Oat Densities Research Articles

Effects of different densities of wild oat (Avena fatua L.) and nitrogen rates on oilseed rape (Brassica napus L.) yield

Abstract A Two-year field experiment was carried out in 2009 and 2010 to evaluate the effects of different densities of wild oat and nitrogen (N) rates on oilseed rape yield and yield components. Experimental design was split plot with three replications. Increased nitrogen rates up to 150 kg N/ha caused an increase in oilseed rape grain yield in weed-free plots (4.26 t/ha; 1t = 10 3 kg), while even at the lowest density of wild oat (15 plants/m 2 ), increasing N fertilizer only up to 50 kg/ha led to a significant increase in grain yield. Wild oat growth was favored by high levels of N. Intraspecific competition reduced biomass, 100-seed weight and number of tillers of wild oat. Both lower N rate and intraspecific competition had negative effect on wild oat growth but the weed was still able to produce a considerable number of tillers and vigorous seeds. It showed that wild oat possess a no table adaptive plasticity and can allocate a greater proportion of its resource toward re -productive organs even under resource shortage conditions and, thus, it may increase the competitive ability of the weed over the crop.Our results suggest that effective weed management should be done to prevent wild oat seed production in crops preceding oilseed rape as well as to control the weed at early season in oilseed rape fields.

Species domination in oats phytocenosis and its yield

The paper presents an analysis of oats phytocenosis (the crop and weeds) treated as a competitor group as concerns the species domination developing within it. The study covered oats cultivated on plots after potatoes (in crops rotation system with 25% share of oats) and twice after oats (75% share of oats in the rotation system) during the years 1990-2000. Simpson's species domination ratio and domination structure in the association identifying groups of: dominants, subdominants, influents and accessory species, were computed and studied. Relations between the studied phytocenosis features and weather conditions and oats yield were also determined. It was shown that quantitative relations in the assessed competitor associations were characterized by high variability between years and vegetation periods while no major differences were found between positions in the crop rotation systems. The density of spring phytocenosis during 11 years of studies increased resulting from increasing numbers of weeds appearing; during the late vegetation period they changed the density of associations slightly. In the spring, the groups competitive to the group of dominants consisted usually of the crop and <i>Thlaspi arvense</i> as well as <i>Chenopodium album</i>; with the passage of years their position strengthened. The enrichment of species in phytocenosis was represented mainly by an increase in numbers of accessory species. At the end of vegetation the importance of oats as a dominant increased significantly; during some seasons <i>Chenopodium album</i> co-dominated, however, with the passage of years the group of subdominants grew. Domination ratios for the studied competitor groups decreased with the passage of years, parallel to decrease of oats share in them. The studied features of phytocenosis showed a stronger correlation to the passage of years than the weather development. Invasiveness of weeds increased during consecutive seasons of cultivation while it showed less correlation with the density of oats. Oats yields showed a slight decreasing trend from year to year and was highly determined by the density of the entire weeds assemblage and in the spring by density and share of dominating species.

Effect of Plant Density on Wild Oat Competition with Competitive and Non-Competitive Wheat Cultivars

Abstract Wild oat (Avena ludoviciana) is one of the worst weeds in wheat fields. The effect of wheat density on wild oat competition with more or less competitive wheat cultivars (Triticum aestivum) was investigated at the Experimental Farm of Plant Pests and Diseases Research Institute, Karaj, Iran. The experiment was established as a factorial combination of wheat varieties Roshan as non-competitive and Niknejad as competitive; three wheat densities (recommended density, recommended+25%, and recommended+50%, corresponding respectively with 300, 375, and 450 plants m- 2 for Roshan and 400, 500, and 600 plants nr 2 for Niknejad) and four wild oat densities (0, 25, 50, and 75 plants nr 2) were selected for this experiment. Hyperbolic equations were used to describe relationship between yield and weed density. Increase in wheat density reduced wild oat biomass. Maximum wild oat biomass was achieved at the highest density of the wild oat together with the lowest wheat density. The results showed that higher densities of wheat are able to suppress wild oat dry matter production. Inter-specific competition in Niknejad was 1.7 times more than that in Roshan. Maximum yields of Niknejad and Roshan in the presence of wild oat were obtained at recommended density+25% and recommended density, respectively. Increase in wheat density leads to a decrease in wheat yield due to an increase in intra-specific competition. Increase in wild oat density results in the reduction of wheat yield through decrease in fertile tiller per plant and spike nr 2.

Discrimination of sterile oat ( Avena sterilis) in winter barley ( Hordeum vulgare) using QuickBird satellite images

Site-specific weed management implies detecting the location of weeds in order to generate maps of their spatial distribution. This information facilitates a more accurate application of herbicides, spraying them in the exact areas of weed growth and in the required doses. In order to explore the potential of commercial satellites to discriminate and map weeds, we used the information contained in high spatial resolution images acquired by the QuickBird satellite to assess the density of sterile oat ( Avena sterilis) present in a winter barley field at two different dates (March and June). Our results confirmed the potential of using satellite images in the spectral discrimination of weed patches in infested fields. The results of binary logistic regressions showed that the best matches in the classification of three categories (low, medium, or high sterile oat densities) corresponded to the March image. QuickBird’s March image provided reliable estimates of sterile oat patches in barley crops when weed density was relatively high (between 86% and 94% of agreement between predicted and observed densities). However, when weed densities were lower than 10 plants/m 2 there were serious difficulties to distinguish them from weed-free zones (between 72 and 75% of global agreement in the classification) with large underestimation of medium density weed patches (10 plants/m 2). This is a potential limitation considering than the thresholds used for herbicide application decisions are generally close to this density. However, the information obtained may still be useful for producing field maps to describe the spatial distribution of this weed. Moreover, these studies have provided valuable information on the best spectral regions and/or vegetation indices for approaching discrimination between sterile oat and cereal crops and the most suitable period for it.

Structural equation modeling in the plant sciences: An example using yield components in oat

Lamb, E. G., Shirtliffe, S. J. and May, W. E. 2011. Structural equation modeling in the plant sciences: An example using yield components in oat. Can. J. Plant Sci. 91: 603–619. Structural equation modeling (SEM) is a powerful statistical approach for the analysis of complex intercorrelated data with a wide range of potential applications in the plant sciences. In this paper we introduce plant scientists to the principles and practice of SEM using as an example an agronomic field trial. We briefly review the history of SEM and path analysis and introduce the statistical concepts underlying SEM. We demonstrate the use of observed and latent variable structural equation models using a multi-site multi-year field trial examining the effects of seed size and seeding density on the plant density and yield of oat in Saskatchewan. Using SEM allowed for insights that a standard univariate analysis would not have revealed. We show that seeding density has strong effects on plant and panicle density, but has very limited effects on final yield. Plant density has a consistent non-linear effect on panicle density across location that was not affected by precipitation. In contrast, the implicit effect of precipitation on seed number appears to be the main driver for final yield. Incorporating precipitation data into the model demonstrates how mechanistic models can be developed by including in the path diagram variables that would normally treated as random factors in a mixed model analysis. Finally, we provide a guideline to assist plant scientists in determining whether SEM is an appropriate method to be used for the analysis of their data.

Integrated effect of seeding rate, herbicide dosage and application timing on durum wheat (Triticum turgidum l. var durum) yield, yield components and wild oat (avena fatua l.) control in south eastern Ethiopia

Knowledge of optimal combinations of crop densities, herbicide dose and time of application could improve the effectiveness and net benefit of commonly used herbicides. A study was conducted at two locations in SARC on-station and farmer’s field, South Eastern Ethiopia for two years from 2007 to 2008. The experimental design was randomized complete block (RCB) design with split-plot arrangement. Durum wheat (Triticum turgidum) seeding rates (recommended, 25% and 50% plus recommended rate) were arranged in the main plot. Four wild oat (Avena fatua) herbicide, Topik, doses (0, 25, 50 and 100 % of the recommended dose) and three timing of applications (14 DA, 32 DAE and 50 DAE) were used as sub-plot treatments. The treatments were compared to determine their effect on durum wheat yield, yield components wild oat densities and control efficacies. Durum wheat seeding rates significantly influenced grain and biomass yield, spike per unit area and kernel weight. Seeding rate of 225 kg ha-1 produced highest grain yield (3810.4 kg ha-1) while 150 kg ha-1 recorded the lowest. Mean wild oat density count before herbicide application timings varied over the two locations averaging 37 and 87 seedlings m-2. Increasing seed rate by 25 and 50% increased wild oat control efficacy by 16.9 and 21.5% respectively. Spraying the herbicide at later growth stages caused greater wild oat seedling density and reduced wheat yield at both locations. The highest efficacy (94.04%) was obtained in the second time of application (30 DAE) of 1 l lit ha-1. The highest reduction in population density was occurred in 100% herbicide rate. There was a general decline in wild oat density in the early application and as the herbicide dose increased, but the effect of seeding rate varied very slightly. In contrast to the wild oat control efficacy the highest grain yield ha-1 was obtained in the first application date (14 DAE). Durum wheat yield losses in the absence of herbicide application were increased by about 16%. Maximum yield (3870.73 kg ha-1) was obtained at 100% of the herbicide dose very closely followed by 50 and 25% of the recommended rate reducing durum wheat yield only by about 1.6 and 2% respectively. Durum wheat seeding rate, herbicide dosage and application timing had statistically no significant interaction effect. Key words: Durum wheat, Wild oat, Herbicide dose, Seeding rate, Application timing.

Competitive ability of Ethiopian spring bread wheat cultivars with <i>Avena fatua L.</i>

Competitive interactions of four spring bread wheat cultivars ( Triticum aestivum L.) with four wild oat ( Avena fatua L.) seedling densities were assessed in field studies in southeastern Ethiopia during three cropping seasons (1991-93). Grain yield of wheat was linearly proportional to the seedling density of wild oats, but yield reductions at the maximum density of 90 weed seedlings m-2 ranged from 26 to 63% across the wheat cultivars. The semidwarf cultivar Dashen was the most sensitive to wild oat competition, while the intermediate height cultivar Enkoy was the least affected. Wheat cultivars varied markedly in their ability to suppress A. fatua tillering and seed production, differentially affecting wild oat seed and straw yield, panicle production, seed number panicle-1, and thousand kernel weight. Given the limited access of Ethiopian peasant farmers to grass herbicides, wheat breeders should be encouraged to exploit such variability, and develop germplasm with a greater inherent ability to compete with wild oats.

Evaluation of yield–density relationships and optimization of intercrop compositions of field-grown pea–oat intercrops using the replacement series and the response surface design

In a 2-year field experiment (2002/2003) on a loess soil near Göttingen/Germany, pea ( Pisum sativum L.) and oat ( Avena sativa L.) were grown alone and intercropped at a range of densities. Shoot biomass, grain yields and amount of N in grain were evaluated and optimized using two different replacement series and a hyperbolic yield–density equation describing a response surface to address the following questions: (i) what is the optimal composition of the pea–oat intercrop with regard to maximum yields, (ii) which intercropping design is most suitable to describe competition effects in pea–oat intercrops and the optimal intercrop compositions and (iii) which intercropping design is best suited for the evaluation of field data. For (i), the optimal intercrop compositions varied depending on the growth conditions for the crops. Furthermore, optimal intercrop compositions were found above the recommended sole crop densities. The density of oat had to be reduced more than that of pea, especially when optimal grain-N yields were desired and soil-N content was high. For maximum grain-N yields, pea could be sown at high densities in combination with 5–50% of the recommended density of oat. Thus, density can be used as a yield regulator for specific purposes such as a high N yield. The effects of competition at final harvest were described equally by both designs (ii). Oat was the clearly stronger and pea the inferior competitor. In contrast to the replacement series design, the hyperbolic yield–density equation was capable of adding valuable information about the extent of intra and interspecific competition. As intraspecific competition was consistently more important than interspecific competition, resource complementarity could be hold responsible for intercrop advantages. The highest intercrop advantage was found when total intraspecific competition was low, as shown by the relative yield total (RYT) and niche differentiation index (NDI) values >1. However, due to the RYT dependence on sole crops and total densities, the replacement series design led to misleading interpretations of the yield advantages. Both experimental designs were able to describe the field-data reliably (iii), but the response surface design had the advantage of being unaffected by insufficient field emergences, as it is not based on total densities. Numbers of plants m −2 instead of seeds m −2 can be used for the evaluation. Data from sole crops are not needed for the response surface design and thus the feared high experimental effort of this design can be reduced. However, when using the replacement series design, experimental effort should be greater than normal, as different sole crop densities and more intercrop compositions within a replacement series can lead to a more precise interpretation of the competition effects.

Management of wild oat (Avena fatua L.) in tame oat (Avena sativa L.) with early seeding dates and high seeding rates

Traditionally, farmers have delayed seeding to manage wild oat (Avena fatua L.) in tame oat (Avena sativa L.) crops, but this practice can adversely affect grain yield and quality. The objectives of this study were: (1) to evaluate the effectiveness of using high seeding rates with early-seeded oat to maintain grain yield and quality, and (2) to determine an optimum seeding rate to manage wild oat and maximize grain yield and quality. The factors of interest were wild oat density (low and high density), seeding date (early May, mid May, early June and mid June), and tame oat seeding rate (150, 250, 350 and 450 viable seeds m-2). The study was conducted at Indian Head and Saskatoon, SK, in 2002, 2003 and 2004, at Winnipeg, MB, in 2002, and at Morden, MB, in 2003 and 2004. Wild oat biomass, wild oat panicle density and wild oat seed in the harvested sample decreased as seeding rate increased, while tame oat biomass and grain yield increased. Wild oat density ranged between 0 and 100 plants m-2 with averages of 10 plants m-2 in the low density treatment and 27 plants m-2 in the high density treatment. At low seeding rates, grain yield decreased with increasing wild oat density. The difference in grain yield between the two wild oat densities decreased as the seeding rate increased. There was a curvilinear decrease in grain yield as seeding was delayed. A seeding date × seeding rate interaction was noted for test weight, plump seed, thin seed and groat yield. Seed quality improved as seeding rate increased for only the mid-June seeding date. Even though the mid-June test weight increased as the seeding rate increased it was always lower than the early May test weight at any seeding rate. The results from this study established that in the presence of wild oats, early seeding of tame oat is possible providing high seeding rates, 350 plants m-2 are used.Key words: Wild oat competition, wild oat density, wild oat biomass, grain yield, grain quality

Effect of Land Rolling on Weed Emergence in Field Pea, Barley, and Fallow

In the northern Great Plains, fields are land rolled after the planting of annual pulse and forage crops to push rocks back into the soil to prevent damage to harvest equipment. Field trials were conducted in 2004 and 2005 to determine if land rolling influenced weed density or biomass associated with field pea, forage barley, and summer fallow. The experiment included two planting dates, conventional and delayed, for both barley and pea. Separate fallow plots were included with each planting date. Preplant tillage was conducted with a field cultivator for all treatments. Across years, crops, and planting dates, land rolling approximately doubled densities of tumble mustard, Russian thistle, kochia, and redroot pigweed shortly after crop emergence and at harvest compared with nonrolled. Land rolling increased density of early-emerging green foxtail but density at harvest was not affected. Wild oat densities were not influenced by rolling. Weed biomass at harvest was greater after land rolling than nonrolled. Land rolling after planting decreased subsequent pea yield by 330 kg/ha, but did not influence water use or water use efficiency. Land rolling is advantageous by hastening depletion of soil broadleaf weed seed banks in forage barley, but may increase problematic broadleaf weeds in pea.

Oat Grain Density Measurement by Sand Displacement and Analysis of Physical Components of Test Weight

ABSTRACTTest weight or bulk density of oats (Avena sativa L.) has a major influence on the monetary value of oat grain. We hypothesize that test weight can be attributed to grain density and packing efficiency. We have measured oat grain volume and density by a sand‐displacement method and derived the packing factor for six oat cultivars grown in three environments. Volumes of individual grains were 31–38 mm3 and were highly correlated with grain mass. Grain densities were 0.96–1.03 g/cm3. Packing efficiency, defined as the space proportion occupied by the grains, was 53–55%. Regression analysis suggested that 78% of the variation in test weight could be attributed to grain density. Size fractionation of grain by sieving and analysis by digital image analysis indicated that smaller grains within an oat sample packed more efficiently than larger grains and larger grains in a sample were less dense than the smaller grains. Analysis of oat grain components indicated groat densities were ≈1.29 g/cm3 and hull densities were ≈0.69 g/cm3. The difference in densities between groat and hull provide a physical basis for the recognized relationship between groat percentage and test weight.

Developing an Empirical Yield-Prediction Model Based on Wheat and Wild Oat (Avena fatua) Density, Nitrogen and Herbicide Rate, and Growing-Season Precipitation

To develop a more complete understanding of the ecological factors that regulate crop productivity, we tested the relative predictive power of yield models driven by five predictor variables: wheat and wild oat density, nitrogen and herbicide rate, and growing-season precipitation. Existing data sets were collected and used in a meta-analysis of the ability of at least two predictor variables to explain variations in wheat yield. Yield responses were asymptotic with increasing crop and weed density; however, asymptotic trends were lacking as herbicide and fertilizer levels were increased. Based on the independent field data, the three best-fitting models (in order) from the candidate set of models were a multiple regression equation that included all five predictor variables (R2= 0.71), a double-hyperbolic equation including three input predictor variables (R2= 0.63), and a nonlinear model including all five predictor variables (R2= 0.56). The double-hyperbolic, three-predictor model, which did not include herbicide and fertilizer influence on yield, performed slightly better than the five-variable nonlinear model including these predictors, illustrating the large amount of variation in wheat yield and the lack of concrete knowledge upon which farmers base their fertilizer and herbicide management decisions, especially when weed infestation causes competition for limited nitrogen and water. It was difficult to elucidate the ecological first principles in the noisy field data and to build effective models based on disjointed data sets, where none of the studies measured all five variables. To address this disparity, we conducted a five-variable full-factorial greenhouse experiment. Based on our five-variable greenhouse experiment, the best-fitting model was a new nonlinear equation including all five predictor variables and was shown to fit the greenhouse data better than four previously developed agronomic models with anR2of 0.66. Development of this mathematical model, through model selection and parameterization with field and greenhouse data, represents the initial step in building a decision support system for site-specific and variable-rate management of herbicide, fertilizer, and crop seeding rate that considers varying levels of available water and weed infestation.

Effects of crop density and tillage system on grain yield and N uptake from soil and atmosphere of sole and intercropped pea and oat

Pea ( Pisum sativum L.) and oat ( Avena sativa L.) were grown as sole and mixed crops in various densities under two different tillage systems on a loess soil near Göttingen/Germany in a 2-year field experiment (2002/2003). In the conventional tillage system a mouldboard plough (CT) was used and in the minimum tillage system a rotary harrow (MT) was employed. The effect of crop density and tillage system on the grain dry matter and grain N yields, N 2 fixation and soil N uptake were determined to address the following questions: (i) which mixture compositions exhibit the highest grain yields compared to the sole crops, (ii) which mixture compositions also fix a high level of N 2 and leave low levels of residual inorganic soil N after harvest, and (iii) whether the intercrop advantage is influenced by the tillage system. For (i) the result in 2002 showed that the highest grain yields of both sole cropped pea and oat and intercropped pea and oat were achieved at the highest densities. In 2003, when the inorganic soil N content was higher and weather conditions were warmer and drier, grain yields were significantly higher than in 2002, but sole as well as intercropped pea and oat gave their highest grain yields at lower densities. For both years and tillage systems, the highest intercrop advantages were achieved in mixtures with densities above the optimal sole crop densities. The result for (ii) was that a distinctly higher proportion of nitrogen was derived from the atmosphere (Ndfa) by intercropped pea than by sole cropped pea. However, the uptake of soil N by intercropped pea and oat was not reduced in comparison with that of sole cropped oat as the decrease in the uptake of N from the soil by oat at lower oat densities in the mixture was compensated for by the soil N uptake of pea. Additionally, the N min-N content of the soil following the mixtures and sole cropped oat did not differ, especially in the deeper soil layers because oat in mixture was forced to take up more soil N from deeper layers. Therefore, the risk of soil N losses through leaching after mixtures was lower compared to sole cropped pea. The tillage system (iii) had no significant influence on grain yield and soil N uptake, but N 2 fixation and the competitive ability of intercropped pea were higher under CT than with MT. An additional result was that intercropping led to a significantly increased grain N content of both pea and oat compared to the sole crops. The increase in grain N content from sole to intercrop was from 3.30 to 3.42% for pea and from 1.73 to 1.96% for oat as a mean for both years and tillage systems. The present study confirms that growing pea and oat as intercrops highlights potential economic and environmental benefits which still need to be understood in more detail in order to exploit intercropping to a greater extent.

Integrating herbicide rate, barley variety and seeding rate for the control of sterile oat ( Avena sterilis spp. ludoviciana) in central Spain

Three field experiments, each repeated over three seasons, were conducted to determine the effects of herbicide rate, winter barley variety and seeding rate on the control of sterile oat ( Avena sterilis spp. ludoviciana) and the yield of barley. The herbicide rate giving 50% reduction in the weed fresh weight (ED 50) was generally higher with diclofop than with imazamethabenz or tralkoxydim (26.6, 16.0 and 16.4% of full rate, respectively). Under adequate rainfall, reducing herbicide rate 50% resulted in sterile oat seed outputs very similar to those obtained with the full rate. However, in the presence of water stress, seed production was significant with low herbicide rates, particularly when weed pressure was high. Barley yields decreased gradually with decreasing herbicide rate. Although practically no yield losses were obtained by reducing the rate 50% of the recommended rate, reducing the rate down to 12.5% resulted in yields that were similar to the untreated control. Yield responses were variable in the 3 years. Reducing tralkoxydim to 50% of the recommended rate resulted in 32% crop yield loss in 1997 and only 2.7% yield loss in the other 2 years. The high yield losses in 1997 were associated with high weed densities and water stress conditions. Crop variety interacted with tralkoxydim rate to determine sterile oat growth and reproduction. The ED 50 of tralkoxydim was 8% for ‘Albacete’ (tall and late maturing) and 18% for ‘Barbarrosa’ (medium height, medium maturing). The effectiveness of low tralkoxydim rates in reducing sterile oat fresh weight and seed production did not improve with high seeding rates. The results support the view that reducing herbicide rates down to 50% of the label rate is a safe practice when sterile oat densities are low or moderate. However, reducing the rates even further may increase the risks of yield losses and increased weed populations in subsequent years. This risk can be lowered by growing competitive barley varieties.

Effects of Spring Wheat Seed Size and Reduced Rates of Tralkoxydim on Wild Oat Control, Wheat Yield, and Economic Returns

Spring wheat competitive ability has recently been demonstrated to co-vary with seed size. The objective of this study was to determine if spring wheat seed size would influence the effects of variable tralkoxydim rates on wild oat control, wheat yield, and economic returns. The factorial treatment arrangement consisted of three spring wheat seed size classes and five tralkoxydim rates. Wild oat density, panicles, and biomass decreased as spring wheat seed size and tralkoxydim rate increased, with the combined effect being additive. Wild oat variables decreased in a log-logistic manner as tralkoxydim rate increased during both years. However, tralkoxydim was less effective in 2000 than 2002, as indicated by the higher dosage required to reduce the wild oat variables by 50% (greaterI50values). In contrast, the effect of large seeded wheat in suppressing wild oat was more consistently expressed, with wild oat variables decreasing linearly as seed size increased. Wheat yield and economic returns increased exponentially as tralkoxydim rate increased. At the same time, wheat yield and economic returns were greater for wheat plants derived from large seed compared to those derived from small seed. Averaged over all other factors, adjusted gross returns of 578, 657, and 703 $/ha were realized for the small, medium, and large seed size classes, respectively. The combined use of large seeded wheat plus tralkoxydim applications provided greater wild oat control than did either single tactic. The use of large seeded wheat had a stabilizing effect that increased the consistency and durability of the weed management system while simultaneously improving economic returns.

Compensatory Mechanisms Associated with the Effect of Spring Wheat Seed Size on Wild Oat Competition

Crop seed size affects the competitive relationship between spring wheat (Triticum aestivum L.) and wild oat (Avena fatua L.). However, the mechanisms associated with the process are not known. The effect of wheat seed size on wild oat competition was assessed by a mechanistic approach involving yield and its determinants in these species. Wheat plants established from large and small seed were evaluated under different seeding rates and wild oat densities during 1999–2001 near Kalispell, MT. Linear structural model systems based on ontogenic diagrams were constructed for each seed size class. Spikes m−2 and panicles m−2 had the greatest positive effect on yield within each species. For wheat, the impact of the two later‐formed yield components on yield decreased in an ontogenic manner, whereas for wild oat, their relative contributions were similar in magnitude. Wheat plants derived from large seed had a noticeable negative effect on wild oat via a reduction in panicles m−2 and seed weight, whereas wheat established from small seed mainly affected wild oat panicles m−2 Wild oat competition reduced wheat spikes m−2 and kernels spike−1 in both seed size classes. However, these reductions were less for plants derived from large seed, which demonstrated enhanced compensatory ability. In summary, nongenetic variations in crop seed size affected the competitive dynamics between these species, where the major crop–weed interference mechanism involved wild oat seed weight.

Barley (Hordeum vulgare) and Wild Oat (Avena fatua) Competition Is Affected by Crop and Weed Density1

Wild oat is the most serious grass weed in Argentine barley crops and its control has concentrated on herbicide strategies. Increasing crop density could be an effective strategy to reduce the effect of wild oat on barley yield. However, limited research has been conducted to evaluate the effect of crop density on the competitive balance between barley and spontaneous populations of wild oat. A field experiment was conducted in 1992, 1993, and 1999, to study the effect of spontaneous populations of wild oat on barley sown at densities of 160, 220, and 280 plants/m2. Wild oat density averaged 84 plants/m2. Wild oat biomass increased linearly with weed density in all treatments but was reduced by increasing barley seeding rates. Barley biomass and yield were not affected by wild oat at high crop sowing densities, but for the low and medium barley densities, yield loss was almost 25% when 70 wild oat plants/m2 were established. Barley yield loss was mostly related to competition from the early emerged wild oat. The relationship between yield losses and wild oat density was equally significant when the whole population or only early emerged individuals of the weed were considered.Nomenclature: Wild oat, Avena fatua L. #3 AVEFA; barley, Hordeum vulgare L.Additional index words: Wild oat interference in barley, integrated wild oat management, seeding rates of barley.

Effects of relative time of emergence and density of wild oat (Avena fatua L.) on oat quality

Selective control of wild oat with herbicides is not possible in oat (Avena sativa L.) crops and, consequently, the high quality that is imperative to market success is continually jeopardized. Field experiments were conducted to determine the effects of relative time of emergence and density of wild oat on oat kernel size and weight. Thousand-kernel weight and percentage plump kernels were generally reduced, and percentage thin kernels were generally increased with increasing wild oat densities and earlier wild oat emergence. However, reductions were generally small and occurred only at the highest wild oat densities, which are not commonly observed in commercial fields. These findings suggest that oat growers should not control wild oat based on perceived reductions in oat physical grain quality. Key words: Competition, emergence, physical grain quality, test weight, 1000-kernel weight

Influence of wild oat (Avena fatua) relative time of emergence and density on cultivated oat yield, wild oat seed production, and wild oat contamination

Abstract Wild oat is a serious weed in cultivated oat because there are no herbicides to selectively control it. Considering the effect of time of emergence on weed–crop interference is critical for the development of accurate crop yield loss models and weed density thresholds. Therefore, field experiments were conducted at two locations in Saskatchewan, Canada, in 2002 and 2003 to determine the effect of wild oat density and time of emergence on cultivated oat yield and quality. Wild oat was planted at 50 growing degree day (GDD) intervals ranging from 100 GDD before to 100 GDD after crop planting. Wild oat density ranged from 0 to 320 plants m−2. High densities of early emerging wild oat greatly reduced cultivated oat yield and increased wild oat contamination, with observed oat yield losses as great as 70% and wild oat contamination levels of 15%. Wild oat that emerged before cultivated oat caused considerably more yield and quality loss and had higher reproductive output than wild oat that emerged aft...

The productivity of oats and berseem clover intercrops. II. Effects of cutting date and density of oats on annual forage yield

AbstractAnnual forage yields of intercrops of berseem clover (Trifolium alexandrinum L.) and oats (Avena sativa L.), as affected by timing of initial harvest and sowing rate of oats, were investigated. Berseem clover was intercropped with oats at 0, 30, 60, 90 and 240 plants m−2 of oats in 1999 and 2000 in Alberta, Canada. Cutting date treatments involved initial harvest at 10‐d intervals between 35 and 88 d after planting (DAP), and one or two subsequent harvests of regrowth. Total intercrop dry‐matter (DM) yield averaged 12·9–13·3 t ha−1 with proportions of 0·21–0·43 of berseem clover in the forage. Treatments with an initial cut at the silage stage of oats (76 DAP in 1999, 88 DAP in 2000, at about soft‐dough stage of oats) had greater yields of oats, lower yields of berseem clover, and lower proportions of berseem clover in total annual yields than treatments with an earlier initial cut. Total crude protein (CP) yield was greater with an initial cut at 65–66 DAP than with a silage‐stage initial cut. With an initial cut at 35 DAP (before stem elongation of oats) or after 65 DAP (after heading of oats), yield potential of oats was sometimes reduced compared with silage‐stage treatments, but this was balanced by a greater yield of berseem clover. The impact of harvest timing on total yield decreased as the proportion of berseem clover in the intercrops increased. With decreasing density of oats, DM yield of first‐cut intercrops and total DM yield of oats decreased, while regrowth and total DM yields of berseem clover increased. Intercrops with oats at 60 plants m−2 had equal or greater total DM and CP yields than intercrops with 240 plants m−2 of oats. For intercrops with oats at 60 plants m−2, with initial cuts at 65–66, 75–76, or 88 DAP, yields of regrowths were 0·30–0·35, 0·16–0·26 and 0·09 of the total yield respectively. Oats–berseem clover intercrops showed potential to manipulate the pattern of annual forage yield and to provide flexibility of harvest without reducing annual yields.