Some aspects of leaf death during the regrowth of a perennial ryegrass (Lolium perenne L.) white clover (Trifolium repens L.) sward : a thesis presented in partial fulfilment of the requirements for the degree Master of Agricultural Science at Massey University

Abstract

In order to achieve high animal production from grass-legume pastures such as are used in New Zealand, it is necessary to meet three basic requirements. (a) large amounts of high quality feed must be grown, the seasonal distribution of which must approximate the seasonal curve of animal requirements. (Conservation practices can be used to rectify minor discrepancies.) (b) A large proportion of this feed must be harvested by the animal. (c) Efficiency of conversion within the animal must be at a high level. (McMeekan 1956) Agronomists are concerned primarily with the first of these factors, but as maximum production for a system is approached, the second factor assumes major importance. These aspects must be studied against the background of a wide range of management techniques that may be employed in defoliating pastures. In the past, the importance of both leaf area grass tiller density and organic reserve materials have been studied as they are influenced by defoliation management, and their role has to some extent been determined. (Milthorpe and Davidson 1965). The emphasis in such investigations has been on the initial stages of regrowth from defoliation and there remains a number of aspects of primary productivity at medium and high Leaf Area Index values (L.A.I. i.e. the area of leaf per unit area of ground) requiring investigation (Brougham 1962, Alberda 1965a, Brown and Blaser 1968). One of these aspects, leaf death, is the subject of the investigation reported below and has been selected because of its significance to both productivity and utilisation. [From Introduction]