Naoto Kato

Potassium fertilizer and other materials as countermeasures to reduce radiocesium levels in rice: Results of urgent experiments in 2011 responding to the Fukushima Daiichi Nuclear Power Plant accident

Abstract 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.

Dissolution of slag fertilizers in a paddy soil and Si uptake by rice plant

Abstract The dissolution of 20 slag samples in a flooded soil was studied with or without the application of cellulose. A pot experiment was also carried out to examine the availability of Si in the slags for a rice plant (Oryza sativa L. var. Nihonbare) and to investigate the effect of the plant root on the Si dissolution from the slags. In the treatment without cellulose (hereafter referred to as −Cellulose) and at the early growth stage in the pot experiment, in some slag application treatments the Si concentration in the soil solution was lower than in the treatment without slag (control). Also, the Si concentration was negatively correlated with the A/Si ratio (ratio of alkalinity to 0.5 M HCl-soluble SiO2 content in the slags). These results were presumably due to the increase in the soil ability to adsorb Si which was caused by the increase in the soil solution pH. The continuous dissolution of the slags could be also depressed by the increase in the pH and Ca concentration in the soil solution. On...

Evaluation of Si Availability in Slag Fertilizers by an Extraction Method Using a Cation Exchange Resin

Abstract A new extraction method for the evaluation of Si availability in slag fertilizers was developed based on findings on the dissolution process of the slags in paddy fields. In the method, the slags were dissolved in water with the addition of a weakly acidic cation exchange resin (H form). The effects of the slag/water ratio, the amount of resin, and temperature on the Si dissolution from the slags were examined in order to determine adequate extraction conditions. The Si dissolution from the slags was enhanced by the addition of the resin. The pH of the extractant was well controlled between 6 and 7 during the extraction. The percentage of the amount of Si extracted by traditional evaluation methods using 0.5 м HCl or an acetate buffer solution to the total amount of Si in the slags was much higher than the Si recovery rate by rice plant (Oryza sativa L. var. Nihonbare) which was measured in our previous study. Moreover, there was no correlation between these values. On the other hand, the percent...

The ability of chemical extraction methods to estimate plant-available soil P and a better understanding of P availability of fertilized andosols by using isotopic methods

Abstract Plant-available P content in soils differing in P fertilization history was determined by both the isotopic dilution method (pot experiment) and isotopic exchange method (laboratory test) using phosphate ions labelled with 32P in order to evaluate the residual effect of P fertilizers applied to the soils. Another isotopic technique was also used to evaluate the ability of chemical extractions, Truog and Bray No. 2 methods, to extract plant-available soil P. Four soil samples of a Humic Andosol taken from experimental plots, which did not receive fertilizer (J1 treatment), or received a readily soluble fertilizer (RSF) (J2 treatment), RSF plus a fused magnesium phosphate (FMP) (J3 treatment), and RSF plus Florida phosphate rock (J4 treatment), were analyzed. In a pot experiment, maize (Zea mays) was grown on the soils where available P was labelled with 32P. P uptake and specific radioactivity in shoot were measured. The fraction of P in plant derived from fertilizer (%Pdff in plant) and pool size...

Radioactive particles in soil, plant, and dust samples after the Fukushima nuclear accident

Abstract Environmental samples of soil, plant and air dust collected after the Fukushima Daiichi Nuclear Power Plant accident were analyzed by autoradiograph, and significant amounts of radioactive particles containing higher cesium-134 (134Cs) and cesium-137 (137Cs) were found. Most of the radioactive soil particles were clay sized. The main part of the radioactivity and radioactive particles of air dust was detected from the 1.1–2.0μm fraction of an Andersen sampler filter. A considerable part of the radioactive particles on the air dust filter were not water soluble. Radioactive particles attached to outdoor plant leaves persisted for nearly 1 year. Thus, soil, leaf and air dust similarly contained sparingly water-soluble, micron-sized radioactive particles each with comparable ranges of elevated radio-Cs. A sheet dilution method was proposed and used to select and purify these radioactive particles. Using selected radioactive particles, the relation between area × gray value on autoradiograph and radioactivity was estimated. Radioactivity per particle was up to a few Bq and the geometrical average radioactivity of detected particles was around 0.1 Bq per particle or less. The configuration, chemical composition, origin and formation mechanisms of the radioactive particles require clarification.

Changes in natural 15N abundance in paddy soils under different, long-term soil management regimes in the Tohoku region of Japan

Abstract Long-term temporal changes in natural 15N abundance (δ15N value) in paddy soils from long-term field experiments with livestock manure and rice straw composts, and in the composts used for the experiments, were investigated. These field experiments using livestock manure and rice straw composts had been conducted since 1973 and 1968, respectively. In both experiments, control plots to which no compost had been applied were also maintained. The δ15N values of livestock manure compost reflected the composting method. Composting period had no significant effect on the δ15N value of rice straw compost. The δ15N values increased in soils to which livestock manure compost was successively applied, and tended to decrease in soils without compost. In soils to which rice straw compost was successively applied, the δ15N values of the soils remained constant. Conversely, δ15N values in soils without rice straw compost decreased. The downward trend in δ15N values observed in soils to which compost and chemical N fertilizer were not applied could be attributed to the natural input of N, which had a lower δ15N value than the soils. Thus, the transition of the δ15N values in soils observed in long-term paddy field experiments indicated that the δ15N values of paddy soils could be affected by natural N input in addition to extraneous N that was applied in the form of chemical N fertilizers and organic materials.

Measurement of Si adsorption and “Active Si” in a soil amended with slag fertilizers by using stable isotope 30SP

Abstract The silicic acid adsorption by a soil (Eutric Gleysols) where slag fertilizers were applied was measured by the addition of a silicic acid solution labelled with 30Si after soil incubation, in order to study the effect of slag application on the specific Si adsorption by the soil and to estimate the amount of Si in the soil solid phase which can easily enter the soil solution. It was evident that the application of slags increased the ability of soil to adsorb Si. It was also shown that the 30Si added was diluted with not only the Si present in the soil solution but also the Si dissolved from the soil solid phase. We proposed the use of the term “active” for Si in soil which can take part in the isotopic dilution within 1 h. The amount of active Si in the soil solid and liquid phases (D 60 - value) was calculated from the 30Si content in the soil solution and compared with the amount of Si taken up by rice plant (Oryza sativa L.), which was determined in our previous study. The buffering capacity...

Fate of nitrogen derived from 15N-labeled cattle manure compost applied to a paddy field in the cool climate region of Japan

Abstract To estimate the fate of nitrogen (N) derived from cattle manure compost with sawdust (CMC) in a paddy field in the cool climate region of Japan, well-composted 15N-labeled CMC was applied to a microplot field experiment. Throughout the experimental period of three crop seasons, N from CMC was taken up by rice plants without a marked decline. The percentages of N taken up derived from CMC to applied N as CMC (%CNRp) were 2–3% for each year. The N from CMC was taken up by rice plants over the entire growth period by 1–2, 2 and 2–3% as %CNRp at the panicle initiation, heading and maturity stages, respectively. A significant positive linear correlation was found between the cumulative compost N uptake and the number of days transformed to standard temperature (25°C) over the entire experimental period, including the fallow season. The %CNRp was identical at CMC application rates ranging from 1 to 4 kg m−2. Using 15N-labeled CMC, the results showed that well-composted CMC was a stable N source for rice plants for at least 3 years, regardless of the CMC application rate (ranging from 1 to 4 kg m−2) in the cool climate region of Japan. The distribution of CMC N was 7% in the rice plants accumulated over 3 years, 66–69% in the soil and 24–27% was un-recovered at the end of the third crop season.

Effect of soil solarization on subsequent nitrification activity at elevated temperatures

Abstract Soil solarization is a nonchemical method of soil disinfection achieved by covering the soil surface with sheets of vinyl plastic to generate elevated soil temperature, generally over 45°C. Such elevated temperatures may be detrimental to some nitrifying microorganisms and favorable to others. However, little information exists to indicate how nitrification activity in soil is affected after solarization. We performed several experiments to investigate the effects of soil solarization on nitrification activity. We found that: (1) if a soil was subjected to pretreatment of 45 or 50°C for as little as 1 d, nitrification activity in a subsequent incubation at 30°C was less than that of a soil that did not receive any high-temperature pretreatment. However, if a soil received pretreatments of 45 or 50°C for more than 7 d, nitrification activity in a subsequent incubation at 45 or 50°C was greater than that of soil that did not receive high temperature pretreatment. (2) Nitrification activity in three kinds of soil taken from 0–5 cm depth after solarization treatment was greater at 45°C than 30°C. (3) Nitrification activity at 45°C in soil that had received solarization in the preceding year was greater than that in soil that had not been subjected to solarization. This was consistent with the fact that the population densities of ammonia oxidizers were greater in soils that had been subjected to solarization. These results suggest that soil solarization induces nitrifying microorganisms that are more active at 45–50°C than they are at 30°C, and that the effect of solarization on nitrification persists until the next crop season.

Trends of lettuce and carrot yields and soil enzyme activities during transition from conventional to organic farming in an Andosol

Abstract It has been reported that crop yields drop and then increase during the first few years of organic farming, and these yield recoveries have been attributed to gradual improvements in soil properties, such as soil microbial activities to mineralize nitrogen (N) or to suppress plant disease. To clarify whether yield increase during organic transition is caused by improvement of soil microbial activities, we compared identically managed organic and conventional plots of 1-year lettuce (Lactuca sativa L.)–carrot (Daucus carota L.) rotation for 3 years (organic plots: first 3 years after switching from conventional to organic management; conventional plots: managed in the same way as organic plots for 3 years but receiving chemical fertilizer, fungicide, insecticide and herbicide) in an Andosol field. During organic transition, yields of organic lettuce and carrots were lower than those of conventional lettuce and carrots for only the first year. Yield drop and recovery of lettuce were thought to be caused by changes in the amount of N uptake, though yield fluctuation of carrots was mainly caused by damage from insects. Although soil enzyme activities may be responsible for N mineralization, various soil enzyme activities promptly responded to organic amendment to become higher under organic management than under conventional management even after the first lettuce cropping (6 months after switching to organic management; much shorter than the period of organic transition). However, discriminant analysis using activities of six soil enzymes (dehydrogenase, β-glucosidase, β-galactosidase, α-glucosidase, cellulase and protease) indicated that 18–24 months (a period close to that of the organic transition) were needed for the pattern of various soil enzyme activities to be in a steady state after switching to organic management. The pattern of soil enzyme activities fluctuating to a plateau during the second lettuce cropping seemed to show a tendency similar to that of N uptake and yield of lettuce during organic transition. Soil available N in organic plots also became higher than that in conventional plots in the third year. These results suggested that improved N uptake and yield of lettuce during organic transition in an Andosol might be caused by either improvement in various soil enzyme activities or accumulation of soil available N. Yield response of carrots demanding less N was attributed not to N mineralization but to damage from insects.