Seeding rate and seed size as management techniques for ryegrass (Lolium Multiflorum, Lam) in winter wheat

Abstract

Higher seeding rates and larger seed sizes could enhance the competitiveness of wheat with ryegrass. Growth room and field research evaluated the effects of wheat seeding rates and seed size in competition with Italian ryegrass. Winter wheat seeds cultivar “Ogallala” were divided into three seed sizes: small seed passed through a sieve with 2.08mm round holes, large seed which did not pass through a sieve with 3.18mm round holes, and bulk seed directly from a commercial seed bag. These wheat seed and seed of the Italian ryegrass cultivar AGulf@ were planted in plastic pots containing fritted clay. A replacement series design with 12 plants per pot compared the relative growth in pure culture and competitiveness in mixtures of the two species. The planting proportions of each wheat seed group and ryegrass were 100% and 0%, 50% and 50%, and 0% and 100%, respectively. Wheat seed size did not affect the growth of the wheat plants in pure culture. Wheat seed size did not affect competitiveness with ryegrass. There were no differences related to seed size among the pure or mixed cultures of wheat. The failure of increased wheat seed size to affect competition with ryegrass may be the result of the relative seed size difference between the two species. Even the small wheat seed in this study were almost 9-fold greater inweight than the ryegrass seed. Field experiments conducted for two years from fall 2002 through spring 2004 at the Texas A&M University Agronomy Farm measured wheat yields at the same three wheat seed sizes, two wheat densities of 250 plants m-2 and 400 plants m-2, and three ryegrass densities of 0, 100 and 200 plants m-2. Small, bulk, and large wheat seed produced similar yields in both years: one season favorable (2003) for growth and the other (2004) unfavorable. Thus, seed size in the field under favorable or unfavorable conditions or in the growth room experiment did not affect the competitiveness of wheat in the presence of ryegrass. Increasing the wheat plant population from 250 to 400 plants m-2 in the field also failed to enhance the competitiveness of wheat in either year.