National Agriculture and Food Research Organization
Radioactive cesium contamination of grasslands in Japan
Yasuko Togamura
Institute of Livestock and Grassland Science, NARO
Overview in 2011
1
● March 11, The Great East Japan Earthquake occurred
●Government notification（MAFF）
March 19, Precaution regarding feed, water, feeding locations, etc.
(Ex. Feeding forage and rice straw harvested before the accident)
April 14, The provisional reference value for radioactive Cs in forage （300 Bq/kg assumed 20%DM )
April 22, Guideline on the production and utilization of feed for avoiding radioactive contamination (monitoring for forage grass)
●Cancellation of voluntary restriction of feeding forage grass
May 24, Saitama prefecture May 31, Gunma prefecture June 16, Chiba
and Ibaraki prefectures Sep. 1 , Tochigi prefecture
Sep. 16, Miyagi prefecture
※Voluntary restriction had been continued in a part of Fukushima and Iwate
●TEPCO Fukushima Daiichi NPP
Revise the reference value for feeds
Group Old level (Bq/kg) Drinking
water 200
Milk/dairy
product 200 Vegetable
500 Grain
Meat/Egg/
Fish
Group New standard (Bq/kg) Drinking
water 10
Milk 50
Infant
food 50
Others 100
Animal Old level (Bq/kg) Cattle 300
Horse 300
Pigs 300
Chickens 300 Cultured
fish 100
Animal New level (Bq/kg) Cattle 100
Horse 100
Pig 80
Chickens 160 Cultured
fish 40
<Food>
<Feed>
April 2012
Decontamination (renovation) of grassland has implemented in area where it is predicted to exceed a new reference value based on the result of monitoring survey of 2011‐2012 .
Area required decontamination
Iwate
Miyagi Fukushima
Tochigi Gunma
Use of decontaminated
grassland has to be determined by the result of survey.
2
0 50 100 150
1st cut
2nd cut
3rd cut
1st cut
2nd cut
3rd cut
1st cut
2nd cut
3rd cut untilled Disk
hallow
Bottom plow
Radioactive Cs in grass （Bq/kg, water content 80%)
Plowing reduces radioactive Cs concentrations of grass by mixing of soil and root mat layer
Bottom plowing in NILGS (2011)
(Shibuya et al. 2013)
3 Radioactive Cs concentration of grass harvested in 2012
harrow
-0.53
-0.63
牧草 Cs
リン酸吸収係数
全炭素
粘土
RIP
交換性カリ
-0.74 -0.59
0.38
0.72
交換性Cs 土壌Cs
-0.40 0.51
0.78
pH CEC
交換性Cs 土壌Cs
-0.41 0.34
交換性石灰
交換性苦土
仮比重
-0.73 0.55
-0.47
The result of grassland survey in 2012 was reported that 8.1% of renovated grassland produced forage containing radioactive Cs higher than the reference value for feed.
Analysis of soil factors on RCs concentration of grass (2012)
Grass RCs
Soil RCs
Ex-K
2O
Ex-RCsRCs
Ex-RCs
Ex-CaO Ex-MgOTotal C
Bulk density P absorption coefficient
Cray
RIP: Radiocaesium Interception Potential 4
Soil exchangeable potassium reduces radioactive Cs transfer to grass
The target value of exchangeable K
2O
content (0-15 cm depth) is 30-40 mg/100g.
Transfer factor＝radioactive Cs of grass÷radioactive Cs of soil 0
2 4 6 8
0 20 40 60 80 100 120
Transfer factor from soil to grass
Soil exchangeable K (mgK2O/100g)
(Yamada et al. 2013) 5
0 50 100 150 200 250 300
Andosol else Radioactive Cs in grasses (Bq/kg, water content of 80%）
0 1000 2000 3000 4000 5000
Andosol else
RIP(mmol/kg)
Andosol (volcanic ash soil) has lower RIP and higher radioactive Cs of grass after renovation
In the survey of 2012 for grasslands where radioactive Cs
concentrations of grass after renovation exceeded 100 Bq/kg, andosol showed higher radioactive Cs than the other soil types.
Andosol was classified by using the criteria of phosphorus absorbance coefficient > 1500. p <0.01 shows significant difference by U test.
RIP
p<0.01
Grass Cs
p<0.01
(Harada and Yamada 2014)
6
(Shibuya et al. 2014)
7
Effect of plowing method on radioactive Cs concentration of grass
Deep plowing is effective to reduce radioactive Cs of grasses
(Shibuya et al. 2014) 8
Effect of plowing method on radioactive Cs concentration of grass
Fine clod breaking is effective to reduce radioactive Cs of grasses
Soil pulverization :percentage by weight of soil particles passing through a sieve of 2cm mesh
Buried root mat and litter layer
11900Bq/kg, 31mg-K2O/100g
0-5cm: 200Bq/kg, 22mg-K2O/100g
5-10cm: 1000Bq/kg, 8mg-K2O/100g
10-15cm: 2000Bq/kg, 16mg-K2O/100g
Grassland exceed the reference value of feed (100Bq/kg)
Radioactive Cs concentration of grass was 280Bq/kg(DM20%）
Yamada et al. unpublished 9
Results of the survey of grass on
decontaminated (renovated) grassland
Survey Year
Total Reported samples ( Number, %)
～50Bq/kg ～100Bq/kg 100Bq/kg～
2012 1,893
(100%)
1,578 (83.4%)
161 (8.5%)
154 (8.1%)
2013 18,158
(100%)
17,081 (94.1%)
725 (4.0%)
352 (1.9%)
2014 10,319
(100%)
9,999 (96.9%)
230 (2.3%)
90 (0.9%)
2015 10,999
(100%)
10,678 (97.1)
230 (1.6%)
115 (1.3%)
10
(Shibuya et al. 2015）
An application of only nitrogen fertilizer on meadow caused a decrease of soil exchangeable K
2O content and an increase of radioactive Cs concentration of forage
0 20 40 60 80 100 120 140 160
2012 2013 2014 2012 2013 2014
牧草中放射性セシウム濃度 (134+137CsBq/kg水分80%換算)
標準施肥 窒素単肥
●:1番草●:2番草●:3番草●:暫定許容値超え :暫定許容値
Radioactive Cs in grass ( Bq/kg, DM 20%)
N:P2O5:K2O=
150:150:150 kg/ha/yr
N:P2O5:K2O=
150:0:0 kg/ha/yr
Reference value for feed
1st 2nd 3rd >100Bq/kg
Renovated in 2011 by disc harrow 11
0 20 40 60 80 100 120
2012 2013 2014 2012 2013 2014
土壌(0‐5cm)中交換性カリ含量 (mg‐K 2O/100g乾土)
標準施肥 窒素単肥
N:P2O5:K2O=
150:150:150 kg/ha/yr
N:P2O5:K2O=
150:0:0 kg/ha/yr
Exchangeable K2O in soil ( 0-15cm depth, mg/100g dry soil)
N:P2O5:K2O (kg/ha/yr)
Grass production
(DM t/ha/yr) K2O output (kg/ha/yr) K2O balance (kg/ha/yr)
2012 2013 2014 2012 2013 2014 2012* 2013 2014
150:150:150 8.9 10 11.2 280 370 360 -30 -220 -210
150:00:00 8.2 9.8 9.8 260 280 240 -160 -280 -240
*:K2O input in 2012 includes the amount applied in the grassland renovation in 2011.12
Renovation of steep slope grasslands by using radio-controlled tractor
Newly developed rotary
Rotary tilling
Growth situation (after 2 months)
Seeding Fertilization
Cutting pre-vegetation
Soil packing
13
