Kaori Matsuoka

Effects of the application of heated sewage sludge on soil nutrient supply to plants

Abstract We previously reported that heating sewage sludge significantly changes the rate of N mineralization. The present study was undertaken to examine the extent to which these changes affect plant growth and nutrient supply after application to different soils. A pot experiment in which komatsuna plants (Brassica campestris L. var. rapa) were grown in a Fluvisol or an Arenosol indicated that the amount of N taken up by the plants increased significantly by heating air-dried sludge at 120°C and decreased significantly by heating at 180°C. Heat-drying of the sludge at 120°C or 180°C also increased the N uptake significantly. These plant responses could be explained by the heat-induced changes in the release of inorganic N from the sludge. In contrast to N, the sludge materials containing Fe as a coagulant immobilized soil soluble P. When the sludge was applied to an Andosol, the N-supplying effects on plant growth were offset by P adsorption onto the sludge and soil. In a successive pot experiment conducted without additional sludge application, it was further suggested that frequent sludge application is required to maintain plant growth. However, it will also lead to the accumulation of sludge components in the soil because less than 40% and 15% of the sludge N and P, respectively, were apparently recovered in two harvests of the plants. In conclusion, heated sludge materials can act as an effective organic N fertilizer provided that they are applied to a suitable soil and that the short-term effects on soil productivity are balanced with the long-term effects on environmental quality.

Effect of heating treatments on nitrogen mineralization from sewage sludge

Abstract Heating of sewage sludge has multifunctional benefits for agricultural recycling of sludge, one of which is the heat-induced changes in N mineralization from the sludge. To enhance the understanding and practical use of this phenomenon, we subjected sewage sludge to heating treatments at 120°C or 180°C for 16 h with or without air-drying as a pretreatment. During the 84-day aerobic incubation period, N mineralization from the sludge mixed with samples of an Andosol, a Fluvisol, an Arenosol and an Acrisol was significantly accelerated by the heating of air-dried sludge at 120°C and was significantly retarded by heating at 180°C, regardless of the soil types and temperatures during the incubation period. More conventional heat-drying of moist sludge at 120°C or 180°C also exerted similar but less pronounced effects. These heat-induced changes were attributed to the transformation of sludge organic N, because volatilization of N during the heating treatments was negligible. Sequential extraction of sludge N enabled detection of the heat-induced N transformations accounting for some but not all of the incubation results, indicating that mineralization of N in the heated sludge materials was determined not only by chemical extractability but also by other factors. Our results suggest that heating of sewage sludge regulates the rate of N mineralization and presents a promising method for producing various organic N fertilizers from sewage sludge.

Changes in radiocesium concentration in a Japanese chestnut (Castanea crenata Sieold & Zucc.) orchard following radioactive fallout

Abstract We investigated changes in radiocesium concentrations in a Japanese chestnut (Castanea crenata Sieold & Zucc.) orchard in Ibaraki prefecture for 3 years after the Tokyo Electric Power Company’s Fukushima Daiichi nuclear power plant accident in March 2011. The radiocesium concentrations in the aboveground organs of Japanese chestnut trees were almost the same, while the concentration in the roots was the lowest among all the organs investigated. The concentration of radiocesium decreased exponentially for 3 years in nuts, leaves and current shoots. The radiocesium concentrations in soils were higher in the surface layer, and the trend of an annual decrease in radiocesium in the soils was similar to that of the natural decay of radiocesium. The transfer factor of radiocesium from soils to nuts of Japanese chestnut decreased annually. These results suggest that radiocesium adhered directly to the aboveground organs of Japanese chestnut trees in March 2011, and that the accumulation of radiocesium in nuts is mainly due to radiocesium transfer from the branches and trunk to nuts several years after the nuclear power plant accident.

Soil color analysis for statistically estimating total carbon, total nitrogen and active iron contents in Japanese agricultural soils

Abstract Soil color originates mainly from organic matter, iron mineralogy and moisture content. We aimed to find a suitable method to measure soil color sensitively and to evaluate the extent to which the color parameters can be useful for statistically estimating total carbon (C), total nitrogen (N) and active iron (Fe) contents in Japanese agricultural soils. A soil color reader (SPAD-503) was applied to two sample sets: (1) 100 surface soils collected throughout a 0.5-ha paddy field (field scale) and (2) 147 surface soils collected from agricultural fields in Japan (national scale). For analysis with this instrument, about 2 g of air-dried, finely-ground samples were packed firmly in a plastic cell, and their colors as they appeared on windows in both sides of the cell were measured. A CIE 1976 (L*, a*, b*) color space was used for color description. For the field-scale samples, the values of the coefficient of variation were around 15% for total C, total N and acid oxalate extractable iron (Feo). The L* value (lightness) was negatively correlated with the content of total C and total N (R2 = 0.18** and 0.26**, respectively), and the b* value (yellowness) was positively correlated with the Feo content (R2 = 0.59**). For the national-scale samples, the values of the coefficient of variation were around 60% for total C, total N and Feo. The L* value was negatively correlated with the content of total C and total N (R2 = 0.70** and 0.59**, respectively), but the b* value was not correlated with the content of Feo (R2 = 0.00). When the analysis was limited to 65 samples frequently used for paddy fields, the b* value was positively correlated with the Feo content (R2 = 0.52**). In conclusion, the proposed method enabled us to measure soil color sensitively with a small sample size. The L* and b* values obtained can be useful for rapid estimation of total C, total N and Feo contents in agricultural surface soils in Japan.

Changes in radiocesium concentration in a blueberry (Vaccinium virgatum Aiton) orchard resulting from radioactive fallout

Abstract We investigated changes in the radiocesium concentration in a blueberry (Vaccinium virgatum Aiton) orchard in Fukushima prefecture to clarify the radiocesium contamination for 3 years after the Tokyo Electric Power Company’s Fukushima Daiichi nuclear power plant accident occurred in mid-March 2011. In the aboveground part of blueberry bushes, the concentrations of radiocesium in branches that were directly affected by radioactive fallout were the highest among the samples investigated, and the concentrations in fruits were the lowest. The concentration of radiocesium decreased exponentially in the fruits and leaves over 3 years. The radiocesium concentrations in soils were higher in the surface layer. The amount of radiocesium in organic matter on the soil surface under the canopy greatly decreased from 2011 to 2012. The transfer factor of the radiocesium from soil to blueberry fruits decreased annually. These results suggest that radiocesium adhered directly to the aboveground organs of blueberry bushes in March 2011, and it is possible that the accumulation of radiocesium in fruits is mainly due to radiocesium transfer from the branches and trunk to fruits for several years after the nuclear power plant accident.

Differences in the distribution of radiocesium in deciduous and evergreen fruit trees: A case study

Abstract We investigated the distribution of radiocesium (134Cs and 137Cs) in three orchards in Tsukuba, 170 km southwest from the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant 9 months after the accident. The radiocesium was distributed mainly in the surface soil. The distribution of radiocesium differed between deciduous and evergreen plants. In deciduous blueberry (Vaccinium virgatum Aiton), the concentration was high in the old branches because the bushes had no leaves at the time of the accident. Therefore, the concentration per bush was greater in unpruned than in pruned bushes. More radiocesium was present in the trunk and rootstock of each bush, although the concentration was low. In evergreen Satsuma mandarin (Citrus unshiu Marcow), the concentration was high in the leaves, and it was higher in old leaves that expanded before the accident than in new leaves that expanded after the accident, because the old leaves were contaminated by direct deposition of the fallout. However, the total radiocesium was higher in the new leaves than in the old leaves because of the greater amount of new leaves. The radiocesium concentration in fruits was higher in trees with fewer fruits than in trees with many fruits, but the total radiocesium in fruits was higher in trees with many fruits.

An Overview of the Studies on Biochar Fertilizer Carried Out at the Beginning of the Twentieth Century in Japan

Biochar is a recently coined term for charred organic matter used as a soil amendment. Although the term is relatively new, the substance has been used for a long time throughout the world, including Japan. After we read a Japanese book entitled Nibai Shukaku Tenri Nouhou (How to Double Crop Yield by Almighty Farming System) originally published in 1912, we found that there were conflicting opinions between the author (Mr. Katsugoro Oyaizu) and soil scientists of the time (Dr. Gintaro Daikuhara and others) on the benefits of the use of biochar fertilizer. Previous publications on this topic have been written in Japanese from a sociological viewpoint. By referring to the literature published at the beginning of the twentieth century in Japan, we attempt to shed light on the conflict between traditional knowledge of biochar fertilizer and new concepts of soil science imported from the Western countries. We also describe briefly the socioeconomic impacts on the use of biochar fertilizer in the later generations.

Decadal sustainability of spatial distribution of soil properties in a paddy field as a fingerprint reflecting soil-forming factors and field management

Abstract Spatiotemporal variations of soil properties were measured in a Japanese paddy field in order to evaluate how they were created and sustained through various field managements. The field was subjected to land consolidation during 1960s, heterogeneous application of manure in the late 1970s and land leveling in 1986, 1987 and 2003. Surface soils were collected from throughout the field in 2002 and 2012, and the physicochemical properties were analyzed. Additional analyses were carried out for relative altitude in 1986, 1999 and 2012, and soil hardness in 2012. In the field examined, the distribution of field attributes reflected past field managements. The heterogeneous distribution of relative altitude was partly explained by the passage of agricultural machinery, whereas the heterogeneous distribution of soil organic matter was partly explained by both past and recent applications of animal dung manure. In general, the measured soil properties were maintained from 2002 to 2012, and the pattern of spatial distribution did not change significantly for many of the properties. The correlation coefficient of the distribution patterns between 2002 and 2012 was highest for yellowness (0.95), followed by sand (0.90), acid-oxalate extractable iron (Fe; 0.88), available phosphorus (P; 0.87), redness (0.82), lightness (0.77), sand-size organic matter (0.74) and total nitrogen (N; 0.72). Land leveling carried out in 2003 barely influenced the distribution of these properties. Among these properties, soil color parameters and sand content can be measured rapidly without reagents and will be useful for characterizing paddy fields according to the distribution of stable soil properties. The analysis of the natural abundance of 15N in soil was also effective to suggest the contribution of the application of animal dung manure to the accumulation of soil organic matter at a within-field scale. It can be concluded, as a general rule, that each paddy field has its own fingerprint which is unveiled by precise soil sampling and analyses of stable properties.

Increase in the Capacity of Interlayer Sites in a Paddy Soil as a Possible Factor Affecting the Dynamics of Fixed Ammonium at the Initial Stage of Anaerobic Incubation

To evaluate whether the capacity of interlayer sites affects the dynamics of fixed ammonium (NH4+) in a paddy soil, a combination of potassium (K)–saturation treatment and stepwise extraction of nonexchangeable K with 0.01 mol L−1 hydrochloric acid was applied to a soil incubated anaerobically up to 70 days. The capacity of interlayer sites increased with an increase of weakly fixed NH4+ during the initial 28 days (r = 0.78, P < 0.01), and remained stable thereafter. On the other hand, the concentration of exchangeable NH4+ increased curvilinearly during the whole incubation period, which was correlated with an increase of weakly fixed NH4+ (r = 0.85, P < 0.01). These results suggested that the dynamics of weakly fixed NH4+ in a paddy soil is regulated not only by the chemical equilibrium between exchangeable and weakly fixed NH4+ but also by the capacity of interlayer sites within a few weeks after flooding.

Ball milling pretreatment affects the content of fixed ammonium in soils in response to the content of exchangeable ammonium

ABSTRACT Analysis of fixed ammonium (NH4+) in soils by the most common method requires the subsample to be ground to pass through a 100-mesh sieve. We tested a hypothesis that the ball milling pretreatment for the analysis of fixed NH4+ may influence the analytical results depending on the content of exchangeable NH4+. Five paddy soils collected from the surface layer in Japan were treated with 15N-labeled ammonium sulfate at 0, 100, 500, or 1000 mg N kg−1, incubated aerobically at 30°C for 7 days, and air-dried. Part of each soil was then ground in a vibration ball mill at 1200 rpm for 10 min as a pretreatment (BMP treatment). The samples with and without the BMP treatment were analyzed for exchangeable NH4+ and total fixed NH4+. The samples that received 0 or 1000 mg N kg−1 were also analyzed for nonexchangeable 15N (total fixed 15NH4+ plus organic 15N) and hot KCl-extractable organic N. At 0 mg N kg−1, the BMP treatment significantly decreased total fixed NH4+ in all soils and significantly increased exchangeable NH4+ in two of the five soils. The fixation of exchangeable NH4+ started to occur when its content is greater than around 300 mg N kg−1, and its ratio to total fixed NH4+ is greater than around 1.0. At 1000 mg N kg−1, the BMP treatment significantly decreased exchangeable NH4+ and significantly increased total fixed NH4+ in all soils especially two clayey, vermiculitic soils. On the average of all soils applied 1000 mg N kg−1, the increase in total fixed NH4+ explained 55% of the decrease in exchangeable NH4+, and the decrease in exchangeable NH4+ was almost equal to the increase in nonexchangeable 15N. The rest of the NH4+ unaccounted by the fixation was partly due to the transformation of exchangeable NH4+ to hot KCl-extractable organic N, because the content of hot KCl-extractable organic N was significantly increased by the BMP treatment. In conclusion, the milling treatment prior to the analysis of fixed NH4+ in soils might cause either underestimation or overestimation depending on the content of exchangeable NH4+.