Sewage Sludge and Cashew Bagasse Biochars Promote Changes in Selected Physical Attributes Related to the Structure of Degraded Dryland Soil

Quantitative characterization of pore connectivity using NMR and MIP: A case study of the Wangyinpu and Guanyintang shales in the Xiuwu basin, Southern China

Changes in soil pore network in response to twenty-three years of irrigation in a tropical semiarid pasture from northeast Brazil

Carbon in soil affects the formation and stabilization of aggregates (groups of primary particles that adhere to each other more strongly than to surrounding soil particles)1. Soil aggregation is important for preventing soil loss through wind and water erosion, and the size distribution and abundance of water-stable aggregates influences a range of physical, chemical, biological and agricultural properties of soil2. The effects on soil biota and nutrient cycling of increases in soil carbon availability, brought about by increased CO2, are well studied, but the consequences for soil aggregation and structure have not been examined. Here we show for three ecosystems that the water stability and size distribution of aggregates is affected by long-term CO2fumigation, and we propose a mechanism for this that involves the production by fungi of the glycoprotein glomalin.

Soil tillage and machinery traffic influence soil water availability and air fluxes in sugarcane fields

Wang, E., Cruse, R. M., Chen, X. and Daigh, A. 2012. Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability. Can. J. Soil Sci. 92: 529–536. Freeze/thaw cycles can affect soil aggregate stability, which in turn impacts wind and water erosion. The objectives of this laboratory study were: (1) to determine the effect of variable freeze/thaw cycles and soil water conditions on aggregate size distribution and stability; and (2) to evaluate differences in aggregate size distribution and stability between disturbed soil and undisturbed soil cores as affected by freeze/thaw cycles and soil water conditions. Surface soil was collected before freezing in late fall of 2009. Aggregates isolated from disturbed soil or intact soil cores were subjected to a factorial combination of 3 gravimetric water content treatments: 0.15 m3 m−3, 0.23 m3 m−3 or 0.30 m3 m−3, and 3 freeze/thaw treatments: 0, 3, or 9 cycles. A freeze/thaw cycle involved soil freezing at –10∘C for 24 h, followed by thawing at 5∘C for 24 h. Most aggregate size classes were affected significantly (P<0.05) by freeze/thaw cycles except for wet-sieved aggregates >5 mm. Dry-sieved aggregates were relatively more sensitive to the freeze/thaw treatment than wet-sieved aggregates. The mean weight diameter (MWD) of dry-sieved aggregates was significantly (P<0.05) greater at 0.30 m3 m−3 than 0.15 m3 m−3 water content, but the opposite trend was observed for MWD of wet aggregates and aggregate stability. There was a significant (P<0.05) response of the MWD in dry-sieved aggregates to the interactive freeze/thaw×water content effect that differed for aggregates obtained from disturbed soil and those in the undisturbed soil core, but not for the MWD of wet-sieved aggregates and aggregate stability.

As the basic units of soil structure, soil aggregate is essential for maintaining soil stability. Intensified freeze–thaw cycles have deeply affected the size distribution and stability of aggregate under global warming. To date, it is still lacking about the effects of freeze–thaw cycles on aggregate in the permafrost regions of the Qinghai-Tibetan Plateau (QTP). Therefore, we investigated the effects of diurnal and seasonal freeze–thaw processes on soil aggregate. Our results showed that the durations of thawing and freezing periods in the 0–10 cm layer were longer than in the 10–20 cm layer, while the opposite results were observed during completely thawed and frozen periods. Freeze–thaw strength was greater in the 0–10 cm layer than that in the 10–20 cm layer. The diurnal freeze–thaw cycles have no significant effect on the size distribution and stability of aggregate. However, < 0.25 mm fraction dominated wet sieving aggregate with the highest proportion during thawing period, while the < 1 mm fraction reached the highest during completely frozen period in the 10–20 cm layer (P < 0.05). Likewise, the mean weight diameter and water-stable aggregate were decreased during thawing period compared with the other periods, which were influenced by soil microbial biomass carbon and belowground biomass. Hence, the seasonal freeze–thaw processes destroyed macro-aggregate (> 0.25 mm) and reduced aggregate stability. Our study has scientific guidance for evaluating the effects of freeze–thaw cycles on soil steucture and provides a theoretical basis for further exploration on soil and water conservation in the permafrost regions of the QTP.

Influence of soil properties on the aggregation of some Mediterranean soils and the use of aggregate size and stability as land degradation indicators

Soil structure stability under conventional and reduced tillage in a sandy loam

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.

Direction-dependent behaviour of hydraulic and mechanical properties in structured soils under conventional and conservation tillage

&lt;p&gt;A two-year field trial on maize (&lt;em&gt;Zea mays&lt;/em&gt; L.) production was established to determine the influence of biochar, maize straw, and poultry manure on soil aggregate stability, aggregate size distribution, total organic carbon (TOC), and soil microbial biomass carbon (MBC). Seven treatments with four replications, namely CK, control; S, 12.5 Mg ha-1 straw; B1, 12.5 Mg ha-1 biochar; B2, 25 Mg ha-1 biochar; SB1, straw + 12.5 Mg ha-1 biochar; SB2, straw + 25 Mg ha-1 biochar; and M, 25 Mg ha-1 manure were tested at four soil depths (0–10, 10–20, 20–30, and 30–40 cm). Aggregates were grouped into large macro-aggregates (5–2 mm), small macro-aggregates (2–0.25 mm), micro-aggregates (0.25–0.053 mm) and silt + clay &lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;(&amp;lt;0.053 mm). Biochar, straw,&lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt; and manure applications all had significant effects (&lt;span style="font-family: TimesNewRomanPS-ItalicMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;&lt;em&gt;p &lt;/em&gt;&lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;&amp;lt; 0.05) on aggregate stability, with B&lt;span style="font-family: TimesNewRomanPSMT; font-size: 5pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;2 &lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;at&lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt; 20 cm soil depth showing the greatest increase (62.1%). SB&lt;span style="font-family: TimesNewRomanPSMT; font-size: 5pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;1 &lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;of small macro-aggregate fraction&lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt; showed the highest aggregate proportion (50.59% ± 10.48) at the 20–30 cm soil depth. The highest TOC was observed in SB&lt;span style="font-family: TimesNewRomanPSMT; font-size: 5pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;2 &lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;(40.9 g kg&lt;span style="font-family: TimesNewRomanPSMT; font-size: 5pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;-1&lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;) of large macro-aggregate at 10–20 cm soil depth. Treatment effects on soil MBC was high, with B&lt;span style="font-family: TimesNewRomanPSMT; font-size: 5pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;1 &lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;showing the greatest value (600.0 µg g&lt;span style="font-family: TimesNewRomanPSMT; font-size: 5pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;-1&lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt;) at the 20–30&lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt; cm soil depth. Our results showed that application of biochar, straw, and manure to soil increased&lt;span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"&gt; aggregate stability, TOC as well as MBC.&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;br style="font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" /&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;

Core Ideas Long‐term effects of tillage, rotation, and residue management studied. Residue retention increased porosity, air permeability, and gas diffusivity. Residue retention alleviated negative effects of reduced tillage on soil pores. Moldboard plowing caused best topsoil (0‐20 cm depth) quality. Direct drilling resulted in highest air permeability at the 18‐ to 27‐cm depth. Conservation agriculture (CA) is regarded by many as a sustainable intensification strategy. Minimal soil disturbance in combination with residue retention are important CA components. This study examined the long‐term effects of crop rotation, residue retention, and tillage on soil pore characteristics of two Danish sandy loams. Rotation R2 is a rotation of winter crops (mainly cereals) with residues retained, rotation R3 a mix of winter and spring crops (mainly cereals) with residues removed, and rotation R4 the same mix of winter and spring crops, but with residues retained. Each rotation included the tillage treatments: moldboard plowing to 20‐cm depth (MP), harrowing to 8‐ to 10‐cm depth (H) and direct drilling (D). Soil cores were taken from the topsoil (4–8, 12–16, 18–27 cm) in mid‐autumn 2013 and early spring 2014. Water retention, air permeability, and gas diffusivity was determined for the first two depths (100‐cm 3 cores), and air permeability for the 18‐ to 27‐cm depth (250‐cm 3 cores). Moldboard plowing resulted in the best soil quality at two upper depths with higher total porosity, air‐filled porosity, air permeability, and gas diffusivity compared with reduced tillage. For instance, the volume of pores &gt; 30 µm was more than 0.03 m 3 m ‐3 larger for MP than for D in spring 2014 at the 4‐ to 8‐cm depth. At the 18‐ to 27‐cm depth, direct drilling resulted in a better air permeability and pore continuity index (e.g., air permeability of 18.2 and 11.2 μm 2 for D and MP, respectively at −10 kPa for the Foulum location). Residue retention, especially when combined with direct drilling, increased total porosity, air‐filled porosity, air permeability, and gas diffusivity and decreased blocked air porosities. Our results suggest residue management can be used to alleviate the negative effects of reduced tillage on soil structural quality.

Soil aggregates are important drivers of soil productivity. However, the relative importance of soil abiotic and biotic agents in driving aggregate formation and stabilization remain largely unexplored, especially in coastal mudflat saline soils. We amended saline soil with sewage sludge at rates of 0, 30, 75, and 150 t ha−1 to investigate the effects of sewage sludge on the particle size distribution and stability of soil aggregate and the underlying mechanisms induced by soil environmental factors and fungal community. Results revealed that the sewage sludge amendment significantly (p &lt; 0.05) increased the proportion of macroaggregates with sizes larger than 0.25 mm (R0.25) and enhanced aggregate stability. Moreover, alleviation of saline‐alkali stress and nutrient (C, N, and P) deficiency conditions were significantly (p &lt; 0.05) observed in sewage sludge‐amended soils. Additionally, restructured fungal communities in amended soils harbored significantly (p &lt; 0.05) distinguishable structures and core and unique microbiomes. Particularly, fungal species belonging to Moterella significantly (p &lt; 0.05) enriched in sludge reclaimed soils. Results derived from the random forest (RF) model accompanied by linear regression analysis revealed that soil pH, soil organic carbon, and fungal structural diversity were significantly (p &lt; 0.05) related to aggregate composition (R0.25) and stability (geometric average diameter, GMD). Furthermore, fungal consortia composed of 20 closely interconnected operational taxonomic units (OTUs) affiliated with Ascomycota, Basidiomycota, and Zygomycota explained 28.36% and 49.88% variance of R0.25 and GMD, respectively. Overall, our results revealed the effect of sewage sludge on soil aggregation improvement in coastal areas and highlighted the respective importance of soil chemical properties and fungal microbiome in predicting aggregation status.

Three soils which had been amended for several years with pig slurry, cattle slurry, and sewage sludge were dry-sieved to obtain microaggregates in the size range of 250–125, 125–50, and <50 μm. With amendments, aggregate size distribution of whole soils was shifted to larger sizes, especially for the most fragile soil, whereas percent content of microaggregates decreased except for the lower size aggregates of the fragile soil. Particle size distribution of microaggregates revealed an increase in percent sand and a reduction of percent silt and clay in the <50 μg size fraction for all soils. These results showed the aggregation effect induced by the organic waste additions. Aggregate stability of microaggregates revealed significant correlation with humic substances content (humic acids alone and humic plus fulvic acids) and non significant with total organic matter substantiating the belief that humic substances are the predominant binding agents in this aggregation range. Molecular weight distribution of humic acids extracted from microaggregates of unamended soils demonstrated that the lower the soil aggregate size distribution, the larger the contribution of the high molecular weight fraction. All microaggregates from amended soils showed a progressive increase of the high molecular weight humic acids with decreasing size, reaching a maximum in the <50 μm fraction. In this aggregate size a parallel enhancement of the aggregate stability was also evident. It is concluded that a close relationship exists between aggregate stability and high molecular weight humic substances. Additions to soils of organic material containing high molecular weight constituents would represent a useful management practice to improve aggregate stability.

Misfolded amyloid-β strains and their potential roles in the clinical and pathological variability of Alzheimer's disease.