Mean Weight Diameter Research Articles

Sodium-rich water containing calcite can stabilize soil macroaggregates in arid regions

Sodium-rich water may deteriorate calcite-stabilize soil. The objective of this work was to determine whether calcite solution prepared with sodium-rich water were capable of forming stable soil macroaggregates. Calcite solutions were 2.6 g Ca2+ L−1 of CaCO3 mixed with water containing 2.6, 5 or 10 g Na+ L−1 from NaCl. Arid desert soil (5 cm layer, packed at 1.1 g cm−3) was moistened with calcite solution at 50% or 75% of the water holding capacity. Then, the calcite-treated soil was incubated for up to 30 d at average 35 °C and 19% relative air humidity. Clay flocculation rate was estimated from the decline in extractable Ca2+ and Na+ concentrations during macroaggregate formation. We observed carbonate precipitation in voids of the macroaggregates using micro-CT scanning, which is evidence of cementation. Aggregate stability was the mean weight diameter of macroaggregates. Macroaggregate stability depends upon calcite interactions with clay, so a higher proportion of Ca2+ to Na+ favors the formation of flocculants and cements the flocculants within macroaggregates with carbonate materials, which is surmised to be sodium carbonate with low resistance to abrasion. There was 40% more cementing material within macroaggregates treated with pure calcite and Ca2+: Na+ solutions than with solutions containing Ca2+: 2 Na+, Ca2+: 4 Na+ and Na+. We conclude that calcite-stabilized macroaggregates will persist longer when formed by a calcite solution with equal proportions of Ca2+:Na+, since macroaggregates disintegrate more quickly when formed from calcite made with brackish water at ratios of Ca2+ ≤ 2 Na+.

Impact of adding xylooligosaccharides encapsulated in butter: Microstructural, optical, rheological and sensory aspects

This study investigated the microstructure, rheological properties, and sensory characteristics of butters produced with free and encapsulated xylooligosaccharides (XOS). Four formulations of butter were processed: BCONT: 0 % w/w XOS (control); BXOS: 20% w/w free XOS; BXOS-ALG: 20% w/w XOS microencapsulated with alginate (XOS-alginate ratio of 3:1 w/w); and BXOS-GEL: 20% w/w XOS microencapsulated with alginate-gelatin (XOS-alginate-gelatin ratio of 3:1:1.5 w/w). The microparticles showed a bimodal distribution, low size and low span values, demonstrating physical stability to be included in emulsions. The XOS-ALG presented surface weighted mean diameter (D3.2) of 90.24 µm, volume-weighted mean diameter (D4.3) of 131.8 µm, and Span of 2.14. In contrast, the XOS-GEL presented D3.2 of 82.80 µm, D4.3 of 141.0 µm, and a Span of 2.46. Products with XOS were characterized by higher creaminess, sweet taste, and lower salty taste than the control. However, the addition form significantly impacted the other evaluated parameters. The utilization of XOS in a free form (BXOS) resulted in smaller droplet sizes (1.26 μm) than encapsulated XOS and control (XOS-ALG = 1.32 µm / XOS-GEL = 1.58 µm, / BCONT = 1.59 µm), and changes in the rheological parameters (higher values of shear stress, viscosity, consistency index, rigidity (J0), and Newtonian viscosity (ηN) and lower elasticity (τ)). Furthermore, it changed the color parameters (more yellow and dark color, lower L* and higher b* values). On the other hand, the utilization of micropaticles of XOS (BXOS-ALG and BXOS-GEL) kept shear stress, viscosity, consistency index, rigidity (J0), and elasticity (τ) more similar to control. The products had a less intense yellow color (lower b* values) and was perceived with more consistency and butter taste. However, the presence of particles was perceived by consumers. The results suggest that consumers were more attentive to reporting flavor-related attributes than texture. In conclusion, adding microparticles of XOS could improve butter's rheological and sensory properties. In conclusion, adding microparticles of XOS could improve butter's rheological and sensory properties.

Responses of soil organic carbon cycle to land degradation by isotopically tracing in a typical karst area, southwest China.

The loss of soil organic carbon (SOC) under land degradation threatens crop production and reduces soil fertility and stability, which is more reflected in eco-sensitive environments. However, fewer studies simultaneously compared SOC variations and δ13CSOC compositions under diverse land uses, especially in karst areas. Soil profiles from two agricultural lands and a secondary forest land were selected to analyze SOC contents and their stable isotope composition (δ13CSOC) in a typical karst area located in southwest China to understand the response of the SOC cycle to land degradation. Moreover, the relationships between SOC contents and mean weight diameter (MWD) and soil erodibility (K) factor were comprehensively analyzed for assessing the response of SOC to soil degradation risk. The mean SOC content was found to be the lowest in abandoned cropland (6.91 g/kg), followed by secondary forest land (9.31 g/kg) and grazing shrubland (34.80 g/kg), respectively. Meanwhile, the δ13CSOC values exhibited the following trend: secondary forest land (mean: -23.79‰) ≈abandoned cropland (mean: -23.76‰) >shrubland (mean: -25.33‰). The isotopic tracing results suggested that plant litter was the main contributor to SOC in the secondary forest land. Whereas abundant nitrogen from goat feces enhanced plant productivity and resulted in additional accumulation of SOC in the grazing shrubland. Conversely, long-term cultivation led to the depletion of SOC sequestration by the loss of calcium. In surface soils, the fractionation of δ13CSOC were considerably affected by the decomposition of SOC by soil microorganisms and covered vegetation rather than agricultural influences. The findings indicate that the cycling of SOC and soil stability in the calcareous soil of southwest China are largely regulated by different land uses and the presence of vegetation cover. The depletion of SOC and soil physical degradation pose significant challenges for abandoned cropland, particularly in the karst area, where land degradation is inevitable. Nevertheless, moderate grazing enhances SOC levels, which is beneficial to the land fertility maintenance in the karst region. Therefore, more emphasis should be placed on the cultivation methods and management strategies for abandoned cropland in the karst area.

Eight-year impacts of conservation agriculture on soil quality, carbon storage, and carbon emission footprint

The conventional method of intensive tillage alters the soil environment, destroys soil aggregates, depletes soil organic carbon (SOC), emits more carbon, requires higher energy, alters microbial activities and ultimately degrades the soil health. These ill-effects of conventional tillage can be severe in rainfed soils with poor workability such as Vertisols of Central India. To minimize these negative effects of conventional tillage (CT), conservation agricultural (CA) practices such as reduced tillage (RT) and no-till (NT) with crop residue retentions are advocated as sustainable practices that can improve the soil health. Four cropping systems [soybean+pigeonpea (CS1); soybean–wheat (CS2); maize–chickpea (CS3); maize+pigeonpea (CS4)] were established as sub-plots under CT, RT and NT management. Soil samples were collected at 0–10 cm, 10–20 cm and 20–30 cm depths. The effects of 8 years of continuous use of CA were evaluated on soil physical, chemical and biological properties in Vertisol of Central India. After that, 20 key soil properties were subjected to calculating soil quality indices (SQI) in each tillage systems. Results indicated that mean weight diameter (MWD) and water-stable aggregates (WSA) were significantly higher (P < 0.05) in NT (1.57 mm and 79.4%) and RT (1.05 mm and 76.2%) than CT (0.71 mm and 63.8%) at 0–10 cm depth, respectively. The soil under NT had the highest SOC concentration (1.12%) followed by that under RT (1.02%), and the least was found in CT (0.91%) at 0–10 cm depth. The proportion of large macro-aggregates (LM) was the highest under NT than CT (P < 0.05) whereas that of micro-aggregates was highest under CT. The aggregate associated organic C (AOC) tended to decrease with the decrease of aggregate size. Soil dehydrogenase activity, fluorescein diacetate hydrolysis activity, β-glucosidase activity and easily extractable glomalin content were significantly higher under NT than CT (P < 0.05). The soil quality index was significantly highest in NT, followed by RT and CT at all soil depths. CA based practices favoured carbon storage, lowered carbon emission, foot print and soil quality compared to conventional farming. Therefore, under Vertisols, 8 years of CA practices likely to improve several soil quality indicators, allowing a positive trend for soil preservation.

Soil carbon stabilization and potential stabilizing mechanisms along elevational gradients in alpine forest and grassland ecosystems of Southwest China

Alpine ecosystems potentially store a large amount of soil organic carbon (SOC), but they are highly sensitive to climate change. The assessment of SOC stabilization mechanisms in these ecosystems is therefore vital to understanding the C dynamics in terrestrial ecosystems. Here, we investigated the soil aggregate distribution, aggregate stability, and associated SOC contents within alpine forest and grassland soils along an elevation gradient (2600–3900 m a.s.l) in the Yulong Mountains of Southwest China. Our results showed that the SOC contents in bulk soils and aggregates were higher within grassland soils than in forestland soils, with higher levels in the topsoil (0–10 cm) than in the subsurface soil (10–20 cm) layers at each elevation. The large macroaggregates (>2000 µm) accounted for the largest proportions of aggregate fractions (50.54% and 49.11%) and contributed the greatest proportions of C (55.44% and 52.12%) to the whole soil C within forest and grassland soils, respectively. Generally, the proportions of large macroaggregates, microaggregates (53–250 µm), mean weight diameter, and geometric mean diameter increased significantly with increasing elevation across different soil depths and land types, suggesting that soil C stability was improved with increasing elevation. The SOC contents in bulk soils and aggregates also showed an increasing trend with increasing elevation, with the highest level observed at 3900 m within forestland and 3200 and 3900 m within grassland soils at both soil depths. Climate factors, soil factors, Al/Fe oxides, and aggregate stability indices interactively explained 86% and 52% of the variation in soil C within forest and grassland soils, respectively. Among them, the incorporation of the Al/Fe oxides increased the total explained SOC variations by approximately 10%, exceeding the SOC variations explained by climate or soil factors. Overall, our results provide useful insights into the patterns and mechanisms of soil C stabilization along elevation gradients in alpine ecosystems.

Forest soil inoculation with Bacillus subtilus reduces soil detachment rate to mitigate rill erosion

Rill erosion is one of the most important types of soil erosion that has caused the destruction of many lands in recent decades, and its management has become an essential issue in world research. This study has evaluated the effects of soil physical properties induced by Bacillus subtilis OSU 142 (B. subtilis) on the soil detachment rate (Dc) and rill erodibility (Kr) in the inoculated soil, compared to the uninoculated soil in rill erosion-prone areas of Northern Iran. For measuring Dc, a hydraulic flume was used at 5 slopes (from 4.3% to 34.2%) and 5 water discharges (from 0.31 l m−1 s−1 to 0.67 l m−1 s−1) with 7 replications. Moreover, three physical properties of soils including the bulk density, mean weight diameter and total porosity of soils were measured before and after inoculation. Dc was found to be significantly lower (on average - 52% for the average slopes) in the inoculated soil with the B. subtilis (IB) compared to the uninoculated soil (UB). Rill erodibility (Kr), also was notably reduced in the IB soil (−70%) relative to the UB soil. The variability of Dc in the two studied soils showed a positive correlation to bulk density (R2 = 0.87), and a negative correlation to mean weight diameter (P < 0.01) (R2 = 0.89). The clustering of soils in two distinct classes (inoculated and uninoculated) by agglomerative hierarchical cluster analysis (AHCA) revealed a clear difference based on the physical properties of the treated and control soils. Based on the findings of present study, direct inoculation of B. subtilis can be proposed as a new and suitable technique for the improvement of soil physical properties and the reduction of soil detachment rate, especially in rill erosion-prone areas.

Organic amendments effects on soil aggregation and carbon sequestration in saline‐alkaline croplands in China

AbstractSaline‐alkaline soils are wide‐spread and approximately 6.5% of the world's land area is reported as being saline and sodic. Increasing soil organic carbon (SOC) concentration and aggregate stability in saline‐alkaline soils has been challenging due to the deleterious effects of soil salinity and sodicity. To address this issue, a 2‐year filed experiment was conducted to evaluate the effects of biochar (BC), farmyard manure (FM), corn straw (CS), and sheep manure (SM) in combination of chemical fertilizer (CK) on soil aggregation and C sequestration in mildly and moderately alkaline soils in Hetao Irrigation District, China. For mildly alkaline soil, the proportion of macroaggregates (&gt;0.25 mm) was significantly higher under FM, CS, and SM (34.6%–51.2%) compared with CK (13.2%). The mean weight diameter (MWD) and geometric mean diameter (GMD) of water‐stable aggregates significantly increased under FM, CS, and SM by an average of 172.7% and 58.7% over CK. In addition, FM, CS, and SM enhanced the distribution of organic carbon (OC) in macroaggregates (&gt;0.25 mm) and accelerated the accumulation of particulate organic matter within macroaggregates. Treatment BC enhanced OC distribution in microaggregates (0.053–0.25 mm) and exhibited a 7.40 g kg−1 SOC content, followed by SM and FM which exhibited SOC contents of 7.10 and 6.76 g kg−1. For moderately alkaline soil, data obtained in this study showed a slight influence from organic amendments on soil aggregates and C sequestration, suggesting that the moderately alkaline soil was not as sensitive to organic amendments as the mildly alkaline soil. Overall, the results of this study demonstrated that FM and SM combined with chemical fertilizer were the top organic amendments to improve soil aggregation and C sequestration in the mildly alkaline soil but not the moderately alkaline soil over the short term.

The Impacts of the Hydrological Regime on the Soil Aggregate Size Distribution and Stability in the Riparian Zone of the Three Gorges Reservoir, China

The impoundment of the Three Gorges Reservoir (TGR) has greatly altered the hydrological regime and thus formed a distinctive riparian zone with anti-seasonal inundation and exposure, which may affect the soil aggregate properties in this riparian zone. Yet, the soil aggregate size distribution and stability influenced by the hydrological regime along the step-impounded elevation have rarely been documented. This study aimed to elucidate how the hydrological regime of the TGR affected the aggregate size distribution and stability in the riparian zone. Based on the step-impounded elevation, topsoil samples were collected from four elevation-dependent transects in a middle section of the TGR. Dry-sieving and wet-sieving methods were employed. The results showed that, with a decrease in the elevation gradient, the mass percentage of the &gt;5 mm aggregates significantly decreased, while the proportions of the other size classes presented an increasing trend. Additionally, the mean weight diameter (MWD), geometric mean diameter (GMD), aggregate stability rate (ASR), and percentage of aggregate destruction (PAD) of the fractal dimension showed a successive decrease with a decrease in the elevation gradient, whereas PADMWD, PADGMD, PADASR, and the fractal dimension demonstrated a reverse trend. It can thus be deduced that the hydrological regime of the TGR significantly modified the aggregate size distribution and dramatically reduced the aggregate stability, which may provide a crucial basis for assessing the soil erosion in similar riparian zones.

Artificial humic acid regulates the impact of fungal community on soil macroaggregates formation

Artificial humic acid (A-HA), which is synthesized from agricultural wastes and has high similarity to a natural humic substance (HS) extracted from soil, has been proven by our group to have potential for biological carbon sequestration in black soils. However, the mechanism involves in the application of A-HA on soil aggregation processes resulting from microbial activity stimulation and modifications to microbial communities remains unclear. This study investigates the correlation between the formation and stability of soil aggregates and fungal communities with various amounts of A-HA added to the rhizosphere and non-rhizosphere soil. A-HA can increase the total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations in soil, promoting macroaggregate formation and increasing the mean weight diameter (MWD). In addition, soil aggregate binding agents such as polysaccharides, protein, extracellular polymeric substances (EPS), and glomalin-related soil protein (GRSP) are significantly increased by the addition of A-HA. A-HA can drive microaggregate to assemble into macroaggregate by increasing the abundance of beneficial fungi (e.g., Trichoderma and Mortierella). The co-occurrence network supports that A-HA shifted the key species and increased interactions of fungal taxa. This study will lay a solid foundation for sustainable agricultural development of A-HA application for soil fertility restoration in the future.

Effects of tillage on soil organic carbon and crop yield under straw return

No-tillage with straw mulch is an effective way to achieve soil sustainability. However, the specific redistributions of soil organic carbon composition, stocks, and crop yield remain unclear. The hypothesis that no-tillage had a minor effect on soil organic carbon stocks in 0–50 cm but decreased crop yield compared to plow-tillage under straw return was tested in this study. Soils properties from two decades of rice-wheat rotation field experiment were related to the yield of rice and wheat depending on tillage: 1) plow-tillage without straw return, 2) no-tillage with straw mulch, and 3) plow-tillage with straw return. No-tillage with straw mulch had the highest mean weight diameter of soil aggregates, the contents of macro-aggregates (>0.25 mm) organic carbon, particulate organic carbon (>53 µm), and soil organic carbon across tillage practices in 0–5 cm. However, it decreased the contents of macro-aggregates (>0.25 mm) organic carbon in 5–15 cm, the particulate organic carbon in 5–50 cm, and soil organic carbon in 5–30 cm compared to plow tillage with straw return due to less carbon input from roots and straw. Organic carbon stocks in micro-aggregates (<0.25 mm) and mineral-associated organic matter (<53 µm) did not vary between tillage practices. Hence the soil organic carbon stocks of plow tillage without straw return (48 Mg ha−1) were similar to that of no-tillage with straw mulch (51 Mg ha−1) but lower than that of plow tillage with straw return (57 Mg ha−1) in 0–50 cm. The mean annual yields of wheat and rice under no-tillage with straw mulch (14 t ha−1) were lower than that of plow tillage without straw return (15 t ha−1) and plow tillage with straw return (16 t ha−1). No-tillage-induced high soil bulk densities limited the rice yields. The yield losses of no-tillage with straw mulch were higher in rice than in wheat. The rice yield losses of no-tillage with straw mulch compared to plow tillage with straw return increased with experiment duration due to decreased available nitrogen in 7–14 cm and phosphorus contents in 0–14 cm over time. Conclusively, plow-tillage is more efficient for carbon sequestration and yield increase than no-tillage under straw return in rice-wheat farming by increasing carbon input in deep soils, soil available nutrients, and decreasing soil compactness.

Application of Computational Intelligence in Describing Dust Emissions in Different Soil Tillage Applications in Middle Anatolia

Soil degradation is an increasing problem in Turkey, especially in the Middle Anatolia region where the annual precipitation is approximately 300 mm, resulting from conventional farming methods. To address this issue, the artificial neural networks (ANNs) are used, as they are flexible mathematical tools that capture data. This study aims to investigate the relationships between dust emission (PM10) and the mean weight diameter, shear stress, and stubble amount of the soil, which were measured in eight different tillage practices (conventional tillage, six types of reduced tillage, and direct seeding). The results show that the mean weight diameter, shear stress, and stubble amount of the soil varied between 4.89 and 14.17 mm, 0.40–1.23 N·cm−2, and 30.5–158 g·m−2, respectively, depending on the type of tillage works. Additionally, dust emissions generated during different tillage applications ranged from 27.73 to 153.45 mg·m−3. The horizontal shaft rototiller produced the highest dust emission, approximately 150% higher than those of disc harrow and winged chisel plows. The impact of tillage practices on dust emission was statistically significant (p &lt; 0.01). A sophisticated 3-(7-7)-1 ANNs model using a backpropagation learning algorithm was developed to predict the concentration of dust, which outperformed the traditional statistical models. The model was based on the values of mean weight diameter, shear stress, and stubble amount of the soil after tillage. The best result was obtained from the ANN model among the polynomial and ANN models. In the ANN model, the coefficient of determination, root mean square error, and mean error were found to be 0.98, 6.70, and 6.11%, respectively. This study demonstrated the effectiveness of ANNs in predicting the levels of dust concentration based on soil tillage data, and it highlighted the importance of adopting alternative tillage practices to reduce soil degradation and dust emissions.

Soil resistance to flowing water erosion as affected by tea planting age in Three Gorges Reservoir Area of China

Soil erosion resistance is influenced by intrinsic soil properties and multiple external factors. This study investigated the effect of tea planting age on soil resistance to flowing water erosion (reflected by rill erodibility (Kr) and critical shear stress (τc)) in Three Gorges Reservoir Area. One slope farmland (as the control) and five tea plantations cultivated for 3 to 34 years were selected for sampling sites. The results indicated that bulk density (BD), soil cohesion (Coh), water stable aggregate (WSA), mean weight diameter (MWD), soil organic carbon (SOC), litter density (LD), and root mass density (RMD) increased generally with tea planting age. Compared to the control, Kr of tea plantations reduced by 71.1%–85.3%. The temporal variation in soil erosion resistance was controlled greatly by the variations in most near-surface characteristics. Kr decreased with WSA, Coh, LD, RMD, and SOC following a power function (P < 0.01); τc increased with MWD, LD, RMD, and SOC as an exponential function, with BD a power function, and Coh a logarithmic function (P < 0.01). In this study, Kr could be simulated well by WSA and LD with a power function, and τc could be simulated well by MWD and RMD with an exponential function.

Potential functional differentiation from microbial perspective under dryland-paddy conversion in black soils

Improving soil carbon sequestration and reducing greenhouse gas emissions in farmland require understanding how the microbial communities that control the agroecosystem function. Here, we surveyed the soil microbial communities in neighboring pairs of dryland and paddy fields in the black soils of northeastern China. Soil moisture, mean weight diameter of aggregates, fluorescence index and biological index of dissolvable organic matter, total anion concentration, and prokaryotic community α-diversity were higher in paddy soils than in dryland soils, while soil saturated hydraulic conductivity (SHC), dissolvable total nitrogen, and fungal community α-diversity were lower in paddy soils than in dryland soils. Moreover, soil moisture (P < 0.01) and SHC (P < 0.05) had significantly positive correlations with the α-diversity of prokaryotic and fungal communities, respectively. The co-occurrence network complexity of microbial communities was lower in paddy fields than in dryland fields, while the co-occurrence network tightness and cooperation of microbial communities were higher in paddy fields than in dryland fields, which may help paddy microbiome resist environmental disturbances. Taken together, both dryland and paddy fields had their own advantages in evaluating soil biological health from microbial community diversity and network stability. Additionally, the differential groups of CH4 production, S cycle, and Fe cycle (e.g., Bathyarchaeota, Bacteroidetes, and Geobacter) increased, while those of environmental remediation and biological control (e.g., Blastococcus and Roseiflexus) decreased after the change from dryland to paddy fields. Further combined with metagenomic analysis, the functions of CH4 production, CO2 fixation, N fixation, and sulfur reduction were enhanced in paddy soils, while those of CH4 oxidation, nitrification, and N2O production were reduced. In conclusion, the ecological functioning of the differential groups may lead to the increase of CH4 emission and CO2 fixation, and the decrease of N2O emission in paddy fields of black soil, even in non-flooding period.

Effects of coal gangue on soil property and plant growth in mining area.

With indoor and outdoor treatments, coal gangue with different ratios (10%, 20%, 30%, 40% and 50%) and different particle sizes (0-2, 2-5, 5-8 and 8-10 mm) were mixed into soil, and formed reconstructed soil with different soil bulk densities (1.3, 1.35, 1.4, 1.45 and 1.5 g·cm-3). The effects of soil reconstruction modes on soil water condition, structure stability of aggregate and the growth of Lolium perenne, Medicago sativa, and Trifolium repens were investigated. Soil saturated water (SW), capillary water (CW), and field water capacity (FC) were decreased with increasing coal gangue ratio, particle size, and bulk density of reconstructed soil. >0.25 mm particle size aggregate (R0.25), mean weight diameter (MWD), and geometric mean diameter (GMD) increased first and then decreased with the increases of coal gangue particle size, reaching the peak at 2-5 mm coal gangue particle size. R0.25, MWD and GMD were significantly and negatively correlated with coal gangue ratio. Based on boosted regression tree (BRT) model, the coal gangue ratio contributed 59.3%, 67.0% and 40.3% to the variation of SW, CW and FC, respectively, which was a main influencing factor of soil water content. The coal gangue particle size contributed 44.7%, 32.3% and 62.1% to the variation of R0.25, MWD, and GMD, respecti-vely, which was the greatest influencing factor. Coal gangue ratio had a great effect on the growth of L. perenne, M. sativa, and T. repens, which contributed to 49.9%, 17.4% and 10.3% of their variations, respectively. Soil reconstruction mode of 30% coal gangue ratio and 5-8 mm coal gangue particle size was the best condition for plant growth, indicating that coal gangue could change soil water content and structure stability of aggregate. The soil reconstruction mode of 30% coal gangue ratio and 5-8 mm coal gangue particle size was recommended.

Soil macropore characteristics and aggregate stability with poly‐γ‐glutamic acid amendment under wetting–drying cycles

AbstractSoils are typically subjected to multiple wetting–drying (WD) cycles due to irrigation and seasonal climate cycles, which directly impact soil pore structure and soil aggregate stability. Poly‐γ‐glutamic acid (γ‐PGA) is a polymer used to improve soil water holding capacity and plant growth. However, the impact of γ‐PGA on soil pore structure requires further research, particularly under WD cycles. Therefore, we investigated the different amounts of γ‐PGA on soil structure, including soil aggregate stability, macropore (&gt;100 μm) structure characteristics and the relationship between macropore characteristics (equivalent pore diameter, pore shape factor, soil porosity, fractal dimension (FD), soil connectivity and the percentage of aggregate content with particle size larger than 0.25 mm) and soil aggregate stability by structural equation modelling (SEM) under WD cycles. A sandy soil and a loam soil were studied, and amended with γ‐PGA at three different concentrations: 0 (P0), 0.4% (P4) and 0.8% (P8) (w/w, %). Results showed that γ‐PGA amendment increased the mean weight diameter (MWD) and the percentage of aggregate content with particle size larger than 0.25 mm (R0.25) under WD cycles in both sandy and loam soils, while the MWD between P4 and P8 did not differ significantly. As the number of WD cycles increased, soil porosity (TP) increased due to an increase in pores of 100–500 μm. With γ‐PGA added to soil, large microporosity (&gt;1000 μm) increased in sandy soil, but decreased in loam soil. In addition, 8WD cycles also increased the FD (2.6%–4.2%) and pore connectivity (Con) compared with 4WD. Structural equation modelling (SEM) revealed that soil pore characteristics accounted for 74% and 98% of the variation in sandy and loam soils, respectively. TP, FD, Con and R0.25 directly contributed to MWD, according to the SEM. These findings improve our understanding of pore characteristics and aggregate stability, which are key factors influencing soil quality when amended with γ‐PGA during the seasonal WD period.

Effects of Glomalin-Related Soil Protein Driven by Root on Forest Soil Aggregate Stability and Carbon Sequestration during Urbanization in Nanchang, China.

Glomalin-related soil protein (GRSP) is a hydrophobic protein released by arbuscular mycorrhizal fungi. It is an important component of the soil carbon pool, and it improves the soil aggregate structure; however, it remains unclear whether GRSP can enhance soil carbon sequestration and improve soil quality during rapid urbanization. The built-up area in Nanchang, China was the study area, and the proportion of impervious surface area was the parameter of urbanization intensity. A total of 184 plots (400 m2) were set up to collect soil samples (0-20 cm) for analysis. Aggregates of five particle sizes were sieved, and the percentage amounts of soil organic carbon (SOC) and GRSP for them were determined. The results showed that the easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP) contents of the four aggregates of <2 mm were 22-46% higher in low urbanization areas than those in high urbanization areas (p < 0.05), indicating that the higher urbanization intensity was associated with the lower GRSP content of different aggregates. The GRSP was significantly positively correlated with SOC (p < 0.05). Moreover, the contribution of GRSP to the SOC pool in the <0.25 mm aggregate was significantly higher than that in other aggregates. In addition, the EE-GRSP content was significantly positively correlated with mean weight diameter (MWD) and geometric mean diameter (GMD) in the four aggregates of <2 mm, whereas it was negatively correlated with fractal dimension (D) in the >2 mm, 1-2 mm and <0.053 mm aggregates. The T-GRSP content showed significant correlations only with MWD, GMD, and D in the 1-2 mm aggregate. This study revealed that increasing urbanization intensity can significantly reduce the GRSP content of different sized aggregates. Moreover, the GRSP content significantly promoted SOC sequestration, and the EE-GRSP content more significantly promoted soil aggregate stability than that of the T-GRSP. These findings provide new ideas for exploring the improvement of soil quality during the process of urbanization.

Preservation of labile organic compounds is the pathway for carbon storage in a 23-year continuous no-till system on a Ferralsol in southern Brazil

No-till (NT) system has the potential to sequester soil organic carbon (SOC) in the topsoil and increase soil quality. However, SOC accumulation in the soil profile and the mechanisms for SOC stabilization in NT are still a matter of debate, especially for soils of the tropics. Therefore, this study was conducted to investigate the long-term effects of two tillage systems (conventional tillage – CT and no-till – NT) on chemical and physical mechanisms of SOC stabilization and how these are related to the accumulation of SOC in the soil profile. Soils were sampled (0–100 cm depth) from a long-term experiment (23 years) established on a Rhodic Ferralsol in southern Brazil. Soils under native vegetation (NV) were used as a baseline. Results showed that conversion of NV to agriculture decreased on average the SOC stock by 70.8 Mg ha−1 (−33%) in the 0–100 cm soil layer. Between tillage systems, higher SOC stock was observed under NT than that under CT in the 0–5 and 5–10 cm soil layers, resulting in higher SOC stock in the entire topsoil (0–20 cm) in the conservation system. In the subsoil (20–100 cm), SOC was similar for both tillage systems. Fourier-transform infrared spectroscopy showed differences in the C composition between the tillage systems; an accumulation of labile compounds in the uppermost layer was observed under NT, which resulted in a lower SOM aromaticity index under this treatment than that in soil under CT management. Adoption of NT increased the proportion of large macroaggregates (> 2.0 mm) in 0–5 cm soil layer, resulting in a greater mean weight diameter (MWD) than under CT. Principal component analysis (PCA) and correlation analysis of data for 0–20 cm soil layer showed that SOC stock is positively associated with labile compounds, the proportion of large macroaggregates, and MWD, and negatively with small macroaggregates, aromatic compounds, and aromaticity index. These results indicated that the pathway for SOC accumulation in the topsoil of NT is influenced less by selective preservation but driven by the maintenance of labile organic compounds, a process achieved by the low turnover of large macroaggregates in the NT system.

Quantifying the effect of freeze–thaw on the soil erodibility of gully heads of typical gullies in the Mollisols region of Northeast China

The soil erodibility of gully headwalls is a critical factor influencing gully erosion. In some cold regions, the soil of gully headwalls is subjected to a bidirectional freeze–thaw effect (FT), while the quantification of the influence of FT on the soil erodibility of gully heads is unclear. Therefore, five typical and representative gullies developed in farmlands (GF1 and GF2), along unpaved road (GR), in the woodland (GW) and in stabilized gully bed (GS) were selected to quantify the influence of FT on the soil erodibility of gully heads reflected by five soil erodibility parameters including the K factor (K), soil disintegration rate (SDR), mean weight diameter (MWD), soil shear strength (SS) and saturated soil hydraulic conductivity (SHC). A comprehensive soil erodibility index (CSEI) was constructed by combining the above five soil erodibility parameters. This study revealed that FT significantly affected the five soil erodibility parameters and CSEI, of which the K and SDR increased by 22.7 % and 52.3 %, respectively, but the MWD, SHC and SS decreased by 29.3 %, 30.4 % and 26.1 %, respectively. The change in soil erodibility of the gully heads was closely related to the soil and root properties, of which the contribution of roots to the change in soil erodibility of gully heads was increased by 78.5 % after FT on average. Furthermore, FT significantly increased the CSEI at depths of 0–50 cm in GF1, GF2 and GR, and at depths of 0–80 cm in Gw and GS. FT increased the CSEIs of the five gully heads by 20.1 %-37.3 %, with an average of 26.1 %. Evidently, the organic matter content (OMC), soil texture and temperature dominated the change in the CSEI, of which the extremely low temperature and temperature rangeability during freeze–thaw period exhibited the greatest impact on the soil erodibility of the gully heads.

Soil microorganism regulated aggregate stability and rill erosion resistance under different land uses

How microbial communities respond to soil aggregation and rill erosion resistance has rarely been addressed. Such a knowledge gap hinders the practice of guiding sustainable soil management. Herein, the community composition of bacteria and fungi was evaluated by 16S rRNA gene sequencing. We measured critical shear stress (τc) and rill erodibility (kd) by self-made jet device. The effects of microorganism on soil aggregation and rill erosion resistance were quantitatively analyzed under different land uses.The results indicated that the forest soil supported the colonization and enrichment of Acidobacteria and Basidiomycota on account of the unique vegetation and higher soil organic carbon (SOC). The forest and shrubland contained higher macroaggregate and mean weight diameter (MWD) than those of cropland and bare land, while rill erodibility (kd) was the opposite. MWD and kd had a negative power function (y = 105.64x−0.69). The biotic factors explained 73.50% of the variation in rill erosion resistance and soil aggregation, indicating microorganism are more important in acting on rill erosion resistance.This study suggests that SOC had strong regulatory effects on the soil key groups of bacteria and fungi assemblages; furthermore, their interaction facilitated the formation of stable macroaggregates. The stable macroaggregate structure and vegetation cover make the erodibility of forest soil at a relatively low level. However, cropland are not conducive to stability of aggregates, which easily causes soil erosion. Improving soil SOC and maintaining the relative abundance of key groups of microorganism would be conducive to soil sustainable developing.

Effect of tillage systems combined with plastic film mulches and fertilizers on soil physical properties in a wheat-agricultural site in southern Iraq

This study researches the influence of the three tillage systems (conventional, economical and mulch tillage) when combined with different soil plastic mulching and fertilizer applications on key selected soil physical properties (SPP) at 0-20 cm soil depth in a wheat agricultural site, during summer (from 1st June to 31st July 2015). SPP include soil porosity (Φ), volumetric soil water content 60 days after irrigation to field capacity (q60), and mean weight diameter of aggregates (MWD). The term mulch tillage refers here to a soil conservation practice where the soil surface is disturbed by tillage whereby crop residues are mixed with the soil and a certain amount of residues remain on the soil surface, while mulching refers to the placement of inorganic material over the top of a soil surface to protect it. Soil treatments included tillage system: conventional tillage using a combination of a mouldboard plough and a disc harrow (MP+DH), economical tillage using a rotary cultivator (RC), and mulch tillage using a chisel plough (MT+CP); soil plastic mulching: transparent mulching (TM), black mulching (BM) of 200 cm wide with 0.05 cm thick, and without mulching (WM); and fertilisers: composed organic fertiliser (CoF), no-composed organic fertiliser (NoF), and chemical fertiliser (ChF). The split–split-plot design under the randomized complete block design (RCBD) was established in 27 treatments with 3 replicated, to map Φ, q60, and MWD based on 81 soil samples from all treatments. Results showed that the different soil treatments have diverse impacts on SPP. MP+DH resulted in the higher q60 (0.22 cm3 cm-3), MWD (0.85 mm), and Φ (56.87%). Our findings showed that MT+CP obtained a higher MWD of 0.98 mm and lower Φ of 49% compared to other tillage systems. Soil mulching had significantly modified SPP, with BM resulting in the highest Φ (55.65%), q60 (0.35 cm3 cm-3), and MWD (1.06 mm). Results indicated no significant differences between fertiliser types on SPP. The CoF had a significant effect on MWD and related soil characteristics studied. These findings can help us to understand the individual and combined effects of the tillage system, mulching, and fertilization application on some soil characteristics in wheat agriculture. A further study with more focus on the influence of tillage depths and mulching types (plastic vs organic mulch for different crops) under a variety of soils and climatic conditions, as well as on soil thermal properties needs further investigation.