Associated growth of wheat and annual ryegrass. III. Effects of early competition on wheat

Abstract

The effects of four factors applied in factorial combination, viz. nitrogen application, time of ryegrass germination relative to wheat, roots together or separate and species proportion, were studied during the first few weeks of the associated growth of wheat and annual ryegrass. The experiment was conducted in boxes in a glasshouse at a total density of 355 plants m-2. Many plant variates were measured at 7, 28 and 49 days from sowing. Nitrogen content was determined at 28 and 49 days. Even at 7 days, measurable treatment effects on root and shoot weights of wheat could be detected. The effects could be discerned subsequently in terms of root length, tillering patterns, shoot weight, and ear development. Effects on ear development were observed in the last tiller and on the most recently developed florets. Some of these responses involved interactions of two or more of the factors studied. Treatments modified the relationship between competitive ability and yield in pure culture, more in ryegrass than in wheat. Although nitrogen effects appeared to have a strong influence on the competitive relations between the species, it is suggested that competition for soil factors other than nitrogen may also have been involved.