Maataloustieteellinen A ikakauskirja
Vol. 62: 221—226. 1990

Seed yield and seed quality of subterranean clover
(Trifolium subterranewn L.) in growing conditions of Finland

VARIS, E., PELTOLA, U. and KAUPPILA, R.
University of Helsinki, Dept, of Crop Husbandry
SF-00710 Helsinki, Finland

Abstract. Seed yield and overwintering of seeds of 22 Australian subterranean clover vari-
eties were investigated in 1986 and 1987 at the Viikki Experimental Farm of the University
of Helsinki.

The seed yield varied remarkbly according to the variety and weather conditions of the
two summers. Some varieties, such as Seaton Park, Woogenellup and Karridale, and during
the summer of 1987 also the early variety Dalkeith, produced lots of seed. Some late varieties,
e.g. Treeton, Tallarook and Esperance, produced very few seeds or no seeds at all.

A considerable proportion of the seeds degenerated during the wet autumn conditions,
by the end of October. Many seeds showed embryo dormancy, but complete dormancy or hard
seeds were found only exeptionally. In spring 1988, some seedlings which had developed from
overwintered burrs were found. There seems to be little hope of finding self-seeding subterra-
nean clovers suitable for Finnish growing conditions.

Index words: subterranean clover, seed yield, seed survival

Introduction

Subterranean clover is a winter annual clo-
ver growing in the Mediterranean climate
zone. It includes three species, Trifolium sub-
terraneum L., T. yanninicum Katzn. and T.
brachycalycinum Katzn. and Morley. The spe-
cies differ from each other with respect to
their morpholpgical characteristics and the
growing conditions they require, but they are
all geocarpic, with their seeds developing at
or beneath the soil surface (McGuire 1985).

Subterranean clover grows during the rainy
winter season. The seeds mature before the
hot and dry summer; they survive beneath the
soil surface, to start growing again in the au-
tumn. A typical characteristic of the seeds is
a long-lasting dormancy, which helps lots of
the seeds to remain viable for several years
(Lancer and Hill 1982).

In Australia, subterranean clover has been
developed into a crop plant, which makes it

221

JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND

https://www.c-info.fi/en/info/?token=WEqh9zkdsoBxSBJ2.Okey0y4T24-URQ4PhfldPw.L3OJ1g-C7W-_39kh0vNOYQRdnQAhNyZwr52qA5nKBqdF2dYKCRY8pCKRv-pOU--Pd0I3sl7bXgzFfpJM71mN_fGbrcW663nY1rwiWLUHWyODvO59NwNE0Ow4mikFvifaxQsJsWCEwSd-wyMEpz0oQfS4rReC4wLN1l6H5tcfy2-yZVBd-RZ2PbZxHbuSQ3V5o9q7M0Y


possible to grow pastures with low seed and
nitrogen costs. It has adapted to the cropping
system so that after the pasture phase it sur-
vives in the soil during the 2—3 years of ar-
able cropping to come up spontaneously as the
main species at the beginning of the pasture
phase. It is well able to stand the grazing of
sheep, and because of its growing habit it
produces lots of seed in spite of grazing
(Gladstones 1967, Gladstones and Collins
1983, Taylor 1984, Boyce et al 1985).

In Europe, subterranean clover has spread
naturally not only in the Mediterranean coun-
tries but even in France and the southern
parts of the British Isles. In many European
countries it is sown with imported seed for
green manuring, but its seed production and
self-seeding ability have been investigated
only little (Katznelson 1974, Morgner and
Schafer 1981).

Material and methods

Since 1980, subterranean clover has been in-
vestigated as a green manuring crop at the
University of Helsinki, at the Department of
Crop Husbandry (Varis et ai 1982, Kauppila

1983). At the beginning the varieties studied
were those provided by German and Swiss
seed suppliers such as Clare, but also varie-
ties from Australia were studied. Some of
them grew well and flowered well, and they
also seemed to produce seed. Thus the growth,
seed production, dormancy of seeds and the
possible survival over the winter were studied
more in detail.

Seeds for the study reported here were
received from the Western Australian Depart-
ment of Agriculture in Perth. The varieties
were: Clare, which belongs to the subspecies
Trifolium brachycalycinum, Dalkeith, Esper-
ance, Green Range, Junee, Karridale, Nunga-
rin, Seaton Park, Tallarook, Treeton and
Woogenellup (subsp. T. subterraneum) and
Larisa, Meteora and Trikkala (subsp. T. yan-
ninicum). Eight lateflowering breeding lines
were also included.

The first trial in 1986 was established with
single plants. The seeds were sown in a green-
house at the beginning of April. In the middle
of May the seedlings were transplanted in the
field as one plant plots, two meters apart,
with four replicates. In addition, 5 m long
rows, 1 m apart, were sown at the neighbour-
ing field for studying the survival of the seeds.
In 1987, the varieties were sown in the field
at the end of May, in single rows of 5 meters,
20 plants/m with a row distance of one meter.

The flowering of the plants was observed
during the summer. In the autumn of 1986,
all subterranean clover plants were dug up
from the field, with their roots and burrs, at
the end of October. The plants were washed
up and dried in 45°C, and their seeds and bio-
mass were weighed. During the winter the
numberof burrs containing seeds were count-
ed. The seeds were separated from the burrs
manually. The yields of the seeds were
weighed, and the average seed weights were
determined. The seeds were germinated in a
Jakobsen germinating basin, four times 100
seeds if there were enough seeds. The seeds
were divided into four groups: normally ger-
minated, swollen (emryo dormancy), hard
(complete dormancy) and degenerated seeds.
Samples of 0.5 m were taken from the rows
sown in 1987, for yield and germinating ana-
lyses, respectively.

In the spring of 1987 and of 1988, the trial
site was investigated to find out whether seeds
survived.

Growing conditions

The trial site in 1986 was sandy clay, pH
6.1. In 1987, the trial field was fine sand soil,
pH 5.9. The weather conditions of the grow-
ing seasons were totally different. In 1986, the
effective temperature sum was 1318°C until
October 27 and only 1097°C in 1987 until Oc-
tober 9; the latter was one of the lowest tem-
perature sums of this century in southernFin-
land. The rain sums were 518 mm and 428
mm, respectively.

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Results

The diameterand dry weight of the plants,
the number of burrs, seed yield, and thousand
seed weight from the 1986 trial are presented
in Table 1. The varieties are classified in three
classes according to the earliness of their
flowering (early = commencement of flower-
ing before July 2; middle = flowering start-
ed from July 2 to July 9; late = flowering af-
ter July 9). The varieties are listed according
to their seed yields.

The earliness didnot quite correspond with
seed yields. Nevertheless, those varieties which
produced few seeds or no seeds at all were late.
The diameter of the plant, which reflects the
length of runners, varied from 29 to 135 cm
and the dry weight varied between 3.3 and
147.4g. Frost and diseases damaged some var-
ieties, which reflects in low yields. The seed
yields varied highly. Seaton Park produced
more than 1000 seeds per plant. Some late var-
ieties, such as Treeton the most abundant
growing variety of the trial did not produce
any seeds.

The germinability of the seeds and the
dormancy characteristics are presented in
Table 2.

Most varieties had very few normally ger-
minating seeds. Most of the seeds had de-
generated in the wet field already during the
autumn. Some of the seeds were healthy and
swelled during the germination test; this was
an indication of embryo dormancy. There
were only some proper hard seeds which it
could be assumed, would survive over the win-
ter.

In the spring of 1987, no seedlings were
found in the field, so that overwintering of the
seeds seemed to be unlikely.

The results for summer 1987 are presented
in Table 3. The results are expressed per row
of 0.5 m, so the yields are not directly com-
parable with the figures of the previous year.

The best seed producers in the cool summer
of 1987 were the early or fairly early varieties.
The results were somewhat different from
those of the previous year, apparently because
of the exceptional temperature conditions of

Table 1. The biomass and seed yield of subterranean clover varieties in 1986.

Earliness Diameter Dry weight Burrs with seeds/ Seed yield 1000 seed
E =early of plants g/plant empty burrs g/plant weight
M =middle per plant g
L =late

Variety

Seaton Park
Woogenellup
Karridale

M
M
E

120 119.5 524/162
329/166
331/108
104/32
101/66
143/104
82/19

6.97 a

4.11“
3.97“'
1.17»"
1.08bce

1,05b"

0.7l bde

0.60bdf

0.55 bdf

0.53 bdf

0.50 bdf

0.44 bdf

0.28 bdf

0.23 bdf

0.14 bdf

0.12 bdf

0.12bdf

0.00bdf

0

4.54
111 110.0 5.10
109 94.2 4.22

68103H L
E
L

74 92.3 3.41
Nungarin
Junee

96 36.0 4.38
90 123.0 2.77

Trikkala
89774 F
Larisa

M 39 12.3 5.63
L 64 72.2 108/52 2.85
M
L
M

73 105.0 96/54 4.28
897748 73 41.5 107/46 2.23
Green Range
89777 C

55 75.9 49/17 4.79
L
E
E
L
L
L
L
L

60 64.6 63/20 3.57
Clare 135 28.3 37/18 6.36
Dalkeith
89816 F
Meteora
89822 H
89880 J

29 3.3 35/12 3.10
59 113.7 24/49 2.40
49 43.7 14/10 5.76
57 45.5 20/14 2.31
68 101.3 4/4 1.14

Esperance
Tallarook
Treeton

39.740 0/0
M 53 100.8 0/0 0

79L
L

147.4 0/0 O
oGF 183 a-5 49 77.1 0/0

223



224

Table 2. The germinability and dormancy characteristics of subterranean clover seeds in 1986.

Variety Normal Swollen Flard Degenerated
% % % %

Seaton Park 33 35 0 32
Woogenellup 46 0 0 54
Karridale 10 28 0 62
68103 H 13 5 0 82
Nungarin 8 50 3 39
Junee 0 16 1 83
Trikkala 20 21 0 59
89774 F 5 38 0 57
Larisa 4 30 0 66
897748 2 32 0 66
Green Range 4 15 0 81
89777 C 8 12 0 80
Clare 2 21 1 76
Dalkeith 2 32 2 64
89816 F 0 15 0 85
Meteora 3 33 0 64
89822 H 2 I 0 97
89880 G
Esperance
Tallarook
Treeton
GF 183 a-5

Table 3. The biomass and seed yield of subterranean clover varieties in 1987.

Variety Earliness Dry weight Burrs with seeds/ Seed yield 1000 seed
E =early g/0.5 row- empty burrs g/0.5 m weight
M =middle meter per 0.5 m g
L = late

Dalkeith E 4.8 44/1 1,08 8.23
Green Range E 12.1 36/19 .78 6.09
Karridale M 17,0 61/38 .71 3.34
Woogenellup M 19.2 27/38 .62 6.15
Meteora M 58,4 49/58 .52 4.42
Nungarin L 13.5 22/23 .40 5.02
Trikkala M 9.0 15/17 .33 7.73
Seaton Park M 25.4 30/68 .31 4.33
Larisa L 18.0 21/30 .24 4.47
Clare E 6.2 7/4 .12 6.71
Junee M 12.2 11/16 .11 2.83
89816 F L 7.0 11/32 .11 2.88
GF 183 a-5 L 14.1 3/9 .6 5.04
89774 F L 10.9 6/31 .4 3.34
897748 L 18.7 2/25 .2 3.47
89777 C L 16.2 2/17 .2 2.95
68103 H L 13.2 1/4 .1 2.42
89880 J L 8.9 1/17 .1 2.50
Esperance E 16.3 1/1 0 0.75
89822 H L 8.5 0/6 0 3.71
Tallarook L 16.3 0/2 0 0
Treeton L 9.3 0/0 0 0



225

Table 4. The germinability and dormancy characteristics of subterranean clover seeds in 1987.

Variety Normal Swollen Hard Degenerated
% % % %

Dalkeith 4 55 24 17
Green Range 0 15 0 75
Karridale 6 32 1 61
Woogenellup 8 20 0 72
Meteora 0 16 0 84
Nungarin 0 75 0 25
Trikkala 1 64 3 32
Seaton Park 2 20 1 77
Larisa 0 20 0 80
Junee 1 5 0 94
89816 F 0 22 0 78
OF 183 a-5 2 3 0 95
89774 F 0 34 0 66
897748 0 19 0 81
89777 C 0 5 0 95
68103 H 0 0 0 100
89880 J 0 2 0 98
Esperance
899822 H
Tallarook
Treeton

the summer. Seaton Park produced lots of
empty burrs although it had produced plenty
of seed the year before. The early varieties,
Dalkeith and Green Range, gave the best seed
yields, Meteora grew well in wet conditions.

The results characterizing the quality of
seeds are presented in Table 4.

There were few normally germinating seeds,
but many varieties had plenty of swollen seeds
indicating embryo dormancy. Dalkeith had
exceptionally many hard seeds. The seed yield
of many varieties had fully degenerated by the
end of October. The unploughed trial site was
examined in spring 1988 to check for seed-
lings. Six seedlings originating from burrs
were found. Two of these plants kept grow-
ing when transplanted in the greenhouse, and
produced seed during 1988.

Discussion

The results of these small-scale experiments
show that many subterranean clover varieties
were able to produce seed in Finnish growing
conditions. The long day during the growing

season hastens the flowering of several varie-
ties (Aitken 1955, Evans 1959, Collins and
Aitken 1970). Due to the considerable differ-
ences in the earliness of the varieties and to
the highly variable temperature conditions, the
seed yields of the varieties varied in the two
trial years.

Most of the seeds degenerated during the
wet autumn. To reach complete dormancy
and to survive in the field, the seeds of sub-
terranean clover have to dry (Hagon 1974,
Collins and Quinlivan 1980); that apparent-
ly did not occur. In Finnish growing condi-
tions embryo dormancy developed in many
cases, but these seeds can hardly survive over
the winter, due to damage caused by diseases
and freezing of the soil in the winter. Only oc-
cassionally were there real hard seeds, the con-
dition required for the self-seeding ability of
subterranean clover (Williams and Elliot
1960). The fact that there were some seedlings
which developed from overwintered seeds in
spring 1988 may give some hope of finding
types which can develop hard seeds and self-
seed in more northern and wetter conditions



than is normally the case. On the other hand,
it would be theoretically possible to harvest
germinable seed of subterranean clover in

Northern European conditions if the harvest-
ing time were fitted to the maturation time of
the actual variety.

References

Aitken, Y. 1955. Flower initiation in pasture legumes; 1.
Factors affecting flower initiation in Trifolium sub-
terraneum L. Aust. J. Agric. Res. 6; 212—244.

Boyce, K.G., Weber, G.D. & Lake, A.W.H. 1985.
Transfer of the South Australian dryland farming
technology of countries in West Asia and North Afri-
ca. Proceedings of the XV International Grassland
Congress, August 24—31, 1985, Kyoto, Japan.

Collins, W.J. & Aitken, Y. 1970. The effect of leaf
removal on flowering time in subterranean clover.
Aust. J. Agric. Res. 21: 893—903.

Collins, W.J..& Quinlivan, B.J. 1980. The effects of a
continued water supply during and beyond seed de-
velopment on seed production and losses in subter-
ranean clover swards. Aust. J. Agric. Res. 31: 287
—295.

Evans, L.T. 1959. Flower initiation in Trifolium subter-
raneum L. I. Analysis of the partial processes in-
volved. Aust. J. Agric. Res. 10: I—l6.

Gladstones, J.S. 1967. Naturalized subterranean clover
strains in Western Australia: a preliminary agronomic
examination. Aust. J. Agric. Res. 18: 713—731.

Gladstones, J.S. & Collins, W.J. 1983. Subterranean
clover as a naturalized plant in Australia. J. Aust. Inst.
Agric. Sci. 49; 191—202.

Haoon, M.W. 1974. Regeneration of annual winter le-
gumes at Tamworth, New South Wales. Aust. J. Exp.
Agric. Anim. Hush. 14: 57—64.

Katznelson, J. 1974. Biological flora of Israel. 5. The
subterranean clovers of Trifolium subsect. Calycomor-
phum Katzn. Trifolium subterraneum (L.) (s. 1.) Isr.
J. Bot. 23: 69—108.

Kauppila, R, 1983. Viherlannoituskasvit. Biologinen
typensidontapeltokasvien viljelyssä. SA:n sopimustut-
kimuksen 383 loppuraportti: 175—192.

Lancer, R.H.M. & Hill, G.D. 1982. Agricultural
plants. 344 p. Cambridge.

McGuire, W.S. 1985. Subterranean clover science and
technology,p. 515—534. Ed. Taylor, N.L. Madison,
Wisconsin.

Morcner, F. & Schafer, K. 1981. Bodenfriichtiger Klee
eine aussichtsreiche Zwischenfrucht. Tierziichter

33: 260—261.
Taylor, G.B. 1984. Effect of burial on the softening of

hard seeds of subterranean clover. Aust. J. Agric. Res.
35: 201—210.

Varis, E., Hovinen, S., Kansanen, P. & Kauppila, R.
1982: Legumes in Finnish Agriculture. The Second
National Symp. Biol. Nitr. Fix, Rep. I: 219—231.

Williams, W.A. & Elliot, J.R. 1960. Ecological sig-
nificance of seed coat impermeability to moisture in
crimson, subterranean and rose clovers in a medi-
terranean-type climate. Ecology 41: 733—742.

Ms received October 3, 1989

SELOSTUS

Maa-apilan (Trifolium subterraneum L.)
siemenenmuodostus ja siementen laatu
Suomen kasvuoloissa

Varis, E., Peltola, U. ja Kauppila, R.
Helsingin yliopisto. Kasvinviljelytieteen laitos,
00710 Helsinki

Helsingin yliopiston Viikin koetilalla tutkittiin vuosi-
na 1986—87 22 austraalialaisen maa-apilalajikkeen ja lin-
jan siemenenmuodostusta ja siementen talvehtimista.

Lajikkeiden siemensato vaihteli huomattavasti koe-
vuosien kesken. Eräät lajikkeet, kuten Seaton Park,
Woogenellup jaKarridale, jakesällä 1987myös aikainen
lajike Dalkeith, tuottivat runsaasti siementä. Monet
myöhäiset lajikkeet, kuten Treeton, Tallarook jaEsper-
ance, tuottivat siementä hyvin vähän tai ei lainkaan.

Huomattava osa siemenistä pilaantui kosteissa syys-
oloissa lokakuun loppuun mennessä. Useissa siemenissä
todettiin alkion dormanssia, mutta täydellistä dormans-
sia tai kovia siemeniä esiintyi vain satunnaisesti. Kevääl-
lä 1988 koealueelta löydettiin muutamia talvehtineista sie-
menistä kasvaneita taimia. Näyttää olevan vain vähän
mahdollisuuksia löytää maa-apilasta Suomen oloissa it-
sesiementäviä muotoja, joita voitaisiin hyödyntää laidun-
ta! viherlannoituskasveina.

226