ALTERNATIVE ESTABLISHMENT STRATEGIES
FOR WHITE CLOVER SEED PRODUCTION
John McCartin
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Autumn sown white clover after wheat results
in good white clover establishment and large areas can be
sown. Direct drilling white clover into barley stubble in the
autumn also gives very good white clover establishment.
Other methods which include ryegrass and white clover
sown together in autumn, sowing with autumn wheat,
undersowing barley and processed peas in the spring and
oversowing autumn wheat in the spring are less successful.
Keywords: White clover, Trifolium repens,
ASPECTS OF SEED QUALITY
D.J. Scott and J.G. Hampton
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Seed quality refers to a number of seed
properties which may have varying degrees of practical
importance for agriculture. As well as the traditional purity
and germination capacity of seedlots, seed quality also
includes species purity, cultivar purity, vigour, seed size,
seedlot uniformity, seed health and seed moisture content.
The quality of New Zealand herbage seedlots is
reviewed. Data are presented for weed seed contamination,
germination, seed vigour and seed weight. The influence
such factors as analytical and cultivar purity, freedom from
weeds, vigour and seed health have on New Zealand’s
domestic and export seed trade is discussed.
Keywords: Seed quality, herbage seed, analytical purity,
weed seeds, cultivar purity, germination,
vigour,
Chemical Manipulation of Grass Seed Crops
J.G. Hampton, T.G.A. Clemence, B.L. McCloy
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The seed yield potential established at anthesis
in grass seed crops is usually 5-10 times greater than actual
seed yields realised at harvest. Losses in seed yield between
anthesis and harvest result primarily from the death of
fertile tillers and poor seed site utilisation.
Lodging has been identified as one of the most
important factors reducing seed yields, and the use of
growth retardants has significantly increased seed yield in
perennial ryegrass and tall fescue. The effects of the growth
retardant paclobutrazol on the growth, development and
seed yield of perennial ryegrass (Lolium perenne) are
presented and discussed.
Little is known of the effects of leaf and stem diseases
on grass seed yields. Recent research has found that
fungicide application can substantially increase seed yield in
perennial ryegrass through delaying senescence of leaf
tissue. Increased leaf area duration is associated with a
reduction in seed abortion, resulting in more seeds per
spikelet at harvest. The possibilities for fungicide use in the
crop are discussed.
Keywords: Seed production, grasses, fertile tillers, seed
abortion, growth retardants, paclobutrazol,
fungicide, senescence.
CONTAMINATION OF WHITE CLOVER SEED
CROPS BY BURIED SEEDS
J .A. Lancashire, M.P. Ralston, D.J. Scott
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Thirty five certified seed lines of ‘Grasslands
Pitau’ white clover produced under OECD rules showed
marked variations in growth and morphological
characteristics according to their region of origin. Of lines
grown in Oamaru district, South Canterbury, 90% were
significantly different from a Pitau breeders (pre-basic) line
in winter growth scores, leaf size and picric acid scores.
90% of lines grown in Marlborough were similar to a Pitau
breeders line.
Buried white clover seed counts were 260/m’ (2 kg/ha)
in Marlborough and 1060/m (7.5 kg/ha) in Oamaru.
Plants grown from buried seed collected in Canterbury
generally had smaller leaves, less winter growth and lower
picric acid scores than Pitau. The additional possibility that
natural selection of genotypes occurred because some crops
of Pitau have been grown under climates and/or
managements to which it is not adapted, is also discussed.
Preliminary studies of 43 commercial lines of 15
cultivars from 4 countries grown outside New Zealand
indicated that 3540% showed significant differences in
winter growth and leaf size between lines of the same
cultivar. New Zealand grown commercial lines of Huia
obtained overseas showed good uniformity.
It appears that there is a world-wide problem of genetic
contamination in white clover cultivars. High buried seed
loads are a potential long term source of contamination
which is being exaggerated by the increasing numbers of
cultivars. New Zealand has already moved to implement
tighter certification standards than those recommended by
OECD.
Keywords: Trifolium repens, ‘Grasslands Pitau’, buried
seed, seed certification, OECD, genetic
contamination.
EFFECT OF LEAF AREA ON WHITE CLOVER SEED
PRODUCTION
P.T.P. Clifford
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Leaf size is a major determinant of white
clover seed yield. A three-fold increase in leaf size halves
seed yield. From a survey of commercial crops, an optimum
leaf size concept was used to explain the reduction in yield
potential for extremes in leaf size. Overgrazing gave small
leaves and lowered seed yields. Closing too early gave large
leaves and lowered yields. With good management,
optimum leaf size was the smallest size possible, consistent
with ensuring an adequate bulk for efficient harvesting. A
healthy highly-reproductive stolen population has to be
developed before closing. Secondly, moisture regulation
over the crop season, preventing excess watering to
minimise plant exploitation of surplus fertility, reduces the
potential for large leaves to develop. Mid-November
closing coupled with maintaining soil moisture at about
25% plant available, over flowering, are sound
management practices.
Amongst cultivars, differences in seed yield potential
may also be related to leaf size. In general the larger the
mean cultivar leaf size the lower the seed yield.
Keywords: Trifolium repens, white clover, seed
production, leaf size, soil fertiity, moisture,
management options.
FACTORS AFFECTING SCALE OF ENTERPRISE
C. Logan Freeman
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White clover is undersown in the spring with
wheat, barley and peas. Irrigation is used in order to
achieve a heavy flowering in the white clover crop over one
month. Three barley crops must be grown successively in
some paddocks to eliminate yarrow. Lupins, peas and
soybeans are alternative legumes to white clover, but white
clover is still the preferred legume to grow, especially with
new cultivars becoming available.
Keywords: White clover, Trifolium repens, seed
production, yarrow, alternative crops,
overseas markets.
GRASS SEED PRODUCTION: WEEDS, HERBICIDES
AND FERTILISERS
M.P. Ralston, K.R. Brown, M.D. Hare, K.A. Young
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Four weed species (Bromus mollis, Vulpia sp.,
Poa annua, Steltaria media) occur in 30% or more of all
perennial ryegrass seed samples. Of the listed undesirable
species, Avena fatua (wild oat) and Hordeum murinum
occurred respectively in 5.3 and 3.5% of ryegrass seedlots.
Only 6 herbicides are registered for use in grass seed crops
in New Zealand, 2 for wild oat, and 4 for broadleaved
weeds. The results of research on weed control in seedling
and established seed crops (ryegrass, cocksfoot, tall fescue,
phalaris, prairie grass) are presented.
Fertilisers for grass seed crops discussed are nitrogen
(N), phosphorus (P), potassium (K), lime and zinc. Autumn
N is commonly used and will increase seed yields in early
flowering species (Pestuca rubra, F. arundinacea), but in
ryegrass variable results have occurred. Spring N should be
applied at stem elongation. No responses to P have been
reported for ryegrass, while in established cocksfoot
responses to P and K have been reported. Overliming can
induce Zn deficiencies, and of the grass species only prairie
grass may require lime.
Keywords: Lolium, ryegrass, seed production, weed
occurrence, Bromus mollis, herbicides,
fertilisers, nitrogen, phosphorus, potassium,
lime, zinc
HEAT DAMAGE AND DRYING EFFECTS ON SEED
QUALITY
M.J. Hill and C.R. Johnstone
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Heat damage to seed can occur as a result of
the cumulative effects of respiration and fungal heating,
and by the accumulation and retention of radiant heat
within the seed mass following harvest - both situations
being collectively referred to as ‘field heating’. Another
type of heating damage occurs in heated air drying systems.
Excessive drying air temperature can have deleterious
effects on seed quality - this is generally referred to as
“drying damage”.
Both ‘field heating’ and ‘drying damage’ result in loss
of quality due to the thermosensitivity of seeds. This is a
characteristic which is markedly influenced by the seed
moisture content, by the extent and duration of heat
production, and by the retention of heat within the seed
mass.
The role of the thermophilic fungi, Aspergillus spp., in
accentuating heat damage, and the effects of both ‘field
heat’ and ‘drying damage’ on the market acceptability and
quality of seed is also discussed.
Keywords: Respiration heating, fungal heating,
Aspergillus, seed quality
POSSIBLE SOLUTIONS TO CONTAMINATION OF
WHITE CLOVER SEED CROPS BY BURIED SEED
P.T.P. Clifford,M.P. Rolston, W.M. Williams
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Buried hard seed from seed returned to the soil
during harvesting and incorporated by cultivation, poses
the greatest threat of contamination. When a different
white clover (Trifolium repens L.) is sown, contamination
will occur when hard seeds within the germinating zone
soften and emerge. Harvest losses can return 40 to 210
kg/ha of hard seeds to the soil. Flowering management and
efficient harvesting are necessary to minimise quantities of
hard seed returned to the soil. For a buried seed load of
845/m* in the germinating zone of a cultivated seed bed at
sowing in March, 8% of that seed load gave rise to
establishing plants of which one-third (19/m’) were
surviving in mid-October. At closing the percentage crop
contamination within the sown row was directly
proportional to the within-row seeding rate of the sown
cultivar. At wider-than-normal row spaces, (45 cm
compared with 15 cm) either inter-row cultivation or
spraying for removal of contaminants was necessary at
closing to reduce contaminants to a density similar to that
in 15 cm spacing treatments. Physical contamination of the
harvested seedline, compared with levels present at closing,
had doubled for normal, but trebled for wider-than-normal
spacings. Lowest percentage physical contamination of a
seedline gained was 13% for a 6 kg/ha seeding at 15 cm
spacings.
The results indicate that successful cultivar change on
many areas will be difficult. A buried seed count is
considered an essential guideline to aid choice of paddock.
Future management systems now being developed, include
the use of herbicides and direct drilling, and should help to
minimise this problem.
Keywords: White clover, Trifolium repens, seed
production, contamination, cultivar change,
harvest losses, hard seed, cultural practices.
SEED CERTIFICATION - AN ASPECT OF QUALITY
ASSURANCE WITH SPECIAL REFERENCE TO
WHITE CLOVER SEED
D.K. Crump
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Seed certification is discussed in relation to the
concept of industry quality assurance. The present
derivation of product specifications and consumer
preferences is described. Procedures are outlined for
making improvements to the quality assurance system.
Keywords: White Clover, quality assurance, OECD,
certification, consumer preference, product
specifications, consumer protection, Plants
Act 1970, acceptable list, recommended list.
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