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Performance of associations of Brachiaria ruziziensis with Desmodium intortum, Desmodium uncinatum and Stylosanthes guianensis at Dschang, Cameroon

R M Njwe, N D Donfack, J. Djoukam and H N L Endeley

Department of Animal Science
Institut national de développement rural
University Centre of Dschang
BP 222, Dschang, Cameroon

ABSTRACT

The chemical composition, total dry-matter and crude-protein yield, and the grass/legume ratio, were evaluated in a trial involving Brachiaria ruziziensis planted alone or in associations with the legumes Desmodium uncinatum, D. intortum and Stylosanthes guianensis. Plots were cut back after a regrowth interval of two months. Results indicated significant increases in yields of total dry matter (388-524%) and crude protein (403-1012%) from grass/legume treatments over sole plots of B. ruziziensis. The proportion of legume dry matter in grass/legume mixtures ranged from 25 to 38%. The crude-protein contents of B. ruziziensis from mixed grass/legume treatments and from sole plots were not significantly different. Mixtures of B. ruziziensis with D. intortum and D. uncinatum were outstanding in total dry-matter and crude-protein yield.

RESUME

Performances de cultures associées de Brachiaria ruziziensis avec Desmodium intortum, Desmodium uncinatum et Stylosanthes guianensis à Dschang (Cameroun)

La composition chimique, la teneur en matière sèche, le taux de protéines brutes et le rapport graminées/légumineuses ont été déterminés dans un essai réalisé sur Brachiaria ruziziensis en culture pure ou en association avec les légumineuses Desmodium uncinatum, D. intortum et Stylosanthes guianensis. L'intervalle entre coupes était de deux mois. Il ressort des résultats enregistrés que les rendements en matière sèche (entre 388 et 524%) et les taux de protéines brutes (entre 403 et 1012%) étaient plus élevés sur les parcelles à association graminées-légumineuses que sur les parcelles à B. ruziziensis en culture pure. La part des légumineuses dans la matière sèche des mélanges graminées-légumineuses variait de 25 à 38%. La teneur en protéines brutes de B. ruziziensis n'était pas significativement différente entre les parcelles de cultures associées et celles de culture pure. Les rendements en matière sèche et la teneur en protéines brutes des mélanges de B. ruziziensis avec D. intortum et D. uncinatum étaient exceptionnellement élevés.

INTRODUCTION

The high nitrogen content of leguminous species contributes to improving the nutritional quality of the diet of grazing ruminants. The presence of legumes in pasture also increases the nitrogen content of grass species through subterranean absorption from leguminous roots. Moore (1962) reported that the nitrogen content of young Cynodon plectostachyus plants increased from 1.8 to 2.4% in association with Centrosema pubescens while Jones et al (1967) also reported increases in nitrogen content of Paspalum plicatulum from 0.8 to 1% and 1.2 to 1.4% when associated with Macroptilium atropurpureum and Lotononia bainesii.

It has also been observed that association of legumes with grass species tends to increase total dry-matter yield per hectare. Whitney and Green (1969) reported that association of Digitaria decumbens with Desmodium canum and Desmodium intortum resulted in dramatic increases in total dry-matter and crude-protein yields.

The objective of this study was to determine the effect of associating Brachiaria ruziziensis with Desmodium intortum, D. uncinatum or Stylosanthes guianensis on total dry-matter and crude-protein yield, grass to legume ratio and nitrogen content of B. ruziziensis.

MATERIALS AND METHODS

The study was carried out at the University Centre of Dschang, Cameroon (altitude about 1500 m). Climatic data for Dschang are given in Table 1.

Brachiaria ruziziensis was planted in sole stand or with a legume, Stylosanthes guianensis, Desmodium intortum or D. uncinatum, in a randomised complete block design having four treatments and five replicates. The size of each plot was 6 x 4 m, and all plots were separated by a 1-m wide path.

Drills of B. ruziziensis were alternated with those of leguminous species at a spacing of 1 m. After planting the plants were allowed to establish and completely cover the soil surface before data collection commenced. All plots were cut back and allowed a regrowth period of 60 days before they were harvested for data collection. The cutting height was 10 cm. Only the central 2 m² area was harvested to avoid border effects. After harvest of each plot, the total fresh weight of forage and of the B. ruziziensis and legume fractions were determined. Samples (500 g) of fresh forage were collected for laboratory chemical analysis to determine contents of dry matter, ash, crude protein, crude fibre, ether extracts and nitrogen-free extracts. The data obtained were statistically analysed using the procedures of Steel and Torie (198.0) for analysis of variance; differences between treatments were determined using the Duncan's multiple range test.

Table 1. Rainfall and mean temperatures at Dschang, Cameroon (1500 m altitude), 1989

Mouth

Number of rainy days

Monthly rainfall (mm)

Temperatures (°C)

Minimum

Maximum

Average

January

2

9

11.5

27.0

19.3

February

0

0

13.1

28.6

20.8

March

11

133

15.3

28.4

21.8

April

18

126

16.4

26.7

215

May

18

173

16.0

25.7

20.8

June

22

286

15.7

24.8

20.2

July

23

168

15.7

23.4

195

August

27

278

15.7

23.7

19.6

September

24

321

15.7

24.9

203

October

20

140

15.5

25.4

20.4

November

6

20

14.7

265

20.6

December

1

11

13.7

27.0

20.3

Total

172

1655




RESULTS

The effect of associating B. ruziziensis with various legume species on dry-matter yield is indicated in Table 2. Dry-matter yield of B. ruziziensis was significantly (P<0.05) higher in associations with legume species than in sole plantings. The dry-matter yield of B. ruziziensis was higher (P<0.05) when associated with D. uncinatum than with either D. intortum or S. guianensis. There were differences (P<0.05) in the proportions of the legumes in the mixtures, S. guianensis being the most abundant.

The presence of legumes in plots plants with B. ruziziensis boosted total dry-matter production by up to 524%.

Table 3 shows the effect of legumes on total crude-protein yield and crude-protein content of B. ruziziensis. Total crude-protein yields from grass-legume mixtures were significantly (P<0.01) higher than from sole grass plots, and plots with D. uncinatum yielded significantly (P<0.05) more crude protein than plots with the other two legumes.

Table 2. Effect of association of Brachiaria ruziziensis with legumes species on dry-matter yield

Treatment

Grass DM (kg/ha)

% Grass

Legume DM (kg/ha)

% Legume

Total DM (kg/ha)

% Increase in DM yield compared to control

Mean

SE

Mean

SE

Mean

SE

Mean

SE

Mean

SE

Mean

SE

B. ruziziensis (control)

1792

221

100

-

-

-

-

-

1 792

221

-

-

B. ruziziensis + D. intortum

6918

116

67.6

8.5

3316

96

32.4

6.9

10 234

1956

471

51

B. ruziziensis + D. uncinatum

8426

894

75.3

11.3

2764

265

24.7

8.6

11 190

1221

524

63

B. ruziziensis + S. guianensis

5373

769

61.5

5.9

3365

315

38.5

5.9

8 738

999

388

38

Differences between crude-protein content of B. ruziziensis from control plots and from plots with legumes were not significant.

DISCUSSION

The higher total dry-matter and crude-protein yields from mixtures of legumes with B. ruziziensis than from grass monocultures agree with work by Whitney and Green (1969) who found similar yield improvements in work on Digitaria decumbens associated with Desmodium intortum and Desmodium canum. The increase of crude-protein yield may be attributed to the nitrogen-fixing ability of legumes, and the effects this has on nitrogen content of associated grass species.

The presence of legumes in pastures has two important beneficial effects. First, it reduces the need to provide nitrogen supplements to grazing ruminants. And second, the nitrogen-fixing capacity of legumes in pastures offers a cheaper alternative to expensive nitrogenous fertilisers. However, the supply of seed material may constitute an important constraint that needs to be overcome.

Contrary to observations by Moore (1962), Jones et al (1967) and Birch and Dougall (1967) that the N content of grass increased when planted in association with legumes, the present study did not find significant differences in N content of B. ruziziensis in monoculture or mixed with legumes. This is probably a reflection of late harvest of forages, at the stage of seeding, when reserves of nitrogen in roots, stems and leaves have been mobilised for seed production. Harvesting earlier, especially before flowering, may provide a more meaningful assessment of the effect of legume mixture on grass nitrogen content.

Table 3. Effect of association of Brachiaria ruziziensis with legumes on the crude-protein content of the grasses and average crude-protein yield of plots

Treatment

Crude-protein yield (kg/ha)

% increase compared to control

Crude protein content of B. ruziziensis (%)

Mean

SE

Mean

SE

Mean

SE

B. ruziziensis (control)

113

17

-

-

6.30

0.45

B. ruziziensis + D. intortum

851

250

468

78

5.38

0.41

B. ruziziensis + D. uncinatum

1166

204

777

103

7.08

1.04

B ruziziensis + S. guianensis

754

142

408

88

5.62

0.24

CONCLUSIONS

The contribution of legumes to improving the crude-protein yield of pasture is evident This greatly improves the quality and quantity of the ruminant diet during the dry season when the nutritional quality of grasses is poor. Different intervals of cuffing need to be investigated to determine the optimal time for harvesting grass-legume mixtures for feeding to ruminant livestock. The introduction of legumes to pastures and fanning systems is one of the cheapest ways by which the poor countries of the world can sustain soil fertility. This will obviously have a positive impact on ruminant productivity.

REFERENCES

Birch H F and Dougall H W. 1967. Effect of legume on soil erosion and percentage nitrogen in grasses. Plant and Soil 27:292-296.

Jones R J. Davies J G and Whaite R B. 1967. The production and persistence of grazed irrigated pasture in South Eastern Queensland. Australian Journal of Experimental Agriculture and Animal Husbandry 8:117-189.

Moore A W. 1962. The influence of a legume on soil fertility under a grazed tropical pasture. Empire Journal of Experimental Agriculture 30:239-248.

Steel R G D and Torie J H. 1980. Principles and procedures of statistics: A biometrical approach. 2nd edition. McGraw-Hill, New York, USA. 633 pp.

Whitney A S and Green R E. 1969. Legume contribution to yields and compositions of Desmodium spp/Pangola grass mixtures. Agronomy Journal 61:741-745.


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