J. Agronomy & Crop Science, 156, 279—284 (1986)© 1986 Paul Parey Scientific Publishers, Berlin and HamburgISSN 0044-2151

Department of Agronomy, Massey University, Palmerston North, New Zealand

Competition between Grassesduring Establishment and Early Growth

II. Effects of Early Germinationin Determining Competition Relationships

U. R. SANGAKKARA and E. ROBERTS

Authors' addresses: Dr. U. R. SANGAKKARA, Faculty of Agriculture, University of Peradeniya,Peradeniya, Sri Lanka and Dr. E. ROBERTS, Department of Agronomy, Massey University,

Palmerston North, New Zealand.

With 4 tables

Received March 20, 1985; accepted May 20, 1985

Abstract

The effect of early germination in determining the competitive relationships between Grass-lands Nui perennial ryegrass. Grasslands Matua prairie grass and Grasslands Apanui cocksfootwas determined by making up micro swards with seedlings obtained from seeds sown at thesame time transplanted according to the replacement series principle. The results illustrated thatearly emergence had no apparent effect in determining the competitive hierarchy establishedbetween these species. The competitive relationships seem to be determined by initial seedlingsize and the capacity to accumulate greater quantities of dry matter. The species were also seento compete for similar growth resources during the establishment phase.

Key Words: competition, grasses, establishment, early growth. Relative Yield Total, RelativeCrowding Coefficient

Introduction

Many studies conducted with a range of species and in different environments havestressed the importance of early emergence in providing a distinct competitive advantage tocomponent grass species in mixtures (e.g. CHIPPENDALE 1949, BLASER et al. 1956, HARRIS

1968, KING 1971).SANGAKKARA and ROBERTS (1985) illustrated the superior competitive ability of prairie

grass and ryegrass over cocksfoot during early growth stages. As both these speciesgerminate and emerge before cocksfoot, this was considered to be a major factor contribut-ing to the competitive advantage of these more aggressive species. Thus an experiment wasdesigned to investigate the competitive relationships between these species when germina-tion and emergence phase was excluded, by using swards made up of transplanted seedlingsobtained from seed sown into trays at the same time.

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280 SANGAKKARA and ROBERTS

Material and Methods

Cultural

The experiment was conducted at the Seed Technology Centre, Massey University, duringthe period January—June 1980. The micro swards were established in boxes (30 X 30 X 18 cm).The soil used was a Tokomaru silt loam, which was passed through a 4 mm sieve to removestones. The boxes were completely filled and then left for a week to settle and topped up.

The grass species and combinations used for this study were similar to those described in theearlier paper (SANGAKKARA and ROBERTS 1985).

Seeds of the three species were germinated in plastic trays filled with perlite, in a temperaturecontrolled glasshouse (25735°C). After 21 days, the seedlings were placed outdoors near theexperimental site for two days to harden prior to planting.

The seedlings of the three species were transplanted according to the replacement seriesprinciples (DE WIT 1960). The transplanting of seedlings eliminated any advantage of earliergermination of both ryegrass and prairie grass over cocksfoot. Seedlings were planted on a gridpattern with 5 cm centres, in order to obtain an overall density of 400 plants per square metre,which was similar to the earlier study (SANGAKKARA and ROBERTS 1985). Before transplanting,the seedlings were selected for uniformity of size within a species. At the time of planting prairiegrass had the largest seedling with 2—3 leaves, while cocksfoot had the smallest, with 1—2leaves. Ryegrass seedlings had 3—4 leaves, at planting, but were smaller than prairie grassseedlings. These differences in plant sizes enabled the identifications of the importance ofseedling size as a factor affecting competition between these species.

A randomized block design with three replicated and 12 treatments was used for this study,with a box containing 30 plants making up a single treatment. Each replicate made up a blockwithin the experimental design.

The plants were watered during dry periods. A basal fertilizer dressing of 30 g of 12 : 10 : 10 :8 of N : P : K : S fertilizer was added to each box prior to planting, and 30 g of Urea (43 % N)was watered into each box after every harvest.

Measurements

The swards were harvested on four occasions at 7, 12, 16 and 20 weeks after planting. Allplants were cut to a height of 2 cm above soil level. At each harvest, the shoots of the specieswere separated and dried at 80°C for 24 hours in order to obtain dry matter production per plantand per box.

Statistical procedure

The data was analysed according to the procedures described in the earlier study (SANGAK-

KARA and ROBERTS 1985). Competitive relationships and abilities were again evaluated on thebasis of Relative Crowding Coefficients and Relative Yield Totals (RYT).

Results

Dry matter production

a) Shoots: Shoots dry weights of species in mixtures and monocultures are presented mTable 1. The results show that the growth of all species was enhanced in comparison totheir monocultures when grown with 25% of another species. This suggests that at theplant density used, intraspecific competition within monocultures was greater than inter-specific competition in the 75 % combinations. This enhanced growth of a species in its75 % mixture was least prominent in cocksfoot, when grown with prairie grass.

Prairie grass had a greater suppressive effect on the dry matter accumulation ofcocksfoot than ryegrass in its 75 % and 50% mixtures with the other species. Ryegrass hada similar effect on cocksfoot in its 75% and 50% mixtures.

Competition between Grasses during Establishment and Early Growth 281

Table 1 Mean shoot weight per plant (g) of the grown species at every harvest, when grown inmixtures and in monocultures

Species Mixture

A Ryegrass

Monoculture75R with 25P5OR with 50P25R with 75P75R with 25C50R with 50C25R with 75CSignificanceSx

B Prairie Grass

Monoculture75P with 25R50P with 50R25P with 75R75P with 25C5 OP with 50C25P with 75CSignificanceSx

C Cocksfoot

Monoculture75C with 25R50C with 50R25C with 75R75C with 25P50C with 50P25C with 75PSignificanceSx

H i

0.7430.7740.7060.6840.8210.7750.734

• *

0.009

1.4961.6341.5841.4441.7001.6291.485

• *

0.012

0.6540.6570.6200.5830.6550.6040.562

0.008

Mean shoot weightper plant (g)

H2 H3

0.688 0.6580.707 0.6760.666 0.6510.634 0.6420.720 0.6780.709 0.6710.688 0.655

** **0.004 0.009

1.293 0.9981.373 1.0311.339 1.0171.247 0.9831.374 1.0121.336 1.0081.298 0.999

** **0.004 0.007

0.648 0.6180.649 0.6170.616 0.5980.606 0.5920.647 0.6190.617 0.6050.611 0.599

0.027 0.012

H4

0.6490.6610.6440.6250.6660.6590.638

0.007

0.9060.9280.9180.9010.9370.9260.907

**0.005

0.5950.6010.5800.5700.5970.5830.571

**0.017

The more competitive species also increased dry matter production in comparison withits monoculture, when combined with less or equal proportions of the weaker species.

The weaker species had an adverse effect on the growth of the more aggressive species intheir 75% combinations with 25% of the aggressive species. This was expressed both inryegrass and to a lesser extent cocksfoot mixtures with prairie grass.

Shoot weights also illustrate that the capacity of these species to accumulate dry matterwithin a given time lies in the order or prairie grass > ryegrass > cocksfoot.

b) Total dry matter production: Dry matter production per box of the mixtures andmonocultures are presented in Table 2. Swards of prairie grass produced the highest yieldat every harvest and mixtures containing a major proportion of prairie grass out-yielded allother mixtures. The yield of cocksfoot was the lowest. The yields of all mixtures laybetween those of their respective monocultures.

J. Agronomy & Crop Science, Bd. 156, Heft 4 20

282 SANGAKKARA and ROBERTS

Table 2 Dry matter Yields (glbox)* of mixture and monocultures at each harvest

Treatment

lOOR75R25P50R 50P25R75PlOOP75P 25C50P 50C25P 75ClOOC75C 25R50C 50C25C75R

Significance

Sx

(weeks afterplanting)

7 weeks(Hi)

14.9517.9222.3424.7727.0724.3421.6917.0813.3413.8213.6214.57

2.161

Dry matter

12 weeks(H2)

11.3113.8917.3619.8221.4119.1916.9712.899.819.98

10.4810.83

*+

1.232

Yield (g/box)

16 weeks(H3)

11.0813.3116.7718.6320.5718.3816.1112.469.60

10.0010.4810.81

**

1.082

20 weeks(H4)

9.9412.5315.7017.5419.6517.6915.7811.669.069.369.569.70

+ +

1.495

* Conversion factor to g/m^ = Yield per box x 11.11

Competitive indices -

The Relative Crowding Coefficients and their products obtained from the THOMAS(1970) model are presented in Table 3. While the competitive abilities of the grasses lay inthe order of prairie grass > ryegrass > cocksfoot, the products of the Relative CrowdingCoefficients did not deviate significantly from unity. This implies that under the adopted

Table 3 Relative Crowding Coefficients and their products (RCC) of each

Pasture Mixture

Ryegrass — Prairie grass

Prairie grass — Cocksfoot

Cocksfoot — Ryegrass

Harvest Number

1.2.3.4.

1.2.3.4.

1.2.3.4.

^R0.840.750.840.95

Kp

1.241.341.241.27

^C0.870.830.880.81

harvest

RCC

Kp

1.191.331.191.05

^C0.810.740.820.79

^R1.161.211.131.15

Kp X Kp

0.99960.99750.99960.9975

KpxK^

1.00410.99161.01611.0033

K^^xKj^

1.00931.00430.99441.0005

and K^ and the RCC's of ryegrass, prairie grass and cocksfoot respectively)

Competition between Grasses during Establishment and Early Growth 283

Table 4 Relative Yield totals based on shoot weight per plant

Species Combination Wk7 (Hi) Wk 12 (H2) Wkl6(H3) Wk 20 (H4)

Ryegrass - Prairie grass 1.005 + .003 0.996 ± .002 1.005 ± .002 0.999 ± .003

Prairie grass - Cocksfoot 1.001 ± .002 0.998 ± .003 0.997 ± .002 0.999 ± .002

Cocksfoot - Ryegrass 0.996 ± .004 0.994 ± .003 0.995 + .001 0.995 ± .003

experimental conditions, these species compete for the same "biological space" (DE WIT1960).

The Relative Yield Totals (Table 4) calculated according to the method of MCGILCHRIST

and TRENBATH (1971) also illustrate similar competitive relationships, as they do not deviatesignificantly from unity.

Discussion

The results of this experiment using seedlings of the same age are similar to those of theearlier experiment conducted with swards established from seed (SANGAKKARA and ROBERTS

1985). The dominant effect of prairie grass over ryegrass and cocksfoot is illustrated by theshoot weights and Relative Crowding Coefficients. A similar effect of ryegrass oncocksfoot is also observed. Thus the absence of the effect of earlier emergence of bothprairie grass and ryegrass over cocksfoot does not seem to have made an impact on thecompetitive hierarchy established between these species.

An initially large seedling size and the ability to accumulate dry matter at a faster rateensures the success of a species, by obtaining a greater share of the environment in terms ofgrowth requirements. The greater volume occupied by the larger seedling gives it a greatercapacity to exploit its surroundings, thereby depriving the smaller species. The results ofthis study presents such a situation where both prairie grass and ryegrass seedlings arebigger than cocksfoot. Thus competitive superiority of these grasses can be attributed totheir size and ability to accumulate a greater quantity of dry matter, rather than to anyadvantage they may possess by earlier emergence.

The unimportance of early emergence in determining the competitive relationshipbetween these species is also examplified by the competitive superiority of prairie grassover ryegrass. TRENBATH et al. (1977) stated that later emerging species may offset thisdisadvantage by being more efficient in obtaining growth resources from the environmentif they have a larger seedling and more rapid growth rates. As prairie grass shows thesecharacteristics, its competitive advantage over ryegrass can be attributed to its plant sizeand capacity to accumulate dry matter.

These species generally compete for the same environmental resources, as illustrated bythe RYTs and products of the Relative Crowding Coefficients, which is in agreement withearlier published research. The yields also lie between the respective monoculture yields,thus conforming to the general trend (VANDENBERGH 1968, TRENBATH 1974, 1978).

The results illustrated a decline in both yields with successive harvests (Table 2), whichmay have resulted from the limited size of the soil environment available for root growth.This could have effected normal root growth, thereby affecting the shoot system, as thereis a direct relationship between root and shoot growth in pasture species (DAVIDSON 1978).The decline in yield over time could also be attributed to the reduction in the ambienttemperature and light intensity over the experimental period as the study was carriedoutdoors from mid-summer to early winter.

20==-

284 SANGAKKARA and ROBERTS, Competition between Grasses during Establishment

Zusammenfassung

Konkurrenz zwischen Grasern wahrend des Auflaufens und des Jugendwachstums

II. Bedeutung einer friihen Keimung fur die Konkurrenzbeziehungen

Der EinflufJ der friihen Keimung auf Konkurrenzbeziehungen zwischen ,,GrasslandsNui" deutschem Weidelgras, „Grasslands Matua" Prariegras und „Grasslands Apanui"Hiihnerhirse wurde durch die Anlage von Mikro-Narben mit Samlingen, die zur gleichenZeit ausgesat und umgepflanzt wurden, untersucht. Die Ergebnisse zeigen, dafi ein friihesKeimen keinen offensichtlichen EinflufJ auf die Konkurrenzhierarchie zwischen den Artenhatte. Die Konkurrenzbeziehungen scheinen durch die urspriingliche Samlingsgrofie unddie Kapazitat, groftere Mengen an Trockenmasse zu bilden, gekennzeichnet zu sein. DieAnen schienen ferner wahrend des ersten Wachstums um die gleichen Wachstumsfaktorenzu konkurrieren.

Acknowledgements

Gratitude is expressed to Professor B. R. WATKIN for valuable guidance. Dr. M. J. HILL forproviding space for this study and to Mr. G. C. ARNOLD and Dr. V. J. THOMAS for advice andassistance with statistical analysis. Mr. J. B. WALISUNDERA typed the manuscript and associateddocuments.

References

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CHIPPENDALE, H . G., 1949: Environment and germination of grass seeds. Journal of the BritishGrasslands Society 4, 57—61.

DAVIDSON, R. L., 1978: Root systems — the forgotten component of pastures. In: J. R. WILSON(Ed.), Plant relations in pastures. CSIRO, Melbourne, p 86—94.

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