The best choice of fertilizer for maize (Zea mays) and climbing

beans (Phaseolus vulgaris) rotation for rich, mean and poor

farmers in South Kivu, D.R. Congo Bossissi Nkuba1,*, Venant Cidoro2, Janvier Bashagaluke1, Jean Walangululu1 and Peter Pypers3.

1Université Catholique de Bukavu (UCB), Bukavu, DR Congo.

2Institut National d’Etudes et Recherche en Agronomie (INERA), Mulungu, DR Congo.

3Tropical Soil Biology and Fertility Institute of the International Centre for Tropical Agriculture (TSBF-CIAT), Nairobi, Kenya.

Abstract Many studies on fertilization of both beans and maize have been done, but most of the farmers don’t implement the recommendations because they can not afford the fertilizers’ cost at the recommended rate.

From February 2008 to June 2010, an experimental study was conducted to investigate the effect of NPK,

manure and a mixture of NPK and manure, to the rates that rich, mean and poor farmers can afford. The rich farmers could afford the recommended rate, the mean farmers could afford the half and the poor ones

could only afford the quarter. After the first season, the rate of fertilizer was updated according to the

income gained from the previous season’s production by each farmer type. For the five seasons of the

trial, NPK gave the best yield for both crops, followed by the mixture and then manure for rich and mean farmers, but for poor farmers all the fertilizers gave almost the same result. But in water excess condition

manure gave more stability of the climbing beans production, while the NPK’s outcomes were very

unstable and the mixture gave an intermediate result. Farmers who didn’t apply fertilizers had the lowest yield. The farmers’ income followed the same evolution as their yield but not their investment capacities.

All the fertilizers increased the investment capacity so as after four seasons, even poor farmers could

afford the recommended rate. The fastest increase was obtained by both the mixture and NPK, followed

by the manure alone and the lowest increase was obtained by farmers who didn’t use any fertilizer. The results of this study recommend improving agricultural productivity by increasing the use of inorganic

fertilizers.

Key words: Rotation, Fertilizer, Manure, NPK, Investment capacity.

*Author : bossissinkuba@gmail.com; +24381234500; +243990471191

Résumé Des nombreuses études sur la fertilisation du maïs et du haricot ont été réalisées, mais la plupart des fermiers ne

peuvent pas appliquer les recommandations parce qu’ils ne peuvent pas supporter le coût des fertilisants aux doses

recommandées. Une étude a été réalisée de février 2008 à juin 2010 pour déterminer l’effet du NPK, du fumier et du

mélange des deux aux doses que peuvent supporter les paysans riches, moyens et pauvres. Les paysans riches

pouvaient se procurer les fertilisants à la dose recommandée alors que les paysans moyens ne pouvaient s’en

procurer que la moitié et les paysans pauvres que le quart. Après la première saison la dose des fertilisants était actualisée par le revenu issu de la production de la saison précédente pour chaque type de fertilisant. Pour les cinq

saisons de culture le NPK a donné les meilleurs rendements, suivi par le mélange fumier-NPK, suivi par le fumier

pour les paysans riches et moyens, mais pour les paysans pauvres tous les fertilisants ont donné des résultats

comparables. Cependant dans des conditions d’excès d’eau, le fumier a montré une plus grande stabilité du

rendement pendant que celui dû au NPK a vertigineusement chuté, le mélange a donné des résultats intermédiaires.

Les paysans qui n’ont pas appliqué de fertilisant ont obtenu les rendements les plus faibles. Les revenus des

ménages ont suivi la même évolution que les rendements mais pas les capacités d’investissement. Tous les

fertilisants ont augmenté la capacité d’investissement de sorte qu’en février 2010, même les ménages pauvres ont pu

supporter le coût de fertilisant à la dose recommandée. La plus rapide augmentation a été obtenue par le mélange et

le NPK, suivi par le fumier et le plus faible par ceux qui n’ont utilisé aucun fertilisant. Les résultats de cette étude

recommandent pour augmenter la production agricole d’augmenter l’utilisation des engrais inorganiques.

1. Introduction

The CAADP1 has set a goal of 6% of annual

growth rate in agricultural production to reach

the UN’s Millennium Development Goal of

halving poverty and hunger by 2015 (Sanginga, 2010). But the Democratic Republic of Congo’s

growth rate is only 2% though the population

growth rate is 3.1% (Hatungimana, 2001). That situation makes hunger and malnutrition become

the characteristics of DR Congo the same all

sub-Saharan Africa (Conceicao et al., 2011). In

South-Kivu, 42% of illness cases is due to malnutrition (Gaye, 2010). The low production

is due to both the fact that farmers has a little

space because of the high demographic pressure on South-Kivu lands (Gaye, 2010; DSRP, 2005),

and to the little yield of most of the crops in DR

Congo (FAO, 2010). The low yield is mostly due to the low fertility of the lands and

fertilization is the best solution for that problem

(Sebillote, 1989; Debreczeni et Berecz, 2000;

Marton, 2004). Unfortunately in South-Kivu, like in many tropical regions the cost and

availability of the fertilizers is a constrain for

production (Sanchez, 1976; Hinsinger, 2001; Brathwaite, 2008).

We hypothesis that fertilizers should increase

the yield and by the same way the income and the investment capacity. Also inorganic

fertilizers should give a highest yield than

organic ones and the mixture of both should give

an intermediate result. Inorganic fertilizers should also give the highest income. We finally

hypothesis that mixture should give the highest

investment capacity because of its production which is very almost the same as the inorganic

fertilizers one and because of its price which is

intermediate between manure’s one and NPK’s

one.

The objectives of this work was to determine the

best choice of fertilizer according to the farmer’s

investment capacity, to know if a poor farmer who is not able to start with the recommended

1 Comprehensive African Agricultural Development

Program

2 Institut National d’Etudes et Recherches en

rate of fertilizers can increase his incomes until

he becomes able to apply the recommendation.

2. Material and methods

2.1. The trial

The trial has been realized in INERA2/Mulungu

which is the research station for the DR Congo

highlands. Maize was chosen because it’s among the most important food in DR Congo after

cassava and plantain (FAO, 2010) and beans

because it’s the main source of protein in the

African Great Lakes region (Baudouin, et al., 2001).

The climbing beans were cultivated from February to June 2008, 2009 and 2010 (B

seasons) and maize from September 2008 and

2009 to January 2009 and 2010 (A seasons). The rate of fertilizer used in February 2008 was

calculated according to the farmers’ investment

capacity, but after the June 2008’s harvest, their

investment capacity changed and they afforded a different rate of fertilizers. The weather was not

a source of variation but let mention that there

was a rain excess in February 2009 (INERA, 2011).

The trial was realized in a completely randomized design, with four blocks and ten

treatments.

2.2. Farmers status

The CIALCA3 investigation showed that rich,

mean and poor farmers was characterized by the

farm size (respectively 1.33, 0.72 and 0.35

hectares), income from family work (US $42, 2 and 0), yearly expenses (US $739, 286 and 147),

income from other activities (US $59, 12 and 0),

numbers of goats (2, 1 and 0), maize yearly

consumed (425, 273 and 228 kg) and beans

2 Institut National d’Etudes et Recherches en

Agronomie.

3 Consortium for Improving Agriculture-based

Livelihoods in Central Africa

yearly consumed (147, 95 and 78 kg). For the

three groups the average number of family members is 7 and the part of the farm reserved

to maize and beans crops is 20% for each.

The farmers income was calculated by the

following formula: I=[(Y*S*X) – A]*P with:

I : income

Y: yield

S: farm’s surface

X: proportion used for beans or maize

A: auto consumed food

P: production price

The farmers investment capacity was calculated

by: C=(R – E)/(F*S*X) with:

I: Investment capacity

R: Income

E: Family expenses

F: Fertilizers cost

S: Farm’s surface

X: proportion used for beans or maize

And it’s according to these characteristics and to

the yield that the rate of fertilizers was estimated

for the next season.

2.3. Rates and application of fertilizers

Tab.1: Rate ( kg . ha -1) of fertilizer applied by different type of farmers according to choice of fertilizers for B 2008, A 2009, B 2009, A 2010 and B 2010 seasons.

Type of

farmer

Choice

of fertilizer

B 2008 A 2009 B 2009 A 2010 B 2010

Manure NPK Manure NPK Urea Manure NPK Manure NPK Urea Manure NPK

Rich

Manure 5000 0 5000 0 0 5000 0 5000 0 0 5000 0

NPK 0 200 0 200 100 0 200 0 200 100 0 200

Mixture 2500 100 2500 100 50 2500 100 2500 100 50 2500 100

Mean

Manure 2500 0 2925 0 0 5000 0 3024 0 0 5000 0

NPK 0 100 0 200 100 0 200 0 200 100 0 200

Mixture 1250 50 2500 100 48 2500 100 2500 100 50 2500 100

Poor

Manure 1250 0 0 0 0 0 0 0 0 0 5000 0

NPK 0 50 0 11 0 0 92 0 17 0 0 100

Mixture 625 25 0 0 0 0 0 0 0 0 2500 200

Reference None 0 0 0 0 0 0 0 0 0 0 0 0

Manure was manually mixed with the soil after

sampling. That was done on the whole plot.

NPK was put in a furrow near the seeds’ line so

as the roots could easily access on it. For A

seasons, urea were added when the maize plants

was as high as human knees (50 cm) also in a

furrow near the seeds’ line. For applying the

mixture of manure and NPK, manure was

applied first as described above and then NPK

was added in the furrows and for A seasons,

urea was added a little time after.

2.4. Data analyses

R 2.9.0 software was used for analysis of

variance and comparison of means. The

significance level used was P<0.05. And

Microsoft Excel 2007 was used for figures

design.

3. Results

3.1. Yields

Fig 1: Beans yield (kg/ha) of rich farmers for B 2008,

B 2009 and B 2010 season.

For rich farmers NPK and mixture fields had the highest beans yield an average of 1129.33 and

1082.33 kg/ha, followed by manure with 939.67

kg/ha and at least the fields without fertilizers 745.67 kg/ha. Also manure gave a more stable

yield on 2009B season even if it’s not

significantly higher than the yields obtained with other fertilizers. The yield increased from 2009

to 2010 until it became higher than the 2008

one.

Fig. 2: Maize yield (kg/ha) of rich farmers for A 2009

and A 2010 seasons.

For rich farmers, the NPK fields had the highest maize yield with 6399.50 kg/ha of average,

followed by mixture with 5433.00 kg/ha,

followed by manure with 3147.50 kg/ha and at least unfertilized fields with 2679.50 kg/ha. All

the treatment incresed significantly their yield

from 2009 to 2010 except where NPK was used.

Manure increased more the yield than the others treatments.

Fig. 3: Beans yield (kg/ha) of mean farmers for B

2008, B 2009 and B 2010 seasons.

For mean farmers, mixture fields had the highest

beans yield (1261.33 kg/ha), followed by NPK

(1146.67 kg/ha), followed by manure (1034.67

kg/ha) and at least unfertilized fields (745.67 kg/ha). Also manure gave a more stable yield on

2009B season even if it’s not significantly

higher than the yields obtained with other fertilizers. The yield increased from 2009 to

2010 until it became higher than the 2008 one.

Fig. 4: Maize yield (kg/ha) of means farmers for A

2009 and A 2010 seasons.

For mean farmers, NPK gave the highest maize

yields (6086.50 kg/ha), followed by mixture (5299.00 kg/ha), followed by manure (4237.00

kg/ha) and at least unfertilized fields (2679.50

kg/ha). All the treatment incresed their yield from 2009 to 2010 even NPK’s field. Manure

gave the highest increase.

Fig. 5: Beans yield (kg/ha) of poor farmers for B

2008, B 2009 and B 2010 seasons.

For poor farmers, NPK and mixture had the

highest beans yield (1095.67 and 1084.00

kg/ha), followed by manure (980.33 kg/ha) and the unfertilized fields had least yield (745.67

kg/ha). Also manure gave a more stable yield on

2009B season even if it’s not significantly

higher than the yields obtained with other fertilizers. The yield increased from 2009 to

2010 until it became higher than the 2008 one.

Fig. 6: Maize yield (kg/ha) of poor farmers for A

2009 and A 2010 seasons.

For poor farmers, NPK and manure had the

highest maize yield (4250.50 and 4118.50

kg/ha), followed by mixture (3398.50 kg/ha) and

the unfertilized fields had the least yield (2679.50 kg/ha). All the treatment incresed their

yield from 2009 to 2010, but manure gave the

highest increase.

3.2. Income

Fig. 7: Income from beans (US $) of rich farmers for

A 2008, A 2009 and A 2010 seasons.

For rich farmers, NPK fields gave the highest income from beans (US $167.57 of average),

followed by mixture (US $153.75), followed by

manure (US $116.71) and unfertilized fields gave the least income (US $71.72).

Fig. 8: Income from maize (US $) of rich farmers for

A 2009 and A 2010 seasons.

For rich farmers, NPK field gave the highest

income (US $412.55), followed by mixture (US

$330.98), followed by manure (US $138.79) and the unfertilized fields gave the least income (US

$107.59).

Fig. 9:Income from beans (US $) of mean farmers for

B 2008, B 2009 and B 2010 seasons.

For mean farmers, mixture and NPK fields gave

the highest income from beans (US $56.56 and 49.09), followed by manure (US $31.58).

Unfertilized fields gave the least income (US

$13.09).

Fig. 10: Income from maize (US $) of mean farmers

for A 2009 and A 2010 seasons.

For mean farmers, NPK field gave the highest

income (US $461.84), followed by mixture (US $375.27), followed by manure (US $334.38).

Unfertilized field gave the least income (US

$130.88).

Fig. 11: Income from beans (US $) of poor farmers

for A 2008, A 2009 and A 2010 seasons.

For poor farmers, mixture and NPK gave the

highest income from beans (US $18.61 and

18.38) followed by manure (US $7.87). Unfertilized field gave the least income (US

$2.82).

Fig. 12: Income from maize (US $) of poor farmers

for A 2009 and A 2010 seasons.

For poor farmers, NPK and manure gave the highest income from beans (US $46.51 and

43.52) followed by mixture (US $29.84).

Unfertilized field gave the least income (US $14.43).

3.3. Investment capacity

Fig. 13: Investment capacity (% of the recommanded rate of fertilizer) from beans of rich farmers for B

2008, B 2009 and B 2010.

For rich farmers, mixture gave the highest

investment capacity (189.33%) followed by both manure and NPK (175.67 and 175.00%).

Unfertilized fields gave the lowest investment

capacity (75.00%), though the initial rich investment capacity was 100%.

Fig. 14: Investment capacity from maize (% of the

recommended rate of fertilizer) of rich farmers for A

2009 and A 2010 seasons.

For rich farmers, mixture gave the highest

investment capacity (315.00%), followed by

NPK (287.50%) and manure (209.00%). Unfertilized field gave the lowest investment

capacity (75.00%).

Fig. 15: Investment capacity (% of the recommanded

rate of fertilizer) from beans of mean farmers for B

2008, B 2009 and B 2010.

For mean farmers, mixture gave the highest

investment capacity (128.67%) followed by

NPK and manure (94.67 and 87.67%). Unfertilized fields gave the lowest investment

capacity (25.67%).

Fig. 16: Investment capacity from maize (% of the

recommended rate of fertilizer) of mean farmers for

A 2009 and A 2010 seasons.

For mean farmers, manure gave the highest

investment capacity (929.00%) followed by

mixture (659.50%) and NPK (594.00%). Unfertilized fields gave the lowest investment

capacity (168.50%).

Fig. 17: Investment capacity (% of the recommanded

rate of fertilizer) from beans of poor farmers for B

2008, B 2009 and B 2010.

For poor farmers, mixture gave the highest

investment capacity (87.33%) followed by NPK

(73.00%) and manure (45.00%). Unfertilized

fields gave the lowest investment capacity (12.00%). Fertilized fields increased the farmers

investment capacity upper than 100%.

Fig. 18: Investment capacity from maize (% of the

recommended rate of fertilizer) of poor farmers for A

2009 and A 2010 seasons.

For poor farmers, manure gave the highest investment capacity (248.50%) followed by

NPK (123.00%) and mixture (107.50%).

Unfertilized fields gave the lowest investment

capacity (38.00%). Fertilizers increased the farmer’s investment capacity higher than 100%.

4. Discussions

4.1. Yield

Fertilizers increased the beans yield of 41%, at the recommended rate (for rich farmers) because

N, P and K are constrains in most of the

weathered tropical soils (Sanchez and Logan, 1992; Lynch et al., 2003).

Fertilizers increased the maize yield of 86%. The superiority of fertilizers’ effect on maize is

due to the fact maize used N left by beans crop

(Bagayoko et al, 1996) and because of the

changes of microbiologic activities after legumes (Shipton, 1977; Turco et al., 1990) and

VAM (vesicular and arbuscular micorrhizae)

which allow the maize plant to absorb more P (Johnson et al., 1992; Bainville et al., 2005).

On the mean farmers rate fertilizers increased

the beans yield of 54%, more than the increase

of fertilizers to the rich farmers’ rate because the

experimental soil doesn’t need a lot of

fertilizers. Pypers et al. (2010) also found that

little quantities of fertilizers could have a good

effect on cassava and legume intercrop system in

a similar soil in Kabamba.

But for maize the yield was increased of 94%

because of the below reasons.

On poor farmers’ rate fertilizers increased the

beans yield of 41% less than the increase shown

on mean farmers’ rate. Let’s also mention that

fertilizers effect can be more important in the

poor farmers’ fields because they have a little

space so they can apply very well the fertilizers

comparatively to the farmers with very big fields

(Anson et al, 2009).

For maize the yield was increased of 46%, less

than the increased shown for farmers because of

the very little rate of fertilizers.

Among the fertilizers, NPK gave the highest

yield for rich and mean farmers mostly because

it contains more available nutrient than manure

and mixture which is intermediate to the two

above fertilizers (NPK and manure). And also

manure must go through a long mineralization

process so as its contents, especially P, can be

available for the crop (Nachimuthu et al., 2009;

Berger, 1996).

For poor farmers all the fertilizers gave almost

the same results because the rate wasn’t enough

to show the differences among fertilizers’ effect.

The increase seen from 2009 to 2010 was not

mostly due to the accumulation effect of the

fertilizers, it was due to better weather

conditions (INERA, 2011). But manure’s yield

increased more than the other treatment possibly

because of the accumulation effect.

The maize yields of rich farmers didn’t increase

significantly while it increased for all the other

treatments possibly because it had already got to

the variety limit of production.

When there was a rain excess problem in February 2009 (INERA, 2011), manure showed

more stability of the yield. This was due to the

effect of manure on soil’s structure (Cambardella

and Elliott, 1992; Six et al., 2002). Manure

improves soil porosity then soil water movement

trough soil layers. Also organic fertilizers’ content easily runoff with the soil water

movement (Chien et al., 2009). Mixture showed

an intermediate stability because it gives an

intermediate level of stability because it contains the half of the quantity of manure.

4.2. Income

Fertilizers increased the income of the rich farmers of 104% from beans production and

170% from maize production, though the yield

was increased respectively of 41 and 86%. That was due to the fact that the rich farmers consume

425 kg of maize and 147 kg of beans per year

(Ouma et al., 2008) and it’s the production left

that they sell.

For mean farmers, the fertilizers increased the

income of 250 and 198% respectively from beans and maize production, though the

corresponding yield increase due to fertilizers

was 54 and 94%.

For poor farmers, the fertilizers increased the

income of respectively 430 and 177% for beans

and maize. This increase is due to the fact that poor farmers who do not use fertilizers can

hardly produce enough to feed their family,

especially for beans. So the fertilizers, by allowing them to produce enough to have

something left for selling increase highly their

income, compared to the corresponding increase of the yield which was respectively 41% and

46%.

The highest income was obtained by farmers who used NPK, followed by those who used

mixture and then those who used manure. That

was due to the difference yield due to those fertilizers.

4.3. Investment capacity

Fertilizers increased the rich farmers’ average

investment capacity of 140% applied to beans and 261%, because by increasing the farmers

production he could have enough money for his

expenses (Ouma et al., 2008) and still have enough to invest in fertilizers.

For mean farmers, fertilizers increased the

average investment capacity respectively of 304 and 332% when applied to beans and maize.

That was due to the bellow reasons.

For poor farmers, fertilizers increased the

average investment capacity respectively of 470

and 320% when applied to beans and maize.

That was due to the above reasons.

Mixture gave the highest investment capacity for

the five seasons because it costs less than the NPK (Ouma et al., 2008) and gives a yield

which is almost the same as NPK, because

manure improves the efficiency of the NPK it was mixed with (Vanlauwe et al., 2001). It was

followed by NPK because of it’s high yield.

Then finally manure gave the least investment

capacity among the three types of fertilizer.

For poor and mean farmers all the fertilizers

allowed them to get to the recommended rate after four seasons maximum. That was due to

the fact that all the money left after the family

expenses was invest in fertilizers in order to get to recommended rate according to the initial

hypotheses.

5. Conclusion

Our results show that using fertilizers can

increase the yield at any rate, and that all

fertilizers can increase the income of the rich,

mean and especially poor farmers.

They also show that NPK is the best used alone

is the best fertilizer for increasing the yield and

the farmer’s income. But the mixture of both

NPK and manure was the best way of increasing

the investment capacity and so allow them to

apply the recommended rate of fertilizers.

So in order to increase African productivity, our

work can suggest increasing the use of inorganic

fertilizers and mix them to organic fertilizers

only if it’s hard to buy enough inorganic

fertilizers and the organic ones is easily

available.

6. Acknowledgement

We thank Dr. Peter Pypers and the TSBF-CIAT

for initiating this project (Long term) and other

ISFM projects (Integrated soil fertility

management) in South-Kivu.

We also thank CIALCA for making possible the

partnership between TSBF-CIAT, UCB and

INERA from which this work resulted and for

the logistical facilities.

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