The effects of density and proportion on spring wheat and Lolium multiflorum Lam Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qn59q709b

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  • This thesis consists of four chapters. Literature is reviewed in Chapter 1. Chapter 2 describes an addition series experiment to determine the influence of species density and proportion on vegetative and reproductive yield of spring wheat and Lolium multiflorum. Chapter 3 consists of a growth analysis experiment to determine whether proximity factors and time and temperature (incorporated into growing degree day units) affect the growth rates of species height, leaf number, tiller number, and leaf area index. The final chapter contains conclusions drawn from both experiments. A review of competition literature indicates that yield-density relationships can be studied using additive studies, replacement series, and addition series experiments. Intra- and interspecific competitive responses may be quantified best with the latter two approaches. Additive studies confound variables of species density and adequately Spring multiflorum proportion and therefore, do not assess competitive responses of weed and crop. wheat (Triticum aestivum) (L.) and Lolium (Lam.) were grown together in an addition series to examine the influence of species density and proportion on vegetative and reproductive biomass. Wheat grain yields indicated that yield increased with wheat monoculture density. However, the increase in grain yield was not linear, indicating that constant final yield occurred at high wheat monoculture densities. Grain yield decreased with increasing ryegrass density. These observations suggest that both intra- and interspecific competition occurred during the study. Grain yield was highly correlated with total biomass. Therefore mean plant biomass was used as a competitive predictive regression models. Regression results indicate that wheat was a more effective competitor than ryegrass over all species relative and total densities. A model was developed by regressing mean reciprocal weight as a response to final densities of both species. Relative competitive abilities were calculated for each species. The relative competitive ability of wheat suggests that one wheat plant was as competitive as 6.7 ryegrass plants. However, wheat also was more competitive with itself than with ryegrass. Ryegrass relative competitive ability indicated that one ryegrass plant was as competitive as one wheat or ryegrass plant. Species density and proportion and time and temperature (incorporated in growing degree day units (GDD)) were included in the regression model as independent variables to describe relative rates of plant growth for both species. Growth parameters (seed size, height, leaf number, tiller number, and leaf area index (LAI)) were measured throughout the growing season. Analysis of variance and covariance on relative rates of growth and seasonal LAI indicated that proximity factors of species density and proportion influenced relative rates of growth and seasonal LAI of both species. GDD was usually a significant variable in the regression equations, suggesting that time and temperature also influenced rates of growth. The regression equations describing relative rates of growth indicate that wheat, by virtue of a large seed size and high early season LAI, captured a large share of resources by germinating fast and quickly overtopping ryegrass in the mixture. The trend continued throughout the season. However, suppressed ryegrass plants maintained a constant rate of growth. Ryegrass eventually grew as tall or taller than wheat plants and produced a higher LAI than wheat in mixtures. This may be a growth strategy which makes ryegrass a persistent weed in spring wheat cropping systems.
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