Relative Crowding Coefficient Research Articles

Intraspecific Competition of an Insect‐Resistant Transgenic Canola in Seed Mixtures

Seed mixtures are recommended as a strategy to minimize or avoid having insects develop resistance to insect‐resistant transgenic crops. The objective of this study was to evaluate a canola, Brassica napus L., transgenic for a Bacillus thuringiensis cry1Ac gene for its resistance against diamondback moth, Plutella xylostella L., and for its competitive ability with nontransgenic canola in seed mixtures. Transgenic and nontransgenic canola were planted either as pure stands or in mixtures of 75:25, 50:50, and 25:75 in plastic trays in greenhouse experiments or in field experiments at three locations during the 1996 through 1998 field seasons. The trays and plots were either infested with diamondback moth neonates or left without any insect infestation. In diamondback moth‐infested treatments, transgenic plants had low levels of damage both as a pure stand and in mixtures. Nontransgenic plants in diamondback moth‐infested trays and plots suffered high levels of defoliation and produced less biomass and seed yield compared with transgenic plants. Relative crowding coefficient (RCC), a measure of competition between the two plant types, ranged from 0.6 to 1.1 in plots where there was no diamondback moth infestation and 1.1 to 12.8 in plots where there was diamondback moth infestation. No competitive advantage was observed for either plant type in seed mixtures when there was no diamondback moth infestation. Transgenic canola because of its high level of resistance was competitively superior in seed mixtures when there was diamondback moth infestation.

Intercrop performance of maize, sorghum and soybean in response to planting pattern

Mixed cropping of cereals and legumes dominate the cropping systems of most farmers in the northern Guinea Savanna agroecological zone of Ghana. The objective of the study was to determine the appropriate crop mixture ratios for higher productivity of maize/soybean and sorghum/soybean cropping systems. The experiment was conducted during the 1997 and 1998 cropping seasons at the Research Farm of the Faculty of Agriculture, University for Development Studies, Tamale, Ghana. Results showed that seed yields of the monocropping maize, sorghum and soybean were higher than the intercropping yields of maize/soybean and sorghum/soybean. The sorghum/soybean intercropping gave a mean Land Equivalent Ratio (LER) of 0.88 and 0.93 in 1997 and 1998 respectively while the maize/soybean intercropping gave mean LER of 0.82 and 0.81 in 1997 and 1998, respectively. There was lesser interspecific competition between the sorghum/soybean while greater interspecific competition between maize/soybean intercropping was observed. The sorghum/soybean intercropping gave a mean Relative Crowding Coefficient (RCC) of 1.57 and 1.23 in 1997 and 1998 respectively which was more productive than the maize/soybean intercropping with mean RCC of 1.01 and 0.88 in 1997 and 1998, respectively. Based on the LERs and RCCs analyses, three rows of sorghum or maize alternating with three rows of soybean seem more productive. JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 2 No. 2 (2000) pp. 31-35

Growth, competitiveness, and seed germination of triallate/difenzoquat-susceptible and -resistant wild oat populations

Understanding the relative competitiveness and seed germination patterns of herbicide-resistant weeds has implications for integrated weed management. Replacement series experiments were conducted in the greenhouse to compare interspecific competition among two triallate/difenzoquat susceptible (S) and 10 resistant (R) wild oat (Avena fatua L.) populations. Each series included monocultures of each of the populations and three mixtures at relative S:R proportions of 3:1, 1:1 and 1:3. Shoot dry weight tended to be greater in the R than S populations, but results were not always statistically significant at the 5% level. Leaf area was more variable, but in most cases did not differ between R and S populations. With a few exceptions, relative crowding coefficients for shoot dry weight and leaf area were similar for S and R populations indicating little or no differences in competitiveness. In field experiments where two S and five R populations were grown in competition with wheat (Triticum aestivum L.), two of the R populations produced significantly (P < 0.05) greater shoot dry weight and seed yield than the S populations. Otherwise populations did not differ significantly. In seed germination studies, the S populations consistently displayed lower cumulative germination than the R populations. The higher seed germination associated with the R populations suggests that producers should be able to manage these populations effectively with a combination of alternative herbicides and cultural practices. Key words: Avena fatua, herbicide resistance, triallate, difenzoquat, relative competitiveness, seed germination

Interspecific complementary and competitive interactions between intercropped maize and faba bean

Interspecific complementary and competitive interactions between maize (Zea mays L. cv. Zhongdan No. 2) and faba bean (Vicia faba L. cv. Linxia Dacaidou) in maize/faba bean intercropping systems were assessed in two field experiments in Gansu province, northwestern China, plus a microplot experiment in one treatment of one of the field experiments in which root system partitions were used to determine interspecific root interactions. Intercropping effects were detected, with land equivalent ratio values of 1.21–1.23 based on total (grain+straw) yield and 1.13–1.34 based on grain yield. When two rows of maize were intercropped with two rows of faba bean, both total yield and grain yield of both crop species were significantly higher than those of sole maize and faba bean on an equivalent area basis. When two rows of pea (Pisum sativum L. cv. Beijing No. 5) were intercropped with two rows of faba bean, neither total yield nor grain yield of faba bean was higher than of sole faba bean on an equivalent area basis. Interspecific competition between maize and faba bean was relatively weak, with mean relative crowding coefficients of 0.99–1.02 for maize and 1.55–1.59 for faba bean. The microplot experiment in which partitions were placed between root systems showed a significant positive yield effect on maize when the root systems intermingled freely (no partition) or partly (400 mesh nylon net partition) compared with no interspecific root interaction (plastic sheet partition).

Encroachment of Endophyte-infected on Endophyte-free Tall Fescue

Persistence of endophyte-free (E-) tall fescue (Festuca arundinaceaSchreb.) is erratic. Little information exists as to how fast endophyte (Neotyphodium coenophialum)-infected (E+) tall fescue might encroach on E- tall fescue and whether specific conditions might influence the speed of encroachment. Plots of E+ and E- tall fescue genotypes 7 and 17 were established using a modified Nelder's design to compare performance of the E+ forms of the plants in pure and mixed communities at different population densities. The plots were planted at the USDA Southern Piedmont Conservation Research Laboratory in Watkinsville, Georgia, and the University of Georgia Plant Sciences Farm in Bogart, Georgia. Plants were grown over a 5 year period and dry matter yield monitored 1, 3, and 5 years after establishment. Relative crowding coefficients were calculated for each to establish trends of encroachment of the E+ on the E- plants in the mixed communities. Generally, dry matter yields of E+ tall fescue were greater than E- tall fescue regardless of whether they were grown in pure or mixed communities. As time progressed, the difference in dry matter yield between E+ and E- tall fescue grown in mixed communities was greater than that of the pure communities. Relative crowding coefficients increased as time progressed. Relative crowding coefficients at the Watkinsville location were greater after 5 years than those at the Plant Sciences Farm. Therefore, site specific conditions exist which affect the competitiveness of E- tall fescue and degree of encroachment by E+ tall fescue. Research is needed to identify which biotic, abiotic and management variables exacerbate encroachment of E+ tall fescue to better define the conditions which best suit E- tall fescue.

Quantifying the Impact of Arbuscular Mycorrhiza on Plant Competition

From observational studies on succession in the field (Allen 1991) and experimental studies in two-species (e.g. Fitter 1977) and multi-species (e.g. Grime et al. 1987) mixtures, it is argued that AM fungi can alter the competitive balance between species and have a considerable impact on community structure. For example, Allen & Allen (1984) demonstrated an increase in the competitive ability of Agropyron smithui and Bouteloua gracilis in the presence of AM fungi when grown in interspecific competition with the nonmycorrhizal chenopod Salsola kali. Similarly, in a study using a de Wit replacement design to investigate the effect of AM fungi on competitive interactions between S. kali and the mycorrhizal grass Agropyron dasystachyum, Benjamin & Allen (1987) found that in the presence of AM fungi, the grass dominated in terms of biomass, but that in the absence of mycorrhizal colonisation, the chenopod became dominant. Evidence from a range of other experimental studies, in which one species is strongly responsive to the mycorrhizal symbiosis while the other is less mycotrophic or non-mycotrophic, generally indicates that AM fungi influence the outcome of competition when neighbouring species have differential responses to mycorrhizal fungi (Allen & Allen 1990). For example, Crush (1974) and Hall (1978) found that AM fungi improved the competitive ability of legumes when grown with grasses. Furthermore, Fitter (1977) found that AM colonization reduced the growth of Lolium perenne grown in interspecific competition with Holcus lanatus, while Hartnett et al. (1993) showed that the presence of mycorrhizal fungi greatly increased the competitive success of Andropogon gerardii in mixtures of the mycotrophic A. gerardii and predominantly non-mycotrophic Elymrus canadensis. In some of these studies the evidence for competition comes from simple comparisons of the performance of plants in monocultures and in mixtures. In others replacement series experiments have been used to calculate relative crowding coefficients (de Wit 1960) which are used to quantify the impact of mycorrhizal colonization on the competitive process. From a comparison of the effects of mycorrhizal colonization on a range of these coefficients (Allen & Allen 1990) it is clear that the addition of mycorrhizal inoculum did not generally reverse the competitive outcome, but did confer a varying advantage in terms of increased biomass to the mycorrhizal neighbour. Moreover, the response to mycorrhizal colonization in the monocultures and mixtures of a replacement series were not necessarily correlated. Unfortunately, the growth of plants in a replacement series in which monocultures and mixtures are grown at a single overall density does not allow the impact of AM fungi on intraspecific and interspecific competition to be distinguished. In a recent study published in the Journal of Ecology to investigate the impact of AM fungi on two cooccurring and positively mycotrophic grass species, Holcus lanatus and Dactylis glomerata, West (1996) grew the plants with and without AM inoculation at a range of densities in both monoculture and mixtures. Essentially the experimental design involved growing the plants in monocultures at densities of 1, 2, 4, 8 and 16 seeds per pot for each species, plus all paired combinations of the densities of each species. The influence of AM inoculation on the competitive ability of species i in relation to species j was then quantified by calculating the aggressivity index (Snaydon 1991) for each species combination at each density

Impact of Leaf Mining on the Growth of Portulaca oleracea (Common Purslane) and Its Competitive Interaction with Beta vulgaris (Sugarbeet)

1. The combined attack by leaf mining larvae of the sawfly, Schizocerella pilicornis, and the weevil, Hypurus bertrandi, typically resulted in over 80% defoliation of fieldgrown Portulaca oleracea plants in the Central Valley of California. Incorporation of the insecticide aldicarb into the soil prior to planting protected the weed from attack by the insects. Comparison ofinsecticide-treated and non-treated plants demonstrated that the leaf mining reduced weed growth by 60-70%. 2. Under replacement series pot experiment conditions, leaf mining reversed the competitive interaction between sugarbeet and P. oleracea. Sugarbeet grew best in the presence of P. oleracea plants that were attacked by leaf miners; relative crowding coefficients for sugar beet exceeded 1.0. When P. oleracea was protected from leaf-miner attack, relative crowding coefficients for sugarbeet were all below 1.0. 3. Portulaca oleracea caused up to 80% yield loss in sugarbeet in additive field competition experiments. The magnitude of the sugarbeet yield loss increased with increasing density of P. oleracea; between 0.5 and 3.0 P. oleracea plants per m of crop row caused an economic loss depending on year. Soil-applied aldicarb insecticide did not alter the competitive interaction in 3 years out of 4, although the insecticide substantially protected P. oleracea from leaf mining. 4. Although P. oleracea was severely damaged by leaf miner feeding, this injury did not result in sufficient biological weed control to reduce the need for use of other weed management techniques.

Competition Between Triazine-Resistant and -Susceptible Common Waterhemp (Amaranthus rudis)

The relative competitiveness of triazine-resistant (TR) and -susceptible (TS) common waterhemp, as a component of fitness, was assessed using TR and TS biotypes collected from the same field in Fillmore County, Nebraska. Competition between biotypes was evaluated under greenhouse conditions using a set of replacement series experiments with five ratios of TR:TS (1:0, 3:1, 1:1, 1:3, and 0:4) and four plant densities (50, 100, 150, and 300 plants m−2). No difference in final individual plant weight between TR and TS plants was observed in the absence of interbiotypic competition at all plant densities examined. Interbiotypic competition was indicated by ANOVA of plant weight and modified relative crowding coefficients (RCC) for plant weight, height, and volume. Replacement series diagrams showed TS plants were more competitive than TR plants, as measured by plant weight at densities of 50, 100, and 150 plants m−2. TS and TR plants were equally competitive at 300 plants m−2. Individual TS plant weight for 50, 100, and 150 plants m−2was greatest at the 3:1 ratio (TR:TS) and decreased as the proportion of susceptible plants increased. Individual TR plant weight for 50, 100, and 150 plants m−2was greatest at the 1:0 ratio and decreased as the TR proportion decreased. Lack of interbiotypic competition at 300 plants m−2and decreasing TS plant weight with increasing ratios suggest intrabiotypic competition. RCC values for volume and height were calculated weekly during the experiment and indicated the competitive advantage of TS plants was constant from transplanting through harvest.

Growth Characteristics of Selected Dinitroaniline-Resistant and -Susceptible Goosegrass (Eleusine indica) Population

Growth and development of selected dinitroaniline-resistant (DR) and -susceptible (DS) goosegrass populations were compared in field studies in replacement series, in association with cotton, and under noncompetitive conditions. The DR ‘Florence’ (FR) and DS ‘Orangeburg’ (OS) populations were similar in competitiveness as indicated by relative yields (RY) and relative crowding coefficients (RCC) for vegetative and reproductive biomass production in a replacement series. Relative growth of the FR and DS ‘Anderson’ (AS) populations in replacement series was similar when vegetative biomass was considered, but reproductive biomass of the AS population declined as proportion of FR population increased. RCC values also indicated that the FR population interfered with reproductive development of the AS population. In field studies, the FR population produced greater vegetative biomass than either DS population, while similar reproductive biomass occurred for the FR and OS populations. Inflorescence dry weights were greater for the FR than the AS population under noncompetitive conditions and in cotton, but were greater for the AS population in replacement series studies. The competitiveness of DR and DS goosegrass biotypes appears to be more related to growth characteristics of individual populations than to response to dinitroaniline herbicides.

Influence of Phosphorus Fertility on Intra- and Interspecific Interference between Lettuce (Lactuca sativa) and Spiny Amaranth (Amaranthus spinosus)

Greenhouse studies were conducted to determine the effect of phosphorus (P) fertility on intra- and interspecific competition between lettuce and spiny amaranth for 4 wk after emergence. Total lettuce shoot biomass per pot and weight per plant increased 39 and 44% in response to increased P fertility, respectively. P fertility had no impact on growth of spiny amaranth. Total shoot biomass of spiny amaranth increased with increasing density from four to eight plants, however, lettuce did not. Total shoot biomass of both species increased as density increased from 4 to 16 plants. Spiny amaranth, but not lettuce, weight per plant decreased in response to intraspecific competition. Reciprocal yield analysis showed that spiny amaranth produced 2.4 times more biomass than lettuce when competing intraspecifically and four times more biomass under interspecific competition. Lettuce weight per plant was not affected. Relative yield analysis indicated that spiny amaranth was more competitive than lettuce regardless of P fertility. However, increased P fertility increased competitiveness of lettuce. Relative crowding coefficients indicated that spiny amaranth at the low density with low P fertility was 33 times more competitive than lettuce. Addition of P caused lettuce and spiny amaranth to be equally competitive at the lowest density; however, at the highest density, spiny amaranth was 4 tunes more competitive than lettuce regardless of additional P.

Growth Analysis of Mayweed Chamomile (Anthemis cotula) Interference in Peas (Pisum sativum)

Destructive growth analysis of field replacement series experiments with mayweed chamomile and dry field peas was used to determine the competitive relationship between the two species. Mayweed chamomile produced similar amounts of leaf area and dry weight per plant in a dry year and a wet year. On the other hand, dry field peas produced 20% more leaf area and 100% more dry weight per plant in the wet year compared to the dry year. Height, leaf area, and dry weight of peas reached maximum between bloom and pod-set, and then declined. Height and dry weight of mayweed chamomile increased steadily throughout the growing season. Mayweed chamomile leaf area reached a maximum at the beginning of flower stem elongation. Initially, the relative growth rate of mayweed chamomile was about three times greater than the rate for peas, but by 40 to 48 d after planting, rates were similar for both species. Relative yields and relative crowding coefficients for dry weight showed that peas were 3 to 20 times more aggressive than mayweed chamomile. Results of these experiments show that mayweed chamomile is a weak competitor against peas, but because it continues to grow after peas senesce, it could interfere with crop harvest.

Evaluating Larval Competition Between Aedes albopictus and A. triseriatus (Diptera: Culicidae) through Replacement Series Experiments

Potential larval competition between Aedes albopictus (Skuse) and Aedes triseriatus (Say) was examined with replacement series experimental design, an analysis previously used to evaluate competition between plant species. Experimental design was a factorial treatment arrangement with four replications of larval diet (high and low) and species ratio (proportions of A. triseriatus/A. albopictus larvae 1:0, 3:1, 1:1, 1:3, and 0:1). Adult emergence, adult biomass, and sex ratio were evaluated. No competitive effects were observed in the high-diet treatments; however, significant competitive relationships were observed for all parameters in the low-diet treatments. Competition was evaluated by replacement diagrams, relative crowding coefficients, and analysis of variance. All techniques indicated that A. albopictus was a superior competitor to A. triseriatus under low diet. The use of the replacement series design was a powerful method for examining competition through a single experiment. The results indicate that replacement series experimental design can be used to characterize competition between animal species, providing that individual animals can be placed in an experimental habitat in appropriate proportions.

Population and Planting Pattern Effects on Intercropped Maize and Cowpea

AbstractField studies on the nature of competition and the effects of various planting patterns on maize/cowpea intercrop yields were conducted in Southwestern Nigeria. Relative Crowding Coefficient values indicated that maize dominated cowpea. The magnitude of competition between maize and cowpea is related to season and nitrogen fertilizer. Based on grain yields, maize and cowpea compete for N only when it was applied but tended to derive it from different sources in the absence of applied N.Spatial arrangements designed to increase light reaching intercropped cowpea included alternate and double rows of cowpeas between maize rows. These did not, however, increase grain yields of cowpeas over those intercropped with maize in the same row.

The use of nitrogen, phosphorus and lime to limit the competitive ability of Aristida armata in the establishment phase

The de Wit replacement series methodology was used to see if applying phosphorus, nitrogen and lime to the sandy red earth soils of mulga grazing lands can give a competitive advantage to the desirable species Cenchrus ciliaris C.V. U.S.A., Digitaria ammophila, and Thyridolepis mitchelliana over the less desirable Aristida armata. In monoculture, all species responded strongly to added nutrients, especially phosphorus. In mixtures, the preferred grasses responded even more strongly to nutrients, whereas A. armata responsed proportionally less. C. ciliaris, D. ammophila, and T. mitchelliana suppressed the growth of A. amnata in all but three situations: without added nutrients, A. armata was equally competitive with C. ciliaris; when P was added without lime, A. armata suppressed C. ciliaris; if P was added without N, A. armata suppressed T. mitchelliana. Adding either or both nitrogen or phosphorus usually increased the relative crowding coefficients, indicating that the degree of suppression of Aristida was increased by adding nutrients. Thus, C. ciliaris, D. ammophila, and T. mitchelliana appear to be equally competitive with or more competitive than A. armata if the soil is not fertilized and adding nutrients generally enhances this competitiveness. In all cases, except for A. armata/C ciliaris mixtures in soils low in phosphorus, the plants appeared to be competing for the same resource. The study demonstrated that A. armata is not a highly competitive species per se under controlled conditions and was generally suppressed by the preferred grasses, especially when nutrients were added.

Competition between white clover (Trifolium repens L.) and subterranean clover (Trifolium subterraneum L.) in binary mixtures in the field

White clover, (cv. Haifa) and subterranean clover (cv. Seaton Park) were grown in binary replacement series mixtures in the field at proportions of 100:0, 90:10, 50:50. 10:90 and 0:100, and cut every four weeks over three growing seasons from 1985 to 1987 at Scone, New South Wales (NSW) (32°S). Relatively low plant densities minimized competition in 1985, but in subsequent seasons Haifa and Seaton Park competed vigorously for the same resource;.; usually having relative crowding coefficients greater than 1.0, and relative yield totals greater than 1.0 in spring of 1986 and 1987, and autumn 1987. This over-yielding appeared to be due to some complementarity of leaf morphology and canopy architecture. Haifa severely depressed seed production of Seaton Park in mixtures. Haifa regenerated as an annual in 1986, but as a perennial, from surviving stolons, in 1987 owing to lower maximum temperatures and better rainfall distribution in late summer and autumn of 1987. It is concluded that white clover can survive severe competition from subterranean clover as a seedling, and if moisture allows, may severely depress seed production from subterranean clover, regardless of whether plants are annual or perennial in origin. Spatial separation may minimize competition in average years but competition effects may be severe in seasons with sufficient summer rainfall for perennation of white clover, and seasonal autumn rainfall for germination of subterranean clover.

Competition Effects in Juvenile Jack Pine and Aspen as Influenced by Density and Species Ratios

(1) Jack pine (Pinus banksiana Lamb.) and trembling aspen (Populus tremuloides Michx.) seedlings were grown in replacement series (100, 75:25, 50: 50, 25:75, 100) at variable densities (17 to 10 000 plants m2) for 12 weeks in a greenhouse experiment and for 3 years in a field test. (2) Analyses of survival, height, weight, form, resource allocation, relative yields and relative crowding coefficients indicated that aspen dominated in all mixtures and densities except 10 000 plants m-2.

Competitive Relationships Among Winter Wheat (Triticum aestivum), Jointed Goatgrass (Aegilops cylindrica), and Downy Brome (Bromus tectorum)

In three replacement series experiments, winter wheat (Triticum aestivumL.), jointed goatgrass (Aegilops cylindricaHost. #3AEGCY), and downy brome (Bromus tectorumL. # BROTE) were paired in all possible combinations to determine competitive relationships during vegetative growth. Under growth chamber conditions of ample fertility and soil moisture and day/night temperatures of 18/10 C, relative yield totals for the three species were similar, indicating that they compete for the same resources. Both winter wheat and jointed goatgrass had greater plant growth and higher relative crowding coefficients than downy brome, which indicated a hierarchy of relative competitiveness of winter wheat > jointed goatgrass >> downy brome. In other growth chamber studies, winter wheat was slightly more competitive than jointed goatgrass regardless of fertility levels. Winter wheat was the superior competitor at 18/10 C and −33 kPa (soil moisture), whereas jointed goatgrass was superior at 27/10 C and −300 kPa, conditions that are frequently encountered in the Pacific Northwest.

Effect of irrigation and nitrogen on maize-cowpea fodder intercropping at Ludhiana, India: Advantages and intercrop competition

This study was undertaken to examine intercrop competition and the intercropping advantage of maize-cowpea fodder at three irrigation and four nitrogen levels. Another objective was to develop relationships among different measures used for evaluating intercrop competition. The residual effect of intercropping on a following pearl millet fodder crop was also investigated. Yield intercropping advantanges was observed at all irrigation and nitrogen levels. Land equivalent ratio values varied from 1.04 to 1.17 for different nitrogen and irrigation levels. There was an advantage in crude protein production similar to that in yield. Intercrop competition was affected by nitrogen and irrigation. The competitive ratio for maize changed from 0.8 at zero nitrogen to 1.46 at 120 kg N/ha. Pearl millet fodder grown after intercrop yielded 42% more than after maize. Relationships were developed for computing relative crowding coefficients and aggressivities from individual crop land equivalent ratios.

Interference of fathen (Chenopodium album) with lucerne (Medicago sativa) during establishment

Abstract The interference of fathen (Chenopodium album L.) with lucerne (Medicago sativa L.) during establishment was studied by growing the 2 species in pots (in a growth cabinet) according to the replacement series model of de Wit (1960) for an 8-week period after sowing. Pots received either no nitrogen or 50 kg/ha basally. Fathen was more competitive than lucerne, as shown by their relative crowding coefficients, relative yields, plant height, leaf area, root length, shoot dry weight, root dry weight, and total dry weight. The product of the relative crowding coefficients of lucerne and fathen, and their relative yield total were both close to unity, showing that competitive interference occurred between the 2 species and that they were 'mutually exclusive'. The absence of any effect of nitrogen treatments indicated that this was not the factor limiting growth.

Seeding year alfalfa population development as influenced by weed competition and density of establishment

The research in intraspecific competition within an alfalfa stand and interspecific competition between alfalfa and weeds was begun on the Michigan State University farm in East Lansing in 1972. Alfalfa seeding densities of 50, 400 and 800 seeds/m2 were used to determine intraspecific competition. Interspecific competition between alfalfa and weeds occurred mainly in noncontrolled alfalfa stands at various levels of seeding densities. Plant competition was evaluated with importance values and with relative crowding coefficients. Both measurements were found to be suitable for this kind of study. Importance values primarily indicated the quantity relationships of different species. Relative crowding coefficients mainly characterized the competitive ability of a species in a mixed stand. The importance of alfalfa exceeded the importance of weeds in noncontrolled and herbicide controlled stands at the seeding rates of 14 and 7 kg/ha respectively. Relative crowding coefficients show the competitive ability of alfalfa with regard to weeds. In the case of intraspecific competition there was no change in the crowding coefficient of alfalfa in respect of weeds when the seeding rate of alfalfa was increased beyond 9 kg/ha. The crowding coefficient of weeds presented equal values under all treatments thereby indicating the variability and plasticity of weeds. The maximum yield level was obtained in all treatments with the alfalfa seeding rate of 9 kg/ha. The total biomass production per unit area was equal in the noncontrolled system at all seeding densities and in the herbicide controlled system at seeding rates of 9 kg/ha or more.