Managing Lolium perenne L. (perennial ryegrass) in a sub-tropical environment in KwaZulu-Natal, South Africa.
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Date
1994
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Abstract
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.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.
Keywords
Ryegrass--KwaZulu-Natal., Lolium perenne--KwaZulu-Natal., Pastures--KwaZulu-Natal., Theses--Grassland science.