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Productivity of yam-based systems with herbaceous legumes and short fallows in the Guinea-Sudan transition zone of Benin

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The principal driving force in agricultural research is to increase the yield of food crops. For farming to remain productive, it will be necessary to replenish the nutrients removed or lost from the soil. The objective of this study was to determine the impact of yam-based systems on soil productivity (dry matter production, nutrients recycled or removed, profitability and soil fertility changes). We compared smallholders’ traditional systems (1-year fallow of Andropogonon gayanus -yam rotation; maize-yam rotation) with yam-based systems with legumes (intercropped Aeschynomene histrix with maize-yam rotation; intercropped Mucuna pruriens with maize-yam rotation). The production of dry matter (tubers, shoots), nutrients removed or recycled, and soil properties were significantly improved on yam-based systems with legumes in comparison with traditional systems. Year × Treatment interactions influenced significantly the tuber dry matter production. Site × Treatment and Treatment × Farmer interactions affected significantly nutrients removed or recycled. The amount of nutrients recycled or removed was dependent on the dry matter production that, in turn, depended on soil fertility, rainfall and farmers’ effect.Yam-based systems with legumes brought a higher present value than traditional systems in the first 4 years and appeared attractive for land, labour and cash productivities.
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ORIGINAL ARTICLE
Productivity of yam-based systems with herbaceous legumes
and short fallows in the Guinea-Sudan transition zone
of Benin
Raphiou Maliki Mouissou Toukourou
Brice Sinsin Philippe Vernier
Received: 15 February 2011 / Accepted: 15 October 2011
Springer Science+Business Media B.V. 2011
Abstract The principal driving force in agricultural
research is to increase the yield of food crops. For
farming to remain productive, it will be necessary to
replenish the nutrients removed or lostfrom the soil. The
objective of this study was to determine the impact of
yam-based systems on soil productivity (dry matter
production, nutrients recycled or removed, profitability
and soil fertility changes). We compared smallholders’
traditional systems (1-year fallow of Andropogonon gay-
anus -yam rotation; maize-yam rotation) with yam-based
systems with legumes (intercropped Aeschynomene histrix
with maize-yam rotation; intercropped Mucuna prur-
iens with maize-yam rotation). The production of dry
matter (tubers, shoots), nutrients removed or recycled,
and soil properties were significantly improved on
yam-based systems with legumes in comparison with
traditional systems. Year 9Treatment interactions
influenced significantly the tuber dry matter pro-
duction. Site 9Treatment and Treatment 9Farmer
interactions affected significantly nutrients removed or
recycled. The amount of nutrients recycled or removed
was dependent on the dry matter production that, in
turn, depended on soil fertility, rainfall and farmers’
effect.Yam-based systems with legumes brought a
higher present value than traditional systems in the first
4 years and appeared attractive for land, labour and
cash productivities.
Keywords Dioscorea rotundata Crop rotation
Nutrient recycling Herbaceous legumes
Net present value
Introduction
Yam (Dioscorea spp.) is a tuber crop widely cultivated
in the humid and sub-humid lowland regions of West
Africa and the Caribbean (Onwueme and Haverkort
1991). More than 90% of the worldwide production
(40 million metric tons of fresh tubers year
-1
) comes
from West Africa (FAOSTAT 2009). Yam is grown in
Present Address:
R. Maliki (&)M. Toukourou
Institut National des Recherches Agricoles du Be
´nin
(INRAB), P.O. Box 01-884, Cotonou, Benin
e-mail: malikird@yahoo.fr
M. Toukourou
e-mail: mstoukourou@yahoo.fr
R. Maliki
B.P. 2128, Calavi, Benin
B. Sinsin
Faculte
´des Sciences Agronomiques de l’Universite
´
d’Abomey-Calavi (FSA/UAC), P. O. Box 01-526,
Cotonou, Benin
e-mail: bsinsin@gmail.com
P. Vernier
Centre de Coope
´ration Internationale en Recherche
Agronomique pour le De
´veloppement (CIRAD), Avenue
Agropolis, 34398 Montpellier Cedex 5, France
e-mail: philippe.vernier@cirad.fr
123
Nutr Cycl Agroecosyst
DOI 10.1007/s10705-011-9468-7
traditional cropping systems as the first crop after
virgin forest or after a long fallow period yielding
about 10 t of fresh tubers ha
-1
year
-1
(Carsky et al.
2001). But when the soil fertility is high, the potential
yield of species Dioscorea rotundata (D. rotundata)
can easily reach 25–30 t ha
-1
(Vernier and Dossou
2000). The increase in yam production has been due
more to land expansion than to crop improvement
potential (FAO 2003). For example, the yield increase
of 7.6% in West Africa was mainly due to an increase
in area of 7.2% and only 0.4% was due to an
improvement in crop productivity itself (FAO 2003).
Yam is a demanding crop in terms of organic matter
and soil fertility, especially the most appreciated and
market-valued cultivars (early maturing D. rotundata)
used for the popular dish called Fufu (pounded yam)
(Vernier and Dossou 2003). Yam tubers are indeed
known to export from the soil large quantities of
nitrogen (N) and potassium (K) (O’Sullivan and Ernest
2008). According to Degras (1986), the harvest of 30 t
ha
-1
of fresh yam yield takes up 120 N kg ha
-1
,
5.1 P kg ha
-1
, and 111 K kg ha
-1
.
Yam cultivation in West Africa is now confronted
with the scarcity of fertile soil available for clearing
(Cornet et al. 2006). In Benin nowadays, farmers
hardly have the possibility to rely on long duration
fallow and yam is being cultivated in 1 or 2-year
herbaceous fallow–yam or maize-yam rotation sys-
tems with manual incorporation of residue into the soil
(Doumbia 2005; Maliki 2006). Smallholder farmers
removed important quantities of nutrient from their
soil without applying a sufficient quantity of manure
or fertilizer to replenish the soil (Saidou 2006).
The decline in yam yields under continuous culti-
vation has led to the largely accepted conclusion that
yam requires a high level of natural soil fertility
(organic matter and nutrient) (O’Sullivan and Ernest
2008). Since the demand for yam keeps increasing due
to the continued population growth, reserves of arable
land are diminishing, and fallow duration is decreas-
ing. It is becoming necessary to sustainably increase
yam productivity in sedentary cropping systems
(O’Sullivan and Ernest 2008). There is a dire need
therefore to assess in farmers’ conditions the eco-
nomic performance of sustainable cultivation tech-
niques. Ongoing soil degradation could be reduced by
the adoption of new farming techniques such as
improved fallows of herbaceous legumes (Carsky
et al. 1998; Becker et al. 1999).
Studies on improved fallow practices are generally
grain-oriented (cereals, such as maize), whereas very
little has been done on root and tuber crops, especially
yam. Comparative studies are lacking that assess the
effects of yam-based technologies with herbaceous
legumes intercrops and short fallows on yam production
and soil properties in the savannah transition agro-
ecological zone of Benin. We compared in a perennial
experiment for 4 years, with 2-year rotations, small-
holder farmers’ traditional rotations maize-yam or 1-year
Andropogonon gayanus fallow–yam, with rotations
intercropped Aeschynomene histrix with maize-yam or
intercropped Mucuna pruriens with maize-yam. The
amount of nutrients recycled or removed in yam-based
cropping systems could be dependent on plant dry matter
production that, in turn, depend on climate (rainfall) and
soil fertility conditions. The objective of this study was to
determine the impact of yam-based systems on soil
productivity (dry matter production, nutrients recycled or
removed, profitability and soil fertility changes).
Materials and methods
Study sites
The study was carried out in the Guinea-Sudan transi-
tion zone of Benin (centre of Benin) infour sites: Miniffi
(District of Dassa-Zoume
`), Gome
`(Glazoue
´), Akpe
´ro,
and Gbanlin (Ouesse
`) within latitudes 7450and 8400
North and longitudes 2200and 2350East. The climate
is tropical with a bimodal rainfall pattern. The average
annual rainfall levels during the study period were
1,052 mm (2002), 1,386 mm (2003), 983 mm (2004)
and 797 mm (2005) with a variable tendency from one
site to another (Fig. 1). The soils are plinthosols
(Gbanlin and Akpe
´ro), and luvisols (Miniffi and Gome
`)
(Agossou and Mo
¨nou 2002). Miniffi, Akpe
´ro and
Gbanlin are located on a plateau while Gome
`is on
lowland. Akpe
´ro is close to forest while Gbanlin, Miniffi
and Gome
`are far. There is a rising gradient of fertility
from the continuous cropping system on degraded soils
towards the forests. This degradation is related to soil
organic matter decrease, which leads to nutrient deple-
tion (nutrients removed in the crop harvest, leaching and
erosion). Vegetation is a degraded woody savannah
type. Maize, yam, cassava and groundnut are annual
cropping systems and the cash crops are cotton and
soybean.Mineral fertilizer application appears to be
Nutr Cycl Agroecosyst
123
essential. Smallholder farmers use fertilizers on maize
on depleted soils depending on cash and inputs avail-
ability. Cotton is not grown in mixed cropping, but as
pure crop in rotation with other crops (maize or
sorghum). In this cropping pattern the subsequent
cereals benefit from the residual effect of inorganic
fertilizer applied to cotton (150 kg ha
-1
of NPK-SB
14-23-14-5-1 plus 50 kg ha
-1
of urea).
On-farm experiment
The concept of the experiment was to produce residue
biomass followed by planting yam in rotation crop-
ping systems.
We carried out two-year rotations experiment of
yam-based cropping systems repeated twice (2002–
2005) on-farm with single-harvest late maturing variety
of yam ‘‘Kokoro’’ (Dioscorea rotundata). This is one of
the most cultivated species in the study area due to its
good aptitude for conservation and processing into dried
tubers (the so-called chips), flour, and starchy paste
(locally called amala) (Vernier and Dossou 2003). We
conducted the experiment with 32 farmers, eight in each
site (Miniffi, Gome
`,Akpe
´ro, and Gbanlin). For each of
them, we used a randomized block design with four
replications and four levels of treatment. Plot size was
10 m 910 m (total of 1,600 m
2
per farm). The four
treatments were as follows (Table 1):
T0 (Control 1): 1-year fallow-yam rotation, which
is a common practice in the area. A natural fallow
of Andropogon gayanus grass was grown in the
first year.
TM (Control 2): maize-yam rotation, which is also
a common practice in the area. Maize was planted
(at 80 cm 940 cm) in April of the first year.
TMA: Intercropped Aeschynomene histrix with
maize-yam rotation: Maize was planted (at 80 cm 9
40 cm) in April of the first year. A. histrix seeds
(7 kg ha
-1
) were mixed with dry sand (3/4 sand–1/4
seeds) and sown 2 weeks after the maize.
TMM: Intercropped Mucuna pruriens with maize-
yam rotation. Maize was planted (at 80 cm 9
40 cm) in April of the first year. M. pruriens seeds
(25 kg ha
-1
) were sown at spacing 80 cm 9
40 cm in May 6 weeks after the maize.
On treatments TM, TMA and TMM, 100 kg ha
-1
NPK fertilizer (14% N, 10% P, 11.7% K) was applied
to maize in April and 50 kg ha
-1
urea (46% N) in
June. The maize was harvested in July. The grainless
M. pruriens and A. histrix crops were mowed 140 and
180 days respectively after planting. Organic matter
was incorporated in mounds and left on the surface as
mulch in October, and then yam was planted directly
on these mounds, without mineral fertilization.
With recurring drought stress exacerbated by
highly variable and unpredictable rains in the study
area, some farmers grow a second crop, which often
fail. This corroborates the great interest of the maize/
leguminous crop when no second crop is planned.
Data collection
Composite soil samples were collected in each field
before the beginning of the experiment along plot
transects at soil depths of 0–10 cm and 10–20 cm (32
farm fields 92 depths =64 samples) in order to
determine soil characteristics. At the end of 2005
before yam harvesting, composite soil samples were
collected at the same depths in the mounds along plot
transects (32 farm fields 94 treatments 92 depths =
256 samples).
Prior to ridging, in four 1 m
2
quadrats within each
plot the aboveground biomass of herbaceous legumes
and fallow was collected in October 2002 and 2004.
The biomass samples were dried at 60C until constant
weight and then dry weight was determined. At
maturity, maize grain and stover were harvested per
row on each plot and DM determined. The fresh yam
Fig. 1 Annual rainfall distribution in the four village sites
(Akpe
´ro, Gbanlin, Miniffi, Gome
`) in the 2002–2005 cropping
seasons, in the Guinea-Sudan transition zone of Benin
Nutr Cycl Agroecosyst
123
tuber weight and DM of yam tubers and shoots were
estimated on each plot in December 2003 and 2005.
Soil and plant nutrients content
The plant nutrient content was estimated according to
the biomass amount.
Soil and plant macronutrients content (N, P, and K)
were analyzed. Nitrogen (N) content was analyzed
using the Kjeldahl method, available phosphorus with
the Bray 1 method, potassium with the FAO method,
organic carbon with the Walkley and Black method,
soil fractionation with Robinson method and pH
(H2O) (using a glass electrode in 1:2.5 v/v soil
solution). Only yam tuber and maize grain were
removed, and all other plants parts were recycled
(A. gayanus, maize stover, yam shoot, A. histrix and
M. pruriens). Yam or M. pruriens shoot included
leaves. Nutrient removed or recycled was calculated as
a summation of nutrient concentration time dry matter
of the respective plant parts. Dry matter removed or
recycled was calculated as a summation of dry matter
of the respective plant parts.
Statistical analysis
Analysis of variance (ANOVA) was applied to the DM
production (tubers, shoots), nutrient contribution to
the systems and soil properties at depths (0–10 and
10–20 cm) using a randomized block design and a
partial nested model with five factors: Year, Replica-
tion, Farmer, Site, and Treatment. The random factors
were ‘‘Year’’ and ‘‘Replication’’; ‘‘Farmer’’ was also
considered as nested within ‘‘Site’’. The fixed factors
were ‘‘Treatment’’ and ‘‘Site’’. Sites were considered
as fixed, based on certain criteria such as landscape
(lowland, plateau), soil type, population density and
initial soil fertility. The general linear model (GLM)
(SAS 1996) was computed to assess the interactions
between the factors involved. When there were
significant interactions between the main factors,
interaction diagrams were drawn to describe the effect
of each factor. Least square means and standard error
were also computed for factor levels. Treatment
effects were determined by analysis of variance using
computer package SPSS version 11 (SPS Sinc. 2002,
Chicago, Illinois, USA). Significance was regarded at
PB0.05.
Economic analysis
A simple financial analysis was performed to evaluate
the profitability of each yam-based cropping system.
We considered the time horizon 2002–2005 (4 years)
and a discount rate of 10%, World Bank standard, not
too far from bank interest rates. The choice of discount
rate is always an object of controversy among
economists (Stern 2006). We considered discount
rates ranging from 0 to 50% for sensitivity analysis.
The net present value is as follows:
NPV ¼ðTPR TPCÞ
or
NPV ¼X
n
i¼1
Rn
ð1þrÞnX
n
i¼1
Dn
ð1þrÞn¼X
n
i¼1
RnDn
ð1þrÞn
ð1Þ
NPV =Net Present Value (US$), TPR =Total Pres-
ent Revenue (US$), TPC =Total Present Cost (US$),
R
n
=Revenue in the year n (US$), D
n
=Cost in the
year n (US$), r =Discount rate (%).
Returns on investment (RI %) were also computed
through the formula:
Table 1 Design of yam-based cropping systems with 1-year
fallow of Andropgon gayanus-yam rotation, Maize ?100 kg
N
14
P
23
K
14
?50 kg Urea-yam rotation, Aeschynomene histrix/
maize intercropping ?100 kg N
14
P
23
K
14
?50 kg Urea-yam
rotation and Mucuna pruriens var utilis/maize intercrop-
ping ?100 kg N
14
P
23
K
14
?50 kg Urea-yam rotation in the
2002–2003 and 2004–2005 cropping seasons in four villages in
Benin
Treatment
T0 (control 1): (1-year fallow of Andropogon gayanus)-yam rotation
TM (control 2): (Maize ?100 kg N
14
P
23
K
14
?50 kg Urea) -yam rotation
TMA: (Aeschynomene histrix/maize intercropping ?100 kg N
14
P
23
K
14
?50 kg Urea) -yam rotation
TMM: (Mucuna pruriens var utilis/maize intercropping ?100 kg N
14
P
23
K
14
?50 kg Urea) -yam rotation
Nutr Cycl Agroecosyst
123
RI ¼100 NPV=TPC
ðÞ
;ð2Þ
with RI [interest rate on capital, profitability is
implied (2).
Labour productivity US$ per man-day (LP) was
given by:
LP ¼NPV=L;ð3Þ
where L (man day) is the total labour requirement (3).
Economic yields for maize were based on 15%
moisture content while that of yam was based on fresh
weight. Costs of production were divided into land
(hired land cost US$ ha
-1
year
-1
), inputs (maize, yam
and legume seeds, fertilizers costs) and labour (farm
activities costs for yam-based cropping systems
establishment and management). Land, inputs and
labour costs were determined based on local prices in
the 2002–2005 cropping seasons. We considered the
average annual prices for food crops (maize and yam)
based on the prevailing market price (Glazoue
´market
in the central Benin). All amounts of money are
expressed in US dollars (501.8 FCFA to US$ 1, 1
December 2010).
Results
Soil chemical properties
The initial soil organic matter (SOM) contents were
low in all fields, ranging from 0.93 and 2.25%, and the
C:N ratio ranged from 8.7 to 11.7 (Table 2). Available
P levels were very low and varied from 3.0 to
20.1 ppm. Soil N concentration ranged from 0.056 to
0.112%. N, P and SOM contents were significantly
higher in 0-10 cm than in 10–20 cm depth, except at
Gbanlin site for N and SOM. Gome
`site showed for
both soil depths, the lowest values of carbon (C%),
N%, P (ppm), and organic matter (%) whereas Akpe
´ro
had the highest values. The end of study soil analysis
showed soil chemical properties (SMO%, N %, P
(ppm), K
?
cmol kg
-1
, and PH water) significantly
higher in TMA and TMM than in traditional systems
T0 and TM (P\0.001). Soil clay contents were
significantly higher in TMA, TMM and T0 than in TM
(P\0.001) (Table 3). SOM, N, P, K, and pH
increased by 10, 22, 19, 29 and 10% respectively for
both soil depths in TMA and TMM whereas soil clay
contents increased by 8%.
DM production and nutrient contribution
to the systems
Table 4shows the average nutrient composition in
different sources of biomass dry matter (DM). Inter-
cropped M. pruriens with maize-yam rotation (TMM)
gave more DM and nutrient recycled or removed than
the intercropped A. histrix with maize-yam rotation
(TMA). The ANOVA partial nested model on DM
production (tubers, shoots) showed significant differ-
ences between treatments (P\0.001) (Table 5).
Year 9Treatment interactions influenced signifi-
cantly the tuber dry matter production (P\0.01).
Table 2 Initial soil characteristics at the beginning of the experiment at 0–10 and 10–20 cm layers in four villages in Benin
Depth (cm) Akpe
´ro Gbanlin Miniffi Gome
`
0–10 10–20 0–10 10–20 0–10 10–20 0–10 10–20
‘Plinthosols’’ ‘Plinthosols’’ ‘Luvisols ferriques’’ ‘Luvisols ferriques’’
Clay% 6.6 ±0.3 7.3 ±0.3 5.8 ±0.3 5.7 ±0.3 6.8 ±0.3 6.5 ±0.3 6.8 ±0.3 7.9 ±0.4
Silt% 11.7 ±0.6 11.8 ±0.6 5.8 ±0.3 5.6 ±0.3 6.8 ±0.3 7.1 ±0.3 16.1 ±0.8 17.4 ±0.8
Sand% 81.7 ±0.9 80.9 ±0.9 88.4 ±0.5 88.7 ±0.5 86.4 ±0.6 86.4 ±0.6 77.1 ±1.1 74.7 ±1.2
C% 1.31 ±0.1 1.05 ±0.1 0.69 ±0.0 0.79 ±0.0 0.80 ±0.0 0.64 ±0.0 0.65 ±0.0 0.54 ±0.0
N% 0.112 ±0.0 0.092 ±0.0 0.060 ±0.0 0.080 ±0.0 0.081 ±0.0 0.056 ±0.0 0.073 ±0.0 0.062 ±0.0
C:N ratio 11.7 ±0.0 11.4 ±0.1 11.7 ±0.0 9.7 ±0.0 9.8 ±0.3 11.4 ±0.1 8.9 ±0.0 8.7 ±0.0
OM% 2.25 ±0.1 1.81 ±0.1 1.19 ±0.0 1.36 ±0.0 1.37 ±0.1 1.10 ±0.1 1.12 ±0.1 0.93 ±0.0
PH water 6.7 ±0.3 6.7 ±0.3 6.6 ±0.3 6.3 ±0.3 6.7 ±0.3 6.8 ±0.3 6.6 ±0.3 6.6 ±0.3
Bray P 20.1 ±1.1 14.9 ±0.6 7.0 ±0.3 4.0 ±0.2 11.0 ±0.5 3.0 ±0.2 8.0 ±0.4 4.0 ±0.2
Data are the means ±SD (standard deviation)
Nutr Cycl Agroecosyst
123
Amounts of N, P, and K removed in yam tuber and
those recycled in yam shoot were significantly
higher in TMA and TMM than in traditional sys-
tems T0 and TM (Table 6). Site 9Treatment and
Treatment 9Farmers’ interactions were significant
(P\0.001).
Relative profitability of yam-based cropping
systems
Table 7shows the estimated total present production
cost (TPC), the net present value (NPV) (U$$
ha
-1
year
-1
) and labour productivity (LP) (U$$
man-day
-1
) and return on investment (RI) (%) of
yam-based cropping systems with a discount rate of
10%. The yam-based cropping systems with herba-
ceous legumes (TMA and TMM) resulted in the
highest NPV (US$757 and US$822) and corresponded
to a return on investment (RI) that ranged from 145 to
152% respectively. The traditional yam-based systems
(T0 and TM) showed the lowest NPV (US$301 and
US$178) and RI ranged from 62 to 29%. TMM or
TMA showed the highest labour productivity (US$7
man-day
-1
) whereas T0 and TM had the lowest (US$5
and US$2 man-day
-1
) respectively.
Figure 2depicts the NPVs of yam-based cropping
systems with herbaceous legumes (TMA and TMM) in
comparison with controls (T0 and TM) with a time
horizon of 4 years (2002–2005) according to various
discount rates (0–50%). The discount rates reflect the
alternative of the investment opportunities and the
diverse farmers’ preference for investments rather
than an immediate income. For various discount rates,
TMA and TMM would bring a significantly higher
present value than T0 and TM in the first 4 years.
Discussion
Impact of yam-based cropping systems on soil
properties
Soil clay contents improvement in T0, TMA and TMM
at the end of the perennial experiment could be related
Table 3 End of study soil characteristics at 0–10 cm and 10–20 cm soil layers in four villages in Benin
Soil characteristics Depth (cm) T0 TM TMA TMM LSD
Clay% 0–10 5.82a 5.52b 5.94a 5.96a 0.30
10–20 5.93a 5.61b 6.01a 6.05a 0.32
Silt% 0–10 9.55a 9.68a 9.52a 9.53a ns
10–20 9.71a 9.81a 9.67a 9.65a ns
Sand% 0–10 84.63a 84.80a 84.54a 84.51a ns
10–20 84.36a 84.58a 84.32a 84.30a ns
C% 0–10 0.77c 0.76c 0.82b 0.87a 0.05
10–20 0.72c 0.70c 0.78b 0.83a 0.05
N % 0–10 0.06d 0.08c 0.09b 0.10a 0.01
10–20 0.07c 0.09b 0.10a 0.10a 0.01
C:N ratio 0–10 12.0a 10.1b 9.3c 9.0c 0.7
10–20 11.1a 8.3b 8.3b 8.3b 0.7
MO% 0–10 1.32c 1.31c 1.41b 1.49a 0.08
10–20 1.24c 1.21c 1.34b 1.43a 0.09
Bray P mg kg
-1
0–10 10.21c 11.84b 13.43a 14.35a 1.23
10–20 8.75c 10.66b 11.41ab 12.29a 1.36
K
?
cmol kg
-1
0–10 0.33d 0.42c 0.50b 0.54a 0.04
10–20 0.27d 0.33c 0.41b 0.45a 0.04
PH water 0–10 6.0c 6.7b 7.1a 7.0a 0.17
10–20 6.0c 6.6b 7.1a 7.0a 0.18
Means with the same letter within row are not significantly different (P\0.05)
SD standard deviation, LSD least square difference at 5%, ns no significant
Nutr Cycl Agroecosyst
123
to the increase of mounds humidity in these plots
contributing to the enhancement of the earthworms’
activity. Indeed, smallholders mulched the mounds to
protect seed yam from solar radiations. The Earth-
worm casts were not measured. In general, smallhold-
ers perceived earthworms’ casts as an indicator of soil
fertility. Earthworm casts on the mounds could
regulate soil porosity, as a volume of voids equivalent
to that of casts is created inside the soil (Birang 2004).
Earthworms could increase the clay content of surface
soil by selectively bringing up soil richer in clay
(Birang 2004). Furthermore, soil chemical character-
istics were higher in (TMA, TMM) than in (T0, TM).
Organic materials supplied could contribute directly to
the building of soil organic matter (SOM), which itself
performs diverse functionary roles in improving the
physical, chemical and biological composition of the
soil (Sanginga and Woomer 2009).
DM production
DM of yam tubers removed and shoots recycled on
TMA and TMM were significantly higher in the 2005
(dry year) than in the 2003 (rainy year). In our study,
rainfall distribution varied among years and sites,
particularly from January to May, i.e. 20 weeks after
yam was planted. The production of yam yield mainly
depends on the effective duration of the transition to
autotrophy, i.e. the stage of vegetative development of
the crop without the supply of reserves from the mother
tuber (Degras 1986). The beginning of autotrophy,
which occurs when real leaves grow, is determined by
Table 4 Nutrient composition in different sources of biomass dry matter (A. gayanus, maize, A. histrix,M. pruriens, yam shoot, yam
tuber, maize grain) in the 2003 and 2005 cropping seasons in four villages in Benin
Source of biomass N (%) P (%) K (%)
2003 cropping season A. gayanus stover 1.16 ±0.28 0.13 ±0.09 0.49 ±0.16
Maize stover 0.91 ±0.16 0.13 ±0.03 0.50 ±0.12
Maize grain 2.17 ±0.22 0.33 ±0.10 0.27 ±0.08
A. histrix stover 2.02 ±0.31 0.14 ±0.05 0.63 ±0.03
M. pruriens stover 2.21 ±0.59 0.18 ±0.08 0.63 ±0.02
Yam shoot 1.10 ±0.24 0.15 ±0.03 1.38 ±0.20
Yam tuber 0.38 ±0.10 0.04 ±0.02 0.42 ±0.05
2005 cropping season A. gayanus stover 1.20 ±0.37 0.13 ±0.10 0.50 ±0.16
Maize stover 1.05 ±0.30 0.15 ±0.05 0.55 ±0.14
Maize grain 2.15 ±0.23 0.32 ±0.11 0.25 ±0.08
A. histrix stover 2.02 ±0.73 0.14 ±0.08 0.63 ±0.20
M. pruriens stover 2.20 ±0.40 0.18 ±0.08 0.65 ±0.10
Yam shoot 1.08 ±0.24 0.12 ±0.04 1.35 ±0.17
Yam tuber 0.37 ±0.10 0.04 ±0.01 0.41 ±0.06
Data are the means ±SD (standard deviation)
Table 5 Dry matter (t ha
-1
) of yam tubers removed at harvest and yam shoots recycled in the 2002–2003 and 2004–2005 cropping
seasons in four villages in Benin
2002–2003 cropping seasons 2004–2005 cropping seasons
T0 TM TMA TMM LSD T0 TM TMA TMM LSD
DM removed (t ha
-1
)
Yam tubers 5.09b 3.83c 7.20a 7.33a 0.51 4.34b 3.02c 8.00a 8.02a 0.55
DM recycled (t ha
-1
)
Yam shoots 1.27b 0.96c 1.80a 1.83a 0.13 1.09b 0.76c 2.00a 2.00a 0.14
Means with the same letter within row are not significantly different (P\0.05)
DM dry matter, LSD least square difference at 5%
Nutr Cycl Agroecosyst
123
the beginning of the rainy season. Consequently, a
delayed rainy season could be prejudicial to crop
growth and yam production. In 2005, even though there
was a drought, the favorable early rainfall distribution
after yam planting can have positively affected yam
DM production. Furthermore, the chemical fertilizers
applied and the above biomass DM of intercropping
maize and herbaceous legume recycled and accumu-
lated in 2002, 2003 and 2004 could have resulted in a
combined beneficial effect of water, nutrient use and
Table 6 Nitrogen, Phosphorus and Potassium content (kg ha
-1
) removed in yam tubers at the crop harvest and those recycled in
yam shoots in the 2002–2003 and 2004–2005 cropping seasons in four villages in Benin
2002–2003 cropping seasons 2004–2005 cropping seasons
T0 TM TMA TMM LSD T0 TM TMA TMM LSD
Plant nutrients removed (kg ha
-1
)
Yam tubers
N 19.35b 14.57c 27.37a 27.84a 1.95 16.49b 11.48c 30.41a 30.47a 2.08
P 1.99b 1.49c 2.81a 2.86a 0.20 1.69b 1.18c 3.12a 3.13a 0.21
K 21.39b 16.10c 30.25a 30.77a 2.16 18.23b 12.70c 33.61a 33.68a 2.30
Plant nutrients recycled (kg ha
-1
)
Yam shoots
N 14.01b 10.54c 19.81a 20.15a 1.41 11.72b 8.16c 21.60a 21.65a 1.48
P 1.91b 1.44c 2.70a 2.75a 0.19 1.30b 0.91c 2.40a 2.41a 0.16
K 17.57b 13.22c 24.85a 25.28a 1.77 14.65b 10.20c 27.01a 27.06a 1.85
Means with the same letter within row are not significantly different (P\0.05)
LSD least square difference at 5%
Table 7 Estimated annual present production cost, net present
value (US$ ha
-1
), labour productivity (U$$ man-day
-1
) and
return on investment (%) in the 2002–2003 and 2004–2005
cropping seasons in four villages in Benin: time horizon
4 years and discount rate (10%)
T0 TM TMA TMM
Economic yield (t ha
-1
)
Yam 9.43 6.85 15.20 15.34
Maize 1.80 1.68 1.63
Total present revenue (US$ ha
-1
) 775 763 1,380 1,457
Production cost (US$ ha
-1
)
Land 10 10 10 10
Input 349 382 385 390
Labour 219 335 381 392
Total present cost (U$$ ha
-1
) 474 585 623 635
Net present value (U$$ ha
-1
) 301 178 757 822
Return on investment (%) 62 29 145 152
Labour (man-day
-1
) 63 96 111 112
Labour productivity (US$ man-day
-1
)5 2 7 7
Inputs costs: Yam seeds (U$$ 697.5 ha
-1
); Maize grains (U$$ 6.0 ha
-1
); Mucuna grains (U$$ 15.9 ha
-1
); Aeschynomene grains
(U$$ 7.0 ha
-1
); Fertilizers (NPK ?Urea) (U$$ 59.8 ha
-1
)
Labour cost: Land clearing (U$$ 29.9 ha
-1
); Tillage (U$$ 79.7 ha
-1
); Maize planting (U$$ 5.0 ha
-1
); NPK spreading (U$$
27.9 ha
-1
); Urea spreading (U$$ 19.9 ha
-1
); Aeschynomene planting (U$$ 10.0 ha
-1
); Mucuna planting (U$$ 7.0 ha
-1
); Weeding
(U$$ 39.9–47.8 ha
-1
); Maize harvesting ?Transport (U$$ 59.8 ha
-1
); Ridging (U$$ 124.6–149.5 ha
-1
); Seed yam planting (U$$
39.9 ha
-1
); Yam harvesting (U$$ 79.7 ha
-1
)
Nutr Cycl Agroecosyst
123
plant growth in 2005. Table 5shows that in 2005 tubers
and shoots of yam are less on T0 and TM and more on
TMA and TMM: this is in good accordance with the
hypothesis that the accumulation of nutrients in the soil
is the main cause of the differences of yield between
2003 and 2005.
DM amounts of M. pruriens,A. histrix and maize
stover recycled or maize grain removed were higher in
the 2002–2003 (humid year) than in 2004–2005 (dry
year). In fact, plant yields and agronomic productivity
were constrained by recurring drought stress exacerbated
by highly variable and unpredictable rains. M. pruriens
stover showed the highest DM amount followed by
A. histrix whatever the year and this could reach
10 t ha
-1
(Carsky et al. 1998). Indeed, M. Pruriens,
compared with A. histrix, grows more rapidly and close.
Plant nutrients contribution to the systems
The nutrient (N, P, and K) levels removed or recycled
fit the DM production (tubers, shoots) and then varied
according to treatment and cropping season. The
significantly higher nitrogen (N) contributions to the
systems in 2002–2003 and 2004–2005 cropping sea-
sons were recorded in intercropped M. pruriens with
maize-yam rotation (TMM) followed by the inter-
cropped A. histrix with maize– yam rotation (TMA).
All N requirements in the 1-year fallow—yam rotation
(T0) and the maize—yam rotation (TM) were obtained
respectively from fertilizers and soil whereas in TMA
and TMM, N was derived from biological nitrogen
fixation (BNF), soil and fertilizer. The levels of
nitrogen content in TMM and TMA were significantly
higher in the 2002–2003 (rainy year) than in
2004–2005 (dry year). Generally, studies revealed that
the incorporation of the biomass gets more nitrogen to
the succeeding crop than the mulch application on the
soil because the decomposition of organic matter is
more rapid after incorporation (Hulugalle et al. 1985;
Franzen et al. 1994; Ibewiro et al. 2000).
TMA and TMM removed significantly more P than
T0 (Table 6). The high nutrient removal is due to the
high yield observed in those treatments. Our results
showed that M. pruriens improved soil P. Legumes
fallows with M. pruriens, are known especially for
improving the quantity of available P fractions in the
soil for subsequent crops (Salako and Tian 2003).
Nevertheless, it depends on the inherent P levels in the
soils. M. pruriens root exudates could solubilize P
increasing its availability.
As far as K is concerned, the quantity recycled with
maize stover, yam shoots and M. pruriens or A. histrix
stover was twice as high as that which was removed
with maize grain and yam tubers from the systems.
The soil K concentrations were low in our study.
Indeed in this type of soil, there is no K response of the
crops for many years without K fertilization. Igue
´
(2000) showed the soil K concentration of 0.82 cmol
kg
-1
at 0–20 cm depth and decreased significantly
with cultivation.
Profitability of cropping systems
The yam-based systems (TMM and TMA) showed
highest land and cash productivities with net present
value levels significantly higher than the other systems
(T0 and TM). However, TMM and TMA demand an
additional labour compared with local yam-based
systems but allowed for a better labour productivity.
These results agree the work of Adjei-Nsiah et al.
(2007) that revealed the highest net revenue and
returns on investment (62%) in the cropping sequences
M. pruriens-maize with N fertilizer application to
maize in Ghana. Furthermore, former work reported
the profitability of intensification technologies with a
positive effect on farm household income (Olarinde
Fig. 2 Profitability of yam-based cropping systems with
herbaceous legumes in comparison with traditional systems
(time horizon: 4 years) in the transition zone of Benin. NPV net
present value
Nutr Cycl Agroecosyst
123
2006). Annual farm incomes were higher under the
repeated leguminous cover crops method (RLCC) in
southwestern Nigeria for food crops, mainly with yam
and cassava (Olarinde 2006). This also was obtained
where the use of repeated leguminous cover crops
comes into play to enhance soil fertility and to prevent
degradation which is the bane of production in the
study area.
Conclusion
The study highlights how smallholder farmers who
practice Mucuna pruriens var utilis or Aeschynomene
histrix in yam-based cropping systems can meet their
immediate food security and cash needs while main-
taining soil fertility. The production of yam on
marginal land where the biomass of herbaceous
legumes is available and incorporated into the soil
can serve as a means of allowing smallholder farmers
with limited access to finance to improve the fertility
of their soils. The production of dry matter (tubers,
shoots), nutrients removed or recycled, soil properties
were significantly improved on yam-based systems
with legumes in comparison with traditional systems.
The amount of nutrients recycled or removed was
dependent on the dry matter production that, in turn,
depended on soil fertility, rainfall and farmers’ effect.
Yam-based systems with legumes appeared attractive
for land, labour and cash productivities.
Therefore, yam yield increase in the Guinea-Sudan
transition zone of Benin will depend on the capacity to
restore the soil fertility (organic matter, nutrients) and
make water available at least 20 weeks after yam was
planted for a better tuber performance. The study thus
suggests that these yam-based cropping systems with
herbaceous legumes could be an alternative to the
traditional continuous cropping systems and long-
duration fallow.
Acknowledgments The authors express their sincere appreci-
ation and thanks for the financial support received from the
French Agency for Development (AFD) in the framework of the
Support Project for Farm Household development (PADSE), the
Development Project for Roots and Tubers (PDRT), the Food
and Agriculture Organisation of the United Nations (FAO) in the
frame of the project TCP/BEN 3002 (A) entitled ‘Sustainable
production of yams adapted to the markets’, the International
Cooperation Center in Agronomic Research for Development
(CIRAD), the Cooperation Project for Academic and Scien-
tific Research (CORUS), the French Embassy in Benin, the
International Institute of Tropical Agriculture (IITA-Ibadan) and
the International Atomic Energy Agency (IAEA). Finally, our
greatest appreciation goes to farmers who freely agreed to
participate in trials and make part of their fields available for the
research. Their active participation is also highly appreciated.
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... In Côte d'Ivoire, yam is dominantly produced in the northeast part of the Tropical Moist Deciduous Forest and the northeast extreme of the Tropical Rain Forest [22]. In Benin, most of the production is done in the Guinea-Sudan zone [23,24] and within the tropical moist deciduous forest as described by the FAO [22]. It is estimated that about 70% of yam production in Nigeria and Ghana occurs in the Derived Savannah, 20% in the Forest zone, and 10% in the southern Guinea Savannah [12]. ...
... In most cases, the fallow is dominated by grasses such as Andropogon gayanus Kunth. [23], which hardly adds adequate nutrients to the soil. Unfortunately, because of land scarcity, the fallow period has been shortened in many areas and is inadequate to restore the required fertility for sustainable yam farming. ...
... Recently, "artificial fallow" systems have been introduced where "high-value" plants are grown. ese include Chromolaena odorata and some legume cover crops which are effective at improving the nutrient status of soils to increase tuber yields [23,53]. ...
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... observed a maximum recovery of just 30% of N fertilizer in yam tuber, leaving the rest to go waste and to the environment. Therefore, intercropping or rotating yams with legume crops or woody perennials have been observed to be the way forward in supplying N, improving nutrient cycling, and increasing yam productivity Maliki et al., 2012a). ...
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Thesis
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... After two or three consecutive years of yam cultivation, when tuber yields are getting low, either farmers cultivate the field with a legume crop such as cowpea before planting yam again, or they move to a new field which was under fallow. The decline in yam yield in response to shortened fallow periods is one of the biggest challenges faced by yam farmers across the tropics (Maliki et al. 2011;Srivastava et al. 2012). This decline has been partly ascribed to a decrease in soil fertility due to substantial amount of nutrients exported with the tubers at harvest (Frossard et al. 2017). ...
... Yam is usually grown without any external inputs using its own tubers as planting material. In areas where land is scarce, farmers produce yam after only one year of fallow or no fallow [32]. [31] reports that farmers perceive declining soil fertility as a key constraint to yam production in areas with low agricultural intensification. ...
... The yam belt of West Africa spans from the humid forest where yam is cultivated for food security to the northern Guinean savanna where yam is also cultivated as a cash crop ( [23], [24]). Yam is traditionally planted as the first crop, after a long-term fallow as it is considered to be demanding in terms of soil fertility [25]. In the following years, the field is cultivated with other staple crops and/or perennial crops. ...
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... White yam (Dioscorea rotundata) is an extensively cultivated and consumed yam species in Ghana and other West African countries (Kayode et al., 2017;Olatoye and Arueya, 2019;Raymundo et al., 2014). The conventional shifting agriculture practice, in which yam is cultivated continuously for 10 years after clear-cutting a field, does not only lead to yield decline over time but also exacerbates deforestation (Acheampong et al., 2019;Maliki et al., 2012). To sustainably intensify yam cultivation, agronomic practices need to improve yam yield while also enhance soil fertility. ...
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Yam, a major food crop for West Africa, has not been managed to reach its potential productivity. The current practice of planting yam continuously for years after clear-cutting a field is not sustainable and has led to deforestation and nutrient depletion. By examining the effect of improved management on yam cultivation in Ghana, this study aimed to solve the tradeoff between improving yam yield and sustaining soil organic carbon (SOC). We used a calibrated and validated process-based crop simulation model, Systems Approach to Land Use Sustainability, to assess the impact of four management treatments: continuous unfertilized rainfed yam (con-trol), pigeonpea-yam rotation, yam with 3 Mg/ha pigeonpea residue incorporated and yam with 23− 23 N-P 2 O 5 kg/ha fertilizer added. We modeled 10 years of yam yield and SOC across cropland in Ghana with varying levels of soil carbon, rainfall amount, and precipitation pattern. On average, simulated yam tuber yield was the highest with a pigeonpea residue incorporation treatment (4.1-11.9 Mg/ha, average of 7.5 Mg/ha). The rotation (average yield of 6.4 Mg/ha) and fertilizer (average of 7.0 Mg/ha) treatments produced comparable increases in yam yield over the control treatment (1.9-9.2 Mg/ha, average of 4.9 Mg/ha). The low yam yield of the control treatment was mostly attributed to nutrient deficiency (nitrogen and phosphorus). Drought also limited yam growth, particularly in northern Ghana. The three improved management treatments increased soil nutrient availability and thus improved yield. SOC declined under all four tested treatments over the simulated 10 years, but declined least with residue incorporation (average rate-0.3 Mg/ha/year), followed by fertilizer addition (-0.43 Mg/ha/year), rotation (-0.42 Mg/ha/year), and the control (-0.51 Mg/ha/year) management. Our work provides a benchmark for yam yield response to alternative management across Ghana, and highlights pigeonpea's contribution to sustainable intensification of yam. Further research is needed to untangle the interacting effects of land use and agronomic management on SOC.
... In Ghana, crops are already experiencing heat stress, dry spells, pests, and diseases outbreak and shorter planting season as a consequence of the changing climate (Essegbey et al., 2015). Climate change poses a significant threat particularly to the smallholder farmers and to the millions of people who regularly grow rain-fed full season crops such as yam, cocoyam, rice, etc. (Amekudzi et al., 2015;Maliki et al., 2012;Mignouna et al., 2014;Srivastava et al., 2012). Choices about what to grow are often dictated by the ability of the rainfall regime to support soil moisture for plant growth (Oteng-Darko et al., 2018). ...
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Improved technologies (row planting, ridging, seed treatment, weed management, fertilizer application) with a proven record of sustained productivity for yam production are imperative for food security. This study promotes the efficacy of these existing improved agronomic practices using a farmer-based participatory approach in some selected major yam-growing areas in the forest-savannah transition zone of Ghana. The improved agronomic practice treatment included use of ridging as seedbed, seed treatment before planting, fertilizer application at a rate of 30:30:36 N:P2O5: K2O kg/ha plus 15 kg/ha Mg and 20 kg/ha S as MgSO4 and the use of minimum stakes (trellis; 30-50% fewer stakes used by farmers). This was compared with farmers' practice, which consisted of mounding, no fertilizer application, and no seed treatment. A significantly (p ≤ 0.01) higher yam yields (more than 60%) were observed for the improved agronomic practice over the farmers' practice at Ejura, Atebubu, and Kintampo which are major yam-growing communities of Ghana. Sensory evaluation showed that the culinary quality of fertilized yam was as good as unfertilized yam. The contribution of existing improved yam production practices in the selected yam communities of Ghana was quantified in terms of their productivity and economic benefit to smallholder farmers.
... Ce résultat peut s'expliquer par le mode de labour en bute réalisé dans ce système de culture. En effet, ce mode de labour favorise un enfouissement de la matière organique en profondeur et par suite une distribution de cette matière le long du profil du sol (Maliki et al., 2012). Etant donné la complexité des systèmes de culture implémentés sur le bassin versant de Kiti, des travaux plus approfondis à travers l'étude des systèmes de culture par unité de paysage avec des méthodes de traçage du carbone, permettront d'identifier avec plus de précisions les facteurs ainsi que les mécanismes qui interagissent sur la matière organique du sol. ...
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Une teneur élevée en matière organique est généralement recherchée pour les sols cultivés, en raison de son influence positive sur la fertilité des sols. L'objectif de cette étude a été d'évaluer l'effet de différents systèmes de culture et de la pente sur la matière organique du sol dans le bassin versant de Kiti au Centre-Bénin. Des échantillons de sol ont été collectés sur une profondeur de 40 cm, coupés en quatre sections de 10 cm chacune (0-10, 10-20, 20-30 et 30-40 cm). Ces échantillons ont été prélevés sur un sol à pente variable : pente faible et pente moyenne et sur quatre transects parallèles traversant cinq systèmes de culture : maïs-coton, plantation de teck, jachère de 5 ans, igname-maïs et jachère de 30 ans. Les résultats ont montré un effet significatif (p < 0,0001) des systèmes de culture sur la teneur en matière organique du sol. Le taux de matière organique le plus élevé a été observé au niveau de la jachère de 30 ans (4,20%). Dans le plan vertical, Il diminue significativement de la surface vers la profondeur (p < 0,0001), pour tous les systèmes de culture. La distribution de la matière organique dans le profil du sol varie d'un système de culture à un autre (p = 0,0003). Les résultats de cette étude constituent des données de choix pour des travaux plus approfondis sur la recherche de pratiques de gestion durables des sols au Bénin.
... Yam are sensitive to soil fertility and have high nitrogen (N) and potassium (K) requirements (Orkwor and Asadu 1998;Lebot, 2009;O 'Sullivan 2010;Dare et al. 2014;Frossard et al. 2017) which is why yam is traditionally grown as the first crop after a long-term fallow. However, there are not many longterm fallows left in West Africa and famers rarely use inorganic or organic fertilizers to grow yam (Floquet et al. 2012;Maliki et al. 2012). It becomes urgent to develop strategies that will allow cropping yam in crop rotation and sustainably increase tuber yields (Frossard et al. 2017). ...
Article
Information on the nitrogen (N) nutrition of yam (Dioscorea spp) is limited. Our objective was to elucidate the factors controlling N uptake by D. rotundata and D. alata. We analyzed results obtained with improved cultivars of these species grown in three field experiments among which ¹⁵N-fertilizer was used in one. Plant biomass production, leaf area index (LAI), root length density, N and ¹⁵N uptake by the plant were measured in these experiments. Nitrogen uptake was controlled in both species by plant demand and N inputs. A positive relation was observed between N uptake and LAI. Despite the small root system, the ability of the plant to take N up was high. The amount of N derived from the fertilizer recovered in the plant was explained by total N uptake. Finally, avenues to improve the low nitrogen fertilizer recovery (<20%) in yam are discussed.
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Pour contribuer à ralentir la dégradation de la fertilité des sols, le projet de «recherche pour le développement» YAMSYS développe des techniques de gestion intégrée de la fertilité des sols (GIFS), à base des fertilisants minéraux et organiques, testées par les agriculteurs dans leurs propres exploitations. Au regard, de l'exigence de l'igname pour les sols riches en matière organique, la technologie avec la fumure organique devrait être la plus performante. Les données ont été collectées sur les essais paysans de 2017 et 2018 à Tiéningboué, Côte d'Ivoire. Une analyse de sensibilité, basée sur l'inférence statistique et la budgétisation partielle, permet d'évaluer les performances des techniques de GIFS. Les niveaux de rendement et prix actuels montrent que la technique utilisant des engrais minéraux est la plus performante, surtout pour Dioscorea rotundata. Avec les techniques de GIFS, les marges brutes sont positives et globalement supérieures à celles de la pratique courante dans le contexte où seules des charges spécifiques (préparation du sol et achat de produits phytosanitaires) nécessitent une sortie de trésorerie ; tandis que la plupart des travaux sont réalisés avec les ressources familiales des agriculteurs. Les coûts de production varient de 292 201 Fha-1 à 572 481 Fha-1 selon la technique de GIFS et l'espèce d'igname. Bien que, le rendement commercialisable des techniques de GIFS présente un potentiel de 20 tha-1 en milieu paysan, les résultats technico-économiques révèlent une forte variabilité inter et intra-espèces. En définitive, la recherche collaborative devra se poursuivre pour mieux comprendre et atténuer les sources de variabilité, proposer des sources alternatives de matières organiques et minérales plus accessibles et moins coûteuses, et pour accompagner la diffusion des GIFS par le biais de la plateforme d'innovation. Mots clés : Performance, Gestion intégrée de la fertilité des sols, igname, budget partiel, analyse de sensibilité. ABSTRACT INTEGRATED SOIL FERTILITY MANAGEMENT TECHNIQUES IN YAM-BASED SYSTEMS AND THEIR PERFORMANCE IN DIVERSIFIED CONTEXTS IN CÔTE D'IVOIRE To contribute for slowing down soil fertility degradation, the YAMSYS «research for development» project is developing integrated soil fertility management (ISFM) techniques, based on mineral and organic fertilisers, tested by farmers on their own farms. As yam requires soil rich in organic matter, the technology with organic fertiliser is expected to perform best. Data were collected on 2017 and 2018 farmer trials in Tiéningboué, Côte d'Ivoire. A sensitivity analysis, based on statistical inference and partial budgeting, is used to assess the performance of ISFM techniques. Current yield and price levels Agronomie Africaine 34 (1) : 71-91 (2022) 72 E. OKA et al. show that the technique using mineral fertiliser performs best, especially for Dioscorea rotundata. With ISFM techniques, gross margins are positive and overall higher than with current practice in the context where only specific expenses (soil preparation and purchase of phytosanitary products) require a cash outflow; while most of the work is done with farmers' family resources. Production costs vary from 292,201 Fha-1 to 572,481 Fha-1 depending on the ISFM technique and the yam species. Although marketable yield of ISFM techniques has a potential of 20 tha-1 in farmers' fields, the technical and economic results reveal high inter-and intra-species variability. Ultimately, collaborative research should continue to better understand and mitigate the sources of variability, to propose alternative sources of organic and mineral matter that are more accessible and less costly, and to support the dissemination of ISFMs through the innovation platform.
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The Republic of Benin is a very important and dynamic yam producer in West Africa. During the past 30 years the country's yam output was multiplied by more than 3 that represents an annual increase rate of 3.75 %. The traditional yam cultivation is based on slash and burn practices but now cropping techniques are evolving for many reasons. In order to understand and to assess farmers' yam production strategies, a study of yam based farming systems was carried out in the Borgou region which can be considered as the core of Benin's yam belt. 60 farmers have been followed up in detail (including yield measurement) during three cropping years and in addition 300 others farmers were interviewed more rapidly. The comparison between different groups of yam growers as yam chip oriented producers, sedentarized Fulani shepherd recently involved in agriculture or cotton oriented farmers, allow to understand the different strategies used for yam cultivation. In particular the management of the different genetic resources according to various constraints, such as fallow shortening or market demand allow the understanding of how farmers adapt themselves to external changes.
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Traditional upland rice-based cropping systems in West Africa rely on periods of fallow to restore soil fertility and prevent the build-up of insect pests and weeds. Demographic growth and increased demand for land is forcing many farmers to intensify their rice production systems. Declining fallow length and increasing number of crops before leaving the land to extended fallow result in a significant yield reduction. Promising cropping system alternatives include the use of site specific, weed-suppressing, multi-purpose cover legumes as short duration fallows. Constraints to rice production related to intensification were determined in 209 farmers' fields in four agro-ecological zones during 1994 and 1995. Nitrogen accumulation and weed suppression were evaluated in 54 legume accessions, grown for six months during the dry season, under a range of hydrological and soil conditions in 1994/95. Their effect on the yield of upland rice was determined in 1995. To increase benefits from improved fallow technology, the timing of legume establishment in relation to rice and the effect on crop and weed growth of removing, burning, mulching, or incorporating allow residues prior to the rice crop were determined. Intensified land use resulted in a significant plot-level yield reduction that was highest in the derived savanna and the bimodal forest zones where it was associated with a doubling of the weed biomass in rice and a significant reduction in soil N supply. Legume fallows appear to offer the potential to sustain rice yields under intensified cropping. Legume biomass was in most instances significantly greater than in the weedy fallow control and several legume species suppressed weed growth. Nitrogen accumulation by legumes varied between 1-200 kg N ha(-1) with 30-90% Ndfa. Rice grain yield following legume fallows increased by an average of 0.2 mg ha(-1) or 29% above the weedy fallow control. Relay establishment substantially increased legume biomass. However, seeding of the legume at 28 days or earlier significantly reduced grain yield due to interspecific competition. Incorporating or mulching of fallow residues provided no significant yield advantage as compared to burning. Absolute effects varied as a function of site, legume species, and management practice.
Conference Paper
The influence of soil properties on yam growth and tuber production is discussed. Two species were grown with or without fertilization in two agro-ecological zones (forest and savannah) in Ivory Coast. Leaf area index (LAI), and dry matter (DM) accumulation and partitioning among plant parts were measured during plant growth. These data were tested against a model describing the growth of D. alata. DM production of all plant parts of D. alata was always higher than those of D. cayenensis-rotundata for all sampling dates and for both zones. This was explained by the higher LAI of D. alata which intercepted a higher amount of radiation. Fertilizer application increased DM production of both species in the savannah site only. A good agreement between measured and simulated DM was noticed only for D. alata in the forest zone site, and for all other treatments in both sites the DM pattern was similar and with overestimations. The overestimations were attributed to the differences in soil fertility (e.g. higher pH, higher clay and organic matter in forest) between zones and to genetic differences between species.
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In 1989, 15 fallow species were planted on a degraded Alfisol in southwestern Nigeria, but only Pueraria phaseoloides, Senna siamea, Leucaena leucocephala, Acacia leptocarpa and Acacia auriculiformis survived beyond 1993. After clearing different subplots of the fallowed plots in 1993 and 1995, intercropping of cassava + maize was practiced with level (minimum) and mound tillage. Nitrogen fertilizer, between 0 and 60 kg ha, was also applied to subplots of natural regrowth where planted fallows did not survive. Although a maize grain yield of 2.3 t ha and a cassava root yield of 18.3 t ha were obtained with level tillage in 1995, grain yield was increased to 2.6 t ha and cassava yields to about 22 t ha by mounding and 60 kg N ha application. Effects of mounding and N application were pronounced in the second and third consecutive years of cropping. Planted tree fallows like S. siamea, A. leptocarpa and L. leucocephala were highly suitable for soil rehabilitation. For sustainable crop production in the second consecutive year of cropping after a 6-year fallow period, mound tillage was recommended while in the third year, mound tillage with 60 kg N ha was recommended.
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Rotations are important practices for managing soil fertility on smallholder farms. Six cropping sequences (cassava, pigeonpea, mucuna– maize–mucuna, cowpea–maize–cowpea, maize–maize–maize, and speargrass fallow) were evaluated during 2003–2004 in Wenchi district of Ghana for their effects on the profitability of the different rotations and the productivity of subsequent maize. Soil chemical properties were not significantly affected by cropping sequence. On the researcher-managed and farmer-managed plots maize grain yields were significantly influenced by cropping sequence. On the researcher-managed plots maize grain yield ranged from 1.0 t ha À1 after speargrass fallow to 3.0 t ha À1 with cassava cropping when N fertiliser was not applied to maize and from 2.1 t ha À1 with continuous maize to 4.2 t ha À1 with mucuna–maize– mucuna when 60 kg N ha À1 was applied to maize. On the farmer-managed plots where N fertiliser was not applied to maize, maize grain yields ranged from 0.4 t ha À1 on speargrass fallow to 2.2 t ha À1 on plots previously cropped to pigeonpea. High maize grain yields associated with the cropping sequences involving cassava, mucuna and pigeonpea were related to the faster decomposition and N release of the biomass compared with the slower release of N by the poorer quality materials like maize stover and speargrass. Return on investment of the different rotational sequences ranged from À22% with speargrass/maize to 235% with cassava/maize when no N application was made to maize, and from 29% with continuous maize to 196% with cassava/maize when N fertiliser was applied to maize. Cassava/maize rotation was ranked by native farmers as the most preferred rotation whereas migrant farmers ranked cowpea–maize–cowpea–maize as the most preferred rotation. Among natives, male farmers ranked rotation involving cowpea as the next most preferred rotation after cassava/maize. In contrast, female farmers ranked pigeonpea/maize rotation as the second most preferred rotation, due to low labour and external input requirements of pigeonpea compared with cowpea. The choice of a particular rotational sequence is related to access to resources and the needs of the farmer. The study therefore suggests that, in a heterogeneous farming community like Wenchi, technology development should be targeted to suit the needs and resources available to each particular group of farmers. # 2007 Elsevier B.V. All rights reserved.
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Traditional upland rice-based cropping systems in West Africa rely on periods of fallow to restore soil fertility and prevent the build-up of insect pests and weeds. Demographic growth and increased demand for land is forcing many farmers to intensify their rice production systems. Declining fallow length and increasing number of crops before leaving the land to extended fallow result in a significant yield reduction. Promising cropping system alternatives include the use of site specific, weed-suppressing, multi-purpose cover legumes as short duration fallows. Constraints to rice production related to intensification were determined in 209 farmers' fields in four agro-ecological zones during 1994 and 1995. Nitrogen accumulation and weed suppression were evaluated in 54 legume accessions, grown for six months during the dry season, under a range of hydrological and soil conditions in 1994/95. Their effect on the yield of upland rice was determined in 1995. To increase benefits from improved fallow technology, the timing of legume establishment in relation to rice and the effect on crop and weed growth of removing, burning, mulching, or incorporating fallow residues prior to the rice crop were determined. Intensified land use resulted in a significant plot-level yield reduction that was highest in the derived savanna and the bimodal forest zones where it was associated with a doubling of the weed biomass in rice and a significant reduction in soil N supply. Legume fallows appear to offer the potential to sustain rice yields under intensified cropping. Legume biomass was in most instances significantly greater than in the weedy fallow control and several legume species suppressed weed growth. Nitrogen accumulation by legumes varied between 1–200 kg N ha-1 with 30–90% Ndfa. Rice grain yield following legume fallows increased by an average of 0.2 mg ha-1 or 29% above the weedy fallow control. Relay establishment substantially increased legume biomass. However, seeding of the legume at 28 days or earlier significantly reduced grain yield due to interspecific competition. Incorporating or mulching of fallow residues provided no significant yield advantage as compared to burning. Absolute effects varied as a function of site, legume species, and management practice.
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In cover cropping systems in the tropics with herbaceous legumes, plant residues are expected to supply nitrogen (N) to non-legume crops during decomposition. Field experiments were carried out to (i) determine the effects of residue quality on decomposition and N release patterns of selected plants in cover cropping systems, (ii) relate the pattern of residue N release to N uptake by maize in cover cropping systems. To study decomposition, litter bags were used and monitored over two maize growing seasons. The residues studied were mucuna (Mucuna pruriens (L.) DC. var. utilis (Wright) Bruck), lablab (Lablab purpureus (L.) Sweet), and leaves and rhizomes of imperata (Imperata cylindrica (L.) Raueschel). Mucuna and lablab decomposed rapidly losing more than 60% of their dry weight within 28 days. In contrast, imperata decomposed slowly with only 25% of its dry matter lost in 56 days. At 28 days, mucuna had released 154 kg N ha-1 in in-situ mulch systems and 87 kg N ha-1 in live- mulch systems representing more than 50% of its N. More than 64% of N in lablab was released within 28 days amounting to 21 to 174 kg N ha-1. Imperata rhizomes mineralized 4 to 14 kg N ha-1 within 14 days, and subsequently immobilized N until 112 days whereas imperata leaves immobilized N throughout the study period. Decomposition and N release rates from the plant residues were most strongly correlated with the (lignin+polyphenol)/N ratio, N content, lignin/N ratio, polyphenol/N ratio, C/N ratio and lignin content of the residues. Relative to the controls, herbaceous legume residues increased maize dry matter yield and N uptake during the two cropping seasons. At 84 days, the maize crop had utilized 13 to 63 kg N ha-1from mucuna representing 13 to 36% of N released, whereas 16 to 25% of N released from mucuna was recovered by the maize crop at 168 days. The first maize crop recovered 9 to 62 kg N ha-1 or 28 to 35% of N released from lablab. However, at 168 days, N uptake by maize in antecedent live-mulched lablab was 32% higher than the quantity of N released, whereas imperata residues generally, resulted in net reduction of maize N uptake.
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The mechanization of field operations like seeding, spraying and harvesting in continuous zero-tillage may lead to a severe compaction of the surface layer of coarse textured tropical soils, especially when mulch is sparse or missing. Therefore, a 2 year (1982–1984) field experiment was initiated on an Alfisol in Nigeria to study the effect of tillage, mechanization and mulch on soil structure and physical properties. Three zero-tillage treatments and a plough treatment were compared. The disk-plough and one of the no-till treatments were highly mechanized: all the field work was performed with tractors and machines, and consisted of secondary bush clearing, crop cultivation and harvest. On the other two no-till treatments, the impact of machine load was reduced, wither by hand harvesting or by performing all field operations manually. These four tillage-traffic systems were either treated with mulch or left unmulched. There were four growing seasons, with maize (Zea mays L.) as a test crop.