Subsoil Layers Research Articles

Effect of Plow Pan on the Redistribution Dynamics of Water and Nutrient Transport in Soils

Plow pans are an essential part of the agricultural soil structure. By adjusting the soil bulk density and plow pan height, the water and nutrient transport are dynamically redistributed. Plow pans play a crucial role in promoting crop growth, increasing yields, and supporting sustainable land management. In this study, a column experiment was conducted to investigate the effects of plow pan height (10 cm and 15 cm) and bulk density (1.2, 1.4, and 1.6 g cm⁻3) on soil nutrient and water leaching under high-volume (HV) and low-volume (LV) fertilizer applications. The results reveal that the leachate volume decreased by 61.9% at a plow pan height of 10 cm and by 96.2% at a plow pan height of 15 cm when the bulk density was increased from 1.2 to 1.4 g cm⁻3 under HV conditions. There was no leachate when the plow pan bulk density was 1.6 g cm−3. The reserved concentration of alkali-hydrolyzable N in the plow pan soils was the highest when the plow pan had a bulk density of 1.4 g cm−3 and a height of 15 cm. However, when the plow pan height was 15 cm, the available P content in the plow pan soils decreased by 27.0% and 21.0% at bulk densities of 1.4 g cm⁻3 and 1.6 g cm⁻3, respectively, when compared with 1.2 g cm⁻3. Furthermore, the available P concentrations in the plow pan and subsoil layers decreased with an increase in the plow pan height. The available K concentrations in the topsoil decreased by 26.8% and 24.0% when the plow pan bulk density was increased from 1.2 to 1.4 g cm−3 at heights of 10 and 15 cm, respectively. Thus, the optimal plow pan height and bulk density are closely related to the types of soil nutrients. However, it is clear that excessively high bulk densities (e.g., 1.6 g cm−3) negatively impact soil properties. For different nutrient requirements, a bulk density of 1.2 or 1.4 g cm−3 can be chosen, with each providing suitable options based on the specific nutrient needs. This research offers practical insights into changes in nutrient adsorption and fixation in agricultural production associated with alterations in plow pan bulk density.

Effect of 9-year water and nitrogen additions on microbial necromass carbon content at different soil depths and its main influencing factors

Microbial necromass carbon (MNC) is a major source of soil organic carbon (SOC) pool, significantly influencing soil carbon sequestration. The effects of long-term water and nitrogen addition on MNC in soils at different depths, as well as their interactions, remain poorly understood. In this study, we examined the influence of water addition (+51.67 mm), nitrogen addition (25, 50, 100 kg N ha−1 yr−1), and their interactions on MNC accumulation at different soil depths in temperate grasslands. The addition of water and nitrogen over nine years has been observed to exhibit a decreasing trend in the MNC at different soil depths. Notably, MNC in the topsoil layer (0–10 cm) decreased significantly by 18.56 % under low nitrogen addition treatment, while MNC in the subsoil layer (40–60 cm) declined significantly by 27.19 % under high nitrogen addition treatment. Fungal microbial necromass carbon (FNC) contributed 3.25 times more to SOC than bacterial microbial necromass carbon (BNC). In the 0–10 cm soil layer, MNC is primarily governed by both microbial attributes and the physicochemical properties of the soil, in the 20–40 cm soil layer, the physicochemical properties of the soil predominantly control MNC, in the 40–60 cm layer, microbial characteristics exert a more significant influence on MNC. Collectively, our observations suggest that soil MNC decreased with the addition of water and nitrogen in the 0–60 cm soil slope, which could enable the accurate prediction of global change impacts on the accumulation of soil carbon, thus facilitating the implementation of strategies to augment soil carbon sequestration.

Altitudinal Influences on Soil Microbial Diversity and Community Assembly in Topsoil and Subsoil Layers: Insights from the Jinsha River Basin, Southwest China

Altitudinal Influences on Soil Microbial Diversity and Community Assembly in Topsoil and Subsoil Layers: Insights from the Jinsha River Basin, Southwest China

Significant interaction between root system architecture and stratified phosphorus availability for the initial growth of rice in a flooded soil culture

Phosphorus (P) deficiency is a major limiting factor for rice production in the tropics. The root system architecture (RSA) may play a significant role to capture P efficiently in soils; however, its function is poorly understood in flooded and puddled soil cultures. Two near-isogenic lines (NILs) contrasting RSA—qsor1-NIL (nonfunctional allele of qSOR1; shallow RSA) and Dro1-NIL (functional allele of DRO1; deep RSA)—were repeatedly grown for approximately 6 weeks in pots with three stratified P treatments. The treatments simulated P deficient conditions in puddled and subsoil layers, P available in the puddled layer, and P available in puddled and subsoil layers, that is, −P−P: no P applied in either the top-half (0–14 cm) or bottom-half (14–28 cm) layers; +P−P: P applied only in the top-half layer; and +P + P: P applied in the top-half and bottom-half layers, respectively. A significant interaction was observed between genotype and P treatment. The Dro1-NIL had a greater root surface area in the bottom half layer, which was advantageous for capturing P in the subsoil layer and resulted in greater biomass and P uptake in the +P + P treatment. Contrarily, the qsor1-NIL had a greater root surface area and longer root hair, resulting in greater biomass and P uptake in the −P−P treatment. The mechanism is unclear; however, the pleiotropic effect of qsor1, namely enhancing root hair elongation, might be more advantageous to explore P with minimal carbon costs than elongating nodal and lateral roots when P is not available in deep soil layers. No genotype differences were observed in the +P−P treatment, implying no apparent topsoil P-foraging effect of the shallow RSA in the flooded soil culture. The roles of RSA and root hairs should attract further attention for the genotypic improvement of lowland rice under P deficiency conditions in the tropics.

Influence of phosphate and boron addition to mixed liquid fertilizer on the growth and yield of red chili cultivated in the subsoil layer

This study assesses the impact of adding phosphate and boron in a mixed liquid fertilizer (MLF) on the growth and yield of red chili plants cultivated in a subsoil environment. The experiment was conducted to comprehend how these nutrients affect the performance of red chili plants, particularly when cultivated in less ideal conditions such as subsoil, a remnant of excavation for brick production. The research was carried out at the Ciparanje Garden of the Faculty of Agriculture, Universitas Padjadjaran. The research design employed a Randomized Completely Block Design with the following treatments: A = Control (degraded soil without fertilizer), B = 0% MLF + 1 NPK, C = 0.25% MLF + 1 NPK, D = 0.50% MLF + 1 NPK, E = 0.75% MLF + 1 NPK, F = 1.00% MLF + 1 NPK, G = 0.5% MLF + 3/4 NPK, H = 0.5% MLF + 1/2 NPK, I = 0.5% MLF + 1/4 NPK, J = 0.5% MLF + 0 NPK, and K = 1 NPK in normal soil. The results revealed that the addition of phosphate and boron in MLF significantly influenced the growth and yield of red chili in subsoil conditions. The recommended MLF concentration was 0.75%, alongside the standard NPK dose. These findings provide crucial insights for the development of more efficient and sustainable agricultural practices, especially in challenging soil conditions like subsoil, where nutrient availability can be a determining factor for agricultural success.

Polynomial chaos expansion vs. Monte Carlo simulation in a stochastic analysis of wave propagation

The paper deals with the propagation of a stochastic wave in an elastic medium using the example of a seismic wave in a ground medium. Identification of subsoil parameters is never exact or complete which justifies the use of random field models or random variable models for input data; thus, the response of the subsoil is also random. In this paper and in the context of random variables, the focus is on a sensitivity analysis addressing the question of how the uncertainty of the input data (subgrade parameters) influences the obtained results (displacements). Two different methods of stochastic analysis are presented—the intrusive polynomial chaos approach supported by the Galerkin projection and Monte Carlo simulation—and compared by using an example of wave propagation in the elastic half-plane. Consistency in the results of both approaches has been achieved; however, the calculation efficiencies differ. The advantages and disadvantages of both approaches are discussed. The upper subsoil layer influences the variances of the random solutions much more than does the lower layer.

Accelerated Iron Evolution in Quaternary Red Soils through Anthropogenic Land Use Activities

Iron in soil exists in various valence states and is prone to changes with alterations in soil environmental conditions. Its migration and transformation are crucial for soil formation and understanding soil evolution. This study focuses on Quaternary red soils found in woodland, sparse forest grassland, grassland, and cultivated land located in the semi-humid region of the middle temperate zone. For comparison, buried Quaternary red soil was also examined. A soil reconstruction model was used to quantitatively calculate the variation of different forms of iron in order to analyze various forms of iron composition, migration, and transformation within the soil profile, as well as the evolutionary traits of Quaternary red soils influenced by diverse land use activities. This study found that after exposure and use, iron from the topsoil of buried Quaternary red soil migrated to the subsoil, altering the iron distribution. Free iron and crystalline oxides decreased in the topsoil but increased in specific subsoil layers, with woodland and grassland showing the most significant changes. Silicate-bound iron pooled in the soil weathered to form free iron under different land uses, and poorly crystalline iron oxides transformed into crystalline oxides, with grassland exhibiting the highest transformation intensity. Conversion processes predominated over iron migration in the Quaternary red soils. The evolution of Quaternary red soils can be divided into three stages, marked by changes in iron composition and crystallization due to anthropogenic land use activities. Initially, during 140−94 ka BP, iron composition was stable. Then, between 94–24 ka BP, plant decomposition formed iron–metal complexes, releasing and crystallizing poorly crystalline iron oxides. Finally, from 24 ka BP to the present, anthropogenic activities intensified, increasing the formation and conversion rates of these oxides. This study quantifies iron migration and transformation in Quaternary red soils, providing insights for sustainable soil management, especially in regions where human activities have accelerated iron evolution. Based on these findings, the following policy recommendations are proposed: implement sustainable land use practices, encourage land management strategies that preserve natural vegetation, promote research on soil management techniques, develop and implement regulatory policies, and support educational programs to maintain the health and stability of Quaternary red soils, particularly in regions prone to accelerated iron evolution due to anthropogenic activities.

A PLL-Based Doppler Method Using an SDR-Receiver for Investigation of Seismogenic and Man-Made Disturbances in the Ionosphere

The article describes in detail the equipment and method for measuring the Doppler frequency shift (DFS) on an inclined radio path, based on the principle of the phase-locked loop using an SDR receiver for the investigation of seismogenic and man-made disturbances in the ionosphere. During the two M7.8 earthquakes in Nepal (25 April 2015) and Turkey (6 February 2023), a Doppler ionosonde detected co-seismic and pre-seismic effects in the ionosphere, the appearances of which are connected with the various propagation mechanisms of seismogenic disturbance from the lithosphere up to the ionosphere. One day before the earthquake in Nepal and 90 min prior to the main shock, an increase in the intensity of Doppler bursts was detected, which reflected the disturbance of the ionosphere. A channel of geophysical interaction in the system of lithosphere–atmosphere–ionosphere coupling was traced based on the comprehensive monitoring of the DFS of the ionospheric signal, as well as of the flux of gamma rays in subsoil layers of rocks and in the ground-level atmosphere. The concept of lithosphere–atmosphere–ionosphere coupling, where the key role is assigned to ionization of the atmospheric boundary layer, was confirmed by a retrospective analysis of the DFS records of an ionospheric signal made during underground nuclear explosions at the Semipalatinsk test site. A simple formula for reconstructing the velocity profile of the acoustic pulse from a Dopplerogram was obtained, which depends on only two parameters, one of which is the dimension of length and the other the dimension of time. The reconstructed profiles of the acoustic pulses from the two underground nuclear explosions, which reached the height of the reflection point of the sounding radio wave, are presented.

Microenvironment heterogeneity affected by anthropogenic wildfire-perturbed soil mediates bacterial community in Pinus tabulaeformis forests.

In recent years, the frequency and intensity of anthropogenic wildfires have drastically increased, significantly altering terrestrial ecosystems worldwide. These fires not only devastate vegetative cover but also impact soil environments and microbial communities, affecting ecosystem structure and function. The extent to which fire severity, soil depth, and their interaction influence these effects remains unclear, particularly in Pinus tabulaeformis forests. This study investigated the impact of wildfire intensity and soil stratification on soil physicochemical properties and microbial diversity within P. tabulaeformis forests in North China. Soil samples were collected from different fire severity zones (Control, Light, Moderate, High) and depths (topsoil: 0-10 cm; subsoil: 10-20 cm). Analyses included measurements of soil pH, organic carbon (SOC), total nitrogen (TN), and other nutrients. Microbial diversity was assessed using 16S rRNA gene sequencing. Our findings revealed significant variations in soil pH, SOC, TN, and other nutrients with fire severity and soil depth, profoundly affecting microbial community composition and diversity. Soil pH emerged as a critical determinant, closely linked to microbial α-diversity and community structure. We found that fire severity significantly altered soil pH (p = 0.001), pointing to noteworthy changes in acidity linked to varying severity levels. Topsoil microbial communities primarily differentiated between burned and unburned conditions, whereas subsoil layers showed more pronounced effects of fire severity on microbial structures. Analysis of bacterial phyla across different fire severity levels and soil depths revealed significant shifts in microbial communities. Proteobacteria consistently dominated across all conditions, indicating strong resilience, while Acidobacteriota and Actinobacteriota showed increased abundances in high-severity and light/moderate-severity areas, respectively. Verrucomicrobiota were more prevalent in control samples and decreased significantly in fire-impacted soils. Chloroflexi and Bacteroidota displayed increased abundance in moderate and high-severity areas, respectively. Correlation analyses illustrated significant relationships between soil environmental factors and dominant bacterial phyla. Soil organic carbon (SOC) showed positive correlations with total nitrogen (TN) and alkaline hydrolysable nitrogen (AN). Soil pH exhibited a negative correlation with multiple soil environmental factors. Soil pH and available phosphorus (AP) significantly influenced the abundance of the phylum Myxococcota. Soil water content (WC) significantly affected the abundances of Acidobacteriota and Actinobacteriota. Additionally, ammonium nitrogen (NH4 +-N) and nitrate nitrogen (NO3 --N) jointly and significantly impacted the abundance of the phylum Chloroflexi. This study highlights the significant long-term effects of anthropogenic wildfires on soil microenvironment heterogeneity and bacterial community structure in P. tabulaeformis forests in North China, 6 years post-fire. Our findings demonstrate that fire severity significantly influences soil pH, which in turn affects soil nutrient dynamics and enhances microbial diversity. We observed notable shifts in the abundance of dominant bacterial phyla, emphasizing the critical role of soil pH and nutrient availability in shaping microbial communities. The results underscore the importance of soil stratification, as different soil layers showed varying responses to fire severity, highlighting the need for tailored management strategies. Future research should focus on long-term monitoring to further elucidate the temporal dynamics of soil microbial recovery and nutrient cycling following wildfires. Studies investigating the roles of specific microbial taxa in ecosystem resilience and their functional contributions under varying fire regimes will provide deeper insights. Additionally, exploring soil amendments and management practices aimed at optimizing pH and nutrient availability could enhance post-fire recovery processes, supporting sustainable ecosystem recovery and resilience.

Assessing the impact of early and terminal droughts on root growth, grain yield and yield stability in old and modern wheat cultivars on the Loess Plateau

Understanding changes in root traits of high-yielding genotypes that consistently perform during different drought periods is crucial for improving wheat production and yield stability. A 2-year field trial and a pot experiment were conducted to determine the response of root growth and grain yield to early and terminal droughts in old and modern cultivars (FC3: 1960s and CH1: 2010s) under rainfed and irrigated conditions in the field. Rainfed wheat faced terminal drought in 2015–2016 and early drought in 2016–2017. Plants in the pot experiment were exposed to terminal drought, early drought, and well-watered. Both field and pot experiments showed higher grain yield in modern cultivar CH1 compared to FC3. Early and terminal droughts reduced grain yield in both cultivars, with a greater reduction in FC3. CH1 exhibited higher yield stability under drought conditions and experienced less reduction in early drought. Compared to FC3, CH1 produced more root biomass in the early growth stage. At anthesis, CH1 had significantly lower root biomass and root length density in the topsoil layer (00.2 m) and higher in the subsoil layer (0.21.0 m) than FC3, respectively. At maturity, the retention rate of subsoil root biomass in CH1 was higher, especially under early drought (80.2 % in field and 93.9 % in pot experiments). Both cultivars consumed similar seasonal water use, but CH1 reduced pre-anthesis water use and consumed more water after anthesis. This study indicates that modern cultivar had vigorous root growth at early stage. A higher proportion of root biomass preserved in deep soil after anthesis enhanced post-anthesis water use and photosynthetic rate, improved post-anthesis dry matter accumulation, and thus resulted in higher thousand kernel weight. These factors ensure higher yield and yield stability under both early and terminal drought stress.

Assessment of the migration characteristics and source-oriented health risks of heavy metals in the soil and groundwater of a legacy contaminated by the chlor-alkali industry in central China.

The chlor-alkali industry (CAI) is crucial for global chemical production; however, its operation has led to widespread heavy metal (HM) contamination at numerous sites, which has not been thoroughly investigated. This study analysed 122 soil and groundwater samples from a typical CAI site in Kaifeng, China. Our aim was to assess the ecological and health risks, identify the sources, and examine the migration characteristics of HMs at this site using Monte Carlo simulation, absolute principal component score-multiple linear regression (APCS-MLR), and the potential environmental risk index (Ei). Our findings revealed that the exceedance rates for Cd, Pb, Hg, and Ni were 71.96%, 45.79%, 49.59%, and 65.42%, respectively. Mercury (Hg) displayed the greatest coefficient of variation across all the soil layers, indicating a significant anthropogenic influence. Cd and Hg were identified as having high and extremely high potential environmental risk levels, respectively. The spatial distributions of the improved Nemerow index (INI), total ecological risk (Ri), and HM content varied considerably, with the most contaminated areas typically associated with the storage of raw and auxiliary materials. Surface aggregation and significant vertical transport were noted for HMs; As and Ni showed substantial accumulation in subsoil layers, severely contaminating the groundwater. Self-organizing maps categorized the samples into two different groups, showing strong positive correlations between Cd, Pb, and Hg. The APCS-MLR model suggested that industrial emissions were the main contributors, accounting for 60.3% of the total HM input. Elevated hazard quotient values for Hg posed significant noncarcinogenic risks, whereas acceptable levels of carcinogenic risk were observed for both adults (96.60%) and children (97.83%). This study significantly enhances historical CAI pollution data and offers valuable insights into ongoing environmental and health challenges.

Quantitative importance of subsoil nitrogen cycling processes in Andosols and Cambisols under temperate forests

Nitrogen availability often limits plant growth in forest ecosystems. Plants, including trees, utilize soil inorganic nitrogen transformed via nitrogen cycling processes, including mineralization and nitrification. While most plant fine roots are distributed in surface soil layers, plants take up nitrogen even from subsurface soil layers in addition to the surface soil layers, especially under high nutrient competition. However, there is still limited knowledge about nitrogen cycles within deeper soil layers. In this study, we investigated the vertical profiles (0–60 cm) of the net nitrogen mineralization and nitrification rates at four Japanese forest sites with two different soil types (Andosols and Cambisols). The partial least square path modeling (PLS-PM) was used to determine factors affecting nitrogen cycling processes. The net nitrogen mineralization and nitrification rates per unit soil weight were considerably higher in the surface soil layer than in the deeper soil layers in Andosols but not in Cambisols. PLS-PM analysis showed that microbial biomass and soil organic matter quantities were the important factors influencing the net nitrogen mineralization and nitrification rates, indicating that a similar mechanism, which drives the spatial variations of nitrogen cycling processes in the surface soil layer, predominantly regulates the vertical variations of the processes. Moreover, it was estimated that the net nitrogen mineralization rate could be comparable at all soil types and depths when the rate was expressed per unit soil volume. Therefore, subsoil layers could be a quantitatively important source of plant-available nitrogen in Andosols and Cambisols.

Bacterial functions are main driving factors on paddy soil organic carbon in both surface soil and subsoil

Subsoil contains a significant amount of soil organic carbon (SOC) in rice paddies, playing a crucial role in global carbon (C) cycling. However, the mechanisms driving SOC dynamics in topsoil and subsoil remain elusive, as the vertical distribution of soil microbes and their associated functions varies. In our study, we explored the linkages between SOC dynamics and microbial functions across different soil depths (0–10 cm for topsoil, and 10–20 and 20–30 cm for subsoil) within a framework of contrasting tillage managements, including conventional tillage (CT), reduced tillage (RT), and no-tillage (NT). In the topsoil, bacterial biosynthesis and degradation functions negatively contributed (P < 0.05) to SOC accumulation, whereas in the subsoil layers, these functions exhibited a positive effect. Notably, both partial least squares path modeling (PLSPM) and stepwise regression showed that bacterial biosynthesis and degradation functions exert a stronger influence on SOC accumulation than fungal functions. Metagenomic sequencing revealed that the cellulose degradation (K01179) and reductive tricarboxylic acid cycle (rTCA cycle) (K00174 and K00175) were main factors driving SOC variation in topsoil. Starch degradation (K00705 and K01187) and rTCA cycle (K00175 and K00031) contributed to 93 % of the SOC variation in subsoil. Therefore, the rTCA cycle contributed to SOC variation in paddy soil across 0–30 cm soil profile. Moreover, tillage management could influence the abundances of enzymes associated with starch degradation and rTCA cycle. The contrasting driving factors influencing SOC in topsoil and subsoil could be associated with soil microbial functions, which would response differently to tillage managements.

Aridity threshold for alpine soil nitrogen isotope signature and ecosystem nitrogen cycling.

Determination of tipping points in nitrogen (N) isotope (δ15N) natural abundance, especially soil δ15N, with increasing aridity, is critical for estimating N-cycling dynamics and N limitation in terrestrial ecosystems. However, whether there are linear or nonlinear responses of soil δ15N to increases in aridity and if these responses correspond well with soil N cycling remains largely unknown. In this study, we investigated soil δ15N and soil N-cycling characteristics in both topsoil and subsoil layers along a drought gradient across a 3000-km transect of drylands on the Qinghai-Tibetan Plateau. We found that the effect of increasing aridity on soil δ15N values shifted from negative to positive with thresholds at aridity index (AI) = 0.27 and 0.29 for the topsoil and subsoil, respectively, although soil N pools and N transformation rates linearly decreased with increasing aridity in both soil layers. Furthermore, we identified markedly different correlations between soil δ15N and soil N-cycling traits above and below the AI thresholds (0.27 and 0.29 for topsoil and subsoil, respectively). Specifically, in wetter regions, soil δ15N positively correlated with most soil N-cycling traits, suggesting that high soil δ15N may result from the "openness" of soil N cycling. Conversely, in drier regions, soil δ15N showed insignificant relationships with soil N-cycling traits and correlated well with factors, such as soil-available phosphorus and foliage δ15N, demonstrating that pathways other than typical soil N cycling may dominate soil δ15N under drier conditions. Overall, these results highlight that different ecosystem N-cycling processes may drive soil δ15N along the aridity gradient, broadening our understanding of N cycling as indicated by soil δ15N under changing drought regimes. The aridity threshold of soil δ15N should be considered in terrestrial N-cycling models when incorporating 15N isotope signals to predict N cycling and availability under climatic dryness.

The effects of elevated CO2 and temperature on soil organic carbon and total nitrogen contents and mineralization in the 0 to 50 cm paddy soil layer were masked by different land use history

Global warming can accelerate soil organic matter (SOM) decomposition resulting in faster carbon (C) loss and positive climate-C feedback. Previous studies on response of SOM decomposition to climate change mainly focus on plow soil layer. However, the effects of elevated CO2 and soil warming on soil organic carbon (SOC) and total nitrogen (TN) contents and mineralization are rarely studied in subsoil layer. In this study, soil samples were collected from the 0–50-cm paddy soil layer of the Tsukuba free-air CO2 enrichment experimental site with elevated CO2 (+200 ppm) and soil warming (+2 °C), Japan, after 5-year rice growth season. The amounts of SOC, TN, δ13C, and δ15N were analyzed. A 4-week anaerobic incubation experiment was conducted to measure C decomposition and N mineralization potentials. Due to the intrinsic variation in SOC and TN contents in soil layers and fields, the effects of elevated CO2 and soil warming on C decomposition and N mineralization potentials could not be determined here. However, the effect of elevated CO2 on δ13C was only found in 0‒10-cm soil layer. In the 0–50-cm soil profiles, significant correlations were observed among SOC and TN, δ13C and δ15N, decomposed C and mineralized N, and δ13C of decomposed C. The variables associated with soil C and N pools, and dynamics showed large spatial heterogeneity within paddy field, due to variation in the original land use history. Therefore, great caution should be exercised when evaluating the effects of elevated CO2 and temperature on SOM decomposition and sequestration in paddy soil profiles.

Long-term cotton stubble return and subsoiling improve soil organic carbon by changing the stability and organic carbon of soil aggregates in coastal saline fields

Cotton stubble return and subsoiling significantly enhanced soil fertility and cotton yield in coastal saline soils. Despite these benefits, the mechanisms influencing soil organic carbon (SOC) sequestration remain poorly understood. To address this gap, a comprehensive ten-year study was undertaken, focusing on the effects of stubble management (either removal or return) and tillage (either non-subsoiling or subsoiling) on the physicochemical properties of both topsoil (0–20 cm) and subsoil (20–40 cm) layers, as well as on cotton yield. The objectives were to (i) quantify interannual variability (2013–2022), stubble return, and subsoiling on the soil physicochemical properties of the topsoil (0–20 cm) and subsoil (20–40 cm) and cotton yield and (ii) elucidate the mechanism by which these agricultural practices affect SOC sequestration. Findings from this decade-long investigation indicated that ten consecutive years of cotton stubble return and subsoiling at three-year intervals significantly ameliorated soil conditions by reducing the salt content, pH, and the proportion of silt plus clay, while increasing macro-aggregates, mean weight diameter (MWD), aggregates organic carbon (AOC) across various particle sizes, SOC, total nitrogen (TN) in both soil layers, and ultimately, the cotton lint yield. Interestingly, the effect of stubble return on micro-aggregates varied between the two soil layers, leading to a reduction in micro-aggregates by 11.16% in the topsoil, in contrast to a 5.7% increase in the subsoil, when compared to conditions where stubble was removed. The partial least squares path modeling (PLS-PM) indicated that the enhancements in MWD attributable to stubble return and subsoiling were primarily due to significant reductions in soil pH and salt content in both layers, which in turn fostered an increase in AOC, ultimately contributing to higher SOC levels. However, the pathways through which AOC influenced SOC varied significantly between the topsoil and subsoil, with stubble return and subsoiling increasing SOC through an increase in the macro-AOC in the topsoil, and micro-AOC in the subsoil. In summary, long-term cotton stubble return and subsoiling significantly optimize the aggregate particle size distribution and enhance the carbon sequestration potential in coastal saline cotton fields.

Long-Term Effect of Rice and Non-rice Ecology on Pools of Carbon in Surface and Deep Soil in Farmer’s Field

The greatest terrestrial sink of carbon (C) is soil. In addition to improving soil quality, carbon absorption in soil helps reduce atmospheric CO2 loading. Not only the surface soil, but also the deep sub-soil act as a storehouse of C. Besides, the study of C dynamics in tropical rice soil is important in countries like India where rice is the predominant crop and soil C sequestration is at risk due to high temperatures. In this context, this study tried to understand the C dynamics in surface as well as deep soil under rice and non-rice ecology. Representative soil samples were collected from five sites of rice-rice (rice ecology) and vegetable-vegetable (non-rice ecology) cropping systems from three depths viz., 0-20 cm, 100-120 and 120-140 cm from long-term farmer’s field of Nadia district of West Bengal belonging to Alfisols to compare C dynamics of surface and deep soils as well as rice and non-rice ecology. Results indicated that surface soils exhibited higher amount of total C, total organic C and inorganic C in comparison to deep soil irrespective of crop ecologies. The rice ecology showed higher total C and total organic C in comparison to non-rice soil. As per water solubility, water-soluble (room temperature) C and hot water-soluble C which were highest in surface soil compared to deep soil as the former usually receives maximum amount of fresh C input compared to deep soil. Irrespective of crop ecology, water-soluble C (WSC), hot water-soluble C (HWC), recalcitrant C (RC) were highest in surface soil compared to deep soils. Again, irrespective of soil depth, WSC and RC were highest in rice ecology and lowest in non-rice ecology. But, HWC content was highest in non-rice ecology and lowest in rice ecology. Irrespective of crop ecology, per cent contribution of labile pool of C (WSC+ HWC) and that of RC pool towards TOC was the highest and the lowest respectively. However, irrespective of soil depth, per cent contribution of labile pool of C and that of recalcitrant pool of C towards TOC was highest and lowest in soils under non-rice ecology and rice ecology respectively. Thus, this study conclusively indicated the potential of subsoil layer to act as a C sink in comparison to surface soil. The rice soil also has been identified as a niche for soil C sequestration.

Soil Properties Variation Valued in Relation to Land Use and Management Practices in Vietnam

Background: Land use and management practices (LUMPs) have been accelerated globally to serve the increasing socio-economic requirements in recent decades. Methods: This study focuses to assess the impacts of the LUMPs on the properties and composition of soil in the Lam River Basin (LRB), Vietnam based on analysis of ninety-six soil samples collected in the soil profiles (0_60 cm). Result: The results indicated that the sand and clay ratios (34.0~35.7% and 16.2~19.9%) and bulk density (BD) (1.07±0.05~1.34 ± 0.06 Mg m-3) in the natural forest lands (NFLs) were lower and higher perturbed than the plantation forest lands (PFLs) (31.1~ 51.5%, 5.7~38.2% and 0.86 ± 0.03~1.12±0.05 Mg m-3) in the 0-20 cm topsoil layer. The soil texture is mainly sandy clay to clay loam and the BD tends slightly increase in the topsoil layer, then decrease in the 20-60 cm subsoil layer. There is no difference in soil pH between collected soil samples (CSSs) and tends to increase with increasing the subsoil layer. The base cations (BCs) (Ca2+, K+, Mg2+: 0.01~0.29, 0.06~0.11 and 0.06~0.07 Cmolc kg-1) and total organic contents (TOCs) (total carbon (TC), total nitrogen (TN), total phosphorus (TP): 24.11; 2.80 and 0.19 g kg-1) of the NFLs are higher than those of the CSSs (TC, TN, TP: 14.37~23.91, 1.62~2.28 and 0.08~0.17 g kg-1) in the topsoil layer while these values were not different in the topsoil layer.

Biogeochemistry of dissolved organic matter and inorganic solutes in soil profiles of tropical pasturelands

Tropical soils play a critical role in the global biogeochemical cycles and are essential for maintaining the Earth's carbon balance. Understanding the dynamics of dissolved organic matter (DOM) is paramount due to its implications for ecosystem functioning and nutrient cycling. This study comprehensively evaluated the origin, distribution, and composition of DOM and inorganic solutes in Brazilian tropical agricultural soils. Multiple analytical techniques were utilized to assess DOM from soil profiles (0–100 cm depth) across a spectrum of land uses, including a native Atlantic Forest, a degraded pasture, as well as intensive grazing, extensive grazing, and silvopastoral systems. Inorganic elements were quantified to assess the coupling between the organic and inorganic biogeochemical cycles. The dominance of C4 carbon in topsoil layers suggested substantial contributions of organic matter from grasses to the soil organic matter pool. However, with increased depth, C3 carbon inputs became more prominent, indicating the influence of forest vegetation that existed prior to the implementation of agricultural managements. DOM concentrations decreased with soil depth due to reduced carbon inputs, sorption to minerals, or oxidation. DOM composition did not show significant changes among different land use and managements. Lignin was identified as the primary contributor to oxidized DOM with increasing soil depth. The composition of DOM exhibited a shift from more aromatic and higher molecular weight compounds in topsoil layers to smaller, more aliphatic compounds in subsoil layers. Our key findings revealed that aliphatic compounds, particularly fatty acids, tend to accumulate in deeper soil layers. This phenomenon was consistent in pastures dominated by grasses but not in soils near treed vegetation. Overseeding (from C3 plants) did not significantly impact DOM compositions, emphasizing the persistence of C4 plants in these systems. The presence of inorganic elements in soil water extracts showed minimal impact on DOM dynamics, suggesting decoupled organic and inorganic biogeochemical cycles in tropical pasturelands.

Priming of Soil Organic Carbon Decomposition Induced by Exogenous Organic Carbon Input Depends on Vegetation and Soil Depth in Coastal Salt Marshes

The input of fresh organic carbon into soils can stimulate organic carbon mineralization via priming effects (PEs). However, little is known about the characterization of PEs in coastal wetlands. We investigated the PEs of two salt marshes (Suaeda salsa and Phragmites australis) in the Yellow River Delta by adding 13C-labeled glucose to soils collected from the 0–10 cm and 20–30 cm layers of both salt marshes. The addition of glucose produced a significant positive PE in both soil layers for both vegetation types. There were no differences in the PE of the topsoil layer between the two vegetation types (p &gt; 0.05), whereas the PE of S. salsa was 19.5% higher than that of P. australis in the subsoil layer (p &lt; 0.05). In addition, the topsoil layer showed a higher average PE of 29.1% compared to that of the subsoil layer for both vegetation types (p &lt; 0.05). The differences in the PEs between the two vegetation types and the two layers could be associated with a differential soil salinity, substrate availability, and microbial community structure. Our findings highlight the important role of PEs in regulating the soil carbon storage of coastal salt marshes, which should be considered when assessing and modeling the soil carbon cycling of coastal wetlands.