Subsoil Layers Research Articles

Numerical investigations on evolution mechanism of contact erosion in layered soils considering particle-scale parameters

Internal erosion is one of the leading causes of failures in transportation infrastructures including bridges and road embankments. For layered subsoil conditions, contact erosion may occur if the gradation of soil in different layers is not properly selected, and is controlled by the speed of inflowing water and the particle sizes. This phenomenon is difficult to observe on-site or in the laboratory and the underlying mechanism still needs to be clarified as it occurs inside the subsoil layer. This paper presents a particle-scale study that utilizes physical tests and representative volume CFD-DEM simulations to explore the contact erosion process at the interface between soil layers consisting of coarse-grained and fine-grained particles. It is first calibrated and validated by comparing the simulation results with experimental observations. Then the influences of contributing factors on contact erosion initiation and progression from the view of particle scales are analyzed. The results show that particle size ratio is a significant factor that determines the occurrence and development of contact erosion. The specific gravity of particles affects their erosion resistance, while the effect of particle friction is not obvious since the transport of fine non-cohesive particles does not involve significant particle sliding. Particle shape has a major influence on the contact erosion process. Meanwhile, the critical inflow velocity and particle size ratio for contact erosion occurrence can be determined via the coupled model presented in this study.

Vertical dynamic interaction and group efficiency factor for floating pile group in layered soil

AbstractThis paper theoretically estimates the dynamic pile–soil interaction and the group efficiency factor for pile group in layered soil through energy‐based method. The vertical dynamic interaction of partially embedded single piles and their surrounding layered soil is analytically deduced from Hamilton's principle. Combined with a series of numerical simulations, the soil attenuation factor from energy method is modified for adapting to the wave speed variation in various layers. Then, the pile‐to‐pile interaction factor is directly solved with the help of the transfer‐matrix method. The dynamic governing equation of pile group with an elevated rigid cap is established by superposing the pile‐to‐pile interaction factors. Finally, the dynamic impedance of pile group is obtained and derived into a group efficiency factor. Compared with the plane strain method, this present method can produce a more suitable soil attenuation factor and a dynamic interaction factor at low frequency range, which is exploited for practical engineering design. The effects of subsoil layer, subsoil layer, and unembedded pile segment on group efficiency factor are investigated. The results show that the real part of group efficiency factor decreases at high frequency range for a small pile spacing, which may be detriment to the pile group capacity. Besides that, the combined effects of unembedded segment and weak surface soil on group efficiency factor are highlighted.

Effects of reclamation duration on soil nutrients and enzyme activities in the plough layer and subsoil of riparian floodplains

Croplands reclaimed from floodplain wetlands play an important role in food production. As reclamation continues, various agronomic measures affect soil nutrient contents and metabolism. In the lower reaches of the Yellow River, we selected croplands (wheat and maize double-cropped system) reclaimed for 13, 24, and 33 years from natural wetlands (as the control), with similar starting soil characteristics and management practices. We determined total nitrogen (TN) and phosphorus (TP) contents and enzyme activities (including invertase, dehydrogenase, β-glucosidase, urease, protease, acid phosphatase, and alkaline phosphatase) in 0–100 cm soil profile. As results, TN and TP contents increased following reclamation, particularly in the plough layer (0–20 cm) with a clear increase during the chronosequence. The subsoil (20–100 cm) accounted for 55.3–63.9% and 66.6–68.0% of the N and P stocks in croplands, respectively. The TN content was positively correlated with the silt proportion in the 100-cm profile, whereas TP content was positively correlated with the clay proportion in the plough layer, and negatively with pH in the subsoil. Nevertheless, the C: N and C: P ratios in the plough layer were higher in the croplands than in the natural wetlands, and the N: P ratio increased from 0.4 to 2.6 following reclamation. Activities of most enzymes in the plough layer increased along with the chronosequence, and the subsoil generally had higher enzyme activity after 33 years of reclamation than in the natural wetlands. Redundancy analysis revealed that TN content and N: P ratio had strong explanatory power for the enzyme activities in the plough and subsoil layers, respectively. These findings suggest reclamation increases soil nutrient contents and enzyme activities in the floodplains, and the subsoil plays an essential role. However, these croplands remain N deficient. Thus, applying N fertilizer, as well as planting deep-rooted and N2-fixing crops, should be considered for agricultural management.

Diversified crop rotations and organic amendments as strategies for increasing soil carbon storage and stabilisation in UK arable systems

Adaptations in crop rotation with the inclusion of temporary grass-clover leys and organic amendments, have been promoted as effective ways to improve soil carbon (C) sequestration and mitigate climate change in agricultural systems. However, there are still a lot of uncertainties related to i) the combined effects of different crop rotations and different fertilisation sources, e.g., organic amendments, on soil C stocks; and ii) their potential effect on C stabilisation. The objective of this study was to evaluate the effect of different arable crop rotations with varying degrees of diversity in crop type and lengths of grass-clover ley periods and fertilisation sources on soil C stocks and C stabilisation down to 0.60 m soil depth. This was investigated in a long-term factorial field experiment-combining different crop rotation (cereal-intensive conventional vs. diversified legume-intensive organic) with different lengths of grass-clover ley periods (2 vs. 3 years), fertilisation sources (mineral vs. compost), and years (samples taken at the beginning and at the last year of one complete cycle of rotation; 8 years apart)-to explore their individual and interactive effect on soil C stock and C stabilisation at two soil depths (0–0.30 and 0.30–0.60 m). Soil C stabilisation was assessed using a unique combination of three different techniques: physical fractionation for separation of C associated to organic and mineral fractions, thermal analysis combined with differential scanning calorimetry and a quadrupole mass spectrometry (TG-DSC-QMS) for physical-chemical aspects, and pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC/MS) for molecular structural information. The findings showed higher soil C stocks under the diversified organic rotation with 3 years of grass-clover ley period at both soil depths, regardless of the fertilisation source or sampling year. However, the organic rotation seemed to deliver stable soil C stocks only in the subsoil layer. Compost fertilisation, in turn, increased topsoil C stocks between the two sample dates under both rotations, and it appears to be stable. These results suggested that combining a diversified organic rotation with 3 years grass-clover ley with compost fertilisation could be one way for agricultural systems to deliver stable soil C sequestration.

Soil depth and geographic distance modulate bacterial β-diversity in deep soil profiles throughout the U.S. Corn Belt.

Understanding how microbial communities are shaped across spatial dimensions is of fundamental importance in microbial ecology. However, most studies on soil biogeography have focused on the topsoil microbiome, while the factors driving the subsoil microbiome distribution are largely unknown. Here we used 16S rRNA amplicon sequencing to analyse the factors underlying the bacterial β-diversity along vertical (0-240 cm of soil depth) and horizontal spatial dimensions (~500,000 km2 ) in the U.S. Corn Belt. With these data we tested whether the horizontal or vertical spatial variation had stronger impacts on the taxonomic (Bray-Curtis) and phylogenetic (weighted Unifrac) β-diversity. Additionally, we assessed whether the distance-decay (horizontal dimension) was greater in the topsoil (0-30 cm) or subsoil (in each 30 cm layer from 30-240 cm) using Mantel tests. The influence of geographic distance versus edaphic variables on the bacterial communities from the different soil layers was also compared. Results indicated that the phylogenetic β-diversity was impacted more by soil depth, while the taxonomic β-diversity changed more between geographic locations. The distance-decay was lower in the topsoil than in all subsoil layers analysed. Moreover, some subsoil layers were influenced more by geographic distance than any edaphic variable, including pH. Although different factors affected the topsoil and subsoil biogeography, niche-based models explained the community assembly of all soil layers. This comprehensive study contributed to elucidating important aspects of soil bacterial biogeography including the major impact of soil depth on the phylogenetic β-diversity, and the greater influence of geographic distance on subsoil than on topsoil bacterial communities in agroecosystems.

Effects of the construction of fertile and cultivated soil layer on soil fertility and maize yield in Albic soil.

We examined the effects of fertile soil layer construction technology on soil fertility and maize yield with a 3-year field experiment in Albic soil in Fujin, Heilongjiang Province. There were five treatments, including conventional tillage (T15, without organic matter return) and fertile soil layer construction methods [deep tillage (0-35 cm) with straw return, T35+S; deep tillage with organic manure, T35+M; deep tillage with straw and organic manure return, T35+S+M; deep tillage with straw, organic manure return and chemical fertilizer, T35+S+M+F]. The results showed that: 1) compared with the T15 treatment, maize yield was significantly increased by 15.4%-50.9% under fertile layer construction treatments. 2) There was no significant difference of soil pH among all treatments in the first two years, but fertile soil layer construction treatments significantly increased soil pH of topsoil (0-15 cm soil layer) in the third year. The pH of subsoil (15-35 cm soil layer) significantly increased under T35+S+M+F, T35+S+M, and T35+M treatments, while no significant difference was observed for T35+S treatment, compared with T15 treatment. 3) The fertile soil layer construction treatments could improve the nutrient contents of the topsoil and subsoil layer, especially in the subsoil layer, with the contents of organic matter, total nitrogen, available phosphorus, alkali-hydrolyzed nitrogen and available potassium being increased by 3.2%-46.6%, 9.1%-51.8%, 17.5%-130.1%, 4.4%-62.8%, 22.2%-68.7% under the subsoil layer, respectively. The fertility richness indices were increased in the subsoil layer, and nutrient contents of the subsoil layer were close to those of topsoil layer, indicating that 0-35 cm fertile soil layer had been constructed. 4) Soil organic matter contents in the 0-35 cm layer were increased by 8.8%-23.2% and 13.2%-30.1% in the second and third years of fertile soil layer construction, respectively. Soil organic carbon storage was also gradually increased under fertile soil layer construction treatments. 5) The carbon conversion rate of organic matter was 9.3%-20.9% under T35+S treatment, and 10.6%-24.6% under T35+M, T35+S+M, and T35+S+M+F treatments. The carbon sequestration rate was 815.7-3066.4 kg·hm-2·a-1 in fertile soil layer construction treatments. The carbon sequestration rate of T35+S treatment increased with experimental periods, and soil carbon content under T35+M, T35+S+M and T35+S+M+F treatments reached saturation point in the experimental second year. Construction of fertile soil layers could improve the fertility of topsoil and subsoil and maize yield. In term of economic benefits, combination application of maize straw, organic material and chemical fertilizer within 0-35 cm soil, cooperating with conservation tillage, is recommended for the Albic soil fertility improvement.

Soil microbial necromass regulation of long-term fertilizer N retention influenced by maize stover mulching

Microbial immobilization of nitrogen (N) fertilizer is critical for N retention in soils and is mainly influenced by agricultural management, including crop residue return. However, the underlying relationship between microbially mediated processes and long-term fertilizer N dynamics has not been characterized well in arable soil. Here, by tracing in situ the temporal changes of soil amino sugars initially synthesized from the 15N fertilizer applied in the 1st year, we investigated the dynamic contribution of microbial necromass to long-term fertilizer N retention in soil influenced by maize stove mulching. After the 1st year of fertilizer application, microbial necromass contributed to 36.3–43.9 % of the remaining fertilizer N in the topsoil (0–10 cm), but the remaining fertilizer N in the subsoil (10–20 cm) was predominantly attributed to microbial necromass accumulation, regardless of maize stover mulching. During the following 9 years, the fertilizer-derived microbial necromass N decreased at a slower rate (42.3–52.8 %) than the remaining fertilizer N (73.5–76.7 %) in the topsoil layer, while the former decreased synchronously with the latter in the subsoil layer, indicating that microbial necromass played a critical role in long-term fertilizer N stabilization though it could serve as a transitional N pool for N supply. For the microbial necromass of different origin, the residence time of fertilizer N in fungal necromass (34.7–48.7 y) was longer than that in the bacterial necromass pool (21.4–27.1 y) in the cultivated soil layer (0–20 cm), explicitly indicating that the retention of fungal necromass was inclined to contribute to long-term fertilizer N stabilization while bacterial necromass was associated with fertilizer N turnover. Compared with fertilizer application alone, maize stover mulching enhanced the initial fertilizer N retention by increasing microbial necromass accumulation but had no influence on the subsequent dynamics of both the remaining fertilizer N and fertilizer-derived microbial necromass N, thus improving long-term fertilizer N retention. Specifically, maize stover mulching increased the stability of microbial necromass N by enhancing the retention and prolonging the residence time of fungal necromass over bacterial necromass, thus improving the contribution of microbial necromass to the long-term stabilization of fertilizer N in the cultivated soil.

Soil texture and microorganisms dominantly determine the subsoil carbonate content in the permafrost-affected area of the Tibetan Plateau.

Under climate warming conditions, storage and conversion of soil inorganic carbon (SIC) play an important role in regulating soil carbon (C) dynamics and atmospheric CO2 content in arid and semi-arid areas. Carbonate formation in alkaline soil can fix a large amount of C in the form of inorganic C, resulting in soil C sink and potentially slowing global warming trends. Therefore, understanding the driving factors affecting carbonate mineral formation can help better predict future climate change. Till date, most studies have focused on abiotic drivers (climate and soil), whereas a few examined the effects of biotic drivers on carbonate formation and SIC stock. In this study, SIC, calcite content, and soil microbial communities were analyzed in three soil layers (0-5 cm, 20-30 cm, and 50-60 cm) on the Beiluhe Basin of Tibetan Plateau. Results revealed that in arid and semi-arid areas, SIC and soil calcite content did not exhibit significant differences among the three soil layers; however, the main factors affecting the calcite content in different soil layers are different. In the topsoil (0-5 cm), the most important predictor of calcite content was soil water content. In the subsoil layers 20-30 cm and 50-60 cm, the ratio of bacterial biomass to fungal biomass (B/F) and soil silt content, respectively, had larger contributions to the variation of calcite content than the other factors. Plagioclase provided a site for microbial colonization, whereas Ca2+ contributed in bacteria-mediated calcite formation. This study aims to highlight the importance of soil microorganisms in managing soil calcite content and reveals preliminary results on bacteria-mediated conversion of organic to inorganic C.

Combining Rock-Eval® thermal analysis and thermochemolysis to evaluate the influence of forest management on soil organic matter quality and stability

The effect of forest management practices on carbon quality is poorly documented. To assess changes in the quality and stability of soil organic carbon (SOC) of a temperate forest upon human activities, we investigated soil from forests (i) developed following natural regeneration after clearcutting 20 and 40 years ago, (ii) developed following afforestation on an abandoned crop area 40 years ago and (iii) in an area where regular clear-cut (with wood residues input) was conducted 40 years ago. Topsoil and subsoil layers were collected (0–20 cm and 50–80 cm). Soil organic matter (OM) was characterized by elemental analysis (total carbon and total nitrogen), thermal analysis (Rock-Eval®) and thermochemolysis (i.e., Py-GC/MS in the presence of tetramethylammonium hydroxide (TMAH)). In addition, a size fractionation to separate the labile coarse fraction (50–2000 μm) from the fine fraction (<50 µm) was performed. These fractions were analyzed by thermal analysis.Despite no measurable differences in carbon and nitrogen contents, the characterization of the OM by thermal analysis, and the relative quantification of OM compounds revealed differences in the composition in OM for the topsoil layers. The thermal analysis clearly distinguished sites with inputs of woody residues (higher HI) with a higher relative contribution of lignin and cutin/suberin compounds. However, the OM thermal stability seems mainly controlled by the organo-mineral interactions rather than chemical composition. Combination of Rock-Eval® thermal analysis and Py-GC/MS suggests that thermal stability cannot be used as an indicator of stability in specific contexts where pedogenetic processes are deeply modified by regular and extensive anthropogenic inputs of woody residues.

Assessment of zones prone to sinkhole using ground penetrating radar and soil properties in Central Iran

Land subsidence and sinkhole, natural and anthropogenic events, occur globally especially in arid and semi-arid regions. The major problem of this phenomenon is over exploitation of ground water. Identification of important factors in the soils as soil properties were prone to sinkholes detection of subsurface holes as soil texture essentially. For detecting subsurface layers were used Ground Penetrating Radar (GPR) in the study area. The study area is Abarkooh alluvial plain of about 250 km2 is part of the Eghlid-Abarkooh watershed. For assessment potential zones prone to sinkhole, eight routs were determined in two different regions for the measurement of GPR and soil chemical, physical and mechanical properties. In GPR sections around the sinkholes, there were some breaks in subsoil layers and found subsurface cavities and on the side of the mountain slopes, the subsoil layers were uniform and there was no sign of breaks in subsoil layers and cavities. Regarding soil characteristics, soil texture near sinkholes was silt loam, sandy loam and loamy sand and on the side of mountain slope was Skeletal sandy loam, Skeletal loamy sand and Skeletal sand because of the existence of gravel on the slopes of the mountain. For evaluating soil parameters in two selected regions, some differences were observed such as Ca2+/Mg2+ in lime, COLE and Atterberg limits. Mg2+ in lime is more than to Ca2+ near sinkholes and the limes of the soils were dolomitic type and unstable. The amount of COLE and Atterberg limits as divergence index were high near sinkholes but on the side of mountain slopes were low. An increase in Mg2+ in lime, COLE and Atterberg limits near sinkholes proved the activity of clays and their movement underground and the GPR results confirmed the clay activity as breaks in stratigraphy traces to depth of 5 m and these soils are prone to sinkhole phenomenon. It has been concluded that GPR and Soil properties is the best way to determine areas that prone to sinkhole and also to detect the safe area for construction and contracting works. It is suggested that land conservation be introduced as the best alternative near sinkholes and redrawing the plan of urban development, construction of electric tower and railway from lowlands to the piedmonts as detected the safe area.

Characterization and classification of rice-growing soils on Imo clay shale residua in Eastern Nigeria and current suitability for rice production: I. Omasi-Agu and Omor agrarian communities

The soils on Imo clay shale residua at Omasi-Agu and Omor areas in Anambra State, Nigeria were sampled in order to characterize classify and evaluate their current suitability for rice production following standard scientific procedures. The soils generally belong to loamy textural classes or finer, especially in the subsoil layers. The morphological and physical properties of soils showed that the soils were poorly drained favouring high water retentivity due to low hydraulic conductivity and slow permeability. All these soil conditions support good rice performance. Though the soils at Omasi-Agu contained high levels of exchangeable bases, exchangeable acidity was equally high leading to low base saturation of &lt; 35% but at Omor the base saturation was &gt; 35%. Thus, the soils were, respectively, classified as Typic Kandiaquults (Soil Taxonomy) correlated with Gleyic Cambisols of the World Reference Base for Soil Resources (WRBSR) and Typic Kandiaqualfs (Soil Taxonomy) correlated with Gleyic Cambisols (WRBSR). Even though the soils of Omor appeared to be generally more fertile than Omasi-Agu soils, both have similar constraints to rice production, that is, insufficiency of nutrients (f) and possibility of erosion by flooding (e) in limited areas (&lt; 25%). Therefore, the current suitability of the soils for rice production is suitability class 2 with fertility constraints (S2fe). For sustainable rice production, supplementary addition of nutrients especially P2O5 from triple superphosphate and some minor levelling and bunding are required to control erosion due to flooding in the limited areas.

Characterization and classification of rice-growing soils on Imo clay shale residua in Eastern Nigeria and current suitability for rice production: II. Anaku and Igbariam communities.

The soils on Imo Clay Shale residua were sampled at Anaku and Igbariam in Anambra state, Nigeria to characterize, classify and evaluate their current suitability for rice production following standard scientific procedures. After several auger borings, modal profiles were sited, dug, described, and sampled. The soils generally belong to loamy textural classes or finer, especially in the subsoil layers. The morphological and physical properties of soils showed that the soils were poorly drained, favouring high water retention due to low hydraulic conductivity and slow permeability. All these conditions favour good rice performance. Though the soils contained high levels of exchangeable bases, exchangeable acidity was equally high leading to low base saturation (&lt; 35%). Thus, the soils were classified as Typic Kanhaplaquults (Soil Taxonomy) and correlated to Gleyic Cambisols (World Reference Base for Soil Resources). Due to fertility inadequacies, the current suit- ability unit of the soils for rice production is suitability class 2 with fertility constraints (S2f). This implies that for sustainable rice production supplementary nutrients especially P2O5 from triple superphosphate or rock phosphate need to be applied. Based on the soil chemical results the following recommendations were made for optimum rice production: 100.00-120.00 kg ha‒1 urea, 60.00 kg ha‒1 P2O5 from triple superphosphate and 15.00 kg ha‒1 K2O (muriate of potash).

The Effect of Tillage Method on the Nutrient Regime of Soil during the Growing of Trifolium pratense

Abstract The article presents the results of studying the influence of tillage methods on the number of bacteria and fungi in the arable soil layer, nutrient indicators, and, consequently, the yield of Trifolium pratense. The purpose of the study is to determine how tillage affects the feeding regime and yield of Trifolium pratense. The research was conducted at the experimental field of the Educational and Scientific Research Center of Lviv National Environmental University. For the study of microorganisms in the arocenosis of meadow clover, soil samples were taken using a cylindrical drill from arable (0–20 cm) and sub-soil (20–40 cm) layers with an average weight of an individual sample of 300 g. For microbiological analysis, average samples from five individual samples were prepared. The isolation of the main agronomically useful groups of microorganisms from the soil was carried out by the method of microbiological sowing of soil extracts on solid nutrient media: for fungi – wort-agar, for bacteria – meat-peptone agar (MPA). The dilution of the soil extract for fungi and bacteria was, respectively, 1 : 1000; 1 : 100000. Microbiological seeding was performed in triplicate. The calculation of the total number of microorganisms in the soil was carried out by Tepper´s method. The yield of crops and the results of laboratory studies were processed by the method of variance analysis. The application of a tiered tillage allowed to increase the yield of Trifolium pratense green mass by 4.5 t·ha−1 (+17.0%) compared to the control (conventional plowing). It is established that tier ploughing with the PYA-4-40 plough promotes uniform distribution of nutrients in the arable soil layer and formation of homogeneous soil fertility. In such a soil environment, much more favorable conditions are created for the development of microflora and more intensive microbiological processes compared to the options of chisel and conventional (control) tillage, and, consequently, the formation of high yields of green Trifolium pratense.

Increased soil carbon storage through plant diversity strengthens with time and extends into the subsoil.

Soils are important for ecosystem functioning and service provisioning. Soil communities and their functions, in turn, are strongly promoted by plant diversity, and such positive effects strengthen with time. However, plant diversity effects on soil organic matter have mostly been investigated in the topsoil, and there are only very few long-term studies. Thus, it remains unclear if plant diversity effects strengthen with time and to which depth these effects extend. Here, we repeatedly sampled soil to 1 m depth in a long-term grassland biodiversity experiment. We investigated how plant diversity impacted soil organic carbon and nitrogen concentrations and stocks and their stable isotopes 13 C and 15 N, as well as how these effects changed after 5, 10, and 14 years. We found that higher plant diversity increased carbon and nitrogen storage in the topsoil since the establishment of the experiment. Stable isotopes revealed that these increases were associated with new plant-derived inputs, resulting in less processed and less decomposed soil organic matter. In subsoils, mainly the presence of specific plant functional groups drove organic matter dynamics. For example, the presence of deep-rooting tall herbs decreased carbon concentrations, most probably through stimulating soil organic matter decomposition. Moreover, plant diversity effects on soil organic matter became stronger in topsoil over time and reached subsoil layers, while the effects of specific plant functional groups in subsoil progressively diminished over time. Our results indicate that after changing the soil system the pathways of organic matter transfer to the subsoil need time to establish. In our grassland system, organic matter storage in subsoils was driven by the redistribution of already stored soil organic matter from the topsoil to deeper soil layers, for example, via bioturbation or dissolved organic matter. Therefore, managing plant diversity may, thus, have significant implications for subsoil carbon storage and other critical ecosystem services.

Changes in the Availability and Distribution of Microelement Copper in Cadmium Contaminated Soil and its Accumulation in Rice (Oryza sativa L.) After Biochar Application.

This experiment explored the side effect of biochar application on the availability and distribution of the soil microelement copper (Cu) in cadmium (Cd) contaminated soil and its uptake in rice tissues. Biochar was added at 0, 10, 20, 30, and 40 t ha-1 on topsoil. Results observed that both the concentration of available Cu in the topsoil and subsoil layer decreased by 16.3%-28.9% and 7.5%-59.3%, respectively, after biochar application. The Cu concentration in the < 0.053mm and 1-2mm soil aggregates increased as biochar application rate increased. Increasing application rate of biochar reduced the proportion of exchangeable Cu, carbonate bound Cu, and Fe/Mn oxide Cu fraction in the soil profile. However, the fraction of organic bound and residual Cu increased by 5.0%-178.4% and 7.0%-15.6%, respectively. Biochar could immobilize microelement Cu in the soil profile and limit Cu uptake by rice.

Variations in Soil Nitrogen Availability and Crop Yields under a Three-Year Annual Wheat and Maize Rotation in a Fluvo-Aquic Soil.

Optimum tillage practices can create a suitable soil environment, and they improve the soil nutrient status to ensure crop development and yield. In this study, we evaluated the influences of six tillage practices on soil nutrients and maize yields from 2017 to 2019 in fluvo-aquic soil in the North China Plain. The field experiment was carried out by a split design with rotary tillage (RT) and deep tillage (DT) in wheat season in the main plot and no-tillage (NT), subsoiling between the row (SBR), and subsoiling in the row (SIR) in maize season in the subplot. The results showed that the soil nutrient content was higher under the treatments with rotary tillage in the wheat season in the 0-20 cm soil layer, while in the 20-40 cm soil layer, the soil nutrient content was higher under the treatments with deep tillage in the wheat season. The integrated principal component scores indicated that the soil nutrients had improved in the second year. The ecosystem multifunctionality (EMF) index was higher with the treatments with rotary tillage in wheat season in the 0-20 cm soil layer, while it was the highest under DT-SIR at 20-40 cm. Correlation analysis showed that the soil EMF index correlated significantly (p < 0.05) with the soil nutrient content mainly in the 0-40 cm soil layer. The higher maize yield was under the treatments with deep tillage compared to that under the treatments with rotary tillage in the wheat season. The yield-increasing effect was higher under the treatments with subsoiling than those utilizing no-till in the maize season, with the highest average yield of 13,910 kg hm-2 in the DT-SIR during the three years. Maize yield was strongly correlated with nutrients in the subsoil layer. The higher yield stability was found under RT-NT. To sum up, during the three-year experiment, rotary tillage in the wheat season combined with subsoiling in the maize season improved the soil nutrient content and the EMF index in the 0-20 cm layer, while the combination of deep tillage in the wheat season and subsoiling in the maize season improved those indices in the 20-40 cm soil layer, and increased the maize yield, the best one was under DT-SIR.

Divergent seasonal responses of above- and below-ground to environmental factors in alpine grassland.

Under current global warming, the relationship between season changes of plants and environmental factors is focused on high-elevation and latitude regions. Due to the desynchronized growth of above- and below-ground and the buffering of soil, the driving factors in leaf and root show seasonal dynamics. We measured above- and below-ground intensity in the alpine steppe over the non-growing season (October-April) and growing season (May-September). Air temperature, precipitation, soil moisture, and soil temperature were used to analyze the correlation based on the growth rhythm. Results showed that an earlier growth in spring and a delayed dormancy in autumn of root than leaf was observed. Our results strongly suggest that soil moisture plays a more important role in leaf unfolding while temperature is consistent with the withering of the shoots. Soil moisture comes from soil melt driving the spring phenology of roots, which derived from the storage of the subsoil layer in the last autumn. Climate change will affect the strong seasonal patterns that characterized these precipitation-limited systems, especially in the spring and fall shoulder seasons. As seasonality changes in the alpine steppe, divergent responses of leaf and fine root would be explored.

Profile soil organic and inorganic carbon sequestration in maize cropland after long-term straw return

Promoting cropland carbon (C) sequestration through straw return has always been the focus of numerous studies. However, there is still a lack of comprehensive understanding of the straw return effects on soil organic carbon (SOC) and soil inorganic carbon (SIC) sequestration. Therefore, the present study aims to investigate the effects of long-term straw return on SOC and SIC sequestration across the 0–100 cm soil profile in the maize planting cropland in Northeastern China. The results showed an increasing trend in SOC contents in the 0–100 cm soil profile following long-term straw return, while significant decreases in SIC contents were observed in the surface (0–20 cm) and subsoil (20–60 cm) layers, respectively. In addition, the SOC stock increased significantly in the subsoil layer following long-term straw return, by an average value of 44%, which is higher than those observed in other soil layers. On the other hand, the SIC stock in the subsoil layer increased by an average value of 24% and decreased in the surface and under-subsoil layers by average values of 53% and 33%, respectively. Moreover, the exchangeable calcium contents were positively correlated with SOC and SIC stock, demonstrating the soil calcium contributes to SOC and SIC sequestration. The present study highlighted the importance of the subsoil layer for effective straw return strategies in cropland to promote SOC and SIC sequestration in croplands.

Improvement of the design of the plow-subsoiler-fertilizer to increase soil fertility

The use of intensive technologies for the cultivation of agricultural crops provides for the application of fertilizers in the process of tillage. This reduces the compaction of the soil, increases its fertility and the quality of the crop. The purpose of these studies is to develop a universal working tool that allows you to combine several technological operations in one pass of the unit. The authors have developed an original design of a plow-subsoiler-fertilizer. This combined working body includes a reversible plow and a vibratory subsoiler with fertilizer ducts. This solution allows you to combine the application of fertilizers when plowing the field, loosening the subsoil layer and mixing the soil. As a result of the work, the dependences of the geometric dimensions of the structure on the traction resistance to movement in the soil were obtained. To implement the developed idea into a real design, the main parameters of the plow-subsoiler-fertilizer are determined. Particular attention is paid to the calculation of the spring mechanism that ensures the vibration of the subsoiler. The optimal number and location of belleville springs in the block and shock absorber were selected, at which the subsoiler will perform self-oscillations with a given amplitude.

Effects of grazing intensity and pasture type on soil organic carbon stock in the semi-arid tropics of India

Pastures may act as carbon sources and sinks depending on grazing pressure and management practices. Soil organic carbon (SOC) stock and its fractions were quantified under 3 different grazing intensities using 5, 10 and 15 sheep/ha under sown, improved and natural pastures in the semi-arid tropics of India. Results revealed that after 3 years, improved pasture had significantly higher particulate organic carbon (POC ~4.5 g/kg), SOC (~0.53 %), total organic carbon (TOC~7 g/kg) and SOC stock (~15 mg/ha) as compared with sown and natural pastures. Labile carbon (LC ~185 mg/kg) and soil microbial biomass carbon (SMBC ~378 µg/g soil) were higher under natural pasture. A moderate grazing intensity of 10 sheep/ha resulted in significantly greater carbon fractions, TOC and SOC stock. SOC stock and its fractions were significantly higher in the topsoil layers as compared with the subsoil layers. These results indicate that improved pasture management practices with moderate grazing intensity can be recommended for improving SOC stock and its fractions in semi-arid tropical pastures.