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Adoption of the rhizobium inoculation technology for pasture improvement in sub-Saharan Africa

Douglas J. Khonje
Soil Microbiologist,
Department of Agricultural Research,
Chitedze Agricultural Research Station,
P. O. Box 158, Lilongwe, Malawi


Abstract
Introduction
Rationale for using rhizobium inoculants
Benefits from inoculation with Rhizobium spp
Importance of effectively nodulated pasture legumes
Rhizobium inoculant demand
Constraints to adopting inoculants for pasture improvement
Conclusions and recommendations
References

Abstract

The production of high quality livestock and livestock products depends on adequate and nutritious pastures. Such good pastures need to be cheaply produced by incorporation of legumes instead of using large quantities of expensive nitrogen fertilizers. In most sub-Saharan Africa the potential of such pastures is high. However, for proper establishment legumes should be inoculated with an appropriate Rhizobium inoculant. A major constraint to exploiting the Rhizobium inoculation technology is that most farmers are not aware of the technology and its benefits. Efforts should be made to increase farmer awareness and appreciation of the technology through a multi-disciplinary team approach.

Introduction

In most countries of sub-Saharan Africa food and cash crops such as maize, groundnuts, cassava, cotton and tobacco are among the major crops dominating agricultural production. However, the cropping system under most smallholder conditions in this region includes livestock production.

Livestock production relies upon pastures which need to be both highly productive and nutritive. In order to produce high yields of high quality dry matter, large amounts of nitrogen fertilizers are needed. Nitrogen fertilizers are available in most countries of sub-Saharan Africa. However, the cost of such fertilizers is very pohibitive to most smallholder farmers. For example in Malawi, over the past ten years, the price of the three most commonly used nitrogen fertilizers: compound 20-20-0, calcium ammonium nitrate, and sulphate of ammonia has increased by 253%, 255% and 391% respectively. On the other hand, prices of livestock products at the farm gate have not changed equally to warrant use of expensive nitrogen inputs on pastures. Consequently, very few farmers use nitrogen fertilizers on their pastures.

An alternative to the expensive inorganic nitrogen fertilizers is to incorporate legumes and apply the nitrogen fixing bacterium Rhizobium spp. This technology is not a new concept in sub-Saharan Africa (Haque and Jutzi, 1984; Haque et al, 1988; Savory, 1972; Thomas, 1973; Thomas and Addy, 1977).

To successfully adopt use of Rhizobium inoculants in pasture improvement, it is essential that legume varieties suitable for the target ecological zone be identified and matched with appropriate Rhizobia for optimum nitrogen fixation. The inoculation technology itself need to be simple enough both in scope and means of application.

Undoubtedly the use of pasture legumes is not at the same level nor uniform all over sub-Saharan Africa. Consequently any attempt to describe in detail the situation in each country in a paper of this nature would be futile. Therefore this paper mainly describes the Rhizobium inoculation technology in Halawi as an example of exploiting the Rhizobium-legume symbiosis in pasture improvement in sub-Saharan Africa. Wherever possible, examples from other countries in the region are also given. Prospects and constraints to adoption of the inoculant technology and possible solutions are discussed.

Rationale for using rhizobium inoculants

Biological nitrogen fixation is a natural process whereby atmospheric nitrogen is reduced to ammonia. In legume, this system operates in the root nodules formed by the nitrogen fixing Rhizobium spp. In most natural ecosystems, heavy losses of nitrogen occur due to crop uptake, leaching, erosion, denitrification etc. However, significant replenishment of nitrogen occurs in most soils mainly due to biological nitrogen fixation (Hardarson et al. 1987).

Nitrogen provided in this form is not only cheap but also does not impart other undesirable aspects such as pollution hazards due to heavy use of inorganic nitrogen fertilizers. In addition, inoculation of seeds, plants and soil with Rhizobium is even simpler than applying correct doses of inorganic nitrogen fertilizers such as urea or diammonium phosphate.

The inoculation of legume seeds with Rhizobium has been practiced in agriculture for several decades. The mixture of Rhizobium cells and a carrier e.g. peat, filter-mud, bagasse etc is what constitutes the Rhizobium inoculant (Okon and Hardy, 1983). If inoculants are properly used, significant amounts of nitrogen could be fixed. Due to problems in measuring exact quantities of nitrogen fixed, only estimates could be made. The validity of such estimates strongly depends on the method used to estimate nitrogen fixation. Table 1 shows some estimates of nitrogen fixed by some grain and forage legumes. It can be noted that forage legumes fix larger amounts than grain legumes. This is probably a reflection of the duration of the crop: most grain legumes are annuals while most forage legumes are perennials. Comparable data for nitrogen fixation by forage legumes in sub-Saharan Africa are shown in Table 2. With such high amounts of nitrogen provided in a cheap way, it is imperative that exploitation of this natural system be encouraged.

Pasture improvement offers an excellent opportunity for exploiting biological nitrogen fixation in sub-Saharan Africa. Many pasture legumes in addition to providing their own nitrogen for good growth are also rich in protein and highly nutritious to livestock (Sprague, 1975). Use of nitrogen fertilizers on pastures faces strong competition from the demand of nitrogen fertilizers by cereals which provide the bulk of staple food for most people in sub-Saharan Africa. As such, any advocation of applying nitrogen fertilizers to pastures is already a skeptical idea to the smallholder farmer. Thus promotion of using inoculants on pasture legumes in both pure and mixed legume-grass swards seems logical.

Table 1. Estimates of nitrogen fixation by grain and forage legumes.

Legume species

Maximum fixation (kg/ha/year)

A. Grain legumes


Arachis hypogaea

124


Cajanus cajan

280


Canavalia ensirforis

49


Cyanopsis tetragonoloba

220


Glycine max

180


Lupinus spp.

208


Phaseolus aureus (green gram)

342


P. aureus (mung bean)

61


P. vulgaris

64


Pisum sativum

85


Vicia faba

552


Vigna sinensis

354

B. Forage legumes:


Calapogonium muconoides

450


Centrosema pubescens

395


Desmodium unicnatum**

178


Lespedeza spp

193


Leucaena leucocephala*

580


Lotus corniculatus

116


Medicago sativa

463


Melilotus alba

183


Stylosanthes spp

220


Trifolium spp

673


Vicia villosa

184

Source: Adapted from Hardason et al (1987)
* Data reported by Guevarra (1976) quoted by Sanginga
** Data reported by Haque and Jutzi (1984)

Table 2. Some values of Nitrogen fixation in sub-Saharan Africa

Region

Rainfall (mm)

Legume

Nitrogen fixed (kg/ha)

Nigeria (rainforest)

1,143

Centrosema pubescens

280

Nigeria (savanna)

1,085

Stylosanthes guyanensis)

84

Uganda

>1,143

Centrosema pubescens

161

(tropical, subhumid)


Stylosanthes guyanensis


Kenya (W. Province)

1,111

Desmodium uncinatum

178

Zimbabwe
(high rainfall sandveld)

908

Lotononis bainesii

62

Tanzania*

ND

Leucaena leucocephala

110

Malawi*

ND

Stylosanthes guianenses


Source Adapted from Thomas (1975)
* Data from Haque and Jutzi (1984)
ND = No data presented

Benefits from inoculation with Rhizobium spp

Inoculation is a cheap insurance that the legumes will have adequate nitrogen for its growth. In most soils of sub-Saharan Africa, Rhizobium spp of the 'cowpea' miscellany occur freely. As such most pasture legumes nodulate naturally. For example Thomas (1973) reported that Aeschynomene americana, Calapogonium muconoides, Centrosema pubescens, Desmodium intortum, Desmodium uncinatum Indigofera hirsute, Neonotonia wightii, Pueraria phaseoloides and Stylosanthes spp nodulate very well in Malawi without inoculation. According to Thomas (1973), similar responses have been reported for Centrosema pubescens, Pueraria phaseoloides and Stylosanthes guianensis and S. erecta in Tanzania, Stylosanthes guianensis and Desmodium intortum in Uganda, Desmodium spp in Kenya and Zimbabwe.

However for such legumes, it is essential that the amount of nitrogen fixed be quantified because the Rhizobium spp forming the nodules may not be effective. If ineffective nodulation is the case, then inoculation with a highly effective and efficient strain would ensure large amounts of nitrogen to be fixed.

Such improvements in nodulation of legumes which nodulate freely with local Rhizobia have been achieved in groundnuts in India (Nambiar, 1985). According to Nambiar (1985), out of 15 cultivar x Rhizobium strain combinations the average increase in pod yield of inoculated over the uninoculated plots was 16%. It is significant to note that such responses were obtained in fields where the uninoculated plots had 200-600 nodules per plant. Similar responses could be obtained in pastures if legume varieties are properly matched with efficient Rhizobia.

However, some legumes like Leucaena leucocephala are strain specific (Trinick, 1968). Leucaena has been imported into most countries in Sub-Saharan Africa and its Rhizobium strain does not occur naturally in such countries. As such, inoculation of leucaena is beneficial. Sanginga (unpublished data) reported good responses of leucaena to inoculation at two sites in Nigeria (Table 3). The effect of inoculating with an effective strain was equivalent to the application of 150 kg N/ha.

In Malawi inoculation of leucaena has always improved the establishment of this forage legume. (Savory, 1979; Davis, 1982). Responses, however, are influenced by the legume variety, Rhizobium strain and site where the crop is grown.

Similar responses of Stylosanthes guianensis cv Cook have been obtained in Malawi and inoculation mainly enhances establishment (Table 4) (Davis, 1982).

Importance of effectively nodulated pasture legumes

In terms of livestock production higher content of nitrogen in inoculated forage legume (Table 5), implies higher plant protein for livestock and therefore increased liveweight gains.

Thomas and Addy (1977) have demonstrated that legume-based pastures can contribute substantial liveweight gains in both wet and dry seasons (Table 6). More recently, Dzowela (1985) has reported that Stylosanthes guyanensis cv Cook can be effectively used to improve natural grasslands and liveweight gains. Similar improvements in liveweight gains from stylo-based grasslands have also been realised in Swaziland (Ogwang, 1986). In Malawi, unfertilized Chloris gayana - Desmodium uncinatum pasture gave significantly higher average daily liveweight gains than the grass pasture alone (Dzowela, 1986).

It is evident from the above examples that effectively nodulated pasture legumes could contribute significant dividends to the development of livestock industry at the smallholder level of production in sub-Saharan Africa. The major impact of such legume-based pastures is in reducing the cost of producing high quality livestock.

Rhizobium inoculant demand

Despite the realisation of the benefits of inoculating legumes for pasture improvement, there are relatively few data to indicate use of Rhizobium inoculants in sub-Saharan Africa.

Table 3. Effect of urea fertilizer and inoculation with Rhizobium on nodulation, growth and nitrogen fixation leucaena at IITA and Fashola, Nigeria, at 24 weeks after planing.

Treatment

Nodules (number/ plant)a

Nodules from inoculant strains %

Nodule dry wt.a (mg/plant)

Shoot dry (g/)

Shoot N (kg/ha)

Nfixed (kg/ha)

Fashola







Uninoculated

36

69

179

26

82

NDb

150 kg N/ha

36

69

87

72

232

ND

Rhizobium IRc1050

40

78

485

79

228

ND

Rhizobium IRc1045

15

94

174

68

209

ND

IITA







Uninoculated

0

0

0

51

174

0

150 kg N/ha

0

0

0

130

445

0

Rhizobium IRc1050

17

100

187

103

398

224

Rhizobium IRc1045

34

100

277

121

448

274

LSD (5%)







Fashola

11

ND

23

12

53

ND

IITA

12

ND

25

22

66

ND

a At 12 weeks after planting.
b Not determined
Source: Sanginga (unpublished data)

In Malawi, inoculants for several legumes are produced and sold at a modest cost of MK1.50 (USD 0.55) per 50 g packet (Table 7). Sales have increased slowly from 448 × 50 g packets in 1976/77 to 1775 × 50 g packets in 1987/88 (Table 8). The number of inoculant buyers has fluctuated greatly. However the number of buyers does not necessarily reflect the number of inoculant users. The current system in Malawi is that the Agricultural Development Divisions purchase the inoculant in bulk and then distribute it to the respective smallholder farmers. Use of inoculants in pastures is shown in Table 9. As it can be seen from this table, more inoculant use is in grain legume. This is a reflection of emphasis on growing grain legume such that pastures are unfortunately, considered secondary. In Kenya total inoculant sales have increased from 630 packets in 1981 to 5206 packets in 1985 (Nairobi MIRCEN, 1986). The increase in sales is attributed to effective demonstrations at annual agricultural shows.

Table 4. Response of Stylosanthes guyanensis cv Cook to field inoculation with Rhizobium

Rhizobium Treatment

Site

Dzalanyama

Mbawa

MG 5013


11467a

8546

R 3861


10753ab

8730

R 3943


10340abc

9514

R 3811


9711abc

8203

R 3884


9259bc

9789

R 3837


9026bc

9988

R 3871


8662c

9582

Uninoculated


8468c

8716

Mean


9711

9133

SE ±


631.1*

475.8NS

CV%


15.2

18.1

Data followed by the same letter in a column are not significantly different from each other according to Duncan's Multiple Range Test at P = 0.05.

* = Significantly different P = 0.05
NS = Not significant
Source: Davis (1982)

Table 5. Response of Stylosanthes guianensis cv Cook to field inoculation with Rhizobium
% Nitrogen in legume (Data of single harvest only) May 1977.

Rhizobium Treatment

Site

Dzalanyama

Mbawa

MG 5013


1.68a

1.61a

R 3861


1.66ab

1.55ab

R 3943


1.66ab

1.50bc

R 3811


1.65ab

1.49bc

R 3884


1.62abc

1.46bc

R 3837


1.47bc

1.43c

R 3871


1.32cd

1.42c

Uninoculated


1.24d

1.40c

Mean


1.54

1.48

SE ±


0.059***

0.035**

CV%


9.4

5.7

Data followed by the same letter are not significantly different (P = 0.05).
* significantly different at P = 0.01.
*** significantly different at P = 0.005.
Source: Davis (1982).

Table 6a. Total cattle liveweight gain (kg) during the wet season.


Malawi zebu

Friesian × MZ

Grade Fr

Mean

Rhodes grass

72.7

80.4

67.0

73.4

Rhodes grass + legume

78.7

90.5

74.8

81.4

Response to legume

+6.1

+10.1

+7.8

+8.0

Grazing period (days)

163

163

125


Table 6b. Liveweight changes (kg) during the wet season. Cattle grazing Rhodes grass forage with or without cottonseed cake (protein) supplement and Rhodes grass - legume.


Malawi zebu

Friesian × MZ

Mean

Response to protein

Rhodes grass

-3.2

+0.7

-1.3

-

Rhodes grass + legume

+19.0

+300

+24.5

+25.8

Rhodes grass + supplement

+18.0

+286

+23.4

+24.7

Source: Thomas and Addy (1977).

Table 7. Rhizobium inoculants available in Malawi.

Code Number

Legume species

Weight of seed treated by one 50 g packet

CUP












Cowpea


(Vigna unguiculata)

25 kg


Axillaris


(Macrotyloma axillare)

10 kg


Glycine


(Neonotonia wightii)

10 kg


Siratro


(Macroptilium atropurpureum)

10 kg


Joint vetch


(Aeschnomene americana)

5 kg


Stylo


(Stylosanthes guianensis)

5 kg

DES (MG 500)





Silverleaf


(Desmodium uncinatum)

10 kg


Greenleaf


(Desmodium intortum)

5 kg

LOT (MG 5007)



Lotononis


(Lotononis bainesii)

2 kg

LEU (MG 707)



Leucaena


(Leucaena leucocephala)

10 kg

CEN (MG 512)



Centro


(Centrosema pubescens)

10 kg

BNS (MG 336)



Beans


(Phaseolus vulgaris)

25 kg

SOY (MG 614)



Soyabean: all varieties


(Glycine max

25 kg

LUC (MG 400)



Lucerne


(Medicago sativa

10 kg

GNT (TAL 1000)



Groundnut


(Arachis hypogaea)

25 kg

GUA (MG 5017)



Guar


(Cyamopsis tetragonoloba)

25 kg

Inoculants for most other legumes are available by special request from.

Microbiology Section
Chitedze Agricultural Research
Station
P. O. Box 158
Lilongwe
Malawi. Phone: 767 222

Table 8. Total Rhizobium inoculant sales in Malawi, 1976-1988.

Growing season

Number of buyers

Number of 50 g packets sold

Total cost (Kwacha)*

1976/77

ND

448

224.00

1977/78

ND

616

308.00

1978/79

14

1089

544.50

1979/80

20

872

436.00

1980/81

22

1179

520.00

1981/82

23

3481

1741.00

1982/83

11

1741

1384.25

1983/84

18

975

731.25

1984/85

20

1296

972.00

1985/86

16

1145

858.75

1986/87

38

1767

1325.25

1987/88

ND

1775

1221.25

ND = No data.
* = The cost of inoculant was 50 tambala per 50 g packet in 1976/77.
- In 1982/83 the price was raised to 75 tambala.
- Present price since 1988/89 season in MK 1.50 (1 US$ = MK 2.65)

Table 9. Types of inoculants distributed in Malawi during 1986/87 and 1987/88 seasons.

Inoculum type


Legume species


Number of packets distributed

1986/87

1987/88

CUP

General

38

63

DWS

Desmodium spp

32

33

LOT

Lotononis

0

0

LEU

Leucaena

148

62

CEN

Centrosema

12

5

BNS

Common beans

141

1275

SBG & SBH

Soyabeans

1176

0

LUC

Lucerne/alfalfa

10

6

GNT

Groundnuts

8

0

GUA

Guar beans

200

400

PEU

Peuraria

2

0

Total


1767

1869

Source: Microbiology section, (Unpublished data).

Constraints to adopting inoculants for pasture improvement

Several reasons limit farmer adoption of the rhizobium inoculant technology. The most fundamental one is that the majority of smallholder farmers are not well informed of the technology. In sub-Saharan Africa, very few demonstrations have been established to show farmers the beneficial effects of inoculating pasture legume seed.

In Malawi, a recent in-service course on use of inoculants involved 90 participants from both research and extension establishment. The presentations by the participants revealed surprising data. Almost three-quarters of the participants did not know the value of inoculants in agriculture. Less than half had actually seen inoculants and only about a quarter had used inoculants. Most of those that had used inoculants had used them as supplements to high levels of nitrogen fertilizers. Obviously the smallholder farmer in such an environment will not realise the benefits of inoculation readily.

Munthali and Dzowela (1987) have given three other constraints to pasture improvement in Malawi. Communal grazing, high pasture establishment costs and small size of holdings in addition to competition with other crops for labour etc. Similar problems have been reported from Zimbabwe (Clatworthy et al, 1986) and Nigeria (Mohammed-Saleem, 1986). In Gambia (Russo, 1986) and in Swaziland (Ogwang, 1986) land tenure systems are prohibitive to improvement.

Probably a significant constraint is that farmers do not want to take any risks. The inoculation technology has not been demonstrated clearly that it will improve pasture production and thus livestock.

In Malawi, an additional constraint is the adverse publicity that the inoculants advocated require refrigeration. In an experiment comparing the thickness of inoculant packaging material (Davis (1982) had categorically shown that the inoculants produced in Malawi remain viable for up to 12 weeks at 26°C. The optimum planting period in the rainy season in Malawi is 4 weeks. Meteorological data indicate that during the period November to January, average room temperature in Malawi should be between 18°C and 25°C. Under smallholder grass-thatched house conditions, temperature should be about 20 - 26°C or even lower. Considering all the above data, it is recommended that the inoculants produced in Malawi can be stored at room temperature for up to six weeks. However, most research and extension staff immediately think of refrigeration and are reluctant to have inoculants in remote areas until refrigerators are provided.

This is similar to problems encountered in advocating leucaena for rotational grazing in Australia due to the adverse publicity on the extreme effects of mimosine toxicity (Wildin, 1983).

In countries where credit systems are operational e.g. Malawi, credit packages are oriented towards food/cash crops. No component to include pasture seeds and inoculants is included. Farmers are thus inclined to grow crops with readily available inputs. This season (198889), South-Mzimba Agricultural Project in Malawi is including inoculants in the credit package (Gwembere, personal communication).

In addition to the above constraints, the recommendations for establishing pasture legumes under smallholder conditions might be prohibitive to adoption. For example, advocating undersowing pastures in maize appears to be in conflict with the other recommendations that the farmer should keep the crop free of weeds, and, in most regions of sub-Saharan Africa, the cropping system is mostly mixed intercropping. In this situation the farmer needs to be advised properly that the legume/grass pasture is an important crop to his enterprise that has a dairy cattle component in it. Without proper advise, adverse results may be obtained. Mwafulirwa (unpublished data) gives an example from Malawi: two farmers had to experiment further on the establishment of Rhodes grass under maize until they realised no maize grain yield reduction.

Undersowing of pastures in maize is not a new introduction in sub-Saharan Africa (Thomas, 1975). However, in Malawi the technology has not been widely adopted because of lack of institutional support in/form of follow-up extension effort and provision of a credit package (E.S. Mwafulirwa, unpublished data).

Further to the above statements, the legume species being promoted for incorporation in the current cropping systems may be inappropriate for smallholders. For example, the need to inoculate them with Rhizobia might be too demanding on the farmers. In addition the nature of some legume e.g. silverleaf Desmodium adhering to clothes, legs etc makes such legumes unattractive to include in an undersowing enterprise since the farmer experiences discomfort during field visits and maize harvest. The review by Nnadi and Haque (1986) shows that more work is needed on forage legume cereal mixtures in sub-Saharan Africa in order to fit this technology in the traditional farming systems of the region.

Baker et al (1986) discussed some factors for non-adoption of a technology. They further stated that people farm for different reasons and therefore the technology should meet producer goals. Mwafulirwa (unpublished data) has examples to this effect: one farmer had established a beautiful Rhodes grass pasture by undersowing in maize. However in the second year he ploughed the pasture and planted sweet potatoes. Another farmer also had a good pasture which he harvested and cured but left it in the field until it got rotten. This farmer' however' had feed problems but never fed the hay to his livestock. A number of lessons can be learnt from these examples e.g. farmers' priority setting, labour requirement and probably the farmers do not regard livestock as an integral part of their farming system needing more attention.

Finally, the distribution of Rhizobium inoculant and pasture legume seeds is in itself a limiting factor. In most of sub-Saharan Africa inoculants and legume seeds are not readily available at the usual retail outlets for farm inputs. Thus, despite the recommendations, farmers have no access to the inputs. In Malawi, Rhizobium inoculants are produced at Chitedze Agricultural Research Station in Lilongwe. Inoculants are sent to various parts of Malawi only upon request. Some pasture legume seed is available at the National Seed Company of Malawi but the seed might be very expensive for most smallholders to purchase.

Conclusions and recommendations

The Rhizobium inoculation technology can have great dividends to livestock production. However, for the technology to be adopted, more work is needed. A multi-disciplinary team of specialists in agronomy, animal science, farm management and local leaders should work together to provide a package of recommendations for specific areas.

A farming systems approach is required to bring research workers in close co-operation with local extension staff and farmers. This, probably, would streamline the transfer of the technology.

In order to increase awareness, numerous demonstrations at easily accessible sites and highly visible locations representing production areas need to be set up. All available forms of the media should be used to inform farmers of the benefits of inoculating legumes, source of inoculants and legumes seeds and locations where additional information could be obtained.

Finally inorder for technology transfer to be successful, the following are the essential elements that need consideration (Baker et al, 1981).

1. Goals and procedures need to be clearly defined.
2. Competent staff need to be involved.
3. Appropriate disciplines to be involved to farmer's needs.
4. There should be mutual confidence between the farmer and field staff.
5. There should be total community involvement.
6. Adequate funds should be available inorder to execute the programmes.
7. Administrative support should be provided to the technology transfer teams and their programmes.
8. Staff continuity should be guaranteed.
9. Suitable support staff in addition to the component staff should be available.
10. There should be adequate time allowed for the technology transfer since changes occur slowly as farmers do not want to take risks.

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