Soil Organic Matter Content Research Articles

Improving the Estimation Accuracy of Soil Organic Matter Content Based on the Spectral Reflectance from Soils with Different Grain Sizes

Accurate and rapid estimation of soil organic matter (SOM) content is of great significance for advancing precision agriculture. Compared with traditional chemical methods, the hyperspectral estimation is superior in rapidly estimating SOM content. Soil grain size affects soil spectral reflectance, thereby affecting the accuracy of hyperspectral estimation. However, the appropriate soil grain size for the hyperspectral analysis is nearly unknown. This study propose a best hyperspectral estimation method for determining SOM content of farmland soil in the Ibinur Lake Irrigation Area (ILIA) of the northwest arid zones of China. The original spectral reflectance of the 20-mesh (0.85 mm) and 60-mesh (0.25 mm) sieved soil were obtained, and the feature wavebands were selected using five types of spectral transformations. Then, hyperspectral estimation models were constructed based on the partial least squares regression (PLSR), support vector machine (SVM), random forest (RF), and extreme gradient boosting (XGBoost) models. Results show that the SOM content had relatively higher correlation coefficient with spectral reflectance of the 0.85 mm sieved soil than that of the 0.25 mm sieved soil. The transformation of original spectral reflectance of soil effectively enhanced the spectral characteristics related to SOM content. Soil grain size obviously affected spectral reflectance and the accuracy of hyperspectral estimation models. The overall stability and estimation accuracy of RF model was significantly higher compared with the PLSR, SVM, and XGBoost. Finally, the RF model combined with the root mean first-order differentiation (RMSFD) of spectral reflectance of the 0.85 mm sieved soil (R2 = 0.82, RMSE = 2.37, RPD = 2.27) was identified as the best method for estimating SOM content of farmland soil in the ILIA.

Cadmium and pyrene in the soil modify the properties of earthworm-mediated soil

Earthworms are pivotal in soil ecosystems due to their crucial role in shaping soil characteristics through casts and burrow walls. Previous research has predominantly focused on the direct impact of soil pollution on live earthworms, overlooking the subsequent effects on earthworm-mediated soil, such as casts and burrow walls. Using 2D-terraria as incubation containers and the geophagous earthworm species Metaphire guillelmi, this study assessed the change in various properties of earthworm-mediated soil in both uncontaminated soils and Cd- and Pye-contaminated soils. Overall, both Cd and Pye overall improved the ammonium nitrogen (NH4+-N), Olsen's phosphorus (Olsen-P) levels, and invertase and catalase activities while decreasing catalase activities in earthworm-mediated soil. They also fluctuating affected the pH, soil organic matter (SOM) content, soil urease, alkaline phosphatase activities, and microbial functional genes in the cast and burrow walls. These results indicated that earthworms remained crucial “ecosystem engineers” even in polluted soil. Additionally, differences were observed in the responses of properties between casts and burrow walls, showing unequal contributions of transit-through-gut and burrowing processes to soil modification. Specifically, transit-through-gut was found to have a more significant influence on soil NH4+-N and Olsen-P content compared to burrowing behavior. Regarding the pattern of microbial functional genes in earthworm-associated compartments, results revealed that they differed significantly in casts from those in bulk soil and burrow walls under unpolluted conditions, with pollution-enhancing disparities among compartments. Furthermore, NH4+-N and Olsen-P content, urease, and catalase activities in burrow walls and/or casts were identified as potential biomarkers for soil pollution, exhibiting a clear dose-effect relationship. Developing such biomarkers could address ethical concerns related to conventional earthworm biomarkers that require sacrificing earthworms. This study provides insights into the consequences of soil pollution on earthworm-mediated soil components, highlighting the importance of considering the indirect effects of contaminants on soil ecosystems.

Efficient removal of lead from polluted paddy soil by one-pot synthesized Nano-Fe3O4 incorporated stable lignin hydrogel

Lead (Pb) contamination in agricultural soils poses a significant threat to both ecosystems and human health. While nano-Fe3O4 exhibits promising potential for Pb remediation, its practical application in the soil is hindered by its’ biotoxicity, easy aggregation, and the risk of secondary pollution. Thus, this study presents a novel approach wherein Fe3O4 was incorporated into hydrogel via a one-pot synthetic strategy (Fe3O4@LH). This incorporation enhanced the mechanical properties and environmental stability of the hydrogel composites. Based on the mechanical properties, environmental stability, and single-point adsorption results for Pb, we selected Fe3O4@LH-4 for further research. The removal mechanism and the feasibility of employing Fe3O4@LH-4 for Pb removal from paddy soil were investigated through batch adsorption experiments and soil culture studies. Results showed that the adsorption process was primarily governed by swelling adsorption, electrostatic adsorption, ion exchange, precipitation, nanometer effect, and complexation mechanisms. The application of Fe3O4@LH-4 significantly led to the reduction of 16.7 %–25.4 % in soil Pb content, with removal rates escalating alongside increased dosage and application periods of Fe3O4@LH-4. Fitting results of the prediction model indicated that the Pb content in mildly Pb-contaminated soil (186.55 mg/kg) would decrease to be below the risk control standard for soil contamination of agricultural land in China (140 mg/kg) after 112 days of continuous application. Concurrently, cadmium and arsenic contents in the soil decreased by 5.2 %–10.8 % and 7.1 %–16.7 %, respectively. Moreover, the application of Fe3O4@LH-4 positively influenced soil nutrient levels, with total nitrogen and soil organic matter content significant increments of 13.6 %–41.0 % and 4.6 %–16.1 %, respectively. Furthermore, Fe3O4@LH-4 recovery exceeded 88.3 % after a 90-day application period. These findings underscore the potential of Fe3O4 incorporated hydrogel as a promising agent for the sustained removal of heavy metal Pb from paddy soil.

Functional traits and ecological niches as correlates of the interspecific growth–mortality trade‐off among seedlings of 14 tropical tree species

Abstract The interspecific trade‐off between growth versus mortality rates of tree species is thought to be driven by functional biology and to contribute to species ecological niche differentiation. Yet, functional trait variation is often not strongly correlated with growth and mortality, and few studies have investigated the relationships of both traits and niches, specifically encompassing above and belowground resources, to the trade‐off itself. These relationships are particularly relevant for seedlings, which must often survive resource limitation to reach larger size classes. We investigated the functional basis of the interspecific growth–mortality trade‐off and its relationship with ecological niches for seedlings of 14 tree species in a tropical forest in southwest China. We found evidence for an interspecific growth–mortality trade‐off at the seedling stage using 15 functional traits and 15 ecological niche variables. None of the organ‐level traits correlated with growth, mortality, nor the trade‐off, whereas specific stem length (SSL), a biomass allocation trait, was the only trait to have a significant correlation (positive). Moreover, light‐defined niches were not correlated with growth, mortality or the trade‐off, but soil‐defined niches did. Species at the faster growth/higher mortality end of the trade‐off were associated with higher fertility defined by lower soil bulk density and slope, and higher soil organic matter concentration and soil total nitrogen. Our findings indicate the importance of stem elongation and soil fertility for growth, mortality and their trade‐off at the seedling stage in this Asian tropical forest. Our findings contrast with analogous studies in neotropical forests showing the importance of photosynthesis‐related leaf traits related to insolation. Therefore, the functional drivers of demographic rates and trade‐offs, as well as their consequences for ecological niches, can vary among forests, likely owing to differences in biogeography, canopy disturbance rates, topography and soil properties. Moreover, the effects of functional trait variation on demographic rates and trade‐offs may be better revealed when biomass allocation is accounted for in a whole‐plant context. Read the free Plain Language Summary for this article on the Journal blog.

Linking soil nutrients, microbial community composition, and enzyme activities to saponin content of Paris polyphylla after addition of biochar and organic fertiliser

The application of organic fertilisers and biochar has become widespread in agroforestry ecosystems to enhance the yield and quality of crops and medicinal plants. However, their specific impact on both the yield and quality of Paris polyphylla (P. polyphylla), along with the underlying mechanisms, remains unclear. In this study, we investigated the distinct effects of organic fertiliser (at concentrations of 5% and 10%) and biochar application (at levels of 2% and 4%) on P. polyphylla saponin content. This content is intricately regulated by available soil nutrients, enzyme activities, and microbial community compositions and activities. Our results clearly demonstrated a significant increase in the saponin content, including total saponin, polyphyllin I (PPI), polyphyllin II (PPII), polyphyllin VI (PPVI), and polyphyllin VII (PPVII), in P. polyphylla following the application of both biochar and organic fertiliser. Moreover, in comparison to the control group, the addition of biochar and organic fertiliser led to a considerable rise in the activity of glycosyltransferase enzyme (GTS) and cycloartenol synthase (CAS) in P. polyphylla. Additionally, it increased soil available potassium (AK) and soil organic matter (SOM) concentration, along with the activity of urease, acid phosphatase, and catalase, although biochar amendment resulted in a decrease in nitrate nitrogen (NO3−-N) concentration. Crucially, our findings revealed a positive correlation between total saponin content and the activity of CAS in P. polyphylla, soil AK, SOM concentration, and the activities of urease, acid phosphatase, and catalase. Conversely, there was a negative correlation with NO3−-N content. Furthermore, the application of organic fertiliser and biochar significantly influenced microbial community structures and specific microbial taxa. Notably, total saponin content exhibited a positive relationship with the relative abundances of Dehalococcoidia, Saccharomycetes, and Agaricomycetes taxa while showing a negative correlation with the abundance of Verrucomicrobiae. In conclusion, the observed increase in saponin content can be attributed to the modulation of specific microbial taxa in soils, as well as alterations in soil nutrients and enzyme activities resulting from the application of biochar and organic fertiliser. This study identifies a potential mechanism for enhancing saponin content in the artificial cultivation of P. polyphylla.

Reclamation of coastal marshes to croplands shifts molecular composition of soil organic matter in the Bohai Rim

AbstractReclamation of coastal marshes to croplands lost massive reserves of soil organic matter (SOM). However, it is uncertain how reclamation shifts chemical composition of SOM and its size fractions. Here, we investigated this issue at two coastal marshes (Qilihai, degradation with seasonal waterlog; Beidagang, annual long‐term waterlog) along with adjacent long‐term reclaimed croplands on the coast of the Bohai Bay, China. Three SOM fractions: coarse particulate (cPOM, >250 μm), fine particulate (fPOM, 53–250 μm), and mineral‐associated organic matter (<53 μm) were analyzed by pyrolysis‐gas chromatography–mass spectrometry. Compared with the Qilihai marsh, the Beidagang marsh had higher SOM contents and lower proportions of microbial‐derived N‐containing compounds, which was attributed to the waterlogging‐induced weaker decomposition. Reclamation decreased the SOM contents (−53.6% to −63.3%) and proportions of lignin in cPOM (−44% to −52%) at both sites. However, reclamation‐induced shifts of molecular composition of SOM between the two sites diverged. At the Qilihai site, reclamation decreased the relative abundances of N‐containing compounds (−28%) but increased the proportions of lipids (+17%) and phenolics (+40.7%) in mineral‐associated organic matter. At the Beidagang site, reclamation decreased the proportions of monocyclic aromatics (−60.3% to −70.2%), but increased the relative abundances of N‐containing compounds (+175% to +407%) in all fractions. By contrast, the molecular composition of SOM at the two croplands had covergent pattern. In conclusion, despite of marsh locations with different waterlogging conditions, long‐term reclamation of wetlands to croplands generated convergent patterns in storage and molecular composition of SOM, which was attributed to the similar cropland cultivation.

Zinc Oxide Nanoparticles in the “Soil–Bacterial Community–Plant” System: Impact on the Stability of Soil Ecosystems

The use of man-made nanoparticles (NPs) has increased exponentially in recent years, many of which accumulate in significant quantities in soil, including through use in agriculture as nanofertilizers and nanopesticides. ZnO NPs are more environmentally friendly but have specific antimicrobial activity, which can affect soil microbiota, thereby influencing key microbial processes such as mineralization, nitrogen fixation and plant growth-promoting activities. Their behavior and persistence in soil depend on their chemical nature and soil characteristics. This review summarizes the applications of ZnO NPs in soil systems and their effects on various plants and soil microorganisms, particularly rhizobacteria that promote plant growth. A stimulating effect of ZnO NPs on the morphometric and biochemical characteristics of plants, as well as on soil microbiota and its activity at relatively low concentrations of up to 500 mg/mL and 250 mg/kg, respectively, is observed. As the concentration of ZnO NPs increases above these limits, toxic effects appear. The different effects of ZnO NPs are related to their size, dose, duration of exposure, solubility in water, as well as soil type, acidity and organic matter content. The review substantiates the need to study the behavior of ZnO NPs in the “soil-plant-microbiota” system for the possibility of using nanotechnologies in the agricultural industry and ensuring the safety of agricultural products.

Mediterranean beech forests: Thinning and ground-based skidding are found to alter microarthropod biodiversity with no effect on litter decomposition rate

Despite the high ecological value of Mediterranean beech forests, very little is known about the implications of forest operations on soil microarthropod biodiversity and litter decomposition rate. There is also no information concerning the amount of time needed for disturbed forest soil to recover and return to the pre-harvesting conditions. Silvicultural treatments are scheduled about every ten to fifteen years, without taking into account the amount of time necessary for recovery. The purpose of this study was to determine this information. The study started by selecting three study sites located along the Italian Apennine, each including a chronosequence of three forest parcels: one harvested in 2021, one harvested in 2012, and a control parcel which had not been harvested within the last forty years. In the harvested parcels we investigated skid trails which are classified as disturbed, and soil not affected by the passage of a machine which is classified as undisturbed. Thus in each study area there were five experimental treatments including the control area. The soil physico-chemical properties were assessed for each treatment. These included bulk density, penetration resistance, shear resistance, organic matter content, and soil microarthropod biodiversity which was assessed by the QBS-ar index (Soil Biological Quality based on microarthropods, a qualitative index measuring the quality of soil according to the biodiversity of the microarthropod community). We further established a litter decomposition experiment, using teabags as reference material, to check the differences among treatments in litter decomposition rates. We used linear mixed-effects models to investigate the effects of the experimental treatment on the physico-chemical and biological features, and relationships among QBS-ar index and soil physico-chemical features. We analysed the effects of the experimental treatment on the litter decomposition rate using generalised linear-mixed effects models. A significant effect caused by machine passage was found in the recently harvested parcels on soil penetration resistance (∼+70 % comparing to the control), shear resistance (∼+35 %), and QBS-ar index (-25 %). Effects of machine passage on soil bulk density and organic matter content were not significant. All the investigated variables in the skid trails returned to values similar to those recorded in the control after ten years. We did not find effects of any soil physico-chemical features on QBS-ar index. Finally, no effect of the experimental treatment was found on the litter decomposition rate, suggesting that a stronger magnitude of soil disturbance is needed to affect this complex biogeochemical process. Although the initial impact was highly significant, it was found that a 10-year period is sufficient for recovering the investigated soil features in the upper soil layer. This was observed in Mediterranean beech forests when forest operations were done with low-weight machines and a limited number of machine passes on the skid trails. Thus, it can be concluded that planning another operation 10–15 years after the previous thinning, as is currently done, remains in line with the time needed for the forest soil to recover.

Exploration of the passivation effect of different types of passivators on cadmium contaminated soil

The problem of excessive cadmium in farmland soil in China is severe, and it is of great significance to explore suitable passivators for specific polluted soils. Three typical and representative commercially available passivators were selected as the test agents, and simulated the natural production process of irrigation and drainage in farmland soil. Through soil cultivation experiments, the remediation effects of different types of passivators and water management on Cd contaminated farmland soil in a certain area of Sichuan were explored. The results showed that the passivator agent 1# based on organic matter reduced the soil pH value, the passivator agent 2# based on alkaline substance and the passivator agent 3# based on clay mineral could increase the soil pH value in different degrees, and the passivator agent 2# was better than the passivator agent 3#. Under flooding condition, soil pH value can be increased. The three passivator agents can increase the content of soil organic matter in different degrees, and the maximum increase rate was 35.2% under 8%. The three passivator agents can reduce the available Cd in different degrees, and the maximum reduction of passivator agents 1#, 2# and 3# was 61.8%, 67.1% and 46.4% respectively. The correlation analysis showed that the flooding state was conducive to the decrease of available Cd. Under the action of passivator agent 1# , the correlation between available Cd and pH was weak, and there was a strong negative correlation between Cd and organic matter (R=0.9922). Under the action of passivator agent 2#, available Cd had a strong negative correlation with pH (R=0.8702) and a weak negative correlation with organic matter (R=0.4041). Under the action of passivator agent 3#, available Cd was strongly negatively correlated with soil pH value and organic matter.

Impact of Soil Management Practices on Soil Culturable Bacteriota and Species Diversity in Central European a Productive Vineyard under Warm and Dry Conditions

Sustainable management practices are crucial for the longevity of a monoculture vineyard, especially in the context of a changing climate. Therefore, soil management practices in a vineyard (T: tillage, T+FYM: tillage + farmyard manure, G: grass strips, G+NPK1: grass strips + rational rates of NPK, and G+NPK2: grass strips + higher rates of NPK) were tested in a temperate climate of Slovakia (Central Europe) under specific soil conditions (Rendzic Leptosol). We investigated the influence of continuous cropping on soil chemical properties and microbial communities during the dry and warm year of 2022. The results showed that the soil pH was higher by 19%, 21%, 24% and 13% in T, T+FYM, G and G+NPK1, respectively, compared to G+NPK2. The lowest soil organic matter (SOM) content was found in T, and it increased in the following order: T < T+FYM < G+NPK2 < G+NPK1 < G. Similarly, the lowest abundance of soil culturable bacteriota was found in T and it increased in the following order: T < T+FYM = G+NPK2 < G+NPK1< G. Culturable bacteriota was identified using mass spectrometry (MALDI-TOF MS Biotyper). The most numerous species group was Bacillus, followed by Lactobacillus > Staphylococcus > Pseudomonas. The most frequently isolated species were Bacillus megaterium (16.55%), Bacillus cereus (5.80%), Bacillus thuringiensis (4.87%), and Bacillus simplex (4.37%). Positive relationships between SOM and soil culturable bacteriota were found in the G and G+NPK1 treatments. Temperature also affected soil culturable bacteriota in all soil management practices, most significantly in G+NPK1. Overall, the best scenario for the sustainable management of a productive vineyard is the use of grass strips.

Relationship between Ecosystem-Services Trade-Offs and Supply–Demand Balance along a Precipitation Gradient: A Case Study in the Central Loess Plateau of China

Although the theory of ecosystem services (ESs) is important for guiding land-use planning, knowledge of ESs trade-offs and supply–demand mechanisms is still lacking, and the characteristics of the correlation between the size of trade-offs and the balance between supply and demand along the precipitation gradient have not yet been clarified. In order to supplement this area of knowledge of ESs, we selected 30 small watersheds in high-, medium- and low-precipitation areas as study units. A biophysical model and socio-economic data were used to calculate supply and demand for carbon sequestration, soil conservation and water yield. Redundancy analysis and regression analysis were used to study the ESs trade-offs, the supply–demand dynamics, and the characteristics of their correlation. The results were as follows. (1) The supply and balance between supply and demand of the three ESs, the trade-off between carbon sequestration and water yield and the trade-off between soil conservation and water yield trended downwards from the high-precipitation area to the medium-precipitation area to the low-precipitation area. (2) The primary factors influencing balance between supply and demand with regard to carbon sequestration in high-, medium- and low-precipitation areas were population density and soil organic-matter content, and the size of the conditional effects were greater than 53%. The dominant factor affecting the balance between supply and demand with regard to soil conservation in the three precipitation areas was slope gradient, and the conditional effect was greater than 40%. The most significant determinants of balance between supply and demand with regard to water yield in the three precipitation areas were grassland area, forest area and precipitation, and the conditional effects were greater than 22%. (3) The most significant determinants of the trade-off between carbon sequestration and water yield in high-, medium- and low-precipitation areas were forest, soil organic-matter content and population density, and the conditional effects were all greater than 45%; the primary factors affecting the trade-off between soil conservation and water yield in high-, medium- and low-precipitation areas were grassland and slope gradient, and the conditional effects were all greater than 24%. (4) The relationship between the balance between supply and demand and trade-off size often followed a quadratic function; the next-most-common relationship was a monotonous nonlinear response, and a linear response relationship was relatively rare. This study revealed the factors influencing balance between supply and demand and trade-offs with regard to ESs and the characteristics of their correlations in areas with different degrees of precipitation, which provided a new idea for the synchronous regulation of ESs in the context of conflicts and supply–demand imbalance.

Effectiveness of Crop Farmers' Use of Indigenous Knowledge on Land Degradation Control Practices in Imo State, Nigeria

This study analyzed the effectiveness of the crop farmers' use of indigenous knowledge on land degradation control practices in Imo State, Nigeria. A multistage sampling procedure was used to select 180 crop farmers for the study. Data were collected using a structured questionnaire and analyzed using mean, percentages, and multiple regression analysis. Crop farmers perceived zero tillage to help in conserving soil texture (x̄=3.52), replanting of deforested areas enables them to maintain vegetative cover (x̄=3.45), use of organic manure to improve soil's organic matter contents (x̄=3.42) and controlling both water and wind erosions by making ridges (x̄=3.30) and rainwater harvesting (x̄=3.10) as highly effective in controlling soil degradation. Age, marital status, educational level, household size, monthly income, membership of association, extension contact and farm size) They significantly influenced their perceived effectiveness of using indigenous knowledge on land degradation control. The major constraints faced by crop farmers were inadequate funds to practice land degradation control practices (99.44%) and limited availability of farmland (98.31%), poor extension contact (86.44%), poor knowledge and education of land degradation control processes (86.44%), poor government support (81.92%) and poor access to information (75.14%). The study concludes that crop farmers experienced soil degradation and were practicing indigenous land degradation, although some factors constrained them. Therefore, crop farmers should come together to transform their indigenous knowledge and control practices, thereby discussing and looking for the best way to tackle their peculiar land degradation challenges.

Enhancing Corn Yield and Soil Quality in Irrigated Semiarid Region with Coal Char and Biochar Amendments

Sustainable use of croplands is facing a challenge to maintain organic carbon (C) in soil. Pyrolyzed coal or coal char (CC) is a porous C material produced from the pyrolysis of coal containing high organic C, large surface area, and low bulk density like biochar (BC). This study evaluates corn (Zea mays L.) grain yield and selected soil properties in soil amended with CC and BC at two rates (22 and 44 Mg ha−1) with farmyard manure (FM) (66 Mg ha−1) and without FM addition. This field experiment was performed in sandy loam soil at the University of Wyoming’s Sustainable Agricultural Research and Extension Center (SAREC), Lingle, WY, USA. Two years of field study results indicated CC and BC applied at 22 Mg ha−1 with FM resulted in significantly greater average corn grain yields (13.04–13.57 Mg ha−1) compared to the no char’s treatment (11.42 Mg ha−1). Soil organic matter (SOM) content was significantly greater in the higher application rates of CC and BC than in treatments without chars. Overall, soil nitrate nitrogen (NO3-N), phosphorous (P), and potassium (K) were found significantly greater in CC and BC co-applied with FM treatments. Soil water-holding capacity (WHC) significantly improved in sandy loam soil (up to 27.6% more than the no-char treatment) at a greater concentration of char materials. This study suggests that char materials applied at a moderate rate (22 Mg ha−1) with FM can improve soil properties and crop yield.

Enhanced seasonality of the East Asian monsoon indicated by prevailing hydroxy-interlayered vermiculite formation since 1.8 Ma

The seasonality of the East Asian monsoon is characterized by the coexistence of warm and humid summers and cold and dry winters. However, the current understanding of when and why the seasonality of the East Asian monsoon occurs is poor. Hydroxy-interlayered vermiculite (HIV), which is formed under conditions of low soil organic matter content, pH values between 4.6 and 5.8, and oxidizing states with frequent wetting‒drying cycles, may serve as a potential indicator of monsoon seasonality variation. In this study, we present detailed mineralogical and micromorphological investigations of HIV collected from an eolian sequence on the Chinese Loess Plateau (CLP) to explore the evolution of East Asian monsoon seasonality. The mineralogical results deduced from X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy show that a transition from chlorite to HIV occurred at ∼1.8 Ma. Moreover, the authigenic origin of HIV, as indicated by the presence of many neatly arranged flakes in the SEM images and the presence of irregularly interstratified chlorite-HIV observed via transmission electron microscopy (TEM), collectively imply that HIV is the weathering product of chlorite. This transition from chlorite to HIV generally reflects an increase in monsoon seasonality on the CLP since ∼1.8 Ma, which may be caused by the contemporaneous uplift of the northeastern Tibetan Plateau, or global cooling in combination with La Niña-like sea-air interactions. Our study suggests that the HIV serves as an effective index for monsoon seasonality reconstruction, thus providing a new insight into Asian monsoon dynamics.

The potential of magnetic biochar prepared by a solvent-free method as a soil amendment: Metal immobilization performance, soil microbial co-occurrence network and community assembly mechanism

Magnetic biochar (MBC) is widely recognized as an effective soil amendment for the immobilization of heavy metals in soils. However, the most commonly used methods currently for manufacturing MBC necessitate the use of iron salt solutions, leading to energy consumption for dehydration and potential environmental risks. Here, we fabricated a magnetic biochar based on the solvent-free method and applied it as a soil passivator at a rate of 5 % (w/w) for 90 days. The metal immobilization performance of MBC was investigated, together with its soil micro-ecological effects including the impacts of MBC application on soil microbial community diversity, composition, co-occurrence network pattern and assembly mechanism. The results showed that MBC treatment significantly decreased the DTPA-extractable Cd and Zn by 54.1 % and 59.5 % (P<0.05) after the 90-day incubation, respectively, higher than that of biochar (BC) treatment (25.6 % for Cd and 50.4 % for Zn). The transformation of Cd, Zn and Pb from labile fractions to residual fraction was facilitated in MBC treatment. Besides, MBC application significantly increased soil pH, soil organic matter content and cation exchange capacity (P<0.05). The addition of MBC considerably altered the soil bacterial community diversity and composition. Both soil environmental variables and bioavailability of metals shaped microbial communities, while the latter explained more. Compared to CK, the complexity and stability of the co-occurrence network in MBC-amended soil were enhanced. Null model analysis implied that the microbial community assembly was governed by the stochastic process in MBC treatment, while the deterministic process was the dominant mechanism initially. Overall, our findings provide insight into the ecological mechanisms and interactions of soil microbial communities in response to MBC application and demonstrate that MBC is a promising amendment for metal-contaminated soil remediation.

Changes in macroaggregate stability as a result of wetting/drying cycles of soils with different organic matter and clay contents

The wetting–drying (WD) cycles, caused by natural or anthropogenic processes such as rainfall or irrigation, can affect many soil properties. Among these properties, soil aggregate stability has been introduced as a convenient soil health indicator because of its relation to the soil’s primary particles (sand, silt, and clay) and organic matter content (OM). However, previous studies have shown erratic effects depending on soil type and WD cycle setup when measuring aggregate stability. Therefore, this study aimed to characterize the soil primary particles composition and organic matter (OM) content of macroaggregates and measure the effects of WD cycles on aggregate stability. A series of soils with distinctive properties, such as OM and clay contents from five different USDA textural classes (loam, sandy loam, silty clay loam, silty loam, and clay loam) were used. Particle size distribution, OM, and mass fraction were measured in three aggregate size classes (2–1 mm, 1–0.5 mm, and 0.5–0.25 mm), and isolated aggregates were exposed to 3, 6, and 12 wetting and drying cycles. The main results indicate that soils with a high OM content have macroaggregates with finer particles, and the OM in soils is linearly related to the macroaggregate OM content. For 2–1 mm aggregates, a statistically significant reduction (p < 0.05) of water-stable aggregates compared to the control sample (0 cycles) was observed for every cycle, with reduction values between 4.8–7.3 %. An increase was observed only between 6–12 cycles (1.84 %). Additionally, statistically significant reductions were observed after the first three cycles in 1–0.5 mm aggregates and the first six in 0.5–0.25 mm aggregates. Finally, the macroaggregates were more resistant to the WD cycles when their clay and OM contents increased or the soil pH decreased. This study provides high-resolution results of macroaggregate particle size distribution and OM. It relates them to the effects of WD cycles in water-stable aggregates and soils with different land uses.

Analyzing Spatial Distribution and Influencing Factors of Soil Organic Matter in Cultivated Land of Northeast China: Implications for Black Soil Protection

Soil organic matter (SOM) in cultivated land is vital for land quality and food security. This study examines SOM distribution and influencing factors in northeastern China, providing insights for sustainable agriculture. Utilizing 10 m resolution SOM data, the analysis covers regions including the Greater and Lesser Khingan Mountains, Liaohe Plain, Sanjiang Plain, Songnen Plain, the northwest semi-arid region, and the low hilly areas of Paektu Mountain. The Geodetector method is employed to assess various influencing factors. The key findings are as follows: (1) The average SOM content in Northeast China (37.70 g/kg) surpasses the national average, is highest in the Greater and Lesser Khingan Mountains (49.32 g/kg), and lowest in the northwest semi-arid region (26.15 g/kg). (2) SOM content is maximized in regions with high altitudes, steep slopes, low temperatures, and moderate precipitation. (3) The annual average temperature is the primary factor influencing SOM distribution, with a combination of temperature and administrative divisions providing better explanatory power. (4) SOM trends vary across protected areas, with slope being critical in semi-humid plains, elevation in arid regions, and no dominant factors identified in the Sanjiang Plain. These findings underscore the need for tailored black soil protection policies to effectively leverage local resources and preserve ecosystem integrity.

Interaction Effects of Vegetation and Soil Factors on Microbial Communities in Alpine Steppe Under Degradation

To clarify the regulating effect of vegetation and soil factors on microbial communities in the alpine steppe under degradation on the Qinghai-Xizang Plateau, the alpine steppe in the Sanjiangyuan area of the Qinghai-Tibet Plateau was chosen. We analyzed the differences in vegetation and soil factors in different stages of degradation （non-degradation, moderate degradation, and severe degradation） and detected the variations in microbial community characteristics in the alpine steppe under different degradation stages using high-throughput sequencing technology. Eventually, redundancy analysis （RDA） and multiple regression matrixes （MRM） based on the similarity or dissimilarity matrix were used to identify key environmental factors regulating microbial （bacterial and fungal） community changes under degradation. The results showed that the degradation of the alpine steppe significantly changed the community coverage, height, biomass, and important value of graminae； significantly reduced the contents of soil organic matter, total nitrogen, total phosphorus, and silt； and increased the soil bulk density and sand content. Degradation did not change the composition of bacteria and fungi, but their composition proportions changed and also resulted in the loss of microbial richness （Chao1 index and Richness index） but did not significantly change the microbial diversity （Shannon index）. With the occurrence of degradation, the vegetation characteristics, soil physicochemical properties, and microbial diversity showed a consistent change trend. Combined with the characteristics of the network topology changes （the number of nodes and clustering coefficient significantly decreased）, it was found that degradation of the alpine steppe led to the decline of interspecies interactions, decentralization of network, and homogenization of microorganisms, but the cooperation relations among the species were maintained （positive correlation connections accounted for more than 90% in all degradation stages）. Under the alpine steppe degradation, the vegetation-soil interaction had the greatest effect on soil bacterial community, whereas soil physicochemical properties had the greatest influence on soil fungal community. Specifically, vegetation community height, biomass, and soil bulk density were the mutual factors regulating soil microorganisms, whereas the vegetation Simpson index, important value of graminae, soil total phosphorus, total potassium, and silt content were the unique factors affecting the soil bacterial community, and soil pH and total nitrogen content were the particular factors affecting the soil fungal community.

Bacterial and fungal communities exhibit contrasting patterns in response to marsh erosion: A fine-scale observation

Coastal salt marshes, especially their seaward boundaries, are experiencing severe erosion and area loss worldwide because of human disturbances and natural changes. However, how marsh erosion affects soil microbial communities and their potential functions remains poorly understood in subtropical coastal ecosystems. Herein, simultaneous measurements of the abundance, diversity, and composition of bacterial and fungal communities were conducted along a marsh erosion gradient, based on Illumina sequencing of 16S rRNA and ITS genes. Our results indicate that marsh erosion is often accompanied by a loss of plant biomass and a decrease in soil total carbon, total nitrogen, and organic matter concentrations, but an increase in soil water content. We found that the abundance of bacteria and fungi tended to decrease with erosion, especially for bacterial communities. Marsh erosion had opposite effects on the alpha-diversity of bacterial and fungal communities, with bacterial diversity decreasing but fungal diversity increasing with marsh erosion. The beta-diversity and composition of bacterial and fungal communities were altered by marsh erosion, and in particular bacterial communities were clustered into three groups: uneroded, eroding, and eroded. Network analysis demonstrated that the inter-relationships of the bacterial community did not significantly change with the erosion gradient, but the complexity of the fungal networks increased. The diversity and composition of the bacterial and fungal communities can be jointly explained by plant biomass, soil nutrient dynamics, and bulk density. We conclude that marsh erosion-induced changes in soil properties and plant loss altered the diversity and composition of bacterial and fungal communities, which decrease bacterial abundance and diversity but increase fungal diversity and network complexity, suggesting that these microbial taxa contribute differently to soil function and nutrient cycling as marsh erosion continues.

Cover crop quality and quantity influences organic corn performance more than soil context

AbstractCover cropping is a common practice among organic growers, well-known for its potential to supply nitrogen (N) to subsequent cash crops. Uncertainties and challenges exist in understanding how cover crops interact with soil properties and management practices across organic farms to supply N, and if such N supply is synchronous with subsequent cash crop N demand. An on-farm study examined cereal rye (Secale cereale) versus crimson clover (Trifolium incarnatum) planted before corn (Zea mays L.) in five organic farms in Michigan with a range of soil properties and management practices. High quality crimson clover residue [Carbon (C):N ratio 15:1] was associated with higher soil inorganic nitrogen, corn chlorophyll content, tissue N content, and grain yields relative to low quality cereal rye residue (C:N ratio 25:1). There were several lines of evidence that low quality cereal rye residue coupled with substantial biomass and a dry season limited N release during peak corn N demand. Nitrogen uptake efficiency (NUE, ratio of total N removed by corn to total N input) was above 1 for corn farms with low soil organic matter (SOM), active N and C pools, and lower than 1 for farms with high SOM and active N and C pools. Overall, cover crop biomass and cover crop quality was a more important driver of corn performance than background SOM content in organic corn farms. Our research highlights the challenges of ensuring sufficient N supply in organic field production, and the importance of planting a legume cover crop before corn.