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Dry Matter Production, Nutrient Cycled and Removed, and Soil Fertility Changes in Yam-Based Cropping Systems with Herbaceous Legumes in the Guinea-Sudan Zone of Benin

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Traditional yam-based cropping systems (shifting cultivation, slash-and-burn, and short fallow) often result in deforestation and soil nutrient depletion. The objective of this study was to determine the impact of yam-based systems with herbaceous legumes on dry matter (DM) production (tubers, shoots), nutrients removed and recycled, and the soil fertility changes. We compared smallholders’ traditional systems (1-year fallow of Andropogon gayanus -yam rotation, maize-yam rotation) with yam-based systems integrated herbaceous legumes ( Aeschynomene histrix /maize intercropping-yam rotation, Mucuna pruriens /maize intercropping-yam rotation). The experiment was conducted during the 2002 and 2004 cropping seasons with 32 farmers, eight in each site. For each of them, a randomized complete block design with four treatments and four replicates was carried out using a partial nested model with five factors: Year, Replicate, Farmer, Site, and Treatment. Analysis of variance (ANOVA) using the general linear model (GLM) procedure was applied to the dry matter (DM) production (tubers, shoots), nutrient contribution to the systems, and soil properties at depths 0–10 and 10–20 cm. DM removed and recycled, total N, P, and K recycled or removed, and soil chemical properties (SOM, N, P, K, and pH water) were significantly improved on yam-based systems with legumes in comparison with traditional systems.
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Research Article
Dry Matter Production, Nutrient Cycled and Removed, and Soil
Fertility Changes in Yam-Based Cropping Systems with
Herbaceous Legumes in the Guinea-Sudan Zone of Benin
Raphiou Maliki,1Brice Sinsin,2Anne Floquet,3Denis Cornet,4
Eric Malezieux,5and Philippe Vernier4
1Institut National des Recherches Agricoles du B´
enin (INRAB), P.O. Box 2128, Calavi, Benin
2Facult´
e des Sciences Agronomiques de l’Universit´
e d’Abomey-Calavi (FSA/UAC), P.O. Box 01-526, Cotonou, Benin
3Centre B´
eninois pour l’Environnement et le D´
eveloppement Economique et Social (CEBEDES), P.O. Box 02-331, Cotonou, Benin
4Centre de Coop´
eration Internationale en Recherche Agronomique pour le D´
eveloppement (CIRAD),
34398 Montpellier Cedex 5, France
5Centre de Coop´
eration Internationale en Recherche Agronomique pour le D´
eveloppement (CIRAD), UPR Hortsys,
34398 Montpellier Cedex 5, France
Correspondence should be addressed to Raphiou Maliki; malikird@yahoo.fr
Received  December ; Accepted  May 
Academic Editor: Zeng-Yei Hseu
Copyright ©  R aphiou Maliki et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Traditional yam-based cropping systems (shiing cultivation, slash-and-burn, and short fallow) oen result in deforestation and
soil nutrient depletion. e objective of this study was to determine the impact of yam-based systems with herbaceous legumes
on dry matter (DM) production (tubers, shoots), nutrients removed and recycled, and the soil fertility changes. We compared
smallholders’ traditional systems (-year fallow of Andropogon gayanus-yam rotation, maize-yam rotation) with yam-based systems
integrated herbaceous legumes (Aeschynomene histrix/maize intercropping-yam rotation, Mucuna pruriens/maize intercropping-
yam rotation). e experiment was conducted during the  and  cropping seasons with  farmers, eight in each site. For
each of them, a randomized complete block design with four treatments and four replicates was carried out using a partial nested
model with ve factors: Year, Replicate, Farmer, Site, and Treatment. Analysis of variance (ANOVA) using the general linear model
(GLM) procedure was applied to the dry matter (DM) production (tubers, shoots), nutrient contribution to the systems, and soil
properties at depths – and – cm. DM removed and recycled, total N, P, and K recycled or removed, and soil chemical
properties (SOM, N, P, K, and pH water) were signicantly improved on yam-based systems with legumes in comparison with
traditional systems.
1. Introduction
One of the most serious problems of farming system is the
excessive reductions of agricultural productivity resulting
from major degradation of soil fertility. In  Edouard
Saouma wrote that the most serious problem of African
countries in the future can be that of land degradation []. To
understand how and why lands become degraded, one needs
some knowledge of the physical environment, population,
cultivation history, and farming systems [, ].
Current yam-based cropping systems, which involve
shiing cultivation, slash-and-burn, or short fallow, oen
result in deforestation and soil nutrient depletion []. As
long as population pressure was low, the cropping phase was
short compared to the fallow period. ree or four years of
cultivationfollowedbytenyearsormoreoffallow,forexam-
ple, allows the accumulation of easily degradable organic
matter to regenerate soil fertility [, ]. Where population
increases, available land per inhabitant is reduced and fallow
periods shorten. Traditional long-fallow shiing cultivation
Hindawi Publishing Corporation
Scientifica
Volume 2016, Article ID 5212563, 12 pages
http://dx.doi.org/10.1155/2016/5212563
Scientica
can no longer continue in most of humid Sub-Saharan Africa.
Increasing population densities are posing a serious threat
to natural resources and agricultural production. Farmers
response to higher food demand has been either an increase
in cultivated area or a reduction of fallow period. e
minimum fallow duration to maintain crop production was
estimated at  years []. Fallow periods in most of the humid
zone of West and Central Africa are actually between  and
 years [], reinforcing the need to seek alternative food
production systems [].
Yam ( Dioscorea spp.) is a tuber crop widely cultivated
in the humid and subhumid lowland regions of West Africa
andtheCaribbean[].Morethan%oftheworldwide
production ( Mt fresh tubers/year) is produced in West
Africa []. Yam is grown in traditional cropping systems
as the rst crop aer land clearance, yielding about  t of
fresh tuber/ha/year [], but when the soil fertility is high, it
can easily reach – t/ha in farm elds [] with Dioscorea
cayenensis-rotundata varieties. In Benin nowadays, farmers
hardly have the possibility to rely on long duration fallow and
yam is being cultivated in - or -year herbaceous fallow or
maize rotation systems with manual incorporation of residue
into the soil [, ]. Smallholder farmers removed important
quantities of nutrient from their soil without applying a su-
cient quantity of manure or fertilizer to replenish the soil [].
Yam cultivation in West Africa is now confronted with
the scarcity of fertile soil available for clearing []. In Benin
nowadays, farmers hardly have the possibility to rely on
long duration fallow and yam is being cultivated in - or -
year herbaceous fallow-yam or maize-yam rotation systems
with manual incorporation of residue into the soil [,
]. Smallholder farmers removed important quantities of
nutrient from their soil without applying a sucient quantity
of manure or fertilizer to replenish the soil [].
e decline in yam yields under continuous cultivation
has led to the largely accepted conclusion that yam requires
a high level of natural soil fertility (organic matter and
nutrient) []. Since the demand for yam keeps increasing
due to the continued population growth, reserves of arable
land are diminishing, and fallow duration is decreasing. It is
becoming necessary to sustainably increase yam productivity
in sedentary cropping systems []. ere is a dire need
therefore to assess in farmers’ conditions the economic
performance of sustainable cultivation techniques. Ongoing
soil degradation could be reduced by the adoption of new
farming techniques such as improved fallows of herbaceous
legumes [, ].
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. Com-
parative studies are lacking that assess the eects of yam-
based technologies with herbaceous legumes intercrops and
short fallows on yam production and soil properties in
the savannah transition agroecological zone of Benin. We
compared in a perennial experiment for  years, with -year
rotations, smallholder farmers’ traditional rotations maize-
yam or -year Andropogon gayanus fallow-yam with rotations
intercropped Aeschynomene histrix with maize-yam or inter-
cropped Mucuna pruriens with maize-yam. e objective of
F : Study area location in the savannah transitional agroeco-
logical zone of Benin.
this study was to determine the impact of yam-based systems
with herbaceous legumes on dry matter (DM) production
(tubers and shoots), nutrients removed and recycled, and the
soil fertility changes.
2. Materials and Methods
2.1. Study Sites. e study was carried out in the Guinea-
Sudan transition zone of Benin (centre of Benin) in four sites:
Mini (District of Dassa-Zoum`
e), Gom`
e(Glazou
´
e), Akp´
ero,
and Gbanlin (Ouess`
e) with latitudes 󸀠and 󸀠north
and longitudes 󸀠and 󸀠east (Figure ).
e climate is tropical transitional Guinea-Sudan with a
rainfall distribution gradient from bimodal (Southern Benin)
to monomodal (Northern Benin). e average annual rainfall
during the study period was  mm (),  mm
(),  mm (), and  mm (). e rainfall
regime in the study area is variable and unequal distribution
(i.e., number of rainy days per month) varies from one site
to another. e  and  cropping seasons were wet
and had better rainfall distribution with an average annual
precipitation of  mm, whereas  and  were dry
( mm) with relatively low rainfall distribution.
Most of the soils are tropical ferruginous soils [], origi-
nally from Precambrian crystalline rocks (granite and gneiss),
and classied as plinthosols (Gbanlin and Akp´
ero) and luvi-
sols (Mini and Gom`
e) [] (Table ). Mini, Akp´
ero, and
Gbanlin are located on a plateau while Gom`
eisonlowland.
Akp´
ero is close to forest while Gbanlin, Mini, and Gom`
eare
far. ere is a rising gradient of fertility from the continuous
cropping system on degraded soils towards the forests. is
degradation is related to soil organic matter decrease, which
leads to nutrient depletion (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
essential. Smallholder farmers use fertilizers on maize on
depleted soils depending on cash and inputs availability.
Cotton is not mixed cropping, but pure crop in rotation with
other crops (maize or sorghum).
Scientica
T : Cropping calendar of yam-based cropping systems with herbaceous legumes and short fallow in the - and - cropping seasons.
Dec.
Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
2002 or 2004 cropping seasons
T Natural fallow of Andropogon gayanus Slashing and biomass incorporation
(ridging)
TM Land slashing and
ploughing
Maize planting, NPK
application, and weeding
Weeding and
urea
application
Maize harvesting Slashing and biomass incorporation
(ridging) in furrow
TMA Land slashing and
ploughing
Maize planting, NPK
application, A. histrix
planting, and weeding
Weeding and
urea
application
Maize harvesting Slashing and biomass incorporation
(ridging) in furrow
TMM Land slashing and
ploughing
Maize planting, NPK
application, and weeding
Mucuna
planting
Weeding and
urea
application
Maize harvesting Slashing and biomass incorporation
(ridging) in furrow
2003 or 2005 cropping season
T
Seed yam planting, mounds capping with mulch
material
yam staking, and weeding
Weeding Weeding Yam harvesting
TM
Seed yam planting, mounds capping with mulch
material
yam staking, and weeding
Weeding Weeding Yam harvesting
TMA
Seed yam planting, mounds capping with mulch
material
yam staking, and weeding
Weeding Weeding Yam harvesting
TMM
Seed yam planting, mounds capping with mulch
material
yam staking, and weeding
Weeding Weeding Yam harvesting
T: one-year fallow-yam rotation; TM: maize-yam rotation; TMA: Aeschynomene histrix/maize intercropping-yam rotation; TMM: Mucuna pruriens/maize intercropping-yam rotation.
Scientica
2.2. On-Farm Experiment. e concept of the experiment
was to produce residue biomass followed by planting yam in
rotation cropping systems. A previous cover crop (fallows or
intercropped maize/legume) was designed to provide organic
matter for the following main crop (yam) (Table ).
Smallholders carried out two-year rotations experiment
of yam-based cropping systems repeated twice (–)
on-farm with single-harvest late maturing variety of yam
“Kokoro” (Dioscorea rotundata). is 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), our, and starchy paste (locally called amala)[].We
conducted the experiment with  farmers, eight in each site
(Mini, Gom`
e, Akp´
ero, and Gbanlin). For each of them, we
used a randomized block design with four replications and
four levels of treatment. Plot size was  m × m (total of
m
2per farm). e four treatments were as follows:
(i) T0 (Control 1). T is one-year fallow-yam rotation,
which is a common practice in the area. A natural
fallow of Andropogon gayanus grass was grown in the
rst year.
(ii) TM (Control 2). TM indicates maize-yam rotation,
which is also a common practice in the area. Maize
was planted (spacing  cm × cm) in April of the
rst year.
With recurring drought stress exacerbated by highly
variable and unpredictable rains in the study area,
some farmers grow a second crop, which oen
fails. is corroborates the great interest of the
maize/leguminous crop when no second crop is
planned.
(iii) TMA. TMA is intercropped Aeschynomene histrix
with maize-yam rotation: maize was planted in April
of the rst year. A. histrix seeds ( kg ha−1)weremixed
with dry sand (/ sand and / seeds) and sown two
weeks aer the maize.
(iv) TMM. TMM is intercropped Mucuna pruriens with
maize-yam rotation: maize was planted in April of the
rst year. M. pruriens seeds ( kg ha−1)weresown
at spacing  cm × cm in May six weeks aer the
maize.
On treatments TM, TMA, and TMM, kg ha−1 NPK
fertilizer (% N, % P, and .% K) was applied to maize
in April and  kg ha−1 urea (% N) in June. e maize
was harvested in July. e grainless M. pruriens and A.
histrix crops were mowed  and  days, respectively, aer
planting. Organic matter was incorporated in moulds and le
onthesurfaceasmulchinOctoberandthenyamwasplanted
directly on these moulds, without mineral fertilization.
2.3. Data Collection. Composite soil samples were collected
in each eld before the beginning of the experiment along
plottransectsatsoildepthsofcmandcm(farm
elds × depths =  samples) in order to determine soil
characteristics. At the end of  before yam harvesting,
composite soil samples were collected at the same depths in
T : Quantity of biomass (t ha−1) dry matter and nutrients
contents (% and kg ha−1) applied in each plot in the  cropping
seasons, four village sites (Mini, Gom`
e, Gbanlin, and Akp´
ero),
Benin.
Site/treatment DM N P K N P K
tha
−1 %%%kgha
−1 kg ha−1 kg ha−1
Akp´
ero
T . . . . . . .
TM . . . . . . .
TMA . . . . . . .
TMM . . . . . . .
Gbanlin
T . . . . . . .
TM . . . . . . .
TMA . . . . . . .
TMM . . . . . . .
Mini
T . . . . . . .
TM . . . . . . .
TMA . . . . . . .
TMM . . . . . . .
Gom`
e
T . . . . . . .
TM . . . . . . .
TMA . . . . . . .
TMM . . . . . . .
the moulds along plot transects ( farm elds ×treatments
× depths =  samples).
Prior to ridging, in four  m2quadrats within each plot
the aboveground biomass of herbaceous legumes and fallow
was collected in October  and . e biomass samples
were dried at C until constant weight and then dry
weight was determined. At maturity, maize grain and stover
were harvested per row on each plot and dry matter (DM)
determined. DM of yam tubers and shoots was estimated on
each plot in December  and  (Tables  and ).
2.4. Soil and Plant Nutrients Content. e nutrients contents
of the soil samples were performed in the Laboratory of Soil
Sciences, Water and Environment (LSSEE) of INRAB (Benin
National Research Institute). e 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 Bray
 method [], potassium with the FAO method [, ],
organic carbon with the Walkley and Black method [],
and soil fractionation with Robinson method [] and pH
(H2O) (using a glass electrode in  : . v/v soil solution).
Only yam tuber and maize grain were removed, and all other
plantspartswererecycled(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
Scientica
T : Quantity of biomass (t ha−1) dry matter and nutrients
contents (% and kg ha−1) applied in each plot in the  cropping
seasons, four village sites (Mini, Gom`
e, Gbanlin, and Akp´
ero),
Benin.
Site/treatment DM N P K N P K
tha
−1 %%%kgha
−1 kg ha−1 kg ha−1
Akp´
ero
T . . . . . . .
TM . . . . . . .
TMA . . . . . . .
TMM . . . . . . .
Gbanlin
T . . . . . . .
TM . . . . . . .
TMA . . . . . . .
TMM . . . . . . .
Mini
T . . . . . . .
TM . . . . . . .
TMA . . . . . . .
TMM . . . . . . .
Gom`
e
T . . . . . . .
TM . . . . . . .
TMA . . . . . . .
TMM . . . . . . .
therespectiveplantparts.Drymatterremovedorrecycled
was calculated as a summation of dry matter of the respective
plant parts.
2.5. Analyses of Variance to Test the Eect of Site, Year, and
Tre atm ent on Yam Yiel d . Analysis of variance (ANOVA)
using the general linear model (GLM) procedure [] was
applied to the DM production (tubers and shoots), nutrient
contribution to the systems, and soil properties at depths –
and – cm. e experiment was conducted with  farm-
ers, eight in each site. For each of them, a randomized com-
plete block design with four treatments and four replicates
was carried out using a partial nested model with ve factors:
Year, Replicate, Farmer, Site, and Treatment. e random
factors were “Year” and “Replicate” and “Farmer.” Farmer was
considered as nested within “Site” and “Replicate” as nested
within “Farmer.” e xed factors were “Treatment” and
“Site.” Sites were considered as xed based on certain criteria
such as landscape (lowland and plateau), soil type, and initial
soil fertility. Yield values were logarithmically transformed
to normalize the data and to stabilize population variance.
e GLM was computed to assess the interactions between
the factors involved. Least square means and standard error
were also computed for factor levels, and the Newman and
Keuls test was applied for dierences between treatments.
Signicance was regarded at 𝑃 ≤ 0.05.
3. Results
3.1. Initial Soil Characteristics. e relevant general soil
physical and chemical characteristics before are presented in
Table .
Site physical characteristics such as soil texture (sand)
were relatively high (.%–.%) followed by silt
(.%–.%) and clay (.%–.%) with the lowest
content. e soils had a neutral reaction, with pH (HO)
ranging from . to ..
einitialsoilfertilitystatusofdierentsiteswaslow.Soil
organic matter (SOM) contents were low in all elds, ranging
from .% to .%, and the C : N ratio ranged from .
to .. Available P levels were very low and varied from
. to . mg/kg-soil. Soil N concentration ranged from
.% to .%. N, P, and SOM contents were signicantly
higher in – cm than in –cm depth, except at Gbanlin
site for N and SOM. Gom`
e site showed, for both soil depths,
the lowest values of carbon (C%), N%, P (mg/kg-soil), and
organic matter (%), whereas Akp´
ero had the highest values.
3.2. Dry Matter Production and Nutrient Contribution to the
Systems. In the  and  cropping seasons, the highest
biomass dry matter (DM) amount recycled was recorded on
TMM (Table ).
e ANOVA partial nested model shows that yam yield
DM diered signicantly depending on the factor Treatment
(𝑃 < 0.001). e factors Site and Year were not signicant
for yam yields DM. But Replicate (𝑃 < 0.001), Treatment
×Farmer (𝑃 < 0.01), and Year ×Farmer interactions (𝑃<
0.001) were signicant (Table ).
Dry matter (t ha−1) of yam tubers removed and yam
shootsrecycled,N,P,andKcontent(kgha
−1)drymatterof
plant parts removed in the crop harvest, and those returned
to the soil in yam-based cropping systems were signicantly
higher in TMA and TMM than in T and TM during both
cropping seasons (Tables  and ).
erefore, total plant N, P, and K (kg ha−1)drymatter
removed in the crop harvest and those returned to the soil
in yam-based cropping systems were signicantly higher in
TMA and TMM than in T and TM during both cropping
seasons (Table ).
3.3. Eects of Treatments on Soil Characteristics. Aerwards
soil characteristics at the end of the experiment globally
showed relatively low clay, silt, and relatively high sand con-
centration on dierent sites under dierent treatments (T,
TM, TMA, and TMM) in comparison with initial soil char-
acteristics at the beginning of the experiment. Soil organic
matter concentration was improved at –cm depth par-
ticularly in Mini (.%, .%, .%, and .%) on
T, TM, TMA, and TMM, respectively, and Gom`
e(.%,
.%, .%, and .%). Globally, soil N and P concen-
trations were improved on dierent sites on treatments TMA
and TMM in – cm or – cm depth (Tables (a)–(d)).
e end of study soil analysis showed soil chemical
properties (SOM%, N%, P (mg/kg-soil), K+cmol kg−1,and
pH water) signicantly higher in TMA and TMM than in
traditional systems T and TM (𝑃 < 0.001). Soil clay contents
Scientica
T : Initial soil characteristics at the beginning of the experiment at – and – cm layers in four village sites (Mini, Gom`
e, Gbanlin,
and Akp´
ero) with  farmers, Benin.
Akp´
ero Gbanlin Mini Gom`
e
Depth (cm) – – – – – – – –
“Plinthosols” “Plinthosols” “Luvisols ferriques” “Luvisols ferriques”
Clay% . . . . . . . .
Silt% . . . . . . . .
Sand% . . . . . . . .
C% . . . . . . . .
N% . . . . . . . .
C/N . . . . . . . .
OM% . . . . . . . .
PH . . . . . . . .
Bray P . . . . . . . .
C%: soil carbon concentration; N%: soil nitrogen concentration; OM%(=. ×C%): soil organic matter content; C/N: index of biodegradability or ratio of
soil carbon to nitrogen; Bray P (mg kg−1): soil phosphorus.
T : Dry matter (t ha−1 ) of plant parts returned to the
soil signicantly increased according to four cropping systems
(A. histrix/maize intercropping-yam rotation; M. pruriens/maize
intercropping-yam rotation; -year fallow of Andropogon gayanus-
yam rotation; maize-yam rotation) during the  and 
cropping seasons in four villages in Benin.
Cropping system Cropping season  Cropping season 
DM (t ha−1)DM(tha
−1)
T .c.c
TM .d.d
TMA .b.b
TMM .a.a
Means with the same letter within row are not signicantly dierent (𝑃>
0.05).
T (control ): one-year fallow-yam rotation; TM (control ): maize-yam
rotation; TMA: A. histrix/maize intercropping-yam rotation; TMM: M.
pruriens/maize intercropping-yam rotation; DM: dry matter.
were signicantly higher in TMA, TMM, and T than in
TM (𝑃 < 0.001). No signicant dierence was observed
for silt and sand concentrations for dierent treatments
(Table (e)).
4. Discussion
4.1. Dry Matter and Nutrients Recycled in Yam-Based Cropping
Systems. e highest biomass dry matter (DM) amount recy-
cled was recorded on Mucuna/maize intercropping (TMM).
Mucuna grows rapidly and DM production can reach
 t ha−1 [, , ]. In fact, Mucuna creeps and climbs maize
straw in pattern crop allowing the lianas staking. erefore,
Mucuna large leaves prot from solar radiations improv-
ing the photosynthetic activity and the plant productivity.
Mucuna reaches the physiological maturity (owering time)
between  and  days aer grains planting in the study
area in comparison with Aeschynomene (– days) [,
].
DM of yam shoots recycled on TMA and TMM were
signicantly higher in  (dry year) than in  (humid
year). e chemical fertilizers applied and the above biomass
DM of intercropping maize and herbaceous legume recycled
and accumulated in , , and  could have resulted
in a combined benecial eect of water, nutrient use, and
plant growth in . DM amounts of M. pruriens,A.
histrix, and maize stover recycled were higher in -
 (humid year) than in - (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  t ha−1 [] because M. Pruriens, compared with
A. histrix, grows more rapidly and close.
e nutrient (N, P, and K) levels removed or recycled
ttheDMproduction(tubersandshoots)andthenvaried
according to treatment and cropping season.
4.2.ImpactofYam-BasedCroppingSystemswithHerbaceous
Legumes on Soil Properties. Most of the soils as mentioned
above are tropical ferruginous soils, originally from Precam-
brian crystalline rocks (granite and gneiss) and classied
as plinthosols (Gbanlin and Akp´
ero) and luvisols (Mini
and Gom`
e). Mini and Akp´
eroarelocatedonaplateau
(well-drained soils) while Gom`
eisonlowland(morepoorly
drained soils). Gbanlin is located on an undulating plateau
with concretions. Soil chemical analysis showed that the soil
was decient in N, P, and K and soil organic matter (SOM).
is could be due to the mining agriculture and also a con-
sequence of the mechanical destruction of the soil structure
during the ridging for yam crop. In fact yam is a demanding
crop in terms of organic matter and nutrients. Research []
reportedthatyamyieldingabouttoffreshtuberha
−1
removes  N kg ha−1,.Pkgha
−1, and Kkgt
−1.When
land is used too intensively, the SOM is rapidly reduced
in the unstable fraction. In the short and medium term,
this reduction leads to a decrease in soil biological activity
Scientica
T : ANOVA, partial nested model of the eect of the four treatments on logarithmic transformed values of dry matter yields of “Kokoro”
yam (Dioscorea rotundata) (- and -,  sites,  farmers, Benin).
Source DF Adj. SS Adj. MS 𝐹𝑃
Site  . . ∗∗
Farmer (Site)  . . . .
Replicate (Site)  . .  .
Year . . . .
Treatment . . . .
Site ×Treatment . . . .
Tre a tmen t ×Farmer (Site far) . . . .
Ye a r ×Farmer (Site)  . . . .
Ye a r ×Treatment . . . .
Ye a r ×Site . . . .
Ye a r ×Site ×Treatment  . . . .
Error  . .
Adjusted 𝑅-square (%) .
DF: degree of freedom; Adj. SS: adjusted sums of squares; Adj. MS: adjusted mean squares; 𝐹:Fisherstest;𝑃:Fishersprobabilitytest.
∗∗Denominator of 𝐹-test is zero.
T : Dry matter (t ha−1 ) of yam tubers removed and yam shoots recycled in the - and - cropping seasons in four
villages in Benin.
- cropping seasons - cropping seasons
T TM TMA TMM LSD T TM TMA TMM LSD
Yam D M r e m o v e d ( t h a 1)
DM removed .b.c.   a.   a. .b.c.a.a.
Yam s h o o t s D M r e c y c l e d ( t h a 1)
Ya m s h o ot s  .   b.c.a.a. .b.c.a.a.
Means with the same letter within row are not signicantly dierent (𝑃 > 0.05).
DM:drymatter;LSD:leastsquaredierenceat%.
T (control ): one-yearfa llow-yamrotation; TM (control ): maize-yam rotation; TMA: A. histrix/maize intercropping-yam rotation; TMM: M. pruriens/maize
intercropping-yam rotation.
and, then, contributes to soil degradation and depletion [].
Many studies report that soil organic matter (SOM) decreases
in cultivated soils []. is decrease is linked to the depth of
the cultivated soil layer and is probably exacerbated in yam-
based cropping systems.
Nitrogen is the most decient component of these soils
grown with low organic matter content. Total nitrogen
deciency of these soils lies in the fact that nitrogen is the only
major nutrient that does not exist in the bedrock. Further,
the transfer of atmospheric nitrogen to the soil by biological
and chemical process is slow. Losses of nitrogen in these
soils are common because of the high volatility and solubility
of this nutrient. Nitrogen is generated by the breakdown of
inherent organic matter and needs to be supplemented with
other sources of organic materials or mineral fertilizer. Many
studies focusing on these elements conclude that there is an
indisputable need to correct the lack of N and P in the soil in
Africa [, ].
It is possible to reduce or stop ongoing soil degradation
and the decrease in yield with such rotations including
improved short fallows or intercropping with herbaceous
legumes. e use of legumes improves levels of concentration
of the soil parameters. e improvement of the clay con-
centration at the end of the perennial experiment could be
due to the process of the composite soil samples collected
on the ridges resulting from the brewing of the soil deep
layerrelativelyrichinclayandthesoilhorizonsurfaceaer
ridging. Indeed, ridging allows increasing the volume of the
soil deep layer and contributes to the incorporation of organic
residues into the soil.
Signicant dierences in total SOM and nutrients
increase with treatments TMA and TMM in comparison with
T and TM could be due to the faster decomposition of
fermentable green manure (herbaceous legumes) with low
humication coecient (%) added to the moderate decom-
position of lignied maize stover on relatively degraded soils
[]. Our observations are in agreement with those of []
who reported that cropping systems and organic manures
havethemostinuenceontheSOM.RotationswithM.
pruriens and A. histrix represented a source of easily available
N, P, and K for the yam crop which could be related to their
faster decomposition and nutrient release, compared with the
slower release of nutrients by poorer quality materials such
as maize stover and A. gayanus grass. In Ghana, studying the
Scientica
T : Nitrogen, phosphorus, and potassium content (kg ha−1) dry matter of plant parts removed in the crop harvest and those returned
to the soil in yam-based cropping systems (- and - cropping seasons, four cropping system treatments, four village sites,
 farmers, Benin).
- cropping seasons - cropping seasons
T TM TMA TMM LSD SD T TM TMA TMM LSD SD
Plant nutrients removed (kg ha1)
Ya m t u b e rs
N.
b.c.a.a. . .b.c.a.a. .
P.
b.c.a.a. . .b.c.a.a. .
K.
b.c.a.a. . .b.c.a.a. .
Maize grains
N .b.a.a.a. . .c.a.b.b. .
P .b.a.a.a. . .c.a.b.b. .
K .b.a.a.a. . .c.a.b.b. .
Plant nutrients recycled (kg ha1)
Ya m s h o ot s
N .b.c.a.a. . .b.c.a.a. .
P.
b.c.a.a. . .b.c.a.a. .
K.
b.c.a.a. . .b.c.a.a. .
Fallow stover
N.
a.b.b.b. . .a.b.b.b. .
P.
a.b.b.b. . .a.b.b.b. .
K.
a.b.b.b. . .a.b.b.b. .
Maize stover
N .b.a.a.a. . .c.a.b.b. .
P .b.a.a.a. . .c.a.b.b. .
K .c.ab .a.b. . .c.a.b.b. .
Aeschy. stover
N .b.b.a.b. . .b.b.a.b. .
P .b.b.a.b. . .b.b.a.b. .
K .b.b.a.b. . .b.b.a.b. .
Mucuna stover
N .b.b.b.a. . .b.b.b.a. .
P .b.b.b.a. . .b.b.b.a. .
K .b.b.b.a. . .b.b.b.a. .
Means with the same letter within row are not signicantly dierent (𝑃 > 0.05).
T (control ): one-yearfa llow-yamrotation; TM (control ): maize-yam rotation; TMA: A. histrix/maize intercropping-yam rotation; TMM: M. pruriens/maize
intercropping-yam rotation; SD: standard deviation; LSD: least square dierence at %.
T : Total plant nitrogen, phosphorus, and potassium (kg ha−1) dry matter removed in the crop harvest and those returned to the soil
in yam-based cropping systems (- and - cropping seasons, four cropping system treatments, four village sites,  farmers,
Benin).
- cropping seasons - cropping seasons
T TM TMA TMM LSD SD T TM TMA TMM LSD SD
Total nu t r i e n t s r e moval
through harvest
(kg ha−1)
N.
c.b.a.a. . .c.b.a.a. .
P.
c.b.a.   a. . .c.b.   a.   a. .
K.
b.b.a.a. . .b.b.a.a. .
Total nu t r i e n t s r e c y c l e d
through plant biomass
(kg ha−1)
N.
c.d.b.a. . .c.d.b.a. .
P.
c.c.b.a. . .c.c.b.a. .
K.
b.c.a.a. . .c.d.b.a. .
Means with the same letter within row are not signicantly dierent (𝑃 < 0.05).
T (control ): one-yearfa llow-yamrotation; TM (control ): maize-yam rotation; TMA: A. histrix/maize intercropping-yam rotation; TMM: M. pruriens/maize
intercropping-yam rotation; SD: standard deviation; LSD: least square dierence at %.
Scientica
T : (a) Soil characteristics at the end of the experiment (December ), – and – cm layers, on -year fallow of Andropogon
gayanus-yam rotation (T),  farmers, four village sites, Benin. (b) Soil characteristics at the end of the experiment (December ), –
and – cm layers, on maize-yam rotation (TM),  farmers, four village sites, Benin. (c) Soil characteristics at the end of the experiment
(December ), – and – cm layers, on A. histrix/maize intercropping-yam rotation (TMA),  farmers, four village sites, Benin.
(d) Soil characteristics at the end of the experiment (December ), – and – cm layers, on M. pruriens/maize intercropping-yam
rotation (TMM),  farmers, four village sites, Benin. (e) Soil characteristics at the end of the experiment (December ), – and –
 cm layers, four yam-based cropping systems (-year fallow of Andropogon gayanus-yam rotation; maize-yam rotation; A. histrix/maize
intercropping-yam rotation; M. pruriens/maize intercropping-yam rotation),  farmers, four village sites, Benin (all sites confounded).
(a)
Akp´
ero Gbanlin Mini Gom`
e
Depth (cm) – – – – – – – –
“Plinthosols” “Plinthosols” “Luvisols ferriques” “Luvisols ferriques”
Clay% . . . . . . . .
Silt% . . . . . . . .
Sand% . . . . . . . .
C% . . . . . . . .
N% . . . . . . . .
C/N . . . . . . . .
OM% . . . . . . . .
PH . . . . . . . .
Bray P . . . . . . . .
K. . . . . . . .
C%: soil carbon concentration; N%: soil nitrogen concentration; OM%(=. ×C%): soil organic matter content; C/N: index of biodegradability or ratio of
soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K cmolkg−1: soil potassium.
(b)
Akp´
ero Gbanlin Mini Gom`
e
Depth (cm) – – – – – – – –
“Plinthosols” “Plinthosols” “Luvisols ferriques” “Luvisols ferriques”
Clay% . . . . . . . .
Silt% . . . . . . . .
Sand% . . . . . . . .
C% . . . . . . . .
N% . . . . . . . .
C/N . . . . . . . .
OM% . . . . . . . .
PH . . . . . . . .
Bray P . . . . . . . .
K. . . . . . . .
C%: soil carbon concentration; N%: soil nitrogen concentration; OM%(=. ×C%): soil organic matter content; C/N: index of biodegradability or ratio of
soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K cmolkg−1: soil potassium.
(c)
Akp´
ero Gbanlin Mini Gom`
e
Depth (cm) – – – – – – – –
“Plinthosols” “Plinthosols” “Luvisols ferriques” “Luvisols ferriques”
Clay% . . . . . . . .
Silt% . . . . . . . .
Sand% .  . . . . . . .
C% . . . . . . . .
N% . . . . . . . .
C/N . . . . . . . .
OM% . . . . . . . .
PH . . . . . . . .
Bray P . . . . . . . .
K. . . . . . . .
C%: soil carbon concentration; N%: soil nitrogen concentration; OM%(=. ×C%): soil organic matter content; C/N: index of biodegradability or ratio of
soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K cmolkg−1: soil potassium.
 Scientica
(d)
Akp´
ero Gbanlin Mini Gom`
e
Depth (cm) – – – – – – – –
“Plinthosols” “Plinthosols” “Luvisols ferriques” “Luvisols ferriques”
Clay% . . . . . . . .
Silt% . . . . . . . .
Sand% . . . . . . . .
C% . . . . . . . .
N% . . . . . . . .
C/N . . . . . . . .
OM% . . . . . . . .
PH . . . . . . . .
Bray P . . . . . . . .
K. . . . . . . .
C%: soil carbon concentration; N%: soil nitrogen concentration; OM%(=. ×C%): soil organic matter content; C/N: index of biodegradability or ratio of
soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K cmolkg−1: soil potassium.
(e)
Soil characteristics Depth T TM TMA TMM LSD
Clay% – cm .c.d.b.a.
– cm .c.d.b.a.
Silt% – cm .a.a.a.ans
– cm .a.a.a.ans
Sand% – cm .a.a.a.ans
– cm .a.a.a.ans
C% – cm .b.b.b.a.
– cm .b.b.a.a.
N% – cm .d.c.b.a.
– cm .c.b.a.a.
C:N – cm .a.b.c.c.
– cm .a.b.b.b.
MO% – cm .b.b.a.a.
– cm .c.c.b.a.
Bray P (mg kg−1)– cm .c.b.a.a.
– cm .c.b.ab .a.
K+cmol kg−1 – cm .d.c.b.a.
– cm .d.c.b.a.
PH water – cm .c.b.    a.    a.
– cm .c.b.    a.a.
Means with the same letter within row are not signicantly dierent (𝑃 > 0.05).
C%: soil carbon concentration; N%: soil nitrogen concentration; OM%(=. ×C%): soil organic matter content; C : N: ratio of soil carbon to nitrogen; Bray
P (mg/kg-soil): soil phosphorus; K+cmol kg−1: soil potassium; LSD: least square dierence at %;SD:standarddeviation.
T (control ): one-yearfallow-yam rotation; TM (control ): maize-yamrotation; TMA: A. histrix/maize intercropping-yam rotation; TMM: M. pruriens/maize
intercropping-yam rotation; LSD: least square dierence at %;ns:nonsignicant.
Data are the means.
eect of cropping sequences with cassava and legume crops,
[] indicated that only % of M. pruriens litter remained six
weeks aer incorporation of the biomass. References [] and
[] that studied the traditional M. pruriens-maize rotation
in Honduras estimated that % of nitrogen produced by a
mulch of M. pruriens was available for the following maize
crop. ey also observed that available P remained practically
constant, with  to  mg/kg-soil in the surface horizon in
spite of P exports by maize. Reference [] concluded that
the practice of continued rotation with M. pruriens and maize
prevented soil N depletion for at least  years.
Our results showed that legumes 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 []. Nevertheless, they depend on the
inherent P levels in the soils. M. pruriens root exudates could
solubilize P increasing its availability. In the study of [],
organic materials have also been found to reduce P sorption
capacity of soils and increase crop yields in P limiting soils.
e soil K concentrations were improved in our study
(Table ). Reference [] showed soil K concentration of
. cmol kg−1 inthecmsoillayeranddecreasing
Scientica 
signicantly with cultivation. e rate of decline was about
.–. cmol kg−1 year−1 in the – cm soil layer [].
5. Conclusions
e eld of interest of the study is to determine the impact
of yam-based systems with herbaceous legumes on dry
matter production (tubers and shoots), nutrients removed
and recycled, and the soil fertility changes. Yam tuber
dry matter production was signicantly improved in yam-
based systems with legumes in comparison with traditional
systems. Treatment ×Farmer and Year ×Treatment inter-
actions inuenced signicantly the yam tuber dry matter
production. Amounts of N, P, and K recycled in yam shoot
were signicantly higher in yam-based systems with legumes
than in traditional systems. e nutrient (N, P, and K) levels
removed or recycled t the DM production (tubers and
shoots) and then varied according to treatments and cropping
seasons. e end of study soil analysis showed soil chemical
properties (SOM%, N%, P (mg/kg-soil), K+cmol/kg, and pH
water) signicantly higher in treatments with legumes than
in traditional systems. We then propose to promote durable
and replicable yam-based systems with legumes, through a
favorable legislative, economic, and political environment
to support local initiatives. Collaborations between farmers,
research, development, and extension structures should also
befavoredtosupportthedevelopmentanddisseminationof
innovations.
Competing Interests
e authors declare that there is no conict of interests
regarding the publication of this paper.
Acknowledgments
e authors express their sincere appreciation and thanks
for the Cooperation Program for Academic and Scientic
Research (CORUS). Finally, the authors greatest appreciation
goes to farmers who freely agreed to participate in trials and
make part of their elds available for the research.
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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]. ...
... Sadly, none of the studies consulted produced such yields except for D. alata which produced ≥ 50 t ha −1 in a forest soil of Côte d'Ivoire under native soil fertility and mineral fertilizer applications [31,61]. Generally, yam yields are influenced by climatic conditions, site and soil properties, tillage method used, year of cultivation (i.e., first and subsequent cultivation), and species [23,24,31,50,52,61,71,75]. For instance, D. alata is the highest yielding yam species producing at least twice the yield of other species [31,63,71,76] followed by D. rotundata and D. cayenensis [52] irrespective of the ecological zone and soil fertility. ...
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