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Effectiveness of rhizobia strains isolated from South Kivu soils (Eastern D.R. Congo) on nodulation and growth of soybeans (Glycine max)


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Identification of effective indigenous Bradyrhizobium strains which nodulate soybean varieties could trigger development of an industry for inoculant production with use of strains adapted to local conditions. This study was conducted to identify and select effective local rhizobia strains nodulating soybean in South Kivu soils. One hundred and seven isolates collected from root nodules in South Kivu were tested in sterile sand using the modified Leonard's jars and in potted field soils. Each jar and pot was inoculated by 1ml of broth culture concentrated at 10 9 cells per milliliter. From the first screening, only 10% of these isolates produced higher nodules number and plant shoot dry weights (p˂0.001) compared to the commercial strain USDA110 and were selected for evaluation using soils as rooting media in three liters PCV pot in the greenhouse. From the potted soils experiment, among twelve outperforming isolates, only six isolates produced higher nodules and shoots dry weight (p˂0.001) compared to the commercial strains and uninoculated controls, and were considered as effective and competitive strains. This isolates includes NAC10, NAC22, NAC37, NAC67, NAC40 and NAC75. Nodules number highly correlated with Shoot weight. There exist effective indigenous rhizobia in South Kivu soils for inoculants production.
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African Journal of Soil Science ISSN 2375-088X Vol. 5 (3), pp. 367-377, March, 2017. Available online at © International Scholars Journals
Author(s) retain the copyright of this article.
Full Length Research Paper
Effectiveness of rhizobia strains isolated from South
Kivu soils (Eastern D.R. Congo) on nodulation and
growth of soybeans (Glycine max)
1, 2Bintu Nabintu Ndusha, 1Nancy K. Karanja, 3Paul L. Woomer, 4Jean Walangululu, 2Gustave
N. Mushagalusa and Jean Marie Sanginga
1University of Nairobi, Nairobi Kenya, P.O. Box 29053-00100, Nairobi, 2 Université Evangélique en Afrique, D.R.
Congo, P.O. Box 3323, Bukavu DRC, 3N2Africa Program, International Centre for Tropical Agriculture (CIAT) 823-
00621, Nairobi Kenya, 4Universite Catholique de Bukavu, D.R. Congo, P.O. Box 365, Bukavu DRC.
Received 11 July, 2016; Revised 10 November, 2016; Accepted 14 November, 2016 and Published 25 March, 2017
Identification of effective indigenous Bradyrhizobium strains which nodulate soybean varieties could trigger
development of an industry for inoculant production with use of strains adapted to local conditions. This study
was conducted to identify and select effective local rhizobia strains nodulating soybean in South Kivu soils.
One hundred and seven isolates collected from root nodules in South Kivu were tested in sterile sand using the
modified Leonard’s jars and in potted field soils. Each jar and pot was inoculated by 1ml of broth culture
concentrated at 109cells per milliliter. From the first screening, only 10% of these isolates produced higher
nodules number and plant shoot dry weights (p˂0.001) compared to the commercial strain USDA110 and were
selected for evaluation using soils as rooting media in three liters PCV pot in the greenhouse. From the potted
soils experiment, among twelve outperforming isolates, only six isolates produced higher nodules and shoots
dry weight (p˂0.001) compared to the commercial strains and uninoculated controls, and were considered as
effective and competitive strains. This isolates includes NAC10, NAC22, NAC37, NAC67, NAC40 and NAC75.
Nodules number highly correlated with Shoot weight. There exist effective indigenous rhizobia in South Kivu
soils for inoculants production.
Keywords: Indigenous rhizobia, effectiveness, selection, soja, South Kivu.
The identification of effective local Bradyrhizobium strains
that nodulate with Soya has as a goal the development of
a production industry of the inoculants using the
*Corresponding author mail: or
strains adapted to local conditions. This study was
carried out at the IITA Kalambo station and aims to select
the effective local strains that nodulate soya in the soils of
South Kivu. 107 isolates were collected from legume
nodules and tested under sterile conditions in the
greenhouse, using as substrate sterile sand in modified
Leonard jars. Each seed was inoculated with 1 ml of con-
Ndusha et al. 368
centrated culture at 109 cells per milliliter. Only 10% of
these isolates produced a high number of nodules and a
high aerial biomass weight (p˂0.001) compared to the
USDA110 commercial strain and were selected to be
tested in 3L capacity pots using the soils of the fields as
substrate in the greenhouse. Each pot was also
inoculated with 1 ml of isolate. Of the strains tested, only
six produced a high number of nodules and a high
biomass weight compared to the native strains but also to
the USDA110 commercial strain. These strains were
therefore considered effective and competitive. These
strains are: NAC10, NAC22, NAC37, NAC67, NAC40 and
NAC75. Each time the strains produced a large number
of nodules there was also a high weight of biomass.
Keywords: Effectiveness, indigenous Rhizobium,
Selection, Soybean, South Kivu.
The soybean crop is one of the most important crops
worldwide. Soybean seeds are important for both protein
meal and vegetable oil. Soybean is on top of being an
excellent source of quality protein and vegetable oil. The
crop is grown on an estimated 6% of the world’s arable
land, and since the 1970s, the area in soybean
production has the highest percentage increase
compared to any other major crop (Hartman et al., 2011).
It also plays a fundamental role as food and cash crop,
livestock’s feed and as a soil fertility amendment through
Biological nitrogen fixation (BNF) (Giller, 2001; Mapfumo
et al., 2001). In South Kivu (Eastern Democratic Republic
of Congo), soybean demand is increasing as result of
development of industry for soybean processing (IITA,
2014). Therefore increasing soybean production is a
priority. The use of inoculation is the most profitable way
to increase soybean production due to it low cost (Ronner
et al., 2016).
Inoculation is aimed at providing sufficient numbers of
viable effective rhizobia to induce rapid colonization of
the rhizosphere allowing nodulation to take place as soon
as possible after germination and produce optimum
yields (Deaker, 2004). Inoculation of legume seed is an
efficient and convenient way of introducing viable rhizobia
to soil and subsequently to the rhizosphere of legume. It
is necessary in the absence of compatible rhizobia and
when rhizobial populations are low or inefficient in fixing
N (Fening and Danso, 2002; Abaidoo et al., 2007).
Nodulation of soybean (Glycine max (L.) Merrill) requires
specific Bradyrhizobium species. Compatible populations
of these rhizobia are seldom available in soils where the
soybean crop has not been grown previously (Abaidoo et
al 2007). The population size of effective indigenous soil
rhizobia and the concentration of Nitrogen in soils is a
reliable index for the capacity of a legume crop to derive
N through BNF and to determine whether or not the
legume will respond to added rhizobia or fertilizer N
(Zengeniet al., 2006; Appunu and Dhar, 2006).
Nodulation and nitrogen fixation in legumes occurs
effectively if other mineral elements such as Phosphorus
(P), Potassium (K) and Sulphur (S) are present in the soil
(Njeru et al.; 2013).
Inoculation however, is not universal and does not always
elicit positive responses. It is necessary in the absence of
compatible rhizobia and when rhizobial populations are
low or inefficient in fixing N (Brockwell et al., 1995;
Catroux et al., 2001; Fening and Danso, 2002; Abaidoo
et al., 2007). Nodulation of soybean (Glycine max (L.)
Merrill) requires specific Bradyrhizobium species
(Abaidoo et al, 2007).
A common approach to improve symbiotic nitrogen
fixation and legume productivity has been the reliance on
superior of very effective exotic rhizobia strains as
inoculants. This approach has failed to achieve the
desired responses in a lot of environment (Howieson et
al., 2005). In many cases, introduced strains from
commercial inoculants fail to compete the population of
native rhizobia (Zengeni et al., 2006; Appunu and Dhar,
2006). Therefore, continual identification of new, elite
isolates offers the opportunity to improve BNF within fine-
tuned geographical targets. This study evaluates the
effectiveness of indigenous rhizobia isolates from wild
and cultivated legumes across different agroecological
conditions in South Kivu soils.
Collection, isolation, characterization, and
authentication of indigenous rhizobia strains.
Nodules were collected from cultivated and wild legumes
in South Kivu between 400 m and 1600 m of elevation.
In the field, the legumes were identified using botanical
key and plants were uprooted carefully; avoiding
detaching secondary roots from plant as nodules may be
found on lateral roots as well as the taproot.
The growth media used for rhizobial isolation was the
Yeast Extract mannitol Media (Vincent, 1970). Nodules
were surface sterilized and rhizobia isolated as described
369 Afr. J. Soil Sci.
Table 1. Shoot weight (in grams) and effectiveness index (E.I) induced by best performing strains on the two promiscuous soybean
Rhizobia isolates
Plant shoot dry weight(g)
Effectiveness index
by Somasegaran and Hoben (1994). Typical rhizobia
were recognized by their appearance, the growth rate
and the production of alkalinity or acidity on the media
(Somagaran and Hoben, 1994). Rhizobia isolates
obtained were subject of nodulation test as described by
Koala et al, 2010. The cultures of presumptive isolates
were confirmed as rhizobia and were given collection
numbers. From this nodulation test one hundred and
seven isolates were collected.
Strains selection
Two sets of experiments were performed in the controlled
condition of greenhouse to select effective local rhizobia
strains. The temperature in the greenhouse was varied
between 250C and 380C.
Strains testing in sterile conditions
Modified Leonard’s jars assembly were used as growth
unit. A commercially available 1.5 capacity water bottle
was cut into two halves; one portion used for holding the
nutrient solution and the other part was inverted for the
growth media (sterile sand). The assembly was covered
by a grey paper bag to protect roots and nutrients
solution from light. A centrally positioned lantern wick
made from braided cotton, which runs through the length
of the bottle and extends out of the mouth of the bottle
Ndusha et al. 370
Table 2. Nodules number and plant shoot dry weight (in grams) produced by promiscuous varieties inoculated with indigenous rhizobial in the two
site soils
Site soil
nodules number
plant shoot weight
nodules number
Plant shoot
into the reservoir containing the nutrient, was used to
irrigate the growth medium. 750 grams of well-washed and autoclaved sands were used like growth medium
(Burton, 1984). Nitrogen-free nutrient solution (Broughton
371 Afr. J. Soil Sci.
Figure1. Competitiveness index of local rhizobia isolates.
and Dilworth, 1970) was used for growth of Soybean.
This study was conducted at International Institute of
Tropical Agriculture (IITA) situated in Eastern DRC. A
Split plot on Complete Randomized Design with four
replicates consisting of 111 treatments was established in
the greenhouse, 107 indigenous test isolates, two
reference strains (SEMIA5019 and USDA110), and non-
inoculated plants with and without mineral N. Two factors,
soybean variety and rhizobia strains were under study
and the strain was considered as main factor.
Promiscuous soybeans SB19 and SB 24 were used as
the test crop. Soybean seeds were surface sterilized
(Somasegaran and Hoben, 1994), pre-germinated in
sterile sand and three uniform seeds transplanted per
pot, later thinned to two. Test isolates were cultured in
Yeast Extract Mannitol broth (YMB) seven days in
advance (Vincent, 1970), incubated at 280C until turbid
and 1 ml of broth was applied to the roots of each plant.
For the mineral nitrogen control, KNO3 (0.05%) was
applied as described by Broughton and Dillworth, (1970).
After eight weeks, nodulation was observed by careful
recovery of roots and shoots were harvested, oven dried
and weighted. An Effectiveness Index was calculated by
dividing shoot biomass of test isolates by that of USDA
110. With this index and isolate performance relative to
experimental controls, isolates were categorized as
ineffective (less than -N control), partly effective (<75% of
USDA 110), effective (75% or equal to USDA 110) or
highly effective (>USDA 110) and ranked in ascending
Strains testing for competitiveness in potted field’s
Soils collected from farm with no history of inoculation
and soybean cultivation in Walungu and Katana in East
DRC were used as media for competitive screening in the
greenhouse. The soil was characterized for its chemical
composition as follows. Soil pH was measured on a 1:2.5
soil suspension to water using a pH meter as described
by Okalebo et al., (2002). Soil total N was determined by
the Kjeldahl method and available soil P was determined
by Olsen method (Okalebo et al., 2002). This experiment
was established also in the greenhouse at IITA Kalambo
station using the soil with the 12 best performing isolates
from the first screening. This experiment utilized three
liter PVC pot containers. Three seeds per plot were
transplanted in the pot thinned later to two. YMB isolates
preparation was done as described previously and the
test crops included the two soybean promiscuous
Competitiveness index
Rhizobia isolates
Ndusha et al. 372
Figure 2. Relation between nodules number and shoot dry weight
varieties, SB24 and SB19. Indigenous rhizobia
populations in the test soil were determined using the
plant infection technique (Somasegaran and Hoben,
1994). Experimental units were arranged as a Split-Plot
by varieties+ with four replicates. The factor strain was
again considered as main factor. The soil was fertilized
with Sympal, a commercially available blend for legumes
(0-23-15 + Ca, Mg and S) at a rate of 500 kg ha-1 mixed
with two kg of soil pot-1. Pots were regularly watered with
rhizobia-free water. After eight weeks, plants were
carefully uprooted, nodules observed, shoots, roots and
nodules recovered, oven dried at 70°C for 48 hours and
plant biomass recorded. Data was recorded in an excel
spread sheet and submitted to the analysis of variance
and LSD was used to make comparisons among the
means at p (0.05) level of significance using GENSTAT
software version 16.
On sterile media, significant differences in plant
greenness and nodules score were observed (P˂0.001)
among plants inoculated with different strains and non-
inoculated controls (−N treatments) while tested in
aseptic conditions. The scores for greenness showed that
plants inoculation with 10% of isolates improved the
green color than the un-inoculated without nitrogen
control but lower than plus N control (data not presented).
The nodule scores were higher with these same isolates,
and were positively correlated (r=0.65) to the plant
greenness (p˂0.001). Nodules were observed on all
varieties for the majority of isolates. Only the treatment
+N and N produced any nodule. There were more
nodules on the variety SB24 than SB19 (p˂0.046). The
nodules induced by different isolates were highly different
ranging from 1 to almost 30 (p˂0.001). The isolates
NAC42, NAC40, NAC46, NAC19 and NAC66 produced
the highest nodules number. There was no significant
interaction in nodulation response between the soybean
variety and the rhizobial isolates (p˂0.667). The shoot
weight also varied significantly between strains (p˂0.001)
and the two varieties (p˂0.006). The interaction of the two
factors was significant (p˂0.019) on the shoot weight.
The effectiveness index of isolates NAC67, NAC45,
NAC38, NAC22, NAC75, NAC51, NAC19, NAC50,
NAC66, NAC40, NAC10, NAC42, NAC23, NAC46 and
NAC 37 outperformed the reference strain USDA110 as
showed in the table 3 and were considered for testing in
potted field soils. Nodules number and plant shoot weight
highly correlated (r=0.73 and p˂0.001). The indigenous
rhizobia were classed into categories basing on
effectiveness index (EI); highly effective, effective and
Ineffective, where Effectiveness Index (EI) = isolate shoot
y = 0.083x + 1.259
R² = 0.545
0 5 10 15 20 25 30
Shoots dry weight
Nodules number
Shoot dry weight
Linear (Shoot dry weight)
373 Afr. J. Soil Sci.
dry weight/USDA 110 shoot dry weight. Highly effective
indigenous strains outperformed the commercial strain
USDA 110.
Ten best performing isolates in sterile conditions were
selected to be tested for competitiveness in two sites
potted soils in the greenhouse. The results of soil
analysis showed that the Kalehe pH is around the
neutrality while the Walungu pH is acidic. The Kalehe soil
had a pH of 6.57 and contained 0.29 g N kg 1 while the
Walungu soil had a pH of 5.1. The total Nitrogen is 0.29%
in Kalehe soils while this is 0.17% in Walungu soils. 1,
Extractable P content was 14.32 mg kg 1 and 6.29 mg kg
1 at Kalehe and Walungu, respectively and the rhizobial
cell concentration in the soil was 103 and 102.
Nodulation of promiscuous varieties with indigenous
bradyrhizobia isolates across treatments were observed
on all varieties at both sites soils and for all treatments
except the +N treatment, where nodules were very rare.
The nodules number was positively correlated to the
plant shoot weight (p˂0.001 and r=0.46) as shown in
figure 1. There were more nodules per plant and shoot
dry weights at Kalehe than Walungu soils (p˂0.001). The
highest nodules number and shoots dry weights were
recorded with the rhizobial isolates NAC22, NAC40,
NAC37, NAC10, NAC67 and NAC75 in both sites soils
compare to the commercial strain USDA110 (table 2).
When averaged over treatments, nodule numbers ranged
from 7.0 to 170 nodules, fresh weight ranged from 0.25 to
3.19 grams. There was a significant interaction (P<0.05)
between the soil site and type of rhizobial strain in
nodules number and shoot dry weight. In general, the
nodules number and shoot dry weight were higher in
Kalehe soil than Walungu with most of the isolates on the
two test varieties. The local rhizobia strains were classed
into four classes: Competitive and highly effective, Less
competitive and highly effective, Less competitive and
less effective, Competitive and less effective.
For the first experiment in sterile sand, 107 strains were
tested but only ten strains were classified as highly
effective compared to commercial strain and to non-
inoculated control with nitrogen. The same results were
obtained by Waswa et al., (2015) in their study on
identifying elite Rhizobia strains for soybean (glycine
max) in Kenya. Among one hundred indigenous isolates
tested only 10% was higher effective compared to the
reference strains. Musiyiwa et al. (2005) found the same
results. From the 129 indigenous isolates tested, only
three isolates had significantly higher nitrogen fixing
potential in comparison to the commercial strains. The
number of effective rhizobia is Very low in tropical
(Sanginga et al., 2000) and a key to overcoming their
competitive advantage is through the composition and
delivery of legume inoculants (Thies et al., 1991).
The results showed that there was a significant difference
in green color of plants inoculated with different rhizobial
isolates compared to the non-inoculated control without
nitrogen. This elucidates the effectiveness of these
indigenous strains isolated from South Kivu soils in
nitrogen fixing. Nitrogen is the major constituent of
chlorophyll that confers green color to the plant.
Nitrogenous compounds resulting from nitrogen fixation
process are exported from root nodules in the form of
ureides (allantoin and allantoic acids) and translocated to
the leaves where they are catabolized and used for the
biosynthesis of chlorophyll (Winkler et al., 1987). This
parameter of measuring the nitrogen fixing ability of
different strains must be validated by other parameters.
The difference in shoot weight produced by different
varieties is due to the genetic variation in biomass
production. The same results were obtained by Appunu
et al., (2008) in their study on the variation in symbiotic
performance of Bradyrhizobium japonicum strains and
soybean cultivars under field conditions. By this study the
biomass accumulated by different cultivars was highly
different. The same differences have been experimented
by Abaidoo et al., (1999) and Jemo et al., (2006).
The difference in nodulation as well as in shoot dry
weight observed with different indigenous isolates is due
to the difference in the genetic but also in effectiveness of
each strain since the work was conducted in the
greenhouse, where some climatic variations were
controlled. Abaidoo et al. (2007) classified the isolates
tested into four symbiotic phenotypic groups based on
their symbiotic effectiveness as follows: ineffective, less
effective, moderately effective and effective. The group
less effective was constituted by isolates that were likely
to have caused rhizobiotoxine-induced chlorosis on the
soybean genotypes.
Abaidoo et al. (1999) stated that the indigenous rhizobia
that nodulates promiscuous soybeans are present in low
numbers in many soils. Tropical soils are often rich in
less-effective, native rhizobia and a key to overcoming
their competitive advantage is through the composition
and delivery of legume inoculants (Thies et al. 1991).
Some isolates induced higher shoot dry weight compared
the nitrogen plus control and this confirmed observations
by other authors in which the application of small
amounts of N-fertilizer did not provide a major benefit.
Even more, it was observed that the application of 200 kg
N/ha did not improve seed yields in comparison with
Ndusha et al. 374
soybean rhizobial inoculation, as it was previously
demonstrated (Hungrı´a et al., 2006; Albareda et al.,
2009). Rhizobium inoculation is a cheaper and usually a
more effective agronomic practice for ensuring and
adequate supply of nitrogen for legume-based crop than
the application of fertilizer nitrogen (Marufu et al., 1995).
The interaction between the variety and the rhizobial
isolates was also observed on shoot dry weight. This may
be explained partly by the host specificity of some
rhizobial strains and soybean germoplasm. Though the
two test varieties are promiscuous, some rhizobial
isolates may prefer one to another. The difference in
preference may be due to the quality and quantity of
exudates produced by different varieties.
The potted field soils experiment results showed that the
nodules number and shoots dry weight produced by the
tested rhizobial isolates varied largely according to the
site soils. This difference between the two sites soils is
due to differences in physico-chemical properties of the
two sites soils used for potted experiment. In the Kalehe
soils the pH was around the neutrality when in the
Walungu soils the pH was acidic. The nitrogen content as
well as phosphorous was in sufficient level in Kalehe soils
than Walungu, for example phosphorous content was 14
mg Kg-1 in Kalehe soils against 6 mg Kg-1 in Walungu
soils. Plant growth and micro organisms activity depend
upon soil reaction and possible condition of the soil i,e.
soil acidity, neutrality and alkalinity. Soil management
practice, which build up organic matter content and arrest
pH decline e.g. limiting are likely to create soil condition
that encourage survival, persistence and higher
population of Rhizobium in soil. Phosphorus is known to
stimulate the Rhizobial growth (Subba Rao, 1999). A
study conducted by Jemo et al., (2006) showed that P
application highly significantly increased shoot dry matter,
P uptake, nitrogen fixation and grain yields of the grain
legumes. Two of the soybean and two of the cowpea
genotypes were more efficient at using P. Another study
conducted by Wasike et al., (2009) showed that P
improved nodulation across tested varieties at both sites
although the magnitude of this response was higher at
Bungoma which had a low inherent soil P status and
most of the nodules contained leghaemoglobin indicating
active nitrogen fixation.
The significant interaction between site and treatments
(rhizobial strains) in nodulation response at both sites
suggests that some strains may be pH sensitive and may
require relatively specific amount of phosphorus than
others for optimal nodulation (Munns et al., 1981). Soil
type affects the ability of introduced organisms to
colonize the rhizosphere or root soil interface (Kluepfel,
1993). It was reported that the survival of Rhizobium
leguminosarum in natural soil was greatly affected by
certain protozoa, fungi and bacteriophage (Chonkar and
Subba Rao, 1966; Subba Rao, 1999) and the number in
these organisms varied according to soils.
The study showed also that there is a high significant
difference between the selected rhizobial isolates from
South Kivu soils. Their differential abilities in nodules
number and plant shoots dry weight might be due to their
genotypic differences since soil and climatic variations
were minimal. Six indigenous rhizobial isolates (NAC22,
NAC40, NAC75, NAC37, NAC67 and NAC10) out-
competed the commercial strain USDA110 in nodulation
and dry matter production of the two promiscuous
soybeans when soil was used as media and were
classified as competitive and effective. Musiyiwa et al.
(2005) reported the presence of indigenous rhizobia
nodulating promiscuous soybean varieties in many soils
in Zimbabwe. Some of the isolates were as good or
superior in N2 fixation effectiveness to commercial
inoculants strains under greenhouse conditions.
Among the tested isolates, some were classified as
effective in sterile sand but less effective in potted-soils
because of the presence of indigenous rhizobia. Streeter
(1994) stated that the presence of B. japonicum in the
inoculated soil sites might compromise nodulation
competitiveness of the introduced rhizobia (Streeter,
1994). The survival of Rhizobium depends on their ability
to compete favorably with indigenous soil Rhizobia and
subsequently from a large proportion of nodule (Elkins et
al,.1976). This may be also associated with ability of
rhizobia to induce signals for nodulation with many types
of soybean germoplasm (Martı´nez-Romero, 2003).
Some authors stated that the survival of Rhizobium is
lower in natural soil than in sterile soil or media. Soil is a
complex matrix that is difficult to manipulate to control
environmental factors and to prefect interaction with the
indigenous microbial community (Young and Burns,
1993). From a study conducted by Saleh (2013) the
highest number of Rhizobial population was observed in
sterile soil than in non sterile, suggesting that the viability
of Rhizobium was more in sterile soil.
The two varieties, SB24 and SB19 produced no
significant differences in shoots weight. This suggested
that as both of them are promiscuous, they nodulated
samely with different isolates. This result is similar to that
obtained by Appunu and Dhar (2006). They tested six
soybean cultivars for variation in symbiotic performance
with five B. japonicum. Analysis of data revealed that
among the six cultivars tested, only two cultivars
recorded higher dry matter accumulation after inoculation
with different B. japonicum strains. The same average dry
matter production was observed for other cultivars.
375 Afr. J. Soil Sci.
The significant interaction was observed between variety
and site on nodules number. Soybean varieties differ
significantly in their tolerance to acidity, salinity and
different level of nutrients. Assa (2002) has studied the
effect of salinity stress on growth and nutrient
composition of three soybeans cultivars. By this study,
there was a high significant difference on shoots dry
weights between the three cultivars under different
The nodules number and plant shoots weight positively
correlated suggesting that there is a clear response of the
soybean variety to inoculation. Nodules number also
positively correlated with the nodules dry weight
highlighting the rhizobial isolates effectiveness observed
in the sterile sand. This may be due to the fact that
nodules of introduced effective strains are often
numerous as well as of large sizeDifferent concentration
of broth cultures used for inoculation was not considered
in this study because in the study conducted by Albareda
et al., (2009), all determined parameters (nodule dry
weight, seed yield and seed N content) of soybean
inoculated with different isolates were not significantly
different (P < 0.05) among the bacterial concentrations
tested. In the case of USDA110, nodulation and seed
yield of soybean were not statistically different when the
inoculum rate exceeds 105 rhizobia/seed.
The N2 Africa project of CIAT/TSBF is acknowledged for
the financial support. The IITA Kalambo DRC station
assisted in advising and logistical support. The University
of Nairobi and Université Evangélique en Afrique
provided scientific support. The agriculture faculty’s dean
of Universite Evangelique en Afrique, Dr. Katcho Karume
is acknowledged for his comments on this paper.
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Full-text available
RÉSUMÉ. Le front cotonnier camerounais dans l’espace soudano-sahélien connaît une dynamique productive du soja impulsée par une demande croissante du secteur agroalimentaire national et du marché transfrontalier avec le Nigeria. Cette dynamique est porteuse de profondes mutations des agro systèmes locaux. D’une simple culture de case non référencée dans les statistiques agricoles régionales, le soja occupe depuis l’année 2010, le 2ème rang des légumineuses cultivées après l’arachide, le niébé et le voandzou. L’évolution rapide des superficies cultivées de 6705 ha en 2008 à 15 020 ha en 2018 est révélatrice de l’engouement manifesté par les agriculteurs pour cette spéculation qui, malgré la quasi absence d’encadrement des pouvoirs publics, structure désormais une chaîne de valeur porteuse d’opportunités de construction d'une politique de Science et Technologie (S&T) dans le secteur agroalimentaire d'une part et d’amélioration des revenus des agriculteurs d'autre part. Cette dynamique est à un second niveau porteuse d’enjeux environnementaux dans un espace exposé à la dégradation accélérée de son milieu naturel. L’objectif de cette recherche est donc d’analyser les enjeux environnementaux induits par la culture du soja. Les résultats montrent que le développement de cette culture induit la régression accélérée du couvert végétal et la dégradation des sols. Le premier enjeu est lié à l’extension des superficies cultivées par des défrichements. Le second est inhérent à l’intensification de l’utilisation des produits phytosanitaires et principalement du glyphosate, dont l’usage pour la lutte contre les adventices contribue à accélérer l’acidification des sols. ABSTRACT. The Cameroonian cotton basin front in the Sudano-Sahelian area is experiencing a soybean production dynamics drivin by growing demand from the national agri-food sector and the cross-border market with Nigeria. This dynamic is bringing about profound changes in local agro-systems. From a simple crop not referenced in regional agricultural statistics, soybean has become since 2010 the second most important legume crop after groundnuts, cowpeas and voandzou. The rapid increase in cultivated areas from 6,705 ha in 2008 to 15,020 ha in 2018 is indicative of the enthusiasm shown by farmers for this speculation, which, despite the lack of supervision from the Government, is now forming a value chain. This dynamics is also at a second level carrying environmental issues in a space exposed to the accelerated degradation of its natural environment. Thus, the objective of this research paper is to analyse the environmental issues generated by soybean production. The results show that soybean production causes vegetation cover loss and soil degradation. The first issue deals with the extension of cultivated areas through land clearing. The second is inherent in the massive use of phytosanitary products, especially glyphosate, whose use to control weeds contributes to accelerating soil acidification. MOTS-CLÉS. Système Soja, dynamique agricole, front cotonnier, soudano-sahélien, Cameroun. KEYWORDS. Soybean, agricultural dynamics, value chain, environment and Cameroon. JEL: O13, O31, O32, O33, O38, O55
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Cancer bush (Sutherlandia frutescens), which is facing extinction, can be conserved through cultivation using best agricultural practices that include nodulation with effective rhizobia bacteria. The objective of the study was to compare the efficacy of commercial and native nodulation bacteria on productivity of S. frutescens over two seasons. Seasonal interaction on productivity variables was not significant (P < 0.05), with pooled data (n = 75) subjected to analysis of variance. Treatments had a significant effects on plant variables, contributing from 58 to 91% in total treatment variation (TTV) of the variables. Relative to untreated control, commercial strains significantly increased plant variables from 31 to 44%, whereas wild strains increased the variables from 17 to 195%. Similarly, both commercial and native strains significantly increased nitrogen, protein and symbiotic efficiency, with magnitudes of native strains being significantly higher than those of commercial strains. Treatments had no significant effects on K and protein in leaf tissues of S. frutescens. In conclusion, the native strains as investigated in the current study have the potential for use in the husbandry of cancer bush.
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There has recently been concern in Brazil whether biological N2 fixation (BNF) is capable of meeting the increased N needs of newly released more productive cultivars, as well as doubts about the advantages of annual reinoculation of seeds. Forty experiments were performed over 3 yr in oxisols containing at least 103 cells of Bradyrhizobium g-1 in the State of Paraná, southern Brazil to estimate the contributions of BNF and of N fertilizer. The experiments were performed at two sites, Londrina and Ponta Grossa, under conventional (CT) or no-tillage (NT) systems, with two cultivars [Embrapa 48 (early-maturing) or BRS 134 (medium-maturity group)]. Treatments included non-inoculated controls without or with 200 kg of N ha -1, and inoculation without or with N fertilizer applied at sowing (30 kg of N ha-1), or at the R2 or R4 stage (50 kg of N ha -1). Compared with the non-inoculated control, reinoculation significantly increased the contribution of BNF estimated by the N-ureide technique (on average from 79 to 84%), grain yield (on average 127 kg ha -1, or 4.7%) and total N in grains (on average 6.6%). The application of 200 kg of N fertilizer ha-1 drastically decreased nodulation and the contribution of BNF (to 44%), with no further gains in yield. Application of starter N at sowing decreased nodulation and the contribution of BNF slightly and did not increase yields, while N fertilizer at R2 and R4 stages decreased the contribution of BNF (to 77%) and also yields. Estimates of volatilization of ammonia ranged from 15 to 25% of the N fertilizer applied, and no residual benefits of the N fertilizer in the winter crop were observed. The results highlight the economical and environmental benefits resulting from replacing N fertilizer with inoculation in Brazil, and reinforce the benefits of reinoculation, even in soils with high populations of Bradyrhizobium.
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We investigated the current use of legumes in soil fertility management and the feasibility of promoting use of pigeonpea in smallholder farming systems of a Communal Area in Northeast of Zimbabwe. Participatory rural appraisal methods were used to establish farmer management strategies and perceptions on major constraints to crop productivity. Soil fertility parameters were evaluated through farmer participatory experiments. The study revealed limited cultivation of legumes for both human nutrition and soil fertility management. Legumes were generally regarded as women's crops, and therefore minor, because of men's domination over women in the household decision-making process. Balancing gender interests in terms of allocation of inputs and distribution of benefits at household level was identified as a major challenge to the implementation of legume technologies. Poor extension thrusts with respect to legume production, and poor agronomic practices were identified as major production constraints. Over-emphasis on maize in the current extension packages led to the relegation of legumes to the status of 'minor crops'. Participatory experiments suggested that pigeonpea can be successfully grown by farmers under poor soil fertility conditions. The crop yielded about 3 to 9 t ha-1 of shoot biomass in a single cropping season, and up to 23 t ha-1 after two seasons of growth. High amounts leaf litter released by the crop in one season (up to 3 t ha-1) are considered a potentially viable source of nutrients for subsequent crops, as confirmed by a 22% maize yield increase obtained from a field that was previous cultivated with pigeonpea.RÉSUMÉ Les investigations sur l' utilisation des légumineuses dans la gestion de fertilité du sol ainsi que les possibilités d' incorporer le pois cajan dans le système agricole de petits fermiers ont été fait dans un milieu rural au Nord-Est du Zimbabwe. La méthode "Participatory rural appraisal" a été utilisée pour déterminer les stratégies de gestion du sol et les perceptions qui contribuent à la réduction de la productivité de la récolte. Les paramètres de fertilité du sol ont été analysés en collaboration avec des agriculteurs. Cette étude a révelé qu' il y a une utilisation limitée de légumineuses dans l' alimentation des gens ainsi que dans la gestion de fertilité du sol. Les légumineuses sont géneralement considérées commes la récolte pour les femmes, sur ce, de peu d' importance, et à cause de la domination des hommes dans la prise de décision dans le foyer. L'exécution des téchnologies d' incorporer les légumineuses dans le système de production agricole s' est heurtée à un problème majeur de domination de l'homme, ses préférences dans la répartition et la distributions des intrants et les bénéfices. Un autre problème identifié, c'est une vulgarisation très limitée de la production de légumineuses et une difficile adaptation agronomique de variétés de légumineuses qui sont déjà dans le système. Le système de vulgarisation existant s'est concentré plus sur la production du maïs, ce qui a mené à considérer les lègumineuses commes les plantes de moins d' importance. Les expériences participatives ont suggeré que le pois cajan peut être produit par les fermiers dans des sols moins fertiles. La production a été estimée de 3 à 9 t ha-1 de biomasse dans une seule saison de production, et de 23 t ha-1 après deux saisons. Une quantité considérable de litière de feuilles venant de plantes dans une seule saison (jusqu'a 3 t ha-1) est considéree comme une source importante de nutriments pour les plantes consécutives, comme l' augmention de 22% de production de maïs l'a confirmé après une culture de pois cajan. (Af Crop Science and Production: 2001 9(4): 629-644)