The effects of defoliation systems on the productivity of perennial ryegrass/white clover swards

Frame, John (1967) The effects of defoliation systems on the productivity of perennial ryegrass/white clover swards. PhD thesis, University of Glasgow.

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There is an evergrowing awareness of the vital role of grassland in providing animal feed and ultimately animal products. As a result, there has been a concurrent increase in grassland research. The need for suitable and accurate techniques to measure and compare grassland productivity under various conditions of management has thus never been more urgent than at the present time. The need has been made more acute because of the necessity to evaluate the flood of new herbage varieties released by home and overseas plant breeders. In the Organisation for Economic Co-operation and Development (O.F.C.D.) scheme for the varietal certification of herbage seed moving in international trade, 873 cultivars of 81 species from sixteen member countries were listed in 1965 (O.F.C.D., 1965). In Scotland, a programme of herbage variety evaluation was devised in 1950 by the Grassland Committee of the Scottish Agricultural Improvement Council. Trials termed 'variety potentiality trials' were conducted in two stages: (a) single plant work on structure and development, measured and expressed solely in botanical terms and carried out by the Scientific Services Station of the Department of Agriculture and Fisheries for Scotland, East Craigs, Edinburgh. (b) co-oridinated sward trials under cutting schedules (usually monthly cutting) to determine herbage quantity, growth rhythm and quality, and carried out by the three Scottish agricultural colleges at Aberdeen, Edinburgh and Ayr. To date, 171 herbage varieties have been evaluated by the colleges in this way. The techniques used in the evaluation programme outlined above have the merits of speed, ease and economy in relation to the large volume of information derived, but are open to the criticism that at no stage is the evaluation work referred to the grazing animal. As in situ grazing is the most important method of grassland utilization, the introduction of the grazing animal at some stage in the measurement of productivity would seem logical. Yet historically this logic was not appreciated until the turn of the present century when Somerville and Middleton in their classical experiments at Cockle Park assessed grassland output in terms of animal products; prior to this, output had normally been measured by simple cutting techniques and expressed in terms of herbage yield. However, because of the requirements of land, labour, animals, equipment and finance associated with animal production trials, agronomic cutting techniques are still mainly used to evaluate grassland (McMeeken, 1960; O.E.E.C., 1960). The shortcomings of present evaluation techniques are recognized in the United Kingdom and consequently there are no official lists of recommended varieties. Instead, the National Institute of Agricultural Botany issue Farmers' Leaflets, which detail herbage varieties most likely to be satisfactory for general use. For example, assessment of grass varieties is made on the basis of lateness of heading, early spring growth, autumn growth, persistency, winter hardiness, hay yield and aftermath yield. In contrast, there are recommended lists for crops such as oats, barley, wheat, potatoes and sugar beet, for which suitable techniques of evaluation exist. The experiment reported in this thesis were initiated in 1960 at Auchincruive and designed to determine the productivity of perennial ryegrass* and perennial ryegrass/white clover swards under various cutting and grazing systems. In the grazing systems, sheep were used simply to defoliate the swards and to supply the effects of trampling, selective grazing and excretion. The object was to establish yield relationships between the various cutting and grazing systems. If relationships could be shown to exist, the simpler cutting systems could be retained and the results under grazing predicted. Only a few studies of this nature have been conducted (Taylor et al., 1960; Bryant and Blaser, 1961). This approach would seem warranted since cutting per se cannot simulate grazing yet the volume of grassland evaluation work makes it impossible for the widespread adoption of grazing techniques in place of cutting techniques. From the experiments described in this thesis, a paper entitled "The effects of cutting and grazing techniques on productivity of grass/clover swards" (Frame, 1965a; Appendix 11) was read for the author by Mr. F.E. Alder of the Grassland Research Institute, Hurley, Berkshire, at the 9th International Grassland Congress, Sao Paulo, Brazil in the session on experimental techniques in pasture research. A further paper entitled "The evaluation of herbage production under cutting and grazing regimes" (Frame, 1966; Appendix 12) was presented by the author at the 10th International Grassland Congress, Helsinki, Finland in the section on grassland production. *Common and scientific names of grasses, legumes and other plants mentioned in the thesis are listed in Appendix 1.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: D S Hendrie
Keywords: Range management
Date of Award: 1967
Depositing User: Enlighten Team
Unique ID: glathesis:1967-72225
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 May 2019 15:12
Last Modified: 24 May 2019 15:12

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