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Maize is the dominant staple crop across most of southern Africa—it is so dominant in some areas that more than 80 per cent of the smallholder land area is planted with maize. Soyabean was identified as the crop with a potential to address the need for diversifying the cropping systems, which could assist in overcoming the pervading soil fertility constraints and could provide smallholder farmers with an opportunity to earn income while also addressing the nutritional security of households. An initiative was launched in the 1996/97 cropping season in Zimbabwe, to test soyabean as a potential smallholder crop. From an initial 55 farmers in the first year, soyabean production expanded rapidly to an estimated 10,000 farmers three years later. Since then, soyabean has diffused spontaneously to most smallholder farming areas in the higher rainfall zones of Zimbabwe. Thus, the initiative has assisted a large number of smallholders to grow soyabean, and exploded a long-held belief in Zimbabwe that soyabean is not a suitable crop for smallholders.
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Soyabeans and sustainable agriculture
in southern Africa
Ken E. Giller1,4*, Mazwita S. Murwira2, David K. C. Dhliwayo3, Paramu L. Mafongoya4and
Sheunesu Mpepereki4
1
Plant Production Systems, Wageningen University, P.O. Box 430, 6700AK Wageningen, The Netherlands
2
Soil Productivity Research Laboratory, Post Bag 3757, Marondera, Zimbabwe
3
Chemistry and Soil Research Institute, P.O. Box CY 550, Causeway, Harare, Zimbabwe
4
Department of Soil Science and Agricultural Engineering, University of Zimbabwe, MP 167, Harare, Zimbabwe
Maize is the dominant staple crop across most of southern Africa – it is so dominant in some areas that more than 80
per cent of the smallholder land area is planted with maize. Soyabean was identified as the crop with a potential to
address the need for diversifying the cropping systems, which could assist in overcoming the pervading soil fertility
constraints and could provide smallholder farmers with an opportunity to earn income while also addressing the
nutritional security of households. An initiative was launched in the 1996/97 cropping season in Zimbabwe, to test
soyabean as a potential smallholder crop. From an initial 55 farmers in the first year, soyabean production expanded
rapidly to an estimated 10,000 farmers three years later. Since then, soyabean has diffused spontaneously to most
smallholder farming areas in the higher rainfall zones of Zimbabwe. Thus, the initiative has assisted a large number
of smallholders to grow soyabean, and exploded a long-held belief in Zimbabwe that soyabean is not a suitable
crop for smallholders.
Keywords: nitrogen fixation; rhizobial inoculants; rotational benefits; soil fertility
Background
In the 1950s, soyabean became an important crop for
large-scale farming in Zimbabwe. As in North
America, farmers seized the opportunity to replace
green manures in their rotation plans with soyabean
a valuable crop because of the dual products of vege-
table oil and animal feed obtained from the grain.
Soyabean rapidly displaced sunnhemp (Crotalaria
juncea L.) from rotations on large-scale farms and
became an important crop with national production
up to 100,000 tonnes a year. Surprisingly, despite
sporadic occurrence of soyabean on smallholder
farms and promotion campaigns in the 1980s
(Mabika and Mariga, 1996), it remained a minor
crop in smallholder agriculture. By the 1990s it had
become accepted that soyabean was not a suitable
crop for smallholder farmers. This was due to both
the limited extension support for smallholder soya-
bean production and the marginal soil and rainfall
conditions in the majority of communal farming areas.
In 1995, an initiative led by the University of Zim-
babwe brought together a wide range of representa-
tives from research, extension and private sector
agro-industrial organizations to discuss why soyabean
was not widely grown by smallholders and to assess
the possible constraints (Mpepereki et al., 1996a).
The enthusiasm of the workshop participants led to
the establishment of a Soyabean Promotion Task
Force (SPTF), which went on to become the ‘cham-
pion’ of soyabean promotion in smallholder farming
areas of Zimbabwe. The task force was comprised
of members of the University of Zimbabwe (UZ),
the Department of Research and Specialist Services
(DR&SS), the extension service (AGRITEX), the
Zimbabwe Farmers’ Union, the Commercial
Farmers’ Union and the main company purchasing
soyabean and processing it into vegetable oil and
other products, Olivine Industries. Crop diversifica-
tion away from maize monoculture using soyabean
to improve soil fertility through biological nitrogen
fixation was the main starting point from the
*Corresponding author. Email: ken.giller@wur.nl
INTERNATIONAL JOURNAL OF AGRICULTURAL SUSTAINABILITY 9(1) 2011
PAGES 50–58, doi:10.3763/ijas.2010.0548 #2011 Earthscan. ISSN: 1473-5903 (print), 1747-762X (online). www.earthscan.co.uk/journals/ijas
scientists’ perspective, but the multiple benefits of
soyabeans such as cash income, household nutrition,
livestock feed and increased maize yields in rotation
were also important for farmers. Soyabean was also
perceived to be more resistant to disease and pests
than other candidate legumes for crop diversification
such as the common bean (Phaseolus vulgaris L.) or
cowpea (Vigna unguiculata [L.] Walp.), and given
that substantial quantities of soyabean were imported,
there appeared to be a ready market.
Soyabean is notoriously ‘specific’ in its require-
ment for rhizobial strains, meaning that only a few
types of rhizobia are able to form nodules on soyabean
roots and actively fix nitrogen. These varieties need to
be inoculated with effective rhizobium strains in order
to nodulate and fix nitrogen. Many other tropical
legumes, notably cowpea, groundnut and common
beans, are more permissive and form nodules and
fix nitrogen with a wide range of rhizobia that are
present in most soils. These are termed ‘promiscuous’
or ‘naturally nodulating’ legumes, and they make
effective use of the inherent soil biodiversity of rhizo-
bia indigenous to the soils (Giller, 2001). Some var-
ieties of soyabean available in southern Africa are
also ‘promiscuous’ and can nodulate well with indi-
genous rhizobia (Mpepereki et al., 2000).
Using the inputs donated by local private sector fer-
tilizer and seed companies, the SPTF established dem-
onstration plots in 11 villages with five farmers in each
village (a total of 55 farmers) in the 1996/97 season.
Each farmer planted an area of 0.1ha of each of four
soyabean varieties (two promiscuous and two
specific). Every plot included four rows without rhizo-
bium inoculant, which dramatically demonstrated the
significant positive impact of rhizobium inoculation
on the growth and yield of the specific soyabean var-
ieties. The positive results persuaded the Rockefeller
Foundation to avail a small grant to facilitate monitor-
ing of the demonstration plots that emphasized inocu-
lation and good agronomy. These large demonstration
fields were established in central locations close to
rural growth points so that they could be seen by
many people passing by. The demonstration plots
stimulated substantial interest from farmers so that
more than 1,000 farmers demanded access to inputs
the next year. In the second and subsequent seasons,
all of the inputs of seed, inoculum and basal fertilizer
were purchased by the farmers, mostly as combined
‘starter packs’. Farmers paid the transport costs
when their produce was collectively delivered and
sold at the factory gate. The role of the project was
to assist farmers with access to inputs on time, and
to link farmers to the market. Farmers were keen to
grow both the specifically nodulating varieties,
because of their greater yield potential as a cash
crop, and the ‘promiscuous’ varieties that they
regarded as more robust as their production does not
depend on the farmers being able to obtain inoculants.
Farmers also recognized the greater potential of the
promiscuous varieties for fodder and soil fertility
improvement, as illustrated by the dramatic residual
fertility effects that often doubled the yield of maize
grown in rotation (Mpepereki et al., 2000).
Success was achieved by implementation of exist-
ing knowledge rather than by extensive research,
although applied research continued to address the
problems encountered. A strong emphasis was
placed on enhancement of farmers’ knowledge and
learning about good varieties and agronomic practices
(rhizobial inoculation, seeding rates, row spacing and
the need for small amounts of basal lime and P fertili-
zer). The SPTF arranged for printing of leaflets
written for development workers (extension and
NGOs) both in English and in the local language
(Shona) directly for farmers, with guidance on
simple agronomy, on how to handle inoculants and
on pest and disease management. As soyabean was
a new crop for many farmers, extension staff gave
training in local processing of soyabean for a variety
of uses: for milling with maize meal to give a fortified
porridge for children, baking soya bread, making soya
milk and as a relish. The training was given through
field days and field demonstrations.
Although the initial aim was to promote the promis-
cuously nodulating soyabean variety ‘Magoye’ (Mpe-
pereki et al., 2000), the programme has largely relied
on assisting farmers to access seed of specifically
nodulating varieties, together with carefully educating
smallholder farmers on the use of rhizobial inoculants.
Specifically nodulating varieties were promoted
together with rhizobial inoculation (with Bradyrhizo-
bium japonicum) because there was not enough seed
of Magoye to meet the rapid increase in farmers’
demand. Excellent soyabean varieties are available
in Zimbabwe from a long-standing and continuing
breeding programme of the Crop Breeding Institute
(CBI) of DR&SS and a private company, Seed Co.
Limited. These varieties give excellent grain yields
1
of up to 5t ha
21
, have medium to large white seeds
that give a good oil yield and are resistant to major dis-
eases (bacterial pustule, frogeye, etc.). Soyabean rust
(Phakapsora pachyrhizi) first appeared in the
large-scale farms and later spread to the smallholder
farms, necessitating the use of fungicides and
Soyabeans and sustainable agriculture in southern Africa 51
INTERNATIONAL JOURNAL OF AGRICULTURAL SUSTAINABILITY
thereby increasing production costs. Another key part
of the input package was a small amount of lime and
P:K:S fertilizer
2
to overcome the other nutrient con-
straints on the highly weathered sandy granitic soils
that predominate in the smallholder farming areas of
Zimbabwe.
The major purchaser of soyabean in the country,
Olivine Industries (a vegetable oil company), tested
a wide range of samples of soyabean grain from small-
holders and were so impressed with the quality that
they agreed to change the grading of smallholder
soyabean grain from ‘D’ grade to ‘B’ grade with an
associated higher price. The smallholder grain was
cleaner (less chaff and stalk) than grain produced on
large-scale farms because it was hand-harvested and
cleaned. Soyabean was publicized as a profitable
smallholder crop by radio, television and in the
popular press. Interest in soyabean production
among smallholders was stimulated to the extent
that villagers often travelled up to 300km to the Uni-
versity of Zimbabwe by bus to request extension
support activities in their villages. The SPTF gave
substantial assistance in marketing soyabean from
communal farming areas to Harare during the first
years when production was expanding rapidly. Tech-
nical staff employed by the Task Force through a
small grant from the Rockefeller Foundation assisted
groups of smallholders to consolidate their production
at rural centres. Once a group had managed to collect
together 30 tonnes of soyabean they contacted the
Task Force coordination unit, who in turn phoned a
haulage contractor to collect the soyabean load by
truck and deliver it for sale to the oil-processing
factory in Harare. From the payment for the load,
the Task Force then deducted the cost of transport
and arranged to repay the farmers in proportion to
their contributed produce quantities that ranged
from as little as 7kg for one woman farmer to more
than 3 tonnes for other wealthier farmers. Payment
for the grain was then remitted to the farmers
through local banks with the transport costs deducted.
Although this approach helped to raise soyabean from
a fledgling crop to widespread production, it could not
be sustained in the long term because of the trans-
action costs for the bank of handling small sums of
money for tens of thousands of farmers. Other market-
ing arrangements emerged with the SPTF providing
market information, informing traders where substan-
tial soyabean was available for purchase and inform-
ing farmers of current prices. Small to medium scale
processing plants have been established at many
rural service centres, allowing farmers easier access
to local markets. Although it was hoped that traders
would take up the role of buying smallholder pro-
duction and delivering it to the central markets, the
recent economic problems mean that accessing
markets for their produce remains a major problem
for smallholder farmers in Zimbabwe.
Rhizobial inoculants
A key to success was the existence of the inoculum
production facility at the Soil Productivity Research
Laboratory (SPRL), Marondera, Zimbabwe. This
semi-commercial facility was established in 1964
and largely served the commercial farming sector
until the expansion of smallholder soyabean pro-
duction. The long history of inoculant production
means that there is a solid body of expertise in inocu-
lant production, including expert technical staff. More
than 90 per cent of the inoculants produced are for
soyabean and are made from pure cultures of B. japo-
nicum (strains MAR 1491 and 1495, which are USDA
110 and 122, respectively). The carrier used is steri-
lized (heated to 1208C for 1h) bagasse impregnated
with nutrients. Quality control is conducted on the
mother culture and on all batches using plating for
purity and counts, and plant infection tests for nodula-
tion and nitrogen fixation. The inoculants have a shelf
life of up to six months when refrigerated at 48C. If the
inoculants are kept cool, by storage in clay pots
away from the sun in a shaded place in the house,
they can be stored for up to four months before
use by smallholders (Mabika and Mariga, 1996).
During the early phase of activities of the SPTF, a
grant from the International Atomic Energy
Agency supported SPRL through the training of
researchers, provision and maintenance of equip-
ment for inoculant production, quality control,
plant and soil sample analyses and a vehicle to
improve mobility. Fridges were provided for the
main inoculant distribution centres to improve the
longevity of the product. Staff of Agricultural Tech-
nical and Extension Services (Agritex) were key
partners in working with communities in the rural
areas.
Production of inoculants increased until the col-
lapse of commercial agriculture in 2001 to a peak of
136,000 sachets (Figure 1). Since 2000, a large
amount of inoculant has been used in smallholder
agriculture, with production gradually gaining
ground in response to demand until 2006. In recent
years, problems of intermittent electricity supply
K. E. Giller et al.52
INTERNATIONAL JOURNAL OF AGRICULTURAL SUSTAINABILITY
have hampered production, but the committed staff
have worked at night when power was available
(often from 22:00h until 4:00h the following
morning!) to ensure production.
Agronomic and adaptive research
Substantial background research was conducted in
parallel to the promotion campaigns to gain a better
understanding of the benefits and constraints of
growing soyabean on smallholder farms. Agronomic
research was conducted to measure the responses in
growth and yield of soyabean to rhizobial inoculation.
Some responses to inoculation in farmers’ fields were
spectacular (Figure 2). In this experiment, yields of
the specific soyabean varieties increased from
0.51.5t ha
21
to 2.8 3.3t ha
21
. Magoye and Local
are two promiscuously nodulating varieties that
have not been subjected to intensive breeding for
higher yield. In this experiment both stover and
grain yields of the promiscuous varieties were
improved by inoculation. The specifically nodulating
varieties, Roan, Nyala, Sonata and Solitaire, all pro-
duced much less stover, but with inoculation they
yielded more than a tonne of extra grain compared
with Magoye and Local, demonstrating the advantage
of the breeding programmes of increased yield and
disease resistance. The amounts of nitrogen fixed
from the atmosphere by soyabean ranged from
60130kg N ha
21
on smallholder farmers’ fields to
160260kg N ha
21
on the fertile soils of the Univer-
sity of Zimbabwe farm (Kasasa, 1999). Strong
rotational benefits were observed by breaking the con-
tinuous cultivation of maize. In experiments under
farm conditions, maize grown after maize commonly
yielded only 0.5t ha
21
, whereas yields of maize after
soyabean were more than 1.5t ha
21
(Kasasa et al.,
Figure 1 |Production of soyabean inoculants (indicated in number of 100g sachets) at SPRL, Marondera, Zimbabwe since 1995
Figure 2 |Response to inoculation in a smallholder farmers
field in Zango, Hurungwe District, Zimbabwe (drawn from
the data in Kasasa, 1999). See the text for further explanation
Soyabeans and sustainable agriculture in southern Africa 53
INTERNATIONAL JOURNAL OF AGRICULTURAL SUSTAINABILITY
1999). Growing soyabean was sufficient to replace the
basal N fertilizer, but in order to achieve yields of 3
4t ha
21
of maize, extra N fertilizer as top-dressing is
required.
Soyabean does not grow well on the very coarse
sandy granitic soils found in many smallholder
farming areas in Zimbabwe. Pronounced gradients
of soil fertility are found from relatively fertile infields
close to the homesteads compared with ‘outfields’ that
may only be 50m further away, but do not receive
much in the way of inputs of manure or fertilizer
(Zingore et al., 2007). Highly variable responses of
the promiscuous variety Magoye were found across
these gradients with yields of around 1.2t ha
21
only
found on the better infield soils (Zingore et al.,
2008). On the degraded outfields, yields were only
around 0.3t ha
21
even when P fertilizer was added,
indicating that rehabilitation of the soils using
manure is needed before soyabean can yield well.
Research on rhizobia in Zimbabwe
Microbiological studies revealed that a wide range of
soils in Zimbabwe contained rhizobia that were com-
patible with ‘specific’ varieties of soyabean, even
where there was no history of inoculation (Mpepereki
et al., 1996b; Musiyiwa et al., 2005a). A variety of
serological and physiological methods showed that
these indigenous isolates were highly diverse (Davis
and Mpepereki, 1995; Mpepereki et al., 1996b;
Musiyiwa et al., 2005a). All of the strains isolated
and authenticated on soyabean were shown to be
slow growers (Musiyiwa et al., 2005a).
Adding more than the recommended dose of the
inoculant from SPRL improved the response in crop
growth and nitrogen fixation on sandy soils (Chirinda
et al., 2003). Screening and comparison of a wide
variety of rhizobial isolates led to the isolation of a
number of strains that performed better than the stan-
dard inoculant strains currently used (Musiyiwa et al.,
2005b; Zengeni and Giller, 2007). This indicates that
there is considerable scope to improve the quality of
the rhizobial inoculants through further research on
inoculant formulations and strain identification.
A question often raised by farmers is whether
re-inoculation is necessary every year. Zengeni et al.
(2003, 2006) assessed the persistence of the soyabean
rhizobial inoculant strain MAR 1491 (USDA 110) in
52 soils from Guruve, Hurungwe and Goromonzi dis-
tricts of Zimbabwe, which had been inoculated up to
six years previously. Most probable number estimates
of rhizobia in the soils showed that population sizes
decreased with increasing time since the last inocu-
lation. Rhizobial populations of up to 10
2
cells g
21
soil were found in soils inoculated three years
earlier from Guruve, while persistence in Hurungwe
and Goromonzi soils was significant for soils inocu-
lated two years earlier. The greater rhizobial persist-
ence in Guruve soils was attributed to their higher
clay (.20 per cent) and organic C (.1 per cent) com-
pared with the sandier, less fertile soils from Hur-
ungwe and Goromonzi. This suggests that soyabean
can be grown for at least three years without the
need for repeat inoculation on soils richer in clay
such as those in Guruve. Application of cattle
manure led to increased indigenous rhizobial
numbers and greater persistence of rhizobia in the
sandy soils from Goromonzi (Zengeni et al., 2006).
Pests and diseases
Soyabean has relatively few pests compared to other
grain legumes. It is subject to attack by leaf eaters
such as semi-loopers and leaf rollers. The crop can tol-
erate up to 30 per cent defoliation without significant
yield loss, above which economic yield loss occurs
and insecticides are needed. When the SPTF first
introduced soyabean into the smallholder sector in
1996, the only disease of consequence was frog-eye
leaf spot. The problem was solved through the use
of new disease-tolerant varieties that did not need
spraying of fungicides. In 1997/98 soyabean
rust appeared, which required the application of
expensive fungicides. The SPTF persuaded chemical
companies such as Syngenta to package fungicides in
500ml bottles, thereby improving access for small-
holder farmers. New rust-tolerant soyabean varieties
are now available from Seed Co., (J. Tichagwa, per-
sonal communication, 2010) that do not require
fungicides.
Understanding marketing problems
Before the SPTF embarked on promotion, an econ-
omic study was conducted to assess models for invol-
vement of farmers’ organizations, and to confirm the
market demand for soyabean (Rusike et al., 2000).
Once the production constraints were addressed, the
farmers faced marketing problems due to the scattered
production of soyabeans and the small volumes of the
crop (Figure 3). This, together with poor information
flows and lack of trader capital, created hurdles for
K. E. Giller et al.54
INTERNATIONAL JOURNAL OF AGRICULTURAL SUSTAINABILITY
traders that needed to be overcome typical for
expansion of a fledging crop. Support for marketing
in the early years was key to increasing the amounts
of soyabean produced in rural areas to volumes that
were interesting for traders. Consolidation of
produce into 30 tonne loads was necessary to bring
down transport costs. Initially payments were
remitted as cheques to individual producers, but the
transaction costs were too large so that the banks can-
celled this arrangement after one season. Further
support was provided in cash payments remitted
back to farmers, but this involved drivers carrying
large quantities of cash around that was deemed to
be too risky to continue. It was hoped that once the
crop had become established, external support for
marketing could be scaled down as private traders
would take over the role of marketing, and early
signs indicated that this role of support worked as a
‘stepping stone’ to functional markets. Unfortunately,
the collapse of the economy in Zimbabwe has
impeded this trade.
Analysing the success
The initial impetus for this initiative came from a
group of researchers and extension workers with a
strong drive to see the application of their knowledge
to improve the livelihoods of smallholder farmers.
From a relatively small-scale demonstration exercise,
the interest generated in the smallholder farming com-
munities led to rapid expansion of the crop. The
approach focused on using best practice and ensuring
that all components were available seed, inoculants,
basal fertilizer and lime coupled with strong exten-
sion in management practice and local processing.
The SPTF, which brought together researchers and
government extension workers with farmer organiz-
ations, input suppliers and purchasing companies,
was instrumental in promoting the crop. Local proces-
sing provided a domestic use for soyabean that has
clear nutritional benefits for the households, and
direct consumption stimulated substantial interest.
But the local market for soyabean was readily satis-
fied, and further expansion of the crop was dependent
on assisting farmers in marketing their produce. Key
elements for success included the strong commitment
of the SPTF to demonstrate the tangible multiple
benefits of soyabean to farmers (cash income, food
and nutrition for humans and livestock and residual
soil fertility) and the timely engagement of relevant
stakeholders at each stage of the value chain. In
many ways the approach used is similar to the
much-lauded ‘innovation systems’ approach that has
gained widespread support in the research and devel-
opment community in Africa in recent years. The
underlying reason that soyabean took hold in small-
holder farming relied on the development of both a
strong technology and a strong institutional setting
(Figure 4). With the high yields of soyabean due to
good varieties, inoculum and agronomy, the crop
was economically attractive for farmers. Only when
there was sufficient volume of production was the
crop economically valuable for traders.
Figure 3 |Once the production constraints were addressed, the farmers faced marketing problems due to the scattered
production of soyabeans (from Rusike et al., 2000). See the text for further explanation
Soyabeans and sustainable agriculture in southern Africa 55
INTERNATIONAL JOURNAL OF AGRICULTURAL SUSTAINABILITY
The NGO community became major partners in the
promotion of soyabeans among smallholders. In
Matabeleland, ORAO and OXFAM were distributing
soyabean as part of their drought relief and engaged
the SPTF as technical partners to train farmers and
women in processing soyabeans for home consump-
tion. In wetter areas of Mashonaland, AFRICARE
and World Vision sought to diversify the cropping
systems of target smallholder communities with the
SPTF providing training and advisory services for
soyabean production. The Lutheran World Federation
also worked with the SPTF to introduce soyabean in
Midlands and Masvingo provinces. These partner-
ships with NGO and private sector actors allowed
the SPTF to reach out to all of the eight rural provinces
of Zimbabwe. Many other NGOs have recognized the
benefits of soyabean and have continued the pro-
motion of the crop, but further investment is needed
to promote local agro-dealers to facilitate access to
inputs of seed, inoculum and fertilizer and to act as
intermediaries in purchasing the crop and selling to
the large market for processing.
Early adopters had a clear advantage in selling seed
locally and profited the most from the introduction of
soyabean. Gains were proportional to the area planted
with soyabean, so that better-resourced farmers who
had the land and labour (including animal traction)
undoubtedly benefited more than poorer farmers.
The small amounts of grain (,10kg) marketed by
some individual farmers indicated that poorer
farmers were also participating actively. In terms of
domestic consumption and nutritional benefits to the
households, it is likely that introduction of soyabean
had more immediate direct benefits for the poorer
farmers.
Small to medium enterprises (SMEs) were estab-
lished using soyabean as the raw material. In
Musana Communal Lands near Bindura, farmers put
up a factory building and commissioned soya oil
presses, grinders and roasters and blenders for
making soya-based feeds. In Mount Darwin, farmers
set up a soy-milk processing plant that supplied both
‘fresh’ and ‘sour’ milk to local schools and commu-
nity. In a discussion with women from Kazangarare,
in Hurungwe district in 1999, a total of 17 supermar-
ket grocery items were identified that could be substi-
tuted with soyabean-based products. These ranged
from milk, butter, coffee, cooking oil, cakes, bread
and various relishes. Training of women in home pro-
cessing and consumption of soyabean had the greatest
stimulatory effect on adoption. Indeed, many HIV/
AIDS infected people in the promotion areas under-
went remarkable improvements in their health con-
ditions when they were put on soya-based diets. The
popularization of soyabean as a health food has
gone some way to ease the plight of the poor who
cannot afford the expensive supplements prescribed
for AIDS patients.
Environmental benefits
The rotational benefits often lead to a doubling of
maize yields in soils where maize has been grown
for many years. These benefits are due to breaking
the continuous cultivation of maize and the addition
of nitrogen to the soil from the residues of soya-
bean that gives a small but significant improvement
in soil fertility. The first certified agricultural
methodology for reducing carbon dioxide (CO
2
)
emissions under the United Nations Clean Devel-
opment Mechanism issued in 2008 was rotation
with soyabean. The reductions in C emissions are
largely due to substitution of nitrogen fertilizer in
soyabeanmaize rotations, which is highly relevant
in North America. It is unlikely that smallholder
farmers in Africa can be easily registered under
such a scheme, as they currently use little N
fertilizer.
Figure 4 |The need for both strong technology
development and strong institutions (taken in a broad
sense to include extension, input and output markets).
From a starting point, point A, if attention is given only to
technology development, a strong fledgling technology is
likely to fail due to the lack of functioning institutions
(point B). If only attention is given to developing the
institutional environment, a technology vacuum prevents
overall development (point C). Only when a strong
technology is embedded in a strong institutional
environment (point D) will it take hold and expand. From
Giller (2001), adapted from Dorward et al. (1998)
K. E. Giller et al.56
INTERNATIONAL JOURNAL OF AGRICULTURAL SUSTAINABILITY
Current status and future prospects
Soyabean has become established as a smallholder
crop in Zimbabwe. Whereas in the 1990s soyabean
was grown on small plots in just a few rural areas, it
is now widespread throughout the higher rainfall
areas of Zimbabwe. Detailed surveys that quantify
soyabean production in the smallholder sector and
its contribution to rural livelihoods are lacking.
Given that at least 10,000 farmers were growing soya-
bean in 2001, a conservative estimate would be tens of
thousands, and the true number could be well over
100,000 farmers. A significant statistic is the fact
that smallholders contributed only 415 tonnes to the
formal soyabean market in 1995, just one year prior
to the promotion, but this leaped to 10,900 tonnes
by 2001 (Ministry of Lands and Agriculture, 2001).
Estimated mean yields per hectare also increased
from 495 to 1,014kg ha
21
over the same period.
This success owes much to the commitment of the
SPTF to championing the production of soyabean in
the smallholder farming sector.
Given the collapse of the commercial farming
sector in Zimbabwe and the massive demand for soya-
bean for the national food and animal feed market
(current processing capacity in Harare is estimated
to be around 400,000t year
21
) there is an insatiable
demand for the crop. Yet the total national production
in the past season was estimated at only 20 30,000
tonnes due to collapse of the commercial farming
sector and the problems smallholders face in market-
ing. Soyabean is a particularly valuable crop because
of the multiple products for food, vegetable oil and
animal feed obtained from the grain. Much of the
pressed soy cake is used in the rapidly expanding
chicken and pig industries. As Zimbabwe is a land-
locked country, the costs of importation make local
production economically competitive. A further
potential market opportunity for Zimbabwe and
other countries of southern Africa (excepting South
Africa) is that all soyabean varieties used are from
classical breeding programmes and can thus be mar-
keted as free of genetic modification. All these
factors indicate that there is a great potential for
expansion of soyabean production in the smallholder
sector.
A new initiative entitled ‘Putting Nitrogen Fixation
to Work for Smallholder Farmers in Africa’ (www.
N2Africa.org) aims to replicate this success in eight
countries of sub-Saharan Africa. This project aims
to assist smallholder farmers to access the best avail-
able technologies for production of the major grain
legumes – not only soyabean – so that the benefits
from symbiotic nitrogen fixation can help to build
profitable and sustainable futures for smallholder
farmers.
Acknowledgements
We thank the Rockefeller Foundation, and particu-
larly Malcolm Blackie, for recognizing the potential
of soyabean and funding the early adaptive research
and extension activities.
Notes
1. Grain yields of up to 6t ha
21
have been recorded in
replicated plots in Zimbabwe by Seed Co., with one
exceptional yield in a long growing season of around
7t ha
21
(J. Tichagwa, personal communication 2010).
2. Just 0.5t ha
21
of Dolomitic lime was recommended to
supply calcium and magnesium and a small amount of
basal fertilizer (about 10kg P ha
21
, 12kg K ha
21
and
12kg S ha
21
).
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INTERNATIONAL JOURNAL OF AGRICULTURAL SUSTAINABILITY
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Promiscuously nodulating varieties of soyabean have been developed which nodulate abundantly and effectively in most soils in southern Africa. Bred from genotypes collected in East Asia these promiscuous varieties nodulate with fast and slow-growing rhizobia representing several different genera. The symbiotic interaction between different soyabean genotypes and different rhizobial isolates varies widely both in terms of ability to nodulate and effectiveness in N2 fixation, but all plant genotypes tested, including varieties considered to be highly specific, nodulated with indigenous isolates in at least one soil.Promiscuity in nodulation allows soyabean to be introduced into a range of environments where lack of suitable inoculants would otherwise preclude growing the crop. Smallholder farmers need only access to seed to be able to grow soyabean, which brings multiple benefits in improved household nutrition from the high protein and oil content, cash income from sales of the crop and inputs of N which enhance soil fertility and contribute to the sustainability of their cropping system. Promiscuous soyabean varieties therefore represent a highly appropriate technology for cultivation of soyabeans for smallholder farmers, whereas use of varieties with greater yield potential together with rhizobial inoculants is an appropriate technology for commercial production of soyabeans by farmers who have ready access to agricultural inputs.
Article
Presence of indigenous rhizobia nodulating promiscuous soyabean was determined in 92, mainly sandy soils, from wetter agro-ecological zones of Zimbabwe suited to soyabean production. A total of 129 isolates were obtained from nodules of promiscuous soyabean varieties, Magoye and Hernon 147, and a specific variety, Roan grown in potted soils. Magoye nodulated in 80%, Hernon 147 in 50% and Roan in only 25% of the 92 soils tested. Rhizobia populations ranged from undetectable to 2.4×104 cells g−1 of soil. Twenty-one of these isolates were tested for symbiotic effectiveness on two varieties, promiscuous Magoye and specific Roan. Differences in parameters such as nodule numbers, nodule weights and total N fixed reflected diversity among the indigenous isolates. Three isolates had significantly higher N2-fixing potential in comparison with the commercial strain MAR 1491 on promiscuous Magoye. Host ranges of 34 isolates were evaluated on nine legume species: Arachis hypogaea, Cajanus cajan, Crotalaria juncea, Glycine max, Macroptilium atropurpureum, Phaseolus vulgaris, Sesbania sesbania, Vigna subterranea, Vigna unguiculata. Of these 34 isolates, 33 formed nodules with M. atropurpureum of which 61% were moderately effective to very effective while all nodulated V. unguiculata with 58% being moderately effective to very effective. Twenty-eight isolates nodulated V. subterranea and C. cajan (short season variety) with 76 and 36% of these being moderately to very effective, respectively. None of the isolates formed nodules on Phaseolus vulgaris, Arachis hypogaea or Sesbania sesban. Our results indicate that the ability of even specific varieties of soyabean to nodulate with indigenous isolates in African soils is greater than generally assumed.
Article
The second edition of this book, first published in 1991 and intended for students and researchers, contains revised and updated material on the theory and practice of nitrogen fixation in tropical cropping systems. There are 15 chapters in 3 parts. Part I, Introduction, contains 5 chapters on tropical environments (climate, soils and cropping systems), nitrogen fixing organisms, the process of nitrogen fixation, assessment of the role of nitrogen fixation, and cycling of nitrogen in tropical cropping systems. Part II, Tropical crops and cropping systems, comprises 7 chapters on freeliving, root-associated and endophytic nitrogen fixing bacteria of cereal crops and grasses, cyanobacteria and Azolla as green manure for wetland rice, grain legumes, legumes as green manures and cover crops, forage legumes, understorey legumes and shade trees in plantation crops, and nitrogen fixing trees in agroforestry. Part III, optimizing nitrogen fixation, includes 3 chapters on environmental constraints, approaches to enhancement, and future impacts on nitrogen fixation in tropical agriculture. A list of common names and subject index are included.
Article
Rhizobial isolates were obtained from nodules of promiscuous soyabean varieties Hernon 147 and Magoye and specific Roan grown in a range of Zimbabwean soils. A total of 129 isolates authenticated as true rhizobia were characterized using growth rate, elasticity, colour, size, colony shape, acid/alkali production on YEM and tolerance to low and high pH, elevated temperature and salt concentration. Isolates separated into 2 major clusters at a similarity level (%SSM) of 66%. Cluster I contained isolates forming dry colonies (77%) which separated into 9 groups and Cluster II contained those forming the wet colonies (23%) with 4 groups. Acid and salt tolerance patterns did not differ among the two main clusters (the dry and the wet colony types). More isolates forming wet colonies (47%) survived at 40°C than those forming dry colonies (13%). Salt, temperature and acid pH tolerance were not related to geographic origin of the isolates. The promiscuous soyabean variety Magoye nodulated with the widest range of rhizobia (12 groups) followed by Hernon 147 (11 groups) and then Roan (9 groups). Guruve soils had the most diverse range of isolates belonging to 12 groups followed by those from Chiweshe (9 groups) and then those from Chikomba (8 groups). Our results indicate that soyabean is nodulated by a wide range of indigenous rhizobia in African soils.