Search

Sediment that has deposited after the flood generated by the 2019 typhoon (referred to as Flood Sediment, FS) was collected along two rivers in eastern Fukushima Prefecture, Japan to determine the total and exchangeable radiocesium ($^{137}\mathrm{Cs}$), and acid-extractable potassium (K) contents. Then, these FS parameters were compared with those of decontaminated soils (DS) in nearby agricultural fields to discuss the potential transfer risk of $^{137}\mathrm{Cs}$ from rivers to nearby remediated soils. While FS had about four times higher total $^{137}\mathrm{Cs}$ content, it showed a three-times lower exchangeable $^{137}\mathrm{Cs}$ content than DS. Furthermore, acid-extractable K referred to as non-exchangeable K (Nex-K) content was high enough to restrict $^{137}\mathrm{Cs}$ transfer from soil to crops for both FS and DS. From these comparisons, we concluded that deposition of FS onto DS may not increase the transfer of $^{137}\mathrm{Cs}$ from soil to crops.

To investigate how the long-term application of inorganic fertilizer and organic amendments affects the turnover rates of organic matter in physico-chemically fractionated components in paddy soils and how their rates are related to their amounts, we studied the effect of variable management of inorganic fertilizer and organic amendments for > 50 years on the ∆14C values of accumulated soil organic carbon (SOC) in fractionated components of 5 soil samples from three paddy fields. SOC was fractionated into four components based on their physico-chemical properties: (1) light fraction (LF) derived from plant residues, (2) heavy fraction (HF) containing stable aggregates, (3) oxidizable fraction (OxF) and (4) non-oxidizable fraction (NOxF) forming organo-mineral complexes with fine-textured minerals. The ∆14C values were determined by accelerator mass spectrometry using graphitized samples. The ∆14C values of SOC in NOxF (from −305‰ to − 90.5‰) were much lower than those of HF (from −123‰ to − 3.7‰) and OxF (from −215‰ to 21.0‰). Lowest values for NOxF suggested slowest turnover rates as expected, and higher and comparable values for OxF and HF implied much faster turnover rates of SOC in OxF compared with upland soils. This could be one of the characteristics of SOC dynamics in paddy soils, probably reflecting repeated puddling of plow layer soils. ∆14C values in all the fractions increased in response to the application of inorganic fertilizer and organic amendments, suggesting faster turnover rate. Soils with clayey and weathered characteristics had the lowest ∆14C values, or slowest turnover rates among the study fields. The relationship between the ∆14C value and the amount of accumulated C for HF, OxF and NOxF indicated that the more the SOC accumulated, the faster the turnover rate of the SOC was, regardless of the fractions, and the relationship of the HF was considerably different from those of OxF and NOxF. In conclusion, these results can be the basis for understanding the C dynamics and for improving soil fertility status and soil C sequestration in paddy soils. [ABSTRACT FROM AUTHOR]

To investigate the interactive effects of parent material and topography as soil forming factors, we examined the distribution of soil materials in an alluvial plain, where two types of surface geology were situated upstream and different parent materials supplied accordingly. We hypothesized that these two types of parent material make it possible to trace alluvial processes by analyzing their spatial distribution based on soil physicochemical properties. We collected 101 soil samples from the alluvial plain and nine soil samples from two types of unmixed upstream areas, i.e., granite and mélange. Particle size distributions and total concentrations of 32 elements were analyzed for spatial variabilities. Elemental composition of unmixed upstream samples and isarithmic maps of elemental composition of the soils in the alluvial plain based on geostatistical analysis revealed that gravel, coarse sand and total Na, Al, K, Ca, and Mn concentrations were higher at the southern part close to granite rock areas, whereas silt+clay content and total C, N, Mg, Ti, and Fe concentrations were higher at the northern part close to the mélange area, suggesting strong influence from parent material. In contrast, fine sand content and total P and Si concentrations showed west-east trends, suggesting topography effects reflecting particle size selection. Directional semivariograms suggest coarse sand and silt+clay content, as well as total C, N, Na, Mg, Al, K, Ca, Ti, and Mn concentrations were more strongly affected by parent material, whereas gravel and fine sand and total P concentration were more strongly affected by topography. Accordingly, the combination of elemental composition analysis and geostatistics revealed that the contribution of parent material and topography to total elemental contents in paddy surface soils in the alluvial plain varied among elements. In conclusion, evaluation of the interactive effects of parent material and topography on spatial variability of soil material characteristics enabled better understanding of soil formation processes and their potential fertility. [ABSTRACT FROM AUTHOR]