3 , (21/14°C control treatment), 700 µg m -3 25/16°C, 1400 µg m -3 25/16°C, 1400 µg m -3 21/14°C were examined. Data analysis . The collected data of field, laboratory and pot experiments during 2004-2006 were analyzed by ANOVA and correlation-regression analysis at  95%, 99% and 99.9% probability levels. The treatment effects and standard errors (SE) were tested for significance using the Sigma Stat (Spss Science, 1997) and the strength of the correlation between the variables was tested using the Sigma Plot (Spss Science, 2000) software.  RESULTS AND DISCUSSION  UVB and PAR radiation.  While estimating the effects of different stand densities of barley on weed incidence, we measured the amount of PAR and UV-B radiation reaching the ground. Analysis of the UV-B and PAR radiation of the years 2004, 2005 and 2006 suggests that with increasing spring barley stand density the amount of PAR and UV-B radiation reaching the soil surface declined. The most intensive interception of solar radiation (PAR and UV-B) occurs at spring barley heading and milk maturity stages, i.e. during the intensive growth and mass accumulation period. In a barley stand of a higher density (280 kg ha -1  seed rate) the amount of PAR and UV-B radiation reaching the soil consistently declined due to the increasing leaf area. Weed incidence in the spring barley crop. The lowest amount of PAR and UV-B radiation reaching the soil was recorded in the spring barley stand of the highest density (280 kg ha -1 seed rate) at barley heading and milky maturity stages. The reduction in the amount of solar radiation reaching the soil influenced the number of weeds in the crop. In the stands of a higher density, increasing competition between spring barley and weeds reduced the number of weeds and their mass. In 2004, in the barley stand of the lowest density (120 kg ha -1 seed rate) the number of weeds was by 27.2 % higher compared with the stand of the highest density (280 kg ha -1  seed rate). Similar trends were observed in weed dry mass data: in the stand of the lowest density (120 kg ha -1 seed rate) weed dry matter mass was by 39.4 % higher than that in the stand of the highest density (280 kg ha -1  seed rate). Increasing of barley stand
density determined a regular reduction in weed number and mass in the crop. In 2005, when increasing the sowing rate to 280 kg ha -1 , the number of weeds declined, however the greatest amount of dry mass (63.8 g m -2 ) was in the stand of the lowest density. In 2006 when increasing stand density, similar reduction trends were observed as in 2004 (Fig.1).    2004 2005 2006 Number of weeds Weed mass Number of weeds Weed mass Number of weeds Weed mass 500 50 500 80 500 15 46.02463.85*6043000010 400 40 00 300 31.46 27.90 30 300 39.76 41.10 40 200 5 200 99.3 84.0 72.3 20 200 100101002010000 0 0 0 0 120 200 280 120200280120 k2g0 0ha 1 280  Seed rate kg ha -1 Seed rate - Seed rate kg ha-1    Fig.1.  The total weed incidence in the spring barley crop, 2004 - 2006     Note:  significant differences from the control treatment (200 kg ha -1 ); * - at P  < 0.05.   Summarised experimental evidence suggests that the level of weed incidence is determined by the stand density formed: the stand of the lowest density (120 kg h -1 seed rate) tended to increase the number a of weeds as well as their dry mass. When increasing the stand density to 280 kg seed ha -1 , the increasing number of spring barley stems reduced weed incidence. Dynamics of weed emergence and death in spring barley. The different barley  stand density formed  influenced  weed emergence.  At the beginning of the growing season weed emergence was the most intensive and the number of emerged weeds accounted for 57.7 % -51.7 % of the total number of weeds emerged during the growing season, which corresponds to their biological properties. The different stand density formed did not have any effect on spring weed emergence. At the tillering stage the weeds emerged intensively, but during the booting stage the intensity of weed emergence started to decline due to the competition conditions between species and within species and amounted to 37.7 % - 20.1%, and at later stages it declined significantly (Fig 2.). Having analysed weed seedling death, it turned out that a large part of spring-emerged weeds die until the end of spring barley growing season. In 2004, at the end of tillering the greatest number of dead weeds was recorded in the stand of medium density (200 kg ha -1  seed rate) where there were found 22.5 dead weeds m -2 (Fig.2). In the stands of the other densities the number of dead weeds was similar. At booting and heading stages weed death rate tended to increase with increasing seed rate. In 2005 only at tillering stage weed death rate was similar in all stand densities (~8.5 weeds m -2 ). Whereas at booting, heading, and hard maturity stages weed death rate increased with increasing seed rates. In 2006 at tillering  booting stages, with increasing seed rate the weed death rate increased, but very weakly. When at tillering stage, increasing stand density tended to increase the number of dead weeds, significant differences were established compared with the control (Fig.2). The greatest number of dead weeds was identified at milky maturity stage, in the stand of the highest density (280 kg ha -1 seed rate) the number of dead weeds was 25.7 weeds m -2 , compared with the control treatment, significant differences were established (Fig. 2). Having estimated weed emergence and death in the stands of spring barley differing in density it was found that in the stands of higher density the number of weeds proportionally declined. During the first assessment (at spring barley tillering), when barley plants were short, the emergence of weeds did not depend on the stand density (Fig.2). It was found that the highest suppressive power was exhibited at spring barley heading and milky maturity stages, due to the considerably declined weed emergence and increasing weed death rate. Besides, competition between species revealed itself at these stages, when in the spring barley stands of the highest density weed emergence was the lowest, and weed death rate was the highest.     
0 kg ha-1 120 kg ha-1 number of emerged weeds 200 kg ha-1 280 kg ha-1 600 02 0k0g  khga -h1a -1 122800  kkgg  hha--11 number of dead weeds 60 a 00 53 50 00 383** 35* 49 47 43 46 40 319 32 41 39 28 0000213**232835243200 20 19* 12 22 13** 69 4* 39 4 100 74 7 3 10 * 0 0 14 7 17 1 2 11 6 5 4 7 11 0 Beginning of End of tillering Booting Heading Milk maturity Hard maturity tillering Spring barley growth stages                                                            
2005  600 598**127122130 110 500 622** 433 79 96* 5390 400 66 66 70 300 29 51 50 200 151172 141 17 41 27** 15** 30 100 91962610 10 0 0 8 22 80 63 11 18 11 8 4 6 6 4 4 -10 Beginning of End of tillering Booting stage Heading Milk maturity Hard maturity till  e r  i n  g    Spring barley growth stages    
100 40 80 73 31** 35 5775752730 60432018132205 40 33 21 14 8* 9 15 20514164755111293277510 0 0 2 1 3 4 1 2*6* 0 Beginning of End of tillering Booting Heading Milk maturity Hard maturity tillering Spring barley growth stages  Fig. 2. Weed emergence and death dynamics in a spring barley crop, 2004-2006  Note:  significant differences from the control treatment (200 kg ha -1 ) *- at P  < 0.05. Spring barley yield. The different stand density formed, affected spring barley yield and 1000 grain weight. Due to the highest weed death rate in the stands of higher density and due to the lower weed emergence at booting stage, the spring barley yield was the highest (2.2-4.0 t ha -1 ) in the stands of medium density (200 kg ha -1 seed rate) (Fig.3).    
2004 2005 2006 Spring barley growth stages S ro 1000 grain weight 10pr0i0n gg rbaairnl ewyeigghtw th stagesS10pr0i0n g rbaairnl ewye igrohtw th stages 4 4 57 4 57 50 3 48 3 52 3 52.5 50.4 49.8 52 46 2 2 47 2 47 44 1 42 1 42 1 42 120 200 280 120 200 280 120 200 280   Seed rate kg h -1  Seed rate kg ha -1  Seed rate kg ha -1 a  Fig. 3. Spring barley grain yield and 1000 grain weight, 2004-2006  Note:  significant differences from the control treatment (200 kg ha -1 ) *- at P  < 0.05.   The effect of anthropogenic factors (pH, Cd, UV-B, O 3 , CO 2 ) on weed growth. The  warming climate, changes in environmental pollution alter the course of agricultural crops stand formation and its optimal parameters. Increasing pollution results in the changes in the plant needs for nutrients as well as in the changes in the quality of produce (Lazauskas et al., 2005). For this reason we studied the effects of anthropogenic factors on weed growth (Pot and laboratory experiments).  Different concentrations of pH influence on weeds. Weed seedling formation, evaluating its height, was mostly suppressed in the solutions under pH 3.5 and 9.5 (Fig. 4) as well as seed germination by pH 9.5 except R. crispus . Seedling height of T. perforatum , C. arvense and C. album achieved only 1 mm and was usually less than the seed itself under solution acidity pH 3.5. Besides, in the mentioned environments of critical pH levels, some seedlings were not appropriately developed and had only roots or sprouts, even though percentage of germinated seeds was the highest, except C. arvense . Seedlings of Rumex crispus were adapted best again, so that their height in Petri dishes under pH 4.58.5 did not differ significantly. Seedlings of the investigated weeds grew best under pH 6.5  T. perforatum and C. arvense , pH 7.5  C. album and pH 4.58.5  R. crispus (Fig. 4).  
. Tr 5 i 5 p . l 5 euros 5 p 1 e . r 0 mum per 9 f * orat 5 u 1 m 4600 Chenopodium album 51 3 33.8 60 63. .7 41 7* 37.1 45.7 36.7 . 40 20 8.5* 20 5.8* 1.0* 1.0* 00 3,5 4,5 5,5 6,5 7,5 8,5 9,5 3,5 4,5 5,5 6,5 7,5 8,5 9,5 Solution acidity pH Solution acidity pH   64 2 Rumex crispus 63.8 58.5 61.1 60 Cirsium arvense 54.2 60.58.84028.637.331.437.6 40 27.8* 20 14.1* 20 12.7* 1.0* 0 0 3,5 4,5 5,5 6,5 7,5 8,5 9,5 3,5 4,5 5,5 6,5 7,5 8,5 9,5 Solution acidity pH Solution acidity pH   Fig. 4.  Height (mm) of weed seedlings after 10 days of laboratorial experiment. Note: Vertical bars indicate standard errors ±SE. * - significant differences with control treatment (pH 5.5) at P <  0.05.   Cd of different concentrations influence on Chenopodium album . Evaluating Cd of different concentrations influence on C. album (Table 1), it was established that weeds  are sensitive to the effect of Cd and even the smallest concentration of Cd (0.01 mM) suppressed their growth more than 50%. C. album did not grow at all when concentration of Cd was 0.5 mM (Table 1).