Abstract Full‐pattern fitting of X‐ray powder diffraction (XRPD) data using reference materials has attracted increasing attention as a high‐throughput method to determine the contents of long‐range‐ordered (i.e., crystalline) materials in soils. We hypothesized that this XRPD method can also be used to quantify short‐range‐ordered (SRO) materials with low crystallinity, despite their much weaker and broader diffraction. To obtain soil samples with a wide range of allophane and organic matter (OM) contents, surface and subsurface soils were collected from five profiles in northern Japan. A full factorial design was used to identify the optimal combination of reference SRO materials, including allophane, OM, and phytolith, for XRPD method using full‐pattern fitting. The allophane and OM contents determined by XRPD were broadly but unexpectedly consistent with those obtained by conventional methods. In addition, the allophane and OM contents determined by XRPD showed significant positive correlations with phosphate absorption coefficient and cation exchange capacity, respectively (Spearman's rank correlation, p < 0.001), consistent with the relationships observed by the conventional methods. These results suggest that, although accurate quantification of samples with low contents (i.e., OM < 10 wt.%) remains challenging, state‐of‐the‐art XRPD method using full‐pattern fitting alone provides a promising new approach for rapid evaluation of soil properties and functions through the quantification of both crystalline and low‐crystalline materials.

ABSTRACT The Mehlich 3 (M3) method is one of the most widely used universal extractants for multielement soil testing of nutrient availability, yet its performance across spatial scales that encompass diverse pedogenic contexts remains unclear. To assess the comparability of the Mehlich 3 method with conventional extraction methods across contrasting pedogenic contexts, M3 extraction was compared with conventionally extracted nutrient contents for 10 elements (Ca, Mg, K, P, Mn, Zn, Ni, Fe, Cu, and Si) in paddy soils collected across three spatial scales (local, regional, and national) in Japan. Regardless of spatial scale, the M3 method showed comparable extracted amounts to conventional methods for Ca, Mg, K, Mn, Zn, and Ni, thereby confirming its reliability as a universal extractant. Regarding P, the extracted amounts of M3 were about half those of Bray 2 and about twice those of Truog. Furthermore, the correlation coefficient between M3 and these conventional methods for P decreased at broader spatial scales, including soils with variable amorphous Fe/Al (hydr)oxide content. The present results demonstrate that the M3 method provides robust and scalable estimates for most nutrients, while also revealing that its performance for P is sensitive to pedogenic variability. This highlights the importance of incorporating pedogenic context when defining M3 applicability domains, particularly for P assessment, thereby improving the comparability of soil testing results across small‐ and large‐scale soil monitoring frameworks.

Although soil health indicator is extensively examined worldwide, Japan has yet to establish a soil health assessment framework calibrated to the unique properties of Andosols. In this study, we evaluated a long-term (19-year) organically managed soybean field and generated soil health scores using a cumulative normal distribution function to develop a site-specific benchmark. Treatments were tillage (no-tillage, moldboard plowing, and rotary tillage), cover crop (rye, hairy vetch, and fallow), and the addition of fertilizer or biochar in four replications. Intensive tillage reduced soil health, with soil health score under moldboard plowing significantly lower than no-tillage during 2020–2022 (p < 0.05). No-tillage with cover crop and biochar enhanced soil health status by sustaining soil organic carbon (SOC) at 3.8–4.8%. Overall soil health score was positively correlated with SOC (r = 0.7; p < 0.01), while higher soil health score was strongly associated with reductions in net global warming potential (rs = − 0.95; p < 0.01). SOC emerged as one of the most influential indicators, directly influenced soil ß-glucosidase activity (r = 0.84, p < 0.001), substrate-induced respiration (r = 0.7, p < 0.001), NO3– (r = 0.65, p < 0.05), and EC (r = 0.36, p < 0.01). Although NT-based systems may not achieve the highest yields due to interannual variability, they may offer substantial environmental benefits by contributing to long-term climate change mitigation.

Enhanced rock weathering (ERW) is a promising carbon dioxide (CO2) removal (CDR) strategy that involves applying powdered rocks such as basalt to croplands to accelerate the natural weathering of rock minerals. However, despite numerous recent field investigations, direct evidence for the weathering of rock minerals in soils is lacking because most studies rely on cation budgets to estimate ERW-induced CDR. In this study, buckwheat was cultivated for 2.5 months in plots with and without basalt powder applied at a rate of 150 t ha- 1, and the decrease in basaltic mineral contents of the soils during the cultivation period was measured using quantitative X-ray powder diffraction (XRPD). Applying basalt powder significantly increased the contents of basaltic minerals such as plagioclase (e.g., labradorite and bytownite) and pyroxene in the soils, and the basaltic mineral contents subsequently decreased significantly in the rootzone after cultivation. The decrease was about 8.5 times greater in the rootzone than outside the rootzone. The percentage decrease relative to the input in the rootzone was 25.6% for labradorite, 58.8% for bytownite, and 65.1% for pyroxene, reflecting the theoretical dissolution mass and the more rapid weathering of bytownite and pyroxene compared to labradorite. The maximum CDR associated with the weathering of these minerals was estimated as 7.2 t CO2 ha- 1 over 2.5 months. These results provide the first quantitative evidence for the weathering of basaltic minerals applied to cropland and demonstrate the feasibility of applying state-of-the-art XRPD analysis to the monitoring, reporting, and verification of ERW-induced CDR under field conditions.

Enhanced Rock Weathering (ERW) has attracted increasing attention as a carbon dioxide removal (CDR) approach, yet its implementation depends on monitoring, reporting, and verification (MRV) strategies that can reliably detect and attribute CO2 removal under different field conditions. Flooded rice paddies are considered a potentially favorable environment for ERW due to continuous water fluxes, but strong hydrological and biogeochemical dynamics also complicate signal detection. Thus, two-year field experiments were conducted at four rice paddy sites in Japan with contrasting silicon (Si) supply capacities. Finely ground basalt was applied prior to cultivation at rates of 0, 100 (5 wt%), or 200 (10 wt%) t ha-1. ERW of reactive minerals was quantified by directly tracking temporal changes in Ca-plagioclase using quantitative X-ray powder diffraction (XRPD). These mineral-based estimates were compared with cation-based estimates derived from X-ray fluorescence (XRF) measurements of total Ca loss. XRPD analyses revealed that plots amended with 10 wt% basalt exhibited significant reductions in Ca-plagioclase within one year after application across all sites, whereas such reductions were not consistently observed in the 5 wt% plots. These results provided direct field evidence of in situ mineral weathering under flooded conditions. Estimated CDR potentials for all basalt-amended plots derived from XRPD ranged from 1.1 to 9.3 t CO2 ha-1 yr-1 and were broadly consistent with, but systematically higher than, XRF-based estimates. This discrepancy likely reflects the influence of external Ca inputs that can mask Ca depletion in XRF-based approach, as well as the uncertainties associated with estimated Ca-bearing minerals from idealized mineral stoichiometries in XRPD-based calculations. Notably, both methods consistently indicated higher weathering rates and CDR potentials at sites with lower initial Si availability. In parallel, basalt application increased plant-available Si and rice straw Si uptake over two growing seasons and was associated with reduced proportions of immature grains. However, the persistence of minerals after one year underscores the need for multi-year assessments. Overall, this study demonstrates that mineralogical monitoring provides a robust MRV pathway for ERW in dynamic paddy systems and that site selection is critical for reliable detection and attribution of CDR signals under field conditions.

Paddy soils in Java have been experiencing prolonged fertilization with macronutrients, in particular with N, P, and K fertilizers, while fertilization of micronutrients is only minor if not at all. It is necessary to evaluate the micronutrient status of paddy soils in Java for a better balance fertilization. This research was aimed to evaluate the status of Fe, Mn, Zn, and Cu in paddy soils in Java and to correlate some soil chemical properties with the availability of Fe, Mn, Zn, and Cu. There were 23 soil samples analyzed, 7 samples from West Java, 11 samples from Central Java, and 5 samples from East Java. The amount of Fe, Mn, Zn, and Cu were extracted by diethylenetriaminepentaacetic acid and then measured by atomic absorption spectrophotometer. The results showed that in general, the status of Mn and Cu was sufficient. Iron was sufficient in West and Central Java, but mostly deficient in East Java. Zinc varied from deficient to sufficient in all areas. There were a significant negative correlations between Fe, Mn, Zn, Cu and pH and significant negative correlation between Fe, Mn and Bray 1-P. The results suggested that micronutrients need more attention in fertilization program.

The storage of soil organic matter (SOM) is essential for maintaining and improving soil fertility. To obtain basic information about the status of SOM in paddy fields in Nepal under various ecological settings, we investigated the amount and turnover rate of stored carbon (C) in fractionated SOM in the surface layer. Soil samples from the top 15 cm plough layer were collected from 21 sites along an elevation gradient ranging from 78 to 2002 m a.s.l. in the central region of the country, and in eight sites in the lowland area in the eastern region to investigate regional differences in SOM status. SOM was fractionated into four components: (1) light fraction (LF, < 1.8 g cm(-3)), (2) heavy fraction (HF) consisting of physically stable aggregates, (3) oxidizable clay + silt fraction (OxF), and (4) nonoxidizable clay + silt fraction (NOxF) forming organo-mineral complexes with fine-textured minerals. The amounts of C in all fractions were determined, and the triangle C-14 values of selected samples were evaluated as indices of C turnover rate. The amount of stored C increased with elevation from 78 m (13.3 g kg(-1)) to ca. 1700 m a.s.l. (28.0 g kg(-1)). However, the total C content and C contents in LF, OxF, and NOxF exhibited decreasing trends from 1700 to ca. 2000 m a.s.l. (20.4 g kg(-1)), probably because of decreased biomass production and decreased amorphous soil minerals at ca. 2000 m. The Delta C-14 values indicated that the C turnover rates in HF, OxF, and NOxF were faster at higher elevations (1221 m) than at lower elevations (78 m). These results suggest that mineralogy can have greater influence on C turnover than the climate difference in these mineral-associated C fractions through SOM stabilisation. In lowland, the amounts and turnover rates of stored C in the soil fractions were larger and slower in the central region than in the eastern region, respectively, reflecting differences in soil texture and mineralogy. Multiple regression analysis showed that the amount of C was negatively influenced by the mean annual temperature in all fractions and positively influenced by amorphous Al minerals (Alo-Alp) in OxF and NOxF. The coefficients for temperature further suggest that the relative vulnerability of C to temperature increase is in the order of LF>HF>OxF>NOxF. These findings can serve as a basis for the maintenance and improvement of paddy soil fertility in Nepal for sustainable agricultural management.

Aims Silicon (Si) is a beneficial element for gramineous plants. Si in soil primarily originates from soil minerals but plant-derived phytoliths have recently attracted attention as an important alternative source of available Si. As the controlling factors of solubility of phytoliths remain unclear, this study investigated the solubility of phytoliths from different species and organs of gramineous plants, clarifying the physicochemical factors determining their solubility. Methods Phytoliths were prepared from the culms, branches, and leaves of moso bamboo ( Phyllostachys pubescens ), the stems and leaves of sugarcane ( Saccharum officinarum ), and the straw and husks of rice ( Oryza sativa ) using a wet digestion method. The solubility of the phytoliths was determined via 0.2-M NaOH extraction. Their crystallinity was evaluated based on X-ray diffraction analysis. Results The initial Si dissolution rate and maximum Si dissolution amount of the phytoliths ranged from 71.1 to 205 g Si kg⁻¹ h⁻¹ and 223 to 429 g Si kg⁻¹, respectively. Both parameters exhibited an increasing trend from the proximal to distal parts. The amounts of the opal-A and α-quartz of the phytoliths ranged from 66.7% to 97.5% and from 3.5% to 7.8%, with a negative correlation (p < 0.01). The opal-A increased from the proximal to distal parts of the plants. The initial dissolution rate and maximum dissolution amount exhibited a positive and negative correlation with the opal-A and α-quartz, respectively (p < 0.01). Conclusion These findings elucidate the mechanism controlling Si supply from phytoliths and provide fundamental insights into their role in Si cycling in soils.

Non-exchangeable potassium (Nex-K) released slowly from minerals is a key component of long-term K fertility of agricultural soils. Two extraction methods are widely used to determine soil Nex-K: the boiling nitric acid (HNO 3 ) method and the tetraphenylborate (TPB) method. However, it is unclear from which minerals the methods extract the Nex-K. The Nex-K was determined for 322 agricultural soils sampled across Japan using both methods. The major soil minerals, including three K-bearing minerals—trioctahedral micas (Micas[Tri]), dioctahedral micas (Micas[Di]), and potassium feldspar (K-feldspar)—were determined by X-ray powder diffraction (XRPD). The multiple regression analysis revealed that the boiling HNO 3 method extracts Nex-K mainly from Micas(Tri) and partly from K-feldspar, whereas the TPB method extracts Nex-K mainly from Micas(Di) and partly from Micas(Tri) and K-feldspar. The cluster analysis, based on the XRPD-based mineral content, revealed that the soils had at least three geological parent materials. The soils with granitic mineralogical characteristics had high Micas(Tri) and Nex-K contents, as determined by the boiling HNO 3 method. In conclusion, the mineralogy of the parent material influences the types and quantities of K-bearing minerals present in soil, thereby controlling the amount of Nex-K and its extractability by different methods. This understanding allows for the estimation of long-term K fertility of agricultural soils.

Nonexchangeable potassium (neK) derived from micaceous minerals is a key K source in less-weathered granitic soils across the world, including Europe and eastern Asia. Plant use of neK may vary based on soil particle size, specifically coarse (> 20 mu m) and fine (< 20 mu m) fractions. This study quantified neK in both fractions of soils from different parent materials and evaluated its contribution to crop K uptake under varying K fertilization levels. In total, 55 soil samples were collected from vegetable fields with diverse soil groups or parent materials. Soils derived from granite and sedimentary rock, with high- and low-neK content, respectively, were used in pot experiments with sweetcorn under four K fertilizer rates of 10%, 40%, 70%, and 100%. Soils were fractionated into coarse (> 20 mu m) and fine (< 20 mu m) fractions, and neK was evaluated using hot HNO3 extraction. Compared with neK in the fine fraction, neK in the coarse fraction exhibited a stronger linear relationship with total neK (< 2 mm), indicating its greater influence on overall neK content. Granite-derived soils showed relatively high neK levels, proportional to micaceous mineral content in the coarse fraction. In micaceous-rich granitic soils, neK in the coarse fraction of 1066 mg kg(-1) decreased by 8%, 9%, 11%, and 15% after the pot experiment under K fertilizer rates of 10%, 40%, 70%, and 100% (two-way analysis of variance, p < 0.05), whereas fine-fraction neK of 404 mg kg(-1) did not decrease significantly. The reduction ((sic)neK(coarse)) correlated positively with K balance in granitic soils. In contrast, sedimentary rock-derived soil had smaller neK levels (coarse- and fine-fraction neK; 31 and 200 mg kg(-1), respectively), with no decline in either fraction after the same pot experiment. These findings suggest that coarse micaceous minerals serve as a geologically controlled neK source in soils. In high-neK soils, the coarse fraction contained double the neK content of the fine fraction, leading to greater root accessibility and enhanced K release from neK through root uptake and exudates. In less-weathered granitic soils, promotion of root elongation by basal K fertilization improves accessibility to the coarse fraction and may replace K topdressing by utilizing neK in the coarse fraction.

Andosols are the soil type that potentially has the highest radiocesium (RCs) transfer risk due to their deficiency in micaceous minerals (micas) that can strongly retain RCs in their interlayer sites. However, an exogeneous source of micas as a component of Asian dust may have contributed largely to increase the RCs retention ability for Andosols in Tohoku Region, Japan. We investigated 29 pasture soils with andic soil properties that were collected at various places across this region to clarify the provenance of micas whether they originated from Asian dust or local lithological materials. Mica content in bulk size fraction (<2.0 mm) positively and strongly correlated with the factor related to felsic elemental composition obtained by principal component analysis (r = 0.90, p < 0.01). Fine micas in the <20 m fraction (Mica<20 m) accounted for a large fraction (72 +/- 16%) of the total mica contents and positively correlated with the content of fine quartz derived from Asian dust (Qz(ad_<20 m)) (r = 0.86, p < 0.01), which were distinguished from fine quartz derived from igneous bedrock materials (Qz(ig_<20 mu m)) by using the delta 18O values for quartz isolated from the <20 m fraction. Furthermore, Mica(<20m) correlated positively with radiocesium interception potential (RIP) of this fraction. These results for the first time demonstrated the importance of Asian-dust-derived micas relative to those from another local sources on the RCs retention abilities in Andosols in Tohoku, Japan.

X-ray powder diffraction (XRPD) is an effective technique for identifying and quantifying mineral types in soil. However, few studies have compared quantitative values based on XRPD with those from conventional wet chemical methods (WCMs). Here, we determined the primary mineral content in artificial mineral mixtures and 79 agricultural soils from across Japan using WCMs and two XRPD-based quantitative methods: the mineral intensity factor (MIF) and the full-pattern summation (FPS) methods performed with the powdR package for R. For artificial mixtures, the accuracy of mineral content determination (i.e., micas, quartz, K-feldspar, and plagioclase) followed the order: WCMs > FPS > MIF. For Japanese agricultural soils, the contents of each mineral were highly similar between WCMs and FPS, based on mean absolute differences and correlation coefficients. Alternatively, MIF displayed lower similarities with WCMs, likely due to preferred orientation and peak shift or overlap issues. Using the FPS method, the mica and amorphous phase contents were positively and significantly correlated with nonexchangeable K content and cation exchange capacity, respectively. Additionally, the plagioclase content was negatively and significantly correlated with clay content. Thus, the powdR-based FPS method is recommended for determining the mineral composition of soils, as it allows for a clearer and more quantitative demonstration of the relationship between individual minerals and soil properties.

The weights of light fraction organic matter (LF) separated from soils using saturated CaCl2 solution (1.4 g cm-3) were compared to those separated using NaI solution (1.6 g cm-3 and 1.4 g cm-3) to examine the possibility of using CaCl2 solution for LF separation, to examine more cost-effective LF separation procedure. In terms of the recovery weight and carbon and nitrogen content, the LF characteristics of 19 samples of the plow layer or A horizon soils separated using CaCl2 solution were similar to those of LF separated using NaI solution (1.6 g cm-3), which is commonly used for LF analysis. These results suggest that CaCl2 solution could be used for LF analysis. The applicability of the CaCl2 separation procedure for the analysis of LF from soil containing charcoal material was further confirmed by examining another set of 16 samples of the plow layer. The recovery weights of LF from soil containing organic matter and charcoal material with CaCl2 solution were similar to those with sodium polytungstate (1.6 g cm-3), which is conventionally used not only for LF but also for charcoal material separation from soils.

To investigate how the long-term application of inorganic fertilizer and organic amendments affects the accumulation of organic matter in physico-chemically fractionated components in paddy soils and how the accumulation is determined by soil properties and anthropogenic carbon input, we studied the effect of variable management of inorganic fertilizer and organic amendments for > 50 years on the amounts of accumulated soil organic carbon (SOC) in fractionated components in three paddy fields. SOC was fractionated into four components based on their physical and 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. On average, the amount and percentage of accumulated C in the four fractions were as follows: OxF (6.63 gC kg(soil)(-1), 46%) > NOxF (5.32, 35) > LF (1.68, 12) > HF (1.12, 7.2), suggesting about 80% of SOC was in fine, stable fractions. The amount of accumulated C in all fractions increased slightly with the application of inorganic fertilizer, while it increased considerably with the use of organic amendments. In addition, the application of fertilizers and amendments raised the proportion of C content in LF and HF, which are labile and related to soil fertility. Stepwise multiple regression analysis using two principal component analysis scores of soil properties and anthropogenic C input further revealed that the labile fractions (LF and HF) were more strongly determined by the management of fertilizers and amendments, while the stable fractions (OxF and NOxF) were more strongly determined by soil-specific properties, mainly the amorphous nature of the soil. These results indicate that the use of certain amounts of organic amendments would be recommended to carry out rational management to improve soil fertility and C sequestration in paddy fields, with the application of amorphous minerals as an additional option.

The frayed edge site (FES) of micas, a partially weathered interlayer site, selectively adsorbs Cs radioisotopes. Despite extensive research on Cs+ adsorption, the interactive dynamics of FES elements remain unclear. This study employs experimental and computational methods to examine how interlayer cations at the FES affect Cs stability. We measured the solid-liquid distribution coefficients of Cs+ for partially expanded K- and Rb-fixed biotite using chemical extraction and adsorption methods. We evaluated the standard Gibbs free energy for the Cs exchange reaction between the FESs of K- and Rb-fixed muscovite models and bulk water, expanding the d001 spacing from collapsed to fully expanded conditions. Our results reveal that the interlayer cation significantly influences Cs+ affinity for FES, with the substitution of K+ with Rb+ largely reducing Cs+ stability. The computational approach further disclosed that the K+ to Rb+ replacement only at the wedge-shaped part of the FES contributed to the decrease in Cs+ stability whereas the replacement at other interlayer sites caused little impact. Our studies offer microscopic structural insights into FES, highlighting the critical role of the wedge-shaped part of FES in Cs+ stability.

To prove the hypothesis that paddy rice utilizes soil nonexchangeable potassium (neK) and causes associated structural changes in clay minerals, K status and clay mineralogy of 22 surface soils from three paddy fields under long-term fertilizer management for 51-93 years were investigated. Soil neK content was determined as the difference between 1 mol L-1 hot HNO3 extractable K and 1 mol L-1 ammonium acetate exchangeable K. Clay mineralogy was identified by X-ray diffraction (XRD). The radiocesium interception potential (RIP), an index of frayed edge sites in the interlayer sites of 2:1 type clay minerals, was also determined. The neK contents under the -K and NPK treatments were considerably lower than those under the unfertilized treatment in all the fields, indicating the exploitation of soil neK by rice. XRD analysis of the clay samples revealed 7% shift from the 1.0 peak to 1.4 nm one under the -K treatment compared with the unfertilized one, and the amounts of neK were negatively correlated with those of RIP (p < .01), suggesting the expansion of interlayer spaces of the 2:1 type phyllosilicates such as mica due to the release of neK. In addition, the neK content positively correlated with K balance of the long-term experiments (p < .05). The differences of neK between unfertilized K and -K treatments corresponded to 22-157 kg K ha(-1), or 0.42-1.68 kg K ha(-1) year(-1). In conclusion, utilization of considerable amount of soil neK under K depleted conditions should be considered to establish sustainable K management for paddy rice.

Abstract Nickel (Ni) is an essential micronutrient for plants although it is considered toxic when present in excess in the soil. This study investigated the transfer of Ni from the soil to rice in terraced paddy fields affected by serpentinite, which contains an anomalously higher Ni content compared with other geological materials. Soils, soil solutions, and rice plants were collected at several different growing stages from three adjacent terraced paddy fields subject to the same water and fertilizer management. Temporal changes in their elemental compositions revealed that a higher concentration of Ni was dissolved in the soil solution during flooded conditions, probably due to the co-solubilization with Mn oxides under low redox potential conditions. However, rice accumulated Ni at a higher rate during the drainage period than in the flooding period. Although the Ni concentration in the soil solution was lowest in the drainage period, the relative concentration to Fe (i.e., Ni/Fe ratio) was much higher than that in flooded conditions. These relationships suggest that a potential measure to counter the transfer of Ni from the soil to rice in serpentine-affected paddy fields is to increase Fe phytoavailability during the drainage period.

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 melange. 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 melange 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.

HAK family transporters primarily function as K+ transporters and play major roles in K+ uptake and translocation in plants, whereas several HAK transporters exhibit Na+ transport activity. OsHAK2, a rice HAK transporter, was shown to mediate Na+ transport in Escherichia coli in a previous study. In this study, we investigated whether OsHAK2 is involved in Na+ transport in the rice plant. Overexpression of OsHAK2 increased Na+ translocation from the roots to the shoots of transgenic rice. It also increased both root and whole-plant Na+ content, and enhanced shoot length under low Na+ and K+ conditions. Meanwhile, OsHAK2 overexpression increased salt sensitivity under a long-term salt stress condition, indicating that OsHAK2 is not involved in salt tolerance, unlike in the case of ZmHAK4 in maize. These results suggest that OsHAK2 is permeable to Na+ and contributes to shoot growth in rice plants under low Na+ and K+ conditions.