To mitigate radioactive cesium from soil to plant, increasing and maintaining the exchangeable potassium (ExK) level during growth is widely accepted after Tokyo Electric Company's Fukushima Dai-ichi ...Nuclear Plant accident in Japan. This is because the antagonistic relationship between soil solution K and 134Cs + 137Cs (RCs) concentrations changes the transfer factor (TF: designated as the ratio of radioactivity of plant organ to soil) of RCs. As the relationship between ExK and TF depends on the soil types, crop species, and other environmental factors, the required amount of ExK should be set to a safe side. Eleven years after the accident, as the activity of 134Cs was almost negligible, 137Cs became the main RCs in most of the agricultural fields in Fukushima Prefecture. We propose a new indicator, the concentration ratio of plant 137Cs to soil exchangeable 137Cs (Ex137Cs), instead of TF, which showed a better correlation with ExK even among soils with different properties (or mineralogy).
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•Exchangeable K level is known to be a detrimental factor to mitigate 137Cs uptake by plant.•Relationship between exchangeable K and the transfer factor was not equal at different soils.•The amount of exchangeable 137Cs is also an important factor to explain the radioactivity of the plant.•The concentration ratio of plant 137Cs to soil exchangeable 137Cs showed a significant correlation with exchangeable K.
Non-exchangeable K released from soil minerals can reduce radiocesium transfer to plants, as well as exchangeable K. We investigated the effect of non-exchangeable K on radiocesium transfer to ...soybean, and the non-exchangeable K extraction method most suitable for estimating the transfer risk. In Fukushima Prefecture, Japan, 106 soils were collected from 89 soybean fields during 2014–2018 to analyze non-exchangeable K contents using three methods: boiling nitric acid extraction, tetraphenyl‑boron extraction, and mild tetraphenyl‑boron extraction. The non-exchangeable K contents quantified by the former two methods were dependent on the amount of micas, which are K-bearing minerals. The non-exchangeable K content by mild tetraphenyl‑boron extraction depended on the amount of K fertilizer application and K-fixing minerals but not on micas, indicating that it reflects fertilizer K fixed by the minerals. The soil-to-plant transfer factor of radiocesium was most correlated with the non-exchangeable K content by the mild extraction (rs = −0.67). This correlation was also stronger than that between exchangeable K and the transfer factor (rs = −0.40). As non-exchangeable K content increased, the exchangeable radiocesium fraction decreased, indicating that radiocesium was fixed together with K. Additionally, multiple regression analysis indicated that non-exchangeable K by the mild extraction significantly decreased the transfer factor even if the exchangeable radiocesium fraction was kept constant. Thus, the fixed K was considered to repress radiocesium transfer to soybean through both radiocesium fixation and K supply. With the criterion of total extracted K, the sum of exchangeable and non-exchangeable K, as 65 mg K2O 100 g−1 by the mild extraction, fields with high and low transfer factors were able to be differentiated more effectively than with a current criterion of exchangeable K as 50 mg K2O 100 g−1. The results revealed that mild tetraphenyl‑boron extraction is effective for estimating radiocesium transfer to soybean.
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•Ne-K content analysis by 3 methods showed varied patterns in Fukushima soils.•Ne-K by TPBM method was the most correlated with radiocesium transfer to soybean.•TPBM-Ne-K content increased, reflecting K fixation, causing radiocesium fixation.•Fixed K repressed radiocesium transfer to soybean through fixation and K supply.•TPBM extraction method effectively estimated radiocesium transfer risk to soybean.
Abstract
Agro-food systems require nutrient input from several sources to provide food products and food-related services. Many of the nutrients are lost to the environment during supply chains, ...potentially threatening human and ecosystem health. Countries therefore need to reduce their nutrient/nitrogen footprints. These footprints are importantly affected by links between sectors. However, existing assessments omit the links between sectors, especially between the agriculture, manufacturing, and energy sectors. We propose a novel approach called the nutrient-extended input–output (NutrIO) method to determine the nutrient footprint as a sum of direct and indirect inputs throughout the supply chains from different sources of nutrients. The NutrIO method is based on a nutrient-based material flow analysis linked to economic transactions. Applying this method, we estimated the nitrogen footprint of Japan in 2011 at 21.8 kg-N capita
−1
yr
−1
: 9.7 kg-N capita
−1
yr
−1
sourced from new nitrogen for agriculture and fisheries, 7.0 kg-N capita
−1
yr
−1
from recycled nitrogen as organic fertilizers, and 5.1 kg-N capita
−1
yr
−1
from industrial nitrogen for chemical industries other than fertilizers. A further annexed 55.4 kg-N capita
−1
yr
−1
of unintended nitrogen input was sourced from fossil fuels for energy production. The nitrogen intensity of the wheat and barley cultivation sector, at 1.50 kg-N per thousand Japanese yen (JPY) production, was much higher than that of the 0.12 kg-N per thousand JPY production for the rice cultivation sector. Industrial nitrogen accounted for 2%–7% of the nitrogen footprint of each major food-related sector. The NutrIO nitrogen footprint sourced from new nitrogen for agriculture and fisheries, at 8.6 kg-N capita
−1
yr
−1
for domestic final products, is comparable to the food nitrogen footprint calculated by other methods, at 8.5–10.5 kg-N capita
−1
yr
−1
. The NutrIO method provides quantitative insights for all stakeholders of food consumption and production to improve the nutrient use efficiencies of agro-food supply chains.
Huge amounts of radionuclides, particularly radiocesium, were discharged from the Fukushima Daiichi Nuclear Power Plant (FDNPP), and widespread of contamination of the land, including paddy fields, ...was observed. Because rice is a staple food in Japan, contamination of paddy fields is a serious problem, and practical countermeasures to reduce radiocesium contamination of rice are urgently required. Potassium (K) fertilization was previously shown to be an effective countermeasure in fields contaminated by the Chernobyl accident, but researchers did not study the effects on rice (Oryza sativa L.). In the present study, we performed urgent field experiments to test the use of K fertilization, as well as other soil amendments, to reduce radiocesium contamination of rice. We found that K fertilization was an effective and practical countermeasure to reduce radiocesium uptake by rice from several soil types in Japanese paddy rice culture. Other treatments, including the application of expanded vermiculite or manure, were effective, and the effect appears to be explained by their K content. Based on these results, the recommended level of exchangeable soil potassium to lower the radiocesium content of rice to acceptable levels is about 200 mg K kg –¹ soil before the usual fertilization. This K fertilizer application criterion was applied in a wide, low-contaminated area from the 2012 cropping season, and satisfactory results have been obtained generally.
Field and pot experiments were conducted to evaluate the effectiveness of coarse Finnish phlogopite application to reduce radiocesium uptake by paddy rice (Oryza sativa L.). The application of ...phlogopite was expected to reduce radiocesium uptake by crops through K supply and radiocesium retention. Three fields were set in Fukushima Prefecture, and coarse (mean particle size of 450 μm) phlogopite from Siilinjärvi (Finland) was applied at a rate of 5 t ha−1. Paddy rice was cultivated for 2–4 successive years. In all fields, the average 137Cs transfer factor (TF) of brown rice harvested from plots with added phlogopite was significantly lower than that of brown rice from plots without added phlogopite over the 2–4-year experiments. TF was decreased by up to 80% following phlogopite application, without an adverse effect on yield. Exchangeable K and soil solution K were higher in the soils with added phlogopite, suggesting K released from phlogopite reduced 137Cs uptake by paddy rice. Moreover, in a pot cultivation experiment, even when 55% of the total K was removed from phlogopite prior to application, the TF in pots with phlogopite application was less than half of that in pots without added phlogopite. The results from the field study and the pot cultivation experiment suggested that the application of Finnish phlogopite is effective to reduce the TF of brown rice. Exchangeable K and tetraphenylborate-extractable-K (TPB-K) at rooting stage, and soil solution K at tillering and heading stages showed significant negative correlation with TF. TPB-K was significantly positively correlated with soil solution K at tillering stage and heading stage, whereas exchangeable K at rooting stage did not exhibit significant correlation with soil solution K at heading stage. The results suggest that TPB-K is more reliable than exchangeable K, which could facilitate as a basis of K fertilizer recommendation for radiocesium-contaminated fields.
•Finnish phlogopite application reduced 137Cs uptake by paddy rice.•Phlogopite was effective throughout 2–4-year field trials.•Tetraphenylborate-extracted K is a more reliable soil test than exchangeable K.
The ability to characterize rapidly and repeatedly exchangeable potassium (Kex) content in the soil is essential for optimizing remediation of radiocaesium contamination in agriculture. In this ...paper, we show how this can be now achieved using a Convolutional Neural Network (CNN) model trained on a large Mid-Infrared (MIR) soil spectral library (40,000 samples with Kex determined with 1 M NH4OAc, pH 7), compiled by the National Soil Survey Center of the United States Department of Agriculture. Using Partial Least Squares Regression as a baseline, we found that our implemented CNN leads to a significantly higher prediction performance of Kex when a large amount of data is available (10000), increasing the coefficient of determination from 0.64 to 0.79, and reducing the Mean Absolute Percentage Error from 135% to 31%. Furthermore, in order to provide end-users with required interpretive keys, we implemented the GradientShap algorithm to identify the spectral regions considered important by the model for predicting Kex. Used in the context of the implemented CNN on various Soil Taxonomy Orders, it allowed (i) to relate the important spectral features to domain knowledge and (ii) to demonstrate that including all Soil Taxonomy Orders in CNN-based modeling is beneficial as spectral features learned can be reused across different, sometimes underrepresented orders.
•Knowing soil potassium content is key to restore farmland after nuclear accidents.•Deep Learning models trained on large spectral libraries allow to predict potassium.•Model interpretability allows to relate learned spectral features to domain knowledge.•Inclusion of all Soil Taxonomy Orders improves model performance.
Potassium (K) and radiocaesium (RCs) were chemically extracted from soils derived from granite (G soils) and sedimentary rock (S soils) in Fukushima, Japan. The extractants employed were 1 M HNO
3
, ...concentrated HNO
3
, and HF + HClO
4
. As S soils contain a lower amount of trioctahedral 2:1 phyllosilicates than G soils, the RCs/K ratio was higher in S soils than in G soils with 1 M HNO
3
extraction, indicating that the potential risk of soil-to-plant transfer of RCs is higher in S soils than in G soils. In conclusion, information about surface geology is important in predicting the spatial pattern of soil characteristics related to transferability of RCs.
The effect of soil exchangeable potassium (K) and cesium (Cs) levels on Cs uptake and accumulation in different parts of rice (Oryza sativa L.) plants were examined using paddy soils with diverse ...exchangeable K and Cs in pot experiments. Aboveground Cs uptake decreased with higher exchangeable K and was linearly correlated with exchangeable Cs/K ratios, indicating competitive absorption of these elements by roots. Variation in Cs concentration in brown rice among soils was also related to the exchangeable Cs/K ratio. The exchangeable Cs/K ratio was positively reflected in the Cs/K concentration ratio in each plant part, with a specific slope, suggesting that Cs transport was coordinated with K transport and that there were regulated discriminations of Cs against K in the translocation process among parts. The Cs/K ratio was higher in brown rice and dead leaves than in active leaves, stems and husks. The distribution of Cs accumulation in brown rice was 14.5% on average, but it was variable and negatively related to K concentration in the stem. The Cs distribution in aboveground plant parts also decreased with higher K concentration in the root. These results imply the importance of the competitiveness with K in the root absorption and translocation of Cs within the plant. Based on the observed relationship between Cs and K, effective K management and other measures to control Cs accumulation in plant parts are discussed.
A pot cultivation experiment was conducted to elucidate the influence of the nonexchangeable potassium (K) of mica on radiocesium (137Cs) uptake by paddy rice (Oryza sativa L. cv. Koshihikari), and ...to evaluate the potential of mica application as a countermeasure to reduce radiocesium transfer from soil to paddy rice. The increase in the exchangeable K concentrations of soils, measured before planting, due to mica (muscovite, biotite, and phlogopite) application was negligible. However, in trioctahedral mica (biotite and phlogopite)-treated soil, the release of nonexchangeable K from the mica interlayer maintained the soil-solution K at a higher level during the growing season in comparison to the control, and consequently decreased the 137Cs transfer factor for brown rice (TF). The sodium tetraphenylboron (TPB)-extractable K concentration of the soils, measured before planting, was strongly negatively correlated with the TF, whereas the exchangeable K concentration of the soils, also measured before planting, was not correlated with the TF. Therefore, we conclude that TPB-extractable K is more reliable than exchangeable K as a basis of fertilizer recommendations for radiocesium-contaminated paddy fields. Phlogopite-treated soils exhibited higher TPB-extractable K concentrations and lower TF values than biotite-treated soils. We thus conclude that phlogopite application is an effective countermeasure to reduce radiocesium uptake in paddy rice.
•Nonexchangeable K of added trioctahedral mica decreased 137Cs uptake by paddy rice.•TPB-extractable K would be a more reliable indicator than exchangeable K.•Phlogopite would be a good amendment for radiocesium-contaminated paddy fields.
Pot and field experiments were conducted to clarify the effect of soil exchangeable potassium (K) and cesium-137 (¹³⁷Cs) on ¹³⁷Cs accumulation and to establish soil index in rice (Oryza sativa L.). ...Four paddy soils in Fukushima Prefecture, Japan, showing different transfer factors for radioactive Cs derived from the accident of Fukushima Daiichi Nuclear Power Station in the field were compared in terms of ¹³⁷Cs accumulation in rice in a pot experiment. ¹³⁷Cs accumulation in shoots and brown rice widely varied among soils with the transfer factor ranging from 0.018 to 0.068 for shoots and 0.004 to 0.065 for brown rice. ¹³⁷Cs concentration in brown rice and shoots tended to decrease with higher levels of soil exchangeable K, and they were more closely related to the exchangeable Cs/K ratio. Similar relationships between the Cs/K ratio and Cs accumulation in plants were obtained for the stable isotope cesium-133 (¹³³Cs). The distributions of ¹³⁷Cs and ¹³³Cs in grains were also similar and variable among soils. The transfer factors obtained in pot experiments mostly agreed with field observations. The results imply that the exchangeable ¹³⁷Cs/K can be a potential soil index to estimate ¹³⁷Cs accumulation in rice.
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