E.N. Sabiiti
Crop Science Department, Faculty of Agriculture and Forestry, Makerere University
P.O. Box 7062, Kampala, Uganda
P.R. Henderlong
Agronomy Department, Ohio State University
Columbus, Ohio 43210, U.S.A.
J.S. Mugerwa
Animal Science Department, Faculty of Agriculture and Forestry, Makerere University
P.O. Box 7062, Kampala, Uganda
Introduction
Materials and methods
Methodology
Results
Discussion
Acknowledgements
References
Abstract
The natural grasslands of Uganda comprise about 80% of the total land area and are regarded as a national asset because they support nearly 99% of Uganda's livestock and game animals. They contain numerous indigenous forage species which have not been developed to increase the productivity of these grasslands which is below their potential.
The objective of the study was to evaluate a local forage legume (Desmodium adscendens [Sw.] DC) when planted vegetatively in ley and natural pastures.
The results indicated that D. adscendens established well when vegetatively planted in ley and natural pastures. However, it was more successful in ley than in natural pastures. The legume has a high potential for dry-matter yield, % crude protein and N2 fixation. D. adscendens exhibited remarkable persistence.
It is, thus, suggested that more detailed studies using an interdisciplinary approach be conducted to determine the contribution of the legume to pasture productivity, animal production, soil fertility and subsequent crop yield.
The natural grasslands of Uganda comprise about 80% of the total land area (Horrell and Tiley, 1970) and are regarded as a national asset because they support nearly 99% of Uganda's livestock and game animals. Unfortunately, the productivity of these grasslands in terms of herbage quality and quantity and animal production is extremely below their potential. For example, estimated milk production per cow ranges from 400-600 litres in a six- to seven-month lactation period, and this is considerably below that of cows grazing improved grass/legume pastures. Even the ley pastures which constitute a small proportion of the natural pastures are below their potential.
Their potential could be increased by incorporating forage legumes such as Stylosanthes gracilis, Desmodium intortum, D. uncinatum, Centrosema pubescens, Macroptilium atropurpureum, Medicago sativa and Indigofera hirsuta (Stobbs, 1969a b; Otim, 1973; Horrell and Court, 1965; Mugerwa, unpublished; Sabiiti, 1979; UNDP/FAO, 1973).
However, one of the major constraints in the improvement of pastures has long been the consistent lack of pasture seeds (both legumes and grasses). Nearly all the pasture seeds are imported and are very expensive (about 5,000/= per kg of legume seed) and are still scarce in the country. The situation was further aggravated by political instability in the last 15 years or so and nearly all the pasture germplasm is confined to research stations or has disintegrated as at Kabanyolo Makerere University Farm. Furthermore, there is evidence to show that most of the recommended forage legumes fail to combine both productivity and persistence for a long time under various pasture management practices and ecological zones (Sabiiti, 1979).
To overcome some of the above constraints, it is important to evaluate local pasture species, especially legumes before they are extinct under the current rapid environmental degradation in the country. The need to develop local pasture species has long been emphasised by Henderlong (1973) and others.
One of the forage legumes which we have identified is Desmodium adscendens (Sw.) DC. It has been observed to grow well in the Lake Victoria crescent region of high rainfall (1000-1500 mm/annum). The crescent region is important for dairy farming but there is scarcity of legumes on these farms. The legume appears to be grazed by livestock and game animals, especially during the dry season when the grasses are very dry. It roots at the nodes, and it could be established vegetatively to reduce the dependence on importation of expensive seeds. This method has been used successfully in Kenya to establish D. intortum and D. uncinatum (exotic species) by Keya et al. (1971). However, there is no data on this aspect. The legume makes excellent fodder and could be used as a soil cover and green manure. In Indo-China, Malaysia, East and South Africa, it is planted in tea and coffee plantations as a cover and for green manure.
However, no work has been done on this legume here to determine its contribution to pasture productivity. The objectives of the study were to determine a method of establishment, assess dry-matter yield, feeding value (CP) and persistence of D. adscendens under various management practices.
Study Area Description
The first study (under planted pastures) was conducted at Kabanyolo Makerere University Farm. Kabanyolo is in the fertile lake crescent area, 19 km north of Kampala (0°28'N, 32°37'E, 1,200 m.a.s.l.). The upland soils of Kabanyolo are classified as Latosols, or ferrallitic soils. They are deep, highly drained red soils. The pH varies from 5.0-5.8 (Mohiddin and Mukiibi, unpublished; Reid et al., 1973) with a very low level of phosphorus (4 ppm P Truog), medium potassium (18 mg/100 g) and ample organic matter (3.1%) (Olsen and Moe, 1971).
The area has a moist tropical climate with mean maximum temperatures varying from 28.5°C in January to 26.0°C in July and minimum temperatures from 17.4°C in April to 15.9°C in July and August. Mean annual rainfall is about 1,300 mm, with two peaks in April and November and two periods of low rainfall in January and July when the monthly mean drops to 60 mm.
The second study (under natural pasture conditions) was conducted at Buwambo, 24 km north of Kampala (0°35'N, 32 34'E, 1300 m.a.s.l.). The soils and climate of the area are similar to those of Kabanyolo. The vegetation is dominated by a natural low medium tropical deciduous forest and abundant elephant grass (P. purpureum) in areas that have been cleared. Other important vegetation include perennial shrubs, native pasture legumes; D. adscendens being the dominant one followed by Neonotonia wightii and grass species Cymbopogon, Imperata, Digitaria, Panicum and Brachiaria. The area is commonly grazed by cows, goats and sheep.
Study I: Evaluation of D. adscendens under planted pastures
Mature stem cuttings (15 cm long) were planted at a spacing of 0.5 x 0.5 m into an established pasture of Chloris gayana Kunth., Cynodon dactylon Linn., and Brachiaria brizantha at Kabanyolo University Farm. The stem cuttings were collected from Buwambo, 24 km north of Kampala where the legume grows naturally in a mixture of P. purpureum, Brachiaria spp., Hyparrhenia spp., Imperata cylindrica and Panicum spp. They were planted into holes of about 7 cm deep and firmed with the soil. The pasture paddock was divided into four plots (10 x 10 m) each and were excluded from grazing for ten months. Planting was done during the long rainy season in March in 1979 to ensure maximum establishment. Before planting, single superphosphate at the rate of 250 kg/ha was broadcast onto the plots to promote legume root growth (Olsen and Moe, 1971).
Establishment
Observations on the establishment of the legume were made after three and six months from planting because after that the senior author left the University. The total number of cuttings which had sprouted were determined.
Dry-Matter Yield, Crude Protein and Persistence
These parameters were determined in 1986 following the senior author's appointment at the University. However, the paddock had been grazed several times in the past but no observations were made. Conventional methods for herbage sampling of the old plots and dry-matter estimation were used. Crude protein content was determined by the Marcro-Kjeldhal method (AOAC, 1965).
Study II: Evaluation of D. adscendens under natural pastures
Four plots (10 x 10 m) were randomly located at Buwambo, where the legume grows naturally. Mature stem cuttings of 15 cm long were planted onto a natural pasture dominated by B. brizantha, I. cylindrica, H. rufa and P. maximum. Any existing legume was removed before planting. The cuttings (one cutting/hole) at a spacing of 0.5 x 0.5 m were planted in March 1979 during the rainy season to ensure maximum growth. There was no application of single superphosphate fertilizers.
Establishment
Observations on establishment of the legume were made after three and six months from planting because of similar reasons as in the above.
Dry-Matter Yield, % CP and Persistence
These were determined in 1986 from the old plots. Similar sampling methods and dry-matter estimation and crude protein content analysis were used as above. A 't' test was used to compare the treatment means of the two types of pastures as outlined by Zar (1984).
Establishment of D. adscendens in Ley and Natural Pastures
The results in Table 1 show that D. adscendens was successfully established through vegetative propagation under both pastures (fey and natural); however, a significantly (P<0.05) higher percentage of establishment was obtained under ley pastures. This is expected because of the excellent seedbed conditions obtained in this method.
The cuttings started producing shoots after three weeks from planting and by the fourth month most of the plants were fully established with many leafy shoots (5-10 shoots/plant). Growth was vigorous but especially under ley pastures. Unfortunately there were no further observations on the performance of these plants after 1979 because the senior author left Makerere University after completing his M.Sc. research programme.
Persistence
The legume has persisted very well both at Kabanyolo and in Buwambo under grazing, nearly eight years from planting. D. adscendens is more abundant in nearly all the paddocks at Kabanyolo than the introduced forage legumes mentioned in the introduction. The same observation is true under natural pastures. The legume has spread over large areas where it was not abundant before. Also the legume modulates profusely without inoculation, especially under ley pastures so it could be fixing N2 as most of the nodules exhibited red pigment when cut open. The legume is prostrate and this makes it better adapted to grazing conditions.
Table 1. Total number and percentage of vegetatively established plants of D. adscendens in ley pastures at Kabanyolo Makerere University Farm (A) and at Buwambo (B) in 1979.
|
Site |
Plot |
Number of established plants |
% Establishment |
|
A |
C |
360 |
90.0 |
|
D |
360 |
90.0 |
|
|
E |
350 |
87.5 |
|
|
F |
370 |
92.5 |
|
|
Mean |
|
360 ± 8 |
90.0 ± 2 |
|
B |
G |
265 |
66.3 |
|
H |
258 |
64.5 |
|
|
I |
300 |
75.0 |
|
|
J |
290 |
72.5 |
|
|
Mean |
|
278.3 ± 20 |
69.6 ± 5 |
't' - test
P<0.05
± SD, n=4.
Dry-Matter Yield and % Crude Protein
It is clear from Table 2 that D. adscendens has a high potential of productivity in terms of DM yield (2830 and 1620 kg/ha) and % CP (22.5 and 17.8) in ley and natural pastures, respectively. The plants under ley pastures produced significantly (P<0.05) higher DM yield and % CP. These are two of the major indices for evaluating a new cultivar.
Table 2. Total DM yield (kg/m²) and % crude protein of D. adscendens collected from ley pastures at Kabanyolo Makerere University Farm (A) and from natural pastures at Buwambo (B) in 1986.
|
Site |
Plot |
DM yield kg/m² |
% CP |
|
A |
1 |
.218 |
21.5 |
|
2 |
.258 |
21.8 |
|
|
3 |
.357 |
24.3 |
|
|
4 |
.300 |
22.4 |
|
|
Mean |
|
.283 ± 0.06 |
22.5 ± 1.3 |
|
B |
1 |
.146 |
15.8 |
|
2 |
.178 |
18.5 |
|
|
3 |
.190 |
19.4 |
|
|
4 |
.135 |
17.6 |
|
|
Mean |
|
.162 ± 0.03 |
17.8 ± 1.5 |
't' - test
P<0.05;
± SD, n=4.
The plants under natural conditions mainly suffered from severe competition from shrubs, trees and tall grasses of Hyparrhenia spp., P. purpureum and I. cylindrica. Management under natural pastures would require removal of tall species and topping of the existing vegetation to reduce shading and competition.
The genus Desmodium has about 200 species (perennial or annual) which occur in temperate and tropical regions where they are used for grazing (Whyte et al., 1953). Unfortunately, only two species (D. intortum and D. uncinatum) have been studied in detail in Uganda (Mugerwa, unpublished; Otim, 1973; Olsen, 1973; Reid et al., 1973; Olsen and Moe, 1971; Ochodomuge, 1978). This is also true for other countries (see Kategile, 1984; Anon, 1985). Even then the success of these two legumes in pastures in Uganda has been limited by lack of sufficient pasture seed and other limitations which have been reviewed by Sabiiti (1979).
Therefore, the results we have reported on D. adscendens are promising in that we can reduce dependence on imported seeds of exotic species and rely on a local legume species that establishes well by vegetative propagation and has a high potential for DM yield and % CP. It has shown admirable persistence in both ley and natural pastures under grazing conditions. However, we do not know the stocking rate and frequency of grazing that were used because no records were made. The legume appears to be dispersed by animals through either the seeds which stick on their skins and are dropped or by the broken stems which get trapped between the hoof and are later dropped in other paddocks. Also humans could have assisted in the spread of the legume on the farm.
The profuse natural nodulation of the legume might be important in increasing pasture productivity, soil fertility- and subsequent crop yields. Currently, we have no published data on D. adscendens in East Africa to compare with although Keya et al. (1971) have shown that other Desmodium species were easily established from root splits (40-80%). In South America, Lazier unpublished did not clearly indicate how the legume was established. In Taiwan, Byran (1969) successfully established D. intortum and D. uncinatum by planting individual splits.
Since D. adscendens occurs abundantly in the regions that are important for dairy industry in Uganda, farmers should be encouraged to collect and plant the legume in their paddocks and then apply single superphosphate to encourage root formation and growth. The early establishment and higher survival rate in ley pastures were partly attributed to single superphosphate. Once the plants have established, they form several prostrate shoots which grow rapidly, and these can again be used to plant in other paddocks.
Future Research
Our present data are not yet conclusive and since there is little information on this important legume, there is a need to investigate further other indices of evaluation, namely, response to defoliation (mechanical or biological), regrowth physiology to understand mechanisms of persistence, nutrient analyses, digestibility studies, grazing trials, (voluntary intake) and animal production (live weight gain or milk production), N2 fixation and soil fertility and crop production from pastures previously planted to D. adscendens.
Our current evaluation programme of D. adscendens at the University Farm is geared towards the above studies using an interdisciplinary approach. We have got soil scientists microbiologists, animal nutritionists, agronomists and physiologists because we believe we can achieve great success in a short time.
We wish to acknowledge Dr. B. Dzowela (PANESA Coordinator) for inviting the senior author to participate in the PANESA Workshop. Professor J.L. Parsons, USAID Project Team Leader in the Faculty of Agriculture and Forestry, is thanked for securing a USAID grant to the senior author to travel to Kenya where he met Dr. Dzowela. The Secretary, Sam Mubiru of Crop Science Department, is thanked for typing the manuscript.
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