FOA 4 Rapport
C 4491-A4
Maj 1972
FLANT UPTAKE OF 137 Cs FROM OIFFERENT DEPTHS
IN A HOMOGENEOUS SUBSOIL LAYER
nu
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Försvarets forskningsanstalt
FOA 4 rapport
Avdelning 4
C 4491-A4
Stockholm 80
Maj 1972
PLANT UPTAKE OF
157f
^ Cs FROM DIFFERENT DEPTHS IN A HOMOGENEOUS
SUBSOIL LAYER
Ike Eriksson och Lars Fredriksson
Antal blad 13
Summary
Reclamation of heavily contaminated land used for cultivation
is a serious problem. Part of this problem was attacked by a
series of field experiments in 1961-65. They concerned the
possibilities to reduce the root uptake of contaminants by
different crops by placement of the contaminated surface soil
at different depths in the soil profil».
In the experiment the root uptake of
137
Cs from thin layers of
contaminated soil en 7, 15f 35, 60, 85 and 110 cm depth was
studied»
Among the crops the root uptake from the 7 cm depth decreased
in the following order: p c££ > white mustard »
oats > rye-
grass > barley. The relative uptake decreased strongly with
the depth in the profile. For peas, white mustard and rye-grass
the uptake from the 35-110 cm layer was £ 10 per cer.t of the
total, Including ä 5 per cent from the 35-60 cm layer. For oats
and barley the root uptake from the 35-110 cm layer was £ 30
per cent of the total, including 15-20 per cent from the 35-60
cm layer, 5-10 per cent from the 60-85 cm layer and 2-5 per cent
from the 85-110 cm layer.
Sammanfattning
Sanering av odlad mark som drabbats av tungt radioaktivt nedfall är ett allvarligt problem. En del av detta problem bearbetades genom en serie fältförsök 1961-65* De berörde möjligheterna att minska rotupptagningen i olika grödor av kontaminerond* ämnen genom att placera den kontaminerade yt jorden på olika djup i markprofilen»
1a
1b
I en markprofil studerades rotupptagningen av 137Cs från tunna
kontaminerade markskikt på 7, 15» 35, 60, 85 och 110 cm djup.
Upptagningen från det ytligaste skiktet avtog bland grödorna
enligt: ärter > vitsenap » havre > rajgräs > korn. Den relativa upptagningen avtog starkt med djupet i profilen» För
ärter, vitsenap och rajgräs var upptagningen från 35-110 cm
skiktet s 10 % av den totala, inbegripet ^ 5 % från 35-60 cm
skiktet* För havre och korn var rotupptagningen från 3!>-110 cm
skiktet £ 30 % av den totala, inbegripet 15-20 % från 35-60 cm
skiktet, 5-10 % från 60-85 cm skiktet och 2-5 % från 85-110 cm
skiktet.
Uppdragsnr; A4 35
Nyckelord;
Cesium, växtupptag, djupplöjning
Cesium, plant-uptake, deep plowing
Rapporten utsänd till;
ÖBF, AB Atomenergi (3 ex), Statens råd f atomforskning, Statens
strål8kyddsinst (2 ex), Statens medicinska forskningsråd (försvarsmed sekt), Statens institut f folkhälsan, Inst f klinisk
kemi Veterinärhögskolan (2 ex), Radiofysiska inst Lund, Gbg och
Umeå, Inst f radiobiologi Ultuna (50 ex), Statens livsmedelsverk,
FOA 1, FOA P
FOA 4: 421, 480, 481, 482 (10 ex)
Contents
I. Introduction
II. Materials and methods
1. Experimental site and period
2. Experimental technique
3. Soil quality
h. Crops and crop management
5. Analyses
III. Results
TV, Discussion
V. Conclusions
VI. References
VII. Tables 1-4
Page
2
3
3
3
3
3
h
k
6
8
9
10
I. Introduction
After heavy radioactive fallout on agricultural land and
on living areas the land has to be reclaimed in some way
or another to normalize the food production. Such reclamation measures may,beside changes in the liming and fertilization practice consist in the turning down of a contaminated soil surface layer by deep ploughing, or in collecting and taking away the soil material of the contaminated
layer to dig it dovm in the subsoil layer.
The feasibility of such enterprises depends on the resources available and on the expected reduction in the
health hazard for the population by decreased external
radiation and by decreased transfer of radioactive cesium
and strontium from the soil through the food chain to man
in the long term situation. However, to evaluate the possibilities in these respects data on the plant root activity
in deeper soil layers are needed,
The aim of this work has been to provide data on genetically
determined plant root profiles of five crops with respect
to their absorption of cations at different depths in the
subsoil. With the aid of these data and others (Fredriksson
et al., 1969) the measures for reclamation of contaminated
land can be further discussed.
The investigations were supported by grants from the
National Council for Forestry and Agricultural Research.
• Materials and methods
1. Experimental site and period
The experiments were carried out at Uppsala-Näs field
station (ef. Fredriksson, I963) during the years 1961-1965»
2.
Exgerimental_technitjue
By excavation an experimental bed, 1.2 m deep and 3x10 m
in area, was prepared. Before refilling with the subsoil
material used, a loamy sand, it was divided into 12 plots
by plates of asbestos cement. Each plot was 0.75 x 2.25 n».
During the construction in May 1961 the soil was moistened
up to thelevel of field capacity. The tracer, 889 p.Ci
carrier free 137Cs per m2 , was evenly distributed on packed
smooth soil surfaces at different depth by spraying. Thereby
only a thin layer of the soil was contaminated. The contaminated layers were situated on six different depths repeated twice. The distances from the upper surface to the
contaminated layers were 7, 15 t 35» 60, 85 and 110 cm respectively. During the refilling operation all soil layers
were duly packed. No shrinking of the experimental bedwas
observed later on. Except for the plot size, the micro plot
experimental technique used for crop cultivation was the
same as that described by Fredriksson (1963) and Fredriksson
et al. (1966).
3. Soil quality
No special top soil layer was applied and so the soil profile was throughout homogeneous. For crop production the
soil material, loamy sand, could be classified as very rich
with respect to the content of extractable phosphorus and
sufficient with respect to the content of exchangeable
potassium. However, as it was a sandy soil the cation exchange capacity and the calcium content were low. The soil
pH was 6,9»
Five crops were cultivated: peas and barley in 1961, white
mustard in 19^3» oats in 196** and perennial r/e-grass in
1965» The amount of seed sown per unit area was that recommended for field practice in the district (cf» also
Fredriksson et al., 1969)* Fertilizers were applied as top
dressings by spraying of water solutions. Peas obtained
30 kg N per hectare, barley and oats 60 kg N per hectare,
white mustard by three applications in total 100 kg N per
hectare. The perennial rye-grass obtained 50 kg nitrogen
and in addition 20 leg phosphorus and 35 kg potassium per
hectare at sowing.
When the precipitation was low, as some years happened in
June, the experimental area was irrigated to prevent otherwise unavoidable drought damage^.
5. Analyses
After harvest the crops were dried and, except for ryegrass, threshed, and milled. The radioassay was carried
out by gamma spectrometry. The activity data have been
corrected for decay and refer to the start of the experiment in May 1961»
III. Results
The intention was to study the integrated root activity in
a homogeneous soil profile and so the plough layer is
missing. The characteristics of this layer vary widely
between soil types. It is generally characterized by a
higher humus content, a better soil structure and with
respect to sandy soil also by a more favourable water
holding capacity and soil aeration than the subsoil layer.
The fact that the experimental top layer In some respects
was less favourable for plant production than in general
resulted in somewhat lower yields than the county means.
However, it should not have influenced the genetically
determined patterns of root development of the different
crops. The specific root activity at different depths as
shown by the 137'Cs-content in the crop products should
then be independent of the size of the yield.
m
7
The experimental yields and tht- "1-3' Cs-content in the crop
products are given in Table 1. Country means for the crops
in question during 1966-/0 are given in Table 2»
7
As shown by Table 1 the IT Cs-content in the crop products
differed greatly between crops. Placement of the tracer
at a depth of 7 cm gave the following order between them:
peas 2> white mustard :*• oats >* rye-grass > barley. This
difference between peas and white mustard on one side and
cereals on the other has been found in earlier* investigations and depends on different affinity of the plant
species for absorption of cations. When the potassium state
of the soil is high the 137Cs-uptaJce is low and so is the
difference also between the plant species (Fredriksson et
al,, 1966). For the crops cultivated on the loamy sand used
in the experiments the large differences in 137Cs-uptake
can be explained by the low 137
^ Cs-fixing capacity and by
the limited potassium resources of the soil»
t
I
I
The root activity at different depths, integrated over the
137
whole season, is indicated for each crop by the
Cscontent per kg dry matter and by the relative numbers in
Table 1. From these numbers on the root distribution in
the soil profile it can be concluded that peas and white
mustard have shallower root systems than barley and oats*
The roots of the former were concentrated to the upper soil
layer. There was a rapid decrease in tho relative root
activity of white mustard from 7 cni and v. »wnwards, in that
of peas from 15 cm and downwards. The relative root activity
of barley also decreased markedly frcm 7 to 15 cm depth
but from there and downwards it was kept at comparatively
even level down to a depth of 85 cm. The relative root
i
I
I
v
I
|.
activity of oats showed a rather slow decrease from 7 to 35
cm depth and not until between 35 and 60 cm depth did a
marked decrease take place. According to the
Cs-content
of the grain it was found that the relative root activity
of oats was higher than that of barley at the 15 and 35 cm
depth whereas the situation was reversed at 60 and 85 cm
depth.
For
thv
r y -;,Ta;::> i h o v.vor* ni.'iri.f ci a« i p ' a s c
in
the
r« 3 a t i v c
root activity took place betueon i'"> «.na 35 C M depth. Then
a moderate decrease uown to 1.1 G Cii* cpth was observed.
Related to a general decrease in Uie mineral content in
grass from summer to autumn (ef. Olofsson, 196^) a similar
decrease also took place in the crop of
Cs taken from
the upper soil layers. However, during the same time a
chan i also took place in the root distribution pattern
vitu depth in the profile. According to the
Cs-content
in the grass a relative decrease in the root activity at
15 cm depth '.<is followed hy its doubling on the 35» 60, 85
and 110 cm depths. Obviously, the root system continuid to
grow downwards during the season from the time of et t No. 1
to that of No. 2. It was certainly not limited to tlic:
0-110 cm layer.
s .ion
Altho igh genetically determined the development and distribution of the plant root systems can be in/laenced by
ecological factors such as the structure ai,.d the textural
composition of the sui soil which largly governs the porosity, i.e. the water holding capacity, aeration etc. and
the nutrient content. In addition, these factors may vary
between different layers in natural subsoils which also
might influence the result of the root penetration work
carried out by genetically different plant species.
The subsoil used in the experiment was homogeneous and a
special ca'-e among the- combinations possible in nature.
The question then i si in what respect was the root penetration work observed in the experimental subsoil representative for that in many others under different conditions?
The answers shot Id be: 1, that relative indices were obtained for the different crops} 2. that the results may be
fairly representative i or texturally coarse "light" subsoils; 3» that it may not be representative for texturally
fine heavier subsoils which contain large portions of silt
and clay.
In these the root penetration downwards may be
hampered by a higher ;;ioi-i rtisisianic, Inceptions are subsoil
typos, where stable crack sys •cents a;r<* developed such as in
the case of some occasionally drained layora of glacial
clays and gyttja clays. .'In iheso t lie conditions fox" root
penetration and root activity arc lavourabte down to the
water table (cf. Viklert, I960),
Observing these exceptions the experimental results obtained
may be regarded as rather representative or as medians of
what can be expected under field conditions, i 01 further
analyses of the experimental results the (iata of Table»
3-5 were computed«
Table 3 is based on the content of J"'"'Cs p*-r kg dry matter
of the crop products (Table l) and on the moan yield level
of the five crops during 1966-1J/7O (Table 2 ) . It intends
to give the total amount of 1 °7Cs accumulate»' i.ix the crop
products at mean yield levels.. Table H is derived by transformation of data in Table 3 on the uptake from thin layers
to data on the
""Cs-uptake from the layers of a homogene-
ously contaminated soil down to 110 em depth.
Table 4 shows thai the total uptake of " ' C s by peas ia
4-12 times that of the other crops. About the same rela90
tionship between the crops exist with regard to the
Sr
uptake
(Fredriksson et al., 1969)» Cultivation of peas
or other legumes is
thus not suitable on containino.ted
lands or where fission products may be found on a depth
less than ho cm. Ley (grass) and barley are the most suitable crops under such conditions. At depths of 60 cm and
more there is no difference between the crops with regard
to the amounts of 137Cs taken from the soil. Less than
10 ppm of the amount of 1T7
- 'Cs in the soil from below that
level is found in the crops. On subsoils rich in clay and
potassium less than 1 ppm should be the expected level for
90
accumulation
in
a crop. Corresponding values for
Sr can
be estimated to 100 ppm of that in the soil and half or a
third of that from a subsoil rich in calcium. Intense use
of potassium fertilizers and lime for crop cultivation may
furthermore reduce the uptake from the subsoil and dilute
337
90
in the plants the amounts of
Cs and
Sr taken up.
V, C onelus ions
Krom the data obtained i i e,->u b*:- co;?c..i.udoii that
1. After a liäavy In.lioul h;u; boei; "i:i\ud :inio t lie top soil
layer- crops like peas and oth^r .l.(>^imi«\s and white
mustard should be avoided. Cereals and grasses contribute much less than these to the total transport of
fission products along the food chain.
2» At reclamation of contaminated land by deep plowing,
i.e. turning; down the surface layer, a placement depth
of 3O~hO era considerably reduces the uptake of fission
products by the crops. The absolute amounts taken up
may still be high for peas and oats. Theusfi not feasible
by ploughing a placement depth of 60 cm and more should
give better results for these crops.
3, When contaminated land is reclaimed by taking away the
contaminated surface layer the collected material can
be placed with comparative safety in most subsoils at
a depth of one metre or more. The ion uptake from these
levels seems to be rather small.
VI.
Fredriksson,
L . (1963)
Stuxii.es
or? p i a i j t
i:•; •••;:.,-• >••' :-r. ><•;,, ^ r
fission products under Swedish co-u . • i v-is« Vi * A
new experimental technique for stui;T-
o? t>.l a i ab
sorption of nutrients and fission pro-.v-xcx---. irnd'.:r
i'ield conditions. FOA 4 rapport A h'j::"•• -'*i-?3 -• försvarets f orslaiingsans t n± t,
};Xre(5riksson, L*f
Kriksson, A.
S
&
iö.ns jö,
}i* "i 9o*> * bt utin •••
on plant accumulation of fission pr-oduf :,s un*Jer
Swedish conditions, VIII. Uptake of ~~''Cs xv. agricultural crops as ini'l uenced by soil charuetevistie-.
and rate of potassium
ferti.1 i^ation ?.r* a throe ya-w
micro plot experiment. !"0A ''i "rapport A hh^(>^h(>2'}.
Försvars i:s f orslcnin^^an-vtai t, Stockholm
Fredriksson, L. , iiaak, E . & Eriksson, .A • 1969» Stu-die.s oxi
plant accuinulation of fission products under Swrdisb
conditions. XI» Uptake of "' Sr by different crops
as influenced by liming ;ux<\ soil tillage operations.
FOA k rapport C '(395-28. Försvarets
forsioiin^sanstal
Stoclcholm
Olofsson, S, I962. Tillväxt och kemisk sammansättning ho:
några vallgräs under våren och försommaren t Staten:-:-
Jordbruksförsöks Medde Nr 135»
Wiklert, P. i960. Studior av rotutvecklingen hos några
nyttoväxter med särskild hänsyn till markstrukttiren6
Grundförbättring, 13, 113-1^8.
f
T. O .
Table 1. Yields, and the content of
IT'
"'Cs in the crop products, obtained in
the experiments. (Contrcnin:«.tion 3.ovel: £80 ^Ci perrc*~ir. May 196l.)
Crop,
*" e a r „, .
Barley
(196D
Placement
Yield, f* dry
Content of
depth of
natter per EI"
dry natter
13T
Seed
Gtrav
Seed
2^1
301;
2*>2
277
123
207
2P.5
286
333
ii;.:>
e.5
C s 4 cm
7
15
35
60
85
110_
Mean
Peas
(1961)
7
15
35
60
3H3
279
__197__ ___262_
232
268
370
137
139
170
85
255
lHl
110
206
Mean
YJhite
mustard
(1963)
Oats
(196U)
(1965)
303
631
38.9
20.
22.7
11. 8
1):.6
18.0
9.
8.0
l.U
lU.2
7.It
1.7
0.9
ljL31_.l
720. B
100.0
2168,1
100. 0
HI*. 2
1281.2
16U.9
lfi.?
10.1
2U8.2
1.0
3'f.O
U6. 3
9.,0
l.,2
1.5
1.0
0.02
8.1
0..3
0.1
0.002
3-2
0.,1
100.,0
5.0
7U7.O
181.5
U9.0
1.1
20.0
2,.7
0.6
lU.5
1,.9
o.i»
10.8
1,.U
»4? 3
1?3J>..5
59
76
192
255
221.0
60
225
85
65
66
62.0
lU.O
110
81
233
275
7.1*
H.5
Mean
68
230
7
363
273
318
320
2Ul
klk
3U5
U27
377
*»95
100.0
17.8
100.0
163.0
120.5
2U.5
9.5
63.9
U7.2
9.6
3.7
0
0
»406
3U2
U06
310
(1st cut) (2nd cut) (1st cut)
295.0 100.0
83
179
65.8
19^.0
168
80
86
198
200
85
175
110
200
Mean
100. 0
23.0
200
7
15
35
60
Ctraw
192.8
61
15
35
60
C s , nCi per kg
100.0
7
15
35
05
110
Mean
Ryeprass
U7U
U6H
636
10£.3,
13T
83
87
78
6.U
H.8
fc.o
2U..3
6,.6
32LJ0 100 .0
21H.0 65
1U3.0 U3 .7
9 .9
32,5
H .7
15.5
5.8
1 .8
.u
(2nd cut)
157.0 100 .0
66.0 h?..0
lU.O
8 .9
2.2
11.9
1.6
l.U
5.9
U.l
7 .6
3 .8
2 .6
11
Table 2. Mean yields in Gveden for the years 19&6-197O in g dry matter
2
per E
2
Yield, % dry matter per w
Crop
Seed
Straw
Hay
Barley
2hO
300
-
Peas
210
300
-
White nustard
120
300
-
Oats
2U0
300
-
1st cut
-
-
3^0
aftermath
-
-
170
Ley
a) estimated value
a/
J
i;».
T a b l e 3 . C a l c u l a t e d ? i e e u n a ! o . t . i o n r-r ' ' ( : - •?r>. t n - :
* •; . '.'
''• f
I.lit'
I • > ,
mean yield data in Table 2. """Cs -con..or
ppr; of ~ ''Cs placed on different
Placement
dejln-
1*S7
~ C G accumulated ir the crop,
depths in ppm of """' Cs in soil (nCi/n /•'
Crop
Peas
cm
Seed
ntrav
Seed
7
385. it
9U0.1*
1325. 8
15
170. 3
391.9
1)62.2
35
39. 0
63.8
122. 8
60
h.0
11.5
15.
85
0.
2.7
3.Q
0.02
1.1
1
110
White
mustard
Oats
7
167. 3
252.I
i;l?.
15
29. 9
61.3
91.
35
3.h
16.5
?u.9
60
1.9
6.8
8,7
fc.9
5..9
l
85
0
110
0.6
3.7
7
68. 0
110. h
15
hh.,0
f C . £-
35
6o
32,.5
6,,6
US. 3
11.0
05
2,,6
110
Barley
7
15
^.3
3 79.,3
U6.,2
80.,8
17..6
7,.8
0
2.0
2,.0
28.. 7
6,. 6
65.I
93,.8
13.1
19..7
•
35
0..1
7-7
13 .0
60
k..2
6.1
10..3
85
2,.3
h.8
7.1
110
0,.»4
0.6
1 .0
Ley (rye -Krass)
1st cut
aftermath 1 s t «:u
30.1
1^2 .9
15
11? . 8
Ik <->
12.6
35
5 .6
2.7
Gd
2. 5
C . J
65
1.8
1.2
86.8
8.3
.8
3.0
110
1 .5
O.O
2 ^ ->
7
: . T ~>'";•"M.""f.G
ir.
Table k. C o n t r i b u t i o n from d i f f e r e n t
of
A
Goi.l l a y r s U. t h e ;-.cnr'Vilati.or
"'C3 in t h e cropi; a t ;i hoTrsoronooua e<:>r;t:t?-i n a t i o n of t h e
0-110 cm s o i l p r o f i l e with 1 raCi ~'~'lCs per r;'' ,
of d a t a in Table 3 . The uptake w i t h i n
fe
("Jransformction
l.-^yer 0 - 7
crn i c
regarded a s c o n s t a n t and equal t o tue c o u t r i b u t i o u from t h e
l a y e r a t 7 cm depth.
Soil
layer,
ii
ii
nCi
137
Peo.s
cm
imite
Oat G
DarIcy
(rye crass)
iraistard
0- 15
153.0
15- 35
35- Co
62.3
15.7
60- 85
85-110
Total
Cs in the cro£_ per n"
1.5.S
10.6
25?.?
10.1
17.9
3.0
P
3.B
11.?
2.1
1.5
?..!
1.7
2.?
?.O
0.9
0.5
1.2
1.1
0.9
0.6
233.6
62.5
18.7
29.0
1T.I.
^