The Influence of Species Diversity on Sward Yield and Quality

Abstract

SUMMARY (1) An investigation of the yield and population structure of contrasting types of sward is described. The objective was to compare the quantity of herbage under cutting from swards consisting of species which had been bred for high yield, with that from swards which contained these species together with several indigenous grasses. (2) The swards were obtained by sowing one or more of the following seven herbage species: Agrostis stolonifera L., A. tennis Sibth., Festuca rubra L., Holcus lanatus L., Lolium perenne L., Poa pratensis L. and Trifolium repens L. The populations consisted of a mixture of Lolium and Trifolium, and complex mixtures containing all seven species. The latter were sown by broadcasting to give a random distribution of species, or in three alternative mosaic configurations of discrete colonies. Mosaics were used in order to reduce interspecific competition during establishment. The resulting swards received two levels of fertilizer nitrogen (and associated phosphorus and potassium) and were cut five times per year for 5 years. (3) At the lower level of nitrogen (50 kg N ha-1 year-'), the Lolium-Trifolium swards gave up to a 15% higher dry matter yield, and higher contents and yields of digestible organic matter and nitrogen than the complex mixtures. (4) At the higher nitrogen level (300 kg N ha-1 year-'), Lolium-Trifolium did not have an advantage over the complex mixtures in the yield of dry matter, digestible organic matter or nitrogen. (5) The results indicate that the presence of indigenous grasses does not inevitably reduce productivity below that of swards consisting entirely of improved species. Thus it may not always be necessary to renovate swards containing indigenous species in order to maximize production in the farm situation.