American Journal of Plant Sciences, 2012, 3, 1654-1660 Published Online November 2012 (
Evaluation of Biological Soil Fertility Management
Practices for Corn Production in Oxisols
Mupala G. Muyayabantu1, Bakach D. Kadiata1, Kabwe K. Nkongolo2*
1Faculty of Agronomy, University of Kinshasa, Kinshasa, DR-Congo; 2Department of Biological Sciences, Laurentian University,
Sudbury, Canada.
Email: *
Received August 5th, 2012; revised September 12th, 2012; accepted October 15th, 2012
Field trials on the management of soil biological fertility with aim to increasing corn production were conducted in a
savannah region of the DR-Congo. Three organic matters including fresh biomass of Entada abyssinica, Tithonia diver-
sifolia, Stylosanthes gracilis and a mineral combination of nitrogen and phosphorus (NP) (115-63-0) along with a con-
trol (without fertilization) were evaluated for corn crop growth and production. The field trial was a completely ran-
domized design with four replicates. Plant height, basal stem diameter, and yield components were assessed. Irrespec-
tive of fertilization treatments and variety, maize showed a similar growth up to 20 days after sowing (DAS), and then
two distinct trends were observed. At 60 DAS, plant height and basal diameter were significantly bigger in plots treated
with NP, T. diversifolia and E. abyssinica compared to S. gracilis treatment and control (NoF). This pattern was also
confirmed with agronomic traits such as cob length, number of kernel per cob, and net grain yield. The local variety was
the least productive under any treatment. In general, the response of corn crop to organic and inorganic fertilization
showed that the mineral combination (NP) increased the most grain yield and other yield components compared to un-
fertilized trial, followed by T. divessifolia and E. abyssinica. NP and T. diversifolia treatments increased significantly
and equally soil potassium content compared to control and other treatments. Application of T. diversifolia appears a
more cost effective approach for small farmers to improving fertility of the oxisol prevailing in Central Africa compared
to mineral fertilizers.
Keywords: Oxisols; Organic and Inorganic Fertilization; Corn Crop Production; Soil Fertility; DR-Congo
1. Introduction
Maize is the third world most grown grain cereal after
wheat and rice and is the main staple food in many sub-
Saharan African countries including the DR-Congo. Its
production in these region depends on the rain-fed tradi-
tional agriculture prone to slash-and-burn characterized
by quick soil degradations. This agronomic system
makes the soil very impoverished in nutrients.
In fact, soil factors are among the most determining
constraints which affect the crop production in the de-
veloping countries, particularly under the tropics, where
low levels of nitrogen and phosphorus especially consti-
tute the most limiting factors to plant growth [1,2]. It is
therefore necessary to replenish soil with these nutrients
in order to sustain its productivity [3-5].
However, inorganic fertilizers which are known to in-
crease the productivity of soil are rather difficult to ac-
cess for farmers due to their high cost [6,7]. They also
induce degradation of the ecosystems and cause some
risks for human health. In addition, farmers have limited
knowledge on chemical fertilization application and
management. Thus, organic farming stands to be the ap-
propriate solution for improving and preserving soil fer-
tility [8-10]. Use of organic manure remains one of the
reliable ways to improving sustainably tropical acid soils
in which high deficiency of available phosphorus pre-
vails [11,12]. The main challenges are the determination
of the required quantity of organic fertilizers, the assess-
ment of a balanced ratio of nutrients from organic ma-
nures as well as the synchronization of their availability
in response to crop demand [7,13].
Kretzschmar et al. [14] reported that mulch application
to sandy soil significantly induced a change in soil
chemical characteristics such as CEE, pH, available K
and P from P solubilization out of Al and Fe chelates in
exchange of organic acids. The application of organic
manure to soil is proven to improve chemical, physical
and biological soil characteristics which increase nutri-
ents availability and their assimilation by the crops [15].
Several studies have shown that use of T. diversifolia
*Corresponding author.
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Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols 1655
foliages increased crop yields through solubilization of
available phosphorus [7,16]. It is thus assumed that the
use of leafy biomass of S. gracilis, E. abyssinica or T.
diversifolia could sustain fertility of nutrient-deficient
Thus, the present study was undertaken with the ob-
jective of assessing three organic matters (E. abyssinica,
T. diversifolia and S. gracilis) as manures compared to
mineral N-P combination on corn crop production in a
savannah region of DR-Congo.
2. Materials and Methods
2.1. Study Site
The study was carried out at the research station of the
DR-Congo National Institute for Agronomic research
(INERA) in Gandajika, in Eastern Kasaï province. The
region falls within the Aw4 climate type according to
Köppen classification characterized with 4 months of dry
season (from mid-may to august) coupled with 8 months
of rainy season, sometimes interrupted by a short dry
season in January/February. Daily temperature averages
25˚C and annual rainfall is close to 1500 mm.
2.2. Soil Characterization
The study site was on one-year fallow and colonized
mainly by Imperata cylindrica prior to the experiment
setup. In general, the soil of the targeted locations of
Eastern Kasaï (Gandajika) is made up of a sandy overlay
on loamier sediment that often rests at low depth on an
ancient lateritic slab. The adsorbing complex is relatively
well saturated and it remains still some alterable minerals.
The clay fraction less important seems not only consti-
tuted of kaolinite alongside in relation to the depth of
loamy sediment. The site topsoil has a high rate of grav-
els and very few fine elements.
Soil samples were collected according to standard
protocols. Soil pH was measured in water and a neutral
salt solution pH (CaCl2). Total nutrients in soil samples
were analyzed at MIRARCO laboratories in Sudbury
(Ontario, Canada) following the procedure outlined by
Abedin et al. (2012). Aqua Regia extraction was used. A
0.5 to 0.05 g soil sample was digested with 5 ml each of
concentrated HNO3 and HCL using a MARS 5 Micro-
wave Oven, with the supernatant made to 50 ml volume
with deionized water for analysis by a combination of
Inductively-Coupled Plasma-Optical Emission Spectro-
metry (ICP-AES), inductively-coupled Pasma-Mass Spec-
trometry (ICP-MS) and hydride generation atomic emis-
sion spectrometry (HG-AAS). The quality control meas-
ures included duplicate samples, internal blind reference
materials (IRM’S), spiked blanks, spiked replicates, re-
agents/instrument blanks, preparation control samples,
certified reference materials and instrument control sam-
ples. Detection procedures for carbon and nitrogen were
as described by Abedin et al. [17].
Bioavailable potassium and phosphorus were esti-
mated by extracting 5 g of soil with 20 ml of 0.01 M
LiNO3 in a 50-ml centrifuge tubes in a shaker under am-
bient lighting conditions for 24 hours at 20˚C [17]. The
pHs (LiNO3) of the suspension was measured prior to
centrifugation at 3000 rpm for 20 minutes, with filtration
of the supernatant through a 0.45 um filter into a 20 ml
polyethylene tube and made to volume with deionized
water. The filtrate was preserved at approximately 3˚C
for chemical analysis by ICP-MS. The quality control
program completed in an ISO 17025 accredited facility
(Elliot Lake Research Field Station of Laurentian Uni-
versity) included analysis of duplicates, Internal Refer-
ence Materials (IRM’s), procedural and calibration blanks,
with continuous calibration verification and use of inter-
nal standards to correct for any mass bias. All concentra-
tions were calculated in mass/mass dry soil basis.
The data for the nutrient levels in soil samples were
analyzed using SPSS 7.5 for Windows, with all data be-
ing transformed using a log10 transformation to achieve a
normal distribution. Variance-ratio test was done with an
assumption of data normality in the underlying popula-
tion distributions of the data. ANOVA, followed by
Tukey’s HSD multiple comparison analysis, were per-
formed to determine significant differences (p = 0.05)
among the sites. Data from analysis of samples from
limed and no limed areas were compared using Stu-
dent—T test.
2.3. Genetic Material
The plant materials include three corn (Zea mays L.) va-
rieties, one local (Varloc) and two genetically improved
accessions (Mus and Salongo II). All varieties were pro-
vided by the INERA research station in Gandajika. Leafy
biomass of T. diversifolia and E. abyssinica were col-
lected from trees in the surroundings of Gandajika while
S. gracilis leaves were collected from old pastures.
2.4. Experimental Trials
The land was tractor-plowed, harrowed and surface-lev-
eled with hoes before delimitating experimental plots
within blocks. Field trials were undertaken using a ran-
domized complete block design with four replicates. The
treatments include a control (NoF), a mineral fertilizer
consisting of a combination of nitrogen and phosphorus
(NP 115-63), organic manures with E. abyssinica (E), T.
diversifolia (T) and S. gracilis (S). The quantity of or-
ganic matters to be applied was determined according to
Ikerra et al. (2007) at a rate of 10 kg of leafy biomass per
plot representing 8 t·ha1. Each block measured 21 m ×
Copyright © 2012 SciRes. AJPS
Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols
20.5 m and was made of 20 plots of 4 m × 3 m separated
by 1.5 m and 2 m within and between blocks, respec-
The organic fertilizers were applied four days prior to
sowing through soil incorporation alongside the sowing
rows while the di-ammonium phosphate (DAP) was lo-
cally applied around seedlings ten days after sowing
(DAS) and, then supplemented with urea 30 days later.
Corn seeds were sown in holes at 1 m × 1 m spacing, at ±
4 cm depth.
To assess the effect of each treatment on the three va-
rieties under trial, plant growth (height and stem base
diameter) at 10, 20, 30, 40, 50 and 60 DAS and yield
components (cob length, numbers of grain rows and of
grains by cob, net yield) were determined. The growth
measurements were performed in morning up to 60 DAS
while yield parameters were assessed at crop harvest.
Corn cobs length was measured and then kernel rows
counted. Grains were sun-dried up to 17% of moisture
content and later counted and then weighed to determine
the net yield.
To compare the effect of various treatments on corn
crop, collected data were subjected to the analysis of
variance (ANOVA) using the GENSTAT software (Ed.
Discovery Free Version). The least significant difference
(LSD) test and Tukey’s HSD multiple comparison analy-
sis served in separating treatment means at 5% probabil-
ity level.
3. Results
3.1. Soil Nutrient Content
Previous analyses of the soil at experimental sites re-
vealed no significant differences for nutrient content and
distribution as well as the pH levels. In the present study,
nutrient content in soil at plant maturity stage was as-
sessed after various treatments. There were significant
differences for total potassium in plots fertilized with NP,
E. abyssinica, and T. diversifolia compared to soils from
control sites (Tables 1 and 2). The highest amount of this
nutrient was found in soil from NP and T. diversifolia
treatments. No significant differences were observed
among soil samples for total phosphorus content. The
total level of nitrogen was below detectable levels in all
the samples analyzed. The proportion of total nutrient
that was phytoavailable (bioavailable) was determined
for each element with the analytical results revealing that
most of the total nutrient in the soil matrix is not in forms
available for plant uptake. For example, the amount of
bioavailable potassium varied from 9.95 mg·kg1 to 14.0
mg·kg1 and from no detectable to 0.54 mg·kg1 for
phosphorus (Table 1). Soil pH was not affected by any
treatment with values varying from 5.08 to 5.18 (Table
2). Soil samples from plots treated with S. gracilis were
Table 1. Total and bioavailable (in parenthesis) concentra-
tions of nutrients in soil samples from areas treated with
inorganic [Nitrogen-Phosphorus (NP)], and organic matters
[Entada abyssinica (E) and Tithonia diversifolia (T)] in Gan-
Elements (mg·kg1)
Treatments N P K
NoF <DL 121 (0.54) 95 (10.2)
NP <DL 119 (<DL) 402 (9.25)
E. abyssinica<DL 112 (<DL) 238 (9.95)
T. diversifolia<DL 108 (0.53) 371 (14.0)
LSD (p = 0.05)- 19.5 58 (5.1)
Data in parenthesis represents concentrations for bioavailable nutrients. <DL
means that the data are below the detectable level of 0.084% for Nitrogen
and 0.369 mg·kg1 for phosphorus.
Table 2. pH and carbon concentrations in in soil samples
from areas treated with inorganic [Nitrogen-Phosphorus
(NP)], and organic matters [Entada abyssinica (E) and
Tithonia diversifolia (T)] in Gandajika-DR-Congo.
Treatments Carbon (%) pH (H2O) pH (CaCl2)
NoF-1 0.632 5.15 4.46
NP-1 0.565 5.18 4.46
E. abyssinica0.577 5.08 4.37
T. diversifolia0.526 5.17 4.53
LSD (p = 0.05)0.08 0.35 0.29
not included in this nutrient analysis.
3.2. Plant Growth
Plant heights for corn varieties under different fertilizers
treatments are illustrated in Figure 1. Irrespective of va-
rieties, two trends of plant growth were discernable from
20 DAS. The first pattern showed a rapid growth rate of
all genotypes fertilized with the NP mineral combination,
T. diversifolia (T) as well as E. abyssinica (E) compared
to control. The second trend was a slow growth rate
based on height measurements for the plants growing in
plots fertilized with S. gracilis and in unfertilized plots.
Throughout the growth period, all corn varieties re-
mained below 60 cm of height for these later treatments
(Figure 1).
Basal stem diameter growth for all varieties exhibited
the same trend from 10 to 60 DAS with the NP mineral
combination, T. diversifolia (T) as well as E. abyssinica
(E) showing significant effects compared to control
(Figure 2). These growths varied with corn varieties
evaluated. From 10 to 20 DAS, the control (NoF), the NP
combination as well as S. gracilis supply could not sig-
nificantly stimulate the basal stem diameter growth of
Copyright © 2012 SciRes. AJPS
Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols 1657
Figure 1. Plant height of three corn varieties as under dif-
ferent fertilization regimes in Gandajika (DR-Congo).
Figure 2. Corn plant diameter at the stem base of three
corn varieties subjected to different fertilization regimes in
Gandajika (DR-Congo).
Copyright © 2012 SciRes. AJPS
Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols
Copyright © 2012 SciRes. AJPS
Varloc (Figure 2). From 10 DAS, Varloc under E. abys-
sinica and T. diversifolia ap plications showed a stem
base diameter growth significantly (p = 0.05) greater than
under other treatments. The average diameter measures
after 20 DAS were similar for all the three varieties for
plots under NP combination, E. abyssinica and T. diver-
sifolia treatments. Plants in control trial (NoF) and S.
gracilis treatment (Figure 2) showed the smallest diame-
ter growth, although each variety performed variably.
3.3. Crop Yield
The mean numbers of corn cobs were significantly (p =
0.05) higher under NP combination, T. diversifolia and E.
abyssinica compared to control (NoF) and S. gracilis
treatments (Table 3). Analysis of kernel rows per cob
also showed that the unfertilized treatment and the ap-
plication of S. gracilis resulted in the lowest numbers of
rows irrespective of varieties (Table 3). The highest
numbers of rows ranged from 13 to 16 for other treat-
ments. Likewise, the numbers of grains per cob was sig-
nificantly (p = 0.05) higher under NP combination, E.
abyssinica and T. diversifolia treatments with an average
of 425 grains, compared to unfertilized control (NoF) and
the S. gracilis treatment that yielded less than 300 ker-
nels per cob irrespective of crop varieties (Table 4).
For grain production, Mus variety under NP treatment
had the highest net yield (3.134 t·ha1), followed by T.
diversifolia (2.324 t·ha1) and E. abyssinica (2.271 t·ha1),
S. gracilis and the control (NoF), respectively (Figure 3).
This trend was the same for the Salongo II and the local
4. Discussion
In general, nutrients and metal adsorption by plants is
relatively low at low pH values. Adsorption then in-
creases at intermediate pH from near zero to near com-
plete adsorption over a relatively small pH range [18].
The more acid is the soil, the more zinc, manganese,
copper, iron, and aluminum will be dissolved into the soil.
In very acid soils with pH below 5.5 such as soil from the
experimental sites of the present study, the availability of
manganese and aluminum is increased to the point that
they could become toxic to plants [19,20]. Calcium and
magnesium deficiency along with reduced nitrogen trans-
formations are also major problems associated with acid
soils [19,20]. It should be pointed out that corn crop re-
quires a pH ranging between 5.5 and 7 for optimal
The initial slow plant growth during the first 20 DAS
for all treatments could reflect the initial low level of soil
fertility mostly for N [6]. However, it is likely that be-
yond this period, the mineralization of T. diversifolia and
E. abyssinica biomass in soil was significant. This pro-
moted a dynamic growth of corn plants compared to S.
gracilis and the control treatments.
Moreover, the NP application did likely coincide with
mineralization of T. diversifolia and E. abyssinica that
released equivalent amount of nutrients to corn crop [14].
This could explain the similarity for plant growth among
these treatments. In general, the assimilation of nutrients
depends on genetics of each variety studied. That is re-
flected by the variable responses of the three varieties
evaluated. This occurred in three phases for each of the
varieties. The first phase was slow from 10 to 20 DAS,
corresponding to the period of slow assimilation; the
second was exponential and extended from 20 to 50 days,
matching with the intense period of activity and of fast
assimilation of nutrients by corn plants. The last phase
from 50 to 60 DAS marked the end of the ascending
growth cycle. On the other hand, the poor plant growth
(height and diameter at stem base) observed with the S.
gracilis treatment could be ascribed to the slow decom-
position rate of this organic matter that is rich in cellu-
lose and lignin. The decomposition of such a biomass
requires more energy. In this case, a strong competition
for nutrients (immobilization) probably occurred between
soil microorganisms and corn plants and resulted in a
Table 3. Cob length and number of kernel rows of three maize varieties under different fertilization regimes with inorganic
[Nitrogen-Phosphorus (NP)], and organic [Entada abyssinica (E), Tithonia diversifolia (T), and Stylosanthes gracilis] fertilizers
in Gandajika-DR-Congo.
Cob length (cm) Kernel rows per cob
Varloc Mus Salongo II Varloc Mus Salongo II
NoF 7.8 c 5.1c 6.0d 8.5b 6.0d 7.3c
NP 12.5a 15.5a 14.5a 13.8a 16.0a 15.0a
E. abyssinica 11.8b 12.9b 12.3b 13.3a 14.5b 14.5b
T. diversifolia 12.1a 12.8b 14.4a 13.5a 14.3b 15.8a
S. gracilis 8.6c 7.8c 7.1c 9.5b 9c 7.8c
Within a column, mean numbers followed by the same letter are not significantly different at p = 0.05 based on Tukey’s HSD multiple comparison analysis.
Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols 1659
Figure 3. Net yield (t·ha1) of three corn varieties under different fertilization regimes in Gandajika (DR-Congo).
Table 4. Numbers of maize kernels per cob of three maize
varieties under different fertilization regimes with inorganic
[Nitrogen-Phosphorus (NP)], and organic [Entada abys-
sinica (E), Tithonia diversifolia (T), and Stylosanthes gracilis]
fertilizers in Gandajika–DR-Congo.
Maize varieties
Varloc Mus Salongo II
NoF 204c 158d 190c
NP 404a 540a 483a
E. abyssinica 346b 404c 436b
T. diversifolia 330b 454b 438b
S. gracilis 209c 238d 189c
Within a column, means followed by the same letter are not significantly
different at p = 0.05 level based on Tukey’s HSD multiple comparison
poor height growth. Few S. gracilis leaves that decom-
posed earlier might have contributed to the rapid growth
of corn crop resulting to the high plant height observed in
plots treated with this organic matter compared to the
control. The cob length and kernel rows per cob (R/C)
seem to follow the same pattern as does the crop yield.
The low level of nutrients especially nitrogen in soil at
plant maturity suggested that most of the available ele-
ments were up taken by plants resulting in slight or no
changes of this oxisol chemistry.
The level of soil fertility and pH is strongly correlated
with corn yield which depends on the inherent genotypes
of crop varieties under study. Ikerra et al. [7] reported
that application of Tithonia alone increased soil ex-
changeable Ca content and the solubility of P available
while significantly reducing the exchangeable Al and
increasing soil pH with a consequent significant increase
of maize yield equivalent to the application of Tithonia
associated to TSP. The same authors reported that T. di-
versifolia increased the pH of acid soil in Tanzania most
probably due to a high Ca concentration. This could be
also valid for E. abyssinica. Such results are consistent
with Cong [21] and George et al. [22] data that showed a
similar rise in pH due to the application of Tithonia in
Vietnam and Kenya, respectively. But the results of the
present study, revealed no significant changes in pH
among soil treatments.
5. Conclusion
A similar growth pattern was observed for all varieties
studied during the first 20 days after sowing regardless of
fertilizing treatments applied. After this stage, two dis-
tinct growth trends arose that revealed the efficiency of
NP, T. diversifolia and E. abyssinica treatments over S.
gracilis and the control. This trend was also duly trans-
lated into net dry grain yield per ha. The local variety
was the least productive under any treatment. Although
the NP application increased significantly the net grain
yield and other agronomic parameters over T. diversifolia,
the differences observed between the effects of these two
treatments do not justify the cost of mineral fertilizers.
Thus, soil application of T. diversifolia and E. abyssinica
manures could be recommended as a biological approach
of managing the fertility of the oxisol prevailing in Cen-
tral part of D. R. Congo. The adoption of such practice is
likely to be high considering the low incomes of local
6. Acknowledgements
This research was conducted through a partnership be-
tween Laurentian University (Ontario, Canada), Univer-
sity of Kinshasa (DR-Congo), and Caritas Congo. The
authors are grateful to the Canadian International Devel-
Copyright © 2012 SciRes. AJPS
Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols
opment agency (CIDA) for financial support.
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