Soil Physical Structure Research Articles

Carbon and nitrogen stoichiometry across plant-soil system accounts for the degradation of multi-year alfalfa grassland.

Alfalfa (Medicago sativa L.) grassland is prone to degradation following multi-year maintenance. Yet, its mechanism regarding the stoichiometry of carbon (C) and nitrogen (N) across plant-soil system is still unclear. To address this issue, the method of space-for-time sampling was employed to investigate alfalfa grasslands with five planting years (5-, 8-, 10-, 15-, and 20-year periods) in the semiarid Loess Plateau. The results showed that the alfalfa above- and underground biomass decreased steadily decrease after the fifth to eighth years, showing a degradation tendency with the extension of planting duration. The mean weight diameter of aggregate registered an increase with planting years. However, the C and N stocks decreased with planting years in five soil aggregate fractions. Specifically, they were the highest in the fifth year and then started to gradually decrease along the 8th, 10th, 15th, and 20th year. Redundancy and correlation analysis confirmed that the C and N stocks of soil aggregates were closely positively associated with those of plant. Overall, the highest stability of soil physical structure was found during the period from the fifth to eighth year, and, afterward, the stability declined. In conclusion, alfalfa plantation improved soil structure stability but aggravated soil C and N stocks, and biomass and soil aggregate indicators accounted for alfalfa field degradation after a certain year of plantation.

Successive monoculture of Eucalyptus spp. alters the structure and network connectivity, rather than the assembly pattern of rhizosphere and bulk soil bacteria

Eucalyptus as a fast-growing timber tree plays a crucial role in maintaining wood supplication and ecosystem balance worldwide. Nonetheless, the management practices of Eucalyptus plantation in southern China have resulted in productivity decline and soil degradation due to high-intensity successive cultivation. Soil bacteria is a sensitive indicator of soil quality, how does the successive planting of Eucalyptus regulate the soil bacterial community structure for instance the abundance of oligotrophic bacteria, network complexity, and soil bacteria assembly remain ambiguity. To explicate the underlying influencing mechanisms of successive cultivation of Eucalyptus plantations on soil bacterial community structure. Four harvests of Eucalyptus plantations that underwent 0, 1, 2, and 3 times of harvesting were conducted to examine variations in the bacterial community between rhizosphere and bulk soils after successive planting of Eucalyptus. An adjacent evergreen broadleaf forest was employed as control. The present study revealed that successive planting of Eucalyptus increased and reduced the relative abundance of Chloroflexi (oligotrophic bacteria) and Proteobacteria (copiotrophic bacteria), respectively. Continuous planting of Eucalyptus did not modify the assembly pattern of soil bacterial communities, which was governed by stochastic processes. Successive planting of Eucalyptus decreased co-occurrence network complexity, and elevated the proportion of rare microorganisms in the keystone bacterial taxa. Soil particle size composition (clay, silt, sand) indirectly influenced the structure of soil bacterial communities by directly affecting pH, carbon, nutrients, and their stoichiometric ratios. Improving soil physical structure, increasing the input of soil carbon, nitrogen, and other nutrient resources, and maintaining a balanced resource allocation may be effective strategies for ensuring enhanced productivity and sustainable utilization of soil in successive Eucalyptus plantations.

No-tillage with straw retention influenced maize root growth morphology by changing soil physical properties and aggregate structure in Northeast China: A ten-year field experiment

Conservation tillage, particularly the implementation of no-tillage and straw retention (NTS), has been proposed as an effective practice to enhance soil structure and improve soil quality in Northeast China. However, the impact of NTS on maize (Zea mays L.) root growth morphology and the influence of tillage practices on maize root morphology through soil physical properties and structure in Northeast China remain understudied. To address this knowledge gap, a continuous ten-year experiment was conducted to assess the effects of NTS on soil physical properties, aggregate structure, maize root morphology, and their interconnections. Our findings demonstrate that the NTS treatment significantly increased soil water content and soil bulk density at depths of 0–5 cm (1.6%) and 5–10 cm (2.2%), while decreasing soil porosity at depths of 0–5 cm (1.4%) and 5–10 cm (2.0%) compared to conventional tillage (CT). Additionally, NTS resulted in a higher content of soil macro-aggregates (> 0.25 mm) and improved soil aggregate stability compared to CT. Notably, root length, root surface area, root volume, and root biomass in the NTS treatment were 6.04%, 22.15%, 10.04%, and 9.29% higher than those in CT, respectively. However, there was no significant difference in root diameter between the two tillage practices. These results reveal that NTS induces alterations in soil physical properties, aggregate size distribution and aggregate stability, thereby affecting maize root growth morphology.

Effects of composite soil conditioner on soil properties and corn yield in a saline–alkali soil

AbstractBiochar is widely used in agricultural production because of its ability to improve the physical and chemical properties of soil and promote crop growth. In this study, a combination of different biochar and lake sediments were used to improve saline soils. The four raw materials, including corn stalk and chicken manure liquefaction product (SMLP), rice husk charcoal (RHC) and two types of sediment (S‐1 and S‐2), which was used to improve the saline–alkali soil, respectively. The most significantly effective applied on the soil was when the composite soil conditioner (CSC) prepared by mixing SMLP, RHC, S‐1 and S‐2 at 5:20:6000:500 t·100 ha−1. The results of soil experiments using the above blending levels showed that the spike weight, plant height and root length of corn increased by 12.49%, 47.17% and 22.10%, respectively, and the pH and electrical conductivity (EC) of soil decreased by 4.83% and 24.02%, respectively. The contents of soil nutrients, soil organic matter (SOM), water content (WC) and soluble cations (K+, Ca2+ and Mg2+) all presented an increasing trend, and the contents of Na+ and soluble anions (Cl−, CO32−, HCO3− and SO42−) of soil showed a downward trend. Accordingly, the composite soil conditioner with biochar and dredged sediment achieves a synergistic improvement in soil physical structure and an increase in nutrient content, which is beneficial for promoting the growth characteristics and yield of corn.

Traffic induced compaction and physical quality of grassland soil under different soil moisture deficits

Soil compaction is widely recognised as one of the key contributors to soil degradation in Europe. Information is needed for farmers and land managers to guide management decisions and prevent traffic-induced soil compaction. Predicted soil moisture deficit (SMD) from the hybrid SMD model may provide information on when soil conditions are suitable for machinery trafficking. The objective of this study was to investigate the relationship between soil water content and traffic induced soil compaction and if a predicted SMD threshold level could be identified, above which soils can be trafficked without significant soil compaction occurring. The study also evaluated the capacity of selected soil physical indicators such as soil bulk density and water stable aggregates to indicate soil physical degradation across a range of soil water contents. The experiment was carried out on grassland with moderately drained soil, located in Wexford, Ireland. Machinery trafficking of the soil with a tractor equipped with a fully loaded slurry tanker, was assessed in the field across the four seasons of the year. Traffic was imposed at target predicted SMD + 10 mm (relatively dry soil), 0 mm (relatively moist soil), and −10 mm (relatively wet soil). After each traffic event, samples were taken in the middle of the wheel track at three depths (0–10, 10–20 and 20–30 cm) to assess soil bulk density. Water aggregate stability was evaluated at the same three depths following the fourth traffic event. Results showed that when planning field machinery operations, especially repeated trafficking events, soil becomes prone to physical degradation when predicted SMD ≤ 0 mm. Traffic on soil at predicted SMD 0 mm (close to field capacity) lead to compaction after two traffic events. However, when predicted SMD was −10 mm, soil bulk density indicated no significant difference from the non-trafficked soil. When water-stable aggregates were measured on the predicted SMD 0 mm and −10 mm trafficked soils, it indicated physical degradation of soil. Hence, bulk density alone did not give an accurate indication of soil structural quality when soils where trafficked under relatively wet or saturated conditions (SMD −10 mm). These results indicate that avoiding machinery trafficking of grassland soils at predicted SMD ≤ 0 mm will help protect soil physical structure. On soils where multiple machinery operations are likely to occur over the year, trafficking when the predicted SMD > 0 mm is recommended to minimise loss of soil physical quality.

Responses of soil microbial community activities and soil physicochemical properties to coal fly ash soil amendment

BackgroundHundreds of millions of tons coal fly ash are produced annually to support economic development and industrial production. However, directly applying coal fly ash to agricultural production can decrease the land productivity and pose a threat to the ecosystem due to the poor physicochemical properties and seriously heavy metal pollution.MethodsIn this study, a field experiment to investigate the effects of coal fly ash as a soil amendment was conducted in Hebei province, China. The coal fly ash (CFA) soil field was mixed with the carrier soil (CS, without containing coal fly ash) at different rates (0–40% mass content) in the 0–20 cm layer of top soil and then mixed with a rotovator. The soil was then amended with 0.45–1.80 kg·m− 2 of G1 soil amendment for planting corn.PurposeThe purpose of this study is to investigate the response mechanism of soil microbial community activities, and soil physicochemical properties to soil amendment and carrier soil in coal fly ash soil.Key resultsThe study found that the G1 amendment, which consisted of humic acid, polyacrylamide, zeolite powder, and FeSO4·7H2O, improved the soil chemical properties and physical structure by increasing soil bulk density and macroaggregates. The highest corn yield was observed in B5 (20% CS and 1.3500 kg·m− 2 G1). Meanwhile, the abundance of microorganisms that facilitate the circulation of soil nutrients such as Acidobacteria (77.05%), Sphingomonas (25.60%), Nitrospira (20.78%), Streptomyces (11.32%), and Gaiella (10.20%) was increased.ConclusionsOverall, our results indicate that the use of coal fly ash soil as a amendment can enhance soil sustainability by improving soil microbial functions. These findings provide a reference for the development and application of coal fly ash soil amendments.

Effect of coal gasification coarse slag on soil water and nutrition at an arid opencast coal mine site in Northwest China

AbstractThough amendment using coal gasification coarse slag (CGCS) has garnered attention, the intrinsic mechanism of how CGCS, a glassy material, works to amend physicochemical properties in the soil is not yet clear. This study aimed to analyze the effects of different CGCS particle sizes on soil water infiltration and nutrient retention, and to identify the relationship between the physicochemical properties of the amended soil and the water nutrient amendment. The continuous infiltration pattern of soil water and plant growth after the amendment was measured using an indoor continuous dynamic soil column simulation experiment and a field pot experiment of CGCS with different particle sizes (0.25, 1, and 2 mm). The CGCS amendment loosened the soil, improved the pore channels, and amended the water infiltration. However, this process was negatively correlated with CGCS particle size. The Kostiakov performed better in simulating soil water infiltration of heterogeneous dump soil. The CGCS amendment had no heavy metal risk and promoted plant growth. Though amendment enhanced nutrients, in terms of soil organic matter (SOM), the presence of C must be verified by a long team of nutrient cycling if it can be transformed into accessible SOM. Therefore, CGCS amended water nutrition by amending the soil's physical structure. Soil pore adsorption improved water nutrient availability and had a positive effect on chemical properties, which promoted crop growth. The amendment effect was greatest at 0.25 mm particle size.

SOC bioavailability significantly correlated with the microbial activity mediated by size fractionation and soil morphology in agricultural ecosystems

Despite the fact that physical and chemical processes have been widely proposed to explicate the stabilization mechanisms of soil organic carbon (SOC), thebioavailability of SOC linked to soil physical structure, microbial community structure, and functional genes remains poorly understood. This study aims to investigate the SOC division based on bioavailability differences formed by physical isolation, and to clarify the relationships of SOC bioavailability with soil elements, pore characteristics, and microbial activity. Results revealed that soil element abundances such as SOC, TN, and DOC ranked in the same order as the soil porosity as clay > silt ≥ coarse sand > fine sand in both top and sub soil. In contrast to silt and clay, which had reduced SOC bioavailability, fine sand and coarse sand had dramatically enhanced SOC bioavailability compared to the bulk soil. The bacterial and fungal community structure was significantly influenced by particle size, porosity, and soil elements. Copiotrophic bacteria and functional genes were more prevalent in fine sand than clay, which also contained more oligotrophic bacteria. The SOC bioavailability was positively correlated with abundances of functional genes, C degradation genes, and copiotrophic bacteria, but negatively correlated with abundances of soil elements, porosity, oligotrophic bacteria, and microbial biomass (p < 0.05). This indicated that the soil physical structure divided SOC into pools with varying levels of bioavailability, with sand fractions having more bioavailable organic carbon than finer fractions. Copiotrophic Proteobacteria and oligotrophic Acidobacteria, Firmicutes, and Gemmatimonadetes made up the majority of the bacteria linked to SOC mineralization. Additionally, the fungi Mortierellomycota and Mucoromycota, which are mostly involved in SOC mineralization, may have the potential for oligotrophic metabolism. Our results indicated that particle-size fractionation could influence the SOC bioavailability by restricting SOC accessibility and microbial activity, thus having a significant impact on sustaining soil organic carbon reserves in temperate agricultural ecosystems, and provided a new research direction for organic carbon stability.

Effect of Land Use on the Stability of Soil Organic Carbon in a Karst Region

The composition of soil organic carbon and its stability mechanism are the key to understanding the terrestrial carbon sink capacity. The stability of soil organic carbon in a karst ecosystem greatly affects the soil carbon fixation capacity. In order to understand the impact of human activities on the stability of soil organic carbon in karst areas, the karst valley area of Zhongliang Mountain in Chongqing was selected as an example, and soil samples of four typical land use modes (mixed forest, bamboo forest, grassland, and cultivated land) were collected in layers to analyze the total organic carbon (TOC) and heavy fraction organic carbon (HFOC). The distribution characteristics of light fraction organic carbon (LFOC), labile organic carbon (LOC), and recalcitrant organic carbon (ROC) were analyzed quantitatively by using a structural equation model to provide basic data for soil carbon sink assessment and soil quality protection in karst areas. The results showed that the organic carbon components under different land use patterns in karst areas had obvious surface accumulation, and the content of organic carbon components in the surface layer was 1.2 times that in the bottom layer. Except for LFOC, the content of other organic carbon components was the highest in the mixed forest, followed by that in the bamboo forest and wasteland, with the lowest in cultivated land. Mixed forest ω(TOC) content was the highest, 42.5 g·kg-1, followed by that of bamboo forest (36.6 g·kg-1) and grassland (18.7 g·kg-1), and cultivated land content was the lowest, 13.4 g·kg-1. The soil organic carbon content of cultivated land was 68.5%, 63.5%, and 28.3% lower than that of mixed forest, bamboo forest, and grassland, respectively. Mixed forest had the highest content of ω(HFOC), 21 g·kg-1, followed by those of bamboo forest (20.9 g·kg-1), grassland (18.2 g·kg-1), and cultivated land (13.5 g·kg-1). The mixed forest ω(LOC) content was the highest, 16.3 g·kg-1, followed by those of bamboo forest (14.9 g·kg-1), grassland (11.5 g·kg-1), and cultivated land (5.3 g·kg-1). Mixed forest ω (ROC) content was the highest, 25.7 g·kg-1, followed by those of bamboo forest (21.6 g·kg-1), grassland (15.9 g·kg-1), and cultivated land (10.3 g·kg-1). The bamboo forest land ω(LFOC) content was 15.9 g·kg-1, followed by those of mixed forest (13.9 g·kg-1), grassland (7.3 g·kg-1), and cultivated land (4.9 g·kg-1). The recalcitrant organic carbon index (ROCI) was used to indicate the stability of soil organic carbon. The variation range of ROCI was 33.9%-64.5%, of which the highest was mixed forest (64.5%-66.3%), and the lowest was cultivated land (33.8%-39.6%). The ROCI of mixed forest, bamboo forest, and grassland were 1.8 times, 1.6 times, and 1.4 times that of cultivated land, respectively. Karst area ω (inert organic carbon) content and ROCI showed that human agricultural activities caused the reduction in soil organic carbon content and the destruction of soil physical structure, resulting in the accelerated decomposition and turnover rate of soil organic matter. The most important factor affecting soil stability in karst areas was soil pH. Tillage activities caused soil pH to rise, reduced soil microbial activity, and were not conducive to the accumulation of the inert organic carbon and soil organic carbon pool in the soil.

Long-term warming altered soil physical structure and soil organic carbon pools in wheatland field

Summary The impacts of long-term warming on soil physical structure and soil organic carbon (SOC) pools are currently disputed and uncertain. We conducted an eleven-year warming experiment in wheatland field in Henan, China. We found that long-term warming significantly increased soil bulk density by 4.5%, and significantly decreased total porosity and non-capillary porosity by 3.4% and 5.0%, respectively. Besides, long-term warming decreased the &gt;2 mm fraction proportion and increased &lt;0.053 mm fraction proportion of dry and wet aggregates. The mean weight diameter value for dry and wet aggregates in long-term warming treatment was significantly decreased by 7.0% and 6.7%, respectively. Moreover, long-term warming significantly decreased the total SOC, very labile pool (F1) and labile pool (F2) content by 10.6%, 30.6%, and 43.6%, and significantly increased the less labile pool (F3) and non-labile pool (F4) content by 94.2% and 21.1%, respectively. Long-term warming increased the passive carbon pool percentage but decreased the active carbon pool (ACP) percentage. Our results suggest that long-term warming negatively affected the soil's physical structure and impaired soil ACP accumulation. The findings of this study help improve our understanding of the response of farmland soils in northern China to climate change and provide scientific basis for establishing carbon management measures in farmland.

Effect of land configuration and fertilizer dosage on growth and yield of African marigold under vertic ustochrept soil regimes

Adopting proper land management systems and nutrient levels could improve growth, yield and quality by rendering better soil physical structure and mineral nutrition under heavy rainfall areas. An experiment was conducted to identify appropriate land configuration and fertilizer dose for African marigold var. Punjab Gainda-1, in split plot design with three land configuration methods viz., flat bed, raised bed and ridge &amp; furrow system as main plots, and three fertilizer doses (RDF/ha) viz., 100%, 80% and 60% as subplots with recommended dose of fertilizer (RDF) being 10 t FYM + 150:100:100 kg/ha NPK. Results showed that adopting raised bed method of land configuration with the application of 8 t FYM + 120:80:80 kg/ha NPK exhibited enhanced vegetative growth and flower yield (16.26 t/ha) with greater benefit cost ratio (2.88) and, hence, found economically best for commercial production of African marigold.

Enhancing Soil Resilience: Bacterial Alginate Hydrogel vs. Algal Alginate in Mitigating Agricultural Challenges.

Erosion and tillage changes negatively the soil physical structure, which directly impacts agricultural systems and consequently food security. To mitigate these adverse modifications, different polymeric materials from synthetic and natural sources, have been used as soil conditioners to improve the hydro-mechanical behavior of affected soils. One of the most interesting and used natural polymers is the alginate hydrogel. Although commercially available alginate hydrogels are primarily sourced from algal, they can also be sourced from bacteria. The gelation capacity of these hydrogels is determined by their molecular properties, which, in turn, are influenced by the production conditions. Bacterial alginate hydrogel production offers the advantage of precise control over environmental conditions during cultivation and extraction, thereby maintaining and enhancing their molecular properties. This, in turn, results in higher molecular weight and improved gelation capacity. In this study, we compared the effects of bacterial alginate (BH) and algal alginate (AH) hydrogels over the mechanical, hydraulic, and structural behavior of coarse quartz sand as a model soil. Mechanically, it was observed that the treatment with the lowest concentration of bacteria alginate hydrogel (BH1) reached higher values of yield strength, Young's modulus (E), shear modulus (G) and strain energy (U) than those treatments with algal alginate hydrogel (AH). Furthermore, the increase in the aggregate stability could be associated with the improvement of mechanical parameters. On the other hand, a greater water retention capacity was observed in the BH treatments, as well as a greater decrease in hydraulic conductivity with respect to the AH and control treatments. All these changes could be explained by the formation of bridge-like structures between the sand particles and the hydrogel, and this alteration may result in a shift in the mechanical and wettability characteristics of the treated soils. Finally, our findings emphasize the superior impact of bacterial alginate hydrogel on enhancing the mechanical and hydraulic properties of coarse quartz sand compared to traditional algal alginate. Besides, the use of bacterial alginate hydrogel could be useful to counteract erosion and water scarcity scenarios in agricultural systems.

Impacts of long-term organic manure inputs on cultivated soils with various degradation degrees

With an increasing concern of soil health and sustainable development, organic manure application has been readdressed in recent years. In Northeast China, the agricultural industry is highly developed and organic manure resources are abundant, but soil degradation is serious due to extensive expansion of cultivation. Currently, limited information is available on how soils with various degradation degrees respond to long-term manure fertilization. Given that, a comparative study was conducted based on soil functional assessment of croplands with over 35 years of manure fertilization (maize straw compost, SA; cattle manure, CA) and various degradation degrees (none, light, moderate, and heavy). Soils in these croplands were loess-derived Mollisols and concentrated on a gentle to flat slope. Except for the difference in manure fertilization (SA and CA), similar field managements were adopted for these croplands during the past 35 years. Results showed that the impacts of erosion degradation and manure fertilization on soil physical structure lasted across the whole profile (0 ∼ 120 cm), while their impacts on soil nutrient properties were concentrated in shallow layers (<50 cm). Meanwhile, erosion degradation dominated 17.9% of the variance of soil physical structure, and soil profile depth contributed to 15.9% of soil nutrient variation. According to field validation regarding soil erosion modulus and crop yield, principal component analysis (PCA) with a nonlinear scoring method showed a good performance on the integrated soil functional index (ISI) assessment in this study area. The ISI of these croplands was found to be minimally characterized by BD, SOC, TN, AK, sand content, and CEC (R2 >0.64, p < 0.001). In addition, manure fertilization could significantly improve the ISI and maize yield for degraded soils, but had a slight impact on these two indicators for non-degraded soils. In terms of contribution to ISI improvement, SA (1.79% ∼ 283.73%) generally outperformed CA (4.53% ∼ 212.83%), while the latter was more effective in altering soil structure in deep layers (>70 cm). Generally, the ISI and maize yield were more susceptible to erosion degradation than manure fertilization. The obtained results provide useful information for a better cropland management in Northeast China.

Diversity of Indicator and Dominant Plant Species along Elevation Gradients in Prince Mohammad Bin Salman Nature Reserve, KSA

It is essential to protect and preserve biodiversity, especially in habitats in which natural resources are scarce. The differing flora and vegetation distribution on the broad, arid landscape at the Crown Prince Mohammed Bin Salman Nature Reserve has yet to be investigated. Based on GPS coordination and the transitional zone of plant communities, 48 symmetric plots of 50 × 50 m2 were distributed evenly over six elevations. In this study, we recorded 70 species in 33 families and elucidated floristic traits correlated with elevation. High species richness was recorded for the families Fabaceae, Poaceae, Asteraceae, and Chenopodiaceae. High numbers of chamaephyte and phanerophyte species were observed. In the chorotype, the mono-regional component contained 47% of the species, the bi-regional component 35.7%, and multi-regional and worldwide species comprised 10% and 7%, respectively. This study noted the growth habits of 23 herbs, 15 shrubs, 10 trees, and a single species of grass, vine, climber, and mistletoe. Diversity indices, indicator species, dominant plant communities, and soil profiles were compared for the defined zones of elevation. Alpha and beta diversity were high at elevations of ≥1000, 800, and ≤100 ma.s.l., compared to elevations of 600 m, 400 m, and 200 m. The highest species richness and species turnover were recorded at elevations of ≥1000, 800, and ≤100 m, while species evenness was greater at elevations of 600, 400, and 200 m. Vegetation analyses and indicator species (based on relative abundance) showed species variation with elevation. Species domination was influenced by physical soil structure and soil chemistry. Microclimates, including temperature and relative humidity variations, were found to be a significant driver in the ecosystem, resulting in varying plant diversity and species distribution at different elevations. Through canonical correspondence analysis (CCA), we used an autocorrelation of elevations, plant species, and soil properties to identify three phytogeographic categories that were presumed to be a proxy of microclimate change: Category I: elevations 1000 m and 800 m, including Retama raetam, Zilla Spinosa, and Vachellia gerrardii linked with sandy soil; Category II: elevations 600 m and 400 m, including species Haloxylon salicornicum, Rhazya stricta, and Leptadenia pyrotechnica linked with enriched soils containing CaCO3 and HCO3 and having a clay texture; and Category III: elevations 200 m and 100 m, including Zygophyllum coccineum, Tamarix nilotica, and Hyphaene thebaica, which thrived in salinity and silt soils. The spatial vegetation patterns of the xeric environment and its transition zones in Prince Mohammed Bin Salman Nature Reserve were also documented. It is recommended that microclimate effects on species nominated for vegetation restoration or afforestation be considered for the optimal management of this important nature reserve.

Soil physical structure drives N-glycan mediated trophic interactions in soil amoebae: Mechanisms and environmental implications

Soil protozoa are an essential part of the terrestrial ecosystem, playing a vital role in the global element cycling and energy flow. However, one research gap is what are the key factors driving their diversity and environmental fates. In this study, we hypothesized that soil texture could affect soil protozoa's predation and their interactions with environmental pollutants, and we tested it by using a soil amoeba Dictyostelium discoideum as a model system. We found that soil texture affected amoeba's growth and development. In addition, environmental factors cannot explain the variation of amoeba's fitness in different soil textures. Soil sandy particles and water content rather than particle size contribute to amoeba's fitness. Furthermore, different soil textures induced distinct transcriptional responses to amoebae, especially N-glycan-related and multiple signaling pathways and the expression of key genes (e.g., Ras superfamily, cxgE, trap1). The expression of N-glycan-related pathways, which is positively correlated with amoeba predation, was inhibited in sand soil, decreasing amoeba's fitness. Finally, the results showed that soil texture also affects amoeba's interaction with environmental pollutants. In conclusion, this study shows that soil physical structures affect amoeba's interactions with bacteria and environmental pollutants. SynopsisSoil texture affects soil protozoa's growth and development and their interactions with environmental pollutants.

Long-term aged fibrous polypropylene microplastics promotes nitrous oxide, carbon dioxide, and methane emissions from a coastal wetland soil

Microplastics (MPs) has been suggested that it can greatly affect soil greenhouse gases (GHGs) emissions via altering soil physical, chemical, and biological properties. However, the difference in GHGs emissions, especially for those from coastal wetland soils, between varied aged MPs was rarely explored and the underlying mechanisms of GHGs emissions affected by the aged MPs were poorly understood. Therefore, the implications of fibrous polypropylene MPs (FPP-MPs) exposure on N2O, CO2, and CH4 emissions were examined by a 60-day soil incubation experiment. Compared with the control, the additions of un-aged FPP-MPs with both two rates (0.2 and 2 %) and aged FPP-MPs with a low rate (0.2 %) showed an insignificant effect on N2O emission, while the aged FPP-MPs added with a high rate (2 %) resulted in a remarkably increase in N2O emission, especially for those of the 30-day-aged FPP-MPs. A significant increase in CO2 emission was only observed in the 30-day-aged FPP-MPs treatments, compared with the control, and a higher addition rate produced a higher increase of CO2 emission. Regarding CH4 emission, it was significantly increased by adding aged FPP-MPs, and a longer aging period or/and a higher addition rate generated a higher degree of promotion of CH4 emission. However, compared with the CO2 emission, the quantity of CH4 emission was extremely low. These increased GHGs emissions can be ascribed to the improvements in soil physical structure and other chemical properties (e.g., pH and contents of soil organic matter and dissolved organic carbon) and enhancements in the abundances of denitrification- and carbon mineralization-related microorganisms. Overall, our results highlight the risk of elevated GHGs emissions from the soil polluted with 30-day-aged FPP-MPs, which should not be ignored as long-term aged FPP-MPs continue to increase in coastal wetland soils.

Maize residue types and soil fertility levels influence sequestration of newly associated carbon in aggregates with in situ experiments

Soil physical structure plays a key role in the sequestration of organic carbon (C) and affects soil fertility and global climate change. However, the dynamics of the residue-derived C in different aggregate fractions are poorly understood. The objectives of this study were to explore the changes in soil aggregate composition and organic C distribution at different fertility levels after the addition of maize residues (roots, stems, and leaves, labeled with 13C). In this study, soil samples with high fertility (HF) and low fertility (LF) levels were formed through a long-term fertilization experiment (29 years), and different types of maize residues were added to the two types of soils. The 13C abundance was quantified in four fractions of soil aggregates large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), microaggregates (0.053–0.25 mm), and silt and clay (<0.053 mm) on the 60th, 90th, 180th and 540th day following the addition of residues. The findings indicate that the mass proportions of small macroaggregates and microaggregates in the LF soil were lower, whereas those of the other fractions were higher compared with HF soil. Moreover, greater amount of residue-derived C was found to be associated with soil aggregates in LF soil than that in HF soil, and the residue-derived C in different soil aggregate fractions differed with the residue type. The percentages of residue-derived C distributed in the large macroaggregate fractions averaged 19.9% and 15.3% in the LF and HF soils, respectively. Stem and leaf treatments of HF soil improved the stability of soil aggregates. The addition of roots significantly increased the soil organic C content in the aggregates; the residue-derived C content was the highest in the silt and clay fractions and the lowest in the large macroaggregate fraction (>2 mm). These results suggest that the potential benefits of adding maize residue to regulate SOC sequestration and stabilization of soil aggregates, especially in infertile soils.

Pelletized Straw Incorporation in Sandy Soil Increases Soil Aggregate Stability, Soil Carbon, and Nitrogen Stocks

In China, increasing the quantity and quality of total carbon and nitrogen stocks in sandy soil used for crop production is an important research issue. Soil amendment with pelletized straw could improve both soil physical structure and fertility in sandy soils, but these aspects remain understudied. The present pot and field experiments examined the dynamic changes in sandy soil water holding capacity, soil bulk density, soil total carbon and nitrogen stocks, and the distribution of water-stable aggregates and soil total carbon stocks related to aggregates across the following treatments: no fertilization (i.e., study control (CK)), normal fertilizer rate (NM), soil amendment at 150 Mg ha−1 (S150), manure amendment at 150 Mg ha−1 (M150), pelletized straw amendment at 75 Mg ha−1 (PS75), and pelletized straw amendment at 150 Mg ha−1 (PS150). The results show that the pelletized straw incorporation significantly increased water holding capacity and decreased soil bulk density. PS150 notably increased the large macroaggregates (&gt;2000 μm) proportion and decreased the ratio of &lt;250 μm aggregate size fractions in comparison with CK, NM, S150, and M150 at 0–20 and 20–40 cm soil depths. Compared with the CK treatment, the bulk soil carbon and nitrogen stocks in the 0–20 cm layers under the PS150 treatment were significantly increased by 85.2% and 302.9%, and in the 20–40 cm layers those increased by 136.4% and 257.1%, respectively. The PS150 treatment resulted in higher soil organic carbon (SOC) and particulate organic carbon content than the CK and PS75 treatments, whereas the PS75 treatment achieved maximum soil inorganic carbon content. The pelletized straw treatment increased the large macroaggregate-associated soil total carbon content at 0–20 and 20–40 cm soil depths. The maximum soil total carbon stocks were in the small macroaggregates (250 &lt; WSA &lt; 2000 μm) rather than in the large macroaggregate and microaggregates under the PS75 and PS150 treatments. Additionally, the pelletized straw and manure amendments increased the yield of silage corn, which was dependent on the increase in soil total carbon and nitrogen content in the macroaggregates, whereas the soil and manure amendments did not facilitate sandy soil aggregation and soil total carbon stock increases. In conclusion, PS150 was found to be the optimal amendment for maintaining sandy soil profile physico-chemical properties through macroaggregate stabilization. These results will be beneficial for arid and semi-arid regions, thus contributing to soil carbon and nitrogen conservation.

Post-farming land restoration schemes exhibit higher soil aggregate stability and organic carbon: Evidence in the Three Gorges Reservoir Area, China

The Three Gorges Reservoir Area was dominated by a farming landscape but has been the target of restorative land management schemes over recent decades, wherein croplands have been converted to forests or citrus woodlands run by commercial enterprises or, alternatively, abandoned for natural vegetation succession. How these ongoing restorative land management schemes imprint soil systems remains poorly understood. Accordingly, in this study, a space-for-time substitution approach was applied to compare soil aggregate stability and organic carbon stocks between lands used for ongoing arable production and areas subjected to restorative practices. Composite soil samples from reforestation woodlands, abandoned croplands, citrus woodlands, and present-day croplands were collected, and a variety of soil metrics (i.e., water-stable aggregate percentage, mean weight diameter, geometric mean diameter, erosion resistance of the aggregates, bulk soil organic carbon and aggregate-specific soil organic carbon) were used as a basis for comparison. Reforestation woodlands and abandoned croplands exhibited a higher mass percentage of macro-aggregates, higher values of mean weight diameter and geometric mean diameter, and higher organic carbon content within the sampled 0–40 cm depth soil profiles. Reforestation and cropland abandonment significantly increased the stability of soil aggregates and organic carbon stocks. Moreover, abandoned cropland samples exhibited higher soil aggregate stability and organic carbon stocks than reforestation woodlands. In contrast, soil aggregate stability for all sampled soil depths and organic carbon content except for the topsoil (0–10 cm) of citrus woodlands exhibited lower values than those for present day croplands. Exclusion of crop farming and reestablishment of restorative vegetation have therefore contributed to changes in soil physical structure and organic carbon stocks, with reforestation and cropland abandonment being more beneficial for soil aggregate stability and soil organic carbon stocks in the Three Gorges Reservoir Area.

Seaweed extract enhances drought resistance in sugarcane via modulating root configuration and soil physicochemical properties

Seaweed extract is widely used in sustainable agricultural management and can promote sugarcane growth even under low-water availability conditions. However, to date, little information has been gained regarding the role of seaweed extract in regulating sugarcane root configuration and soil physicochemical properties under drought conditions. In this study, the effects of seaweed extract on soil physicochemical properties of sugarcane were studied by soil culture experiments, and the effects of seaweed extract on root architecture of different sugarcane varieties “YT03–393” (drought-sensitive variety) and “cv. ROC22” (drought-resistant variety) were explored by hydroponic experiments. The results revealed that the application of seaweed extract increased the proportion of aggregates > 0.25 mm in the soil and increased the moisture content of the soil under water deficiency conditions. Furthermore, the seaweed extract application increased the activities of urease, sucrase, acid phosphatase, and glucosidase in soil and increased the soil contents of available nutrients such as N, P, and K. Under drought stress, seaweed extract promoted root growth in deeper soil. The proportions of root dry weight and root length density in the soil of 20–40 cm depth increased by 45.0% and 9.8%, and 38.3% and 8.9% in cv. YT03–393 and cv. ROC22, respectively. Additionally, seaweed extract application improved the activities of antioxidant enzymes, including SOD, CAT, and POD, in roots and alleviated the oxidative damage of roots caused by drought stress. It can be concluded that seaweed extract application can improve soil physical structure, promote enzyme activities, and increase the available N, P, and K of the soil. Furthermore, seaweed extract can promote root growth, change root architecture, and improve the water use efficiency of roots, thus improving drought resistance of sugarcane plants.