Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols

doi:10.4236/ajps.2012.311201

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American Journal of Plant Sciences, 2012, 3, 1654-1660

http://dx.doi.org/10.4236/ajps.2012.311201 Published Online November 2012 (http://www.SciRP.org/journal/ajps)

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: *[email protected]

Received August 5th, 2012; revised September 12th, 2012; accepted October 15th, 2012

ABSTRACT

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.

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

oxisols.

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·ha−1. Each block measured 21 m ×

Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols

1656

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-

tively.

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·kg−1 to 14.0

mg·kg−1 and from no detectable to 0.54 mg·kg−1 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-

dajika-DR-Congo.

Elements (mg·kg−1)

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·kg−1 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

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).

Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols

1658

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·ha−1), followed by T.

diversifolia (2.324 t·ha−1) and E. abyssinica (2.271 t·ha−1),

S. gracilis and the control (NoF), respectively (Figure 3).

This trend was the same for the Salongo II and the local

varieties.

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

growth.

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

Fertilizer

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·ha−1) 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

Fertilizer

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

analysis.

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

farmers.

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-

Evaluation of Biological Soil Fertility Management Practices for Corn Production in Oxisols

1660

opment agency (CIDA) for financial support.

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