Maataloustieteellinen A ikakauskirja
Vol. 63: 341—51, 1991

Influence of different barley varieties on competition and yield
performance in barley-oats mixtures at two levels of nitrogen fertilization

KARI JOKINEN
Kemira Oy, Espoo Research Centre, P.O. Box 44,
SF 02271 Espoo, Finland

Abstract. Competition between barley and oats, and yield performance of mixtures were
evaluated in a two component replacement series field experiment at two levels of nitrogen
applications (80 kgN/ha and 120 kgN/ha). Three barley cultivars (Aapo, Agneta ja Ida) and
one oats cultivar (Veli) were used.

The competitive relationship was independent of the pure stand yield of the cultivar. Ida
and Agneta were more competitive than oats irrespective of nitrogen dose. Ida was the most
dominant variety which was very likely due to the early development of the seedlings. Oats
was slightly more competitive than the shortest cultivar Aapo at high nitrogen, although bar-
ley seedlings emerged before oats. Thus the competitive ability of a cultiyar was not deter-
mined by one character of the plant only.

The competition in mixtures had a greater effect on number of generative shoots and num-
ber of grains per head than on grain weight. The results revealed that the yield per plant in
mixtures may be even the same as in monoculture, but the relative significance of different
yield components may vary.

The grain and protein yield of mixtures did not differ significantly from the yield of the
highest yielding component grown alone. However, the ratio of actual and expected yield and
the relative yield total were in most cases higher than one, indicating that some yield advan-
tage may have been achieved. The genotypic composition of the stand had the greatest influence
on the grain protein content of oats.

Index words: Competition, yield, barley, oats, nitrogen fertilization, mixtures

INTRODUCTION

Competition among plant species has long
been recognized as a major factor affecting
crop production. Individual plants living with-
in a mixed community will be exposed to com-

petition from like and unlike individuals
whenever and wherever the demand for an es-
sential resource exceeds its immediate supply.
Because each plant requires both above- and
below-ground resources, its ability to grow in
a habitat will be determined by the availabili-

341

JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND

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ties of these resources relative to the plant’s
morphological and physiological abilities to
acquire these resources.

Beneficial competition between two crop
species is often incorporated into cropping
systems (Vandermeer 1989). It is argued that
the main benefits of growing mixtures, wheth-
er at the level of genus, species or variety, may
include: higher yields, lower variability of
yield from season to season, a better spread
of production over the growth period, less sus-
ceptibility to disease or lodging and a superi-

MATERIALS AND METHODS

The replacement series field experiment was
carried out in 1986 on the Kotkaniemi Ex-
perimental Farm of Kemira Oy in southern
Finland (60° 22'N, 24° 22'E) with barley and
oats seeded separately (500 seeds/m2 ) and in
an equal mechanical mixture (250/250). Three
different barley cultivars (Aapo, Agneta and
Ida) and one oats cultivar (Veli) were used.
The general characters of the cultivars were
(Rantanen and Simojoki 1987):

Variety Grain yield Growing Height 1000- Grain
time grain weight protein

kg/ha days cm g content %

Aapo (2-row) 4740 97 62 37.3 11.8
Agneta (6-row) 5100 87 81 37.2 12.0
Ida (2-row) 4940 91 70 44.9 12.8
Veli 4714 94 92 34.4 13.9

or quality of the product (Wolfe 1985).
Many studies of barley-oats mixtures, as

reviewed by Jokinen (1991 a), indicate that
yield increases over the mean of the compo-
nents in monoculture have been observed.
Some results from the field experiments even
suggest that overyielding may occur. Accord-
ing to Trenbath (1974, 1976), the mechan-
isms that might lead to the yield advantage of
mixtures can be differing growth rhythms,
differing rooting depths and nutritional com-
plementation of the components. Also en-
hanced light and water use efficiency may be
involved. Thus combining different kinds of
genotypes it may be thought that one combi-
nation might more efficiently utilize the en-
vironment than the other.

The present study was initiated to inves-
tigate whether cultivars of spring barley
differed in their relative performance in pure
stands and in 50:50 mixtures with oats and,
if so, to see if the differences could be related
to competition effects on mixture compo-
nents. The influence of nitrogen fertilization
on competition and yield advantage was also
evaluated.

A split-plot design (nitrogen levels in main
plots and genotypic composition of stand in
subplots) was used with four blocks. The soil
was finer fine sand with pH 5.7. The plot size
was 30 m 2 (3 m x 10m) with rows spaced 12.5
cm apart. The granular fertilizer was NPK (N
16%, P 7%, K 13%) applied at the rate of 80
kgN/ha and 120 kgN/ha. The sowing date
was 12 May. The crops were kept free of
weeds by one application of the herbicide Ac-
tril S (2 —3 liters/ha mixed with 300 liters of
water) containing MCPA (235 g/1), dichlor-
prop (184 g/1), ioxynil (38 g/1) and bromox-
ynil (24 g/1) at the time of shoot emergence.

The number of plants in each plot was de-
termined by counting the number of seedlings
in four randomly selected 1-m-longrows/plot
about three weeks after sowing and before the
initiation of tillering. The number of genera-
tive shoots was determined similarly after the
complete ear emergence of all the cultivars.
The emergence time of the seedlings as well
as the height of the stands were evaluated
visually.

At maturity the entire area of each plot was
harvested (on 15 August) and the grain yields

342



were determined (kg/ha at 15% moisture con-
tent). From each mixture a 50 g sample was
taken for determinationof the seed yield of
the barley and oats components. The separat-
ed samples of each mixture as well as samples
of each pure stand yield were used for deter-
mination of the protein content (%) of the
grain by the Kjeldahl method (500 mg with
two subsamples) and 1000-grain weights (g) (3
x 100 seeds/sample). The number of
grains/head was calculated using on data of
yield, number of generative shoots and 1000
grain weight.

Relative yield (RY) and relative yield total
(RYT) were calculated according to the
methods of de Wit and van den Berg (1965).
Relative protein yield and relative protein yield
total were determined similarly. Competitive
ratio (CR) was determined according to the
method of Wiley and Rao (1980). The mean
yield/area of four replications was calculat-
ed before computing the indices.

The grain yields, 1000grain weight, num-
ber of generative shoots, the protein content
of grain and protein yields were subjected to
analyses of variance for split-plot design
(Steel and Torrie 1980). Mean separation
was accomplished by Tukey’s honestly signifi-

cant difference test (HSD) (P = 0.05) (Steel
and Torrie 1980).

RESULTS

The development of the stands

All the barley varieties emerged a few days
earlier than oats. The six-row barley Agneta
and the two-row barley Aapo emerged more
slowly than the two-row barley Ida. At the be-
ginning of the growing season the density was
approximately the same (0.95—1.05) as ex-
pected (data not given). The height of the
stands in descending order after the ear emer-
gence was Veli, Agneta, Ida and Aapo.

Grain yield

In addition to the main effects there was
also a significant interaction (p<0.05) be-
tween nitrogen fertilization and the genotyp-
ic composition of the stand. There were sig-
nificant yield differences between the mixture
yields only at low nitrogen, the mixture yield
of Agneta and Veli being the smallest and the
mixture yield of Aapo and Veli the greatest

Table 1. The grain yield (kg/ha) of monocultures and mixtures of barley (Agneta, Ida and Aapo) and oats (Veli).
A/E is the ratio of the actual and expected yield of the mixtures. CV =Coefficient of variation of grain yields. Grain
yield means in different nitrogen columns, grain yield means in the average column and grain yield means in the
average row followed by the same letter are not significantly different at the 5% level (HSD test).

Nitrogen fertilization (kgN/ha) CV

Stand 80 120 Average

A/E A/E A/E

Veli (Ve) 5149 b 5380 ab 5265 b 7.1
Agneta(Ag) 4711 a 5312 a 5012 a 8.3
Ida (Id) 5054 ab 5783 cd 5419 be 9.9
Aapo (Aa) 5279 be 6058 d 5669 c 12.1
AgVe 4998 ab 101 5692 be 106 5345 b 104 9.1
IdVe 5237 be 103 5766 cd 103 5502 be 103 7.9
AaVe 5506 c 106 5715 bed 100 5611 c 103 8.8

Average 5133 a 5672 b 5402
Mono 5048 100 5633 100 5341 100
2-mixture 5247 104 5724 102 5486 103

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(Table 1). In contrast to barley varieties grown
in monoculture Veli oats was rather insensi-
tive to added nitrogen. At a low level of nitro-
gen fertilization Veli was as a good producer
as the best barley variety Aapo. At a high level
of nitrogen oats yielded the same as the lowest
yielding barley variety, Agneta.

The yield of a given mixture was the same
as or higher than the mean yield of the com-
ponents grown in monoculture. The mixture
yield was greater than the yield of the highest
yielding component grown in monoculture in
three cases out of six (Veli/Ida and Veli/Aapo
at low nitrogen and Veli/Agneta at high nitro-

gen). These differences varied from 2% to 6%
and were not statistically significant (p>0.05).

Relative yield, relative yield total
and competitive ratio

The results of relative yields of different
barley varieties show that the Ida barley used
the space in mixtures more efficiently than ex-
pected and more efficiently than the other bar-
ley varieties (Fig. 1). The relative yield of
Agneta increased and Aapo decreased with in-
creasing nitrogen fertilization. The relative
yields of oats varied, mainly due to the bar-

Figure I. Relative yields (RY) of different cultivars of barley (Agneta, Ida and Aapo) and oats (Veli), and relative
yield totals (RYT) of the mixtures at two levels of nitrogen fertilization.

344



ley variety in the mixture being lowest in the
mixture with Ida.

At low nitrogen level all the barley varie-
ties were more competitive than oats, Ida be-
ing the most competitive barley variety (Ta-
ble 2). An increase in nitrogen fertilization
reversed only the competitive relationship be-
tween Aapo barley and Veli oats.

Both the barley variety and the level of
nitrogen fertilization affected the relative yield
total value which was equal to or greater than
unity (Fig. 1). The highest value was 1.07 both
in the mixture of Agneta and Veli at the high

Table 2. The competitive ratio (CR) of barley to oats.

Nitrogen fertilization (kgN/ha)

Barley 80 120 Average

Agneta 1.13 1.10 1.12
Ida 1.58 1.58 1.58
Aapo 1.10 0.92 1.01

Table 3. The influence of nitrogen fertilization and the
genotypic composition of the stand on the number of ge-
nerative shoots per plant of barley (Agneta, Ida and Aa-
po) and oats (Veli). Analysis of variance is done separa-
tely for each variety. Means in the average column and
in the average row followed by the same letter are not
significantly different at the 5% level (HSD test).

Nitrogen fertilization
(kgN/ha)

Variety Stand 80 120 Average

Agneta(Ag) Mono 0.67 0.67 0.67 a
Mixture(Ve) 0.72 0.67 0.70 a

Average 0.70 a 0.67 a 0.68
Ida(ld) Mono 1.04 1.04 1.04 a

Mixture(Ve) 1.01 1.19 1.10 a

Average 1.04 a 1.12 a 1.07
Aapo(Aa) Mono 1.15 1.24 1.20 a

Mixture(Ve) 0.97 1.22 1.10 a

Average 1.06 a 1.23 b 1.15
Veli(Ve) Mono 0.63 0.60 0.62 a

Mixture(Ag) 0.85 0.79 0.82 b
Mixture(ld) 0.88 0.82 0.85 b
Mixture(Aa) 0.85 0.86 0.86 b

Average 0.80 a 0.77 a 0.79

level of nitrogen and in the mixture Aapo and
Veli at the low level of nitrogen.

Yield components

In general the grain weight varied relative-
ly less than the other yield components wheth-
er the components were grown in mixtures or
in monocultures (Tables 3,4, 5, and 6). The
greater tillering of oats in all the mixtures
compared with monoculture decreased the
number of grains per head more than the grain
weight. The amount of undercompensation
was greatest in the mixture with Ida.

In mixtures where relative yield of a barley
variety was higher than expected this was due
not only to the higher relative number of
grains per head but also in some cases to the
higher relative shoot number. The considera-
bly lower shoot number of Aapo in mixtures
at low nitrogen was overcompensated by the
grain number. The lower yield per plant of
Aapo in mixtures than in monoculture at high

Table 4. The influence of nitrogen fertilization and the
genotypic composition of the stand on the number of
grains per head of barley (Agneta, Ida and Aapo) and
oats (Veli).

Nitrogen fertilization
(kgN/ha)

Variety Stand 80 120 Average

Agneta(Ag) Mono 33 37 35
Mixture(Ve) 33 41 37

Average 33 39 36
Ida(Id) Mono 19 22 21

Mixture(Ve) 25 24 25

Average 22 23 23
Aapo(Aa) Mono 20 21 21

Mixture(Ve) 26 21 24

Average 23 21 22
Veli(Ve) Mono 47 51 49

Mixture(Ag) 33 41 37
Mixture(ld) 28 32 30
Mixture(Aa) 37 39 38

Average 36 41 39

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Table 5. The influence of nitrogen fertilization and the
genotypic composition of the stand on the thousand grain
weight of barley (Agneta, Ida and Aapo) and oats (Ve-
li). Analysis of variance is done separately for each va-
riety. Means in the average column and in the average
row followed by the same letter are not significantly dif-
ferent at the 5% level (HSD test).

Table 7. The influence of nitrogen fertilization and the
genotypic composition of the stand ongrain protein con-
tent of barley (Agneta, Ida and Aapo) and oats (Veli).
Analysis of variance is done separately for each variety.
Means in the average column and in the average row fol-
lowed by the same letter are not significantly different
at the 5% level (HSD test).

Nitrogen fertilization
(kgN/ha)

Variety Stand 80 120 Average

Agneta(Ag) Mono 38.3 38.6 38.5 a
Mixture(Ve) 37.7 38.8 38.2 a

Average 38.0 a 38.7 a 38.4
Ida(Id) Mono 47.2 46.5 46.8 a

Mixture(Ve) 46.5 46.3 46.4 a

Average 46.9 a 46.4 a 46.6
Aapo(Aa) Mono 42.3 42.0 42.2 b

Mixture(Ve) 41.1 40.7 40.9 a

Average 41.7 a 41.4 a 41.5
Veli(Ve) Mono 31.3 31.9 31.6 a

Mixture(Ag) 31.0 31.2 31.1 a
Mixture(ld) 29.9 30.0 29.9 b
Mixture(Aa) 29.6 30.3 29.9 b

Average 30.5 a 30.9 a 30.6

nitrogen was mainly due to the lower grain
weight.

Grain protein content and protein yield

The occurrence of oats in the stand had no

Nitrogen fertilization
(kgN/ha)

Variety Stand 80 120 Average

Agneta(Ag) Mono 11.1 12.3 11.7 a
Mixture(Ve) 10.3 12.3 11.3 a

Average 10.7 a 12.3 a 11.5
Ida(Id) Mono 11.0 11.9 11.5 a

Mixture(Ve) 10.6 11.9 11.3 a
Average 10.8 a 11.9 a 11.4

Aapo(Aa) Mono 10.5 11.4 11.0 a
Mixture(Ve) 10.6 12.1 11.4 a
Average 10.6 a 11.8 a 11.2

Veli(Ve) Mono 11.8 13.1 12.5 a
Mixture(Ag) 12.7 14.2 13.5 b
Mixture(ld) 11.7 13.6 12.7 ab
Mixture(Aa) 11.6 13.4 12.5 a

Average 12.0 a 13.6 b 12.8

significant effect on the protein content of the
barley varieties (Table 7). The protein content
of oats was higher in the mixture with Agne-
ta than in monoculture or in the other mix-
tures.

No overyielding in respect to protein yield

Table 6. Plant relative yields (PRY) and plant relative yield components of barley (Agneta, Ida and Aapo) and oats
(Veli).»

Nitrogen fertilization (kgN/ha)

Variety 80 120
Character Character

PRY PRS PRG PRW PRY PRS PRG PRW

Agneta(Ag) 1.08 1,08 0.99 1.02 1.11 1.01 1.11 0.99
Ida(Id) 1.27 0.99 1.32 0.99 1.26 1.14 1.12 0.98
Aapo(Aa) 1.11 0.85 1.27 0.97 0.96 0.99 1.00 0.96
Veli(Ag) 0.95 1.36 0.71 0.99 1.02 1.30 0.80 0.97

(Id) 0.80 1.40 0.60 0.96 0.80 1.36 0.62 0.94
(Aa) 1.01 1.35 0.78 0.95 1.04 1.43 0.76 0.95

* PRY =Yield per plant in mixture/Yield per plant in monoculture.
PRS=Number of shoots per plant in mixture/Number of shoots per plant in monoculture.
PRG =Number of grains per head in mixture/Number of grains per head in monoculture.
PRW = Grain weight in mixture/Grain weight in monoculture.

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Table 8. The protein yield (kg/ha) of monocultures and mixtures of barley (Agneta, Ida and Aapo) and oats (Veli).
A/E is the ratio of the actual and expected yield of the mixtures. Yield means in the average column and yield means
in the average row followed by the same letter are not significantly different at the 5% level (HSD test).

Nitrogen fertilization (kgN/ha)

Stand 80 120 Average
A/E A/E A/E

Veli (Ve) 608 704 656 b
Agneta(Ag) 522 653 588 a
Ida (Id) 556 688 622 ab
Aapo (Aa) 554 690 622 ab
AgVe 573 101 752 110 663 b 107
IdVe 577 99 722 104 649 b 102
AaVe 609 105 730 105 670 b 105

Average 571 a 705 b 638
Mono 560 100 683 100 622 100
2-mixture 586 105 735 108 661 106

of a mixture existed (Table 8). The protein
yield of a mixture was usually higher than ex-
pected. The relative protein yield totals were
in most cases above one (Table 9).

DISCUSSION

Grain yield advantage

The grain yield results of the present experi-
ment suggest that mixtures of barley and oats

Table 9. The relative protein yields (RY) of barley (Ag-
neta, Ida and Aapo) and oats (Veli) and the relative pro-
tein yield total of the mixtures (RYT) at two levels of nit-
rogen fertilization.

Nitrogen fertilization (kgN/ha)

80 120

Mixture RY RYT RY RYT

Agneta 0.50 0.56
Veli 0.510.55

1.01 1.1l

Ida 0.61 0.63
Veli 0.38 0.41

0.99 1.04

Aapo 0.560.48
Veli 0.490.56

1.051.04

Average 1.021.06

may yield more than the mean of the compo-
nents grown alone and even overyield. How-
ever, the reader should observe that the grain
yield of any mixture did not differ statistical-
ly significantly from the yield of the highest
yielding component grown in monoculture.
The results of other experiments in respect to
overyielding of mixtures of barley and oats
have been quite variable (for example Syme
and Bremner 1968, Bebawi and Naylor

1978, Taylor 1978, Fejer et al. 1982 and
Jokinen 1991 a, b).

The grain yield advantages of mixtures, es-
pecially when overyielding has occurred has
not been statistically significant in most cases.
This is partly because of the large variance
usually associated with field experiments.
Thus the failure to demonstrate an increase
in the yield of a mixture need not necessarily
mean the absence of a yield increase although
it is in many cases rather small (i.e. below the
limit of detection).

In two particular mixtures the relative yield
total was 1.07. This result suggests that these
mixtures possibly exploited the resources more
efficiently than both monocultures (Tren-
bath 1978). The deviation of relative yield to-
tal from unity may also indicate that the den-
sity used in the experiment was not the opti-
mum, as emphasized also by Trenbath

347



(1976), Connolly (1986) and HAkansson
(1988). Recently it was shown (Jokinen 1991
c) that at rather low densities the relative yield
total can be higher than at higher densities.
The reader should observe that the yields of
the small grains per area are not very sensi-
tive to the change of density close to those
used in commercial production (Kirkby 1967,
Erviö 1983). Because the objective of this
study was first to identify possible beneficial
crop combinations, a constant, near commer-
cial density was used. However, in the next
stage of the investigation, to evaluate the mix-
ture advantage thoroughly, several densities
and possibly proportions should be used.

The combination of Agneta barley and Veli
oats may be worth further investigation in
more variable environments. This is because
by now in six experiments out of seven (in-
cluding also some unpublished results) the
relative yield total of the mixture has been
higher than one at normal density and with
normally used nitrogen fertilization (80—120
kgN/ha). These results also suggest that there
might be possibilities to identify specific com-
binations of barley and oats which could ex-
ploit the environmental resources more effi-
ciently when grown in mixtures than in
monocultures without increasing the costs of
production.

Competitive ability

There were differences between the com-
petitive abilities of the barley varieties. Two
barleys, Ida and Agneta were always more
competitive than oats. Ida was a superior com-
petitor possibly because of its greatest seeds
and its earliest emergence. According to Spit-
ters (1984) differences in seedling size may
be partly due to differences in seed weight.

Although all the barley varieties started
their development earlier than oats, Aapo, the
shortest variety, was a weaker competitor than
oats at high level of nitrogen. This indicates
that oats can be even more competitive than
barley, agreeing with the results of de Wit

(1960), Syme and Bremner (1968) and Joki-
nen (1991 a).

The reduced competitive ability of Agneta
in the present experiment compared with earli-
er results at the same level of nitrogen fertili-
zation (Jokinen 1991 a, b) suggests that
Agneta might suffer from the low pH of the
soil as also discussed earlier (Jokinen 1991 c).
According to de Wit (1960), the competitive
ability of barley may even decrease with
decreasing pH, although in monoculture the
yield of barley is not significantly affected.

Although during vegetative growth it is
question of biomass production, differences
in biomass production will usually determine
also the final yield. This is because harvest in-
dex is little affected by intergenotypic compe-
tition (Spitters 1979) and yield is the product
of biomass and harvest index or the product
of growth rate, growth duration and harvest
index. Thus the final productivity of the plants
like Aapo or Agneta in mixtures is not only
determined by their initial growth but also by
their ability to cope with the free space in the
later stages of growth as shown by Spitters
and Kramer (1985).

As a rule the results of the present experi-
ment suggests that the competitive ability or
genotype predominance in a mixture is not
necessarily related to a single character of a
genotype like the initial status, plant height,
tillering capacity or yielding ability, but is de-
termined by the interaction of several plant
traits.

Yield formation and yield components

The primary yield components of the small
grain cereals develop sequentially in the order,
panicles per plant, seeds per panicle, and
weight per seed (Brinkman and Frey 1977,
Briggs 1978 p.273). However, in the present
study only the yield component analysis lead-
ing to the final yield was performed only.
Thus the collected data were too restricted for
the thorough analysis of the yield formation
occurring especially during the early part of
the growing season.

348



The reduced grain weight of Aapo grown
in the mixture may indicate that oats shaded
the shorter and later developing Aapo plants,
decreasing the photosynthesis during grain fill-
ing. Shading has been shown to affect single
grain weights (Peterson 1986). The reduced
grain weight might be also due to the deple-
tion of the limited supply of water and
nutrients. Thus the earlier developing compo-
nent like Ida in the mixture Veli or Veli in the
mixture withAapo might force the other com-
ponent to ripen earlier. Subjecting the plant
to nutrient and water stress during the criti-
cal period shortly after anthesis reduced the
number of endosperm cells and mature dry
weight commensurately (Peterson 1986).

Attention needs to be paid to the result that
in mixtures the relative importance of yield
components may be different than in
monoculture leading even to the same final
yield per plant. Thus the plants did display
phenotypic plasticity. The significance of
different yield components to yield formation
of oats and barley, whether grown in mixture
or in monoculture have been rather variable
in other experiments (for example Syme and
Bremner 1968, Taylor 1978, Jokinen 1991
a). This shows that the yield formation is a
complicated event in nature, especially if all
three yield components are to be taken up for
discussion in relation to each other and to
several growth factors. In the present study,
little informationwas available to interpret the
effect of numerous factors and their interac-
tion on dynamic a living system in which
changes occurred from germination to matu-
rity and on how resource availability might be
modified by the competitors. Such informa-
tion is really needed, as emphasized also by
Reekie and Bazzaz (1989).

Resource partitioning

The results for the behaviour of Aapo and
Veli indicate that the dominant-suppression
relationship was not always complete. At low
nitrogen, adjacent oat plants provided less in-

terference than adjacent Aapo plants when
grown alone and adjacent Aapo provided the
same interference as adjacent oats plants when
grown alone leading to the mixture advantage
by overcompensation (RYT>I, RY>O.5).
However, at high level nitrogen fertilization
when there is usually an increased competition
for the light (Tilman 1982) the mutual com-
petititon was so strong that the yield forma-
tion of Aapo was reduced and the dominant-
suppression relationship was complete
(RYT = 1). Thus, fertilization with nitrogen
led to a mixture stand which was dominated
by the species which was superior competitors
for non-nutrientresource light, agreeing with
the results of Jokinen (1991a). In natural
plant communities there will be a decline in
diversity (less coexistence) due to the enrich-
ment of the community with nutrients (Til-
man 1982).

It is also important to note that in the pres-
ent experiment the mutual competition was
weak in the case of Agneta and Veli, especially
at a high level of nitrogen fertilization instead
of low nitrogen as reported recently (Jokinen
1991 a). This may indicate the fact that the

reduced competitive ability of Agneta in the
present experiment (see section competitive
ability above) reduced competition for the
light.

As a conclusion the results suggest that the
growing oat plants used the resource pool in
different ways than the growing Aapo (or
Agneta) plants at a certain point along the
productivity gradient. This might indicate re-
source partitioning between components.
Consequently, partitioning of light intercep-
tion even under high productivity conditions
may lead to weak mutual competition and
yield advantage of a mixture. In the same
sense as two species will coexist, two crop
types will overyield if the mutual competition
is sufficiently weak (Vandermeer 1989).

Protein content and protein yield

The results of relative protein yield totals
suggest that at high nitrogen some yield ad-

349



vantage may be achieved by growing mixtures
instead of monocultures, although significant
overyielding did not occur. Benefits seem to
relate closely to the amount of grain yields of
the components whether grown in mixture or
in monoculture.

The only significant differences in respect
to protein content were found in the case of
oats especially growing with Agneta barley.
The increased protein content of oats grown
in mixture is in agreement with earlierresults
from three experiments (Jokinen unpubl.).
This was always associated with lower grain

yields of oats grown in mixtures than in
monocultures, and thus no significant advan-
tage of mixture in respect to protein yield was
achieved. Also Rao and Prasad (1987) found
that the weaker competitor in a mixture had
higher protein content than the stronger com-
petitor but the losses and gains of the protein
yields of the component cultivars were of
equal magnitude. In general, the grain protein
content in cereals is negatively correlated with
grain yield (Welch and Yong 1980,Peterson
1986).

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SELOSTUS

Eri ohralajikkeiden ja typpilannoituksen
vaikutus kauran ja ohran väliseen
kilpailuun ja seosten satoon.

Kari Jokinen

Kemira Oy. Espoon tutkimuskeskus, PL 44, 02271
Espoo

Kenttäkokeella selvitettiin, miten kolme ohralajiketta
(Aapo, Agneta ja Ida) kilpailevat saman kauralajikkeen
(Veli) kanssa kahden komponentin seoksessa, kun kas-
vuston typpilannoitusmuuttuu koemallin ollessa korvaus-
sarja. Kilpailun lisäksi tutkittin myös seoksesta saatavan
satoedun määrää.

Lajikkeen kilpailukyky oli riippumaton lajikkeen puh-
daskasvustosadon määrästä. Ohralajikkeidenkilpailukyky
vaihteli Idan ja Agnetanollessa dominoivampia kuin kau-
ra riippumatta kasvuston typpilannoituksenmäärästä (80
kgN/ha tai 120 kgN/ha). Ida oli kaikista lajikkeista do-
minoivin johtuen mitä todennäköisimmin lajikkeen no-
peimmasta alkukehityksestä. Kun seoskomponentti oli oh-
ralajikkeista lyhin Aapo, typpilannoituksenlisäys muut-
ti kilpailusuhteita kauran ollessa lievästi dominoivampi
kuin ohra.

Seoksessa tapahtuvakilpailu vaikutti suhteellisesti voi-
makkaammin versojen lukumäärään ja tähkän jyvälu-
kuun kuin jyvänpainoon osoittaen, että kilpailusuhteet
määräytyvät ja siten resurssien jakautuminen tapahtuu
jo melko aikaisessa kehitysvaiheessa. Tulokset osoittivat,
että lajikkeen yksilösato voi olla yhtä suuri seoksessa kuin
puhdaskasvustossa,mutta eri satokomponenttien suhteel-
linen merkitys voi olla kuitenkin erilainen.

Seoksen jyvä- japroteiinisato ei eronnut tilastollisesti
merkitsevästi seoksen komponenteista satoisimman kom-
ponentin puhdaskasvustosadosta.Seoksen toteutuneen ja
odotetun sadon määrän välinen suhde ja seoksen suhteel-
linen kokonaissato osoittivat, että joistakin seoksista voi-
daan saada lievää satoetua. Kasvuston genotyyppinen
koostumus vaikutti eniten kauran jyväsadonvalkuaispi-
toisuuteen.

351