Journal of Environmental Radioactivity 130 (2014) 22e32
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Potassium fertilization and 137Cs transfer from soil to grass and barley in Sweden after the Chernobyl fallout K. Rosén a, M. Vinichuk a, b, * a b
Department of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, SE-750 07 Uppsala, Sweden Department of Ecology, Zhytomyr State Technological University, 103 Chernyakhovsky Str., 10005 Zhytomyr, Ukraine
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 June 2013 Received in revised form 18 December 2013 Accepted 19 December 2013 Available online 9 January 2014
Fertilization of soils contaminated by radionuclides with potassium (K) and its effect on 137Cs transfer from soil to crops is well studied in field conditions; however experiments over many years are few. The effects of potassium fertilization on cesium-137 (137Cs) transfer to hay, pasture grass, and barley growing on organic rich soils and mineral sand and loam soils in a number of field experimental sites situated in different environments in Sweden are summarized and discussed. The basic experimental treatments were control (no K fertilizers were applied), 50, 100, and 200 kg K ha1. In the experiment, which lasted over 3e6 years, 137Cs transfer factors in control treatments ranged between 0.0004 m2 kg1 (barley grain on sand soil) and 0.07 m2 kg1 (pasture grass on organic rich soil). Potassium application on soils with low clay content i.e. mineral sand and organic rich soils was effective at the 50e100 kg ha1 level. Application of 200 kg K ha1 resulted in a five-fold reduction in 137Cs transfer for hay and up to four-fold for barley grain. The effects of potassium application were generally greater on sand than organic rich soil and were observed already in the first cut. After K application, the reduction in 137Cs transfer to crops was correlated with 137Cs:K ratios in plant material. Additional application of zeolite caused a 1.4 reduction of 137Cs transfer to hay on sand and 1.8-fold reduction on organic rich soil; whereas, application of potash-magnesia and CaO had no effect. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Countermeasures Radiocesium Potassium Pasture grass Soil
1. Introduction The nuclear accidents at Chernobyl and Fukushima highlighted that agriculture is unprotected against radioactive contamination. Cultivation of 137Cs contaminated soils with low fertility and low K status present farmers with huge challenges and problems. The downward migration of cesium in the majority of soil types is generally slow, but radionuclide bioavailability and transfer rates through the soileplant system in soils with low K status are high (Rosén et al., 1999, 2009). Several studies conducted in both field (Pietrzak-Flis et al., 1994) and lysimeter experiments (Yera et al., 1999) indicate the concentration of 137Cs in crops varies and depends upon the type of soil, being higher in sand and peat and lower in loam and clay soil. Since the transfer factors for 137Cs are
* Corresponding author. Department of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, SE-750 07 Uppsala, Sweden. Tel.: þ46 18 671442; fax: þ46 18 672795. E-mail addresses: [email protected], [email protected] (M. Vinichuk). 0265-931X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvrad.2013.12.019
higher in peatlands and in organic soils than in mineral soils (Veresoglou et al., 1995), cultivation of peatland increases longterm radiocesium contamination of crops. The inhibitory effect of potassium addition on the uptake of radiocesium in a relatively infertile soil in lysimeters under simulated field conditions has been shown to depend on the stage of plant growth, age-related demand for potassium by the plant (Zhu et al., 2000) and its concentration in the growth solution (Zhu, 2001). Commonly used agricultural practices such as liming and the use of increasing amounts of NPK fertilizers generally decrease 137Cs transfer to plants in natural meadows (Vidal et al., 2000). Cesium uptake is inhibited when the potassium concentration in soil solution increases (Waegeneers et al., 2009). Thus, potassium fertilizers are an effective countermeasure, especially on nutrient poor soils with low K status (Smolders et al., 1997) and low degree of base saturation (Rosén et al., 2011). Thus, the application of fertilizers containing potassium at elevated rates is one of the most effective countermeasures for reducing radiocesium uptake (Perepelyatnikov et al., 2007); however, the effectiveness varies according to both soil characteristics and plant species (Vinichuk et al., 2013). Cultivation of peatlands in
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
northern conditions limits the selection of plants and increases long-term radiocesium contamination of crops (Root et al., 2005), although regional features of soil and climate require additional studies on radionuclide transfer within food chains. Other absorbents, such as bentonite also affect the equilibrium of cesium in soil and its availability to grass (Vandenhove et al., 2003). Although the long-term effect of biotite on reducing 134Cs uptake by ryegrass from peat soil is reported (Paasikallio, 1999), a significant reduction (up to a factor of 8) in uptake of 134Cs by winter wheat has been obtained after application of mineral zeolite in pot experiments (Shenber and Johanson, 1992). Studies on the inhibitory effect of potassium on root uptake of cesium by crops growing on nutrient poor sandy and organic soils are limited. Prior to 1986, in Sweden and in the other Nordic countries, only pot and mini-plot field experiments dealing with the effect of potassium on 137Cs transfer to crops have only been carried out on soils artificially contaminated with radionuclides (Lönsjö and Haak, 1986). During the period 1987e1992, our experiments with potassium fertilizers and other specific clay minerals that mitigate 137Cs transfer to hay, pasture grass and barley grown on organic rich soil, mineral sand and loam soils indicated that repeated annual potassium fertilization was an effective and practicable countermeasure for reducing contamination of agricultural products by radiocesium. However, the Chernobyl accident made it possible to perform wide-ranging field studies aimed at reducing cesium transfer to crops in number of new environments and practical conditions, including “sensitive” with respect to cesium bioavailability organic rich soil and mineral sandy soils (Rosén et al., 1996). Results from field experiments on the effects of potassium fertilization on cesium transfer to plants growing on peatlands are limited and it is not known how long lasting the effect of potassium application on peat soils can be. The objective of this study was to investigate the effect of potassium application on cesium transfer to grass and barley under
23
field conditions on organic rich soil and mineral soils in northern Europe after the Chernobyl fallout. The hypotheses tested within this field study were whether potassium fertilizers could reduce uptake of cesium on organic rich soil and sand soils efficiently; how long lasting could the residual effect after fertilization be; and, if there were any combined effects of potassium and liming or potassium and zeolite. In this study, different fertilizers and doses were tested and 137Cs transfer to hay, barley, and pasture grass were assessed after application of an increasing supply of potassium fertilizers on organic rich soil, mineral sand and loam soils. The investigation started in 1987 and lasted between 3 and 6 years depending on the crop cultivated. Data obtained within this study have not been previously published in international journals, yet they are of practical interest; to our knowledge, few field studies have been conducted on organic rich soil and sand soils since the Chernobyl accident in 1986. The release of radionuclides at Fukushima Daiichi in Japan has re-invigorated interest in the transfer of 137Cs from soil to agricultural plants and potential countermeasures (Smolders and Tsukada, 2011). 2. Materials and methods The field experiment was conducted in four different counties in Sweden: Uppsala county (C), Gävleborg county (X), Västernorrland county (Y), and Jämtland county (Z). There were nine different farms, referred to here as CU, X, Y, Z, within which there were fourteen experimental 14 sites (Table 1). Latitude and longitude were determined by GPS (GeoExplorer CE Series) with error of 2e 5 m. The soil at all experimental fields was not plowed after the fallout in 1986, except for barley fields (X9 and X11), which were plowed each year. In 1986, the age (the number of years since the land was last plowed) of grasslands varied between 1 and 5 years (CU711, X9, X11, Y48, Y56 and Z2) and 15e35 years (C2, Z1 and Z3) (Table 1).
Table 1 County and sites for experiment, soil characteristics, 137Cs deposition at the beginning of the experiment. Farm numbera
Exp. plotb
Site
Treatmentc
pHH2 O
OM,d %
KAL
KHCl
CaAL
CaHCl
Deposition, kBq m2
GPS
74.1 74.1 51 202 202
59 570 5300 N, 59 570 5300 N, Nearby C1 60 440 0700 N, 60 440 0600 N,
170 170
60 490 0700 N, 17 130 4600 E 60 490 0800 N, 17 130 5200 E
mg/100 g d. wht.e Organic rich soil CU711 CU711 C2 X9 X9
C-1 C-1 C-2 A B
Järlåsa Järlåsa Järlåsa Hille Hille
K KþZ K K K
5.8 5.8 6.0 6.2 6.2
Sandy soil X11 X11
A C
Trödje Trödje
K K
6.5 6.5
Loamy sand soil Y48 Y56 Y56 Y56
A A A A
Holmsta Berge Berge Berge
K þ Mg K KþZ K þ CaO
Silt loamy sand soil Z1 A Z2 A
Hammarstrand Hammarstrand
Gravely sandy loam soil Z3 A
Blåsjön
a b c d e
40 40 83 51 77
17 140 1300 E 17 140 1300 E
9.1 9.1 17.5 8.8 13.5
88 88 47 44 56
745 745 1301 537 584
1364 1364 3235 1807 1493
5.0 5.0
6.1 6.1
163 163
77 77
145 145
6.0 5.9 5.9 5.9
6.8 6.8 6.8 6.8
18.7 15.1 15.1 15.1
154 52 52 52
304 77 77 77
562 195 195 195
27.1 82.5 82.5 82.5
63 160 1500 62 420 2900 62 420 2900 62 420 2900
K K
5.9 5.5
9.3 18.7
15.1 31.6
52 160
98 171
260 623
38.0 33.2
63 050 5500 N, 16 210 5800 E 63 040 4500 N, 16 210 1600 E
K
5.9
9.3
18
142
186
182
44.2
64 500 3900 N, 14 080 5600 E
Farm numbers referred to counties: Uppsala e C; Gävleborg e X, Västernorrland e Y, Jämtland e Z. Soil depth 0e10 cm. Treatments: K e potassium, Z e zeolite, Mg e potash-magnesia, CaO e lime. OM e organic matter. Extracted with ammonium lactate (AL) and hydrochloric acid (HCL) (Egner et al., 1960).
N, N, N, N,
17 120 0500 E 17 110 5800 E
16 420 5500 17 510 4300 17 510 4300 17 510 4300
E E E E
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K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
2.1. Experimental layout and treatments
2.2. Sampling
The experimental crops were hay grass (8 experimental plots), pasture grass (4 experimental plots), and barley (2 experimental plots) grown on organic rich soil, mineral sand and loam soils and plants were grown during 3e6 successive years (Table 2). All experiments were randomized; some had a completely randomized design (CRD) and some with a randomized block design (RBD) or a split plot design (SPD). A basic annual fertilization regime with nitrogen (N) 60 kg ha1, and phosphorus (P) 20 kg ha1 was applied to all experimental plots. Potassium (K) fertilizer (50% KCl) was applied annually in the range of 0e200 kg K ha1 for most plots except CU711* (C-1, hay) and X11* (A, hay) (Table 2). Experimental plots CU711* (C-1, hay) and X11* (A, hay) were repeatedly fertilized with potassium until 1990 (the fourth year): fertilization was then discontinued to evaluate the residual effects in the fifth and sixth years (1991, 1992). As Y48 (A, hay, ecological farming) field experiments had higher K-supplied soils, moderate potash-magnesia (in the form of potassium-magnesium sulfate, 23% K and 6% Mg) fertilizers were applied, whereas, Z1, Z2 and Z3 experimental plots were given a complete fertilizer, NPK 20-5-9 and 200 kg K was applied first time in 1988 (the first year, Table 2). The 100 þ 100 kg K ha1 treatment comprised 100 kg K ha1 being applied to the first cut, and a further 100 kg K ha1 being applied to the second cut (Table 2). At farm Y56 þ CaO (A, hay), 4000 kg of CaO ha1 was applied once (1988) to split plot arrangements. The same amount of a natural zeolite (4000 kg ha1 aluminosilicate minerals, similar to clay soils, referred here as þ Z) was applied once in 1988 (the first year) to grassland on experimental plots CU711 þ Z (C1, hay) and Y56 þ Z (A, hay) (Table 2). Unfertilized plots were used as controls. Each treatment was replicated three times on all experimental plots.
The sizes of individual plots were 16, 25, or 50 m2 (Table 2). Within each experimental plot, 4 sub plots of 0.25 m2 in size were randomly selected for sub sampling of the crops at harvest time. Each year, ley and pasture were harvested twice and barley once. The sub samples were pooled into a bulk sample. Plants were cut at a height of 5 cm above the soil surface and the grains and straw of barley plants were separated. To describe the soil properties of the experimental plot, soil samples were taken from each treatment. Ten soil samples were randomly sampled to a depth of 0e10 cm with a cylindrical core of 57 mm in diameter. For the calculation of deposition (137Cs Bq m2), the soil was sampled randomly over a 100 m2 area around the experimental plots to the depth of 0e5 cm with a core 57 mm in diameter. Bulk soil samples were formed by pooling 10 or 15 cores. 2.3. Analysis 137
Cs activity concentrations in all plant and soil samples were determined by calibrated HP-Ge detectors at the low background laboratory at the Department of Radioecology, Swedish University of Agricultural Sciences and corrected for decay. Before measurement, all samples were dried at a maximum temperature of 40 C and sieved through 2 mm sieves. The measuring time varied from 1 to 24 h in order to obtain a statistical error (of less than 5%) due to the random process of decay. Soluble K and Ca were extracted with ammonium lactate (AL) and hydrochloric acid (HCl) according to the methods described by Egner et al. (1960) Organic matter was derived from weight loss on ignition. To describe the transfer of 137Cs from soil to harvested material, an aggregated transfer factor (Tag) (IAEA, 2010) was used, defined as the ratio of the mass activity concentration in plant material dry weight (d. wht.)/unit area activity density (Bq kg1 d. wht./ Bq m2 d. wht.):
Table 2 Treatments, crops, duration of the experiment, and plot size on different soil types. Farm number
Exp. plot
Treatments,a annual amount of potassium (K) applied, kg ha1
Organic rich soil CU711b CU711b C2 X9 X9
C-1 C-1 C-2 A B
0K 0K þ Z 0K 0K 0K
50K 50K þ Z 50K 100K e
100K 100K þ Z 100K 100 þ 100K 100K
200K 200K þ Z 200K 200K 200K
Sandy soil X11b X11
A C
0K 0K
100K e
100 þ 100K 100K
Loamy sand soil Y48 Y56 Y56 Y56
A A A A
0K þ Mg 0K 0K þ Z 0K þ CaO
50K þ Mg 100K 100K þ Z 100K þ CaO
Silty loam sand soil Z1 A Z2 A
0K 0K
Gravely sandy loam soil Z3 A
0K
1
1
Crop
Duration of exp., years
Years
Plot size, m
e e e e e
Hay Hay Pasture Hay Barley
6 5 3 4 4
1987e1992 1988e1992 1987e1989 1987e1990 1987e1990
5 5 5 5 5
200K 200K
e e
Hay Barley
5 3
1987e1991 1987e1989
5 10 5 10
100K þ Mg 100 þ 100K 100 þ 100K þ Z 100 þ 100K þ CaO
200K þ Mg 200K 200K þ Z 200K þ CaO
e e e e
Hay Hay Hay Hay
3 5 5 5
1987e1989 1988e1992 1988e1992 1988e1992
5 4 4 4
23K 23K
45K 45K
90K 90K
200Kc 200Kc
Pasture Pasture
4 3
1987e1990 1987e1989
5 10 5 10
23K
45K
90K
200Kc
Pasture
3
1987e1989
5 10
5 5 10 10 10
10 4 4 4
Z ¼ zeolite e 4 t ha and CaO e 4 t ha applied once on starting year. a Annual fertilization with N (60 kg ha1), P (20 kg ha1), K e potassium fertilizer (contains 50 %of K) and Mg e potash-magnesia fertilizer (contains 23% of K and 6% of Mg). b Repeated fertilization was done until 1990 and then excluded. c Applied first time in 1988.
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
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and straw. The data in Tables 3and 4 present average values for the period of study. 137Cs reduction factors in hay (1st and 2nd cuts) and barley (grains and straw) during successive years after K application to selected experimental sites were calculated and are presented in Figs. 7 and 8. 3.1. soil
Fig. 1. The deposition of 137Cs over Sweden after the Chernobyl accident. The map is based on measurements preformed in MayeOctober 1986. The locations for seven investigated sites have been added. See Table 1 for details. Modified from Sveriges Nationalatlas (2008).
Tag ¼ radioactivity in plant material; Bq kg1 =radioactivity on ground; Bq kg1 ; m2 kg1 d: wht: (1) After potassium application, the reduction factors of crops were calculated as follows:
137
Cs in the
Reduction factors ¼ 137 Cs Tag without potassium ðcontrolÞ= 137
Cs Tag with potassium; m2 kg1 d: wht:
=m2 kg1 d: wht: (2) 137
1
Cs offtake by crops (kBq ha ) was calculated as an average Cs activity concentration in crop (kBq kg1) multiplied by crop production (kg ha1). To evaluate the differences in 137Cs activity among treatments, data were subject to analysis of variance and 2-sample t-tests with Minitab (Ó2010 Minitab Inc.) software. Analyses of variance and independent 2-sample t-test we used allowed us performing a hypothesis test and computing a confidence interval of the difference between two population means. 137
3. Results For presentation and discussion of the results (Fig. 1), the experimental sites have been divided into two soil groups: organic rich soil (Table 3, Figs. 2 and 7) and mineral soil (sandy and loamy soil, Table 4, Figs. 3e6 and 8). In the tables, data are presented as average values of three replicates over three to six years of study. In Jämtland County (Z1, Z2, and Z3), K (90 kg ha1) was only applied once in 1987, therefore data for this treatment are omitted in Table 4 but shown in Fig. 5 (Year 1). In order to demonstrate the trend and variation in 137Cs transfer to crops, the annual data in Figs. 2e6 are presented separately for the 1st and 2nd cuts, grains
137
Cs transfer to hay, pasture grass and barley on organic rich
Grass (hay and pasture grass) production on organic rich soil was similar on all experimental plots and varied between 2.6 and 4.9 t ha1 for the first cut and 1.5e2.4 t ha1 for the second cut. The effect of potassium application on yield of hay was small, whereas the increment in pasture grass production (first cut, C2) was significant (p < 0.01) at 50e200 kg K ha1. The yield of barley grain (X9) increased from 5.4 t ha1 in the controls to 7.6 t ha1 in treatment 200K (Table 3). The application of potassium on organic rich soil caused 137Cs reduction in experimental crop hay (CU711, CU711 þ Z, X9): the percentage range from the control to the 1st and 2nd cut was: 34e 51% for 50 kg K ha1, 43e59% for 100 kg K ha1, and 41e83% for 200 kg K ha1. In pasture grass (C2) and barley (X9), 137Cs reduction was noticeable, although less pronounced. Even though reduction in 137Cs offtake by crops (kBq ha1) occurred at 50 kg K ha1, the reduction was only significant (p < 0.01) at 100 kg K ha1 and 200 kg K ha1 (Table 3). At harvest, there was a corresponding shift in 137Cs:K ratios after application of potassium fertilizer: in most experiments at 200 kg K ha1, 137Cs:K ratios decreased twelve-fold on the first cut and five-fold on the second cut. After potassium application, 137Cs:K ratios in plants changed, even in the first cut at 50 kg K ha1, and resulted in reduction in the potassium uptake and reduced potassium content in the plants. Potassium concentration in hay (CU711, 100 kg K ha1) dropped from 21 to 23 mg g1 d. wht. in 1987e1990 to 12e13 mg g1 d. wht. in 1991e1992 (data not shown). Fertilization reduced 137Cs offtake and 137Cs:K ratios in pasture grass (C2): this reduction was significant (p < 0.01) at 100 and 200 kg K ha1 (Table 3). In barley grain, potassium fertilization at 100 kg K ha1 and 200 kg K ha1 reduced 137Cs offtake. Although 137 Cs:K ratios were reduced at 100 kg K ha1, the reduction was only significantly different from the control at 200 kg K ha1. The additional application of zeolite (CU711 þ Z, Table 3) resulted in a similar decrease in 137Cs offtake by hay (kBq ha1), the 137Cs:K ratios in plants reduced and the percentage of the total deposition of 137 Cs accumulated in crops in both 1st and 2nd cuts decreased, compared to control. There was no difference in 137Cs between the K and K þ Z treatments. An increase in potassium e.g. from 50 to 200 kg ha1 reduced the 137Cs Tag by a factor of 3e6 in hay, 1e5 in pasture grass, about 2 in barley grain and about 1 in straw. In the second cut of hay, the 137 Cs Tag was generally lower than in the first cut, with some exceptions, e.g. in year 5 (CU711 and CU711 þ Z, Fig. 2a, b) and in year 1 (X9, hay, Fig. 2d). The reduction in 137Cs Tag was most pronounced at 50 and 100 kg K ha1 in the first cut and at 200 kg K ha1 in the second cut. Similarly, in pasture grass, the potassium rate of 50 kg K ha1 only reduced 137Cs Tag in the first cut, whereas, 100 and 200 kg K ha1 were equally effective for both the first and second cuts. 137Cs Tag was lowest in barley grain (X9) (Fig. 2e) and highest in pasture grass (C2) (Fig. 2c). The effect of potassium application on 137Cs Tag tended to decrease over time, but was still well pronounced after 5e6 years (CU711, Fig. 2a, b). In order to estimate the residual effect no potassium was applied in years 5 and 6 on the experimental plot CU711 (Fig. 7a, b). However, the effect of 137Cs reduction in hay due to potassium application on organic rich soil was similar in both cuts at the rate
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K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
Table 3 Mean crop production and Farm Crops number
137
Cs uptake by crops on organic rich soil, mean SE.
Treatments Production, ton per ha d. wht.
137
Cs Output by crops, kBq ha1 Reduction in 137 Cs in crops as % of the control
1st Cut 2nd Cut 1st Cut/grain grass/grain grass/straw CU711
Hay
CU711
Haya
C2
Pastureb
X9
Hay
X9
Barley
Control 50K 100K 200K Control 50K þ Z 100K þ Z 200K þ Z Control 50K 100K 200K Control 100K 100 þ 100K 200K Control 100K 200K
3.8 4.0 4.4 4.4 3.6 3.7 4.1 3.9 2.6 3.9 3.9 4.3 3.7 4.6 4.8 4.9 5.4 6.4 7.6
0.4 0.5 0.4 0.5 0.4 0.4 0.4 0.4 0.3 0.4** 0.3** 0.3** 0.5 0.5 0.6 0.7 1.5 1.9 2.3
1.9 1.8 1.9 2.2 2.0 1.9 2.1 2.4 1.9 2.4 2.1 2.3 1.5 1.5 1.5 1.6 1.7 1.6 1.8
0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.2 0.2 0.3 0.3 0.2 0.3 0.2 0.2 0.2
3454 737 2019 508 1843 538 773 231** 1328 165 811 166 704 161* 303 92*** 7093 966 7255 696 3475 626** 1720 535*** 10 972 2203 5556 950* 3746 1215* 4194 1828* 1017 183 399 102** 319 70**
137
Cs:K ratios in plants
2nd Cut/straw 1st Cut/ 2nd Cut/ 1st Cut/ grain straw grain 1091 676 626 227 899 545 502 229 8120 9415 3208 1664 5042 3140 1262 1111 1489 1064 663
217 182 167 66*** 129 100* 142* 64*** 1392 1055 627** 607** 1084 1144 554** 325** 456 474 245
e 51 58 83 e 44 59 83 e 34 68 88 e 56 72 41 e 52 45
e 41 47 80 e 34 51 80 e 2 61 81 e 43 78 80 e 15 22
69.9 24.5 18.3 6.7 31.8 17.8 12.5 4.1 391 138 47.5 14.7 299 79.5 49.1 83.0 76.8 34.5 21.1
10.2 2.9*** 3.4*** 1.2*** 3.8 4.1* 2.9** 1.1*** 99 23* 8.9** 4.6** 77 15.9* 15.1** 57.4* 22.5 15.6 7.8*
2nd Cut/ straw 45.2 26.9 20.2 6.7 37.5 25.6 16.9 6.1 395 268 88.4 28.9 622 186 45.4 53.6 103 65.6 24.1
10.9 8.2 5.5 2.3** 9.9 7.0 5.1 1.8** 66 39 16.3** 9.7*** 182 63* 18.1** 16.6** 17.1 25.7 7.7***
137
Cs in crops as % of total deposition 1st Cut/grain
0.80 0.45 0.43 0.18 0.31 0.19 0.16 0.07 1.39 1.42 0.68 0.34 0.55 0.28 0.19 0.21 0.05 0.02 0.02
0.17 0.12 0.13 0.05** 0.04 0.04* 0.04* 0.02*** 0.19 0.14 0.12** 0.11*** 0.11 0.05* 0.07* 0.09* 0.01 0.01 0.01
2nd Cut/ straw 0.25 0.16 0.15 0.05 0.20 0.13 0.12 0.05 1.73 1.85 0.63 0.33 0.25 0.16 0.06 0.06 0.08 0.05 0.03
0.05 0.04 0.04 0.02*** 0.03 0.02* 0.03* 0.01*** 0.27 0.21 0.12** 0.12** 0.05 0.06 0.03** 0.02** 0.02 0.02 0.01
*p < 0.05; **p < 0.01; ***p < 0.001 e the level of differences significance from the control. a 1st Cut for the year 1988: all data missing. b Crop production data for the year 1987: 1st cut was estimated as a mean value of 1988 and 1989.
50 and 100 kg K ha1. The reduction of 137Cs in hay at 200 kg K ha1 was pronounced and reached a maximum for first cut in the second year after fertilization, and for second cut in the fourth year after fertilization (Fig. 7a, b). At experimental site X9 hay, the effect of potassium application on 137Cs reduction in hay increased over time, being higher in the second cut at 100 þ 100 kg K ha1 (Fig. 7c, d). At X9 barley, the reduction factors of 137Cs in barley grains due to potassium application were highest during the second to fourth year after fertilization and at both 100 and 200 kg K ha1 (Fig. 7cee). 3.2.
137
Cs transfer to hay, pasture grass, and barley on mineral soil
Potassium application on sandy soil had no effect on hay production (X11, first and second cut) or effect was small (Y56, Y48 first and second cut) (Table 4). For barley grains (X11), production increased appreciably from 2.3 to 4.0 t ha1. The application of complete NPK fertilizer (potassium range between 23 and 45 kg ha1) on loam soil increased the yield of first cut pasture grass (Table 4). On sandy soil, 137Cs offtake by hay (kBq ha1) decreased at both X11 and Y56 experimental sites at 100 þ 100 and 200 kg K ha1. The reduction in 137Cs in hay (X11 and Y56), as a percentage of the control due to fertilization, was about 55% at 100 kg K ha1 and about 76% at 100 þ 100 and 200 kg K ha1. In barley grains (X11), the reduction in 137Cs was between 63 at 100 kg K ha1 and 74% at 200 kg K ha1. At Y48, the reduction in 137Cs in hay was different: 137 Cs offtake by hay decreased with an increased rate of potassium only marginally (Table 4). Potassium fertilization at 100 and 200 kg K ha1 narrowed the 137 Cs:K ratios in both hay and barley grains. These effects were less pronounced in the K þ Mg treatment, however, the 137Cs:K ratios in treatments with K were two-fold narrower than on the control treatment in both first and second cuts (Table 4). 137 Cs in crops, as a percentage of the total 137Cs deposition, decreased in hay after potassium application at X11 and Y56. The uptake of 137Cs, as a percentage of total cesium deposition, was higher on pasture (Z2, Z3) than on other grasslands (Table 4).
The additional application of CaO in combination with potassium generally had no effect on 137Cs transfer to hay, and the addition of zeolite (Y56) or potash-magnesia (Y48) only had a small effect on 137Cs transfer (Table 4). In experiments X11 and Y56, there was a four to five-fold reduction in 137Cs Tag in hay for the 100 kg K ha1 potassium and 200 (or 100 þ 100) kg K ha1 potassium treatments (Figs. 3a and 4b). In pasture grass (Z1, Z2, Z3), potassium did not affect the 137Cs Tag (first and second cut) when a complete fertilizer was used, at 200 kg K ha1, the effect was positive in both the first and second cuts. An appreciable (about three to four-fold) decrease in 137Cs Tag was observed in barley grain (X11) (Fig. 3b). The additional application of zeolite resulted in a (one and a half-fold) decrease of 137Cs Tag in hay (Y56) in the control and 100 kg K ha1 potassium treatment: this effect was not seen with 200 (or 100 þ 100) kg K ha1. In the treatment with potashmagnesia (Y48), the reduction of 137Cs Tag in hay was most pronounced at 50 kg ha1 potassium: 137Cs Tag reduced by 50%; whereas, at 200 kg ha1 potassium, the reduction was about 30%. Additional application of CaO had no effect on the 137Cs Tag in hay. With complete fertilization (NPK), the effect of potassium on 137Cs Tag in pasture grass was negative at 23 kg K ha1 (2nd cut), small at 45 kg K ha1, and had no effect at 200 kg K ha1 (Fig. 5b). In barley grains growing on sandy soil (X11, Fig. 3b), the reduction of 137Cs uptake during successive years was similar to that observed on organic rich soil (X9, Fig. 7e). The reduction factors were highest during the second and third years after potassium application at both 100 kg K ha1 and 200 kg K ha1. In the experimental plot at X11 hay, no potassium was added after year 4 and the reduction factor of 137Cs uptake in the fifth year dropped to the level observed in the first year. The reduction in 137Cs uptake by hay on sandy soil (X11, Fig. 8a, b) gradually increased over time and reached a maximum in both cuts in the fourth year after potassium application. Both rates of potassium application at 100 þ 100 and 200 kg K ha1 had similar effects. In pasture grass (Z1, Table 4), there was no effect of complete NPK fertilizer application (either 23 or 45 kg ha1 potassium) on 137 Cs offtake: 137Cs Tag reduced slightly (first cut) or increased
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
a
CU711, hay
0.040
0.035 0.030
CU711, hay
0.020
Control Z 50 K+Z 100 K+Z 200 K+Z
0.015
0.025
Cs Tag
Cs Tag
b
Control 50 K 100 K 200 K
27
0.020
0.010
0.015
0.005
0.010 0.005
0.000
0.000
2nd
1st 2nd 1st 2nd 1st 2nd 1st 2nd 1st 2nd 1st 2nd 1
2
3
4
5
1st
2nd
1
6
1st
2
Year, cuts
c
C-2, pasture
0.16
d
Control 50 K 100 K 200 K
0.14
1st
2nd
1st
2nd
4
X9, hay
5
Control 100 K 100+100 K 200 K
0.12 0.10
0.12
0.08
0.10
Cs Tag
Cs Tag
2nd
3 Year, cuts
0.08 0.06
0.06 0.04
0.04
0.02
0.02 0.00
0.00
1st
2nd 1
1st
2nd
1st
2 Year, cuts
1st
2nd 3
e0.020
2nd
2nd 2
X-9, barley
1st
Year, cut
2nd 3
1st
2nd 4
Control 100 K 200 K
0.016 Cs Tag
1st
1
0.012 0.008 0.004 0.000 1
2
3
4
1
Grain
2
3
4
Straw Year
Fig. 2. Transfer of
137
Cs on organic rich organic rich soil, mean SE: hay (a, b, d): pasture (c) and barley (e). No potassium was applied in year 5, 6 (a) and year 4, 5 (b).
(second cut). Similarly, 137Cs:K ratios reduced in the first cut of pasture grass, but increased (23 kg ha1) or did not change (45 kg ha1) in the second cut. However, the positive effect of potassium application on 137Cs reduction in pasture grass (Z1) was only seen at 200 kg ha1. In pasture grass at Z2 (Table 4), the effects of complete NPK fertilizers application (23 and 45 kg ha1 potassium) on 137Cs reduction were similar to at Z1 (Table 4, Fig. 5a, b). In pasture grass (Z3, Table 4); the effect of potassium application on 137Cs Tag was negative in both cuts at 23 kg K ha1, but positive in both cuts at 45 and 200 kg K ha1. The reduction in 137Cs activity concentration in pasture grass at 200 kg K ha1 on loamy soil was similar (ca. 80%) to the reduction on organic rich soil and mineral sand soils, and resulted in three to six-fold decrease of 137Cs Tag (Table 4, Fig. 6). 4. Discussion Organic rich soil. For six successive years of potassium application on organic rich soil at the rate of 50 kg ha1 yearly caused on average a two-fold reduction in cesium transfer to hay. The increased amount of potassium, applied from 50 to 200 kg ha1, led to future substantial decrease in 137Cs Tag from soil to hay. Thus, a
fertilization rate of 100 kg ha1 resulted in a two to three-fold decrease in cesium uptake, and subsequent increment of potassium application at the rate of 200 or 100 þ 100 kg K ha1 resulted in a four to five-fold decrease in cesium transfer to hay during the study period. Thus, in pasture grass on organic rich soil fertilized with 200 kg K ha1, an 80%, reduction in 137Cs (Bq kg1, Tag), as a percentage of the control, appeared achievable. Maximum 137Cs uptake reduction in hay (up to a factor of 20 or even higher) appeared realistic in the third or fourth years after potassium application (CU711, Fig. 7). The attenuation in 137Cs reduction years 5 and 6 was probably due to potassium loss through leaching, as the last fertilization was in year 4. Plant available potassium is depleted from soil through plant uptake/harvesting or through fixation on clay minerals, therefore, the annual application of potassium fertilizers is necessary to restore elemental losses from organic rich soil and reduce radiocesium contamination of crops. For both barley grain and straw, the effect of potassium fertilization on organic rich soil was similar to that observed for hay. This indicates that an average 80% reduction in 137Cs (Bq kg1, Tag), as a percentage of the control might be also achievable. 137Cs uptake reduction in barley increased during following second, third and fourth years after potassium application: the reduction factors of
28
Table 4 Mean crop production and Farm number
Crop
Sandy soil X11
Hay
X11
Barleya
Y56
Hayb
Y56
Hayb,c
Y48
Hay
Silt loam soil Z1
Pastureb
Z2
Pastured
Gravelly sandy loam soil Z3 Pasture
Cs uptake by crops on mineral soils, mean SE. Treatments
Production, t ha1 d. wht.
137
1st Cut/grain
1st Cut/grain
2nd Cut/straw
Control 100K 100 þ 100K 200K Control 100K 200K
4.0 3.8 4.1 4.2 2.3 4.0 4.0
0.7 0.7 0.7 0.8 0.4 0.7 1.0
1.7 1.4 1.8 1.7 4.7 5.6 5.3
0.2 0.3 0.3 0.2 1.3 1.4 1.4
Control 100K 100 þ 100K 200K Control 100K þ CaO 100 þ 100K þ CaO 200K þ CaO Control 100K þ Z 100 þ 100K þ Z 200K þ Z Control 50K þ Mg 100K þ Mg 200K þ Mg
4.4 4.8 4.8 4.6 4.2 4.4 4.6 4.6 4.4 4.9 4.5 4.7 0.9 1.1 1.1 1.1
0.4 0.3 0.3 0.4 0.4 0.4 0.3 0.3 0.4 0.5 0.5 0.4 0.2 0.3 0.3 0.3
1.9 1.9 2.3 2.6 2.3 2.0 2.5 2.5 1.8 2.3 2.1 2.6 0.9 1.0 1.2 1.2
Control 23K 45K 200K Control 23K 45K 200K
0.9 1.6 2.1 2.3 0.7 1.8 1.6 1.5
0.1 0.2* 0.4** 0.4** 0.1 0.4 0.2** 0.2**
1.1 1.5 1.8 1.6 1.1 1.2 1.1 0.9
Control 23K 45K 200K
0.4 1.0 1.3 1.7
0.1 0.1*** 0.1*** 0.2***
0.5 1.1 1.5 1.3
Cs Output by crops, kBq ha1 2nd Cut/straw
Reduction in 137Cs in crops as % of the control
137
1st Cut/grain
2nd Cut/straw
1st Cut/grain
137
Cs:K ratios in plants
Cs in crops as % of total deposition
2nd Cut/straw
1st Cut/grain
2nd Cut/straw
2103 1112 539 612 131 69 45
400 332 154** 221** 33 20 12*
1353 370 157 246 818 749 591
376 140* 60** 99* 332 386 240
e 54 78 73 e 63 74
e 72 89 84 e 37 50
34.7 11.0 4.4 5.7 10.2 3.9 2.8
2.5 2.0*** 0.8*** 1.5*** 2.6 1.3* 0.8*
41.9 9.6 3.1 4.7 9.8 4.9 4.7
3.9 1.8*** 0.6*** 1.0*** 2.4 1.8 1.0
0.12 0.07 0.03 0.04 0.008 0.004 0.003
0.02 0.02 0.01** 0.01** 0.002 0.001 0.001
0.08 0.02 0.009 0.014 0.048 0.044 0.035
0.02 0.01* 0.004** 0.006* 0.02 0.02 0.01
0.2 0.2 0.2 0.2* 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.2** 0.2 0.2 0.2 0.2
787 404 227 212 904 505 276 225 496 241 202 175 25.9 14.1 12.6 17.5
239 90 63* 55* 255 168 86* 68* 100 61* 62* 45** 8.4 5.2 2.7 5.9
464 198 88 116 437 262 139 146 306 141 104 101 22.0 11.9 20.3 17.8
121 62 26* 36* 96 86 39* 55* 83 44 32* 26* 6.2 3.8 4.5 4.2
e 53 76 78 e 50 73 79 e 54 58 66 e 48 47 22
e 57 82 82 e 33 73 74 e 64 72 78 e 44 21 34
10.5 3.8 1.6 1.4 13.2 4.1 2.2 1.6 6.5 2.6 2.3 1.7 1.4 0.6 0.6 0.8
3.2 0.9 0.4* 0.3* 3.3 1.2* 0.6** 0.4** 1.3 0.8* 0.8* 0.5** 0.2 0.2** 0.1** 0.2
14.3 4.9 1.6 1.9 13.1 6.2 2.3 2.6 8.6 2.7 1.8 1.6 1.1 0.5 0.7 0.5
3.8 1.6* 0.5** 0.6** 3.1 1.9 0.7** 0.9** 2.2 0.8* 0.5* 0.4** 0.2 0.2* 0.2 0.1*
0.07 0.04 0.02 0.02 0.08 0.05 0.03 0.02 0.05 0.02 0.02 0.02 0.007 0.004 0.004 0.005
0.02 0.01 0.01* 0.01* 0.02 0.02 0.01* 0.01* 0.01 0.01* 0.01* 0.01** 0.002 0.002 0.001 0.002
0.04 0.02 0.01 0.01 0.04 0.02 0.01 0.01 0.03 0.02 0.01 0.01 0.006 0.003 0.006 0.005
0.01 0.01* 0.002* 0.003* 0.01 0.01* 0.01** 0.01** 0.01 0.004 0.003* 0.002* 0.002 0.001 0.001 0.001
0.2 0.2 0.3* 0.3 0.2 0.2 0.2 0.2
139 255 313 65.4 395 829 701 370
35 47 80 16.9 117 246 120 107
266 702 510 146 627 817 348 247
69 200 151 87 287 324 141 82
e 4.5 8.4 76 e 15 11 56
e 65 15 72 e 17 38 40
10.4 8.4 6.6 1.4 32.4 16.8 14.4 5.6
2.9 1.2 1.9 0.4* 10.3 3.2 3.4 2.5
13.0 22.4 12.7 2.7 26.9 33.4 15.1 11.9
3.4 5.1 3.9 1.3* 7.9 6.3 3.9 3.1
0.04 0.07 0.08 0.02 0.12 0.26 0.22 0.12
0.09 0.01 0.02 0.004 0.04 0.08 0.04 0.03
0.07 0.19 0.14 0.04 0.19 0.26 0.11 0.08
0.02 0.05 0.04 0.02 0.09 0.10 0.04 0.03
0.1 0.1*** 0.2*** 0.1***
870 2622 2116 909
98 341*** 289*** 235
1621 3023 3065 556
264 499* 786* 211**
e 8 29 82
e 2 34 87
157 136 68 12
29 20 9.4** 2.9***
323 223 115 15
57 32 24** 6.6***
0.28 0.82 0.66 0.28
0.03 0.11*** 0.09*** 0.07
0.51 0.95 0.96 0.17
0.08 0.16* 0.25 0.07**
*p < 0.05; **p < 0.01; ***p < 0.001 e the level of differences significance from the control. a Grain, data for straw (production 137Cs output 137Cs reduction and % of total 137Cs deposition) except b Data for the year 1991, 2nd cut are missing. c 137 Cs:K ratios in plants for the year 1991, 1st cut are missing. d 137 Cs:K ratios in plants for the year 1987, 1st cut are missing.
137
Cs:K ratios only for the years 1987 and 1989.
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
Loamy sand soil Y56 Hayb
137
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
X-11, hay
0.035 0.030 0.025
0.020 0.015
0.000 1st 2nd
1st
2nd
1st
2
2nd
1st
3 Year, cut
b
2nd
1st
4
1st
2nd
b Control 100 K 200 K
Tag 137Cs
0.0015 0.0010 0.0005
2nd
1st
1 2
3
1 Straw
2
3 Fig. 5. Transfer of
Year Fig. 3. Transfer of 137Cs on sandy soil, mean SE: hay (a); barley (b). No potassium was applied for hay in 1991, year 5.
137 Cs in barley grains (X9) appeared highest during the second to fourth years for both the 100 and 200 kg ha1 potassium treatments.
a
Y-48, hay
Control 50 K+Mg 100 K+Mg 200 K+Mg
0.002 0.001
Cs Tag
0.001 0.001
Control 23 K 45 K 200 K
2nd
1st
Cs on silty loam sand, mean SE: pasture Z-1 a, Z-2 b.
Y-56, hay
Control 100 K+Z 100+100 K+Z 200 K+Z
0.010 0.008 0.006 0.004 0.002
0.000
0.000
0.000 1st
1
2nd
1st
2 Year, cut
b
1st
2nd 3
Y-56, hay
0.010
0.006
2nd 2
1st
2nd
1st
3 Year, cut
Fig. 4. Transfer of
4
137
1st
2nd 5
1st
1st
4
Y56, hay
2nd 5
Control 100 K+CaO 100+100 K+CaO 200 K+CaO
0.006
0.002 1st
2nd
3 Year, cut
0.008
0.004
2nd
1st
0.010
0.002 0.000
2nd 2
0.012
0.004
1
1st
d Cs Tag
0.008
1st
2nd 1
Control 100 K 100+100 K 200 K
0.012
2nd 3
137
0.012
0.000
2nd
2nd 4
2 Year, cut
c
Cs Tag
0.001
1st
1st
The fertilization of pasture grass growing on organic rich soil with potassium at 100 or 200 kg K ha1 reduced 137Cs Tag, as a percentage of the control, by an average of 60e80% for both the first and second cuts. Although the 50 kg K ha1 treatment appeared sufficient for reducing 137Cs Tag in grass by about 30% in the first cut, it was insufficient for the second cut: in pasture grass from the second cut, the fertilization effect gradually decreased with time. This is probably due to a lack of potassium fixation in organic soils
0.001
Cs Tag
2nd 3
Z-2, pasture
0.045 0.040 0.035 0.030 0.025 0.020 0.015 0.010 0.005 0.000 1st
1 Grain
1st
2 Year, cut
5
0.0020
2nd 1
2nd
X-11, barley
0.0025
0.0000
Control 23 K 45 K 90 K 200 K
0.005
1
Tag
Z-1, pasture
0.040
0.010
1st
137Cs,
a
Control 100 K 100+100 K 200 K
Tag
0.010 0.009 0.008 0.007 0.006 0.005 0.004 0.003 0.002 0.001 0.000
137Cs
137Cs
Tag
a
29
0.000 1st
2nd 1
1st
2nd 2
1st 3 Year, cut
Cs on loamy sand, mean SE: hay Y48 (a) and Y56 (bed).
2nd
1st 4
1st
2nd 5
30
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
Z-3, pasture
reduction of cesium transfer to hay with the 100 kg K ha1 treatment, and about five to six-fold reduction with the 200 (100 þ 100) kg K ha1 treatment. Thus, in hay on sand soil treated with 200 kg K ha1, an average 70e80% reduction in 137Cs (Bq kg1, Tag), as a percentage of the control, might be achievable. A maximum 137Cs Tag reduction (up to a factor of 15 or higher) on sandy soil could be obtained during the third or fourth successive years after potassium application; with an average reduction of 137 Cs activity concentration in barley grain and straw on sandy soil of 50e60%. The maximum reduction in 137Cs Tag in barley on sandy soil might be attained during the second and third year after fertilization. Discontinuation of potassium application on sandy soil did not result in residual effect on cesium transfer to barley; therefore annual application of fertilizer on sandy soils is necessary. Both the 200 kg K ha1 and 100 þ 100 kg K ha1 treatments appeared equally efficient in reducing 137Cs uptake and had similar effects: the 137Cs transfer to crops at both rates decreased by about 80%, compared to the control treatment. Similar results are reported by Andersson et al. (2000), who showed that the transfer of Cs to plants after fertilization with 150 kg of K per ha1 on sandy and potassium-deficient soils was reduced by nearly 70%. However, in terms of applicability, 200 kg K ha1 (one application) is considered more feasible than 100 þ 100 kg K ha1.
Control 23 K 45 K 90 K 200 K
0.18 0.16 0.14 Tag
0.10
137Cs
0.12 0.08 0.06 0.04 0.02 0.00 1st
2nd
1st
1
Fig. 6. Transfer of
2nd 2
137
1st
2nd
1st
1st
3 4 Year, cut
2nd
1st
5
2nd 6
Cs on gravely sandy loam, Z-3 pasture, mean SE.
and increased leaching from organic rich soil, particularly with incremental watering in peat (Prasad and Woods, 1971). Mineral soils: The effect of potassium application on sandy soil appeared similar on organic rich soil: about two to three-fold
b
CU711, hay 1st cut
reduction factors
25 20 50 K
15
100 K
200 K
10
137Cs
137Cs
reduction factors
a
5
CU711, hay 2nd cut 30
50 K
25
1
20 15 10 5
2
3
4
5
1
6
2
3
d
X9, hay 1st cut
5
6
X9, hay 2nd cut 25
reduction factors
25 20 100 K
15
100+100 K
200 K
10
137Cs
reduction factors
4 Years
Years
137Cs
200 K
0
0
c
100 K
5
100 K
20
100+100 K
200 K
15 10 5 0
0 1
2
3
1
4
2
3
4
Years
Years
137Cs
reduction factors
e
X9, barley
8
100 K, grain 100 K, straw
6
200 K, grain 200 K, straw
4 2 0
1
2
Years
3
4
Fig. 7. 137Cs reduction factors in hay and barley on organic rich soil during successive years after potassium application, 137Cs TF without potassium divided by 137Cs Tag 50K, 137Cs Tag 100K, 137Cs Tag 100 þ 100K or 137Cs Tag 200K. Hay (aed); barley (e). No potassium was applied in year 4 and 5 (CU711 a, b).
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
b
X11, hay 1 cut 20
X11, hay 2 cut 20
100 K
100+100 K
200 K
Cs reduction factors
Cs reduction factors
a
31
15 10 5
100 K
100+100 K
200 K
15 10 5 0
0 1
2
3 Years
4
Cs reduction factors
c8
1
5
2
3 Years
4
5
X11, barley 100 K, grain 100 K, straw
6
200 K, grain 200 K, straw
4 2 0 1
2 Years
3
Fig. 8. 137Cs reduction factors in hay and barley during successive years after potassium application, 137Cs Tag without potassium divided by (100 þ 100K), or 137Cs Tag 200K. Sandy soil: hay (a, b); barley (c). No potassium was applied for hay in 1991.
The transfer of 137Cs to barley grain is generally lower than in hay grass and the increase in potassium application from 100 to 200 kg K ha1 only slightly affected 137Cs transfer to barley grain on organic rich soil, but had a distinct effect for this crop on sandy soil. As the transfer of 137Cs from organic rich soils to barley grain was noticeable, a two-fold decrease of 137Cs Tag in grain after potassium application may be achieved. This was in agreement with other studies (Anisimov et al., 2002) in which, an increase in potassium in the soil decreased the amount of exchangeable 137Cs in two-weekold barley seedlings by a factor of 1.5e2. Due to a higher mineral content in the barley straw than in grains, the cesium transfer to the straw was two times higher than to the grains. Conversely, complete fertilizer (NPK 20-5-9) used on loam soil in the range of 23e90 kg K ha1 although increased production noticeably, did not affect cesium uptake by pasture grass: the effect was only observed at 200 kg K ha1, with a four-fold decrease of 137 Cs Tag from soil to grass in experimental plot Z1 and a six-fold decrease at Z3. At Z2, the potassium effect at the same rate (200 kg K ha1) was less pronounced. Nitrogenous fertilizers can increase biomass but may also decrease plant concentration of radionuclide due to dilution effect. This may result in low tissue radionuclide concentration, even the total uptake increases with increasing biomass (Ekvall and Greger, 2003). It is also known that increased NHþ 4 concentration in the soil may inhibit the potassium effect and increase 137Cs uptake by plant roots (Kruglov et al., 2005). Thus, the complete fertilizer, which contains nitrogenous compounds, probably inhibited the effect of potassium application on 137 Cs uptake by pasture grass, particularly at low doses (23e 90 kg K ha1). Experimental plot Z3 is situated in pasture land in the mountain district of Jämtland County. The soil is gravelly sandy loam with natural grasses and other plant species. The site has low productivity with an annual harvest of about 3000 kg dry matter ha1. The soil and plant cover conditions contribute to the high soil to plant transfer of 137Cs obtained in the control treatment: cesium transfer to pasture grass was high and persistent. On such soils, 200 kg potassium per ha1 is required and is recommended for reducing radiocesium uptake appreciably. Cesium activity tended to increase in pasture grass (Z1, Z2 and Z3), especially when lower rates of potassium were applied. It was assumed that removal of the crop
137
Cs Tag 100K,
137
Cs Tag 200K
from soils with low potassium content in soil dismissed most of the available potassium at the first cut: crop removal of potassium from sandy soils was among the largest loss. The addition of zeolite was an effective countermeasure for reducing 137Cs transfer to grass. Zeolite is more effective in reducing cesium uptake by ryegrass from peat soil compared to other minerals, such as heavy clay, bentonite, biotite, and apatite (Paasikallio, 1999). The use of potash-magnesia instead of potassium (K þ Mg treatment) was less effective than potassium alone (K) or in combination with zeolite (K þ Z). Potash-magnesia was effective for reducing 137Cs in hay at a rate 50 kg K þ Mg ha1: 137Cs activity concentration in harvest and 137Cs Tag decreased by a factor of about two. However, increased potash-magnesia rates (100 and 200 kg K þ Mg ha1) had the opposite effect. Because the high levels of Mg in the soil solution decrease rates of K uptake (Dibb and Thompson, 1985), 137Cs uptake by crops could be affected as well. The liming of calcium-deficient soils with low pH in combination with potassium fertilization aimed to reduce root uptake of cesium. However, lime application did not affect 137Cs transfer to grass: reduction of 137Cs activity concentration in harvested crops and 137Cs Tag in the K þ CaO treatment was similar or less than with the K treatment. In the long-term perspective, it appeared necessary to conserve or even improve the potassium status in soils, as the amount of K in the soil studied was insufficient to maintain a positive K balance, which affected crop uptake of 137Cs. The transfer of 137Cs from the soil to plant is described (Figs. 2e 6) by transfer factors, which is affected by many environmental factors (Ehlken and Kirchner, 2002). Variability in transfer factors can be understood through 137Cs:K ratios. In harvested material the 137 Cs:K ratios narrowed as result of potassium application. This narrowing appeared positively (r ¼ 0.98, p < 0.01) correlated with 137 Cs Tag and presumably reflected differences in soil solution composition, that is, increasing K and decreasing 137Cs concentrations. Peat soils have a lower capacity for binding cesium than mineral soils, and are generally low in potassium, such as in the Gävle area and northern Uppland (CU711, C2 and X9). The transfer of cesium to agricultural crops cultivated on peat soils tends to be higher (Gulyakin and Yudintseva, 1958); thus, periodic fertilization of soil
32
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
with potassium at rates of at least 50 kg ha1 would be a feasible and effective measure for reducing 137Cs uptake by crops on both organic rich soils and mineral sand soils. When analyzing the effect of potassium application over years of study (Tables 3 and 4) the differences between treatments are often hidden. This is because the effect (reduction of cesium activity in crops) decreases over time. 5. Conclusions During the five-year period following atmospheric deposition from the Chernobyl accident, radiocesium from this source equilibrated in the agricultural environment. With regard to cesium uptake by crops and the effect of potassium fertilizers, the results were consistent with earlier investigations in micro plot experiments (Lönsjö and Haak, 1986); however, the opportunity to undertake experiments in the field with different soils in varying agricultural environments was unique. In spite of the time since the experiment was conducted the data within the literature with different levels of potassium fertilization and its effect on 137Cs transfer to crops grown on organic rich soils and sandy soils are limited. Data obtained within this study are valuable and can be used for predictive modeling, soil-based countermeasures and further management of contaminated soils to reduce radionuclide transfer along food chains. Potassium application on soils with low clay content, such as sand and organic rich soils was an effective countermeasure resulting in substantial reduction of 137Cs in crops even at a rate of 50e100 kg K ha1. The effectiveness of potassium fertilization appeared higher on sandy soils than on organic rich soils and the effect of potassium application on 137Cs Tag tended to decrease over time, but was still pronounced after 5e6 successive years. Potassium application at 100 þ 100 kg ha1 and 200 K kg ha1 had similar effects. The additional application of zeolite reduced 137Cs transfer to hay by a factor of 1.4 on sand soil and 1.8 on organic rich soil, whereas, the application of potash-magnesia and CaO had no effect. Acknowledgments The project was funded by the Swedish Radiation Safety Authorities (SSM), Swedish University of Agricultural Sciences (SLU), Sweden and Zhytomyr State Technological University (ZSTU), Ukraine. The authors are grateful to Dr. M. Simonsson, Department of Soil and Environment (SLU) for kind assistance in analyzing some data. References Andersson, K.G., Rantavaara, A., Roed, J., Rosén, K., Salbu, B., 2000. A Guide to Countermeasures for Implementation in the Event of a Nuclear Accident Affecting Nordic Foodproducing Areas. Nordic Nuclear Safety Research, Roskilde. Report NKS-16. Anisimov, V.S., Kruglov, S.V., Aleksakhin, R.M., Suslina, L.G., Kuznetsov, V.K., 2002. The effect of potassium and soil activity on the 137Cs status in soils and its accumulation by barley plants in a pot experiment. Eurasian Soil Sci. 35, 1169e 1177. Dibb, D.W., Thompson, W.R., 1985. Interaction of potassium with other nutrients. In: Munson, R.D. (Ed.), Potassium in Agriculture. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Madison, Wisconsin, pp. 515e533. Egner, H., Riehm, H., Domingo, W.R., 1960. Untersuchungen über die chemische Bodenanalyseals Grundlage für die Beurteilung des Nährstoffzustandes der
Böden. II Chemische Extraktionsmethoden zur Phosphor und Kaliumbestimmung. Kungl. Lantbr. Ann. 26, 45e61 (in German). Ehlken, S., Kirchner, G., 2002. Environmental processes affecting plant root uptake of radioactive trace elements and variability of transfer factor data: a review. J. Environ. Radioact. 58, 97e112. Ekvall, L., Greger, M., 2003. Effects of biomass-producing factors on Cd uptake in two Swedish ecotypes of Pinus sylvestris. Environ. Pollut. 121, 401e411. Gulyakin, I.V., Yudintseva, E.V., 1958. Uptake of strontium, cesium and some other fission products by plants and their accumulation in crops. In: Proceedings of the 2nd International Conference on Peaceful Uses of Atomic Energy. 1958 Sept 1e13; Geneva, pp. 476e485. IAEA, 2010. Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Terrestrial and Freshwater Environments. Technical reports series, no. 472. Vienna, 194 pp. Kruglov, S.V., Suslina, L.G., Anisimov, V.S., Aleksakhin, R.M., 2005. Mechanism of the 137 effect of Kþ and NHþ Cs accumulation by two-week-old barley plants 4 ions on from soddy-podzolic soils. Eurasian Soil Sci. 38, 1082e1090. Lönsjö, H., Haak, E., 1986. Effects of Placement and Potassium Fertilization on the Uptake of Cesium and Strontium by Agricultural Crops. Report SLU-REK-60. Swedish University of Agricultural Sciences, Uppsala (Swedish with an English summary). Paasikallio, A., 1999. Effect of biotite, zeolite, heavy clay, bentonite and apatite on the uptake of radiocesium by grass from peat soil. Plant Soil 206, 213e222. Perepelyatnikov, G., Perepelyatnikova, L., Ivanova, T., Kalynenko, L., Grytsyuk, N., Zhurba, M., 2007. Radiological efficiency of agricultural countermeasures applied in radiocontaminated fields. J. Environ. Eng. Landsc. 15, 243e252. Pietrzak-Flis, Z., Krajewski, P., Krajewska, G., Sunderland, N.R., 1994. Transfer of radiocesium from uncultivated soils to grass after the Chernobyl accident. Sci. Total Environ. 141, 147e153. Prasad, M., Woods, M.J., 1971. Leaching and nutrient uptake of tomatoes in peats. J. Sci. Food Agric. 22, 564e568. Root, T., Tattari, S., Rantavaara, A., 2005. Northern conditions influencing the selection of countermeasures after radioactive fallout in Finland. J. Environ. Radioact. 83 (3), 359e370 (special issue). Rosén, K., Eriksson, Å., Haak, E., 1996. Transfer of radiocaesium in sensitive agricultural environments after the Chernobyl fallout in Sweden. I. County of Gävleborg. Sci. Total Environ. 182, 117e135. Rosén, K., Öborn, I., Lönsjö, H., 1999. Migration of radiocesium in Swedish soil profiles after the Chernobyl fallout in Sweden 1987e1995. J. Environ. Radioact. 46, 45e66. Rosén, K., Vinichuk, M., Johanson, K.J., 2009. 137Cs in a raised bog in central Sweden. J. Environ. Radioact. 100, 534e539. Rosén, K., Vinichuk, M., Nikolova, I., Johanson, K.J., 2011. Long-term effects of single potassium fertilization on 137Cs levels in plants and fungi in a boreal forest ecosystem. J. Environ. Radioact. 102, 178e184. Shenber, M.A., Johanson, K.J., 1992. Influence of zeolite on the availability of radiocesium in soil to plants. Sci. Total Environ. 13, 287e295. Smolders, E., Tsukada, H., 2011. The transfer of radiocesium from soil to plants: mechanisms, data, and perspectives for potential countermeasures in Japan. Integr. Environ. Assess. Manag. 7, 379e381. Smolders, E., Sweeck, L., Merckx, R., Cremers, A., 1997. Cationic interactions in radiocesium uptake from solution by spinach. J. Environ. Radioact. 34, 161e170. Sveriges Nationalatlas: Stockholm e Mälardalen. Solna, SNA, 2008. Vandenhove, H., Smolders, E., Cremers, A., 2003. Potassium bentonites reduce radiocesium availability to plants. Eur. J. Soil Sci. 54, 91e102. Veresoglou, D.S., Tsialtas, J.T., Barbayiannis, N., Zalidis, G.C., 1995. Cesium and strontium uptake by two pasture plant species grown in organic and inorganic soils. Agric. Ecosyst. Environ. 56, 37e42. Vidal, M., Camps, M., Grebenshikova, N., Sanzharova, N., Ivanov, Y., Rigol, A., et al., 2000. Effectiveness of agricultural practices in decreasing radionuclide transfer to plants in natural meadows. Radiat. Prot. Dosim. 92, 65e70. Vinichuk, M., Mårtensson, A., Ericsson, T., Rosén, K., 2013. Effect of arbuscular mycorrhizal (AM) fungi on 137Cs uptake by plants grown on different soils. J. Environ. Radioact. 115, 151e156. Waegeneers, N., Sauras-Yera, T., Thiry, Y., Vallejo, V.R., Smolders, E., MadozEscande, C., 2009. Plant uptake of radiocesium from artificially contaminated soil monoliths covering major European soil types. J. Environ. Radioact. 100, 439e444. Yera, T.S., Vallejo, V.R., Valcke, E., Colle, C., Förstel, H., Millán, R., 1999. 137Cs and 90Sr root uptake prediction under close-to-real controlled conditions. J. Environ. Radioact. 45, 191e217. Zhu, Y.-G., 2001. Effect of external potassium (K) supply on the uptake of 137Cs by spring wheat (Triticum aestivum cv. Tonic): a large-scale hydroponic study. J. Environ. Radioact. 55, 303e314. Zhu, Y.-G., Shaw, G., Nisbet, A.F., Wilkins, B.T., 2000. Effect of potassium (K) supply on the uptake of 137Cs by spring wheat (Triticum aestivum cv. Tonic): a lysimeter study. Radiat. Environ. Biophys. 39, 283e290.
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Potassium fertilization and 137Cs transfer from soil to grass and barley in Sweden after the Chernobyl fallout K. Rosén a, M. Vinichuk a, b, * a b
Department of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, SE-750 07 Uppsala, Sweden Department of Ecology, Zhytomyr State Technological University, 103 Chernyakhovsky Str., 10005 Zhytomyr, Ukraine
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 June 2013 Received in revised form 18 December 2013 Accepted 19 December 2013 Available online 9 January 2014
Fertilization of soils contaminated by radionuclides with potassium (K) and its effect on 137Cs transfer from soil to crops is well studied in field conditions; however experiments over many years are few. The effects of potassium fertilization on cesium-137 (137Cs) transfer to hay, pasture grass, and barley growing on organic rich soils and mineral sand and loam soils in a number of field experimental sites situated in different environments in Sweden are summarized and discussed. The basic experimental treatments were control (no K fertilizers were applied), 50, 100, and 200 kg K ha1. In the experiment, which lasted over 3e6 years, 137Cs transfer factors in control treatments ranged between 0.0004 m2 kg1 (barley grain on sand soil) and 0.07 m2 kg1 (pasture grass on organic rich soil). Potassium application on soils with low clay content i.e. mineral sand and organic rich soils was effective at the 50e100 kg ha1 level. Application of 200 kg K ha1 resulted in a five-fold reduction in 137Cs transfer for hay and up to four-fold for barley grain. The effects of potassium application were generally greater on sand than organic rich soil and were observed already in the first cut. After K application, the reduction in 137Cs transfer to crops was correlated with 137Cs:K ratios in plant material. Additional application of zeolite caused a 1.4 reduction of 137Cs transfer to hay on sand and 1.8-fold reduction on organic rich soil; whereas, application of potash-magnesia and CaO had no effect. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Countermeasures Radiocesium Potassium Pasture grass Soil
1. Introduction The nuclear accidents at Chernobyl and Fukushima highlighted that agriculture is unprotected against radioactive contamination. Cultivation of 137Cs contaminated soils with low fertility and low K status present farmers with huge challenges and problems. The downward migration of cesium in the majority of soil types is generally slow, but radionuclide bioavailability and transfer rates through the soileplant system in soils with low K status are high (Rosén et al., 1999, 2009). Several studies conducted in both field (Pietrzak-Flis et al., 1994) and lysimeter experiments (Yera et al., 1999) indicate the concentration of 137Cs in crops varies and depends upon the type of soil, being higher in sand and peat and lower in loam and clay soil. Since the transfer factors for 137Cs are
* Corresponding author. Department of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, SE-750 07 Uppsala, Sweden. Tel.: þ46 18 671442; fax: þ46 18 672795. E-mail addresses: [email protected], [email protected] (M. Vinichuk). 0265-931X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvrad.2013.12.019
higher in peatlands and in organic soils than in mineral soils (Veresoglou et al., 1995), cultivation of peatland increases longterm radiocesium contamination of crops. The inhibitory effect of potassium addition on the uptake of radiocesium in a relatively infertile soil in lysimeters under simulated field conditions has been shown to depend on the stage of plant growth, age-related demand for potassium by the plant (Zhu et al., 2000) and its concentration in the growth solution (Zhu, 2001). Commonly used agricultural practices such as liming and the use of increasing amounts of NPK fertilizers generally decrease 137Cs transfer to plants in natural meadows (Vidal et al., 2000). Cesium uptake is inhibited when the potassium concentration in soil solution increases (Waegeneers et al., 2009). Thus, potassium fertilizers are an effective countermeasure, especially on nutrient poor soils with low K status (Smolders et al., 1997) and low degree of base saturation (Rosén et al., 2011). Thus, the application of fertilizers containing potassium at elevated rates is one of the most effective countermeasures for reducing radiocesium uptake (Perepelyatnikov et al., 2007); however, the effectiveness varies according to both soil characteristics and plant species (Vinichuk et al., 2013). Cultivation of peatlands in
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
northern conditions limits the selection of plants and increases long-term radiocesium contamination of crops (Root et al., 2005), although regional features of soil and climate require additional studies on radionuclide transfer within food chains. Other absorbents, such as bentonite also affect the equilibrium of cesium in soil and its availability to grass (Vandenhove et al., 2003). Although the long-term effect of biotite on reducing 134Cs uptake by ryegrass from peat soil is reported (Paasikallio, 1999), a significant reduction (up to a factor of 8) in uptake of 134Cs by winter wheat has been obtained after application of mineral zeolite in pot experiments (Shenber and Johanson, 1992). Studies on the inhibitory effect of potassium on root uptake of cesium by crops growing on nutrient poor sandy and organic soils are limited. Prior to 1986, in Sweden and in the other Nordic countries, only pot and mini-plot field experiments dealing with the effect of potassium on 137Cs transfer to crops have only been carried out on soils artificially contaminated with radionuclides (Lönsjö and Haak, 1986). During the period 1987e1992, our experiments with potassium fertilizers and other specific clay minerals that mitigate 137Cs transfer to hay, pasture grass and barley grown on organic rich soil, mineral sand and loam soils indicated that repeated annual potassium fertilization was an effective and practicable countermeasure for reducing contamination of agricultural products by radiocesium. However, the Chernobyl accident made it possible to perform wide-ranging field studies aimed at reducing cesium transfer to crops in number of new environments and practical conditions, including “sensitive” with respect to cesium bioavailability organic rich soil and mineral sandy soils (Rosén et al., 1996). Results from field experiments on the effects of potassium fertilization on cesium transfer to plants growing on peatlands are limited and it is not known how long lasting the effect of potassium application on peat soils can be. The objective of this study was to investigate the effect of potassium application on cesium transfer to grass and barley under
23
field conditions on organic rich soil and mineral soils in northern Europe after the Chernobyl fallout. The hypotheses tested within this field study were whether potassium fertilizers could reduce uptake of cesium on organic rich soil and sand soils efficiently; how long lasting could the residual effect after fertilization be; and, if there were any combined effects of potassium and liming or potassium and zeolite. In this study, different fertilizers and doses were tested and 137Cs transfer to hay, barley, and pasture grass were assessed after application of an increasing supply of potassium fertilizers on organic rich soil, mineral sand and loam soils. The investigation started in 1987 and lasted between 3 and 6 years depending on the crop cultivated. Data obtained within this study have not been previously published in international journals, yet they are of practical interest; to our knowledge, few field studies have been conducted on organic rich soil and sand soils since the Chernobyl accident in 1986. The release of radionuclides at Fukushima Daiichi in Japan has re-invigorated interest in the transfer of 137Cs from soil to agricultural plants and potential countermeasures (Smolders and Tsukada, 2011). 2. Materials and methods The field experiment was conducted in four different counties in Sweden: Uppsala county (C), Gävleborg county (X), Västernorrland county (Y), and Jämtland county (Z). There were nine different farms, referred to here as CU, X, Y, Z, within which there were fourteen experimental 14 sites (Table 1). Latitude and longitude were determined by GPS (GeoExplorer CE Series) with error of 2e 5 m. The soil at all experimental fields was not plowed after the fallout in 1986, except for barley fields (X9 and X11), which were plowed each year. In 1986, the age (the number of years since the land was last plowed) of grasslands varied between 1 and 5 years (CU711, X9, X11, Y48, Y56 and Z2) and 15e35 years (C2, Z1 and Z3) (Table 1).
Table 1 County and sites for experiment, soil characteristics, 137Cs deposition at the beginning of the experiment. Farm numbera
Exp. plotb
Site
Treatmentc
pHH2 O
OM,d %
KAL
KHCl
CaAL
CaHCl
Deposition, kBq m2
GPS
74.1 74.1 51 202 202
59 570 5300 N, 59 570 5300 N, Nearby C1 60 440 0700 N, 60 440 0600 N,
170 170
60 490 0700 N, 17 130 4600 E 60 490 0800 N, 17 130 5200 E
mg/100 g d. wht.e Organic rich soil CU711 CU711 C2 X9 X9
C-1 C-1 C-2 A B
Järlåsa Järlåsa Järlåsa Hille Hille
K KþZ K K K
5.8 5.8 6.0 6.2 6.2
Sandy soil X11 X11
A C
Trödje Trödje
K K
6.5 6.5
Loamy sand soil Y48 Y56 Y56 Y56
A A A A
Holmsta Berge Berge Berge
K þ Mg K KþZ K þ CaO
Silt loamy sand soil Z1 A Z2 A
Hammarstrand Hammarstrand
Gravely sandy loam soil Z3 A
Blåsjön
a b c d e
40 40 83 51 77
17 140 1300 E 17 140 1300 E
9.1 9.1 17.5 8.8 13.5
88 88 47 44 56
745 745 1301 537 584
1364 1364 3235 1807 1493
5.0 5.0
6.1 6.1
163 163
77 77
145 145
6.0 5.9 5.9 5.9
6.8 6.8 6.8 6.8
18.7 15.1 15.1 15.1
154 52 52 52
304 77 77 77
562 195 195 195
27.1 82.5 82.5 82.5
63 160 1500 62 420 2900 62 420 2900 62 420 2900
K K
5.9 5.5
9.3 18.7
15.1 31.6
52 160
98 171
260 623
38.0 33.2
63 050 5500 N, 16 210 5800 E 63 040 4500 N, 16 210 1600 E
K
5.9
9.3
18
142
186
182
44.2
64 500 3900 N, 14 080 5600 E
Farm numbers referred to counties: Uppsala e C; Gävleborg e X, Västernorrland e Y, Jämtland e Z. Soil depth 0e10 cm. Treatments: K e potassium, Z e zeolite, Mg e potash-magnesia, CaO e lime. OM e organic matter. Extracted with ammonium lactate (AL) and hydrochloric acid (HCL) (Egner et al., 1960).
N, N, N, N,
17 120 0500 E 17 110 5800 E
16 420 5500 17 510 4300 17 510 4300 17 510 4300
E E E E
24
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
2.1. Experimental layout and treatments
2.2. Sampling
The experimental crops were hay grass (8 experimental plots), pasture grass (4 experimental plots), and barley (2 experimental plots) grown on organic rich soil, mineral sand and loam soils and plants were grown during 3e6 successive years (Table 2). All experiments were randomized; some had a completely randomized design (CRD) and some with a randomized block design (RBD) or a split plot design (SPD). A basic annual fertilization regime with nitrogen (N) 60 kg ha1, and phosphorus (P) 20 kg ha1 was applied to all experimental plots. Potassium (K) fertilizer (50% KCl) was applied annually in the range of 0e200 kg K ha1 for most plots except CU711* (C-1, hay) and X11* (A, hay) (Table 2). Experimental plots CU711* (C-1, hay) and X11* (A, hay) were repeatedly fertilized with potassium until 1990 (the fourth year): fertilization was then discontinued to evaluate the residual effects in the fifth and sixth years (1991, 1992). As Y48 (A, hay, ecological farming) field experiments had higher K-supplied soils, moderate potash-magnesia (in the form of potassium-magnesium sulfate, 23% K and 6% Mg) fertilizers were applied, whereas, Z1, Z2 and Z3 experimental plots were given a complete fertilizer, NPK 20-5-9 and 200 kg K was applied first time in 1988 (the first year, Table 2). The 100 þ 100 kg K ha1 treatment comprised 100 kg K ha1 being applied to the first cut, and a further 100 kg K ha1 being applied to the second cut (Table 2). At farm Y56 þ CaO (A, hay), 4000 kg of CaO ha1 was applied once (1988) to split plot arrangements. The same amount of a natural zeolite (4000 kg ha1 aluminosilicate minerals, similar to clay soils, referred here as þ Z) was applied once in 1988 (the first year) to grassland on experimental plots CU711 þ Z (C1, hay) and Y56 þ Z (A, hay) (Table 2). Unfertilized plots were used as controls. Each treatment was replicated three times on all experimental plots.
The sizes of individual plots were 16, 25, or 50 m2 (Table 2). Within each experimental plot, 4 sub plots of 0.25 m2 in size were randomly selected for sub sampling of the crops at harvest time. Each year, ley and pasture were harvested twice and barley once. The sub samples were pooled into a bulk sample. Plants were cut at a height of 5 cm above the soil surface and the grains and straw of barley plants were separated. To describe the soil properties of the experimental plot, soil samples were taken from each treatment. Ten soil samples were randomly sampled to a depth of 0e10 cm with a cylindrical core of 57 mm in diameter. For the calculation of deposition (137Cs Bq m2), the soil was sampled randomly over a 100 m2 area around the experimental plots to the depth of 0e5 cm with a core 57 mm in diameter. Bulk soil samples were formed by pooling 10 or 15 cores. 2.3. Analysis 137
Cs activity concentrations in all plant and soil samples were determined by calibrated HP-Ge detectors at the low background laboratory at the Department of Radioecology, Swedish University of Agricultural Sciences and corrected for decay. Before measurement, all samples were dried at a maximum temperature of 40 C and sieved through 2 mm sieves. The measuring time varied from 1 to 24 h in order to obtain a statistical error (of less than 5%) due to the random process of decay. Soluble K and Ca were extracted with ammonium lactate (AL) and hydrochloric acid (HCl) according to the methods described by Egner et al. (1960) Organic matter was derived from weight loss on ignition. To describe the transfer of 137Cs from soil to harvested material, an aggregated transfer factor (Tag) (IAEA, 2010) was used, defined as the ratio of the mass activity concentration in plant material dry weight (d. wht.)/unit area activity density (Bq kg1 d. wht./ Bq m2 d. wht.):
Table 2 Treatments, crops, duration of the experiment, and plot size on different soil types. Farm number
Exp. plot
Treatments,a annual amount of potassium (K) applied, kg ha1
Organic rich soil CU711b CU711b C2 X9 X9
C-1 C-1 C-2 A B
0K 0K þ Z 0K 0K 0K
50K 50K þ Z 50K 100K e
100K 100K þ Z 100K 100 þ 100K 100K
200K 200K þ Z 200K 200K 200K
Sandy soil X11b X11
A C
0K 0K
100K e
100 þ 100K 100K
Loamy sand soil Y48 Y56 Y56 Y56
A A A A
0K þ Mg 0K 0K þ Z 0K þ CaO
50K þ Mg 100K 100K þ Z 100K þ CaO
Silty loam sand soil Z1 A Z2 A
0K 0K
Gravely sandy loam soil Z3 A
0K
1
1
Crop
Duration of exp., years
Years
Plot size, m
e e e e e
Hay Hay Pasture Hay Barley
6 5 3 4 4
1987e1992 1988e1992 1987e1989 1987e1990 1987e1990
5 5 5 5 5
200K 200K
e e
Hay Barley
5 3
1987e1991 1987e1989
5 10 5 10
100K þ Mg 100 þ 100K 100 þ 100K þ Z 100 þ 100K þ CaO
200K þ Mg 200K 200K þ Z 200K þ CaO
e e e e
Hay Hay Hay Hay
3 5 5 5
1987e1989 1988e1992 1988e1992 1988e1992
5 4 4 4
23K 23K
45K 45K
90K 90K
200Kc 200Kc
Pasture Pasture
4 3
1987e1990 1987e1989
5 10 5 10
23K
45K
90K
200Kc
Pasture
3
1987e1989
5 10
5 5 10 10 10
10 4 4 4
Z ¼ zeolite e 4 t ha and CaO e 4 t ha applied once on starting year. a Annual fertilization with N (60 kg ha1), P (20 kg ha1), K e potassium fertilizer (contains 50 %of K) and Mg e potash-magnesia fertilizer (contains 23% of K and 6% of Mg). b Repeated fertilization was done until 1990 and then excluded. c Applied first time in 1988.
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
25
and straw. The data in Tables 3and 4 present average values for the period of study. 137Cs reduction factors in hay (1st and 2nd cuts) and barley (grains and straw) during successive years after K application to selected experimental sites were calculated and are presented in Figs. 7 and 8. 3.1. soil
Fig. 1. The deposition of 137Cs over Sweden after the Chernobyl accident. The map is based on measurements preformed in MayeOctober 1986. The locations for seven investigated sites have been added. See Table 1 for details. Modified from Sveriges Nationalatlas (2008).
Tag ¼ radioactivity in plant material; Bq kg1 =radioactivity on ground; Bq kg1 ; m2 kg1 d: wht: (1) After potassium application, the reduction factors of crops were calculated as follows:
137
Cs in the
Reduction factors ¼ 137 Cs Tag without potassium ðcontrolÞ= 137
Cs Tag with potassium; m2 kg1 d: wht:
=m2 kg1 d: wht: (2) 137
1
Cs offtake by crops (kBq ha ) was calculated as an average Cs activity concentration in crop (kBq kg1) multiplied by crop production (kg ha1). To evaluate the differences in 137Cs activity among treatments, data were subject to analysis of variance and 2-sample t-tests with Minitab (Ó2010 Minitab Inc.) software. Analyses of variance and independent 2-sample t-test we used allowed us performing a hypothesis test and computing a confidence interval of the difference between two population means. 137
3. Results For presentation and discussion of the results (Fig. 1), the experimental sites have been divided into two soil groups: organic rich soil (Table 3, Figs. 2 and 7) and mineral soil (sandy and loamy soil, Table 4, Figs. 3e6 and 8). In the tables, data are presented as average values of three replicates over three to six years of study. In Jämtland County (Z1, Z2, and Z3), K (90 kg ha1) was only applied once in 1987, therefore data for this treatment are omitted in Table 4 but shown in Fig. 5 (Year 1). In order to demonstrate the trend and variation in 137Cs transfer to crops, the annual data in Figs. 2e6 are presented separately for the 1st and 2nd cuts, grains
137
Cs transfer to hay, pasture grass and barley on organic rich
Grass (hay and pasture grass) production on organic rich soil was similar on all experimental plots and varied between 2.6 and 4.9 t ha1 for the first cut and 1.5e2.4 t ha1 for the second cut. The effect of potassium application on yield of hay was small, whereas the increment in pasture grass production (first cut, C2) was significant (p < 0.01) at 50e200 kg K ha1. The yield of barley grain (X9) increased from 5.4 t ha1 in the controls to 7.6 t ha1 in treatment 200K (Table 3). The application of potassium on organic rich soil caused 137Cs reduction in experimental crop hay (CU711, CU711 þ Z, X9): the percentage range from the control to the 1st and 2nd cut was: 34e 51% for 50 kg K ha1, 43e59% for 100 kg K ha1, and 41e83% for 200 kg K ha1. In pasture grass (C2) and barley (X9), 137Cs reduction was noticeable, although less pronounced. Even though reduction in 137Cs offtake by crops (kBq ha1) occurred at 50 kg K ha1, the reduction was only significant (p < 0.01) at 100 kg K ha1 and 200 kg K ha1 (Table 3). At harvest, there was a corresponding shift in 137Cs:K ratios after application of potassium fertilizer: in most experiments at 200 kg K ha1, 137Cs:K ratios decreased twelve-fold on the first cut and five-fold on the second cut. After potassium application, 137Cs:K ratios in plants changed, even in the first cut at 50 kg K ha1, and resulted in reduction in the potassium uptake and reduced potassium content in the plants. Potassium concentration in hay (CU711, 100 kg K ha1) dropped from 21 to 23 mg g1 d. wht. in 1987e1990 to 12e13 mg g1 d. wht. in 1991e1992 (data not shown). Fertilization reduced 137Cs offtake and 137Cs:K ratios in pasture grass (C2): this reduction was significant (p < 0.01) at 100 and 200 kg K ha1 (Table 3). In barley grain, potassium fertilization at 100 kg K ha1 and 200 kg K ha1 reduced 137Cs offtake. Although 137 Cs:K ratios were reduced at 100 kg K ha1, the reduction was only significantly different from the control at 200 kg K ha1. The additional application of zeolite (CU711 þ Z, Table 3) resulted in a similar decrease in 137Cs offtake by hay (kBq ha1), the 137Cs:K ratios in plants reduced and the percentage of the total deposition of 137 Cs accumulated in crops in both 1st and 2nd cuts decreased, compared to control. There was no difference in 137Cs between the K and K þ Z treatments. An increase in potassium e.g. from 50 to 200 kg ha1 reduced the 137Cs Tag by a factor of 3e6 in hay, 1e5 in pasture grass, about 2 in barley grain and about 1 in straw. In the second cut of hay, the 137 Cs Tag was generally lower than in the first cut, with some exceptions, e.g. in year 5 (CU711 and CU711 þ Z, Fig. 2a, b) and in year 1 (X9, hay, Fig. 2d). The reduction in 137Cs Tag was most pronounced at 50 and 100 kg K ha1 in the first cut and at 200 kg K ha1 in the second cut. Similarly, in pasture grass, the potassium rate of 50 kg K ha1 only reduced 137Cs Tag in the first cut, whereas, 100 and 200 kg K ha1 were equally effective for both the first and second cuts. 137Cs Tag was lowest in barley grain (X9) (Fig. 2e) and highest in pasture grass (C2) (Fig. 2c). The effect of potassium application on 137Cs Tag tended to decrease over time, but was still well pronounced after 5e6 years (CU711, Fig. 2a, b). In order to estimate the residual effect no potassium was applied in years 5 and 6 on the experimental plot CU711 (Fig. 7a, b). However, the effect of 137Cs reduction in hay due to potassium application on organic rich soil was similar in both cuts at the rate
26
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
Table 3 Mean crop production and Farm Crops number
137
Cs uptake by crops on organic rich soil, mean SE.
Treatments Production, ton per ha d. wht.
137
Cs Output by crops, kBq ha1 Reduction in 137 Cs in crops as % of the control
1st Cut 2nd Cut 1st Cut/grain grass/grain grass/straw CU711
Hay
CU711
Haya
C2
Pastureb
X9
Hay
X9
Barley
Control 50K 100K 200K Control 50K þ Z 100K þ Z 200K þ Z Control 50K 100K 200K Control 100K 100 þ 100K 200K Control 100K 200K
3.8 4.0 4.4 4.4 3.6 3.7 4.1 3.9 2.6 3.9 3.9 4.3 3.7 4.6 4.8 4.9 5.4 6.4 7.6
0.4 0.5 0.4 0.5 0.4 0.4 0.4 0.4 0.3 0.4** 0.3** 0.3** 0.5 0.5 0.6 0.7 1.5 1.9 2.3
1.9 1.8 1.9 2.2 2.0 1.9 2.1 2.4 1.9 2.4 2.1 2.3 1.5 1.5 1.5 1.6 1.7 1.6 1.8
0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.2 0.2 0.3 0.3 0.2 0.3 0.2 0.2 0.2
3454 737 2019 508 1843 538 773 231** 1328 165 811 166 704 161* 303 92*** 7093 966 7255 696 3475 626** 1720 535*** 10 972 2203 5556 950* 3746 1215* 4194 1828* 1017 183 399 102** 319 70**
137
Cs:K ratios in plants
2nd Cut/straw 1st Cut/ 2nd Cut/ 1st Cut/ grain straw grain 1091 676 626 227 899 545 502 229 8120 9415 3208 1664 5042 3140 1262 1111 1489 1064 663
217 182 167 66*** 129 100* 142* 64*** 1392 1055 627** 607** 1084 1144 554** 325** 456 474 245
e 51 58 83 e 44 59 83 e 34 68 88 e 56 72 41 e 52 45
e 41 47 80 e 34 51 80 e 2 61 81 e 43 78 80 e 15 22
69.9 24.5 18.3 6.7 31.8 17.8 12.5 4.1 391 138 47.5 14.7 299 79.5 49.1 83.0 76.8 34.5 21.1
10.2 2.9*** 3.4*** 1.2*** 3.8 4.1* 2.9** 1.1*** 99 23* 8.9** 4.6** 77 15.9* 15.1** 57.4* 22.5 15.6 7.8*
2nd Cut/ straw 45.2 26.9 20.2 6.7 37.5 25.6 16.9 6.1 395 268 88.4 28.9 622 186 45.4 53.6 103 65.6 24.1
10.9 8.2 5.5 2.3** 9.9 7.0 5.1 1.8** 66 39 16.3** 9.7*** 182 63* 18.1** 16.6** 17.1 25.7 7.7***
137
Cs in crops as % of total deposition 1st Cut/grain
0.80 0.45 0.43 0.18 0.31 0.19 0.16 0.07 1.39 1.42 0.68 0.34 0.55 0.28 0.19 0.21 0.05 0.02 0.02
0.17 0.12 0.13 0.05** 0.04 0.04* 0.04* 0.02*** 0.19 0.14 0.12** 0.11*** 0.11 0.05* 0.07* 0.09* 0.01 0.01 0.01
2nd Cut/ straw 0.25 0.16 0.15 0.05 0.20 0.13 0.12 0.05 1.73 1.85 0.63 0.33 0.25 0.16 0.06 0.06 0.08 0.05 0.03
0.05 0.04 0.04 0.02*** 0.03 0.02* 0.03* 0.01*** 0.27 0.21 0.12** 0.12** 0.05 0.06 0.03** 0.02** 0.02 0.02 0.01
*p < 0.05; **p < 0.01; ***p < 0.001 e the level of differences significance from the control. a 1st Cut for the year 1988: all data missing. b Crop production data for the year 1987: 1st cut was estimated as a mean value of 1988 and 1989.
50 and 100 kg K ha1. The reduction of 137Cs in hay at 200 kg K ha1 was pronounced and reached a maximum for first cut in the second year after fertilization, and for second cut in the fourth year after fertilization (Fig. 7a, b). At experimental site X9 hay, the effect of potassium application on 137Cs reduction in hay increased over time, being higher in the second cut at 100 þ 100 kg K ha1 (Fig. 7c, d). At X9 barley, the reduction factors of 137Cs in barley grains due to potassium application were highest during the second to fourth year after fertilization and at both 100 and 200 kg K ha1 (Fig. 7cee). 3.2.
137
Cs transfer to hay, pasture grass, and barley on mineral soil
Potassium application on sandy soil had no effect on hay production (X11, first and second cut) or effect was small (Y56, Y48 first and second cut) (Table 4). For barley grains (X11), production increased appreciably from 2.3 to 4.0 t ha1. The application of complete NPK fertilizer (potassium range between 23 and 45 kg ha1) on loam soil increased the yield of first cut pasture grass (Table 4). On sandy soil, 137Cs offtake by hay (kBq ha1) decreased at both X11 and Y56 experimental sites at 100 þ 100 and 200 kg K ha1. The reduction in 137Cs in hay (X11 and Y56), as a percentage of the control due to fertilization, was about 55% at 100 kg K ha1 and about 76% at 100 þ 100 and 200 kg K ha1. In barley grains (X11), the reduction in 137Cs was between 63 at 100 kg K ha1 and 74% at 200 kg K ha1. At Y48, the reduction in 137Cs in hay was different: 137 Cs offtake by hay decreased with an increased rate of potassium only marginally (Table 4). Potassium fertilization at 100 and 200 kg K ha1 narrowed the 137 Cs:K ratios in both hay and barley grains. These effects were less pronounced in the K þ Mg treatment, however, the 137Cs:K ratios in treatments with K were two-fold narrower than on the control treatment in both first and second cuts (Table 4). 137 Cs in crops, as a percentage of the total 137Cs deposition, decreased in hay after potassium application at X11 and Y56. The uptake of 137Cs, as a percentage of total cesium deposition, was higher on pasture (Z2, Z3) than on other grasslands (Table 4).
The additional application of CaO in combination with potassium generally had no effect on 137Cs transfer to hay, and the addition of zeolite (Y56) or potash-magnesia (Y48) only had a small effect on 137Cs transfer (Table 4). In experiments X11 and Y56, there was a four to five-fold reduction in 137Cs Tag in hay for the 100 kg K ha1 potassium and 200 (or 100 þ 100) kg K ha1 potassium treatments (Figs. 3a and 4b). In pasture grass (Z1, Z2, Z3), potassium did not affect the 137Cs Tag (first and second cut) when a complete fertilizer was used, at 200 kg K ha1, the effect was positive in both the first and second cuts. An appreciable (about three to four-fold) decrease in 137Cs Tag was observed in barley grain (X11) (Fig. 3b). The additional application of zeolite resulted in a (one and a half-fold) decrease of 137Cs Tag in hay (Y56) in the control and 100 kg K ha1 potassium treatment: this effect was not seen with 200 (or 100 þ 100) kg K ha1. In the treatment with potashmagnesia (Y48), the reduction of 137Cs Tag in hay was most pronounced at 50 kg ha1 potassium: 137Cs Tag reduced by 50%; whereas, at 200 kg ha1 potassium, the reduction was about 30%. Additional application of CaO had no effect on the 137Cs Tag in hay. With complete fertilization (NPK), the effect of potassium on 137Cs Tag in pasture grass was negative at 23 kg K ha1 (2nd cut), small at 45 kg K ha1, and had no effect at 200 kg K ha1 (Fig. 5b). In barley grains growing on sandy soil (X11, Fig. 3b), the reduction of 137Cs uptake during successive years was similar to that observed on organic rich soil (X9, Fig. 7e). The reduction factors were highest during the second and third years after potassium application at both 100 kg K ha1 and 200 kg K ha1. In the experimental plot at X11 hay, no potassium was added after year 4 and the reduction factor of 137Cs uptake in the fifth year dropped to the level observed in the first year. The reduction in 137Cs uptake by hay on sandy soil (X11, Fig. 8a, b) gradually increased over time and reached a maximum in both cuts in the fourth year after potassium application. Both rates of potassium application at 100 þ 100 and 200 kg K ha1 had similar effects. In pasture grass (Z1, Table 4), there was no effect of complete NPK fertilizer application (either 23 or 45 kg ha1 potassium) on 137 Cs offtake: 137Cs Tag reduced slightly (first cut) or increased
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
a
CU711, hay
0.040
0.035 0.030
CU711, hay
0.020
Control Z 50 K+Z 100 K+Z 200 K+Z
0.015
0.025
Cs Tag
Cs Tag
b
Control 50 K 100 K 200 K
27
0.020
0.010
0.015
0.005
0.010 0.005
0.000
0.000
2nd
1st 2nd 1st 2nd 1st 2nd 1st 2nd 1st 2nd 1st 2nd 1
2
3
4
5
1st
2nd
1
6
1st
2
Year, cuts
c
C-2, pasture
0.16
d
Control 50 K 100 K 200 K
0.14
1st
2nd
1st
2nd
4
X9, hay
5
Control 100 K 100+100 K 200 K
0.12 0.10
0.12
0.08
0.10
Cs Tag
Cs Tag
2nd
3 Year, cuts
0.08 0.06
0.06 0.04
0.04
0.02
0.02 0.00
0.00
1st
2nd 1
1st
2nd
1st
2 Year, cuts
1st
2nd 3
e0.020
2nd
2nd 2
X-9, barley
1st
Year, cut
2nd 3
1st
2nd 4
Control 100 K 200 K
0.016 Cs Tag
1st
1
0.012 0.008 0.004 0.000 1
2
3
4
1
Grain
2
3
4
Straw Year
Fig. 2. Transfer of
137
Cs on organic rich organic rich soil, mean SE: hay (a, b, d): pasture (c) and barley (e). No potassium was applied in year 5, 6 (a) and year 4, 5 (b).
(second cut). Similarly, 137Cs:K ratios reduced in the first cut of pasture grass, but increased (23 kg ha1) or did not change (45 kg ha1) in the second cut. However, the positive effect of potassium application on 137Cs reduction in pasture grass (Z1) was only seen at 200 kg ha1. In pasture grass at Z2 (Table 4), the effects of complete NPK fertilizers application (23 and 45 kg ha1 potassium) on 137Cs reduction were similar to at Z1 (Table 4, Fig. 5a, b). In pasture grass (Z3, Table 4); the effect of potassium application on 137Cs Tag was negative in both cuts at 23 kg K ha1, but positive in both cuts at 45 and 200 kg K ha1. The reduction in 137Cs activity concentration in pasture grass at 200 kg K ha1 on loamy soil was similar (ca. 80%) to the reduction on organic rich soil and mineral sand soils, and resulted in three to six-fold decrease of 137Cs Tag (Table 4, Fig. 6). 4. Discussion Organic rich soil. For six successive years of potassium application on organic rich soil at the rate of 50 kg ha1 yearly caused on average a two-fold reduction in cesium transfer to hay. The increased amount of potassium, applied from 50 to 200 kg ha1, led to future substantial decrease in 137Cs Tag from soil to hay. Thus, a
fertilization rate of 100 kg ha1 resulted in a two to three-fold decrease in cesium uptake, and subsequent increment of potassium application at the rate of 200 or 100 þ 100 kg K ha1 resulted in a four to five-fold decrease in cesium transfer to hay during the study period. Thus, in pasture grass on organic rich soil fertilized with 200 kg K ha1, an 80%, reduction in 137Cs (Bq kg1, Tag), as a percentage of the control, appeared achievable. Maximum 137Cs uptake reduction in hay (up to a factor of 20 or even higher) appeared realistic in the third or fourth years after potassium application (CU711, Fig. 7). The attenuation in 137Cs reduction years 5 and 6 was probably due to potassium loss through leaching, as the last fertilization was in year 4. Plant available potassium is depleted from soil through plant uptake/harvesting or through fixation on clay minerals, therefore, the annual application of potassium fertilizers is necessary to restore elemental losses from organic rich soil and reduce radiocesium contamination of crops. For both barley grain and straw, the effect of potassium fertilization on organic rich soil was similar to that observed for hay. This indicates that an average 80% reduction in 137Cs (Bq kg1, Tag), as a percentage of the control might be also achievable. 137Cs uptake reduction in barley increased during following second, third and fourth years after potassium application: the reduction factors of
28
Table 4 Mean crop production and Farm number
Crop
Sandy soil X11
Hay
X11
Barleya
Y56
Hayb
Y56
Hayb,c
Y48
Hay
Silt loam soil Z1
Pastureb
Z2
Pastured
Gravelly sandy loam soil Z3 Pasture
Cs uptake by crops on mineral soils, mean SE. Treatments
Production, t ha1 d. wht.
137
1st Cut/grain
1st Cut/grain
2nd Cut/straw
Control 100K 100 þ 100K 200K Control 100K 200K
4.0 3.8 4.1 4.2 2.3 4.0 4.0
0.7 0.7 0.7 0.8 0.4 0.7 1.0
1.7 1.4 1.8 1.7 4.7 5.6 5.3
0.2 0.3 0.3 0.2 1.3 1.4 1.4
Control 100K 100 þ 100K 200K Control 100K þ CaO 100 þ 100K þ CaO 200K þ CaO Control 100K þ Z 100 þ 100K þ Z 200K þ Z Control 50K þ Mg 100K þ Mg 200K þ Mg
4.4 4.8 4.8 4.6 4.2 4.4 4.6 4.6 4.4 4.9 4.5 4.7 0.9 1.1 1.1 1.1
0.4 0.3 0.3 0.4 0.4 0.4 0.3 0.3 0.4 0.5 0.5 0.4 0.2 0.3 0.3 0.3
1.9 1.9 2.3 2.6 2.3 2.0 2.5 2.5 1.8 2.3 2.1 2.6 0.9 1.0 1.2 1.2
Control 23K 45K 200K Control 23K 45K 200K
0.9 1.6 2.1 2.3 0.7 1.8 1.6 1.5
0.1 0.2* 0.4** 0.4** 0.1 0.4 0.2** 0.2**
1.1 1.5 1.8 1.6 1.1 1.2 1.1 0.9
Control 23K 45K 200K
0.4 1.0 1.3 1.7
0.1 0.1*** 0.1*** 0.2***
0.5 1.1 1.5 1.3
Cs Output by crops, kBq ha1 2nd Cut/straw
Reduction in 137Cs in crops as % of the control
137
1st Cut/grain
2nd Cut/straw
1st Cut/grain
137
Cs:K ratios in plants
Cs in crops as % of total deposition
2nd Cut/straw
1st Cut/grain
2nd Cut/straw
2103 1112 539 612 131 69 45
400 332 154** 221** 33 20 12*
1353 370 157 246 818 749 591
376 140* 60** 99* 332 386 240
e 54 78 73 e 63 74
e 72 89 84 e 37 50
34.7 11.0 4.4 5.7 10.2 3.9 2.8
2.5 2.0*** 0.8*** 1.5*** 2.6 1.3* 0.8*
41.9 9.6 3.1 4.7 9.8 4.9 4.7
3.9 1.8*** 0.6*** 1.0*** 2.4 1.8 1.0
0.12 0.07 0.03 0.04 0.008 0.004 0.003
0.02 0.02 0.01** 0.01** 0.002 0.001 0.001
0.08 0.02 0.009 0.014 0.048 0.044 0.035
0.02 0.01* 0.004** 0.006* 0.02 0.02 0.01
0.2 0.2 0.2 0.2* 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.2** 0.2 0.2 0.2 0.2
787 404 227 212 904 505 276 225 496 241 202 175 25.9 14.1 12.6 17.5
239 90 63* 55* 255 168 86* 68* 100 61* 62* 45** 8.4 5.2 2.7 5.9
464 198 88 116 437 262 139 146 306 141 104 101 22.0 11.9 20.3 17.8
121 62 26* 36* 96 86 39* 55* 83 44 32* 26* 6.2 3.8 4.5 4.2
e 53 76 78 e 50 73 79 e 54 58 66 e 48 47 22
e 57 82 82 e 33 73 74 e 64 72 78 e 44 21 34
10.5 3.8 1.6 1.4 13.2 4.1 2.2 1.6 6.5 2.6 2.3 1.7 1.4 0.6 0.6 0.8
3.2 0.9 0.4* 0.3* 3.3 1.2* 0.6** 0.4** 1.3 0.8* 0.8* 0.5** 0.2 0.2** 0.1** 0.2
14.3 4.9 1.6 1.9 13.1 6.2 2.3 2.6 8.6 2.7 1.8 1.6 1.1 0.5 0.7 0.5
3.8 1.6* 0.5** 0.6** 3.1 1.9 0.7** 0.9** 2.2 0.8* 0.5* 0.4** 0.2 0.2* 0.2 0.1*
0.07 0.04 0.02 0.02 0.08 0.05 0.03 0.02 0.05 0.02 0.02 0.02 0.007 0.004 0.004 0.005
0.02 0.01 0.01* 0.01* 0.02 0.02 0.01* 0.01* 0.01 0.01* 0.01* 0.01** 0.002 0.002 0.001 0.002
0.04 0.02 0.01 0.01 0.04 0.02 0.01 0.01 0.03 0.02 0.01 0.01 0.006 0.003 0.006 0.005
0.01 0.01* 0.002* 0.003* 0.01 0.01* 0.01** 0.01** 0.01 0.004 0.003* 0.002* 0.002 0.001 0.001 0.001
0.2 0.2 0.3* 0.3 0.2 0.2 0.2 0.2
139 255 313 65.4 395 829 701 370
35 47 80 16.9 117 246 120 107
266 702 510 146 627 817 348 247
69 200 151 87 287 324 141 82
e 4.5 8.4 76 e 15 11 56
e 65 15 72 e 17 38 40
10.4 8.4 6.6 1.4 32.4 16.8 14.4 5.6
2.9 1.2 1.9 0.4* 10.3 3.2 3.4 2.5
13.0 22.4 12.7 2.7 26.9 33.4 15.1 11.9
3.4 5.1 3.9 1.3* 7.9 6.3 3.9 3.1
0.04 0.07 0.08 0.02 0.12 0.26 0.22 0.12
0.09 0.01 0.02 0.004 0.04 0.08 0.04 0.03
0.07 0.19 0.14 0.04 0.19 0.26 0.11 0.08
0.02 0.05 0.04 0.02 0.09 0.10 0.04 0.03
0.1 0.1*** 0.2*** 0.1***
870 2622 2116 909
98 341*** 289*** 235
1621 3023 3065 556
264 499* 786* 211**
e 8 29 82
e 2 34 87
157 136 68 12
29 20 9.4** 2.9***
323 223 115 15
57 32 24** 6.6***
0.28 0.82 0.66 0.28
0.03 0.11*** 0.09*** 0.07
0.51 0.95 0.96 0.17
0.08 0.16* 0.25 0.07**
*p < 0.05; **p < 0.01; ***p < 0.001 e the level of differences significance from the control. a Grain, data for straw (production 137Cs output 137Cs reduction and % of total 137Cs deposition) except b Data for the year 1991, 2nd cut are missing. c 137 Cs:K ratios in plants for the year 1991, 1st cut are missing. d 137 Cs:K ratios in plants for the year 1987, 1st cut are missing.
137
Cs:K ratios only for the years 1987 and 1989.
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
Loamy sand soil Y56 Hayb
137
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
X-11, hay
0.035 0.030 0.025
0.020 0.015
0.000 1st 2nd
1st
2nd
1st
2
2nd
1st
3 Year, cut
b
2nd
1st
4
1st
2nd
b Control 100 K 200 K
Tag 137Cs
0.0015 0.0010 0.0005
2nd
1st
1 2
3
1 Straw
2
3 Fig. 5. Transfer of
Year Fig. 3. Transfer of 137Cs on sandy soil, mean SE: hay (a); barley (b). No potassium was applied for hay in 1991, year 5.
137 Cs in barley grains (X9) appeared highest during the second to fourth years for both the 100 and 200 kg ha1 potassium treatments.
a
Y-48, hay
Control 50 K+Mg 100 K+Mg 200 K+Mg
0.002 0.001
Cs Tag
0.001 0.001
Control 23 K 45 K 200 K
2nd
1st
Cs on silty loam sand, mean SE: pasture Z-1 a, Z-2 b.
Y-56, hay
Control 100 K+Z 100+100 K+Z 200 K+Z
0.010 0.008 0.006 0.004 0.002
0.000
0.000
0.000 1st
1
2nd
1st
2 Year, cut
b
1st
2nd 3
Y-56, hay
0.010
0.006
2nd 2
1st
2nd
1st
3 Year, cut
Fig. 4. Transfer of
4
137
1st
2nd 5
1st
1st
4
Y56, hay
2nd 5
Control 100 K+CaO 100+100 K+CaO 200 K+CaO
0.006
0.002 1st
2nd
3 Year, cut
0.008
0.004
2nd
1st
0.010
0.002 0.000
2nd 2
0.012
0.004
1
1st
d Cs Tag
0.008
1st
2nd 1
Control 100 K 100+100 K 200 K
0.012
2nd 3
137
0.012
0.000
2nd
2nd 4
2 Year, cut
c
Cs Tag
0.001
1st
1st
The fertilization of pasture grass growing on organic rich soil with potassium at 100 or 200 kg K ha1 reduced 137Cs Tag, as a percentage of the control, by an average of 60e80% for both the first and second cuts. Although the 50 kg K ha1 treatment appeared sufficient for reducing 137Cs Tag in grass by about 30% in the first cut, it was insufficient for the second cut: in pasture grass from the second cut, the fertilization effect gradually decreased with time. This is probably due to a lack of potassium fixation in organic soils
0.001
Cs Tag
2nd 3
Z-2, pasture
0.045 0.040 0.035 0.030 0.025 0.020 0.015 0.010 0.005 0.000 1st
1 Grain
1st
2 Year, cut
5
0.0020
2nd 1
2nd
X-11, barley
0.0025
0.0000
Control 23 K 45 K 90 K 200 K
0.005
1
Tag
Z-1, pasture
0.040
0.010
1st
137Cs,
a
Control 100 K 100+100 K 200 K
Tag
0.010 0.009 0.008 0.007 0.006 0.005 0.004 0.003 0.002 0.001 0.000
137Cs
137Cs
Tag
a
29
0.000 1st
2nd 1
1st
2nd 2
1st 3 Year, cut
Cs on loamy sand, mean SE: hay Y48 (a) and Y56 (bed).
2nd
1st 4
1st
2nd 5
30
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
Z-3, pasture
reduction of cesium transfer to hay with the 100 kg K ha1 treatment, and about five to six-fold reduction with the 200 (100 þ 100) kg K ha1 treatment. Thus, in hay on sand soil treated with 200 kg K ha1, an average 70e80% reduction in 137Cs (Bq kg1, Tag), as a percentage of the control, might be achievable. A maximum 137Cs Tag reduction (up to a factor of 15 or higher) on sandy soil could be obtained during the third or fourth successive years after potassium application; with an average reduction of 137 Cs activity concentration in barley grain and straw on sandy soil of 50e60%. The maximum reduction in 137Cs Tag in barley on sandy soil might be attained during the second and third year after fertilization. Discontinuation of potassium application on sandy soil did not result in residual effect on cesium transfer to barley; therefore annual application of fertilizer on sandy soils is necessary. Both the 200 kg K ha1 and 100 þ 100 kg K ha1 treatments appeared equally efficient in reducing 137Cs uptake and had similar effects: the 137Cs transfer to crops at both rates decreased by about 80%, compared to the control treatment. Similar results are reported by Andersson et al. (2000), who showed that the transfer of Cs to plants after fertilization with 150 kg of K per ha1 on sandy and potassium-deficient soils was reduced by nearly 70%. However, in terms of applicability, 200 kg K ha1 (one application) is considered more feasible than 100 þ 100 kg K ha1.
Control 23 K 45 K 90 K 200 K
0.18 0.16 0.14 Tag
0.10
137Cs
0.12 0.08 0.06 0.04 0.02 0.00 1st
2nd
1st
1
Fig. 6. Transfer of
2nd 2
137
1st
2nd
1st
1st
3 4 Year, cut
2nd
1st
5
2nd 6
Cs on gravely sandy loam, Z-3 pasture, mean SE.
and increased leaching from organic rich soil, particularly with incremental watering in peat (Prasad and Woods, 1971). Mineral soils: The effect of potassium application on sandy soil appeared similar on organic rich soil: about two to three-fold
b
CU711, hay 1st cut
reduction factors
25 20 50 K
15
100 K
200 K
10
137Cs
137Cs
reduction factors
a
5
CU711, hay 2nd cut 30
50 K
25
1
20 15 10 5
2
3
4
5
1
6
2
3
d
X9, hay 1st cut
5
6
X9, hay 2nd cut 25
reduction factors
25 20 100 K
15
100+100 K
200 K
10
137Cs
reduction factors
4 Years
Years
137Cs
200 K
0
0
c
100 K
5
100 K
20
100+100 K
200 K
15 10 5 0
0 1
2
3
1
4
2
3
4
Years
Years
137Cs
reduction factors
e
X9, barley
8
100 K, grain 100 K, straw
6
200 K, grain 200 K, straw
4 2 0
1
2
Years
3
4
Fig. 7. 137Cs reduction factors in hay and barley on organic rich soil during successive years after potassium application, 137Cs TF without potassium divided by 137Cs Tag 50K, 137Cs Tag 100K, 137Cs Tag 100 þ 100K or 137Cs Tag 200K. Hay (aed); barley (e). No potassium was applied in year 4 and 5 (CU711 a, b).
K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
b
X11, hay 1 cut 20
X11, hay 2 cut 20
100 K
100+100 K
200 K
Cs reduction factors
Cs reduction factors
a
31
15 10 5
100 K
100+100 K
200 K
15 10 5 0
0 1
2
3 Years
4
Cs reduction factors
c8
1
5
2
3 Years
4
5
X11, barley 100 K, grain 100 K, straw
6
200 K, grain 200 K, straw
4 2 0 1
2 Years
3
Fig. 8. 137Cs reduction factors in hay and barley during successive years after potassium application, 137Cs Tag without potassium divided by (100 þ 100K), or 137Cs Tag 200K. Sandy soil: hay (a, b); barley (c). No potassium was applied for hay in 1991.
The transfer of 137Cs to barley grain is generally lower than in hay grass and the increase in potassium application from 100 to 200 kg K ha1 only slightly affected 137Cs transfer to barley grain on organic rich soil, but had a distinct effect for this crop on sandy soil. As the transfer of 137Cs from organic rich soils to barley grain was noticeable, a two-fold decrease of 137Cs Tag in grain after potassium application may be achieved. This was in agreement with other studies (Anisimov et al., 2002) in which, an increase in potassium in the soil decreased the amount of exchangeable 137Cs in two-weekold barley seedlings by a factor of 1.5e2. Due to a higher mineral content in the barley straw than in grains, the cesium transfer to the straw was two times higher than to the grains. Conversely, complete fertilizer (NPK 20-5-9) used on loam soil in the range of 23e90 kg K ha1 although increased production noticeably, did not affect cesium uptake by pasture grass: the effect was only observed at 200 kg K ha1, with a four-fold decrease of 137 Cs Tag from soil to grass in experimental plot Z1 and a six-fold decrease at Z3. At Z2, the potassium effect at the same rate (200 kg K ha1) was less pronounced. Nitrogenous fertilizers can increase biomass but may also decrease plant concentration of radionuclide due to dilution effect. This may result in low tissue radionuclide concentration, even the total uptake increases with increasing biomass (Ekvall and Greger, 2003). It is also known that increased NHþ 4 concentration in the soil may inhibit the potassium effect and increase 137Cs uptake by plant roots (Kruglov et al., 2005). Thus, the complete fertilizer, which contains nitrogenous compounds, probably inhibited the effect of potassium application on 137 Cs uptake by pasture grass, particularly at low doses (23e 90 kg K ha1). Experimental plot Z3 is situated in pasture land in the mountain district of Jämtland County. The soil is gravelly sandy loam with natural grasses and other plant species. The site has low productivity with an annual harvest of about 3000 kg dry matter ha1. The soil and plant cover conditions contribute to the high soil to plant transfer of 137Cs obtained in the control treatment: cesium transfer to pasture grass was high and persistent. On such soils, 200 kg potassium per ha1 is required and is recommended for reducing radiocesium uptake appreciably. Cesium activity tended to increase in pasture grass (Z1, Z2 and Z3), especially when lower rates of potassium were applied. It was assumed that removal of the crop
137
Cs Tag 100K,
137
Cs Tag 200K
from soils with low potassium content in soil dismissed most of the available potassium at the first cut: crop removal of potassium from sandy soils was among the largest loss. The addition of zeolite was an effective countermeasure for reducing 137Cs transfer to grass. Zeolite is more effective in reducing cesium uptake by ryegrass from peat soil compared to other minerals, such as heavy clay, bentonite, biotite, and apatite (Paasikallio, 1999). The use of potash-magnesia instead of potassium (K þ Mg treatment) was less effective than potassium alone (K) or in combination with zeolite (K þ Z). Potash-magnesia was effective for reducing 137Cs in hay at a rate 50 kg K þ Mg ha1: 137Cs activity concentration in harvest and 137Cs Tag decreased by a factor of about two. However, increased potash-magnesia rates (100 and 200 kg K þ Mg ha1) had the opposite effect. Because the high levels of Mg in the soil solution decrease rates of K uptake (Dibb and Thompson, 1985), 137Cs uptake by crops could be affected as well. The liming of calcium-deficient soils with low pH in combination with potassium fertilization aimed to reduce root uptake of cesium. However, lime application did not affect 137Cs transfer to grass: reduction of 137Cs activity concentration in harvested crops and 137Cs Tag in the K þ CaO treatment was similar or less than with the K treatment. In the long-term perspective, it appeared necessary to conserve or even improve the potassium status in soils, as the amount of K in the soil studied was insufficient to maintain a positive K balance, which affected crop uptake of 137Cs. The transfer of 137Cs from the soil to plant is described (Figs. 2e 6) by transfer factors, which is affected by many environmental factors (Ehlken and Kirchner, 2002). Variability in transfer factors can be understood through 137Cs:K ratios. In harvested material the 137 Cs:K ratios narrowed as result of potassium application. This narrowing appeared positively (r ¼ 0.98, p < 0.01) correlated with 137 Cs Tag and presumably reflected differences in soil solution composition, that is, increasing K and decreasing 137Cs concentrations. Peat soils have a lower capacity for binding cesium than mineral soils, and are generally low in potassium, such as in the Gävle area and northern Uppland (CU711, C2 and X9). The transfer of cesium to agricultural crops cultivated on peat soils tends to be higher (Gulyakin and Yudintseva, 1958); thus, periodic fertilization of soil
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K. Rosén, M. Vinichuk / Journal of Environmental Radioactivity 130 (2014) 22e32
with potassium at rates of at least 50 kg ha1 would be a feasible and effective measure for reducing 137Cs uptake by crops on both organic rich soils and mineral sand soils. When analyzing the effect of potassium application over years of study (Tables 3 and 4) the differences between treatments are often hidden. This is because the effect (reduction of cesium activity in crops) decreases over time. 5. Conclusions During the five-year period following atmospheric deposition from the Chernobyl accident, radiocesium from this source equilibrated in the agricultural environment. With regard to cesium uptake by crops and the effect of potassium fertilizers, the results were consistent with earlier investigations in micro plot experiments (Lönsjö and Haak, 1986); however, the opportunity to undertake experiments in the field with different soils in varying agricultural environments was unique. In spite of the time since the experiment was conducted the data within the literature with different levels of potassium fertilization and its effect on 137Cs transfer to crops grown on organic rich soils and sandy soils are limited. Data obtained within this study are valuable and can be used for predictive modeling, soil-based countermeasures and further management of contaminated soils to reduce radionuclide transfer along food chains. Potassium application on soils with low clay content, such as sand and organic rich soils was an effective countermeasure resulting in substantial reduction of 137Cs in crops even at a rate of 50e100 kg K ha1. The effectiveness of potassium fertilization appeared higher on sandy soils than on organic rich soils and the effect of potassium application on 137Cs Tag tended to decrease over time, but was still pronounced after 5e6 successive years. Potassium application at 100 þ 100 kg ha1 and 200 K kg ha1 had similar effects. The additional application of zeolite reduced 137Cs transfer to hay by a factor of 1.4 on sand soil and 1.8 on organic rich soil, whereas, the application of potash-magnesia and CaO had no effect. Acknowledgments The project was funded by the Swedish Radiation Safety Authorities (SSM), Swedish University of Agricultural Sciences (SLU), Sweden and Zhytomyr State Technological University (ZSTU), Ukraine. The authors are grateful to Dr. M. Simonsson, Department of Soil and Environment (SLU) for kind assistance in analyzing some data. References Andersson, K.G., Rantavaara, A., Roed, J., Rosén, K., Salbu, B., 2000. A Guide to Countermeasures for Implementation in the Event of a Nuclear Accident Affecting Nordic Foodproducing Areas. Nordic Nuclear Safety Research, Roskilde. Report NKS-16. Anisimov, V.S., Kruglov, S.V., Aleksakhin, R.M., Suslina, L.G., Kuznetsov, V.K., 2002. The effect of potassium and soil activity on the 137Cs status in soils and its accumulation by barley plants in a pot experiment. Eurasian Soil Sci. 35, 1169e 1177. Dibb, D.W., Thompson, W.R., 1985. Interaction of potassium with other nutrients. In: Munson, R.D. (Ed.), Potassium in Agriculture. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Madison, Wisconsin, pp. 515e533. Egner, H., Riehm, H., Domingo, W.R., 1960. Untersuchungen über die chemische Bodenanalyseals Grundlage für die Beurteilung des Nährstoffzustandes der
Böden. II Chemische Extraktionsmethoden zur Phosphor und Kaliumbestimmung. Kungl. Lantbr. Ann. 26, 45e61 (in German). Ehlken, S., Kirchner, G., 2002. Environmental processes affecting plant root uptake of radioactive trace elements and variability of transfer factor data: a review. J. Environ. Radioact. 58, 97e112. Ekvall, L., Greger, M., 2003. Effects of biomass-producing factors on Cd uptake in two Swedish ecotypes of Pinus sylvestris. Environ. Pollut. 121, 401e411. Gulyakin, I.V., Yudintseva, E.V., 1958. Uptake of strontium, cesium and some other fission products by plants and their accumulation in crops. In: Proceedings of the 2nd International Conference on Peaceful Uses of Atomic Energy. 1958 Sept 1e13; Geneva, pp. 476e485. IAEA, 2010. Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Terrestrial and Freshwater Environments. Technical reports series, no. 472. Vienna, 194 pp. Kruglov, S.V., Suslina, L.G., Anisimov, V.S., Aleksakhin, R.M., 2005. Mechanism of the 137 effect of Kþ and NHþ Cs accumulation by two-week-old barley plants 4 ions on from soddy-podzolic soils. Eurasian Soil Sci. 38, 1082e1090. Lönsjö, H., Haak, E., 1986. Effects of Placement and Potassium Fertilization on the Uptake of Cesium and Strontium by Agricultural Crops. Report SLU-REK-60. Swedish University of Agricultural Sciences, Uppsala (Swedish with an English summary). Paasikallio, A., 1999. Effect of biotite, zeolite, heavy clay, bentonite and apatite on the uptake of radiocesium by grass from peat soil. Plant Soil 206, 213e222. Perepelyatnikov, G., Perepelyatnikova, L., Ivanova, T., Kalynenko, L., Grytsyuk, N., Zhurba, M., 2007. Radiological efficiency of agricultural countermeasures applied in radiocontaminated fields. J. Environ. Eng. Landsc. 15, 243e252. Pietrzak-Flis, Z., Krajewski, P., Krajewska, G., Sunderland, N.R., 1994. Transfer of radiocesium from uncultivated soils to grass after the Chernobyl accident. Sci. Total Environ. 141, 147e153. 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Tonic): a large-scale hydroponic study. J. Environ. Radioact. 55, 303e314. Zhu, Y.-G., Shaw, G., Nisbet, A.F., Wilkins, B.T., 2000. Effect of potassium (K) supply on the uptake of 137Cs by spring wheat (Triticum aestivum cv. Tonic): a lysimeter study. Radiat. Environ. Biophys. 39, 283e290.
