Improved Aggregate Stability Research Articles

Tillage and mulching effects on carbon stabilization in physical and chemical pools of soil organic matter in a coarse textured soil

Characterization of soil organic carbon (SOC) in terms of size, storage inside aggregates and chemical recalcitrance is vital to understand mechanisms of its stabilization and to devise climate smart agricultural management practices. Tillage and residue retention are known to influence carbon (C) storage within soil aggregates and its accumulation as particulate organic matter as well as organomineral complexes. However, the effect of tillage and crop residue retention on C stabilization in coarse textured soils through various mechanisms is not well understood. We studied the effect of conservation agriculture involving no tillage with surface residue mulch (NTM) in maize-wheat sequence on particulate (POC) and mineral associated organic C (MinOC), C storage within aggregates and acid non-hydrolysable C (NHC) in a sandy loam soil. Compared to conventional tillage without residue retention (CTM0), the NTM improved SOC stocks by 23% in top 15-cm soil and significantly increased coarse POC (∼92 to 284%) and fine POC (67 to 123%) with relatively little effect on MinOC. This indicated that MinOC had relatively small contribution towards SOC stabilization in coarse textured sandy loam soils with limited potential to form organomineral complexes. The results further showed that the effects of NTM were brought about by improved aggregate stability and C preservation inside macroaggregates of size >1 mm. Furthermore, greater amount of SOC (2.64 g C kg−1) and macroaggregate associated C (0.35–0.59 g C kg−1) occurred in recalcitrant forms (NHC) under NTM compared to conventional (CT) and deep tillage (DT). The NTM also impacted the belowground C input through improved root length density (RLD) and development of fibrous roots expressed as specific root length (SRL), which influenced SOC build-up and stabilization. It is concluded that compared to the existing practice of CTM0, the conservation agriculture involving NT with residue retention leads to SOC sequestration in coarse textured soils. Its large scale adoption, besides helping in climate change mitigation will lead to soil health improvement.

Temporal Variation in Soil Resistance to Rill Erosion in Cropland of the Dry—Hot Valley Region, Southwest China

In croplands, soil erosion resistance varies with both natural processes and human disturbances. To clarify the temporal variation in soil erosion resistance, nine cropland plots with three treatments (continuous fallow, fallow after tillage and tillage with corn) were established in the dry–hot valley region of China. A total of 144 field runoff simulation experiments were conducted from May to October to measure the soil detachment rate (Dc), rill erodibility (Kr) and critical shear stress (τc). The results revealed that the natural dry—wet alternation had little influence on the continuous-fallowed soil erosion resistance. On the other hand, the tillage disturbance that occurred in May sharply increased the Dc and Kr to 2.24 and 3 times that of the continuous-fallow treatment, respectively. Then, the erosion resistance could be enhanced with surface consolidation for the fallow-after-tillage treatment. However, after three months of fallow, the Kr was still 89.5% of the fresh tilled soil. In contrast, crop growth could significantly improve aggregate stability and reduce the Kr to 38.2% in August and even further to 23.7% in October compared to the fresh tilled soil. It could be concluded that crop growth is more efficient in enhancing erosion resistance than the mechanical effect. The above results would benefit from the accurate modeling of cropland soil erosion dynamics and guide agricultural management in dry–hot climate regions.

Organic carbon sequestration by Fe oxides in aggregates in a Pinus massoniana conifer-broadleaf mixed forest

Stand conversion and Fe/Al oxides are potential variables that collectively determine soil organic carbon (SOC) sequestration. However, the mechanism of SOC sequestration provided by Fe/Al oxides in the conversion of Pinus massoniana plantations (PMs) into mixed conifer-broadleaf forests remains unknown. The increase in SOC content (4.08–151.80%) in PM-converted mixed forest was related to the significant increase in the content of all OC fractions. Light fraction (LF) contents were generally higher in larger aggregates and mixed forest aggregates, reflecting the greater plant C input and the driving effect of soil aggregation in mixed conifer-broadleaf forests. This plant C input to the soil as the core of aggregate formation provides physical protection from particulate organic carbon (POC), but this physical protection was achieved by the greater free Fe oxides (FeD) and amorphous Fe oxides (FeO) content in the mixed forests acting as an aggregate stabiliser. Potential processes are driven by pH-driven FeD and FeO binding to silt to improve aggregate stability and pore occlusion, which promotes physical protection of coarse intra-aggregate particulate organic carbon (c-iPOC). Moreover, this process reduces macroaggregate turnover (c-iPOC/f-iPOC ratio), allowing the transfer of c-iPOC in macroaggregates to microaggregate-associated fine intra-aggregate particulate organic carbon (f-iPOC). The higher mineral-associated organic carbon (MOC) content of conifer-broadleaf mixed forest soils was mainly derived from silt+clay and controlled by chemisorption of Fe/Al oxides (especially complex Fe oxides, FeP), but Fe/Al oxides do not provide physical protection for MOC. In addition, LF, c-iPOC and f-iPOC were significantly positively correlated with SOC content, reflecting the sensitivity of aggregate structure development and stabilization in predicting SOC sequestration, but these OC fractions will shift more towards MOC as conifer-broadleaf mixed forests develop. Overall, Fe oxides provide SOC accumulation and long-term stability by OC fractions associated with physical protection and chemisorption in the conversion of PM into mixed conifer-broadleaf forests.

Vegetation restoration improved aggregation stability and aggregated-associated carbon preservation in the karst areas of Guizhou Province, southwest China.

The change in the soil carbon bank is closely related to the carbon dioxide in the atmosphere, and the vegetation litter input can change the soil organic carbon content. However, due to various factors, such as soil type, climate, and plant species, the effects of vegetation restoration on the soil vary. Currently, research on aggregate-associated carbon has focused on single vegetation and soil surface layers, and the changes in soil aggregate stability and carbon sequestration under different vegetation restoration modes and in deeper soil layers remain unclear. Therefore, this study aimed to explore the differences and relationships between stability and the carbon preservation capacity (CPC) under different vegetation restoration modes and to clarify the main influencing factors of aggregate carbon preservation. Grassland (GL), shrubland (SL), woodland (WL), and garden plots (GP) were sampled, and they were compared with farmland (FL) as the control. Soil samples of 0-40 cm were collected. The soil aggregate distribution, aggregate-associated organic carbon concentration, CPC, and stability indicators, including the mean weight diameter (MWD), fractal dimension (D), soil erodibility (K), and geometric mean diameter (GMD), were measured. The results showed that at 0-40 cm, vegetation restoration significantly increased the >2 mm aggregate proportions, aggregate stability, soil organic carbon (SOC) content, CPC, and soil erosion resistance. The >2 mm fractions of the GL and SL were at a significantly greater proportion at 0-40 cm than that of the other vegetation types but the CPC was only significantly different between 0 and 10 cm when compared with the other vegetation types (P<0.05). The >2 mm aggregates showed a significant positive correlation with the CPC, MWD, and GMD (P<0.01), and there was a significant negative correlation with the D and K (P<0.05). The SOC and CPC of all the vegetation types were mainly distributed in the 0.25-2 mm and <0.25 mm aggregate fractions. The MWD, GMD, SOC, and CPC all gradually decreased with increasing soil depth. Overall, the effects of vegetation recovery on soil carbon sequestration and soil stability were related to vegetation type, aggregate particle size, and soil depth, and the GL and SL restoration patterns may be more suitable in this study area. Therefore, to improve the soil quality and the sequestration of organic carbon and reduce soil erosion, the protection of vegetation should be strengthened and the policy of returning farmland to forest should be prioritized.

Leguminous cover orchard improves soil quality, nutrient preservation capacity, and aggregate stoichiometric balance: A 22-year homogeneous experimental site

Soil and water conservation measures, widely promoted to control soil erosion in erosive orchards, can alter soil aggregates, thereby influencing the soil quality index (SQI). However, it's still unclear how these measures affect soil aggregate nutrients, stoichiometry, and their association with SQI at a long-term timescale. This study focused on a 22-year homogeneous orchard in subtropical hilly region. Five soil and water conservation measures, namely clean tillage (CT), engineering measures (EM), tillage measures (TM), non-leguminous biological measures (NLBM), and leguminous biological measures (LBM), were implemented. Sampling depths were 0–20 cm, 20–40 cm, and 40–60 cm. The results revealed that LBM significantly enhanced SQI across the soil profile, increased the proportion of macroaggregates, and improved aggregate stability, soil organic carbon, and total nitrogen. Additionally, LBM demonstrated the highest capacity for carbon and nitrogen preservation. Soil stoichiometry revealed carbon and nitrogen limitations in the orchard soils, and leguminous cover proved effective in alleviating these limitations and maintaining the stoichiometric balance of soil aggregates. Under a long-term timescale, these measures mitigated or even surpassed the impact of soil depth on soil aggregates and SQI. The improvement of orchard SQI through the measures was primarily achieved by enhancing aggregate stability. There was no significant correlation between soil organic carbon and SQI in relation to fruit yield, ascribed to the intense competition for water and nutrients between cover plants and citrus trees. In conclusion, LBM emerges as the most beneficial soil and water conservation measure for enhancing orchard SQI, preserving nutrients, and maintaining aggregate stoichiometric balance. It holds the potential to improve orchard yield and contribute to sustainable development.

Long-Term Maize Intercropping with Peanut and Phosphorus Application Maintains Sustainable Farmland Productivity by Improving Soil Aggregate Stability and P Availability

The intercropping of maize (Zea mays L.) and peanuts (Arachis hypogaea L.) (M||P) significantly enhances crop yield. In a long-term M||P field experiment with two P fertilizer levels, we examined how long-term M||P affects topsoil aggregate fractions and stability, organic carbon (SOC), available phosphorus (AP), and total phosphorus (TP) in each aggregate fraction, along with crop yields. Compared to their respective monocultures, long-term M||P substantially increased the proportion of topsoil mechanical macroaggregates (7.6–16.3%) and water-stable macroaggregates (&gt;1 mm) (13.8–36.1%), while reducing the unstable aggregate index (ELT) and the percentage of aggregation destruction (PAD). M||P significantly boosted the concentration (12.9–39.9%) and contribution rate (4.1–47.9%) of SOC in macroaggregates compared to single crops. Moreover, the concentration of TP in macroaggregates (&gt;1 mm) and AP in each aggregate fraction of M||P exceeded that of the respective single crops (p &lt; 0.05). Furthermore, M||P significantly increased the Ca2-P, Ca8-P, Al-P, and Fe-P concentrations of intercropped maize (IM) and the Ca8-P, O-P, and Ca10-P concentrations of intercropped peanuts (IP). The land equivalent ratio (LER) of M||P was higher than one, and M||P stubble improved the yield of subsequent winter wheat (Triticum aestivum L.) compared with sole-crop maize stubble. P application augmented the concentration of SOC, TP, and AP in macroaggregates, resulting in improved crop yields. In conclusion, our findings suggest that long-term M||P combined with P application sustains farmland productivity in the North China Plain by increasing SOC and macroaggregate fractions, improving aggregate stability, and enhancing soil P availability.

Combined tillage: A management strategy to improve rainfed maize tolerance to extreme events in northwestern China

Climate warming has increased the frequency of droughts and excessive precipitation, adversely affecting crop growth, particularly under traditional intensive tillage. No-till improves crop tolerance to extreme events by reducing soil evaporation and improving soil structural stability to enhance soil water storage capacity and crop resistance, but long-term mono-no-till cakes the soil, reducing crop yield. Combining intensive tillage with no-till can compensate for some deficiencies arising from conventional tillage or single no-till. A three-year field experiment was conducted in wet (2020) and normal (2019 and 2021, where a drought event occurred in 2021) years to study the effect of tillage practices on summer maize productivity under different precipitation types. Treatments included conventional tillage (CT), no-tillage (NT), ridge cultivation with no-tillage (RNT), and conventional tillage of winter wheat combined with no-tillage of summer maize (NC). Compared with NT, NC and RNT significantly reduced soil bulk density and increased soil porosity in the 0–20 cm soil layer. Compared with CT, NC and RNT significantly improved aggregate stability, NC increased available soil water storage by 19.7% in the dry season (P < 0.05), and NC and RNT significantly reduced lodging rate in the rainy season. Over the three years, NC and RNT maintained higher maize yields (NC: 10.3 t ha–1 and RNT: 10.0 t ha–1) than CT (9.2 t ha–1), and NC had significantly higher yield stability than CT. Meanwhile, NC and RNT had higher precipitation use efficiency (PUE; NC: 21.2 kg ha–1 mm–1, RNT: 20.7 kg ha–1 mm–1) than NT (20.1 kg ha–1 mm–1) or CT (19.1 kg ha–1 mm–1). In terms of combined productivity, NC and RNT provide a more suitable soil environment for crop growth and maintain higher yield than NT and CT. NC rotation is recommended as the optimal tillage system for sustainable crop production under semi - arid agricultural conditions. RNT can be extended to areas prone to flooding with abundant rainfall. These results offer a benchmark for future studies on regional maize production under climate change.

Oriental beech roots improve soil aggregate stability and reduce soil detachment rate in forest lands

In many forestlands, such as Saravan Forest Park, the high capacity of soil detachment from deforestation and subsequent ecological restoration are important issues that need detailed information about plant and tree species for the objectives of soil conservation. To determine if some species are more helpful for the stability of soil aggregates and thus reducing soil erosion, we examined Oriental beech species, compared to three other species (Crataegus ambigue, Primula heterochroma and Rubus persicus) in the Saravan forest park, and measured how root characteristics (root biomass, root length and root weight density) influenced mean weight diameter of aggregates (MWD) and soil detachment rate (Dc). For measuring Dc, undisturbed samples collected from soils under the four studied species and subjected to five slopes (from 4.8 to 31.4%) and five water discharges (from 0.26 to 0.65 l m−1 s−1) by a hydraulic flume. Results showed that Oriental beech roots can significantly influence soil aggregate stability. MWD was greater in soil under Oriental beech species characterized by high values of root biomass, root length and root weight density. Moreover, Dc was significantly lower in soils with Oriental beech species compared to three other species. Pearson's correlation matrix showed a strong positive correlation between MWD and the root characteristics (P < 0.01) (R2 = 0.8). Also, the clustering of soils among the studied species by the principal component analysis (PCA) revealed a clear difference based on the root characteristics and MWD. Generally, this study showed that, compared with other species, the root system of Oriental beech is more effective in the stabilization of slope by the binding effect on the soil, thus improving aggregate stability and reducing soil detachment rates.

Does Increasing the Diversity of Small Grain Cropping Systems Improve Aggregate Stability and Soil Hydraulic Properties?

Wheat (Triticum aestivium L.) and barley (Hordeum vulgare L.) are two commonly grown cereal crops in the northern Great Plains. Adding other crops such as field pea (Pisum Sativum L.), canola (Brassica napus L.), or camelina (Camelina sativa L.) to wheat or barley cropping systems may improve soil quality. However, little is known about the effects of including oilseeds in small grain cropping systems on soil physical properties. We sampled an 8-year dryland study with 10 different cropping systems including continuous spring wheat, continuous winter wheat, continuous barley, pea–spring wheat, pea–barley, pea–winter wheat, pea–barley–camelina–spring wheat, pea–barley–canola–spring wheat, pea–winter wheat–camelina–spring wheat and pea–winter wheat–canola–spring wheat. We measured dry aggregate stability, wet aggregate stability, water retention, hydraulic conductivity, bulk density and total carbon. Continuous barley and winter wheat had a higher fraction of large dry soil aggregates, whereas the pea–barley–canola–spring wheat and pea–spring wheat cropping systems had a higher fraction of small aggregates in the 0–15 cm depth. However, wet aggregate stability, water retention, bulk density, hydraulic conductivity and soil carbon concentration were not affected by the cropping system in the 0–15 cm depth. Diversifying small grain cropping systems by adding canola or camelina oil seeds and peas generally did not affect soil physical properties at this location.

Biochar Addition with Water and Fertilization Reduction Increases Soil Aggregate Stability of 0–60 cm Soil Layer on Greenhouse Eggplant in Mollisols

Biochar application affects the soil organic carbon (SOC) content and distribution, which is relevant to facility agriculture and soil aggregates. However, how the fertilization management of facility agriculture affects the SOC content and aggregate stability at different soil depths in Mollisols is unclear. Intended to provide a basis for developing a reasonable fertilizer amount when adding biochar, the facility vegetable eggplant in Northeast China was used to explore the effects of biochar addition on the distribution and SOC content of whole soils and the organic carbon (OC) content of aggregates of each size in the profile (0–100 cm) of Mollisols. Three treatments were set up: WF (conventional application amounts of water and fertilizer), WFB (conventional application amounts of water and fertilizer and added biochar), and 80%W80%FB (20% water reduction and 20% fertilizer reduction and added biochar). The results demonstrated that the 80%W80%FB treatment significantly increased the SOC content by 56.1% and 34.0% in whole soils at a 0–20 cm soil depth compared to WF and WFB treatments, respectively. Simultaneously, compared with WF and WFB treatments, the significant increase in the OC content of 1–0.25 mm sized aggregates of 81.4–130.2% and 4.3–10.1% and the enhanced proportion of &gt;2 mm sized aggregates of 0.22–16.15- and 0.33–0.83-fold both improved aggregate stability in the 0–20 cm soil layer under the 80%W80%FB treatment, which was proven to result in 32.6% and 30.6% increments in the weight diameter (MWD) value. Therefore, biochar addition with water and fertilizer reductions increases surface soil aggregate stability for greenhouse eggplants in Mollisols.

Soil aggregate variation in two contrasting rice straw recycling systems for paddy soil amendment over two years

ABSTRACT Soil aggregate is important to soil quality. Straw return is beneficial for soil amendment, but the effects of straw and straw-derived biochar on aggregate formation and stability in paddy soil are unclear. This study carried out a field experiment for 2 years in Northeast China with four treatments: conventional fertilization (CF), straw (ST, 7.5 t ha−1 year−1), biochar (BC, 2.5 t ha−1 year−1), and biochar-based fertilizer (BCF, 0.75 t ha−1 year−1). Compared with the CF and BCF, BC and ST improved the macroaggregates and significantly increased soil total carbon and aggregate organic carbon, indicating a sustained positive role in promoting the formation and stability of aggregates. BC significantly improved aggregate stability. Correlation analysis showed that macroaggregates (2–0.25 mm) can be increased by increasing the heavy fraction organic carbon (HFOC), BC and ST significantly increased the HFOC, and BC had a greater effect. Scanning electron microscopy (SEM) showed that the combination of biochar and soil particles can be captured with strong water scouring. BCF showed an increasing trend in the formation and stability of soil aggregates. In comparison, biochar had a greater effect on promoting the formation of macroaggregates and the stability of soil aggregates with a significant sustainable effect.

Effects of cyanobacteria- and moss-biocrusts on soil aggregate stability and splash erosion in croplands of the China Mollisols area.

To investigate the effects of biocrusts development on aggregate stability and splash erosion of Mollisols and to understand its function in soil and water conservation, we collected biocrusts (cyano crust and moss crust) samples in croplands during the growing season and measured the differences in aggregate stability between biocrusts and uncrusted soil. The effects of biocrusts on reduction of raindrop kinetic energy were determined and splash erosion amounts were obtained with single raindrop and simulated rainfall experiments. The correlations among soil aggregate stability, splash erosion characteristics, and fundamental properties of biocrusts were analyzed. The results showed that compared to uncrusted soil, the cyano crust and the moss crust decreased the proportion of soil water-stable aggregates <0.25 mm by 10.5% and 21.8%, respectively, while their soil water-stable aggregates 5-10 mm were 4.0 and 8.8 times as that of uncrusted soil. In contrast to uncrusted soil, the macroaggregate content (R0.25), mean weight diameter (MWD), and geometric mean diameter (GMD) of biocrusts were 31.5%, 76.2%, and 33.5% higher, respectively. In addition, biocrusts reduced raindrop kinetic energy by an average of 0.48 J compared to uncrusted soil. The breakthrough raindrop kinetic energy of cyano crust and moss crust were 2.9 and 26.2 times as that of uncrusted soil, while the reduction of raindrop kinetic energy by cyano crust with high biomass was 1.3 and 6.6 times as that of medium and low biomass, respectively. Under the single raindrop and simulated rainfall conditions, biocrusts reduced splash erosion amounts by 47.5% and 79.4%, respectively. The proportion of aggregates >0.25 mm in the splash soil particles of biocrusts (37.9%) was 40.3% lower than that of uncrusted soil, while the proportion of aggregates >0.25 mm decreased as biocrust biomass increased. Moreover, the aggregate stability, splash erosion amount, and fundamental properties of biocrusts were significantly correlated. The MWD of aggregates was significantly and negatively correlated with the splash erosion amount under single raindrop and simulated rainfall conditions, indicating that the improved aggregate stability of surface soil caused by biocrusts accounted for reducing splash erosion. The biomass, thickness, water content, and organic matter content of biocrusts had significant effects on aggregate stability and splash characteristics. In conclusion, biocrusts significantly promoted soil aggregate stability and reduced splash erosion, which had great significance to soil erosion prevention and the conservation and sustainable utilization of Mollisols.

Soil Aggregates Are Governed by Spacing Configurations in Alfalfa-Jujube Tree Intercropping Systems

Soil aggregates play an important role in affecting the structural stability of the soil, and it is important to understand the relationship between soil aggregate stability and crop yield in herbage-fruit tree intercropping systems. In this study, we determined the optimal spacing configurations for improving aggregate stability while increasing crop yields in alfalfa-jujube intercropping systems. The treatments included three intercropping patterns, i.e., the distances between alfalfa and jujube at 0.5 m (IP0.5m), 1 m (IP1m), and 1.45 m (IP1.45m), along with monoculture alfalfa (CKAL) and jujube (CKJU). The results showed that IP0.5m, IP1m, IP1.45m, and CKJU effectively improved soil aggregate structure compared to CKAL. The IP1m spacing significantly increased the amounts of macro-aggregates (8.2%), and improved soil mechanical properties and aggregate stability among the other treatments, which was partly attributable to increased mean weight diameter (13.6%) and decreased soil aggregate destruction rate of water-stable aggregates (2.9%). The results of the principal component analysis showed that IP1m treatments had a positive effect on PC1. The one-meter spacing of jujube-to-alfalfa intercropping optimized the soil structure while improving the yield (8.3%); thus, it can be considered the most suitable intercropping spacing configuration for growing alfalfa in jujube plantations.

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.

Working with UK farmers to investigate anecic earthworm middens and soil biophysical properties

AbstractThe conversion from conventional tillage to no‐tillage soil management practices is generally associated with an improvement in aggregate stability and anecic earthworm populations. We worked with UK farmers who measured Lumbricus terrestris midden area (%) and earthworm numbers associated with middens compared to the general soil. They found that middens covered up to 42% of the soil surface. Middened soil (i.e., soil underlying the middens) was associated with significantly more earthworms than the general soil (i.e., non‐middened soil) in agreement with research from scientific field trials. We compared the biophysical properties of middened soil to general soil across an experimental field trial recently converted to no‐tillage soil management practices. We measured water‐stable aggregation, soil porosity at scales relevant to water storage and gas diffusion and invertebrate feeding activity. Middened areas covered up to 13% of the field trial and were associated with significantly improved aggregate stability and porosity compared to the general soil. Our findings highlight the importance of considering middens when surveying soil quality and health in arable systems.

Effects of soil erosion and soil amendment on soil aggregate stability in the cultivated-layer of sloping farmland in the Three Gorges Reservoir area

Soil aggregate stability is an important parameter that indicates soil resistance to erosion and the potential productivity of sloping farmland. The cultivated-layer (0–20 cm) of typical sloping purple soil (entisol) farmland around the Three Gorges Reservoir was studied. In-situ controls test and shovel test were used to determine the response of water stable aggregates to two factors, degree of erosion and soil amendment (CK, no fertilizer; F, chemical fertilizer; and BF, biochar with chemical fertilizer) and to analyze regulating pathways of the rational cultivation layer for sloping farmland. Water stable aggregate content for each soil particle size fraction in the cultivated-layer was significantly different for all degrees of erosion. The fraction of particle size > 5 mm in subsurface soil (10–20 cm) was greater than in topsoil (0–10 cm). Erosion significantly affected soil aggregate stability (WR0.25, >0.25 mm particle size water-stable aggregates content; MWD, mean weight diameter of aggregates; GMD, geometric mean diameter of aggregates) in the cultivated-layer. Both MWD and GMD reached maximums for S-0 (erosion of 0 cm). Comparing all treatments, it is BF that showed greater weight increase for MWD and GMD in topsoil (0–10 cm). Percentage of aggregate disruption consistently increased along downward direction of erosion degrees. Shear strength and penetration resistance, which are soil macrostructure parameters, were used to quantify soil stability in a short time. Treatment BF resulted in the greatest increase in shear strength in topsoil for S-10 (erosion of 10 cm) and significantly decreased penetration resistance. This treatment could significantly improve soil tillage performance and facilitate the formation of a loose upper and compact lower cultivated-layer. Shear strength responded very significantly to the interactive effects of erosion and soil treatment and was more sensitive to soil treatment. These results demonstrated that erosion makes soil less sustainable by disintegrating macroaggregates, and BF is the better soil management practice to effectively improve aggregate stability of erodible cultivated purple soil.

Dynamic Variations of Soil-Formation Indicators in Bauxite Residue Driven by the Integration of Waste Solids and Microorganisms.

Soil-formation process is critical to ecological rehabilitation on bauxite residue disposal areas. In this study, a soil column experiment was taken to assess the dynamic variations of soil-formation indicators in bauxite residue driven by the integration of waste solids and microorganisms. Results showed that the combination of waste solids and microorganisms significantly decreased the alkalinity, accumulated organic carbon content, and improved aggregate stability of bauxite residue. Compared with waste solids treatments, the addition of acid-producing microorganisms enhanced the changes of soil-formation indicators. The integration of waste solids and microorganisms increased the content of aliphatic carbon, presenting low thermal stability in the residues. The integration of waste solids and microorganisms provides a potentially effective method for soil formation and ecological remediation on bauxite residue disposal areas.

Organic fertilization increased soil organic carbon stability and sequestration by improving aggregate stability and iron oxide transformation in saline-alkaline soil

Organic fertilization increased soil organic carbon stability and sequestration by improving aggregate stability and iron oxide transformation in saline-alkaline soil

Soil characteristics and tillage can predict the effect of ‘structure lime’ on soil aggregate stability

Context In Sweden, mixtures of 80–85% ground limestone and 15–20% slaked lime (hereafter, ‘structure lime’) are used in subsidised environmental schemes to improve aggregate stability and mitigate phosphorus losses on clay soils. Aims This study investigated different rates of structure lime application and soil variables on aggregate stability on clay soils, and whether soil properties can predict aggregate stability following structure liming. Methods Increasing application rates of 0–16 t ha−1 of structure lime (SL0, SL4, SL8 and SL16) were tested in 30 field trials in Sweden. Soil aggregates (2–5 mm) were collected 1 year after liming and subjected to two rainfall events in a rain simulator. Key results Leachate turbidity after the second simulated rainfall event decreased significantly (13% and 20%, respectively, in SL8 and SL16) compared with SL0, indicating improved aggregate stability. There was a near-significant interaction (P = 0.056) between treatment and trial. Grouping by initial SR21022_IE1.gif (range 6.2–8.3), clay content (10–61%), soil organic matter content (SOM, 2.2–7.1) and clay mineralogy (SmV index, 0.2–3.8) revealed different effects on turbidity. Discriminant analysis of soil characteristics and four tillage variables correctly classified the outcome for 27 of the 30 trial sites. Conclusions Results show that structure liming can improve aggregate stability 1 year after liming, and can thereby prevent particulate P losses from soils with high clay and SOM content, low SmV index and low initial pH. The discriminant analysis also showed the importance of tillage for the outcome of structure liming. Implications Clay soil characteristics such as SOM and pH significantly affected aggregrate stability after structure liming.

Simple method of coffee-shrub biochar-ozonolysis

Biochar, the pyrolysis product of carbon-rich biomass, renders climate benefits because it helps to sequester carbon in soil. Biochar also improves soil health because it increases the nutrient retention capacity in topsoil, improving aggregate stability and water holding capacity. These benefits contribute to agricultural production because biochar provides a good substrate for nourishing root growth and plant health, thereby contributing to the nation’s food security. Biochar’s contribution depends on the quantity and type of oxygen-containing functional groups. These functional groups are determinants in biochar interactions with nutrients and redox reactions. This study aims to develop a simple and economical method to improve biochar’s agronomic traits through ozonolysis. We evaluated ozonolysis reaction time to oxidize a washed and unwashed coffee shrub biochar (WCSB and CSB, respectively). After the exposure of WCSB and CSB to ozone at different intervals, data from both collected by the FTIR-ATR spectra showed that the bands increased in intensity from 3331 to 3441 cm-1 (O-H band) and 1585 cm-1 (carbonyl functional group band). Besides, we observed a decrease in pH and an increase in specific conductance and soluble organic carbon content with the elapsing time of ozonolysis, demonstrating the effectiveness of ozonolysis in the oxidation of the biochar surface. The increase in the E4/E6 ratio suggests that the saturated products from the ozonolysis process increase with time due to the breakdown of the labile organic carbon and the formation of the functional groups of soluble acidic oxygen bonds through the breakdown of the double bonds of carbon. Furthermore, the results indicated that it is unnecessary to wash the biochar before subjecting it to the ozonolysis process.