Achieving persistence and productivity in white clover
K.H. WIDDUP and B.A. BARRETT
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White clover (Trifolium repens) is a valuable forage
and soil fertility resource whose persistence and
contribution to production and profitability can
be constrained by genetic, farm management, and
environmental factors. Here we outline the growth
stages of the plant, and factors affecting persistence at
the plant and the population level in pasture. Breeding
strategies that bring together new germplasm sources
within white clover have improved persistence on farm.
New experimental lines, including some accessing
genetics from related Trifolium species, show advances
in forage productivity and persistence in multi-site,
mixed sward, trial systems under dairy, sheep and cattle
grazing. New germplasm sources and the use of new
tools for characterising and selecting superior plant
material will enable increased genetic gain for traits
including persistence and forage production in white
clover and related forage legumes.
Keywords: Lolium perenne, pasture, persistence,
stolon density, Trifolium repens, white clover
An evaluation of wild populations of perennial ryegrass from dairy
farms in the Waikato and Bay of Plenty districts
D. RYAN and B.M. COOPER
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A ryegrass breeding programme to improve the
seasonal growth and plant persistence of perennial and
hybrid ryegrasses in the Waikato began at AgResearch
Ruakura, Hamilton in 2001. One approach was to
characterise the genetic diversity of the naturalised
populations within 26 dairy farms from different
districts around the Waikato and Bay of Plenty (BOP)
regions. Plants from 26 individual breeding lines were
evaluated as single spaced plants over a 3-year period
in comparison with three commercialised ryegrass
cultivars. Principal Component Analysis was used
to order the plant populations in accordance with the
observed plant variables of seasonal growth pattern,
tillering ability, leaf size and extension, and the
incidence of crown rust. A hierarchical cluster analysis
of the wild populations revealed two distinct plant
groups. A mix of large leaf Italian Lolium multiflorum
and hybrid plants were typical from the warmer drier
areas of the BOP. The Italian ryegrass was prone to
severe crown rust infection whereas the hybrids were
more resistant. Shorter, narrow leaved and densely
tillered plants with a high rust infection dominated
the Waikato populations. Ecotypes that maintained
high plant tiller density throughout the seasons had the
best persistence. Plants that displayed an improvement
in seasonal yield and tillering over the commercial
cultivars were considered an important genetic source
to develop new persistent cultivars for the Waikato and
BOP regions.
Keywords crown rust, drought, ecotypes, Lolium spp.,
plant breeding
Analysing persistence of grass swards in terms of tiller birth and death
C. MATTHEW and N.R. SACKVILLE HAMILTON
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A methodology is developed to analyse the contribution
to sward persistence of the processes tiller birth and
tiller death, and variation in their rate over an annual
cycle. The methodology is tested using previously
published data for timothy grass (Phleum pratense).
The analysis shows that high death rates of timothy
tillers in summer present a problem for persistence in
that tiller appearance rates required to maintain the
tiller population in these conditions require tiller bud
site usage statistics that are biologically unlikely in
field swards. While it is not suggested that ryegrass
has a naturally high tiller death rate in summer as
demonstrated here for timothy, where abiotic stresses
reduce ryegrass tiller survival, the same principles are
likely to apply.
Keywords: Leslie matrix, Phleum pratense, population
stability, tiller birth rate, tiller survival rate, timothy grass
Black beetle: lessons from the past and options for the future
N.L. BELL, R.J. TOWNSEND, A.J. POPAY, C.F. MERCER, and T.A. JACKSON
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An outbreak of the pasture insect pest black beetle
began in the Waikato and Bay of Plenty in 2007/8 and
has persisted. The extent and severity of damage caused
by black beetle during the current outbreak has focused
farmer and researcher attention on methods to maintain
persistent pasture now and in future outbreaks. This
paper reviews previous research in combination with
data from the current outbreak and relates these to
current pasture management practice. The possibility
of being able to predict the distribution, occurrence
and duration of black beetle outbreaks is explored
while actual and potential means of controlling black
beetle are outlined. We conclude that there are methods
available to successfully renew pastures in the presence
of black beetle but that outbreak situations increase
risks and may limit subsequent pasture persistence.
There are fewer readily available options to maintain an
existing pasture and more research is urgently needed
to provide these options.
Keywords: Heteronychus arator, paspalum, pasture,
pasture renewal, pest resistance, pest tolerance, ryegrass
Can pasture persistence be improved through the use of nonryegrass
species?
G. D. MILNE
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Recent discussion about pasture persistence
concentrates on pastures based on perennial ryegrass,
the most commonly used grass species. This paper
raises the question as to whether some of the causes of
poor pasture persistence are due to perennial ryegrass
being used in environments to which it is not suited.
The adaptation to environmental stresses, particularly
water, temperature and nutrient deficiencies, in
different regions of New Zealand of tall fescue,
cocksfoot, phalaris, and lucerne are discussed, and how
this impacts on persistence advantages over perennial
ryegrass.
Keywords: persistence, pasture, Dactylis glomerata,
Festuca arundinacea, Lolium perenne, Medicago
sativa, Phalaris aquatica
Changes in pastoral farming practices and pasture persistence – a
review
D. A. CLARK
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From 1990 to 2010 there have been major changes in
New Zealand pastoral agriculture. The intensification
of the dairy industry has led to higher stocking rates,
lower grazing residual DM, higher N fertiliser use
and increased supplementation. However, there is
little evidence that these changes are responsible for
the decreased persistence of ryegrass-based pastures,
rather the interactions between low summer rainfall,
low water-holding capacity soils, endophyte status
and cultivar ‘type’ have caused significant pasture
damage. These factors, together with plant nutrient
status (especially N) and plant population survival
mechanisms (tiller dormancy, birth and death rates,
seed production and establishment) are hypothesised
to be the primary drivers of ryegrass persistence. A
secondary subset of pests, diseases, weeds and high
grazing intensity (pugging and pasture ‘pulling’)
are considered to interact with the primary drivers
to compromise ryegrass tiller survival. Attention to
plant species and cultivar selection, tiller replacement
mechanisms and ryegrass cultivar development are
required to improve ryegrass persistence.
Keywords: climate, dairy, N fertiliser, perennial
ryegrass, white clover
Dairy farm systems to aid persistence
K.A. MACDONALD, C. MATTHEW, C. B. GLASSEY, and N. MCLEAN
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This manuscript reviews fundamental pasture
management principles relevant to pasture persistence.
We first note some points of context, within which the
debate on pasture persistence is occurring: the release
of new pasture cultivars, the debate about climate
change, and the effects of newly introduced weeds
and pests. We then examine trends in farm practice.
The critical management period (of most concern to
farmers) has shifted from winter/autumn to summer. It
is essential that farmers have and use sets of decision
rules to govern when and how hard to graze, when to
supplement and when to remove cows from pasture to
allow pastures to be grazed appropriately to aid pasture
persistence. Adaptations available to improve pasture
persistence include: the use of nitrogen fertiliser to
increase feed supply going into the summer, the use
of crops or other feed supplements, stocking rate and
on-off grazing to ensure the pastures are appropriately
grazed in the summer. New pastures must be treated
with care in their first year of life to ensure survival. The
response of farmers to these variables to aid persistence
of pastures is discussed.
Keywords: climate, insect pests, pasture growth
model, pasture renewal, weeds
Effect of defoliation strategies on the productivity, population and
morphology of plantain (Plantago lanceolata)
W. AYALA, E. BARRIOS, R. BERMUDEZ, and N. SERRÓN
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This trial provided information about effects of
defoliation frequency, defoliation intensity and winter
management (grazing or rest) on the productivity,
morphology and plant population of a 3-year-old
plantain (Plantago lanceolata) stand. Plant population
density declined drastically over time independently
of grazing management, with the greatest decrease in
summer. Winter grazing had a critical effect on the
productivity and population remaining 6 months later.
Frequent grazing during summer increased plantain
contribution. Grazing intensity reduced crown weight
and diameter of individual plants. Further studies are
required to determine the interactions of defoliation
management with pastures of different age including
the natural reseeding as a mechanism to maintain plant
recruitment.
Keywords: defoliation, grazing, morphology,
population
Effect of soil physical condition, and phosphorus and nitrogen
availability on pasture persistence
A.D. MACKAY, A. GILLINGHAM, C. SMITH, P. BUDDING, P. PHILLIPS, W. CLARKE-HILL and P. JOHNSTONE
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Soils are the substrate at the base of any grazing or
cropping system providing plants with nutrients, water
and physical support, a habitat for beneficial organisms
and a physical base on which animals stand. A change or
a loss of any one of these soil services has the potential
to impact on plant growth and persistence. The findings
of two ongoing field-based studies are presented and
discussed as they relate to the current debate on pasture
persistence. One study is investigating the influence
of the physical condition of the soil on a ryegrassbased
pasture response to added phosphorus (P). The
second study is investigating the P requirements of
high producing perennial ryegrass and tall fescuebased
pastures, where the constraints to pasture growth
and associated P uptake imposed by low nitrogen
availability and low soil moisture over summer-autumn
have been removed. The critical Olsen P value for
maximum pasture production appears to increase as
the constraints to pasture growth are removed. This
challenges the continued use of a single relative yield
Olsen P function and one critical Olsen P value for near
maximum yield regardless of the absolute pasture yield.
Loss of soil pore function also appears to increase the
critical Olsen P value necessary for optimum pasture
growth. Additional P can compensate for a lack of
pore function to a degree, but there appears to be an
upper limit to this effect. Given that the physical
condition of many of our pasture soils in intensive
lowland situations is below optimum, nutrient stress
may be more of a factor in poor pasture-persistence,
than previously thought. Inclusion of a measure of soil
physical condition would appear to warrant further
study in defining the conditions for optimum plant
growth and persistence.
Keywords: fertiliser nitrogen, Festuca arundinacea,
Lolium perenne, Olsen P, pasture persistence, soil pore
function, soil services
Endophytes improve ryegrass persistence by controlling insects
A.J. POPAY and D.E. HUME
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Fungal endophytes reduce populations and damage
by several different insect pests which alone or in
combination with each other can reduce ryegrass
persistence. AR1, AR37, the Standard endophytes and
two endophytes in tetraploid ryegrasses, NEA2 in cv.
Bealey and Endo5 in cvs. Quartet II and Banquet II,
are available to the New Zealand farmer. Their effects
on insects depend on the spectrum and concentration
of alkaloids they produce. Argentine stem weevil is
controlled by all endophytes except perhaps Bealey
NEA2; black beetle is controlled by all endophytes
except AR1; pasture mealybug are controlled by AR1,
AR37 and Standard and likely to also be controlled by
Endo5 and NEA2; porina and root aphid are controlled
by AR37. Increased persistence of ryegrass infected
with endophyte is reflected in increases in endophyte
infection rates in pasture, higher yields and tiller
densities and reduced weed invasion, particularly
where climatic stress is also present. AR37, with the
protection it provides against a range of insect pests, is
the most effective endophyte for improving persistence.
Keywords: alkaloids, Argentine stem weevil, black
beetle, insect damage, Neotyphodium
Identifying the need for pasture renewal and valuing the contribution
of renewal on a dairy farm – Telford Dairy, a case study
D.R. STEVENS and I. KNOWLES
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How do we know which pastures to renew and do
we increase profitability when we renew them? An
inventory of pasture production of the Telford dairy
farm was developed using paddock grazing records to
estimate potential pasture production and variability
from different soil types. Using the difference between
low and high producing pastures as the potential for
improvement, the change in pasture production with
renewal was calculated and valued using several
methods, from the simple conversion of extra dry
matter into milk solids production through to whole
farm systems optimisation using Farmax Dairy Pro. The
cost of pasture renewal was highest when valued by the
Pasture Renewal Charitable Trust model when the cost
of lost grazing was estimated. The return for pasture
renewal was lowest from Farmax Dairy Pro modelling
when whole farm-integration was considered. At the
average value of milk for the last 5 years, the payback
period was between 2.5 and 3.1 years, depending on the
model used.
Keywords: analysis, modelling, pasture production
records, pasture renewal, soil types.
Introduction
G.A. KERR
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Welcome to the Pasture Persistence Symposium. This
Symposium is being held under the auspices of the New
Zealand Grassland Association to help understand
and improve the persistence of particularly ryegrass based
pastures.
Long term effect of superphosphate fertilisers on pasture
persistence
T. J. FRASER, S. DENNIS, R. A. MOSS, K. N. TOZER, N.R. STOCKER, A.L. TAYLOR, M. J. FAVILLE and C. SMITH
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Core samples were taken from 60-year-old pastures on
a long-term fertiliser trial at the Winchmore research
station, in Canterbury, New Zealand. Plots had been
treated with 0, 188 or 376 kg/ha of superphosphate
annually, grazed by sheep, and pasture yields were
recorded. Ryegrass persisted in all treatments, but
was only dominant in the superphosphate treatments,
unsown grasses dominated in the no superphosphate
treatments. White clover was more common with
superphosphate, and both cocksfoot and timothy
required adequate superphosphate in order to persist.
Over 60 years of measurements, yields were 9-15 t DM/
ha with superphosphate, and did not reduce over time.
Given adequate fertiliser, a ryegrass-based irrigated
pasture can continue to produce high yields 60 years
following sowing.
Keywords: ryegrass, cocksfoot, t
Long-term trends in production and composition of ryegrass-white
clover pasture intensively grazed by dairy-beef cattle
G.P. COSGROVE
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A measure of pasture persistence is stability of yield
and proportion of desirable species over a long period.
Long-term data on animal production and pasture
yield and composition of old permanent pasture in
the Manawatu were examined for trends indicative of
persistence. The data were collected from two sets of
replicated 1.6-ha farmlets intensively grazed by dairybeef
bulls stocked at 7.4 yearlings wintered/ha for 16
of 18 years from 1969-1986, and 11 years from 1978
and 1988, respectively. Annual total LWG, total yield
of DM and the yields of ryegrass, white clover and
other species showed year-to-year variation. There
was no long-term decline in production indicating
that for this environment and management system
ryegrass and white clover were inherently persistent
under intensive grazing at high stocking rates. These
results are discussed in the context of anecdotal reports
of poor persistence of modern cultivars, with particular
emphasis on the effects that high stocking rates,
intensive utilisation and defoliation management may
have on persistence.
Keywords: cattle, grazing, pasture, persistence,
ryegrass, white clover
Managing sheep and beef farm systems - where does pasture
persistence fit in?
D.R. STEVENS
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Pasture persistence is highly rated by sheep and beef
farmers as an important factor determining wholefarm
performance. Managing pastures to ensure the
persistence of newly sown pasture species must be
considered as a part of the decision making process
of the whole farm. The farmer aims to optimise the
outcomes of resource use over time, rather than
maximise any single resource, and therefore grazing
decisions must be considered in this context. Pasture
renewal is a major event-driven disruption that replaces
current pasture species with competitive species,
creating a grass-legume complex that has a tendency
to develop towards a community of plants that tolerate
the local environmental stress. Pasture persistence can
be improved through managing the impacts of and
interactions between environmental stressors on the
pasture. Interactions between pasture management
options, such as grazing and fertiliser, and the major
environmental stressors of soil moisture, temperature,
soil fertility, grazing and pests are discussed.
Keywords: ecology, environmental stressors, farm
systems, grazing management, pasture persistence.
Nitrogen leaching implications of poor pasture persistence
K. BETTERIDGE, J. CRUSH, S. LEDGARD and M. & S. BARTON
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Farmers have indicated that perennial pastures sown
in the Lake Taupo catchment revert to low quality
species within 8 to 10 years. These may be renewed
with perennial pasture species following an autumn
then spring cropping regime, or resown pasture-topasture
by direct-drilling into glyphosate-sprayed
turf or following full cultivation. Vegetation which is
desiccated and/or ploughed-under before sowing will
decay and release mineral nitrogen (N). The mineral
N from these sources is available for newly sown
plants but can also be leached. In a large, replicated,
rotationally cattle-grazed trial near Lake Taupo, new
pasture was established with the high sugar ryegrass
(HSG) Aberdart in one treatment only by direct-drilling,
following glyphosate application in late summer.
Existing pasture remained in Control plots. Renovated
pasture leached 63 kg nitrate-N ha-1 in the 8 months
following establishment compared 8 kg nitrate-N ha-1
in Control (P<0.05). There were no differences in the
amount of leached N amongst treatments in the second
year (P=0.1). Nitrogen leaching losses resulting from
pasture renovation and forage cropping practices are
discussed in relation to the impacts these have on future
pasture management and renewal options and on the
potential value of new germplasm in the Lake Taupo
catchment, whose management is constrained by a
N cap.
Keywords: nitrogen leaching, pasture establishment,
Taupo
Non-ryegrass pastures - the science and farmer practice
D.J. MUSGRAVE
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A review of recently published science demonstrates
that relatively simple non–perennial ryegrass mixtures
have performed well in environments as diverse as
under deer grazing in Dunedin and the Manawatu,
under sheep grazing in dryland mid-Canterbury, and
under both irrigated and dryland dairy cow grazing in
the Waikato and Northland. Animal productivity has
been lifted by up to 30% in milk solids and 50% in deer
liveweight gain in non-perennial ryegrass mixtures
compared to perennial ryegrass-based pastures. In
some cases, the ryegrass pasture has produced similar
or more dry matter, yet animal performance has been
greater on the non-perennial ryegrass pastures. In other
cases, dry matter productivity from complex nonryegrass
mixtures has been around 30% higher than
from perennial ryegrass pastures. Interviews with
farmers from South Canterbury to Northland have
all reported positive experiences with non-ryegrass
pastures and most have said they will not be planting
perennial ryegrass-based pastures again.
Observations and insights on pasture persistence in New Zealand
P.M.S. Lane
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This essay contains personal observations and
interpretations by the author on the persistence of
pastures in the northern North Island. Key pasture
stress factors are identified as the increase of farming
intensity over the past two decades, the impact of
pasture renewal techniques and the role of pasture
species on insect pest (particularly black beetle and
clover root weevil) interactions.
Keywords: insect pests, soil fertility, pasture renewal,
cultivars, endophyte
Pasture persistence: farmer observations and field measurements
K.N. TOZER, C.A. CAMERON and E.R. THOM
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Information is presented on farmer perceptions
and concerns regarding key factors leading to poor
persistence of sown pasture species. Forty-seven
farmers from four regions viz. Northland (beef, sheep),
Waikato (dairy), Taranaki (dairy) and North Canterbury
(beef, sheep, deer) were asked for their opinions on
the ‘keys’ to persistence and ‘killers’ of sown species;
i.e., factors leading to a decline in sown species. In
all regions, grazing management was perceived to
be the most important key to persistence and insect
pests the top killer of sown species. Better industry
dissemination of existing information and further
research on forage herbs and insect pest issues are
future requirements. In each region, presence of sown
species was also assessed in 30 paddocks belonging to
the surveyed farmers. There was a significant decline
in pasture chicory presence, but no decline in that of
cocksfoot or plantain. Ryegrass, white clover and tall
fescue were present in nearly all paddocks in which
they were sown. Chicory may be best used as a crop,
while plantain shows greater potential for persistence
as part of a pasture mix.
Keywords: chicory; farmer survey; information gaps;
plantain; research needs
Pasture persistence: how much is it worth?
R. BRAZENDALE, J.R. BRYANT, M.G. LAMBERT, C.W. HOLMES, T.J.FRASER
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The farm system model, Farmax Dairy Pro, was used
to evaluate the impact of new pastures on dairy farm
profitability, assuming a range of pasture yields and
qualities, and different levels of persistence in the new
pastures, which were established on 10% of the farm
annually. Scenarios were tested for Waikato, Taranaki,
Canterbury and Southland dairy farm systems.
Assuming a $6.50/kg MS milk payment and a
response to pasture renewal of 10% in dry matter yield
and a 0.6 MJ ME/kg DM increase in quality, increasing
persistence from 4 years up to 8 years was modelled to
increase dairy farm profitability by $271/ha to $478/ha.
Management practices, including selections of
cultivars and endophytes, that improve pasture
persistence are likely to increase dairy farm profitability.
Keywords: dairy farms, modelling, pasture renewal,
persistence
Pasture renewal in the Waikato and Bay of Plenty regions: An
overview of farmer practice, experience and attitudes
S. KELLY, E SMITH and R. BRAZENDALE
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Pasture persistence and performance, and associated
issues such as black beetle, are of central concern to
dairy farmers. The Pasture Renewal Survey 2010 aimed
to better understand farmers’ confidence in their ability
to make informed decisions on their pasture renewal
practices, their satisfaction with the success of this
decision-making and the performance of their renewed
pastures over time. In addition, the survey investigated
their attitudes to information sources and what barriers
they saw to improving pasture performance on farm.
A postal and online survey elicited responses from
776 dairy farmers in the Waikato and Bay of Plenty
regions. The four main findings of the work were:
1. Farmers are more confident of their ability to
make appropriate on-farm management decisions
for renewed pasture than they are of their ability
to choose appropriate cultivars and endophyte.
2. Farmers, while generally satisfied with their own
success in renewing pasture, reported decreasing
levels of satisfaction with renewed pastures over
the 3 successive years following renewal.
3. Farmers do not rate information sources very
highly in terms of their usefulness in relation to
pasture renewal.
4. Weather-related issues and pest-related issues
(particularly black beetle) were the most
commonly identified barriers to improving
pasture performance.
Keywords: farmer confidence, farmer satisfaction,
information sources, pasture renewal.
Persistence of Grazing Tolerant Lucernes under Australian
Conditions
J.C. SEWELL, R.D. HILL, and J.REICH
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Recent experiments have demonstrated that lucerne
(Medicago sativa) varieties selected for grazing
tolerance will persist far better when grazed for
extended periods than varieties not selected for grazing
tolerance. A field experiment, with lucerne varieties
representing a range of winter activity ratings, was
conducted at Ballarat. After 2.5 years of rotational
grazing the experiment was continuously grazed for
173 days from late spring to early autumn at a stocking
rate equivalent to 50 sheep/ha. This intensity is not
considered much higher than some farmers would adopt
during a drought. Ground cover of some varieties had
significantly declined by the end of the grazing period
but further decline occurred throughout the following
winter months while livestock were excluded. The
grazing tolerant lines persisted better than most
standards, even those within the same dormancy
category, with some standards almost completely dead
while the grazing tolerant lines were over 60% alive.
Keywords: grazing tolerance, lucerne (Medicago
sativa), persistence
Persistence of Grazing Tolerant Lucernes under Australian
Conditions
J.C. SEWELL, R.D. HILL, and J.REICH
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Recent experiments have demonstrated that lucerne
(Medicago sativa) varieties selected for grazing
tolerance will persist far better when grazed for
extended periods than varieties not selected for grazing
tolerance. A field experiment, with lucerne varieties
representing a range of winter activity ratings, was
conducted at Ballarat. After 2.5 years of rotational
grazing the experiment was continuously grazed for
173 days from late spring to early autumn at a stocking
rate equivalent to 50 sheep/ha. This intensity is not
considered much higher than some farmers would adopt
during a drought. Ground cover of some varieties had
significantly declined by the end of the grazing period
but further decline occurred throughout the following
winter months while livestock were excluded. The
grazing tolerant lines persisted better than most
standards, even those within the same dormancy
category, with some standards almost completely dead
while the grazing tolerant lines were over 60% alive.
Keywords: grazing tolerance, lucerne (Medicago
sativa), persistence
Plant responses to climate and relationships with
pasture persistence
D.F. CHAPMAN, G.R. EDWARDS and Z.N. NIE
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Relationships between climatic factors and persistence
of grazed perennial ryegrass and white clover pastures
in New Zealand are reviewed from an ecophysiological
perspective. ‘Persistence’ is defined in terms of physical
survival of plants of sown cultivars: the effects of
climate on plant populations are considered. Substantial
information is available on the population dynamics of
perennial ryegrass and white clover in different climatic
environments, particularly on the influence of drought
on populations. Substantial, direct negative effects
of drought on the density of perennial ryegrass tillers
and white clover stolons have been recorded, though
populations have generally recovered after release from
drought conditions. Otherwise, the effects of climaterelated
resource limitations on population size are more
likely to be interactive, working in concert with other
factors such as management, soil fertility and insect
pest challenges to limit the capacity of homeostatic
responses to restore the optimal (for long term survival)
balance between above- and below-ground resources.
The relative extent to which more recent cultivars
of perennial ryegrass are able to tolerate multiple,
simultaneous resource limitations compared to older
cultivars (with different phenotype) is considered, but
there is little direct evidence on this matter. Issues
that should be considered in future pasture persistence
research are identified and discussed. One of these
concerns is the persistence of trait expression in
cultivars bred for specific traits. More research on
this topic is warranted, since molecular plant breeding
techniques are strongly based on trait manipulation, and
genotype x environment interactions can be expected
in the spatially and temporally variable environment of
grazed pastures.
Keywords: drought, ecology, plant breeding, ryegrass,
white clover
Plant responses to defoliation and relationships with pasture
persistence
G.R. EDWARDS and D.F. CHAPMAN
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The effects of defoliation on plant morphology and
the structure of perennial ryegrass and white clover
populations are reviewed with reference to the
persistence of yield in sown pastures. Maintenance of
high densities of perennial ryegrass tillers and white
clover stolons is fundamental to persistence. Tiller and
stolon population densities are subject to within- and
between-year variation, and are strongly influenced
by defoliation management through processes such
as competition for light, and size-density trade-offs
mediated by self-thinning processes. Spring is a time
when high tiller/stolon appearance and death rates
occur simultaneously. Spring is also the time when
clover populations undergo rapid structural change
as large clover plants fragment to release small,
unbranched plants with limited ability to compete for
light with grasses. The central role of reproductive
stem development in perennial ryegrass for summer
survival of tillers and autumn re-establishment of
tiller populations also highlights the importance
of defoliation management during the spring for
population persistence. Examples of the application
of tactical defoliation management in spring, and at
other times of the year, to manipulate stolon and tiller
densities are presented. In some instances, such tactics
may improve animal production potential, as well as
the persistence of new cultivars. It is notable that the
New Zealand literature on this topic is mostly more than
15 years old. Recent changes in farming systems and
plant genotypes (e.g. tetraploidy in perennial ryegrass,
late flowering perennial ryegrass) may require a reanalysis
of established principles and practices related
to defoliation x plant interactions in grazed pastures
to ensure best possible pasture yield persistence and
profitability of grazing systems.
Keywords: grazing management, perennial ryegrass,
persistence, population dynamics, white clover
Review: The effects of soil compaction on root penetration, pasture
growth and persistence
J.R. CRUSH and E.R. THOM
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A review of the literature shows that soil compaction
by stock treading has been an issue for New Zealand
farmers for over half a century. Soil compaction restricts
root penetration resulting in poor anchorage and
susceptibility of plants to uprooting during grazing. In
addition, access to moisture and soil nutrients is reduced
which decreases the fitness of the sward under stress
conditions. Mechanical treatment of compacted soil
improves soil physical properties but beneficial effects
on pasture growth have been less readily demonstrated.
Options to reduce the impact of soil compaction on
pasture persistency include better soil management to
reduce the incidence and severity of compaction and, in
the longer term, new grasses with root and shoot traits
that mitigate the effects of compaction.
Keywords: roots, ryegrass, soil compaction, soil
moisture, soil nutrients, trampling
Ryegrass in pastures – breeding for resilience
H.S. EASTON, A.V. STEWART and G.A. KERR
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The suggestion that modern pasture cultivars persist
less well than their predecessors is not supported by
facts. However in some regions there is a crisis in
farmer experience of persistence of ryegrass pastures,
and ryegrass breeding can contribute to a resolution.
This paper considers the turnover of tillers in a
pasture, the population structure of a grass sward and
the involvement of endophyte and companion clover.
Knowledge gaps in key processes of pasture persistence
are discussed. The plant breeding process involves
access to relevant genetic variation, its assessment,
and creation of improved populations and eventually
cultivars based on selected superior plants. All these
scientific processes use ever-evolving techniques.
Breeding objectives evolve with industry needs and the
changing environment. The methods employed in the
breeding phases, the breeding objectives and the final
evaluation of cultivars require ongoing revision. Plant
breeding will make a growing contribution to modern
farming if its developing capabilities are interfaced
with other research disciplines providing critical
information on key pasture processes.
Keywords: Lolium perenne, endophyte, persistence,
tillering
Slugs as Pasture Pests
M.J. WILSON and G.M. BARKER
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Several invasive European slug species are thriving
in New Zealand and have become important pests of
many crops. In pasture, they are particularly damaging
to white clover during renovation and the problem may
be exacerbated by direct drilling. Slug feeding causes
both lethal and sublethal damage that reduces clover
establishment and thus pasture quality. Much less is
known about slug damage to established pastures and
the degree to which slugs limit pasture persistence.
Established pastures frequently support large slug
populations that feed on clover and the application of
molluscicides can reduce slug numbers and increase
the proportion and yields of clover. Future research
on these pests should concentrate on determining
damage thresholds, breeding resistant clover varieties
and developing agronomic practices that favour natural
enemies. In the long term, there is much potential for
developing microbiological pesticides that target slugs.
Keywords: molluscs, slugs, clover
Sowing methods for successful pasture establishment – a review
E.R. THOM, T.J. FRASER and D.E. HUME
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Methods of achieving successful pasture establishment
have been broadened over the last 50 years by the
introduction of no-tillage technologies, providing a
viable alternative to cultivation. Parallel developments
in drill technologies for seed and fertiliser placement,
and methods to control competition from the existing
pasture have ensured the success of no-tillage methods.
This review focuses on the effects of the establishment
method on seedling growth over the establishment
period, defined for the purposes of this paper as the
year after sowing. Undersowing existing pasture is the
establishment method least likely to provide a suitable
environment for seedling growth and development.
New pastures must receive different management to
existing pastures for at least 1 year after sowing to
increase their chances of becoming persistent and
productive. Long-term monitoring (5-10 years) of new
pastures has received little research attention, making
assessments of effects of different establishment
methods on persistence difficult. Factors likely to affect
seedling establishment and plant survival are discussed.
Keywords: competition control, cultivation, directdrilling,
first year management, Lolium perenne,
ryegrass, seedling survival, Trifolium repens, white
clover
Summer pasture yield variation in a central Waikato location from
1979 to 2010: implications for pasture persistence.
C.B. GLASSEY
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Three datasets spanning 31 years (1979-2010) of net
herbage accumulation (HA) for Waikato dairy pastures
were studied to determine between-year variability
in summer HA. In addition, a dairy farm at the same
location was modelled with the DairyNZ Whole Farm
Model, using climate data for 15 years to predict HA,
and milksolids production. Measured extremes for HA
over 5 months (1st December to 30th April inclusive)
were from 4.7 to 9.1 t DM/ha, with a mean of 7.0 t DM/
ha ±1.2 t DM/ha SD. Rainfall during these months had
a positive impact on HA, with an extra 849 kg DM/
ha (r2=0.43, p<0.001) grown in December to April
for every additional 100 mm of rainfall. December-
April rainfall during 1979-1993 was 17% more than
December to April 2004-2010. For the modelled
farm stocked at 3.1 cows/ ha, December to April HA
was predicted to average 6.6 ±1.3 t DM/ha, ranging
from 4.7 to 8.7 t DM/ha. In 2 years out of 3, HA was
predicted to be below feed demand from December
to April. Clearly, managing pastures to recommended
post-grazing residuals and pre-grazing leaf stage in
summer can be problematic when the variability in HA
is large and there is limited capacity to reduce stocking
rate and hence feed demand. Repeatedly exceeding
pre-grazing herbage mass targets in good summer HA
years and post-grazing residual targets in poor summer
HA years are both scenarios consistent with the loss of
perennial ryegrass plants from dairy pastures and this
study examines the historical frequency and size of
such events.
Keywords: annual variation, grazing management,
Lolium perenne, summer herbage accumulation,
stocking rate
The impact of invertebrate pests on pasture persistence and their
interrelationship with biotic and abiotic factors
S.M. ZYDENBOS, B.I.P BARRATT, N.L. BELL, C.M. FERGUSON,
P.J. GERARD, M.R. MCNEILL, C.B. PHILLIPS, R.J. TOWNSEND and T.A. JACKSON
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New Zealand pastures are host to a range of native and
exotic invertebrates. Many of these are pests that feed
on the sown plant species, often causing plant death
and deterioration in the productivity and persistence
of the sward. While most research has focused on pest
biology and control, studies of plant productivity show
dramatic acute (short-medium term) and chronic (longterm)
effects. For example, grass grub has been reported
to cause 50% losses to ryegrass swards and Argentine
stem weevil can cause a 20% loss of productivity, but
the long term effects through loss of the sown species
and changes in composition can be even more severe.
Insect damage can be exacerbated by other biotic (e.g.
weed invasion, grazing animals, plant pathogens) or
abiotic factors (e.g. climate, soil fertility) to further
reduce plant persistence. Some biotic and abiotic
factors may interact with insect pests to have positive
effects on pasture persistence, e.g. biocontrol agents
that reduce pest density or addition of fertiliser to enable
plants to recover from insect damage. For many pasture
pests, knowledge of their ecology is based on research
from over 20 years ago that, while still valid, needs to
be updated to account for modern intensive pasture
management practices, such as intensive grazing with
a lack of reseeding, and new cultivars. To improve
pasture persistence, integrated research programmes
are needed that examine the relative importance of
all factors contributing to plant survival and develop
strategies to mitigate their effects.
Keywords: Argentine stem weevil, black beetle, clover
root weevil, drought, grass grub, grazing pressure,
manuka beetle, nematodes, pasture persistence, pasture
quality, pasture yield, porina, soil fertility, striped
chafer.
Use of maize silage to improve pasture persistence in dairy farm
systems: a review
R.J. DENSLEY, I.D. WILLIAMS, J.J KLEINMANS, S.B. MCCARTER, R. TSIMBA
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Maize is a drought tolerant crop that produces high
dry matter yields. Growing maize silage as part of a
pasture renewal programme can help improve pasture
persistence by reducing the level of weeds, insect
pests and carryover ryegrass seed. Feeding maize
silage to dairy cows results in pasture substitution.
This decreases grazing pressure and can be used
to manipulate farm pasture cover levels reducing
overgrazing. The combination of maize silage and a
well-designed stand-off pad with feeding bins allows
farmers to keep cows off wet pastures reducing pugging
damage and subsequent losses in pasture production
without compromising milk production or animal
welfare. Maize hybrid selection is critical to ensure
timely regrassing. Crop simulation models such as
CERES-maize may be useful to determine the best
maize hybrid maturity x planting date combinations
required to maximise silage yield and meet desired
silage harvest and regrassing dates. Best-practice maize
silage management including seed bed preparation,
weed control and insecticide-treated maize seed will
help farmers achieve high yields of silage and assist
in the subsequent establishment of high yielding and
persistent pastures.
Keywords: pasture persistence, maize silage, feed pad
What factors lead to poor pasture persistence and weed ingress?
K.N. TOZER, G.W. BOURDÔT and G.R. EDWARDS
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In an ideal pasture, sown species would persist
indefinitely and there would be no weeds. ‘Poor
persistence’ occurs when the desirable species are
replaced by weedy, undesirable species. Unfortunately,
poor persistence of sown pasture plants is the reality
that most farmers experience. In this paper we
review the literature on three key factors leading to
poor persistence and weed ingress: 1) inter-specific
competition; 2) sward disturbance; and 3) propagule
pressure. We reveal that grazing and other management
decisions, pasture insect pests, nutrients, climate
and the composition of the sown species mix have a
critical influence on these factors, and hence over the
replacement of sown pasture plants by weeds. The key
practical message from this review is that farm practices
that improve the vigour of sown species, reduce pasture
gaps and minimise weed propagule pressure will
improve the persistence of sown species and minimise
weed ingress. An outstanding deficiency is our lack of
knowledge of the economic impacts, and hence weed
status, of most of the ca 187 volunteer plant species that
may invade and replace sown plants in New Zealand’s
pastures.
White clover vegetative persistence under pressure: sharpening New
Zealand’s competitive edge
P.J. GERARD, C.F. MERCER and B.A. BARRETT
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White clover is relied upon as a cornerstone of the
international competiveness of New Zealand’s pastoral
sector, despite its vegetative persistence and yield
being constrained by pests and diseases. The species’
vulnerability has been highlighted by the clover root
weevil (Sitona lepidus) incursion, and the impact of
increased residual pest and pathogen loadings under
minimum tillage techniques. Plant breeding with a
focus on plant health has made improvements in white
clover performance, and there is scope to develop
varieties that ensure a more resilient legume component
in pastures. An exemplar outcome from this approach
is improved vegetative persistence and dry matter
yield under nematode and clover root weevil pressure,
as shown in field trials of elite breeding material. An
enhanced, unified plant breeding and plant health
approach can increase the performance and vegetative
persistence of white clover. Trait selections to increase
resilience and dry matter yield include optimum root
architecture; single and multi-gene resistance or
tolerance mechanisms; multi-pest defence compounds;
and symbiont:clover combinations enabling induced
pest and disease resistance. Cost effective and timely
plant health assays for plant breeding are essential.
Improved breeding strategies will create value on-farm
via perennial forage legumes that perform better under
pressure from pests.
Keywords: white clover, plant breeding, plant genetics,
nematode, pest resistance, pest tolerance
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