JJC/Ei 1 WORKSHDP ON NITROGEN CYCLING IN THE ...
JJC/Ei
1
WORKSHDP ON NITROGEN CYCLING IN THE WEST AFRICAN ECDSYSTEMS
I.I.T.A.
IBADAN -
DECEMDER 1978
A DEFICIENCY OF THE SYMBIOTIC NITROGEN FIXATION IN A DRY TROPICAL
AGROSYSTEM-THE NITROGEN CHLOROSIS OF GROUNDNUT
(ARACHIS HYPOGAEA) IN SENEGAL
3.3. Drevon
Service de Rhizobiologis
C+N.R.A. - Qambey (Scjn9gal)
SUMMA RY
Various types of chlorosis on groundnut occur in Senegal.
Gne that spreads over the Northern.nid Sonegal is describod herc,
and identified as a nitrogon chlorosis dus to a deficiency of pb)t u.
fixation resulting From poor nodulation.
This chlorosis arises in acid soils, wherc there may be
aluminium and manganese tosicity. i\\io micronutrient deficiency hfas
been found SO far. Biotic factors among uhich the inadeouacy of thc
’ rhizobium population and the attaclts of nematodes may Je rosponsi-
ble while the existing antogonisnr of actinomycetes tourard Ri-1izob:i.w
would not interfcre.
Liming and above all, organic matter application have
prooved to be means of control of the chlorosis.
RESUME
Il y a différents types de chlorose de l’arachide au
SQnagal.
L'une d'elle répanclua dans le Centre-Nord du Séncgal, est
ddcrite ici puis identifiée comme une chlorose azotée par suita d’une
deficience de la fixation symbiotioue d'azote résultant d'une iai-
bic nodulation.
Cette chloross s’observe en sols acides, avec toxicite
ûluminique et manganioue, Aucune déficience en oligo-élements n'a
encore étQ trouvée. Les facteurs biologiques parmi lesquelo l*dtat
3e la population de Rhizobium et les attaques de nématodcs peuvent
Stre en cause, tandis !~uL? l'antagonisme existant des actinomycetss
vis-à-vis tiu Rhizobium n'aurait pas d'effet.
Le chauiaga et surtout, l’apport de matibre o r g a n i q u e
constituent des moyens d e l u t t e c o n t r e c e t t e chlorose.
.
2
I- INTRODUCTION
In Senegal,
different types of chlorosis of groundnut
have been observed. They generally show up in ~~ell defined areas oftizi-I
known as "yelloo patches" (1).
A first type of chlorosis is related to a high soi1 pH.
It occurs 3
- at sites of burning whsre houses were locatied
years ago (2) or iuhere tlie crops residucs (strauu) have beeti burnt
;3efore the rainy season,
- at the giace of termite maunds recently levelcd
- in soils whera irrigation with water containing
large amounts of basic cation s increased pH well above 8,0,
A second type of chlorosis may occur in areas where water-
logging prevented diffusion of oxygen in the soil, thus inhibiting I
nodulation and nitrogen fixation. This type of chlorosis has been
obsarved in Casamance in shallow depressidns which fauor waterlogging.
A third type of chlorosis which Will be described here,
o c c u r s i n acid s o i l s . It uas observed in tho regions of Louga, Thies
and Diourbel and in the northern part of Sine Saloum, which are
c a r a c t e r i s e d b y a n i r r e g u l a r r a i n f a l l o f 3 0 0 to 7 0 0 m m during
3 months from July to october and usually a groundnut millet rotation
sometimes accompanied by a one or two years fallow.
II - SYMPTOMS OF THE CHLOROSIS GCCURINC IN ACID SOILS
Symptons of this chlorosis are described here from obserua-
tion made during the 1378 rainy season at Thilmakha (region of Thies)
where the average rainfall is 500 mm, The soi1 is a dior soil,
Tab, I : physico-chemisal caracteristics of .the Dior soi1
!
, Organic
!
!
iclay + ISand , C. ,
2
i C/N !Exchangeable
i pHurac3~
; matter
,limon
i
;
;
;
ibases
i1/2,5 i
.
.
.
.
.
.
.
.
.
!
!
!
!
5,5
!
!
i
!
!
!
!
!
I
!
!
Yellow patches made up of chlorotic groundnuks !!jere compa-
red urith non chlorotic adjacent areas which were used as controis.
c
Faint yellowing of leaves in first seen between the 2Oti1
nnd the 30th day after souing,
The plant gro\\iith and emergenco of neu
leaves is sloueddown. The severity 0f:thi.s type of chlorosis is
v a r i a b l e :
(1) - The plant may turn yellour and remain dwarf, It tilts
and consequently dies after the 60th day.
(2) " The plant may be iess affected by the chlorosis. It
turns yellou but keeps growing slowly (lig.2).
c
3
(3) - Faint yellowish plants may recover after the 30th
day (fig 1) ( such a recovery was also observed in green-houses
cxperiments after the 55th day), New green leaves emerge and normal
growth rate is rapidly restored.
The total number of flowers produced by the chlorotic
plants is lower than by the non chlorotic ones and the rate is
slower (fig.3). The number of nuts in the chlorotic plants is 40 3
less than in the non-chlorotic ones,
The root system of chlorotic plants is more or less atro-
phied. Two kinds of atrophied root syetems were observed.
(1) - Root systems made up of the top root with only ono
or two lateral roots, no radicles (fig.4). Type 1
2) - Root systoms with many lateral roots but only a few
radieles. iYPe I I
There were very few nodules on the roots of chlorotic
plants. While the number of nodules grew steadily till tho 70th day
on the non chlorotic plants, it stayed at a low leva1 after the
30th day on the chlorotic plants (fig.6) : on the 70th day, ths
average number of nodules (mean of 20 plants) is 130 on' the non
chlorotic plants and 10 only on the chlorotic ones.
Moreover a great number of broun
protrusions were found
on chlorotic plant's roots (fig.5). The exact nature of these 0,s mm
long cane-shaped protrusions, which are filled up with bactoria, is
still obsoure.
III - INDUCTION OF THE CHLOROSIS By A NI,TROGE?J DEFICIENCY
By applyiix
100 kg N/ha as ammonium nitrate to field grown
groundnuts,
?
BLONDEL 1968) obtained a satisfactory recovery of
chlorotic plants.
Under green house conditions, the chlorosîs was reproduced
on a soi1 from Thilmakha. Urea application (equivalent to 100 kg N/ha
nitrogen) eliminated the chlorosis symptoms.
Therefore,
the chlorosis studied here appears to result
from a nitrogen deficiency.
This conclusion was confirmed by nodules counts (fig.6)
and by acetylene reducing activity expressed per plant,which was
significantly locver in chlorotic plants than in non chlorotic plants
(fig.7).
Moreover, the specific acctyleno rsducing acti\\Jity of
nodules from chlorotic plants was generally lower than that of nodules
from non chlorotic ones (table II). It may be attributed oither t a
infection by, less efficient strains or to a decrease of the photo-
synthetic activity which caused a reduction in the energy supply of
the nodules of chlorotic plants.
4
-Table I I : Specific acetylene roducing. activity (micromoles acetylene
,‘mq nodules dry weight/hcur) -., Thilmakha ‘78 - averaoe
of 20 plants.
! 55
! 62
!
70
! 81
1
““““““I”““““““““““l
Non chlorotic
:c This low level of activity is due to a
l5 days drought which affec-
ted nuch more the well developped non chlorotic plants than the
chlorotic ones.
IV.- CAUSE OF THE DECREASE OF NITROGE,N FIXATION IN CHLOROTIC PLANTS
Groundnut is more affected by chlorosis when the rainfall
is inadequate or uhen thc seeding is delayed. However, chlorosis
being reproducod on soi1 samples under green house conditions, the
sril itsvifs-:.?q to be mainly responsible for this deficiency, The
different soi1 characteristics that have been thought to cause the
Uccrease of nitrogen fixation by groundnut are as folloms :
11 - The minera1 stetus of the soi1
The soils in Uhich the chlorosis is mostly observed are
of the Dior type tropical Cerruginous and deep soils. They arc
mainly sand (96 $) with only 3 to 4 $ o f clay and O,3 $ o f organic
mûtter.
They progressively become acid undE-r cultivation mith
spaf-ific ir)~ei~siV~ ~g~;~;ltu~s~ [>28C4!iCEs .‘9.10.11.)
a- Soi1 acidity
BLONDEL (3) first noticed that in the case of yello~ &arf
plants of groundnut, the pH (mater pH 1/2,5) was belour 5,O (3).
Later PIERI (8) showed “chat therc mas only a loose rola-
tion between water pH and the chlorosis of groundnut, around the
value of 5,G (measured by the water pH 1/2,5 method) and that this
pH varies much in the soi1 profile,
Measures of pH nide on rhizosphero soils (Thilmakha 1978)
showed that in most cases the PH of the chlorotic plant rhizosphere
stays between 4,7 and 5,2, but some values as high as 5,7 were also
found, Besidss, the pH of the non chlorotic plant rhizosphere some-
times was as low as 5,4 to 5,O.
b- Aluminium, toxicity
According to PIERI (8) a better approach of the noxiaus
zffects of soils acidity would be to measure the saturation of absor-
bi ng complex wikh exchangeablu aluminium. In an experimental study
in glasshouse, he showed , that aluminium ie toxic to the nodulation
tirhen the rate of saturation of the absorbing complax is more than
I
. . I.
- 1 *l.--i +r ..#L.,.‘.. 4.1. .i n r..-enn bhtin r;n 2:; i n i-.hg nosa
5
Exchangeable aluminium appears in the Dior soi.15 when the
measure of water pH is well below 5,5i But the pH KC1 which measures
the exchange acidity is then more sui-table.
c ” Manqanese t0xicit.y
Minera1 analysis of tho acrial vegetation reveals a hibher
proportion of manganese in the chlorotic plants. (777 ppm) in sompa-
rison to non chlorotic plants (267 ppm), at the 21st day after
sowing (Thilmakha 1978 - PANTIER).
.
The manganese would be toxic to the
roundnut whcn the
proportion in the leaves is more than 600 ppm 9 15).
d- The microelement nutrition
The chlqrosis is observed in condition of minera1 ferti-
lization : 150 kg/ha of 8.1827 (containing also sulfur) on groundnut
and 150 kg/ha of 14.7.7, on millet in rotation,
But some micronutrients are necessary fer the nodulation
0;’ groundriut, among thom molybdenum, Baron, Cobalt , Iron, Copper
ûnd Zinc,
A significative effect of Molybdenum was obtained in
field trials (16). 8ut it was not in condition of chloroais,
On the apposite, a foliar spreading of a compiete micronu-
trient solution for legumes, bas no effect on the chlorosis
(Thilmakha 19’78).
21 - The influence of biotic factors
a- Inadequacy of the rhizobium population
A t Thilmakha, rhizobium population uas shown to be ten times
louer in soils with cI2orotic plants than in soils with non chlorc-
tic plants. On the other hand UEY (persona1 comunication) eliminatcd
chlorosis by inoculating groundnuts with CB 756 strain.
But this results could n o t bc confirmed in ths fiold, Sinss
nodulation of bydroponically grown ground-nuts inoculated by a suspan-
sion
of soi1 with chlorosis plants did not differ from nodulation
of’ plants inoculated by a supension of control soil, Rhizobium popu-
lations alone were net thought to be responsiblo for the poor nodu-
lation that occured in the field in chlorotic plots.
b - Microorqanisms antasonistic to rhizobium
PANTIER (12) found actinomycetes antagonistic to rhizobium
i3 s o i l s o f Senegal,
~
'*
But the numbers of these antagonistic actinomycetes . .
' in soils where chlorosis io observed did n o t diffar frr?m
that existing in soils where no chlorosis occured (PANTIER -Table III).
6
Table I I I - Number of actinomycetes antagnnistic to Rhizobium in
one gran
of soi1 - Thilmakha (1978 average of 5 soi.1
samples)
!
1
f A n t a g o n i s t i c !
i Actinomycetes
, actinomycetes
""I""""I~"--""""-"--"-"""""""
~~""""""I"-"""L"""~*
!
rr"r""--""rr""""-
i
?
Soi1 utith chlorotic plants i
T
!
.
l,?
.
105
!
9,5
,
12
!
!
!
““““““““1”““““““““““““““““““” ““““““““““11”““““”
T”“““““‘“‘“‘“3”““t
i
:
! Soi1 with non chlorotic
i
2,8 105
!
9,4 10
0
1 plants
!
!
!
Therefore the interferencc of actinomycetes probably
cannot be held responsible for the lowor nitrogen fixation of chlo-
rotic plants.
c - Influence of. nemat0do.s
In Upper Volta chlorosis was clearly shourn to be caused
by nematode attacks (17).
1 n Senegal , according to thc nematodcgs counts by GE%ANI,thê
contamination of roots by Scutellonoma. cav,e.nessi is much yreater in
chlorotic plants than in non chlorotic ones.
Table IV - Numbor of nematodes Scutellonem,a cavenessi in tho roota
of chlorotic and non chlorotic plants - Thilmakha (I[i78 -
average of 10 plants)
I
1
1
?
!
Numbor of nematodcs 1
Area with :
!
l""""""I""""""T"-"-"-"""-"""~
!
Soi.1
Root
! ““““““-““““““-“““I”“““““““““““““””-””
f “““1 ‘200 ““L” f”““-;“~~;“““-(
i Non chlorotic plants
.
!
!
! chlorotic plants
!
660
!
20 951
I
! “““11”““““““““““““““““““““““““““”~””
!
:““““---““““““~““---““““““““~
o Chlorotic plants years beforc
! t no treatment ‘dith nemagon
i
i
!
506
I
16 420
!
! Chlorotic plants years before
I
0
!
0
!
! t treatment uith nemagon
!
!
!
Up to nw, it has not yet been possible to reproduce tho
uhlorosis by inoculation of a non chlorotic (normal) soi1 urith
nematodes in laboratory conditions,
In a field trial, tho fumigation with nemagon restored
the vegetative growth of groundnuts. Nevertheless, chlorosis was no%
eliminated on the chlorotic areas treated with nemagon. The plants
hrf
a porfectly cuell dcveloppod root system without protrusions but
vsry four nodules.
7
Table V : Effect of soi1 fumigation iith a nematicide (Thilmakha
1978 - average often plants)
I
I
Area with
i C”“““““““““““““““-“I”
i No chlorotic plants
1 """""""""-"~"""-L-""""
.
I Chlorotic plants
""""""I"I"""--""-"-"""
\\l - CONTROL OF CHLOROSIS
Two methods for controling chlorosis have bcen empirically
round tu be efficient : liming and organic matter application.
In a field tria1 at Thilmakha, liming was applied at the
rate of 600 kg/ha, by pelletizing each grain of groundnut. The arma
coverod by the chlorosis has been reducod in the plots treateii
igith l i m e
but still somc yellow plants could be seen and the
vcgetation ha: not totally rocovered.
Farm-yard manure has also been applied since 1973 in the
same triai, Every two years, the plots havc received 10 tons dry
matter per hectare before groundnut planting. After the second
application of manure , yellow patches had been reduced considerably,
and after the third application, 5 years later, not a single symptom
of chlorosis could be soen.
Nevertheless this rate of manure application is very high,
compared to the quantity of organic matter the senegalese farrners
cari rely o n ( 1 8 ) .
VI - CO.NCLUSION
.
This symptom of chlorosis urhich occurs in acid soils appears
to be related to the following characteristics
- Minora1 t o x i c i t i e s
- Low rhizobium populations
(3) - High nematode populations.
It is not yet knourn tuether the decrease in nodulation and
i;J2 fixing activity of thc legumc results (1) from a poor growth of
tho plant (due to minera1 doficiencies or nematode attacks) -(2) from
~OU ,Rhizobium populations or from some mechanism prevonting infection
r;nd nodulation.
8
Further investigations are neoded in order ta elucidate
the interactions between the plant, soi1 minera1 factors anci sdil
microorganisms. The results of such investigations should hslp to
devel.op cultural practices urhich could promote N2 fixation by pre-
ve:lting the effect of limiting factors in Sahelo-soudanian agro-
systems.
AKNDkJLEDGEMENTS
We are grateful to MM, WEY, GANRY, SIBAND and DIATTA of
C.N.R.A. Bambey and WI. BOURREAU, MUGNIER, PANTIER and GEHMANI of
ORSTQM, of the soi1 microbiology and nematology lab.oratcries- for
their comments and their collaboration.
\\ae owe much to M. DCMMERGUE for his criticisms of the
manuscript and his attention during the course of the reseai-ch.
We are greatly indobted ta A, DIRBAYE who has given
technical assistance to this work.
We thank M. NIANG for photographs, M. CADIAGA for
drawings and Mrs SECK for type writting.
R E F E R E N C E S ,
(0 - BOUHOT 1978 :
Le rabougrissement de l'arachide - Agro, Trop. XXIII
nOIl
(2 ) - GERMANT 1975
"Effets des brulis sur la végetation de l’arachide au
Sénégal" - Academie d’agriculture de France - Extrait
de proces verbal de la seanca du '19 novembre 1975.
(3) - BLONDEL (D), 1970
"Relation entra le "Nanisme jaune" de l!arachide eh
sol sableux (Dior) et le pH. Definition d'un seuil
pour 1 lactivitb de rhizobium.
Agron. Trop, XXV, no&7.
(4)
- DUCERF (P,), 1978
"Synthèse des travaux effectués sur la mo&lisation de
la fixation d'azote d’une culture d'arachide au
Sénégal - Ronéo ISRA
(5)
I CHARREAU (C,), NICOU (R.), 1971
“L’amtSlioration’du profil cultural dans les sols sa-
bleux et sabla-argileux de la zone tropicale sPche
Ouest africaine et ses incidences agronomiques,
Bull. Agron. nQ23 CNRA Bambey - IRAT/Sènégal.
(6)
- PIERI (C.}, 1974
“Premiers rQsultats experimentaux sur la sensibilité
de l'arachide a la toxicite aluminique"
Agron. Trop. XXIX, n06-7.
(7)
- NDIAYE (J.P.), 1978
"Enquete fertilité on milieu paysan dans la rkgion du
Sine-Saloum - Rondo ISRR.
(8)
.m PIERI (C.), 1976
"L'acidification d'un sol Dior cultive du Sénégal et
ses consequances agronomiques” Agron. Trop. XXX1 - 3
(9)
- POULAIN (J.F.)
"Résultats obtenun3 avec les engrais et las amendements
calciques. Acidifïcation des sols et correction" -
Colloque sur la fertilite des sols tropicaux. Ed.
IRAT, 1968.
00) - P O U L A I N ( J . F . )
"Premier bilan des essai urge-sulfate : résultats
agronomiques de quatre années 1966-1969. Doc. roneo
IRAT-Senegal.
(11) - CHARREAU (C.), 1971
"Nécessite agronomique et interet économique d'une
intensification des systemes agricoles au Sénégal”
Doc, ronéo IRAT/Paris,
10
(12) - PANTHIER (J.J.), DIEH (H.E.), DOMMERGIJES (y,~.), 1978
"A rapid of method of enumerating actinomycetes an-
toganic toward rhizobia”
Laboratoire de microbiologie des sols ORSTOM/Dakar
(13) - GERMANI (G,), GAUTREAU (J.), 1976
"R6sultats agronomiques obtenus par des traitements
nématicides sur arachide au Sen6gal"
Cahiers ORSTOM Seris biologie vol. XI n03,
(14) - WEY (Je), OBATON (M.), 1978
"Incidence de quelques techniques culturalcs sur
l’activit6 fixatrice d’azote et le rondement de
1) arachide”
A g r o n . T r o p , XxX111, n02.
w - PREVDT, OLLAGNIER, AUBERT, SAUCIERES (1955)
“DBgradation des sols et toxicit6 manganique" Oléa-
gineux vol X na4,
(W " MARTIN (G.), FOUHRIER (P.), 1965
"Les oligo6léments dans la culture de ltarachide du
Nord-S6nBgal” - Oléagineux XX n05.
(W - CERMANI (G.), DHERY (M,), 1973
"Observation et expérimentation concernant le r61o
des nematodes dans dcuxaaffections de l’arachide en
Haute Volta, la “chlorose” et 1s "clump" Oléagineux
2 9/235-242 ?
(W - DREVON (J.J.), 1978
"Eléments pour une étude des apports de mati8re
organique aux sols dans le bassin arachidier du
SénéC)al".
Roneo ISRA.
r
.
ft6. 2 1 POIDS S E C D E S PLAN$S
DRY WEIGHT OF THE PIANTS
Poids soc appareil krien* gffosse
( THICMAKHA 1978)
4 Dry
“57
w&ght nuts
+ leaves
.\\.
a
.a
\\.
.
/J
0 Plantas chlorotiques
* Flanf@s t&oins
,
FIG. 3.: FLORAISON (journalière- cumulée 1
Flowering ( daily cumulative )
Nombre de fleurs
umber of ilowefs
( THILMAKHA 1978 )
Plan tes chlorotiques
CJ Piontes témain
t FtG. 4 1
RACINES
O’ARAWDE
f 56% JOUR )
TYPE xxx
Plante n o n chlorotique - Man chlorotic p l a n t
TYPE I
IPPE XI
Plantrs chlarotiquas - ÇhEoratic plants
(FIG. 5 1 RACINES LATERALES *PRO’WBERAN(bES”
SI’DE ROOTS
* PROTRUSIBNS”
6-.- ._‘ c
1
.J’
Numbur a/ days
1
WORKSHDP ON NITROGEN CYCLING IN THE WEST AFRICAN ECDSYSTEMS
I.I.T.A.
IBADAN -
DECEMDER 1978
A DEFICIENCY OF THE SYMBIOTIC NITROGEN FIXATION IN A DRY TROPICAL
AGROSYSTEM-THE NITROGEN CHLOROSIS OF GROUNDNUT
(ARACHIS HYPOGAEA) IN SENEGAL
3.3. Drevon
Service de Rhizobiologis
C+N.R.A. - Qambey (Scjn9gal)
SUMMA RY
Various types of chlorosis on groundnut occur in Senegal.
Gne that spreads over the Northern.nid Sonegal is describod herc,
and identified as a nitrogon chlorosis dus to a deficiency of pb)t u.
fixation resulting From poor nodulation.
This chlorosis arises in acid soils, wherc there may be
aluminium and manganese tosicity. i\\io micronutrient deficiency hfas
been found SO far. Biotic factors among uhich the inadeouacy of thc
’ rhizobium population and the attaclts of nematodes may Je rosponsi-
ble while the existing antogonisnr of actinomycetes tourard Ri-1izob:i.w
would not interfcre.
Liming and above all, organic matter application have
prooved to be means of control of the chlorosis.
RESUME
Il y a différents types de chlorose de l’arachide au
SQnagal.
L'une d'elle répanclua dans le Centre-Nord du Séncgal, est
ddcrite ici puis identifiée comme une chlorose azotée par suita d’une
deficience de la fixation symbiotioue d'azote résultant d'une iai-
bic nodulation.
Cette chloross s’observe en sols acides, avec toxicite
ûluminique et manganioue, Aucune déficience en oligo-élements n'a
encore étQ trouvée. Les facteurs biologiques parmi lesquelo l*dtat
3e la population de Rhizobium et les attaques de nématodcs peuvent
Stre en cause, tandis !~uL? l'antagonisme existant des actinomycetss
vis-à-vis tiu Rhizobium n'aurait pas d'effet.
Le chauiaga et surtout, l’apport de matibre o r g a n i q u e
constituent des moyens d e l u t t e c o n t r e c e t t e chlorose.
.
2
I- INTRODUCTION
In Senegal,
different types of chlorosis of groundnut
have been observed. They generally show up in ~~ell defined areas oftizi-I
known as "yelloo patches" (1).
A first type of chlorosis is related to a high soi1 pH.
It occurs 3
- at sites of burning whsre houses were locatied
years ago (2) or iuhere tlie crops residucs (strauu) have beeti burnt
;3efore the rainy season,
- at the giace of termite maunds recently levelcd
- in soils whera irrigation with water containing
large amounts of basic cation s increased pH well above 8,0,
A second type of chlorosis may occur in areas where water-
logging prevented diffusion of oxygen in the soil, thus inhibiting I
nodulation and nitrogen fixation. This type of chlorosis has been
obsarved in Casamance in shallow depressidns which fauor waterlogging.
A third type of chlorosis which Will be described here,
o c c u r s i n acid s o i l s . It uas observed in tho regions of Louga, Thies
and Diourbel and in the northern part of Sine Saloum, which are
c a r a c t e r i s e d b y a n i r r e g u l a r r a i n f a l l o f 3 0 0 to 7 0 0 m m during
3 months from July to october and usually a groundnut millet rotation
sometimes accompanied by a one or two years fallow.
II - SYMPTOMS OF THE CHLOROSIS GCCURINC IN ACID SOILS
Symptons of this chlorosis are described here from obserua-
tion made during the 1378 rainy season at Thilmakha (region of Thies)
where the average rainfall is 500 mm, The soi1 is a dior soil,
Tab, I : physico-chemisal caracteristics of .the Dior soi1
!
, Organic
!
!
iclay + ISand , C. ,
2
i C/N !Exchangeable
i pHurac3~
; matter
,limon
i
;
;
;
ibases
i1/2,5 i
.
.
.
.
.
.
.
.
.
!
!
!
!
5,5
!
!
i
!
!
!
!
!
I
!
!
Yellow patches made up of chlorotic groundnuks !!jere compa-
red urith non chlorotic adjacent areas which were used as controis.
c
Faint yellowing of leaves in first seen between the 2Oti1
nnd the 30th day after souing,
The plant gro\\iith and emergenco of neu
leaves is sloueddown. The severity 0f:thi.s type of chlorosis is
v a r i a b l e :
(1) - The plant may turn yellour and remain dwarf, It tilts
and consequently dies after the 60th day.
(2) " The plant may be iess affected by the chlorosis. It
turns yellou but keeps growing slowly (lig.2).
c
3
(3) - Faint yellowish plants may recover after the 30th
day (fig 1) ( such a recovery was also observed in green-houses
cxperiments after the 55th day), New green leaves emerge and normal
growth rate is rapidly restored.
The total number of flowers produced by the chlorotic
plants is lower than by the non chlorotic ones and the rate is
slower (fig.3). The number of nuts in the chlorotic plants is 40 3
less than in the non-chlorotic ones,
The root system of chlorotic plants is more or less atro-
phied. Two kinds of atrophied root syetems were observed.
(1) - Root systems made up of the top root with only ono
or two lateral roots, no radicles (fig.4). Type 1
2) - Root systoms with many lateral roots but only a few
radieles. iYPe I I
There were very few nodules on the roots of chlorotic
plants. While the number of nodules grew steadily till tho 70th day
on the non chlorotic plants, it stayed at a low leva1 after the
30th day on the chlorotic plants (fig.6) : on the 70th day, ths
average number of nodules (mean of 20 plants) is 130 on' the non
chlorotic plants and 10 only on the chlorotic ones.
Moreover a great number of broun
protrusions were found
on chlorotic plant's roots (fig.5). The exact nature of these 0,s mm
long cane-shaped protrusions, which are filled up with bactoria, is
still obsoure.
III - INDUCTION OF THE CHLOROSIS By A NI,TROGE?J DEFICIENCY
By applyiix
100 kg N/ha as ammonium nitrate to field grown
groundnuts,
?
BLONDEL 1968) obtained a satisfactory recovery of
chlorotic plants.
Under green house conditions, the chlorosîs was reproduced
on a soi1 from Thilmakha. Urea application (equivalent to 100 kg N/ha
nitrogen) eliminated the chlorosis symptoms.
Therefore,
the chlorosis studied here appears to result
from a nitrogen deficiency.
This conclusion was confirmed by nodules counts (fig.6)
and by acetylene reducing activity expressed per plant,which was
significantly locver in chlorotic plants than in non chlorotic plants
(fig.7).
Moreover, the specific acctyleno rsducing acti\\Jity of
nodules from chlorotic plants was generally lower than that of nodules
from non chlorotic ones (table II). It may be attributed oither t a
infection by, less efficient strains or to a decrease of the photo-
synthetic activity which caused a reduction in the energy supply of
the nodules of chlorotic plants.
4
-Table I I : Specific acetylene roducing. activity (micromoles acetylene
,‘mq nodules dry weight/hcur) -., Thilmakha ‘78 - averaoe
of 20 plants.
! 55
! 62
!
70
! 81
1
““““““I”““““““““““l
Non chlorotic
:c This low level of activity is due to a
l5 days drought which affec-
ted nuch more the well developped non chlorotic plants than the
chlorotic ones.
IV.- CAUSE OF THE DECREASE OF NITROGE,N FIXATION IN CHLOROTIC PLANTS
Groundnut is more affected by chlorosis when the rainfall
is inadequate or uhen thc seeding is delayed. However, chlorosis
being reproducod on soi1 samples under green house conditions, the
sril itsvifs-:.?q to be mainly responsible for this deficiency, The
different soi1 characteristics that have been thought to cause the
Uccrease of nitrogen fixation by groundnut are as folloms :
11 - The minera1 stetus of the soi1
The soils in Uhich the chlorosis is mostly observed are
of the Dior type tropical Cerruginous and deep soils. They arc
mainly sand (96 $) with only 3 to 4 $ o f clay and O,3 $ o f organic
mûtter.
They progressively become acid undE-r cultivation mith
spaf-ific ir)~ei~siV~ ~g~;~;ltu~s~ [>28C4!iCEs .‘9.10.11.)
a- Soi1 acidity
BLONDEL (3) first noticed that in the case of yello~ &arf
plants of groundnut, the pH (mater pH 1/2,5) was belour 5,O (3).
Later PIERI (8) showed “chat therc mas only a loose rola-
tion between water pH and the chlorosis of groundnut, around the
value of 5,G (measured by the water pH 1/2,5 method) and that this
pH varies much in the soi1 profile,
Measures of pH nide on rhizosphero soils (Thilmakha 1978)
showed that in most cases the PH of the chlorotic plant rhizosphere
stays between 4,7 and 5,2, but some values as high as 5,7 were also
found, Besidss, the pH of the non chlorotic plant rhizosphere some-
times was as low as 5,4 to 5,O.
b- Aluminium, toxicity
According to PIERI (8) a better approach of the noxiaus
zffects of soils acidity would be to measure the saturation of absor-
bi ng complex wikh exchangeablu aluminium. In an experimental study
in glasshouse, he showed , that aluminium ie toxic to the nodulation
tirhen the rate of saturation of the absorbing complax is more than
I
. . I.
- 1 *l.--i +r ..#L.,.‘.. 4.1. .i n r..-enn bhtin r;n 2:; i n i-.hg nosa
5
Exchangeable aluminium appears in the Dior soi.15 when the
measure of water pH is well below 5,5i But the pH KC1 which measures
the exchange acidity is then more sui-table.
c ” Manqanese t0xicit.y
Minera1 analysis of tho acrial vegetation reveals a hibher
proportion of manganese in the chlorotic plants. (777 ppm) in sompa-
rison to non chlorotic plants (267 ppm), at the 21st day after
sowing (Thilmakha 1978 - PANTIER).
.
The manganese would be toxic to the
roundnut whcn the
proportion in the leaves is more than 600 ppm 9 15).
d- The microelement nutrition
The chlqrosis is observed in condition of minera1 ferti-
lization : 150 kg/ha of 8.1827 (containing also sulfur) on groundnut
and 150 kg/ha of 14.7.7, on millet in rotation,
But some micronutrients are necessary fer the nodulation
0;’ groundriut, among thom molybdenum, Baron, Cobalt , Iron, Copper
ûnd Zinc,
A significative effect of Molybdenum was obtained in
field trials (16). 8ut it was not in condition of chloroais,
On the apposite, a foliar spreading of a compiete micronu-
trient solution for legumes, bas no effect on the chlorosis
(Thilmakha 19’78).
21 - The influence of biotic factors
a- Inadequacy of the rhizobium population
A t Thilmakha, rhizobium population uas shown to be ten times
louer in soils with cI2orotic plants than in soils with non chlorc-
tic plants. On the other hand UEY (persona1 comunication) eliminatcd
chlorosis by inoculating groundnuts with CB 756 strain.
But this results could n o t bc confirmed in ths fiold, Sinss
nodulation of bydroponically grown ground-nuts inoculated by a suspan-
sion
of soi1 with chlorosis plants did not differ from nodulation
of’ plants inoculated by a supension of control soil, Rhizobium popu-
lations alone were net thought to be responsiblo for the poor nodu-
lation that occured in the field in chlorotic plots.
b - Microorqanisms antasonistic to rhizobium
PANTIER (12) found actinomycetes antagonistic to rhizobium
i3 s o i l s o f Senegal,
~
'*
But the numbers of these antagonistic actinomycetes . .
' in soils where chlorosis io observed did n o t diffar frr?m
that existing in soils where no chlorosis occured (PANTIER -Table III).
6
Table I I I - Number of actinomycetes antagnnistic to Rhizobium in
one gran
of soi1 - Thilmakha (1978 average of 5 soi.1
samples)
!
1
f A n t a g o n i s t i c !
i Actinomycetes
, actinomycetes
""I""""I~"--""""-"--"-"""""""
~~""""""I"-"""L"""~*
!
rr"r""--""rr""""-
i
?
Soi1 utith chlorotic plants i
T
!
.
l,?
.
105
!
9,5
,
12
!
!
!
““““““““1”““““““““““““““““““” ““““““““““11”““““”
T”“““““‘“‘“‘“3”““t
i
:
! Soi1 with non chlorotic
i
2,8 105
!
9,4 10
0
1 plants
!
!
!
Therefore the interferencc of actinomycetes probably
cannot be held responsible for the lowor nitrogen fixation of chlo-
rotic plants.
c - Influence of. nemat0do.s
In Upper Volta chlorosis was clearly shourn to be caused
by nematode attacks (17).
1 n Senegal , according to thc nematodcgs counts by GE%ANI,thê
contamination of roots by Scutellonoma. cav,e.nessi is much yreater in
chlorotic plants than in non chlorotic ones.
Table IV - Numbor of nematodes Scutellonem,a cavenessi in tho roota
of chlorotic and non chlorotic plants - Thilmakha (I[i78 -
average of 10 plants)
I
1
1
?
!
Numbor of nematodcs 1
Area with :
!
l""""""I""""""T"-"-"-"""-"""~
!
Soi.1
Root
! ““““““-““““““-“““I”“““““““““““““””-””
f “““1 ‘200 ““L” f”““-;“~~;“““-(
i Non chlorotic plants
.
!
!
! chlorotic plants
!
660
!
20 951
I
! “““11”““““““““““““““““““““““““““”~””
!
:““““---““““““~““---““““““““~
o Chlorotic plants years beforc
! t no treatment ‘dith nemagon
i
i
!
506
I
16 420
!
! Chlorotic plants years before
I
0
!
0
!
! t treatment uith nemagon
!
!
!
Up to nw, it has not yet been possible to reproduce tho
uhlorosis by inoculation of a non chlorotic (normal) soi1 urith
nematodes in laboratory conditions,
In a field trial, tho fumigation with nemagon restored
the vegetative growth of groundnuts. Nevertheless, chlorosis was no%
eliminated on the chlorotic areas treated with nemagon. The plants
hrf
a porfectly cuell dcveloppod root system without protrusions but
vsry four nodules.
7
Table V : Effect of soi1 fumigation iith a nematicide (Thilmakha
1978 - average often plants)
I
I
Area with
i C”“““““““““““““““-“I”
i No chlorotic plants
1 """""""""-"~"""-L-""""
.
I Chlorotic plants
""""""I"I"""--""-"-"""
\\l - CONTROL OF CHLOROSIS
Two methods for controling chlorosis have bcen empirically
round tu be efficient : liming and organic matter application.
In a field tria1 at Thilmakha, liming was applied at the
rate of 600 kg/ha, by pelletizing each grain of groundnut. The arma
coverod by the chlorosis has been reducod in the plots treateii
igith l i m e
but still somc yellow plants could be seen and the
vcgetation ha: not totally rocovered.
Farm-yard manure has also been applied since 1973 in the
same triai, Every two years, the plots havc received 10 tons dry
matter per hectare before groundnut planting. After the second
application of manure , yellow patches had been reduced considerably,
and after the third application, 5 years later, not a single symptom
of chlorosis could be soen.
Nevertheless this rate of manure application is very high,
compared to the quantity of organic matter the senegalese farrners
cari rely o n ( 1 8 ) .
VI - CO.NCLUSION
.
This symptom of chlorosis urhich occurs in acid soils appears
to be related to the following characteristics
- Minora1 t o x i c i t i e s
- Low rhizobium populations
(3) - High nematode populations.
It is not yet knourn tuether the decrease in nodulation and
i;J2 fixing activity of thc legumc results (1) from a poor growth of
tho plant (due to minera1 doficiencies or nematode attacks) -(2) from
~OU ,Rhizobium populations or from some mechanism prevonting infection
r;nd nodulation.
8
Further investigations are neoded in order ta elucidate
the interactions between the plant, soi1 minera1 factors anci sdil
microorganisms. The results of such investigations should hslp to
devel.op cultural practices urhich could promote N2 fixation by pre-
ve:lting the effect of limiting factors in Sahelo-soudanian agro-
systems.
AKNDkJLEDGEMENTS
We are grateful to MM, WEY, GANRY, SIBAND and DIATTA of
C.N.R.A. Bambey and WI. BOURREAU, MUGNIER, PANTIER and GEHMANI of
ORSTQM, of the soi1 microbiology and nematology lab.oratcries- for
their comments and their collaboration.
\\ae owe much to M. DCMMERGUE for his criticisms of the
manuscript and his attention during the course of the reseai-ch.
We are greatly indobted ta A, DIRBAYE who has given
technical assistance to this work.
We thank M. NIANG for photographs, M. CADIAGA for
drawings and Mrs SECK for type writting.
R E F E R E N C E S ,
(0 - BOUHOT 1978 :
Le rabougrissement de l'arachide - Agro, Trop. XXIII
nOIl
(2 ) - GERMANT 1975
"Effets des brulis sur la végetation de l’arachide au
Sénégal" - Academie d’agriculture de France - Extrait
de proces verbal de la seanca du '19 novembre 1975.
(3) - BLONDEL (D), 1970
"Relation entra le "Nanisme jaune" de l!arachide eh
sol sableux (Dior) et le pH. Definition d'un seuil
pour 1 lactivitb de rhizobium.
Agron. Trop, XXV, no&7.
(4)
- DUCERF (P,), 1978
"Synthèse des travaux effectués sur la mo&lisation de
la fixation d'azote d’une culture d'arachide au
Sénégal - Ronéo ISRA
(5)
I CHARREAU (C,), NICOU (R.), 1971
“L’amtSlioration’du profil cultural dans les sols sa-
bleux et sabla-argileux de la zone tropicale sPche
Ouest africaine et ses incidences agronomiques,
Bull. Agron. nQ23 CNRA Bambey - IRAT/Sènégal.
(6)
- PIERI (C.}, 1974
“Premiers rQsultats experimentaux sur la sensibilité
de l'arachide a la toxicite aluminique"
Agron. Trop. XXIX, n06-7.
(7)
- NDIAYE (J.P.), 1978
"Enquete fertilité on milieu paysan dans la rkgion du
Sine-Saloum - Rondo ISRR.
(8)
.m PIERI (C.), 1976
"L'acidification d'un sol Dior cultive du Sénégal et
ses consequances agronomiques” Agron. Trop. XXX1 - 3
(9)
- POULAIN (J.F.)
"Résultats obtenun3 avec les engrais et las amendements
calciques. Acidifïcation des sols et correction" -
Colloque sur la fertilite des sols tropicaux. Ed.
IRAT, 1968.
00) - P O U L A I N ( J . F . )
"Premier bilan des essai urge-sulfate : résultats
agronomiques de quatre années 1966-1969. Doc. roneo
IRAT-Senegal.
(11) - CHARREAU (C.), 1971
"Nécessite agronomique et interet économique d'une
intensification des systemes agricoles au Sénégal”
Doc, ronéo IRAT/Paris,
10
(12) - PANTHIER (J.J.), DIEH (H.E.), DOMMERGIJES (y,~.), 1978
"A rapid of method of enumerating actinomycetes an-
toganic toward rhizobia”
Laboratoire de microbiologie des sols ORSTOM/Dakar
(13) - GERMANI (G,), GAUTREAU (J.), 1976
"R6sultats agronomiques obtenus par des traitements
nématicides sur arachide au Sen6gal"
Cahiers ORSTOM Seris biologie vol. XI n03,
(14) - WEY (Je), OBATON (M.), 1978
"Incidence de quelques techniques culturalcs sur
l’activit6 fixatrice d’azote et le rondement de
1) arachide”
A g r o n . T r o p , XxX111, n02.
w - PREVDT, OLLAGNIER, AUBERT, SAUCIERES (1955)
“DBgradation des sols et toxicit6 manganique" Oléa-
gineux vol X na4,
(W " MARTIN (G.), FOUHRIER (P.), 1965
"Les oligo6léments dans la culture de ltarachide du
Nord-S6nBgal” - Oléagineux XX n05.
(W - CERMANI (G.), DHERY (M,), 1973
"Observation et expérimentation concernant le r61o
des nematodes dans dcuxaaffections de l’arachide en
Haute Volta, la “chlorose” et 1s "clump" Oléagineux
2 9/235-242 ?
(W - DREVON (J.J.), 1978
"Eléments pour une étude des apports de mati8re
organique aux sols dans le bassin arachidier du
SénéC)al".
Roneo ISRA.
r
.
ft6. 2 1 POIDS S E C D E S PLAN$S
DRY WEIGHT OF THE PIANTS
Poids soc appareil krien* gffosse
( THICMAKHA 1978)
4 Dry
“57
w&ght nuts
+ leaves
.\\.
a
.a
\\.
.
/J
0 Plantas chlorotiques
* Flanf@s t&oins
,
FIG. 3.: FLORAISON (journalière- cumulée 1
Flowering ( daily cumulative )
Nombre de fleurs
umber of ilowefs
( THILMAKHA 1978 )
Plan tes chlorotiques
CJ Piontes témain
t FtG. 4 1
RACINES
O’ARAWDE
f 56% JOUR )
TYPE xxx
Plante n o n chlorotique - Man chlorotic p l a n t
TYPE I
IPPE XI
Plantrs chlarotiquas - ÇhEoratic plants
(FIG. 5 1 RACINES LATERALES *PRO’WBERAN(bES”
SI’DE ROOTS
* PROTRUSIBNS”
6-.- ._‘ c
1
.J’
Numbur a/ days