J. Agronomy & Crop Science 160, 235—238 (1988)© 1988 Paul Parey Scientific Publishers, Berlin and HamburgISSN 0931-2250

Faculty of AgricultHre, University of Peradeniya, Sri Lanka

A Study on the Establishment of Tropical Grasses and Legumes

U. R. SANGAKKARA

Author's address: Dr. U. R. SANGAKKARA, Faculty of Agriculture, University of Peradeniya, Sri Lanka.

With 2 tables

Received March 19, 1987; accepted May 27, 1987

Abstract

The importance of incorporating compatible legumes into tropical grasslands has been highlighted by manyresearchers. Thus an experiment was conducted to identify optimum times of establishing tropical grasses andlegumes in mixtures. The species selected were Guinea grass (Panicum maximum)-., Brachiaria {Brachiariaruziziensis) and Green leaf (Desmodium intortum).

The grasses were established along with and 4 and 8 weeks after the legume. The growth of the species wasmonitored for 16 weeks. The results identified the importance of prior establishment of the legume toovercome the competitive dominance of the herbage grasses. The growth form of the grasses also had an effecton the success of legume establishment. The legume had no adverse effect on the growth of the grasses.

Key words: Guinea grass, Brachiaria, Desmodium Establishment, Early growth.

Introduction

The limited availability of suitable land forpastures is considered a major constraint in theexpansion of the pastoral industry of SriLanka. Thus, the land available needs to beefficiently utilised to provide high yields ofgood quality herbage. This could be attainedby incorporating tropical legumes with grassesdue to their compatibility and ability toimprove the poor quality of the native pastures(REYNOLDS 1980). In addition, these legumesprovide a longer sequence of feed productionthan grasses under tropical conditions (HUM-PHRIES 1978).

Establishment of both grasses and legumestogether presents problems due to the rela-tively slower growth of tropical legumes whencompared with the grasses, especially duringestablishment (BOGDAN 1977). This slowergrowth of the legume indices the development

of competitive dominance of the grasses. Thusa study was carried out to evaluate the earlygrowth patterns of a tropical legume whenestablished before and along with two tropicalgrasses. The principle objective was to identifyoptimum times for legume establishment toovercome the competitive dominance of gras-ses. The grasses selected were Panicum max-imum cv. Guinea grass B, an erect tuftedspecies and Brachiaria rnziziensis, a prostratecreeping grass. The legume was Desmodiumintortum cv. Green leaf, a semi erect to pro-trate species. These were selected due to theirvalue in the tropics (WHITEMAN 1960, KITA-

MURA 1983) and for the local pasture industry(PATHIRANA et al. 1980). In addition, thesespecies enabled the evaluation of the effects ofdifferent growth habits of grasses on the estab-lishment of tropical legumes, which are gener-ally prostrate species.

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236 SANGAKKARA

Methods and Materials

The experiment was conducted at the University ofPeradeniya, using a randomized block design withfour replicates.

The selected species were established in the fol-lowing manner in plots of 3 X 8 m, as recommendedby CHADHOKAR (1983).(i) Two seeds of Desmodium (germination 93 %

± 2 %) pe hill at a spacing of 45 x 20 cm.(ii) Two tiller planting sets of Guinea (dry weight

1.72 ± .16 g) between the rows ofDesmodium, at a spacing of 15 cm within the

row.(iii) Two tiller sets of Brachiaria (dry weight 0.95 ±

0.11 g) between the rows of Desmodium, at aspacing of 15 cm within the row.

The grasses were established along with, and 4 and8 weeks after, the planting of the legume seeds.Monocultures of the legume and both grasses werealso established at the time of planting Desmodium.A basal dressing of 10 : 30 : 30 N : P : K mixturewas applied at a rate of 350 kg per hectare prior tothe establishment of the legume, and the plots wereirrigated when necessary.

The time taken for 75 % of the plantedDesmodium seeds to emerge was monitored within a1 X 1 m quadrat along with the survival of estab-lished seedlings four weeks after planting. Thelegume was thereafter thinned to one plant per hill.Five plants of the legume and grass were removedfrom each plot at 6, 8, 10, 12 and 14 weeks afterplanting of the legume. The shoots were dried at80 °C for 24 hours to determine dry weights.

Analysis of variance was carried out on the dryweights of Desmodium. The dry matter accumula-

tion rates of the grasses were compared by Iinea:regression analysis based on the equation logg Y = j^+ Bx, where x and Y are weights and time respec-tively.

Results and Discussion

The successful establishment of a speciesdepends upon the interaction of many factors(BROCK 1973). Amongst the environmental fac-tors that affects establishment, the interactionof associated species play a dominant role(WHITEMAN 1980). Table 1 does not highlightany reductions in the establishment or survivalof Desmodium due to the presence of theselected grasses even when planted at similartimes. This suggests that the selected herbagegrasses do not affect the esublishment ofgrowth of the legumes at very early stages ofgrowth.

Grasses which are established from cuttingsgenerally have greater growth reserves whencompared with legume seeds. The grasses alsoshow more vigorous growth during earlystages. This enables the grass to develop acompetitive advantage over legumes andthereby dominate pastures (HAYNES 1980).Table 1 also highlights that the grasses have asignificant detrimental effect on Desmodium,even when established four weeks later. Estab-lishment of the grasses eight weeks later alsoillustrates similar effects although the resultsdo not highlight significant differences. This

Table 1. Germination, survival and shoot dry weights of D. intortum

Time ofEstablishment

A. With B. ruziziensis

8 weeks before grass4 weeks before grasswith grassmonocultureC.V. %

B. With Guinea grass

8 weeks before grasswith grassmonocultureC.V. %

Days togerminate

10a9a

11a10a5.8

11a10a10a46a

/o

Survival

929490956.5

95a92a95a9.0

6 wks

8.5a9.4a9.6a8.8a

10.4

7.9a9.1a8.8a

10.2

Shoot dry8 wks

14.6a

15.8a

12.5b

14.3a

7.6

15.2a

16.0a

14.3a

8.6

weights (g) at10 wks

24.0a

20.5a

16.7b

26.2a

12.4

25.2a

21.5a

26.2a

14.3

each harvest12 wks

39.6a

32.8b

25.7c

37.9a

11.6

41.5a

32.1b

37.9a

11.2

14 wks

47.7a

40.4b

36.7c

50.5a

98

51.5a

40.3c

50.5a

9.1

Within each column, values followed by same letter do not differ significantly P = 0.05.

A Study on the Establishment of Tropical Grasses and Legumes 237

Table 2. Dry matter accumulation rates of grasses grown in mixtures and monocultures during early growth

Species

B. ruziziensis

P. maximHm

Treatment Dry matter accumulation

MonoculturePlanted with legumePlanted 4 weeks earlierPlanted 8 weeks earlier

MonoculturePlanted with legumePlanted 4 weeks earlierPlanted 8 weeks earlier

B10211142 NS1052 NS1076 NS

12131092 NS1211 NS1264 NS

75.271.578.480.3

85.677J72.679.8

NS indicates lack of significance (P = 0.05) at growth rates between species in mixtures and monoculture.

dominant effect of the grass, even when estab-lished after the legume, could therefore beattributed to its more vigorous form ofgrowth, which enables it to develop a competi-tive dominance over the legume.

It is generally accepted that plants with simi-lar growth forms develop competitive relation-ships earlier (RHODES 1970). Thus the earlydetrimental effects imposed by Brachiaria evenwith prior establishment of Desmodium(Table 1) can be attributed to their similarprostrate forms of growth. Thus, the morerapidly growing grass competes more success-fully for environmental resources, therebyaffecting the growth of the legume. In con-trast, Guinea grass, with its upright growthhabit allows sufficient light penetration andthus the legume is affected to a lesser extent atlater stages. Thus, as reported by BOGDEN(1977) and WONG and MANNETJE (1981), theseresults highlight that Desmodium is morecompatible with grasses having as upright sta-ture than with species with a similar prostrateform of growth.

In terms of the time of establishment, thevalue of planting the legume prior to the grassin the tropics is clearly illustrated, especially asthe grasses are not affected by delayed planting(Table 2). In addition, the grasses are bestestablished vegetatively in these regions(CHADHOKAR 1983), which gives them an initialadvantage. The time interval between theestablishment of the grass and legume is thusdependent upon the growth form of thespecies.

Under practical circumstances, prior estab-lishment of legumes is recommended in thetropics, especially due to their comparativelyslower growth rates than grasses. This enablesthe successful establishment of the legume.Thus even when oversowing legumes toimprove natural grasslands, the reduction ofdominance of the grasses by cutting or lightgrazings is recommended. The importance ofremoving this dominance of grasses is stressedas competition between species during earlygrowth can have a great impact on subsequentperformance of species, even when conditionsbecome favourable to the initially suppressedspecies (ENGEL and TROUT 1977).

Zusammenfassung

Eine Untersuchung zur Ansaat tropischerGraser und Leguminosen

Die Bedeutung der Einsaat von vertraglichenLeguminosen in tropisches Grasland ist vonvielen Wissenschaftlern betont worden. Eswurde daher ein Experiment durchgefuhrt, umdie optimalen Zeiten zu bestimmen, die fur dieAnlage tropischer Graser und Leguminosen alsMischungen geeignet sind. Es wurde Guinea-Gras {Panicum maximum) sowie Brachiaria{Brachiaria ruziziensis) und Desmodium intor-tum verwendet.

Die Graser wurden zusammen mit den Le-guminosen sowie 4 und 8 Wochen spater ange-sat. Das Wachstum der Arten wurde fiir 16Wochen iiberwacht. Die Resultate zeigen, dafi

238 SANGAKKARA, A Study on the Establishment of Tropical Grasses and Legumes

es zweckmafiig ist, Leguminosen vor den Gra-sern auszusaen, um die Konkurrenzkraft derGraser zu kompensieren. Die Wachstumsformder Graser hatte ebenfalls einen Einflufi auf dieerfolgreiche Ansaat der Leguminosen. Demge-geniiber hatten die Leguminosen keine ungun-stigen Wirkungen auf das Wachstum derGraser.

Literature Cited

BoGDAN, A. V., 1977: Tropical pasture and fodderplants. Tropical Agriculture Series, Longmans.475 pp.

BROCK, J. L., 1973: Effect of sowing depth and postsowing compaction on the establishment of tallfescus varieties. N. A. Journal of ExperimentAgriculture 1, 11—14.

CHADHOKAR, P . A. , 1983: Forage development fordairy cattle in the mid country of Sri Lanka. WorldAnimal Review 48, 38—45.

ENGEL, R. E. , and J. R. TROUT, 1977: Seedlingcompetition of Kentucky Bluegrass, Red Fescus,Colonial Bent Grass and temporary grasses. Pro-ceedings of the 3rd International Turf GrassResearch Conference. Edited by BEARD, J. B.,Madison, Wisconsin, U.S.A., 379—389.

HAYNES, R. J., 1980: Competitive aspects of thegrass-legume association. Advances in Agronomy33,227—261.

HUMPHRIES, L. R. , 1978: Tropical pastures and fod-der crops. Intermediate Tropical AgricultureSeries. Longmans. 135 pp.

KrTAMURA, Y., 1983: Vegetative regrowth, noduledevelopment and N fixation of tropical legumesafter cutting. 3. Greenleaf Desmodium. Journal ofthe Japanese Society of Grassland Science 2955—58.

PATHIRANA, K. K., N . M . NUGAJIA, J.SiRlWARDENA, and A. JAYAWARDENA, 1980: For-age crop species for diversification of wet midcountry uneconomic sea lands to pasture. CeylonVeterinary Journal 28, 19—23.

REYNOLDS, S. G. , 1980: Contributions to yield,nitrogen fixation and transfer by local and exoticlegumes in tropical grass-legume mixtures in West-ern Samoa. Tropical Grasslands 16, 76—80.

RHODES, I., 1970: Competition between herbagegrasses. Herbage Abstracts 40, 115—121.

WHITEMAN, P . C , 1980: Tropical Pasture Science.Oxford University Press. U.S.A. 392 pp.

WONG, C . C , and L. T. MANNETJE, 1981: Produc-tivity and compatibility of pasture grasses andlegumes in peninsular Malaysia. MARDI ResearchBulletin 9, 1—13.