Interference in Trifolium Repens--Lolium Perenne Mixtures: Short- and Long- Term Relationships

Intra- and interspecific interactions were investigated in mixtures of Lolium perenne L. and Trifolium repens L. Species pairs were collected from pastures sown in 1979, 1970, c. 1945 and c. 1880, and sampled at five times during a single growing season. 2 In 46 of the 48 different combinations of species, harvest time and pasture age, inverse yield-density models described decreases in above-ground dry matter production per plant as species population densities (d) increased. Inverse yield-density models also described cumulative above-ground dry matter production for each species at each source pasture age. 3 Significant interactions in the yield-density models, indicated that intra and inter-specific interference in each species changed with time of harvest and age of the source pasture. 4 Substitution rates, measuring the impact on a species of replacing one of its members by a member of the other species, indicated that Lolium was consistently less affected by Trifolium than by members of its own species. In addition, the impact of Trifolium on Lolium declined during the growing season and with increasing source pasture age. 5 In Trifolium, substitution rates varied widely. In the youngest pastures there was evidence that the presence of Lolium was beneficial to Trifolium, but at intermediate source pasture ages Trifolium was adversely affected by Lolium to a greater extent than by members of its own species. 6 Lolium-Trifolium mixtures used resources more effectively than their corresponding pure stands. Resource utilization was most effective at intermediate harvests and in mixtures from the youngest and oldest pastures.