Associations between soybean yield and soil chemical properties in Japan have largely been examined using regional-scale surveys. However, none of the previous studies in Japan modeled the strong regional heterogeneity inherent in these datasets. This study aims to reanalyze the cross-regional dataset of Takamoto, Takahashi, and Nira (2020) using a linear mixed-effects model (LMM) to identify soil chemical properties associated with soybean yield after accounting for hierarchical structure (random intercepts for prefecture and site nested within prefecture). The dataset comprised 214 sites across 16 prefectures in Japan and included soybean yield and six soil variables: total N, available P, soil pH, and exchangeable K, Ca, and Mg. Fixed effects initially included all variables and all their first-order interactions, and an exhaustive all-subsets search then selected the final fixed effect set. Random effects explained approximately 60% of the variance in yield, whereas the selected fixed effects explained less than 5%. The selected LMM retained only two fixed effects: exchangeable Ca (beta = +0.24, p < 0.001) and exchangeable Mg (beta = -0.22, p < 0.001). These coefficients were significantly larger in the high-yield group than in the low-yield group (groups defined by prefectural mean yields). Although soil chemical properties contribute little to soybean yield at a national scale, exchangeable Ca and Mg represent broadly applicable factors for yield improvement and may help to overcome the long-term stagnation in soybean yields in Japan.
Inland wetlands offer numerous ecosystem services, including water filtration and storage, habitat for migratory birds, and support for diverse wildlife. In the semiarid landscapes of Mongolia, isolated patches of permafrost beneath these wetlands play a crucial role in maintaining these services. They also serve as essential water sources and forage pastures for livestock and agricultural activities. This study examines the effects of anthropogenic activities (mainly livestock grazing) on vegetation and soil properties in permafrost-affected wetlands and adjacent upland grasslands in the Khurkh River Valley. The composition and coverage of vegetation at 35 study sites were assessed through triplicate quadrat harvests, clipped at the soil surface. Pasture degradation was classified as non-degraded, slightly degraded, or moderately degraded based on the proportion of deterioration indicator species. To analyze spatial variability in soil properties, samples were collected from 43 cores (0-30 cm) and analyzed for physicochemical characteristics. The effects of pasture degradation on surface soils varied by reference soil groups, including Phaeozems, Kastanozems, Chernozems, Cryosols, and Histosols. In Phaeozems and Kastanozems, livestock trampling and compaction in moderately degraded pastures tended to decrease water infiltration and accelerate organic matter loss, although these effects were not statistically significant. As a result, soil carbon and nitrogen pools may decrease as degradation intensifies. By contrast, Cryosols underlain by permafrost experienced strong freeze-thaw processes, which promote organic matter accumulation even in pasture-degraded conditions. These differing responses among soil groups highlighted the importance of soil-specific management strategies, including pasture rotation regimes of different durations, to conserve the valuable wetland and grassland ecosystems.
Risks of food insecurity are being aggravated by degradation of soil and environment, and the attendant closure of the Strait of Hormuz, which is a critical shipping route for the transport of fertilizers, food, and energy. Use of modern war also pollutes soil, water, and air, and destroys the agricultural infrastructure. As much as 20% to 45% of critical food inputs and 25% of global fertilizers are dependent on this route. Thus, the number of food-insecure people may increase by an additional 45 million. Gulf countries import 70% of their food through this checkpoint. Furthermore, a complete closure of this shipping route would need to replace 87 M kg of food per day to minimize the risks of food shortage in Gulf Countries. Hunger and desperateness may aggravate risks of political instability because of an increase in human miseries and desperateness. War has 3 parties: two are those which are at war with one another. The third party is the land on which or about which they fight. While different nations or organizations support one party or the other, but no one cares about the land/soil which has been cratered, compacted, polluted, contaminated, and rendered unfit for food production for decades or generations. Thus, the best strategy would be to minimize the risks of such events through political dialogue and empowerment of the United Nations and other organizations to encourage and promote peace and stability. There must also be a soil/environment restoration and rehabilitation plan agreed upon by both parties involved. War and its consequences, human-made tragedies, have dire long-term effects. Destroying soil and polluting environments are crime against nature, which are neither bearable nor acceptable. These acts of violence against nature must be forbidden.
Selenium (Se) is essential for human health, and agronomic biofortification of food crops offers a direct strategy to address global dietary Se deficiency. Plants exhibit pronounced interspecific variation in Se sensitivity, yet whether this differential susceptibility enables concurrent crop biofortification and weed suppression remains unexplored. Garlic (Allium sativum L.) possesses exceptional Se-accumulating capacity due to its sulfur-rich metabolism, whereas Veronica didyma-a pernicious speedwell that heavily infests garlic fields and requires repeated herbicide sprayings - lacks this specialization. Here we demonstrate that foliar Na2SeO3 spraying elicits a sharply divergent hormetic response between these species. At 225 g hm-2, Se significantly promoted garlic growth. Chlorophyll increased 24.01%, photosynthetic parameters (Pn, Tr, and Gs) enhanced by 29.45-39.77%, and Ci reduced by 23.10%. Antioxidant enzyme activities rose, proteins, sugars, amino acids, and glutathione were markedly elevated, while malondialdehyde (MDA) and proline decreased by 21.08% and 25.94%. In contrast, the same treatment induced phytotoxicity in the co-cultivated speedwell. Biomass was inhibited, chlorophyll declined by 20.24%, and photosynthetic parameters (Pn, Tr, and Gs) significantly decreased, while Ci significantly increased. Antioxidant enzymes were suppressed, proline and MDA increased by 20.46% and 21.86%. The tissue Se concentration in speedwell and garlic increased significantly with increasing foliar spray concentration. Higher concentrations (450-675 g hm-2) could induce oxidative stress responses in both plants. Our findings establish a discrete Se spraying window where the element simultaneously acts as a biofortifying biostimulant for garlic and a selective phytotoxic agent against speedwell, eliminating separate herbicide applications and transforming Se fertilization into an integrated crop management tool.
Selenium (Se) is an essential micronutrient for human and animal health; however, its soil concentrations exhibit significant variability due to environmental and land-use influences. Thus, this study examined selenium distribution, fractionation, and bioavailability across 84 vegetable cultivation sites in four provinces of western central Thailand, sampling soils at three depth intervals and the associated edible vegetables. Soil physicochemical properties were determined, and the Se fractions were assessed using a five-step sequential extraction and flow hydride generation atomic absorption spectrophotometry. Total Se in edible plant parts was also analyzed. The results showed that parent material and soil properties, particularly organic matter content, mineral composition, and texture, play key roles in controlling Se fractionation. Soils rich in organic matter and Fe-Mn oxides tended to retain Se in less mobile forms, whereas coarse-textured soils with low organic matter exhibited higher proportions of relatively labile Se. With increasing soil depth, the concentrations of labile Se fractions decreased, while the proportion of residual Se increased. Among the studied crops, Chinese cabbage and other Brassicaceae species showed higher Se accumulation, whereas Solanaceae crops (chili and tomato) contained markedly lower concentrations. A significant relationship was observed between plant Se concentrations and the relatively labile soil Se fractions, indicating that bioavailable Se, rather than total Se, is a more reliable predictor of plant uptake. These findings highlight the importance of site-specific Se management strategies to improve crop nutritional quality and support sustainable agricultural practices in the region.
Nitrogen (N) management in Ethiopian lowland rice systems relies on outdated, suboptimal practices, leading to low N use efficiency (NUE) and significant environmental losses. A two-year field experiment was conducted across four sites to evaluate the effects of N application rate and timing on grain yield, NUE, chlorophyll content (SPAD), and economic returns. The study employed a factorial randomized complete block design with three N rates (92, 138, and 184 kg N ha-1) and five application schedules (two-, three-, and four-split regimes). Results showed that both N rate and timing significantly influenced productivity and efficiency, though their interaction was not significant, suggesting that optimal timing remains consistent regardless of the total N dose. The three-split strategy (1/3 basal +1/3 mid-tillering +1/3 panicle initiation) proved superior, achieving a maximum grain yield of 7.70 t ha-1 and biomass of 16.96 t ha-1 at the 184 kg N ha-1 rate. This strategy optimized sink-source dynamics and maintained higher SPAD values (36.3), while simultaneously enhancing agronomic N use efficiency by 20-30% compared to other regimes. Economic analysis revealed that while 184 kg N ha-1 yielded the highest net return (238,336 ETB ha-1), the 138 kg N ha-1 rate provided the greatest investment efficiency, with a Value-Cost Ratio of 8.7 and a Marginal Rate of Return of 765.8%. These findings demonstrate that synchronizing N supply with key growth stages maximizes both biological potential and economic stability. We recommend 184 kg N ha-1 in three splits for high-input systems, while 138 kg N ha-1 in three splits is the optimal recommendation for resource-constrained farmers to maximize profitability and minimize environmental risks. Future research should focus on sensor-guided and model-based precision N management to further refine these recommendations for Ethiopia's lowland rice systems.
Soil fertility drives crop productivity, with integrated organic-chemical fertilization effectively boosts soil organic carbon (SOC), nutrient availability, and microbial activity, especially in low-fertility soils like Vertisol in the Huaibei Plain. However, the role of labile organic carbon (LOC) fractions in driving yield under diversified fertilization remains unclear. Through a long-term field experiment comparing no fertilizer (NF), chemical fertilizer alone (CF), chemical fertilizer with low or high straw, pig or cattle manure (CFLS, CFHS, CFP, CFC), we demonstrate that organic-chemical treatments significantly increased SOC, LOC, carbon pool management index (CPMI), and nutrients versus NF, with cattle manure (CFC) exhibiting the strongest improvement. Partial least squares path model (PLS-PM) revealed that LOC strongly influenced soil nutrients and microbial traits, while soil nutrients were the strongest predictor of crop yield, explaining 73% of yield variance. Microbial traits had a marginally negative effect on yield, suggesting potential nutrient competition. Therefore, integrating cattle manure with chemical fertilizers optimizes soil quality and crop yield by enhancing LOC-mediated nutrient availability, demonstrating superior efficacy among organic amendments.
Freeze-thaw cycles (FTCs) and microplastic (MP) contamination are common co-phenomena in the black soil of Northeast China. Climate warming increases the frequency of FTCs of soils in northern regions. Nowadays, the effects of repeated FTCs on the spread and proliferation of antibiotic resistance genes (ARGs) have received limited understanding. Whether the existence of MPs will complicate the freeze-thaw effect remains unclear. Therefore, microcosm experiments with two frequencies of FTCs (i.e. 14 and 28 cycles) and two types of MPs (polyethylene and polybutylene adipate terephthalate, added at 1% w/w) were conducted to unravel the effects of FTCs and their interrelation with MP contamination on the spread and proliferation of ARGs. Results showed that FTCs decreased the total abundance of target ARGs in soils. The existence of MPs further reduced their abundance, which was more significant at high FTC frequencies. Changes in the ARG abundance during the above processes were attributed to the decrease in the abundance of integrons intI1 mediating ARG horizontal gene transfer among bacteria and the potential host bacteria. Despite an increase in the abundance of freezing-tolerant bacterium Sphingobium carrying ARGs under FTCs, the total abundance of host bacteria carrying ARGs decreased. There were significant correlations between the available soil nitrogen (AN) and the abundances of ARGs. Moreover, the abundance of pathogenic bacteria carrying multiple ARGs increased after adding MPs under low-frequency FTCs, and their abundance decreased, especially under high-frequency FTCs. These findings expand our understanding of ARG spread and proliferation in the black soil of Northeast China and provide a theoretical basis for the prevention and control of ARGs in the soil.
Humic acids (HAs) are humic substances that are soluble in alkali and insoluble in acid, and occur as self-assembled supramolecular associations of small heterogeneous constituents bound together by weak linkages in solution. In this study, to develop methods for separating and characterizing the constituents of HAs, the associations of soil HA constituents were separated using hydrophilic interaction chromatography (HILIC) with a dihydroxypropyl-bonded stationary phase, and the constituent molecules were separated and optically characterized by reversed-phase high-performance liquid chromatography (RP-HPLC) using a phenylhexyl-bonded stationary phase. When HILIC and RP-HPLC were applied separately, multiple peaks were resolved for the soil HAs using either method. The associations of HA constituents were separated into three fractions based on differences in hydrophilicity using preparative HILIC. The most hydrophilic fraction was the most abundant, accounting for nearly half of the total carbon in the HA. Most of the HA constituents fractionated by preparative HILIC were precipitated by acidification, whereas some constituents in the less hydrophilic fractions did not precipitate. RP-HPLC separated the fractions obtained by preparative HILIC and subsequent acidification into multiple peaks. The constituents of the acid-soluble fractions were generally less hydrophobic than those of the acid-precipitated fractions. When RP-HPLC was performed on the acid-precipitated fractions, most of the constituents were eluted as a mountain-like series of peaks, all of which exhibited featureless absorption spectra with a gradual decrease in absorbance from the UV region to the visible region, and fluorescence spectra with similar excitation and emission wavelengths. In contrast, in the acid-soluble fractions, in addition to the constituents eluted as a mountain-like series of peaks, many constituents with absorption primarily in the UV region and/or intense fluorescence were eluted as sharp peaks. These results demonstrate that HILIC and subsequent acidification are useful for separating the associations of HA constituents with different hydrophilic properties, and that combining with RP-HPLC can be used to separate and characterize the constituents.
Leaching of nitrate (NO3-) from O horizons of tropical forests can be substantial, with its magnitude regulated by the pH sensitivity of nitrification. Our previous study revealed that nitrification rates of O horizons increased sharply above a pH threshold of 5.5 similar to 6.0. In turn, the pH of O horizons is maintained by its acid-neutralizing capacity (ANC), which is primarily controlled by base cation cycling via litterfall. Correspondingly, the pH-buffering effectiveness depends on both base-cation concentrations and the ion composition. However, how base cations control temporal variations in O-horizon ANC and shape nutrient-cycling patterns remain underexplored, particularly in potassium (K)-rich tropical forest soils. This study investigated NO3- and base-cation leaching patterns from the O horizons of two K-rich Inceptisols in the Pasoh forest of Malaysia. The sites - M1 (drier with higher K+ dominance in the base-cation pool) and M2 (wetter with lower K+ dominance) - frequently exhibited O-horizon pH values near the presumed nitrification threshold (5.5 similar to 6.0), making nitrification and NO3--N leaching highly variable in time and space. A one-year field survey revealed that NO3--N was the dominant dissolved N form in O-horizon leachates at both sites, with annual fluxes of 15.5-16.9 kg N ha(-1) yr(-1). Both sites exhibited wide seasonal pH ranges (M1: 3.9-6.1; M2: 4.0-6.3), and K+ accounted for 50%-59% of O-horizon base-cation leaching. The dissolved K+ concentrations displayed a flushing-type leaching pattern that coincided with seasonal increases in NO3--N leaching especially at the drier, K-richer site (M1). These fluctuating patterns are consistent with a K+-dominated base-cation pool having limited pH-buffering effectiveness, allowing pH fluctuations to vary more widely around the nitrification threshold, thereby modulating nitrification and NO3- leaching. As one fate of the leached NO3-, N2O emissions were higher at M2, consistent with wetter mineral soil conditions favoring denitrification. Overall, the NO3--N leaching patterns were driven by changes in pH, which were amplified by the dominance of K in the base-cation pool.
Why do we classify? That is, why do we place objects with similar features into groups? A common answer is that classification helps us organize our knowledge. It enables us to better understand the objects being grouped together. Should soils with similar climates be placed together into classes? There are advantages and disadvantages. First, a distinction needs to be made between climate (a soil-forming factor) and soil climate (a measurable soil property). The main advantage pertains to the concepts of differentiating properties (e.g. andic, oxic, vertic, mollic, etc.) and accessory properties (e.g. fertility, infiltration, aeration, toxicities, etc.). In the Soil Taxonomy system, for example, differentiating properties with many accessory properties were placed high within the hierarchy because it created a system that provides taxa which permit users of the system to make the greatest number of important statements. The statements range from those about land use on the short-term time scale (seasons to decades) to statements about soil genesis on the long-term time scale (centuries to millennia). Disadvantages, on the other hand, include the fact that soil climate is dynamic and requires years of moisture and temperature data to capture its variability, especially soil moisture. Still, soil moisture and soil temperature are among the most important soil properties controlling the uses of the soil and long-term genesis of the soil. However, soil climate is often unnecessary for many classification systems to achieve the goals for which the systems were designed, this is especially true for areas without major geographical differences in climate and for systems concerned about their classifications becoming obsolete with climate change. On the other hand, a classification system explicitly containing soil moisture and temperature data in its taxa provides a baseline for assessing the effects of climate change on soil and provides a language discussing those changes.
Assessing the carbon sequestration potential of agricultural soils with accuracy is essential for global food security and climate change mitigation. We aimed to improve the Rothamsted Carbon (RothC) model for application in Andosol paddy fields by integrating two RothC-based models previously developed in Japan: one tailored for paddy fields and one for Andosol upland fields. The core refinement involved adjusting the decomposition rate of the humified organic matter (HUM) pool within the paddy model using the phosphate adsorption coefficient (PAC). Validation was performed using long-term continuous field data (11-48 years) from five Andosol paddy sites throughout Japan, encompassing control plots (chemical fertilizer only) and plots with varying organic matter amendments. Comparing simulated and observed soil organic carbon (SOC) stocks (to 30 cm), the performance of the improved Andosol-Paddy model showed substantial gains relative to the paddy-specific RothC model. The improved model yielded an average root mean square error (RMSE) of 9.99 and an average absolute mean error (ME) of 7.49, with values < 50% of the original model error (RMSE: 20.32; absolute ME: 16.69). This evidence clearly demonstrates that incorporating PAC-based HUM decomposition into the paddy-specific RothC model significantly elevates the predictive accuracy of SOC dynamics in Andosol paddy fields.
The combined content of oxalate-extractable aluminum (Alo) and 1/2 oxalate-extractable iron (Feo), expressed as Alo +1/2Feo, is a key factor for identifying andic soil properties. Specifically, a value of >= 20 g kg-1 for this variable is needed for andic soil properties in soils with less glass content. In this study, we thus developed a model to estimate the Alo and Feo contents in soils using visible and near-infrared spectroscopy coupled with machine learning. We evaluated the performance of three algorithms, namely partial least square regression, random forest (RF), and convolutional neural network (CNN). The CNN model outperformed the other models in estimating the Alo (R2 = 0.921) and Feo (R2 = 0.723) contents, with mean absolute errors of 2.3 and 2.0 g kg-1 for Alo and Feo, respectively. In evaluating whether the Alo +1/2Feo content of 2245 soil samples was >= 20 g kg-1, the RF and CNN models produced only 124 and 88 misclassifications, respectively. Our method can serve as a time-efficient and chemical-free approach for identifying andic soil properties.
Arsenic (As) contamination in agricultural soils is a pressing environmental concern, particularly in volcanic regions where Andosols dominate and phosphorus (P) fertilizers are intensively applied. Because arsenate and phosphate are chemically similar oxyanions, they compete for sorption sites on soil minerals, thereby controlling their mobility and bioavailability. In this study, we investigated the competitive sorption of arsenate and phosphate on three allophanic Andosols and synthesized allophane under varying pH conditions. Batch sorption experiments were conducted using both single- and binary-component systems. Results showed that arsenate and phosphate sorption were strongly pH-dependent. Maximum sorption on allophane occurred at around pH 4.5, coinciding with the onset of aluminum dissolution. In the binary system, phosphate effectively reduced arsenate sorption. For synthesized allophane, the total amount of arsenate and phosphate sorbed in the binary system (1 mM arsenate +1 mM phosphate) was comparable to the amount of arsenate sorbed in the single-component system (2 mM arsenate), indicating that arsenate and phosphate compete for the same sorption sites. While the order of anion addition had only a minor influence on arsenate sorption compared with the competitive effect of phosphate, phosphate sorption was clearly higher when phosphate was added first. Furthermore, differences among the soils in their sorption behavior toward arsenate and phosphate reflected their contents of active aluminum and iron (operationally defined as oxalate-extractable Al and Fe). These results provide mechanistic insight into the competitive and exchangeable nature of arsenate and phosphate sorption on allophanic Andosols.
