RATE OF CALCIUM CARBONATE ACCUMULATION BY BIOLOGICAL REDUCTION Adnan Hardan College of Agriculture, Soils Department Ah-Ghraib, Traq Introduction A great portion of the agricultural lands in the alluvial plains of Iraq was formed by irrigation and river sedimentation. The soils of the plains are charac- terized by high contents of precipitated carbonates (lime) which may reach 305: or more. The mechanisms of in situ lime formation in the lower Mesopotamian plain were studied by Hardan and Abbas (1971). One of the mechanisms is biological sulfate reduction. The nature of this biological process and its role in soil ripening, acid sulfate formation in soil, and alkali development were studied extensively by Gracie et al. (1934), Abd-El-Yalek and Rizk (1963), Lynn (1963), Idhittip, and Janitzky (1963), Zonneveld (1963), Hardan (1964), Janitzky (1964), and others. No information is available on the rate of lime accumulation by sulfate reduction under favourable field conditions of the Mesopotamian plain. Therefore, this study was conducted to gain information on the rate of lime precipitation under such conditions. Materials and Methods The study was conducted in two locations both of which were adjacent to water ponds with favourable conditions for sulfate reduction. The pond at the first location was formed from seepage and ground water during the construction of a highway near Falluja, shortly before the beginning of this experiment. The pond was about 300 metres long and about 20 metres wide. This selection provided sui- table conditions to study the rate of lime formation in an area where some favou- rable sulfate reduction conditions are just beginning. The second location was selected near an old marsh at Amara to study the lime accumulation in an area where favourable sulfate reduction conditions have prevailed for a long time. Those two locations have made it possible to compare the rate of lime accumula- tion by biological sulfate reduction in newly developed conditions with that in an old marsh area. Four soil samples were taken at four time intervals from each location. The first sample was taken from a depth of 0-30 cm at the rim of the pond. The second,third, 76
Transcript
RATE OF CALCIUM CARBONATE ACCUMULATION BY BIOLOGICAL REDUCTION
Adnan Hardan College of Agricul ture, Soils Department Ah-Ghraib, Traq
Introduction
A great portion of the agricultural lands in the alluvial plains of Iraq was
formed by irrigation and river sedimentation. The soils of the plains are charac-
terized by high contents of precipitated carbonates (lime) which may reach 305:
or more.
The mechanisms of in situ lime formation in the lower Mesopotamian plain were
studied by Hardan and Abbas ( 1 9 7 1 ) . One of the mechanisms is biological sulfate
reduction. The nature of this biological process and its role in s o i l ripening,
acid sulfate formation in soil, and alkali development were studied extensively
by Gracie et al. (1934), Abd-El-Yalek and Rizk (1963), Lynn (1963), Idhittip, and
No information is available on the rate of lime accumulation by sulfate reduction
under favourable field conditions of the Mesopotamian plain. Therefore, this
study was conducted to gain information on the rate of lime precipitation under
such conditions.
Materials and Methods
The study was conducted in two locations both of which were adjacent to water
ponds with favourable conditions for sulfate reduction. The pond at the first
location was formed from seepage and ground water during the construction of a
highway near Falluja, shortly before the beginning of this experiment. The pond
was about 300 metres long and about 20 metres wide. This selection provided sui- table conditions to study the rate of lime formation in an area where some favou-
rable sulfate reduction conditions are just beginning. The second location was
selected near an old marsh at Amara to study the lime accumulation in an area
where favourable sulfate reduction conditions have prevailed for a long time.
Those two locations have made it possible to compare the rate of lime accumula-
tion by biological sulfate reduction in newly developed conditions with that in
an old marsh area.
Four soil samples were taken at four time intervals from each location. The first
sample was taken from a depth of 0-30 cm at the rim of the pond. The second,third,
7 6
and fourth sampling sites were 25, 50, and 150 metres away from the pond, respec- tively. Soil samples of the second, third, and fourth sites were taken from depths
of 0-30 and 30-60 cm.
Depth and composition of ground water were determined at all sampling sites in
the summers of 1964, 1966, 1968, and 1970.
Chemical analyses of the soil and water samples were carried out according to
the methods used by the United States Salinity Laboratory (Handbook 60). The ana- lyses included lime percentage, soluble bicarbonates, soluble Ca+Yg, pH, ECe, and
sulfates.
Results and discussion
Table 1 presents the ECe, SAR, and soluble sulfate values for surface soil and
ground water.
The SAR values of s o i l continuously increased with time in both locations. How-
ever, the rate of SAR increase for Falluja soil was much greater than that of Ama-
ra soil. Although the SAR values of ground water in both locations only slightly increased during six years (1964-1970), those of soil more than tripled and dou-
bled for Falluja and Amara s o i l s , respectively. This indicates that the increase
in SAR values of soil w a s due to the in situ inactivation of Ca+Yg ions as car-
bonates. Inactivation of Ca+Plg ions as lime (Fig.]) is directly related to the
increase in SAR values of soil (Table I ) at the rim of the ponds.
The soluble sulfate in soil of both locations decreased continuously with time
in spite of the continuous feeding of sulfate from the pond water or ground water
as indicated by the continuous increase in ECe of soil.
This decrease in sulfate was due to sulfate reduction as well as slight precipi-
tation of gypsum. The increase in gypsum in the soil at each sampling site and
time was too low to make up for the decrease in sulfate. This could be partially
due to the strong competition of IICOs+C03 for Ca ions which precipitates, rather than gypsum.
1 indicates the precipitation of lime at different distances from the rim
of the Pond (location of highest biological sulfate reduction) at different sam-
pling times. The increase in lime accumulation in Falluja location with distance
and with time was more than twice that of Amara location. The highest increase
was at the rim of the pond and in the first two years. The increase at Falluja
location after two years from the formation of the pond was partially due to the
sudden growth of vegetation and fresh accumulation of organic matter. At Amara
77
area, the marsh was old and the yearly accumulation of organic matter may be less.
Furthermore the water border of the pond at Falluja was much more stagnant than
that at Amara due to the absence of flooding and surface irrigation water in Fal-
luja location. At Amara, flood and irrigation water covers the rim of the pond
at flooding time. This is indicated by the relatively low changes in ECe values
over the six-year period at Amara as compared with those at the Falluja location.
This and other studies indicate that biological sulfate reduction was a major
process for in situ lime accumulation in the soils of the Mesopotamian plain.
Waterlogging, fresh organic matter accumulation, soluble sulfate, and sulfate
reducing bacteria were present at different times and different locations during
the development of the plain. The lime accumulated by this mechanism is believed
to have been redistributed throughout the soils of the reduction and the neigh-
bouring areas. This redistribution was due to many centuries of irregular agri-
cultural practices and flooding.
7 8
s 1970 o 1968 6- 1966 - 1964
DISTANT FROM POND.meter
Fig.]. Precipitated lime at different distances from the reduction site during six years at Amara (a) and Falluja (b)
TABLE I . CHEMICAL ANALYSES OF SURFACE S O I L (0-30 cm) AT THE R I M O F THE POND AND OF
GROUND WATER (GW) AT 25 %TRES FROM THE POND
F A L L U J A LOCATION AMARA LOCATION E C e SAR SOU E C e SAR so,
mhos /cm m.e.11 m h o s / cm m.e./l -__ ______ GW S o i l GIJ S o i l GW S o i l
ABD-EL-MALEK, Y. and RIZK, S . G . 1963. Bacterial sulfate reduction and develop-
ment of alkalinity. J. Appl.Bacter. 26: 7-26.
GRACIE, D.S., RIZK, I f . , NOUKHTAR, A . , and YOUSTAFA, A . H . I . 1 9 3 4 . The nature
of soil deterioration in Egypt. Vin. of Agric. Egypt. Tech. and Sci.Series
Bull. 148: 1-22.
HARDAN, ADNAN. 1964. Development of soil salinity and alkalinity under labora-
tory conditions. Ph.D. Thesis. IJniv. of Calif. Davis.
HARDAN, ADNAN and ABBAS, A.Kh. 1971 . Yechanisms of accumulation and distrihution
of calcium carbonate in marsh soils of the Lower Mesopotamian Plain. In
press.
JANITZKY, P. 1964. Biologically induced soil alkalinity. 8th Inter. Congress of
Soil Science. Bucharest, rlumania. 11: 767-776.
LYNN, W . C . 1963 . A study of chemical and biological processes operative in re-
claimed and unreclaimed tidal marsh sediments. Ph.D. Thesis. Univ. of Calif.
Davis.
WITTIG, L.D., and JANITZKY, P. 1963 . Yechanisms of formation of Na>CO? in soils.
I. Manifestations of biological conversions. J.Soil. 14 : 322-333.
ZONNEVELD, I.S. 1963 . Soil formation in deltaic areas. Proc. Regional Symposium
of Flood Control, Utilization and Development of Deltaic Areas. Bangkok.
pp.106-128.
80
Summary
Periodical analyses of :.)ater s o i l samples in t he border areas odf ponds in the
adesopotamian p l a i n , revealed that, over a p e r i o d of six years , t h e c o m o s i t i o n
o f t he groundwater remained f a i r l y constant, but t he nrec in i ta t ion our l ? k i n
the s o i l i ncreased considerably and pro i ;orc ioml lu to increase o f va lues ,
reduced sulphates and ravourahle condi t ions f o r biological sulphate reduction. Thus it i s bel ieved that biolog?:cal sulphate reduc t ion is a major nrocess f o r i n
situ lime accumulation i n these soils.
?ésumé
L 'analyse périodique du s o l e t de l ' e a u dans les z6nes r ivernines d ' Q t a n p
dans Za plaine de %sopotamie a montré que, pour une période de six am, l a com-
p o s i t i o n de l ' e a u rbestait s tab le pendant dans l e sol il ?d a 7 ~ 7 : t une précini to- t i o n calcaire considérah l e proportionne 2 lement à l 'augmenlation du ijctleur :;il p , au
décroissement d e s sulfates so Zubles e t nux conditions favorahtes n o w l a réduction
biologique des sulfates. On conclut que c ' e s t l a réducl ion hiologique de s u l f a t e
qui e s t l e processus princinal responsable nour 2 'accumulation de calcaire i n
situ dans ces sols.
Pesumen
Se ha analisado periodicarncnte muestrus de suelo LJ de agua en la s or* l lu s de Irrgu--
nas en Za v a l l e de %sopotamia. F'n seis anos la comosic ihn d e l agua ouednha casi igual, mientras en el, suelo hob-ia una acuminZaci6n de cal considerable li ,pronor-
cional a2 aumento d e l oalor SAR, la di.wnInucidn de lo s fiu1futo.s y los condiciones
favorcthles para la reducc idn b7:ológica de sulfato. Asi .se nree que Za redincccidn
b i o l 6 g i r a de s u l f a t o sea e l proceso pr inc ion l nara Za acumulación de cal en s i t i o en esos suelos.
2 usammen fas sung
Periodische Analysen der Boden- und Wassermuster aus I!fergebieten zweier Te iche
in der n d e ~ 5 0 P o t ~ i s c h e n Ebene haben erwiesen, dass die ~a.~serzusa"ensetzung inner- halb der sechs Jahre g l e i c h h Zieh, idährend i m Boden e7:ne he triicht l i che KaZkal4s-
fällung stattfand, 7nnd zwar verhältnismä Abnahmc? l i js l icher Sulphate und zu giinstigen I l e r h ~ l t n i s s e n fiir biologische . S u h h a t -
redukt ion. Die biologische Sulphatredukt ion i n d i e s e n Höden s n i e % t defiholb eine
wich t i ye l o l l e in der KaZkausfäZlung 7:n situ.
g zur Steigerung der SAV-Gierte, z u r
81
BIOLOGICAL SULPHATE-REDUCTION I N THE SPERMOSPHERE AND THE RHIZOSPHERE OF RICE I N SOME ACID SULPHATE SOILS OF SENEGAL
V . /l. Jacq ORSTOM, Dakar (Senegal)
Sulphate-reduction by anaerobic bacteria (Desulfovibrio and Desulfotomaculum sp.)
is a process frequently described in highly reduced horizons of waterlogged
soils: Vamos (1959), Boulaine (1960), Takai and Kamura (1966), Connel and Pa-
trick (1968), Bloomfield (1969).
The number of sulphate-reducing bacteria increases and they produce free hydro-
gen sulphide when three conditions exist simultaneously: 1 ) anaerobiosis, 2)
presence of sufficient sulphates, 3) presence of suitable substrates. When iron
is present it immobilizes free hydrogen sulphide and iron monosulphide (Fes)
precipitates.
These three conditions are met in some soils of Senegal:
-
I ) mangrove soils in tidal swamps; such soils are found along the western
coast of Africa, from Senegal to Cameroon. Before reclamation, they are high in
sulphates and fresh organic matter and very reduced. Sulphate-reduction in such
soils has been described by Hart (1963), Vieillefon (1969) and Baldensperger
( I 969).
2) acid sulphate soils on marine and estuarine sediments high in pyrites and iron monosulphides as in the Senegal River delta.
The paper presents the results of some experiments suggesting that when these
soils are reclaimed for rice cultivation, sulphate- reduction may appear, not
only in the reduced soil as described by Tanaka et a1.(1968), but first, and very
quickly around the germinating seeds and along the roots. Free hydrogen sulphide,
and iron monosulphides produced in the spermosptiere cause the death of seeds, and
in the rhizosphere, the wilting and the death of seedlings. In previous reports
(Jacq 1969-1971) we have described similar deleterious processes in the spermo-
sphere and the rhizosphere of maize on waterlogged saline soil in Tunesia.
A) IN SITU OBSERVATIONS
Two types of deleterious phenomena have been observed in situ in some experimen-
tal stations in the Senegal River delta.
82
h
1 ) Dying of germinating seeds
When heavy rains caused the waterlogging of soil surfaces during the week follow-
ing the sowing, seeds were covered by a black sheath of iron monosulphide strictly
localized in the spermosphere, and produced by sulphate-reducing bacteria.
All the seeds died in a few days, as was observed in Kassak-Nord station last
year, in a moderate saline acid sulphate soil (pH 5.5; sulphate content 2.02
me/100 g) where leaching is very slow because clay content reaches about 70X.
2) Wilting and dying of seedlings
In waterlogged areas, where flooding was caused by rains or inadequate drainage
of irrigation water, at the beginning of bright periods following cloudy ones,
symptoms of disease appeared in rice seedlings: first older leaves, then all the
leaves, wilted and dried. Roots were covered by a black sheath. If sulphide
accumulation was important,seedlings died about 10 days after the manifestation
of the first symptoms. Such disease has been very important in Kassak-Nord soils,
less important in Boundoum-Nord soils (SO:-: 1.5 me/100 g; clays: 60%) and
Kassak-Sud soils (SO:-: 0.77 me/100 g; clays: 57X), where pH is higher: 6.0 to 6.4.
B) EXPERIMENTAL STUDIES
1 ) Yaterial and methods
a) Experiments on soils
Freshly collected samples of mangrove or paddy soils, air-dried and sieved to
2 nun were distributed into flat and transparent columns (50x15~100 mm) described
by Dommergues et al. (1969a). Seeds of rice (IR8 variety) were sown in dry soils.
For spermospherical sulphate-reduction studies, soils were waterlogged immedia-
tely after the sowing. For rhizospherical sulphate-reduction studies, soils were
waterlogged after the seedlings were about 10 cm high. Sulphate-reducing bacteria were enumerated according to Starkey, reported by Pichinoty (1966).
b) Experiments on hydroponic cultures
On large test-tubes (Jacq 1971) rice hydroponic axenic cultures were obtained on
Jacquinot's (1968) or BÖrner and Rodemacher's (Chalvignac 1958) mineral media.
In some experiments an inoculate of sulphate-reducing bacteria was injected into
the medium and sulphide content was periodically measured according to Chaudry
and Cornfield ( I 966).
8 3
Roots exudates were identified by paper chromatography, and dissolved oxygen
partial pressure (po*) was measured with a Radiometer Blovel Yicro System analyzer.
2) Experimental results
I. Spermospherical and rhizospherical sulphate-reductions in some soils of Senegal: Laboratory experiments
a) Sulphate-reduction in mangrove soils of Casamance
Mangrove s o i l s of Ralingore station (Casamance, South of Senegal) have been de-
scribed by Vieillefon (1969). Table I gives some chemical and Dhysical proper- ties of these soils and the results of sulphate-reducing bacteria enumerations
at the middle of dry season (February) and of rainy season (August).
These enumerations show that sulphate-reducing bacteria are very numerous, in these
soils; more than 1,000 cells per g of dry soil during the whole year and, during
rainy season, they are also present in the water.
In flat-column experiments when IR8 rice was sown and soil immediately water-
logged, the number of sulphate-reducing bacteria increased rapidly in spermosphe-
rical soil (table 2) and in the seeds the black sheath of iron monosulphide ap-
peared. A very large part of seeds died in 8 or 10 days: from 63% in bare "tanne"
soil to 100% in a rhizophora mangrove soil (table 3).
The increase in the number of sulphate-reducing bacteria was less around roots of
survival seedlings (table 2) but all nlants were damaged. Of these latter died
subsequently 23% in hare "tanne" s o i l and 30% in rhizophora mangrove soil (table
3). The number of ultimately surviving seedlings (at the 25th day) is low, less
than 27% (table 3), even in the mangrove paddy soil.
b) Sulphate reduction in two paddy soils of Casamance, and influence of deepness
of sowing and waterlogging
Samples were taken from two paddy soils of Casamance. The clay content and pH
(fresh soil) of these soils were respectively: 4 9 . 8 % and 5.0 for Bignona mangrove
saline soil and 31.5% and 6.0 for Djibelor, irrigated, non-saline soil.
In flat column experiments, 4 treatments were given.
(I) Rice seeds sown at 0-1 cm deep; waterlogged soil
( 2 ) Rice seeds sown at 0-1 cm deep; flooded soil (water level at 3 cm above
soil surface)
a4
(3 ) Rice seeds sown at 3-4 cm deep; waterlogged soil
(4) Rice seeds sown at 3-4 cm deep; flooded soil.
The results are reported in Table 4: spermospherical and rhizospherical sulphate-
reduction was always very important for seeds sown 2-4 cm deep: in both soils
up to 90% of these died, as did subsequently half or more of the seedlings.
When seeds were sown into the 0-1 cm horizon, spermospherical sulphate-reduction
was less important, especially in Bignona soil, but in flooded soils, the num-
ber of dead seeds was twice as high as in waterlogged soils. A s a result of rhi-
zospherical sulphate-reduction, about 25 to 30% of the seedlings died, except for
waterlogged Bignona soil, where this percentage reached 59%.
c) Sulphate-reduction in some different paddy soils
Fourteen paddy soils have been tested: seven mangrove paddy soils, four i-rriga-
ted soils and three acid sulphate paddy soils. Table 5 shows some chemical and
physical properties of these soils, and results of flat-column experiments.
Spermospherical sulphate reduction occurred only in some mangrove paddy soils.
It can be noticed that the two soils where all seeds died (Balingore and Yedina 3 )
were very saline and clayey, and have been reclaimed last year. I n three other
soils, the loss of seeds was up to 50%. In sandy mangrove soil, as Enampar soil, no spermospherical sulphate-reduction was observed.
Rbizospherical sulphate-reduction was observed in all fourteen tested soils. But
damage was important only in the Medina 2 mangrove paddy soil, where all the
seedling died out, and in two other mangrove soils where growth of seedlings was
very slow. In these three soils, the number of sulphate-reducing bacteria might have increased because of previous spermospherical sulphate-reduction.
In a non-saline soil (Djibelor 4) and in an acid sulphate soil (Ross-Bethio) rhizospherical sulphate-reduction appeared only at the end of the experiment
(two months after sowing) and no plant died.
11. Rhizospherical sulphate-reduction in hydroponic cultures
a) Inoculation of rice rhizosphere by pure strains of sulphate-reducing bacteria
In four experiments rice hydroponic axenic cultures were inoculated by pure
strains of Desulfovibrio desulfuricans (Hildenborough) or Desulfovibrio eigas.
Results are reported in Table 6.
Numbers of sulphate-reducing bacteria increased after the 4th day. A sheath of
85
iron sulphide appeared on the roots and the medium became grey or black. Growth of
affected plants was stunted, and within 10 days, some of them died. In each test-
tube the number of died plants was correlated with the number of sulphate-redu-
cing bacteria and with the sulphide content per ml of medium: seedlings died
when sulphide content reaches about IxIO-~S-' per ml (which is surely lower than
sulphide content in the rhizospherical sheath).
b) Inoculation of rice rhizosphere by impure strains of sulphate-reducing bacte-
ria
Impure strains of sulphate-reducing bacteria were obtained on Pichinoty's me-
dium, from mangrove and paddy soils of Balingore station. Rice hydroponic axenic
cultures, 7 days old, were inoculated by them. Results of periodic enumerations
are reported in Table 7.
When initial inoculum was sufficient, rhizospherical sulphate-reduction occurred,
in the same manner as with pure strains of sulphate-reducing bacteria, but more
slowly. With impure strains from Rhizophora mangrove, death of seedlings occurred
in 19 days and with two other strains (from mangrove paddy soil and non-saline
Heliocharis "tanne") growth of rice was affected. When the initial inoculum was
slight, the number of sulphate-reducing bacteria decreased and iron-sulphide
was not observed around roots.
111. Rice root exudates
It is known that only a few substrates can be utilized as carbon sources by sul-
phate-reducing bacteria. Such substrates have been identified by paper chromato-
graphy (see Table 8 , results of amino-acids, aliphatic acids and sugars identifi-
cations in IR8 exudates).
Two aliphatic acids are immediately available: lactate (Starkey 1938, Senez 1 9 5 4 )
and succinate (Grossman and Postgate 1953) . When amounts of such aliphatic acids
are insufficient, some amino-acids may be utilized (Yac Pherson and Yiller 1962)
especially aspartic acid, glutamic acid, asparagine, histidine and threonine,
and some sugars, as sucrose, glucose and fructose.
IV. Oxygen diffusion from rice roots
Oxygen partial pressure has been periodically measured with the Radiometer ana-
lyzer, in hydroponic media, where 8 plants of rice per test-tube were growing.
Results are reported on Table 9: oxygen production by rice roots appeared after 6 or 10 days of incubation in glass-house.
86
C ) CONCLUSIONS AND DISCUSSION
The results summarized here show that sulphate-reducing bacteria are present in
two different paddy soils, reclaimed from mangrove soils or from fluvial estua-
rine deposits. They may induce, the death of rice seeds and seedlings only, when
strict anaerobiosis is established by waterlogging. Heavy rains, or insufficient
drainage of irrigation water are main cause of waterlogging, especially when
these soils are very clayey and compacted. Such diseases may occur in saline
paddy s o i l s , or when brackish water is used in irrigation, because numerous
strains of sulphate-reducing bacteria tolerates high sodium chloride contents
(Leban et al. 1966).
Sulphate-reduction appears in the whole profile as described by many Japanese
searchers (Mitsui et a1.1954, Yamada and Ota 1958, Takai and Kamura 1966), but
it appears too, and more quickly, in spermosphere and rhizosphere where availa-
ble substrates are exudated. Spermospherical sulphate-reduction, is more intense
than rhizospherical sulphate-reduction, probably because seeds produce more
exudate than roots, and because seeds do not have the oxidative power of roots.
It can be noticed that light intensity influences the qualitative nature of roots
exudates (Rovira 1956) and so, rhizospherical sulphate-reduction is more intense
under bright sunshine (Jacq and Dommergues 1971).
A s far as we know, no searcher has noticed the death of rice seeds because pro-
duction of sulphides in the spermosphere. But toxicity of the hydrogen sulphide
for rice plant is well known: it is toxic at low concentration because it inhibits
the respiration, retards the uptake of water and various elements such as phos-
phorus and nitrogen (Yamada and Ota 1958), and destroys the oxidising power of
the roots (Tanaka et a1.1968). Thus, without having noticed rhizospherical loca-
lization of the injury, many searchers have pointed out the influence of hydro-
gen sulphide in some rice diseases: "bruzone" (Vamos 1958, 1959) in Hungary,
"rOOt-rOt" (Baba 1955), "akiochi" in Japan and Korea and "bronzing" in Ceylon.
Akiochi, attributed to hydrogen toxicity (Park and Tanaka 1968, Tanaka and Yoshi-
da l 9 7 0 ) occurred in degraded soils, low in active iron, quite different of acid
sulphate Soils. Uith bronzing disease, which may occur in very acid sulphate soils,
initial damage by free hydrogen sulphide in destroying the ability of the roots
to protect the plant from excess uptake of iron (Tanaka et a1.1968) and makes it sus
ceptible to iron toxicity described by Ponnamperuma et al. (1955). \Je have shown that in hydroponic cultures when total sulphides content (free hydrogen sulphide
and iron monosulphide) reaches 3 or 4 ppm, all plants are dying. Perhaps if suf-
87
ficient reduced iron is present to react with all free hydrogen sulphide Droduced
in the rhizosphere, the iron sulphide sheath will prevent the uptake of some
nutrients. Methyl-mercaptan, very toxic too, can also he produced by sulphate-
reducing bacteria (Takai and Asami 1962).
In acid sulphate paddy soils it is possible that sulphate-reduction around seeds and r o o t s occurs more easily when plants have yet suffered from any other toxic-
ity or deficiency. For instance salinity is usually associated with acidity in
the areas concerned. A s spermospherical sulphate-reduction is not promoted hy
toxicity, because germinating seeds are most tolerant to salinity, rhizospherical
sulphate-reduction may be more important in saline acid sulphate soil, especially
at seedling stage, when plants are very sensitive. After this stage, through
the oxidative power of rice roots (Aimi 1960, Barber et al. 1965, Armstrong 1969, Luxmore et al. 1970) iron monosulphide sheaths may he oxidised and their toxici-
ty reduced. This has been noticed in preliminary test-tube experiments, and
field observations show that when plants have been little injured, disease symp-
toms disappear and the growth of surviving plants is better than the growth of
non-affected plants.
Not only rice, but many plants may be affected by spermospherical and rhizosphe-
rical sulphate-reduction: field observations (Dommergues et al.1969) and prelimi-
nary experiments (Jacq 1969) on a saline soil from Tunisia, show that some plants
are very susceptible: legumes (french bean, broad bean, lucerne) and cereals
(ma'ize, sorghum). In Senegal, cotton and sugarcane may he also damaged. The study
of the effects of these processes is of a real practical interest every time acid
sulphate soils may be waterlogged after sowing or during growth of such suscep-
tible plants.
88
TABLE I. scm CHEMICAL AND PHYSICAL PROPERTIES OF MANGROVE AND PADDY SOILS OF CASMANCE AND ENIJKERATIONS OF SULPHATE REDUCING BACTERIA IN THESE SOILS
l a g l a o f number of sulphate
reducers / e of drv soil o r CHEMICAL AND PHYSICAL PROPERTIES
ml of water
Clav Carbon SO6 c1- Soil Soil Water in dry in rainy in rainy season season season C/N pH me. me.
TABLE 2. ENUMERATIONS OF SULPHATE REDUCING BACTERIA IN THE SPERVOSPHERE AND THE RHIZOSPHERE
OF IR8 RICE SOWN ON SOME WATERLOGGED MANGROVE AND PAODY SOILS
Number of sulphate reducing bacteria per g of dry soil ( l o g ~ o )
SOIL
Rhizophora mangrove
Rhizophora mangrove
Avicenia mangrove
Avicenia mangrove
Bare and saline "tanne"
Saline Heliocharis "tanne"
Non-saline Heliocharis "tanne"
Mangrove paddy soil
In soil
nay = o
4.27 3.68 3.59 3.36 2.50 2.88 2.31 4.41
spermospherical s o i l rhizospherical soil
8 1 5 22 12 19 25
5.60 4.53 6.29 3.80 3.96 4 . 1 3 - 6.80
5.61 3.01 5.14
3.35 4.00 5.06 3.72 3.24 5.17 4 . 5 0 3.70 6.66
5.38 3.72 5.13
3.14 6.39
2.62 3 . 6 h
3.52 5.49 5.38 6.46 3.10
7.m 5.62 3.63 8.64
'TABLE 3. IR8 RICE SEEDS KILLED BY SPERMOSPHERICAL SIJLPHATE-REDUCTION AND IR8 RICE SEEDLINGS KILLED BY RHIZOSPHERICAL SULPHATE-REDUCTION IN S O K NANGROVE AND PADDY SOILS
P E R C E N T A G E S
SO11 (A) (BI (C) (D) SEEDLINGS SEEDLINGS SURVIVING SEEDLINGS
(25th day) SEEDS KILLED AFFECTED KILLED
Rhizophora mangrove 87 1 on 30 in Rhizophora mangrove 1 O0 o Avicenia mangrove
Avicenia mangrove
Bare and saline "tanne"
Saline Heliocharis "tanne"
90 I no o I O
90 1 no o in 63 92 23 95 I on O
Non-saline heliocharis "tanne'l 97 I no n Mangrove paddy soil 77 I on 0
27
5 3 23
89
TABLE 4 . IR 8 RICE SEEDS AND SEEDLINGS KILLED BY SPERMOSPHERICAL AND KHIZOSPHERICAL SULPHATE- REDUCTIONS IN TWO PADDY SOILS; INFLUENCE OF DEPTH OF SOWING AND WATERLOGGING
PERCENTAGE OF PLANTS KILLED BY SURVIVING SEEDLINGS Z SOIL DEPTH
TABLE 5 . SULPHATE-REDUCTION IN TKE SPERYOSPHERE AND THE RHIZOSPHERE OF IRE RICE ON SOME PADDY SOILS
SOME PHYSICAL AND CHEMICAL PROPERTIES SULPHATE-REDUCTION
FXPERIeNTAL STATIONS
Vangrove paddy soils (Casamance) :
BALINGORE
MEDINA I
KEDINA 2
MEDINA 3
MEDINA 4
BIGNONA ENAMPAR
Non-saline paddy soils:
DJIBELOR I DJIBELOR 2
DJIBELOR 3 DJIBELOR 4
Paddy soil i n Senegal Delta:
ROSS-BETHIO
BOUNDOUM
RICHARD TOLL
6 . 2 4 5 . 0 13.0
4 . 0 6 6 . 0 2 9 . 6
4 . 3 27 .5 155
4 . 2 6 5 . 8 1 9 . 4
4.5 3 5 . 8 127
5 . 0 4 9 . 8 4 8 . 9
6 .3 25 .5 27 .6
6 . 2 21.0 40.1
6 .1 1 5 . 8 5 6 . 8
6.1 1 3 . 0 1 1 . 8
6 . 0 3 1 . 5 6 8 . 0
4 . 6 6 0 . 5 2 3 . 0
6 .3 47 .7 2 3 . 2
5 . 4 3 4 . 8 12.0
40
28
29
1 9
25
1 4
20
16
13
15
13
18
23
12
28 .7
1 3 . 4
2 3 . 0
4 2 . 9
40 .1
3 . 7
1 3 . 5
4 . 1 3
o O 0
i . 2
0.9
0 . 6
very impor tan t
imDor tan t impor tan t
very im- portant none low
none
none none none none
none
none
none
important important
low
important low
1 ow
low low very important
very important
low low
seeds died
weak seedlings died
seeds died
good weak
good
good
good good good
good
good
good
TABLE 7 . RHIZOSPHERICAL SULPHATE-QEDUCTION IN RICE HYDROPONIC CULTURES INOCULATED BY SULPHATE-REDUCING
BACTERIA OF SO% MANGROVE AND PADDY SOILS
Number of sulphate-reducing bacteria (loglo) /ml of hydroponic culture Rhizospherical Growth of
the rice seedlings
INOCULUM 5 ml of impure strain Inocula- 4 days 7 days 1 2 days 19 days from tion day later later later later reduction
Rhizophora mangrove - I! -
Avicenia mangrove
Bare and saline "tanne" - !I -
Non-saline Heliocharis "tanne"
Mangrove paddy s o i l - 11 -
2 . 0 4
4 .76
2.60
1 .O4
4 . 5 3
i 1 . 0 8
2.78
2 .36
3 . 4 5
1 . I 5
2 .60
2 . 4 8
1 . 4 8
2 .70
1 .26
I .34
1.26
1 . 6 0
1 . 4 8
3 . 4 8
1 . 9 0
1 .26
2 . 4 8
2 .36
3 . 3 4
I . 9 s
2 . 7 8
2 .36
3 . 8 6
I .48
1.95
2 . 6 0
I .48
3 .28
2.48
2 . 9 0
2 . 4 3
4 . 3 4
1 .O8
1 . 6 0
2 .48
1.48
4 . 1 8
2 . 9 0
3 . 8 5
lOW
very important E
none
none low none
very important low
important
weak :eedlings died
good good
weak good weak weak
very weak
TABLE 8. ROOT EXUDATES OF IR8 RICE
AMINO-ACIDS ALIPHATIC ACIDS SUGARS
leucine
isoleucine
p-alanine
tryptophane
valine
methionine
tyrosine
proline
cysteine
a-alanine
threonine
RC+)
3
1
O
O
I
+ O
3
+ 2
2
glutamic acid
serine citrulline
glycine
aspartic acid
arginine
asparagine
histidine
lysine cystine
RC
3
3 5
3
4
4
3
3
4
O
RC
quinate 2
tartrate 3
oxalate 3
citrate 2
malate O lactate I
malonate + succinate 1
fumarate O
raffinose
maltose
SUCKOSe
galactose
glucose
fructose
arabinose
xylose
ribose
rhamnose
+) RC: relative concentration
TABLE 9. OXYGEN DIFFUSION FROM ROOTS OF IR8 RICE INTO THREE HYDROPONIC AXENIC
CULTURE MEDIA
Dissolved oxygen partial pressure (POZ), in Hg Age of
plants
days) (no plant) ponic culture R-C HYDROPONIC MEDIA (in Control Rice hydro-
C+) R+)
BORNER-RODEMACHER 2 139 139 O
pH 6 . 5 7 151 145 -6
10 154 158 +4
BORNER-RODEMACHER I 161 160
PH 4.5 6 162 167
11 152 181
18 150 I78
-I
+5
+29
+ 2 8
JACQUINOT 1 I60 157 -3
pH 6 . 0 6 155 154 -1
1 1 160 I74 + I 4
18 157 I70 + I 3
- RC
3
O 2
1
3
3
O
O
I
o
+) Average of 6 measurements
9 3
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96
Summary
I n acid sulphate s o i l s of Senegal anaerobic condi t ions i n the tonsoi l may f a ~ ~ o u r p r o l i f e r a t i o n of sulphate reducing bac te r ia producing toxic amount.9 o f hydrogen
sulphide especially around germinating seeds and roots o f seedlings. This has heen
observed f o r rice, but a l s o l o r legumes, cereal.s, co t ton and sugar cane. The con-
centrat ion of t he sulphate reducing bac te r ia i n the spermomhere and the rh i zo -
sphere i s ezpla ined by t he ezudates of seeds and roots containing s u i t a b l e suhstra-
t e s f o r the anaerobic bacteria involved iDesul.fovihrio and DesulfotomacuZwn sn.).
Résumé
Dans cer ta in sols su2faté.s acides du SénégaZ des conditions anaérobies peuvent
provoquer l e développement i n t e n s i f des bactériee sul fato$éductr ices produisantes
des quanti tés toziques d'hydroge'ne s u l f u r é sur tou t autour des graines en cours de germination e t des racines de plantes jeunes. Ce processus a été ohserué dans
Zes r i z i d r e s , mais auss i dans l e s cultures des légumineuses, des céréales , du co- ton e t de l a canne à sucre . La concentration des hactéries sul fato-rQductr ices
dans la spermosphe're e t l a rhizosphère s ' e zp t ique par des emdats des grainen e t
racines contenant des substrats afavorables 6 l ' a c t i v i t é des bacte'rien en eauSe
(Desu l fov ihr io e t Desulfotomaculum s p . ) .
Resumen
Fn algunos suelos ácidos s u l f á t i c o s del Senegal e l anaerobiosis nuede mw>oc/ir una pro l i feración de l a s bacterias reductoras de suldfato produciendo h i d d y e n o
sul furado en cantidades tó z i cas , sobre todo a lrededor de las s emi l la s en germina- c idn y las raices jóvenes. Se observd eso fenómeno en arrozales nero tamhien en
cul t ivos de Zeguminosas, cereales, algodón u cana de azúcar. Se e m l i c a l a concen-
t rac ión de las bacterias reductoras de s u l f a t o en l a snermdsfera y l a r i z b s f e r a
por los exudados de las semil las y los raices que contienen sustratos adecuados
Para Las bacterias concernientes (Desulfovibrio Desulfotomaculum sp.).
Zusamenfassung
In schb)efe lsaueren Böden von Senegal können anaerobe Verhäl tnisse e ine starke Znt-
wicklung Suzfatreduzierender Bak ter ien hervormfen, u. m. bes onder.^ in der S,permo- Whäre
Produzierten SchweSeZi,,as,serstofS beschadigt , I)as Phiinomen wurde beohachtet zuntich.5 i,
i n lTeis fe ldern, sowie auch in den Kulturen der Hülsenfriichte und i n cetreide- ,
Baumlolle- und Zuckerrohranhaufliichen. Die Konzentration der sul fatreduzierenden
Bakterien i n der +em"h i i re und Phizosphäre 1,)7'rd e r k l ä r t durch d i e ezudativen Absonderungen d e r So" und Wurzeln, d i e a l s geeignete Substrate f i i r d i e he t re , f -
fenden Rakterien (Desr*Lfovibrio und DesulfotomacuZm sp.) dienen.
Rhi2osphÜi-e; i n fo lgedessen wcrden Samen und Wurzeln durch h a k t e r i o l o g i s c h
97
D I S C U S S I O N
MOORMANN: Are the s o i l s concerned - ì . e . i n the Seneqal Estuary, acid sulphate s o i l s ?
JACQ: Boundoum so i l i s n o t a t rue acid sulphate s o i l , nor a nseudo-acid sulphate so i l ( i t s pH i s a b o u t 6 . 0 ) .
M O O R M A N N : I n how f a r are other t o x i c i t i e s - i . e . HLS o r s a l i n i t y , involved a p a r t from the "Fes sheet"?
JACQ: Both H2S and s a l i n i t y may be involved i n the Boundoum Polder, and a lso toxic methyl-mercaptan, produced by sulphate reducers. The Fes sheet in coverinq seeds and roots prevents the nut r ien ts a n d perhaps the water in the so i l t o reach the plant .
