The role of mineralization of the organic matter of soddy-podzolic and peat bog soils in the accumulation of <Superscript>137</Superscript>Cs by plants

The role of mineralization of soil organic matter (SOM) in the mobilization of ¹³⁷Cs was estimated on the basis of data on the biokinetic fractionation of the organic matter of soddy-podzolic sandy-loam and peat bog soils and on the coefficients of the soil-to-plant transfer of radiocesium under field conditions. The peat bog soils were richer than the soddy-podzolic soils in the total organic carbon (by 7.9–23.8 times), the potentially mineralizable carbon (by 2.4–6.5 times), and the carbon of the microbial biomass (by 2.9–4.6 times). The agricultural use of the soddy-podzolic and peat bog soils led to a decrease in the SOM mineralization capacity by 1.1–1.8 and 1.4–2.0 times, respectively. Simultaneously, the portions of the easily, moderately, and difficultly mineralizable fraction of the SOM active pool changed. The coefficients of the ¹³⁷Cs transfer from the peat bog soils to plants were 3.3–17.6 times higher than those for the soddy-podzolic soils. The content of ¹³⁷Cs in plants grown on the peat bog soils was 2–65 times higher than that in the mobile (salt-extractable) soil pool by the beginning of the growing season. Strong positive linear correlations were found between the coefficients of the soil-to-plant transfer of ¹³⁷Cs and the total content of the SOM, the content of the microbial biomass, the content of the potentially mineralizable carbon, and the intensity of its mineralization. It was concluded that the decisive factors controlling the intensity of the ¹³⁷Cs transfer from mineral and organic soils into plants are the SOM content and its mineralization potential. The mineralization of the SOM is accompanied by the release of both ¹³⁷Cs and mineral nitrogen; the latter facilitates the transfer of radiocesium into plants.     

Radio-caesium fixation dynamics: measurement in six Cumbrian soils

Five peat soils and a mineral soil were artificially contaminated with ¹³⁷Cs. Soil solution activity and radio–lability of ¹³⁷Cs were monitored over 709 days to quantify progressive ¹³⁷Cs fixation. The peat soils fixed large amounts of ¹³⁷Cs, but less than the mineral soil did. Distribution coefficients (K_d, cm³ g^?1) ranged from 30 to 5000 at the end of equilibration. A labile ¹³⁷Cs distribution coefficient, K_dt, was estimated by a method involving solid ? solution equilibration in dilute solution. In a separate study several concentrations of KCl were added to soils in increasing concentration both before and after the addition of ¹³⁷Cs. Differences in apparent adsorption strength of radiocaesium indicated that K⁺ induced the collapse of expanded mineral interlayers, thereby trapping ions. It seemed that ^I37Cs adsorbs at sites in the small micaceous clay fraction of the peat soils. The different rates of ¹³⁷Cs adsorption and fixation in the peat and mineral soils, in which the rate of access of ¹³⁷Cs to fixation sites in peat soils is less, seems to have been caused partly by lack of K, and partly by the scarcity of fixation sites.     

The migration of fallout 134Cs, 137Cs and 106Ru from Chernobyl and of 137Cs from weapons testing in a forest soil

To estimate the accumulation and vertical migration of radiocesium and radioruthenium, the activity concentrations of Chernobyl-derived ¹³⁴Cs, ¹³⁷Cs and ¹⁰⁶Ru as well as of ¹³⁷Cs from the global fallout of weapons testing observed in the upper horizons of a forest soil (Hapludult, spruce stand) were evaluated with a compartment model. The resulting residence half-times were used to estimate the mean rates of transport of these radionuclides. For Chernobyl-derived ¹³⁴Cs and ¹³⁷Cs within the time period of 200–600 days after the beginning of the fallout the rates were between 4 cm/yr (Of1-horizon) and 2 cm/yr (Oh-horizon), and for ¹⁰⁶Ru between 4 cm/yr (Of1-horizon) and 7 cm/yr (Oh-horizon). These rates, though considerably slower than observed in the same soil during the initial infiltration of these radionuclides with a rain shower, are (depending on the soil horizon) still higher by a factor of 3–6, when compared to the rates of transport of ¹³⁷Cs from the global fallout of weapons testing in the same soil. Because global fallout ¹³⁷Cs is in the soil since about 20 years, these results suggest that the fixation of radiocesium in the forest soil is a rather slow process.     

Distribution and mobility of radiocesium in relation to the clay fraction mineralogy and soil properties in the Iput River floodplain

The role of the mineralogy of the clay fraction and the physicochemical properties of alluvial soils in the floodplain of the Iput River and its tributary the Buldynka River (in the region of the settlement of Starye Bobovichi in Bryansk oblast) in the distribution and immobilization of radioactive isotope ¹³⁷Cs from the atmospheric fallout after the Chernobyl accident was studied. The soils had a sandy texture; a significant variation in the content of amorphous iron oxides (0.1–0.77%) and labile manganese (11.2–193 mg/kg), the cation exchange capacity (6.1–54.2 meq/100 g soil), and the base saturation (29–100%) was common; an appreciable content of X-ray amorphous mineral substances in the clay fraction (<1 μm) enriched with organic carbon (7.7–13.1%); the predominance of trioctahedral hydromicas (Me=50%) in the clay fraction; and the presence of fine-disperse quartz and lepidocrocite. The specific activity of the ¹³⁷Cs in the clay fraction of the moderately and strongly contaminated layers increased with the increasing portion of smectite formations and (or) hydromicas. On the whole, the presence of the clay fraction favored a decrease in the ¹³⁷Cs mobility (the correlation between its content and that of exchangeable cesium was r=?0.608, n=17). However, the portion of exchangeable radiocesium (extracted with 1 M CH₃COONH₄, 1:10) had a tendency toward an increase with increasing content of hydromicas in the clay fraction. Thus, the minerals of this group were a potential source of exchangeable ¹³⁷Cs in the soils. The significant role of amorphous and mobile iron forms in the immobilization and migration of radiocesium in the secondary contaminated horizons of the alluvial soils was revealed.     

Distribution of <Superscript>137</Superscript>Cs in the particle-size fractions and in the profiles of alluvial soils on floodplains of the Iput and its tributary Buldynka Rivers (Bryansk oblast)

Pits of sandy alluvial soils were studied in different parts of the floodplains of the Iput River and its tributary the Buldynka River near the settlement of Starye Bobovichi (Bryansk oblast). The ¹³⁷Cs content in the soil horizons varied from 0.01 to 31.2 Bq/g reaching the maximum in the initially polluted layers buried at depths of 6 to 40 cm. Radiocesium was found in all the particle-size fractions with its predominate concentration in the finest fractions. The specific ¹³⁷Cs activity in the fractions of <1, 1–5, 5–10, and >10 μm comprised 44.1 ± 11.5; 33.3 ± 7.6, 20.9 ± 4.9, and 2.4 ± 0.6 Bq/g of soil. However, the contribution of the coarse (>10 μm) fractions to the total radiocesium pool in the soils (19–60%, or 34 ± 2% on the average) was comparable with that of the clay fraction (16–71%, or 38 ± 3% on the average), because of the predominance of the sand-size fractions in the soils. The highest coefficient of variation with respect to the relative contribution of particular fractions to the total soil pool of ¹³⁷Cs was characteristic of the fraction of 5–10 μm; in the other fractions, it varied from 31 to 41%. The portion of ¹³⁷Cs bound with the finest fractions increased in the deeper layers. The total ¹³⁷Cs activity in the polluted horizons of the soils was mainly determined by its concentration in the clay fraction (Spearman’s coefficient of rank correlation (r) for the moderately polluted horizons comprised 0.926 at n = 14). It was experimentally proved that clay particles, upon the destruction of organic films on their surface, could readsorb the released radiocesium for a second time.     

Varietal difference in radiocesium uptake and transfer from radiocesium deposited soils in the genus Amaranthus

Abstract

Within Amaranthaceae, 33 different varieties, including local varieties from Japan, were grown in 2012 in a field in the town of Iino in the Fukushima prefecture, which is located approximately 51 km north of Tokyo Electric Power Company, Fukushima Daiichi Nuclear Power Plant (FDNPP). The contamination level of the soil was 2770 ± 140 Bq kg^?1 dry weight (¹³⁴Cesium (Cs) + ¹³⁷Cs, average ± SE), and the field was also cultivated in 2011. There was a significant varietal difference in the dry weight production, radiocesium accumulation and transfer factor (TF) of radiocesium from the soil to the plant. The ratio of the lowest TF to the highest TF was approximately 3. Because the ratio of ¹³⁷Cs to ¹³³Cs was significantly positive, radiocesium seems to be absorbed in a manner similar to that of ¹³³Cs. It is suggested that the varietal difference in the behavior of radiocesium uptake mainly depends on its genetic background rather than on environmental factors.     

The Efficiency of Moldboard Plowing upon Deactivation and Rehabilitation of Radioactively Contaminated Pastures in the North of Japan

The nuclear disaster at the Fukushima-1 nuclear power plant resulted in the widespread contamination of agrocenoses with radiocesium (¹³⁴Cs and ¹³⁷Cs) on the Honshu Island. Our study was performed on four agricultural fields located on gentle slopes of southern aspect 150 km to the northwest from the nuclear power plant. Three plots were tilled in different periods (in 2012–2013), and one plot remained untilled. The density of soil contamination and the specific activity of radiocesium in plants (June 2014) on tilled plots appeared to be permissible. Thus, the density of soil contamination varied within the range of 1.3–6.5 kBq/m², and the specific radioactivity of plants did not exceed 100 Bq/kg in plants. Such areas may be used as pastures without restrictions. At the same time, an increased density of the soil contamination (13–32 kBq/m²) and the concentration of radiocesium in plants (up to 138 Bq/kg) were detected in some areas not subjected to reclamation works. Such fallow lands are suitable as pastures only for feeding cattle for meat and for milk with their obligatory subsequent processing. On all the plots, the concentration of radiocesium in soils decreased down the soil profile. In general, radiocesium was accumulated on the middle and lower parts of slopes, which is associated with the development of water erosion and initial distribution of radiocesium during the snowmelt season. The air dose rate on the studied plots did not exceed the permissible safety level (0.2 μSv/h) and varied within the range 0.05–0.10 μSv/h. The maximum level of γ-radiation was determined on the fallow (untilled) plot. On tilled plots, γ-radiation was 30–50% lower. Therefore, soil moldboard plowin tillage to the depth of 20 cm with or without shallow cultivation is an efficient measure to reclaim agricultural lands with the initially low level of radiocesium contamination (up to 32 kBq/m²).     

Long‐term root uptake of radiocesium by several crops

Abstract

A greenhouse study was conducted to evaluate the long‐term availability of radiocesium (Cs‐137) to various crops grown on contaminated soil that were limed to pH 6.8 (LIME) or were limed and Zn‐ and Mn‐EDTA chelates added (LIME + CHELATE). Crops were grown either continuously or followed a cropping sequence. Continuously grown clover and bahiagrass accumulated the most Cs‐137 with levels exceeding 2,000 pCi/g dry weight in bahiagrass. Uptake of Cs‐137 was depressed by both the LIME and LIME + CHELATE treatments. Uptake was usually greatest during the first three years but only in unlimed soil. Cesium‐137 is about 3 to 8 times higher in soybean beans than in wheat grain. Uptake of Cs‐137 by plants from contaminated soil can be expected to be high in acidic soils, especially in the absence of lime treatment.     

Distribution and migration of radiocesium in sloping landscapes three years after the Fukushima-1 nuclear accident

The results of the study are presented on the distribution and migration of radiocesium in mountainous (580–620 m a.s.l.) landscapes in the northeast of Honshu Island (Tohoku Region, Miyagi Prefecture) subjected to radioactive contamination after the nuclear accident at Fukushima-1 NPP. In July 2014, the average contamination density with radiocesium (¹³⁴Сs and ¹³⁷Сs) over the territory (150 km to the northwest from NPP) was equal to 16 kBq/m². This contamination is estimated at the acceptable level according to both Japanese and Russian standards and legislation. Three years after the accident, radiocesium is found to be unevenly distributed by the biogeocenosis components, i.e. 45% in litter, 40% in plants, 10% in soil, and 5% in roots. As for the distribution of total radiocesium (Cs tot = ¹³⁴Сs + ¹³⁷Сs) by the profile of volcanic podzolic-ocherous soil (Dystric Aluandic Andosols), its maximal content (about 80%) was found in the surface layer (0–2.5 cm), with the specific activity ranging from 250 to 10070 Bq/kg and sharply decreasing with the depth. Radiocesium amount in the soils of forest ecosystems was on average by 20% higher than in meadow ecosystems. Accumulation of radionuclides in soils of lower and middle parts of a slope with an insignificant vertical migration was found to be the most general regularity. The air dose rate did not exceed the maximal permissible level, and the snow cover acted as an absorbing and scattering screen.     

Radiocesium transfer into the fruit of deciduous fruit trees contaminated during dormancy

Following the accident at the Tokyo Electric Power Company, Fukushima Daiichi Nuclear Power Plant (FDNPP), radiocesium (¹³⁴Cs + ¹³⁷Cs) concentrations in deciduous mature fruits were determined in orchards in the northern area of Fukushima Prefecture. At the time of the nuclear accident, most deciduous fruit trees were in the dormant stage prior to bud burst. To evaluate the relationship between radiocesium deposition in the soil and fruit contamination, radiocesium concentrations were measured from the 5-cm topsoil and from six fruit species across 17 orchards in 2011. The vertical distribution of radiocesium in the topsoil (0–30 cm in depth) and its spatial distribution in the 5-cm topsoil underlying the tree canopy of a peach, Prunus persica (L.) Batsh, orchard (“Akatsuki” cultivar) were also investigated. Significant correlations between the radiocesium concentration in the mature fruit and that in the 5-cm topsoil layer were observed for the 17 orchards as well as for the trees of the peach orchard. However, 93% of the ¹³⁷Cs found in the 30-cm soil core was retained within the top 3 cm of the soil in the peach orchard. Considering the profile of the root of this deciduous fruit tree, we assumed a negligible level of radiocesium uptake via the roots. However, the possibility of inward migration via the bark was undeniable, because some radiocesium adhered to the tree canopy before bud burst while depositing on the soil surface. Additionally, transfer factors for peach and grape, hybrid of Vitis labrusca L. and Vitis vinifera L., from young, uncontaminated trees cultivated with contaminated soil were lower than those previously reported.     

The extent and significance of bioturbation on 137Cs distributions in upland soils

Differences between measured ¹³⁷Cs activity–depth profiles and idealised undisturbed profiles generated from an exponential model suggest that faunal turbation has redistributed ¹³⁷Cs in mineral and organic upland soils in southern Scotland. Bioturbation is also demonstrated by the vertical displacement of other inputs to the soils of known age (non-native tree pollen and spheroidal carbonaceous particles, SCPs). The causes and mechanisms of bioturbation were further investigated by soil micromorphology. Well-drained mineral soils with active populations of earthworms are the most bioturbated, showing near-complete homogenisation to depths of about 20 cm. Enchytraeids also seem to remobilise ¹³⁷Cs by the digestion of organic matter and may be the main cause of ¹³⁷Cs redistribution in organic-rich upland soils. Relative rates of mixing are evaluated by comparing ¹³⁷Cs depth profiles.     

Spatial Distribution of 137CS in Forest SOils of Switzerland

In the framework of the second Swiss forest soil inventory, ¹³⁷Cs-activity from 172 sites was measured systematically for the first time in the topmost soil layer (0–5 cm) and represented on a map. The spatial distribution of ¹³⁷Cs contamination was similar to the pattern observed in 1986 from dose equivalent measurements following the Chernobyl nuclear power plant accident. Forest soils from regions with high precipitation in 1986 showed a higher ¹³⁷Cs activity than regions with low precipitation. At sites with high caesium activities it was possible to discriminate between ¹³⁷Cs originating from global fallout of the fifties and sixties and ¹³⁷Cs from the Chernobyl accident. The results indicate that radiocaesium persists in the top soil layers and is recycled in forest ecosystems.     

Enhanced sorption and fixation of radiocaesium in soils amended with K-bentonites, submitted to wetting–drying cycles

The use of bentonites as soil amendment has met with little success in reducing plant uptake of radiocaesium. However, bentonites exchanged with K⁺ have pronounced Cs⁺ binding capacity when subjected to wetting–drying cycles. Fifty‐four different bentonites were collected and characterized for cation exchange capacity and chemical composition. The radiocaesium interception potential (RIP) increased up to 160‐fold (mean 25) when the bentonites were converted to the K‐form and subjected to wetting–drying cycles. This increase in radiocaesium sorption was ascribed to a collapse of the clay sheets into an illite‐like structure, and was most pronounced in bentonites with a high layer charge. The RIP values of K‐bentonites subjected to 25 wetting–drying cycles ranged from 0.22 to 44.3 mol kg^?1. The RIP yields, i.e. the RIP in soil–bentonite mixtures expressed per unit bentonite added, were even higher and ranged up to 99 mol kg^?1. This upper limit is about 10‐fold higher than the RIP value of illite (～ 10 mol kg^?1), the principal ¹³⁷Cs sorbent in soils of temperate climates. Wetting–drying also promoted fixation of radiocaesium in soils amended with K‐bentonites. About 30% of added ¹³⁷Cs could be desorbed with 1 m ammonium acetate (NH₄Ac) from an unamended soil after 25 wetting–drying cycles, while only between 8 and 21% of ¹³⁷Cs could be desorbed from a soil amended with bentonite and a K‐salt. These findings support the proposition that addition of K‐bentonite may be effective in reducing availability of ¹³⁷Cs in soils.     

Genotype x environment interaction in the uptake of Cs and Sr from soils by plants

The soil‐plant transfer factors for Cs and Sr were analyzed in relationship to soil properties, crops, and varieties of crops. Two crops and two varieties of each crop: lettuce (Lactuca sativa L.), cv. Salad Bowl Green and cv. Lobjoits Green Cos, and radish (Raphanus sativus L.), cv. French Breakfast 3 and cv. Scarlet Globe, were grown on five different soils amended with Cs and Sr to give concentrations of 1 mg kg^–1 and 50 mg kg^–1 of each element. Soil‐plant transfer coefficients ranged between 0.12–19.10 (Cs) and 1.48–146.10 (Sr) for lettuce and 0.09–13.24 (Cs) and 2.99–93.00 (Sr) for radish. Uptake of Cs and Sr by plants depended on both plant and soil properties. There were significant (P ≤ 0.05) differences between soil‐plant transfer factors for each plant type at the two soil concentrations. At each soil concentration about 60 % of the variance in the uptake of the Cs and Sr was due to soil properties. For a given concentration of Cs or Sr in soil, the most important factor effecting soil‐plant transfer of these elements was the soil properties rather than the crops or varieties of crops. Therefore, for the varieties considered here, soil‐plant transfer of Cs and Sr would be best regulated through the management of soil properties. At each concentration of Cs and Sr, the main soil properties effecting the uptake of Cs and Sr by lettuce and radish were the concentrations of K and Ca, pH and CEC. Together with the concentrations of contaminants in soils, they explained about 80 % of total data variance, and were the best predictors for soil‐plant transfer. The different varieties of lettuce and radish gave different responses in soil‐plant transfer of Cs and Sr in different soil conditions, i.e. genotype x environment interaction caused about 30 % of the variability in the uptake of Cs and Sr by plants. This means that a plant variety with a low soil‐plant transfer of Cs and Sr in one soil could have an increased soil‐plant transfer factor in other soils. The broad implications of this work are that in contaminated agricultural lands still used for plant growing, contaminant‐excluding crop varieties may not be a reliable method for decreasing contaminant transfer to foodstuffs. Modification of soil properties would be a more reliable technique. This is particularly relevant to agricultural soils in the former USSR still affected by fallout from the Chernobyl disaster.     

Influence of Organic Amendments on the Accumulation of 137Cs and 90Sr from Contaminated Soil by Three Grass Species

Bahia grass (Paspalum notatum), johnson grass (Sorghum halpense) and switchgrass (Panicum virginatum) werecompared for their ability to accumulate ¹³⁷Csand ⁹⁰Sr from three different contaminated soilsin the presence and absence of either sphagnum peator poultry litter amendments. Above-ground plantbiomass did not differ between plants that were notexposed to these radionuclides and those that wereexposed to soil containing ¹³⁷Cs or ⁹⁰Sr.After three harvests, bahia, johnson and switchgrassplants accumulated from 17.2 to 67.3% of the¹³⁷Cs and from 25.1 to 61.7% of the ⁹⁰Sradded to the soil. Poultry litter and peat mossamendments increased aboveground plant biomass,activity of ¹³⁷Cs or ⁹⁰Sr in plant tissue, %accumulation of ¹³⁷Cs or ⁹⁰Sr from soil andthe plant bioconcentration ratio at each harvestcompared to the control (no amendment) treatment. Thegreatest increases in plant biomass, and radionuclideaccumulation were observed with poultry litter foreach of the three grass species. Johnson grass hadgreater aboveground plant biomass, activity of¹³⁷Cs and ⁹⁰Sr in plant tissue, %accumulation of ¹³⁷Cs or ⁹⁰Sr from soil andbioconcentration ratio in each soil amendment, at eachharvest compared to bahia and switchgrass. Thegreatest accumulation of ¹³⁷Cs and ⁹⁰Sr wasmeasured in johnson grass grown in soil that wasamended with poultry litter. These results suggestthat plant species selection and agronomic practicesmay need to be considered to maximize phytoremediationof radionuclide contaminated soils.     

Effect of 137Cs accumulation by organomineral coarse particles in sandy soils contaminated during the Chernobyl NPP accident

Dark-colored particles in the coarse fractions of sandy soils were found to concentrate ¹³⁷Cs. Up to 94% of the fractional ¹³⁷Cs was associated with these particles in the sand and coarse silt fractions, although their relative mass did not exceed 1–5%. The concentrations of ¹³⁷Cs in the dark-colored particles were up to 400 times higher than those in the light-colored particles. The high values of the radiocesium interception potential (RIP(K) = 1600–4600 mM/kg) indicate the presence of clay minerals in the dark particles.     

Radionuclide Behaviour and Transport in a Coniferous Woodland Ecosystem: The Distribution of Radionuclides in Soil and Leaf Litter

A coniferous woodland in the vicinity of theBritish Nuclear Fuels reprocessing plant atSellafield, Cumbria, was used to examine the spatial,temporal and depth distribution of ¹³⁴Cs,¹³⁷Cs, ²³⁸Pu, ^239+240Pu and ²⁴¹Amin soil and leaf litter. All the radionuclides, withthe exception of ¹³⁴Cs, showed a consistent fallin accumulated soil and litter deposits withincreasing distance from the woodland edge nearest toSellafield. ¹³⁷Cs levels in soil declined from 53to 28 kBq m^-2, ^239+240Pu from 5.5 to 3.6 kBqm^-2 and ²⁴¹Am from 2.9 to 1.1 kBq m^-2within 100 m of the forest edge. This decline isattributed to greater deposition occurring at theleading edge of the woodland. The uniform depositionpattern of ¹³⁴Cs in soil is consistent with thehypothesis that, at the time of sampling, thesedeposits derived largely from wet deposition duringpassage of the Chernobyl plume over Cumbria in May1986. Results for the leaf litter indicate a similarspatial distribution to that observed in soil.Radionuclide concentrations were also similar but thisis not attributable to adventitious soil contaminationbecause significant differences between isotopicratios of ¹³⁴Cs:¹³⁷Cs and ²³⁸Pu:^239+240Pu imply that the contamination on leaflitter is of more recent origin than that in soils.     

Die horizontale Verteilung von Radiocäsium im Waldboden unter Fichte und Buche

Horizontal distribution of radiocesium in forest soils under spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) The horizontal distribution of radiocesium in the soil under the canopy of several beeches and spruces was examined. At the base of spruces mean ¹³⁷Cs activities are about twice, and under beeches 5 to 15 times as high as under more distant parts of the canopy. Between 80 and 95% of the ¹³⁷Cs activity can be attributed to the Chernobyl fallout, the rest to the global fallout from weapons testing in the 1950s and 1960s. While the ¹³⁷Cs accumulation at the base of spruces can be explained by litter fall and remains of bark, the up to 30 times increased values at the base of beeches are explained by stemflow. Mean activity of radiocesium in the bark of spruce (0,62 Bq/g dry weight) is about twice as high as in the bark of a beech. This can be explained by considering that in contrast to beeches the ¹³⁷Cs activity in the soil under spruces is corresponding to some extend with the main rooting zone. Thus, we expect an increased uptake by the roots of this species and a subsequent transfer to the bark.     

Estimation of Plant‐Available Nitrogen in Soils using Rapid Chemical and Biological Methods

The relationships between potential laboratory indices for plant‐available nitrogen (N) and the plant N uptake in a pot experiment with ryegrass were assessed for 13 mineral soils and 2 peat soils. The methods included aerobic soil incubation, soil incubation in a bioreactor, hot potassium chloride (KCl)–extractable mineral N, 0.01 M calcium chloride (CaCl₂)–extractable N, and N loss at heating. The indices for total plant‐available N accounted for 63–93% of the variance in N uptake in a statistical analysis with all soils (n = 15) and 27–89% for the mineral soils (n = 13). Most indices were not a direct quantitative measure of the plant N uptake. The N mineralization indices accounted for 57–86% of the variance in N mineralization for all soils and 5–50% for the mineral soils. Hot KCl‐extractable mineral N and 0.01 M CaCl₂–extractable N were the most promising rapid indices for plant‐available N.     

Rice Bran Addition to Leaf Compost Can Reduce Radiocesium Concentration and Its Uptake by Crops After the Fukushima Daiichi Nuclear Power Plant Accident

Abstract

Leaf composting is an essential technique in organic farming; it improves the physicochemical properties of soil such as texture, structure, water-holding capacity, and nutrient content. However, the use of leaf compost is prohibited in the Fukushima and Ibaraki prefectures because large areas of the Fukushima and Ibaraki forests were contaminated by radiocesium (¹³⁴Cs and ¹³⁷Cs) after the Fukushima Daiichi nuclear power plant (FDNPP) accident. We examined the changes in radio Cs concentration and other physicochemical properties in leaf compost made from Ibaraki and Fukushima forest leaves. At the beginning of the composting process, rice bran-treated compost showed 25%–32% lower radio Cs concentration than the leaf-only compost; however, 2?years after composting, the difference in concentration between these treatments had increased to 35%–63%. Moreover, the incorporation of rice bran significantly increased the compost temperature, moisture, electrical conductivity, bulk density, and total nitrogen during the composting process. Plant uptake of radio Cs was significantly lower in rice bran-treated compost than the leaf-only compost at each level of application; furthermore, the levels of soil radio Cs showed a similar trend. Potassium application combined with leaf compost resulted in a significant reduction of radio Cs plant uptake. Our data revealed that adding rice bran to leaves positively affects radio Cs reduction in leaf compost and also reduces its uptake by plants. Our findings may improve the management of leaf composting after the FDNPP accident.