Enhanced Soil Aggregate Stability Research Articles

Effects of Terracing on Soil Aggregate Stability and Erodibility in Sloped Farmland in Black Soil (Mollisols) Region of China

Soil aggregates are important indicators of soil structure stability and quality. The black soil region of northeast China, known for its high agricultural productivity, faces significant challenges due to soil erosion. This study investigates the impact of terracing on the stability and erodibility characteristics of soil aggregates in sloped farmlands, which is crucial for this important agricultural area. Three research sites with the same basic management modes were selected along a latitudinal gradient, from the mid-temperate zone to the cold temperate zone, in the black soil region of northeast China. The Savinov method was used to analyze the differences in soil aggregate size distribution, stability characteristics, and soil erodibility between terraced and non-terraced slopes at each research site. The results showed that terracing increased the content of large soil aggregates (>0.25 mm) by 5.38–6.35%, with the increase becoming more pronounced from north to south. The improvement in soil structure varied by location and slope position, with the most significant improvement at the middle slope position. Terracing enhanced soil aggregate stability, reduced soil erodibility, and improved soil structure by increasing clay and soil organic matter (SOM) content and reducing soil bulk density (BD), promoting the conversion of small aggregates to large aggregates. Soil stability indicators such as water-stable aggregates (WSAs), mean weight diameter (MWD), and geometric mean diameter (GMD) were dominated by aggregates > 5 mm, while erodibility indicators such as fractal dimensions (Ds) and the soil erodibility factor (K values) were mainly influenced by aggregates < 0.25 mm. Terraces can improve the soil structure and stability of sloping farmland by increasing the content of large soil aggregates and enhancing overall soil quality. The benefits of these improvements increase with latitude. These findings provide critical insights for determining effective management practices for sloped farmlands in the black soil region under various site conditions. They offer scientific evidence for preventing soil erosion and improving soil quality, thus supporting the sustainable development strategy for protecting black soil and ensuring long-term agricultural productivity.

Effects of riparian pioneer plants on soil aggregate stability: Roles of root traits and rhizosphere microorganisms

Pioneer plants are vital in stabilizing soil structure while restoring reservoir drawdown areas. However, uncertainties persist regarding the mechanism of pioneer plants to soil stability in these delicate ecosystems. This study aims to unravel the plant-soil feedback mechanisms from the roles of root traits and rhizosphere microorganisms. We conducted a mesocosm experiment focusing on four common pioneer plants from the drawdown area of Three Gorges Reservoir, China. Using the wet sieving methodology, trait-based approach and high-throughput sequencing technology, we explored soil aggregate stability parameters, plant root traits and rhizosphere microbial communities in experimental plant groups. The interacting effect of pioneer plant species richness, root traits, and rhizosphere microbial communities on soil aggregate stability was quantified by statistical and machine-learning models. Our results demonstrate that diverse pioneer plant communities significantly enhance soil aggregate stability. Notably, specific species, such as Cynodon dactylon (L.) Pers. and Xanthium strumarium L., exert a remarkably strong influence on soil stability due to their distinctive root traits. Root length density (RLD) and root specific surface area (RSA) were identified as crucial root traits mediating the impact of plant diversity on soil aggregate stability. Additionally, our study highlights the link between increased rhizosphere fungal richness, accompanied by plant species richness, and enhanced soil aggregate stability, likely attributable to elevated RLD and RSA. These insights deepen our understanding of the role of pioneer vegetation in soil structure and stability, providing valuable implications for ecological restoration and management practices in reservoir drawdown areas.

Enhancing soil ecological security through phytomanagement of tailings in erosion-prone areas

Revegetation is effective in improving soil quality in ecologically fragile areas. However, little is known about the impact of diverse phytomanagement strategies of tailings on soil quality and ecological security in erosion-prone areas. We investigated the water stability, soil aggregate nutrients, and the risk of heavy metal contamination of abandoned tailings under phytomanagement and in adjacent bare land on the Loess Plateau. The results showed that phytomanagement significantly enhanced soil aggregate stability, as demonstrated by higher contents of soil organic carbon (SOC), glomalin-related soil protein (GRSP), aromatic-C, and alkene-C in macro-aggregates. The pollution load index (PLI) and ecological risk index (RI) of soil heavy metals were lower in shrub/herbaceous mixed forests than in natural grasslands and planted forests. The risk of heavy metal contamination was higher in macro-aggregates (>0.25 mm) than in micro-aggregates (<0.25 mm) and was significantly and positively correlated with the SOC and GRSP contents of the aggregates. Our study demonstrates that soil aggregate quality is closely related to the fate of heavy metals. Diversified tailing revegetation measures can improve soil quality and ensure ecological security.

亚热带退化森林不同恢复方式对土壤团聚体胶结物质及稳定性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 亚热带退化森林不同恢复方式对土壤团聚体胶结物质及稳定性的影响 DOI: 10.5846/stxb202204211092 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(32001298); 湖北省教育厅重点项目(D20201001); 大学生创新训练项目(S202110512085) Effects of different restoration approaches of subtropical degraded forests on bonding materials and stability of soil aggregate Author: Affiliation: Fund Project: The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:退化森林的恢复一直是林业和生态学研究的热点。良好的森林土壤结构有助于林木生长发育,作为土壤最基本的结构单元,土壤团聚体组成和稳定性是衡量土壤肥力和质量的重要指标,其团聚结构的形成依靠土壤胶结物质。然而,土壤胶结物质与团聚体稳定性之间的关系尚不确定。为探明亚热带退化森林的不同恢复方式对团聚体稳定性的影响及其潜在机制,以自然恢复的次生林为对照(CK),选取了亚热带三种常见的人工林:一代杉木林(P1)、二代杉木林(P2)和黄山松林(P3),测定土壤团聚体稳定性及其胶结物质的含量,并分析了各胶结物质对团聚体稳定性的影响。研究发现:不同森林恢复方式显著影响了土壤pH值、碳氮比、速效磷含量、团聚体的组成和稳定性。所有森林类型中,三种人工林的团聚体稳定性显著高于CK,P2的大团聚体所占比例最大,团聚体稳定性最高。恢复方式显著影响了土壤游离氧化铁含量、菌根密度和易提取球囊霉素相关土壤蛋白(EEG)含量。团聚体稳定性与游离氧化铁含量、菌根密度呈正相关,但与EEG含量呈负相关。研究结果表明,亚热带退化森林的人工恢复比自然恢复更有助于增强土壤团聚体稳定性,土壤游离氧化铁、菌根密度和EEG是显著影响团聚体稳定性的胶结物质。 Abstract:The restoration of degraded forest has been a hot topic in forestry and ecology. As a basic structural unit of soil, soil aggregate composition and stability are important indicators of soil fertility and quality, and the formation of soil aggregate relies on aggregate bonding materials. However, the relationship between aggregate bonding materials and aggregate stability is uncertain. To explore the effects of different restoration approaches of degraded subtropical forests on aggregate stability and its underlying mechanisms, we compared the secondary forest (natural restoration) as a control (CK), with three different common subtropical plantations which were: (1) first-generation Cunninghamia lanceolata (P1), (2) second-generation C. lanceolata (P2), and a Pinus. taiwanensis plantation (P3). We measured the aggregate stability and the contents of different aggregate bonding materials, and then analyzed the influence of these materials on soil aggregate stability. Results showed that forest restoration approach significantly affected soil pH, C/N, available phosphorus, as well as the composition and stability of aggregate. Among all the forests, the aggregate stability was significantly lower in CK than in the other three plantations, and P2 had the greatest proportion of large aggregates and the highest aggregate stability. The forest restoration approach also significantly affected soil free Fe oxide content, mycorrhizal density, and easily extractable glomalin-related soil protein (EEG). Aggregate stability was positively correlated with free Fe oxide content and mycorrhizal density, but negatively correlated with EEG. For subtropical degraded forests, the results indicated that artificial restoration was better than natural restoration to enhance soil aggregate stability, with soil free Fe oxide, mycorrhizal density and EEG being the main bonding materials that significantly affected the aggregate stability. 参考文献 相似文献 引证文献

Increased Soil Aggregate Stability by Altering Contents and Chemical Composition of Organic Carbon Fractions via Seven Years of Manure Addition in Mollisols

Mollisols include an abundance of soil organic carbon (SOC) which is easily influenced by fertilization management. Manure addition could enhance soil aggregate stability; however, the dominating factor affecting its stabilization remains controversial. The fertilization practices were initiated in 2012 to investigate the influences of different fertilization managements on the contents and molecular characterization of organic carbon (OC) fractions, and to clarify the underlying mechanism of soil aggregate stability change. NoF (non-fertilizer), CF (only chemical fertilizer), CF + DM (chemical fertilizer plus single dairy manure at 15 t ha−1), and CF + 2DM (chemical fertilizer plus double dairy manure at 30 t ha−1) treatments were established. This research was aimed at exploring the potential mechanism that affects aggregate stability in Mollisols through the variation of contents and chemical composition of OC fractions, and screening out the appropriate fertilization practice on promoting SOC stabilization and crop yield under 7-year manure addition. Compared to CF, 7-year manure addition significantly enhanced SOC content by 17.4–35.9% at 0–10 cm depth, which was evidenced from the contribution of increased aromatic compounds with 4.3–19.9%. Simultaneously, compared with CF, CF + DM and CF + 2DM both significantly enhanced dissolved organic carbon and easily oxidizable organic carbon contents by 12.5–37.7% at a 0–30 cm soil layer. In regard to soil aggregates, the increased OC content and mass percentage of macroaggregates, and the decreased mass percentage of free microaggregates both improved aggregate stability under manure addition at 0-30 cm soil layer, which was proven to be the increment in mean weight diameter (MWD) and geometric mean diameter (GMD) values by 17.6–22.1%. Moreover, CF + DM and CF + 2DM raised aromatic compound amounts of POM fractions within macroaggregates [M(c)POM] by 5.6–11.6% and within free microaggregates (Fm-POM) by 4.3–10%. Furthermore, CF + DM and CF + 2DM both significantly increased maize yield by 5.7% and 4.2% compared to CF, but no significant difference was observed between CF + DM and CF + 2DM treatments. Collectively, physical protection through the occlusion within aggregates of POM might be the central mechanism for soil aggregate stability of manure addition in Mollisols. The manure addition of 15 t ha−1 was the effective management method to enhance SOC stabilization and crop yield in Mollisols.

Evolution mechanism of soil hydrothermal parameters under freeze–thaw cycles: Regulatory significance of straw and biochar

In seasonally frozen regions, soil hydrothermal parameters play an important role in the study of soil water transport and heat transfer. In this study, different initial moisture contents (W1, W2, W3), different straw and biochar applications (S1, S2, B1, B2) and untreated control groups CK were used. A laboratory simulation was designed, and the changes in total soil porosity (TP), pore distribution, soil aggregates, soil saturated hydraulic conductivity (Ksat) and soil thermal conductivity (λ) were analyzed. The results showed that freeze–thaw cycles affected soil porosity and destroyed soil aggregates, while straw and biochar applications increased total soil porosity, enhanced pore connectivity, and enhanced soil aggregate stability. Freeze–thaw cycles and straw and biochar applications increased soil Ksat, and biochar showed a stronger ability to improve soil hydraulic conductivity. After 20 freeze–thaw cycles, compared with the control group, the Ksat of treatments S1 and B1 increased on average by 11.18% and 22.03%, respectively, at different moisture contents, while the Ksat of treatments S2 and B2 decreased on average by 3.65% and 6.17%, respectively. Excessive application of the amendments reduced the soil Ksat. During the freeze–thaw cycles, the soil λ of each treatment first showed a stable trend and then decreased. However, the increase in the initial moisture content induced a significant increase in soil λ. Straw and biochar applications reduced soil λ, and the reduction was proportional to the applied amount, but the thermal insulation effect of biochar was better than that of straw. This study showed that the comprehensive effect of the B1 treatment was better than that of the other treatments for improving the soil structure, and enhancing the soil infiltration capacity and enhancing soil thermal insulation capacity. A 1% biochar application is recommended as the optimal soil amendment.

Long-Term Effects of Straw and Straw-Derived Biochar on Humic Substances and Aggregate-Associated Humic Substances in Brown Earth Soil

Turning maize straw into biochar is useful for improving soil fertility and mitigating climate change. However, the difference between straw and straw-derived biochar on soil aggregate associated humic substances has not been sufficiently studied in brown earth soil. The objective of this study was to investigate how different straw management practices affect soil humic substances and aggregate-associated humic substances in the field. As such, an eight-year study (2013–2020) was conducted on brown earth in Northeast China. Three treatments were applied: 1) CK, in which only chemical fertilizer was applied every year; 2) BC, in which biochar was applied at a rate of 2.625 t ha−1 (the same rate of chemical fertilizer as that in the CK was applied); 3) SR, in which straw was returned at a rate of 7.5 t ha−1 (the same rate of chemical fertilizer as that in the CK was applied). Both biochar and straw improved soil aggregate stability that reflected by the mean weight diameter (MWD) and geometric mean diameter (GMD). Compared to the CK treatment, the BC treatment enhanced humic carbon (HMC) both in bulk soil and different aggregate fractions. Biochar decreased the humic acid carbon (HAC) in bulk soil compared to the initial content, but no differences were observed between BC and CK after the eight-year field experiment. All of the aggregate-associated HAC contents were significantly enhanced in response to BC treatment. SR was an effective way to improve soil organic carbon (SOC) and humic substances in bulk soil and aggregate fractions. SR had a relatively small effect on the relative proportions of the C functional groups. Solid-state 13C cross-polarization magic-angle-spinning nuclear magnetic resonance (CPMAS-NMR) spectra of bulk soils revealed that biochar increased the proportion of aromatic C. The ratios of alkyl C/O-alkyl C, aromatic C/aliphatic C, and hydrophobic C/hydrophilic C increased in response to the BC treatment compared to the other treatments. Taken together, biochar amendment can enhance soil aggregate stability, aggregate-associated HMC and stability of SOC on the scale of an eight-year field experiment. Biochar could be an effective approach to sequestrate carbon and improve the quality of brown earth soil.

APPLICATION OF FRACTAL THEORY IN QUANTIFYING SOIL AGGREGATE STABILITY AS INFLUENCED BY VARYING TILLAGE PRACTICES AND COVER CROPS IN NORTHERN GUINEA SAVANNA, NIGERIA

&lt;p&gt;&lt;strong&gt;Background.&lt;/strong&gt; Soil aggregate stability varies with management practices like tillage and soil organic matter management. &lt;strong&gt;Objective.&lt;/strong&gt; The objectives of this study were to (i) Explore a fractal theory to investigate the extent of soil fragmentation in soil of Samaru, Northern Nigeria, subjected to different tillage practices and covers crops for the purpose of improving soil aggregate stability (ii) Establish a relationship between fractal dimension (D) and mean weight diameter (MWD). &lt;strong&gt;Methodology.&lt;/strong&gt; A three years field trials was conducted with three tillage practices (no-till, reduced till and conventional till) as main treatments and four cover crops (&lt;em&gt;Centrosema pascuorum, Macrotyloma uniflorum, Cucurbita maxima&lt;/em&gt; and &lt;em&gt;Glyine max&lt;/em&gt;), and a bare/control (no cover crop) as sub treatments. The trial was laid out in randomized complete block design, split plot arrangement and replicated three times. Soil samples were collected at 0-15 cm prior to trial establishment for routine soil physical and chemical properties and at depths 0-5, 5-10, 10-15 and 15-20 cm at the end of each cropping season each year for soil aggregate stability test. &lt;strong&gt;Results. &lt;/strong&gt;No-till soils had 12.58% better soil aggregate stability than soils under reduced and conventional tillage systems. Also, no-till soils had 2.40 % less fragmented soil aggregates than Reduced and Conventional till soil as indicated by the fractal dimension of soil aggregates. Soils under &lt;em&gt;Macrotyloma uniflorum&lt;/em&gt; cover crop, were on the average 2.33% less fragmented than soils under &lt;em&gt;Centrosema pascuorum, Glycine max &lt;/em&gt;and&lt;em&gt; Cucurbita maxima&lt;/em&gt; but 4.56% less fragmented than soils with no cover crops. &lt;strong&gt;Implication, &lt;/strong&gt;No-till and reduced till systems; and cover cropping better enhanced soil aggregate stability due to better accumulation of organic matter emanating from crop residues return to soil in these practices. &lt;strong&gt;Conclusion.&lt;/strong&gt; Conservation tillage and the use of cover crops lowered soil aggregate fragmentation relative to conventionally tilled system and bare soil with no cover crop. The strong linear relationship established between MWD and fractal dimension showed over 80% dependency, suggesting that fractal dimension is another useful index for evaluating soil aggregate stability.&lt;/p&gt;&lt;p&gt;.&lt;/p&gt;

Effects of organic mulching on soil aggregate stability and aggregate binding agents in an urban forest in Beijing, China

Urban forest soil is often disturbed by rapid urbanization. Organic mulching is effective for improving soil quality and aggregate stability. This study evaluated how soil binding agents changed aggregate stability through organic mulching in urban forest soils. Three treatments were applied in Jiufeng National Forest Park, Beijing: (1) no organic mulch (control); (2) wood chips alone (5 cm thickness); and, (3) wood chips + wood compost (This mulch was divided into two layers, the upper layer of wood chips (2.5 cm), the lower layer wood compost (2.5 cm)). Soil samples were collected from the surface 10- cm soil layer and fraction into four aggregates. Glomalin-related soil protein and soil organic carbon were measured in bulk soil and the four aggregates. The results show that wood chips + wood compost increased the proportion of large and small macroaggregates, mean weight diameter and geometric mean diameter. The total and easily extractable glomalin-related soil protein were higher in the wood chips + wood compost. However, soil organic carbon was lower in the wood chips alone application compared to the controls and wood chips + wood compost. Easily extractable / total glomalin-related soil protein and glomalin-related soil protein / soil organic carbon ratios of wood chips alone and wood chips + wood compost had increased trend compared to the controls but did not reach significant levels (p > 0.05). Mean weight diameter and geometric mean diameter correlated positively with total and easily extractable glomalin-related soil protein but were not positively correlated with soil organic carbon, the ratios of easily extractable and total glomalin-related soil protein, and the ratios of glomalin-related soil protein and soil organic carbon. Redundancy analysis revealed that total glomalin-related soil protein was the most important driver for soil aggregate stability, especially the total glomalin-related soil protein of small macroaggregates. The results suggest that wood chips + wood compost enhanced soil aggregate stability through the increase of glomalin-related soil protein. Wood chips alone cannot enhance soil aggregate stability in urban forests in the short term.

Microstructure characteristics of aggregates and Cd immobilization performance under a 3–year sepiolite amendment: A field study

Sepiolite is an efficient mineral for the immobilization of Cd in contaminated soils. Here, we conducted a 3–year field experiment to investigate the effect of sepiolite on soil aggregation and porosity, Cd availability, and organic carbon content in the bulk and aggregate soils and Cd accumulation by leafy vegetables. The sepiolite–treated soils showed a 15.4%–53.4% and 5.5%–63.0% reduction in available Cd content in the bulk soil and different particle–size aggregates, respectively. Moreover, the Cd concentrations in the edible parts of Brassica campestris, Lactuca sativa L., and Lactuca sativa var. ramosa Hort. decreased by 5.9%–26.2%, 22.8%–30.1%, and 14.4%–19.1%, respectively, compared with those of the control groups. Treatments with 0.5%–1.5% sepiolite resulted in a significant increase (P < 0.05) in the proportion of 0.25–5.0 mm aggregates, and the increase in the mean weight diameter and geometric mean weight of the soil aggregates indicated that sepiolite treatments enhanced soil aggregate stability. Furthermore, three–dimensional X–ray computed tomography imaging showed that sepiolite treatments resulted in an increase in the total area, average size, and pore perimeter of aggregates, with the maximum values being 1.63–, 1.41–, and 1.401–fold higher than those of the corresponding control groups, respectively. The highest values of soil organic carbon and particulate organic carbon were obtained in 1.5% sepiolite–treated soils and were 2.07– and 1.91–fold higher than those of the control groups, respectively. Additionally, the level of organic carbon functional groups in the bulk soil and different particle–size aggregates generally increased with increasing sepiolite application. Overall, sepiolite, as a soil amendment, not only reduced toxic element bioavailability and uptake by plants but also enhanced soil structure and function.

Influence of Tillage, Straw-Returning and Mineral Fertilization on the Stability and Associated Organic Content of Soil Aggregates in the North China Plain

Agricultural management, such as tillage and straw-returning, affect soil fertility and nutrient cycling in agroecosystems. With the increasing food demand and challenges imposed by climate change, these effects on soil fertility need to be closely monitored, so that short-term agricultural intensification should not threaten the long-term productivity of the land. Therefore, the main objective of this study was to examine the long-term effects of different management practices on soil aggregate stability and associated organic carbon (OC) and nitrogen (N) over a 33-year period in the croplands of the North China Plain. Bulk soils from the surface and subsurface layers were fractionated using the wet sieving approach. The results showed that the silt + clay (SC) fractions (&lt;0.053 mm) were predominant, accounting for 32–56% of the mass at the 0–20 cm depth, and accounting for 41–55% of the mass at the 20–40 cm depth. Additionally, long-term (33 years) no-tillage management and straw-returning at different application rates increased the mass of large soil macroaggregates (LMA), the LMA- and macroaggregate-associated OC content, but decreased the SC-associated OC content. Mineral N and P fertilizers had a minor effect on the stabilization of soil aggregates. The treatment with straw significantly increased the mean weight diameter (MWD) and geometric mean diameter (GWD), compared with the treatment without straw. Our results indicate that carefully regulated management practices would enhance soil aggregate stability, associated OC and N content in the intensive agroecosystem.

Drought-tolerant plant growth-promoting rhizobacteria isolated from jujube (Ziziphus jujuba) and their potential to enhance drought tolerance

Plant growth-promoting rhizobacteria (PGPR) have important roles in improving plant growth and alleviating stress induced damage under drought stress conditions. The aims of this study are: 1) to isolate and identify drought-tolerant PGPR from rhizosphere soil of jujube, a drought-tolerant plant grown in semi-arid and arid regions; and 2) to evaluate the effects of inoculation with the isolated strains on the growth and physiological responses of jujube seedlings under drought stress conditions. Rhizosphere bacteria with 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity were isolated from the rhizosphere of jujube and were identified by 16S rDNA sequencing analysis. Then, the isolates were screened for drought tolerance and plant growth promoting activities. The growth and physiological changes of jujube under drought stress, including the plant height, shoot and root dry matter, malondialdehyde (MDA), indoleacetic acid (IAA), abscisic acid (ABA) content, superoxide dismutase (SOD), and peroxidase (POD) activity, were also detected. Eight ACC deaminase-producing bacterial strains were isolated and identified as Pseudomonas, Bacillus, and Serratia. Under drought stress conditions, Pseudomonas lini and Serratia plymuthica significantly increased plant height, shoot and root dry matter, and relative water content. Moreover, malondialdehyde and ABA levels were decreased, and antioxidant enzyme activities were increased. In addition, they also enhanced soil aggregate stability. The best effect was observed with mixed inoculation. Strains of Pseudomonas lini and Serratia plymuthica played an important role in enhancing tolerance of jujube seedling and can be considered as promising bioinoculants of jujube.

Enhanced soil aggregate stability limits colloidal phosphorus loss potentials in agricultural systems

BackgroundColloid-facilitated phosphorus (P) transport is recognized as an important pathway for the loss of soil P in agricultural systems; however, information regarding soil aggregate-associated colloidal P (Pcoll) is lacking. To elucidate the effects of aggregate size on the potential loss of Pcoll in agricultural systems, soils (0–20 cm depth) from six land-use types were sampled in the Zhejiang Province in the Yangtze River Delta region, China. The aggregate size fractions (2–8 mm, 0.26–2 mm, 0.053–0.26 mm and < 0.053 mm) were separated using the wet sieving method. Colloidal P and other soil parameters in aggregates were analyzed.ResultsOur study demonstrated that 0.26–2 mm small macroaggregates had the highest total P (TP) content. In acidic soils, the highest Pcoll content was observed in the 0.26- to 2-mm-sized aggregates, while the lowest was reported in the < 0.053 mm (silt + clay)-sized particles, the opposite of that revealed in alkaline and neutral soils. Paddy soils contained less Pcoll than other land-use types. The proportion of Pcoll in total dissolved P (TDP) was dominated by < 0.053 mm (silt + clay)-sized particles. Aggregate size strongly influenced the loss potential of Pcoll in paddy soils, where Pcoll contributed up to 83% TDP in the silt + clay-sized particles. The Pcoll content was positively correlated with TP, Al, Fe, and the mean weight diameter. Aggregate-associated total carbon (TC), total nitrogen (TN), C/P, and C/N had significant negative effects on the contribution of Pcoll to potential soil P loss. The Pcoll content of the aggregates was controlled by the aggregate-associated TP and Al content, as well as the soil pH value. The potential loss of Pcoll from aggregates was controlled by its organic matter content.ConclusionWe concluded that management practices that increase soil aggregate stability or its organic carbon content will limit Pcoll loss in agricultural systems.

Effects of maize straw and its biochar application on organic and humic carbon in water-stable aggregates of a Mollisol in Northeast China: A five-year field experiment

In agricultural ecosystems, one optimized crop residue management practice, i.e., incorporating biochar produced from crop residues via pyrolysis to the soil, is considered a promising technology for mitigating climate change and improving soil quality. However, the potential mechanisms are still not well known. In this study, a five-year (2011–2015) field experiment in a Mollisol of Northeast China that included four treatments, i.e., CK (no fertilizer), NPK (mineral nitrogen, phosphorus and potassium fertilizers), NPKS (NPK plus maize straw) and NPKB (NPK plus maize straw-derived biochar), was conducted to evaluate the effects of maize straw and its derived biochar application on the following: 1) the size distribution and water stability of soil aggregates; 2) the concentrations of organic and humic carbon (C) in bulk soil and water-stable aggregate fractions; and 3) the chemical compositions of organic and humic C in water-stable aggregate fractions. Compared with the CK and NPK treatments, the proportion of macroaggregates (>0.25 mm) [mainly large macroaggregates (>2 mm)] increased whereas the proportions of microaggregates (0.25–0.053 mm) and silt + clay fractions (<0.053 mm) decreased in NPKS and NPKB treatments, resulting in the mean weight diameter (MWD) of soil aggregates being higher under NPKS and NPKB treatments than under CK and NPK treatments. The concentrations of organic and humic C in bulk soil and aggregate fractions were also generally higher under NPKS and NPKB treatments than under CK and NPK treatments. The treatment effects were more apparent for NPKB than for NPKS. With respect to other treatments, the NPKB treatment significantly increased the ratios of macroaggregate- to microaggregate-associated organic C as well as humin C. The solid-state 13C cross-polarization magic-angle-spinning (CPMAS) NMR spectra of small macroaggregates (2–0.25 mm) and its humic acid fraction showed that the NPKS treatment did not alter the proportions of the C functional groups. In contrast, the NPKB treatment clearly decreased the proportions of alkyl C and O-alkyl C but increased the proportion of aromatic C, resulting in the alkyl C/O-alkyl C and hydrophobic C/hydrophilic C ratios being higher whereas the aliphatic C/aromatic C ratio was lower under NPKB than under other treatments. These findings indicate that the application of maize straw biochar enhanced soil aggregate stability and aggregate-associated organic and humic C concentrations. Biochar C was preferentially incorporated into macroaggregates and its humin fraction with respect to microaggregates. Moreover, the molecular structure of small macroaggregates and its HA fraction became more stable, hydrophobic and aromatic. Therefore, physical protection through organic C in aggregate fractions, physical-chemical protection through the encapsulation of humic C within aggregate fractions, and physical-biochemical protection through recalcitrant alkyl C and aromatic C within aggregate fractions may be the primary mechanisms for C preservation in biochar-amended soil. Our results suggested that maize straw biochar application was an effective strategy based on the comprehensive goal of mitigating climate change and improving soil quality in Mollisols of Northeast China.

Structural Stability Conditions Soil Carbon Gains from Compost Management and Rotational Diversity

Core Ideas Soil structure and carbon pools were quantified in a 20‐year field crop trial. Compost management influenced soil aggregate size, labile carbon, and total carbon. An increased rotational diversity from one to five crops enhanced soil aggregate stability. Use of moderate compost increased soil carbon by 20% relative to fertilizer. Understanding processes that underlie soil carbon gains and enhance structural stability is key to sustainable production of intensively managed row crops. Long term consequences of crop diversity and interactions with compost management have rarely been tested with economically feasible, moderate rates of organic amendments. We investigated soil aggregation and carbon pools over twenty years on a field crop experiment that allowed quantification of the impact of rotational diversity within two integrated management regimes, one based on compost (3 Mg ha−1) and the other inorganic fertilizer, both at about 100 kg N ha−1 annually. The Living Field Laboratory (LFL) experimental study where the study was conducted is located at the W.K. Kellogg Biological Station in southwest Michigan. The rotational diversity treatments investigated included continuous corn (Zea mays L.) (CC), corn–soybean [Glycine max (L.) Merr.] rotation (CS), corn–soybean–wheat (Triticum aestivum L.) rotation (CSW), and corn–soybean–wheat rotation with a cover crop (CSWco). Soil C status in 1993 was 2584 g m−2 and by 2013 increased in integrated fertilizer and compost plots to 3026 and 3672 g kg−1, respectively. Compost management enhanced soil labile C, organic C and the proportion of large macroaggregates (&gt;2000 μm size fraction). Rotational diversity did not influence total soil C but was positively associated with soil aggregate stability and aggregate carbon pool size. The study findings were consistent with integrated organic and inorganic nutrient management as interacting positively with crop diversity, to support gains in soil structural stability and C accrual.

Effects of straw and biochar amendments on aggregate stability, soil organic carbon, and enzyme activities in the Loess Plateau, China

Soil from the Loess Plateau of China is typically low in organic carbon and generally has poor aggregate stability. Application of organic amendments to these soils could help to increase and sustain soil organic matter levels and thus to enhance soil aggregate stability. A field experiment was carried out to evaluate the effect of the application of wheat straw and wheat straw-derived biochar (pyrolyzed at 350-550°C) amendments on soil aggregate stability, soil organic carbon (SOC), and enzyme activities in a representative Chinese Loess soil during summer maize and winter wheat growing season from 2013 to 2015. Five treatments were set up as follows: no fertilization (CK), application of inorganic fertilizer (N), wheat straw applied at 8tha-1 with inorganic fertilizer (S8), and wheat straw-derived biochar applied at 8tha-1 (B8) and 16tha-1 (B16) with inorganic fertilizer, respectively. Compared to the N treatment, straw and straw-derived biochar amendments significantly increased SOC (by 33.7-79.6%), microbial biomass carbon (by 18.9-46.5%), and microbial biomass nitrogen (by 8.3-38.2%), while total nitrogen (TN) only increased significantly in the B16 plot (by 24.1%). The 8tha-1 straw and biochar applications had no significant effects on soil aggregation, but a significant increase in soil macro-aggregates (>2mm) (by 105.8%) was observed in the B16 treatment. The concentrations of aggregate-associated SOC increased by 40.4-105.8% in macro-aggregates (>2mm) under straw and biochar amendments relative to the N treatment. No significant differences in invertase and alkaline phosphatase activity were detected among different treatments. However, urease activity was greater in the biochar treatment than the straw treatment, indicating that biochar amendment improved the transformation of nitrogen in the soil. The carbon pool index and carbon management index were increased with straw and biochar amendments, especially in the B16 treatment. In conclusion, application of carbonized crop residue as biochar, especially at a rate of 16tha-1, could be a potential solution to recover the depleted SOC and enhance the formation of macro-aggregates in Loess Plateau soils of China.

Combined application of cyanobacteria with soil fixing chemicals for rapid induction of biological soil crust formation

ABSTRACTCombined applications of cyanobacteria with soil fixing chemicals were investigated to generate artificially induced biological soil crust (BSC). Polyvinyl alcohol (PVA) and Tacki-Spray (TKS7) chemicals composed of bio-polysaccharides and tackifiers were examined under laboratory conditions. Following singular applications of chemicals, the mean weight diameter values of soil treated with TKS7 were 1.4–2.5 times higher than those of soil treated with PVA and thus TKS7 was selected for further tests for application with cyanobacteria (Nostoc Vaucher ex Bornet & Flahault, Phormidium Kützing ex Gomont, and Scytonema arcangeli Bornet ex Flahault). Combined application of cyanobacteria and different concentrations of TKS7 enhanced soil aggregate stability, resulting in mean weight diameter values of 0.58–0.69 mm and was comparable to TKS7 singular application (0.18–0.40 mm). Surface hardness values were also highly improved by the combined application of cyanobacteria with TKS7 (4.5 MPa) compared to singular treatment of cyanobacteria (2.3 MPa). In addition, superabsorbent polymer (SAP) was applied as a water-holding material and nutrient supplement in soil. The SAP promoted cyanobacterial cell growth under dry conditions. Chlorophyll a content of soil was improved by the addition of SAP (CST1: 2.93 µg g−1) compared to singular treatment of cyanobacteria (C: 2.25 µg g−1). These results suggest that combined application of cyanobacteria with TKS7 and SAP can induce BSC formation faster than singular application of cyanobacteria. The novel method presented herein can be applied to restoration of degraded soils in arid and semiarid areas.

Restoration techniques affect soil organic carbon, glomalin and aggregate stability in degraded soils of a semiarid Mediterranean region

The first step to restoring degraded mine soils from calcareous quarries in semiarid environments, usually without soil structure, mainly consists in creating a structured topsoil with suitable physical, chemical and biological properties. The aim of this study is to determine the effects of organic amendments and mulches on soil aggregate stability and aggregation-associated soil characteristics, six years after beginning experimental restoration in the Gádor Mountains (Almería, SE Spain). Experimental plots were set up to test two organic amendments (sludge and compost) and two mulches (gravel and woodchip) and their respective control plots. Soil samples from neighboring undisturbed soils were used as the quality reference threshold. The tested variables were total organic C (TOC), glomalin-related soil protein (GRSP), easily extractable glomalin-related soil protein (EE-GRSP) and water aggregate stability evaluated by both wet sieving (WS) and water-drop test (WDT). Relationships among the measured soil properties were checked in order to assess the best indicators for the most suited restoration practices. After 6years, the results showed that the combination of organic amendments and mulches enhanced soil aggregate stability and the content of aggregate binding agents such as TOC and glomalin. Nevertheless, the role of organic amendments, especially compost, was more important than mulch treatments in increasing TOC and glomalin, showing the closest values to the undisturbed reference soils (over 30gkg−1 for TOC and 3.5gkg−1 for GRSP). Despite the considerable improvement in water stable aggregates found in sludge-amended plots (average mean weight diameter of 2.13mm in WS, and 25-drop impacts in WDT), the reference soils provided the highest values (average mean weight diameter of 3.32mm in WS, and 99-drop impacts in WDT). The lack of a good correlation between soil structure-related variables restricted the evaluation of the real effects of restoration treatments, and suggested considering other soil properties (e.g., hydrophobicity, hardening) associated to aggregate stability.

Organic amendment effects on aggregate-associated organic C, microbial biomass C and glomalin in agricultural soils

To evaluate the effects of organic amendments on soil aggregate stability and aggregation-associated soil characteristics, a study was initiated in agricultural soils after 4years of organic amendments. Soil samples were collected from the plow layer (0–20cm) and plow pan (20–40cm) under three cornfield management scenarios: 1) conventional cropping (CK, corn straw removal and no organic manure application), 2) straw retention (SR, incorporation of 9000kgha−1 chopped corn stalk), and 3) manure application (MA, 15,000kgha−1 of chicken manure input). The soil samples were fractionated into three aggregate sizes, i.e., <0.25mm (microaggregates), 0.25–1mm (small macroaggregates), and >1mm (macroaggregates). The results showed that organic amendments increased the proportion of macroaggregate and mean weight diameter (MWD), especially in the plow layer. The macroaggregates accounted for 43.87% and 49.96% of the total soil weight in the SR and MA. The distribution patterns of soil organic C (SOC), microbial biomass C (MBC), total glomalin-related soil protein (TG) and easily extracted glomalin-related soil protein (EEG) within aggregate sizes were affected by organic treatments. In the plow layer, the SOC in MA increased by 35.5% in macroaggregates compared with CK, and significant differences in MBC, TG and EEG in macroaggregates were also found among organic amendments. MWD was positively correlated with SOC, MBC, TG and EEG. Organic amendment, either through crop residues or manure application, enhanced soil aggregate stability through the positive effects on soil binding agents including SOC, MBC and glomalin-related soil protein. The links among binding agents or between binding agents and aggregate stability were aggregate scale-dependent.

Organic Amendments to a Wheat Crop Alter Soil Aggregation and Labile Carbon on the Loess Plateau, China

The Loess Plateau in China is one of the most severely eroded areas in the world. Understanding the characteristics of soil aggregation and the distribution of soil organic carbon (SOC) in aggregates on the plateau is essential for improving regional soil quality. A 2-year study was conducted in a wheat cropping system on the plateau to investigate short-term responses of soil aggregation measured via water stability and total as well as labile SOC (permanganate-oxidizable C [POXC]) fractions to organic amendments (low-, medium-, and high-level maize stalks, stalk composts, and cattle manure) combined with inorganic fertilization (nitrogen/phosphorous/potassium [NPK]). Compared with NPK fertilization, combined organic amendments enhanced soil aggregate stability mostly for 5-to 0.5-mm size classes. Among the treatments, high-level maize stalk plus NPK was associated with the greatest water stability of all aggregates and lowest aggregate deterioration rate (11.3%), followed by cattle manure plus NPK (21.2%). In the 0- to 20-cm soil layer, the SOC content had no significant changes among treatments, whereas the POXC content was significantly higher in the organically amended treatments (especially cattle manure plus NPK, 108.6 %) than in the NPK treatment (P< 0.05). In most aggregate size classes, the SOC content had no significant differences between the organically amended and NPK treatments, whereas the POXC content was significantly higher in the former than in the latter (P< 0.05). There were significant positive relations between the proportions of water-stable aggregates and POXC content (P< 0.05). Application of high-level maize stalk or manure plus NPK was effective for improving soil structure and SOC sequestration of the loess soil.