The Influence of Species Diversity on Sward Yield and Quality

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Abstract
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. The swards were obtained by sowing 1 or more of the following 7 herbage species: Agrostis stolonifera L., A. tenuis 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 7 spp. The latter were sown by broadcasting to give a random distribution of species, or in 3 alternative mosaic configurations of discrete colonies. Mosaics were used to reduce interspecific competition during establishment. The resulting swards received 2 levels of fertilizer N (and associated P and K) and were cut 5 times per yr for 5 yr. At the lower level of N (50 kg N ha-1 yr-1), the Lolium-Trifolium swards gave up to a 15% higher dry matter yield, and higher contents and yields of digestible organic matter and N than the complex mixtures. At the higher nitrogen level (300 kg N ha-1 yr-1), Lolium-Trifolium did not have an advantage over the complex mixtures in the yield of dry matter, digestible organic matter of N. 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 to maximize production in the farm situation.