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Managing Lolium perenne L. (perennial ryegrass) in a sub-tropical environment in KwaZulu-Natal, South Africa.

Lolium perenne L. (perennial ryegrass) generally fails to persist



under the sub-tropical cpnditions of South Africa. Furthermore,



little research data are available on how to manage this species



locally. This study was designed to identify the management



options, particularly with r espect to grazing defoliation, which



would help enhance the longevity of perennial ryegrass pastures.



This was addressed by:



1) reviewing on-farm management practices of perennial



ryegrass in KwaZulu-Natal;



2) conducting a detailed two-year field study of the effects



of grazing frequency (HF, MF and LF = high, medium and low



frequency, respectively) and intensity (HI, MI and LI =



high, medium and low intensity, respectively), rotationally



applied with the addition of a continuous grazing treatment



(CG), on parameters linked to persistency.



tiller population dynamics, dry matter



These included:



(DM) yield and



quality, perennial ryegrass vigour, weed invasion and root



development; and



3) examining effects of different levels of applied nitrogen



(N) during the establishment year on various parameters



linked to persistency. These included: tiller population



densities, DM yield and quality, perennial ryegrass vigour,



weed invasion and root development.



The review of on-farm management practices of perennial ryegrass



growers in KwaZulu-Natal revealed that reasonably high rates of



N application (e.g. 350 and 250 kg N ha¯¹ a¯¹ to perennial ryegrass



as pure and clover-based stands, respectively) are important for



pasture survival. However, a consistent distribution of the



applied N is even more important (i. e. at least seven split



applications of N onto pure stands of perennial ryegrass and five



onto perennial ryegrass-clover). In terms of grazing management,



the period of absence of animals from the pasture during summer



was identified as the most important grazing variable affecting



pasture survival (i.e. ≥ 21 days). Also, the length of the



period of occupation by animals should be as short as possible,



particularly during summer (i. e. ≤ 3 days). Paying careful attention to summer irrigation is also an important variable



contributing to pasture survival. Grazing intensity was not



highlighted as an important contributor to pasture survival.



In terms of tillering potential, DM yield and quality (cellulose



dry matter disappearance and herbage N) and perennial ryegrass



vigour, perennial ryegrass followed definite seasonal trends.



These were highest during autumn and spring and were lowest



during the mid to late summer period. Perennial ryegrass was



most susceptible to general sward degradation through poor



management during the mid to late summer period when the danger



from weed invasion is greatest and its growth potential, vigour



and tillering abilities are lowest within these seasonal



periods, grazing defoliation produced marked effects. In terms



of tiller survival, DM yield, plant vigour, reduced weed invasion



and root production, treatments incorporating low frequency



grazing (e.g. LFLI and LFHI) generally out-performed (P≤0.05)



those incorporating high frequency grazing, irrespective of the



intensity (e.g. HFHI, HFLI, and continuous grazing (CG)). The



defoliation treatment incorporating medium frequency and



intensity (MFMI) (currently the recommended defoliation strategy



for perennial ryegrass) was also out-performed in many instances



(P~0.05) by the low frequency treatments (e.g. LFHI and LFLI) .



During the establishment year, increasing levels of applied N



increased (P≤O. 05) perennial ryegrass DM yields and herbage



quality. Models predicting the response of DM yield and quality



to applied N suggest linear responses up to 720 kg N ha¯¹ a¯¹.



Further refinement of such models and the inclusion of animal



production parameters is recommended. Maximum (P≤0.05) tiller



population densities occurred at applied N levels of 480 kg ha¯¹



a¯¹. Perennial ryegrass vigour increased (P≤O. 05) with increasing



levels of applied N up to 480 kg h¯¹ a¯¹, but individual tiller



vigour decreased. Increasing levels of applied N up to 360 kg



ha¯¹ a¯¹ suppressed (P≤O. 05) weed tiller densities. Increasing



levels of applied N (up to 600 kg h¯¹) increased (P≤O. 05) the



root organic matter (OM) per unit volume of soil in the top 5 cm



of the soil and decreased root OM per unit volume in the 10 - 20



cm soil depth category. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

Identiferoai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10910
Date January 1994
CreatorsMckenzie, Frank Ralph.
ContributorsTainton, Neil M.
Source SetsSouth African National ETD Portal
Languageen_ZA
Detected LanguageEnglish
TypeThesis

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