Mean Weight Diameter Research Articles

Long-term (>90 years) wastewater irrigation effect on the pore characteristics and stability of soil aggregates

Wastewater (WW) agricultural irrigation is becoming a common practice as an alternative to water scarcity. However, WW irrigation may affect the soil structure at different hierarchical levels. This issue was tackled by evaluating the long-term (>90 years) WW irrigation effects on soil structure. Samples of Ap and Ah horizons from eight rainfed and eight WW-irrigated plots were collected for physicochemical characterization. Undisturbed samples were analyzed for aggregate stability, and the pore space of small macroaggregates (0.5–1 mm) from Ah horizons of three rainfed and three WW-irrigated plots was analyzed by x-ray microtomography. Long-term WW-irrigated plots had higher contents of C (Ap = 2.54%; Ah = 1.64%) and N (Ap = 0.24%; Ah = 0.16%) compared to rainfed soils, as well as higher aggregates stability (mean weight diameter = 23.6 mm, p = 0.001). However, soil organic matter accumulation was not the main driver of the higher aggregate stability in WW-irrigated soils (Spearman correlation coefficients of 0.467 and 0.476 for organic C and total N, respectively). It was proposed that a combination of factors including SOM and easily degradable OM (C/N = 2.10) input from WW was the reason for this higher stability. The results did not allow one to conclude on the long-term effect of WW irrigation on the microstructural pore space because the scatter in the data of the rainfed samples was high. Considering a higher number of samples may address this problem. Nevertheless, the findings of this research improve our understanding of the effects of WW irrigation on soil structure and provide a better assessment of the benefits and risks associated with this practice.

Carbon Fixation and Soil Aggregation Affected by Biochar Oxidized with Hydrogen Peroxide: Considering the Efficiency of Pyrolysis Temperature

Biochar, as a carbon-rich material, may have a notable influence on carbon balance, especially that in soil mediums. The oxidation of biochar modifies the biochar’s effects on the soil’s carbon dynamics. To evaluate the alteration in soil carbon storage, biochars derived from wheat straw (WS) and wood residues (WR) produced at 350, 450, and 550 °C (marked BWS350, BWS450, BWS550, BWR350, BWR450, and BWR550) were oxidized with hydrogen peroxide (H2O2) and applied on a loamy soil (2% d.m.) for a 180-day greenhouse incubation period. The highest organic carbon (OC) concentration and carbon pool index (CPI) were obtained from the oxidized BWS550, with 154% and 70% increases, respectively, compared to the unamended control. For both the WS and WR biochars, applying oxidation significantly improved the soil’s aggregation indices, i.e., the mean weight diameter (MWD), water stable aggregates (WSA), and fractal dimension (D). BWS350, BWS450, and BWS550 showed significantly higher WSAs, with percentages of 68, 74, and 76% compared to the control (41%). The fractal dimensions decreased with an increasing pyrolysis temperature in both the biochar types. All the biochar treatments significantly decreased the soil bulk density (BD), while for both the pristine and oxidized biochars, the lowest BD was related to the biochars produced at high temperatures. The structural qualities of the biochars were enhanced by oxidation, particularly their specific surface areas and porosities, and this had a substantial impact on the soil structure and carbon status. The wheat straw biochar was more effective than the wood residue biochar and a higher pyrolysis temperature was more effective than lower ones for supporting the enhancement of the soil carbon pool.

Preferential flow in the understory soil of Hippophae rhamnoides at different stump heights

This study aimed to clarify the effects of stumping on preferential flow in the understory soils of Hippophae rhamnoides and to assess appropriate stumping height for optimization of preferential flow. Root properties, soil properties, and preferential flow for different H. rhamnoides stump heights (0, 10, 15, 20 cm, and no-stumping, labeled conditions S1, S2, S3, S4, and CK, respectively) were studied using in situ dye-tracing and laboratory analysis. The results showed that stumping significantly increased preferential flow development. This effect was maximized in condition S3, with dye-tracing coverage (DC) of 36.77%, maximum dye depth (MaxD) of 40.02 cm, uniform infiltration depth (Unifr) of 14.28 cm, preferential flow ratio (PFfr) of 23.85%, and length index (LI) of 96.72%. In terms of root length density (RLD), root mass density (RMD), root surface area density (RSAD), soil water content (SWC), soil total porosity (TP), mean weight diameter (MWD), and soil organic matter (SOM), the conditions were ranked S3>S2>S1>S3>CK; for root average diameter (RAD), they were ranked S3<S2<S1<S4<CK. Structural equation modeling showed that DC was affected directly by TP, MWD, and SWC and indirectly by RAD, RLD, RMD, RSAD, and SOM, explaining up to 89.1% of the variance. Thus, stumping of H. rhamnoides affected soil properties through the mechanism of root development, thereby improving preferential flow development in the soil and soil infiltration. The optimal stump height was 15 cm. These findings are critical for vegetation recovery and for prevention and control of soil erosion in feldspathic sandstone areas.

Spatial Variability and Mapping of Selected Soil Physical Properties under Continuous Cultivation

Assessments of Soil physical properties and estimation of their associated variability are essential for making site-specific decisions on soil and crop management This study examined the spatial variability of soil hydro-physical properties and variance structure at Sector F1 of the Jibia Irrigation project Katsina State, Nigeria. Grid sampling technique was used to obtain one hundred and forty-four (144) soil samples from 206 ha of land using Google earth. The grids were drawn using Google earth software at intervals of 150 m x 150 m. Surface soil samples (0 - 20 cm) were collected at grid intersection points. The collected soil samples were air-dried and passed through a 2mm sieve, and analyzed using standard laboratory procedures for physical parameters. The ArcGIS software package 10.3 was used to model the variance structure of Sand, Silt, Clay, Bulk density, Particle density, Percent total porosity and Organic Matter (OM). Results obtained revealed that the coefficient of variation (CV) ranged from 5.724% in particle density to 109% in clay. The Semivariogram showed that the range of spatial dependence varied from 0.342m for (Dry mean weight diameter) to 9.3m (Organic matter) for all measured soil properties. High Spatial dependency ratios were observed for Bulk density, Sand, Silt and clay contents. Particle density exhibited moderate spatial dependency (Nugget to sill ratio 0.25 – 0.75%). Wet Mean weight diameter and organic matter content have a weak spatial dependency. The results indicated that sandy textured soils dominated the greater part of the study area with low to moderate organic matter content. The soils being sandy-dominated has a high infiltration rate and low ability to retain moisture and nutrients were observed as the major characteristics of the soil of the study area.

Factors affecting the stability of soil aggregates of plinthosols in the middle reaches of the Yangtze River

Soil aggregate stability is a key factor that affects soil erosion and ecological restoration. In this study, three typical plinthosol profiles in Wuhan (W), Yueyang (Y), and Jiujiang (J) were selected, and the mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension were used as indicators of soil aggregate stability, as well as the erodibility factor (K value). Based on the end-member analysis, it appears that the plinthosols in the three profiles were wind-formed deposits, which greatly affected particle size and erodibility. There was a greater resistance to erosion among the plinthosols developed from finer grains than among those developed from coarse grains. The stability of aggregates in profiles W and Y decreased gradually with depth, while it varied little in profile J. The initial moisture content had a significant effect on the anti-erodibility of the plinthosols, and there were some differences between the profiles: in profile W, the anti-erodibility increased with the increase in initial moisture and reached its maximum value at the initial moisture content of 20%; in profiles Y and J, when the initial moisture content was 15%, the anti-erodibility was the highest. Reddishmatrixhadahigher anti-erodibility than white veins.ProfileJhadthelargeststability gap between white veins and reddishmatrix,followed by profileY and W. These results provide a theoretical basis for the conservation of soil and water in the Yangtze River middle reaches by revealing the stability characteristics of plinthosols.

Non-linear response of sediment size characteristics and associated transport patterns to soil structural stability in sheet erosion under field rainfall simulation

Sediment transport patterns (suspension, saltation and rolling) not only depend on flow hydrodynamic characteristics, but also on sediment properties, both of which are largely influenced by soil structural stability. However, how sediment sizes and transport patterns response to original soils over a wide range of structural stability remains unclear. Herein, field plot rainfall simulation experiments on five soils along an increased gradient of structural stability were conducted at two rainfall intensities of 45 and 90 mm h−1 to investigate effective sediment size characteristics and associated transport patterns in sheet erosion. Differing from runoff and sediment yield, sediment sizes were most influenced by soil structural stability (F = 386.9) rather than rainfall intensity (F = 246.7, p < 0.001). Mean weight diameter of sediment (0.16–0.84 mm) and the proportion of coarse particles (>0.25 mm) exhibited a unimodal variation with increased soil structural stability. The effective sediment size distribution shifted from unimodal with the peak at < 0.10 mm for low and high stable soils to bimodal with two peaks at < 0.10 mm and 0.5–1 mm for medium stable soils. Correspondingly, suspension-saltation (>74 %) dominated sediment transport for low and high stable soils, which was determined by fine sized fragments from aggregate breakdown and small flow transport capacity, respectively; while both suspension-saltation (<0.10 mm) and rolling (>0.25 mm) jointly contributed to sediment transport for medium stable soils, which was controlled by the interaction between fragment size and flow transport capacity. Moreover, the positive effect of rainfall intensity on sediment sizes was more remarkable for the medium than for the low and high stable soils. A conceptual model of sediment transport mechanisms in response to soil structural stability is firstly proposed, which merits consideration in the future development of erosion modeling and soil conservation techniques.

Agricultural soil aggregation is affected by the crop root biomass rather than morphological characteristics

AbstractBackgroundIn areas prone to water erosion, crop selection strategies should be based on assessment of their effects on soil structural properties.AimsThe present study compared the effects of the cultivation of forage maize (Zea mays L.) and forage oat (Avena sativa L.) and their cultivars on soil aggregation relative to potato (Solanum tuberosum L.) or wheat (Triticum aestivum L.) at a hydrothermally limited site on the Loess Plateau, China.MethodsThe water‐stable aggregate (WSA) distribution in soil was measured under three cultivars in each of maize, oat, wheat, and potato (a total of 12 cultivars from four crops) in their flowering stage of three cropping seasons, when root biomass was largest.ResultsIn each year, the water‐stable macroaggregates (&gt;0.25 mm) content and mean weight diameter (MWD) of WSAs in the top 20 cm of soil did not differ between tested cultivars of every crop but increased under maize and oat, compared with those under wheat or potato. The increased soil aggregation under maize and oat, compared with wheat or potato, was consistent with the pattern of change in root biomass but was not consistent with the changes in root length density, root surface area, or root mean diameter across the crops. The water‐stable macroaggregates content and MWD of soil was positively correlated with root biomass across cultivars and crop species within each cropping season.ConclusionsWe suggest that increased root biomass under maize and oat relative to potato or wheat resulted in increased soil aggregation in maize and oat cultivated soils. It is demonstrated that, in areas prone to soil water erosion, planting high‐biomass‐yielding crops such as maize and oat is more beneficial for increasing soil aggregation and stability, compared with low‐biomass‐yielding crops such as wheat or potato.

Crop Residue Removal Effects on Soil Erosion and Phosphorus Loss in Purple Soils Region, Southwestern China

Background: Purple soil has a fragile structure and is highly vulnerable to soil erosion and phosphorus (P) loss risks. Despite this, the region is endowed with abundant crop residue resources. To ensure sustainable agricultural development in this area, we conducted a study to investigate the impact of crop residue removal on soil aggregate structure, soil erosion, and the risk of P loss. Methods: We conducted a three-year on-farm experiment and analyzed various soil parameters. These parameters include mean weight diameter (MWD), geometric mean diameter (GMD), soil aggregates with a diameter greater than 0.25 mm (R&gt;0.25mm), saturated hydraulic conductivity, soil erosion estimated by RUSLE 2, total soil phosphorus (TP) concentration, geometric mean concentration of TP (GMC), and geometric mean concentration of TP adjusted for aggregate size (GMCd). Results: Retaining all crop residue can significantly improve soil saturated hydraulic conductivity, which was 2.56 times higher than the complete removal treatment. After three years of experimentation, compared to four months, the 50% residue removal treatment increased the GMCd by 32.7%, while the 0% removal treatment increased the GMCd by 16.6%. Both improvements were higher than the complete removal treatment. Partial or complete removal of the crop residue can reduce the soil aggregate stability and increase the risk of soil erosion and P loss. Conclusions: The GMC and GMCd have the potential to serve as indicators for evaluating soil P loss risk. Removing crop residues can cause the degradation of the structure of purple soil aggregates, thus resulting in increased soil erosion and P loss. It is not recommended to remove crop residues in the purple soil region to ensure sustainable agricultural development.

Short-Term Effects of Experimental Fire on Physicochemical and Microbial Properties of a Mediterranean Cambisol

Little is known about the bonfire impact on microbial properties in soil. This work aimed to study moderate- to high-severity experimental burning (250 °C) compared to unburned Cambisol in a natural Mediterranean environment (Croatia) on selected soil properties. The soil was sampled immediately and 1, 2, 4, and 6 months after the fire. The fire increased the mean weight diameter, water stable aggregates, and water repellence in different soil fractions, and the observed effect was the strongest immediately after the fire. It also altered soil pH, electrical conductivity, total nitrogen carbon, and sulphur content, and completely destroyed carbapenem-resistant bacteria, but did not significantly affect the soil’s mineralogical properties. Six months after the fire, most microbial properties (save for pH) returned to near control values. Heterotrophic, sporogenic, and phosphate-solubilising bacteria started to recover after a month, whereas the population of carbapenem-resistant bacteria was destroyed initially, but recovered by the fourth month after the fire. Dehydrogenase activity was not significantly affected, but proper recovery started four months after the fire. Even though Cambisol showed some resilience to fire and its properties mostly returned to normal by the sixth month, and a full recovery is expected to occur later, as vegetation returns.

Mixed Plantations Induce More Soil Macroaggregate Formation and Facilitate Soil Nitrogen Accumulation

Nitrogen plays a crucial role in limiting plant growth and determining net primary productivity in forest ecosystems. However, variations and influencing factors of soil nitrogen distribution on the aggregate scale in pure and mixed Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations remain unclear. This study aimed to explore how soil aggregate composition, geometric mean diameter (GMD), mean weight diameter (MWD), total nitrogen (TN), total acidolyzable nitrogen (TAN), available nitrogen (AN), nonacidolyzable nitrogen (AIN), amino acid nitrogen (AAN), nitrate nitrogen (NO3−-N), cidolyzable ammonia nitrogen (AMN), unknown-acidolyzable nitrogen (HUN), amino sugar nitrogen (ASN), and ammonium nitrogen (NH4+-N) contents and stocks varied with aggregate size (&gt;2, 1–2, 0.25–1, and &lt;0.25 mm) and stand type [Chinese fir mixed with Michelia macclurei Dandy (CF + MM), Chinese fir mixed with Mytilaria laosensis Lecomte (CF + ML) and pure stands of Chinese fir (CF)] in 0–20 and 20–40 cm soil depth. Soil N content in different stand types of Chinese fir plantations decreased as the aggregate size increased, whereas the soil N stock exhibited the opposite trend. In contrast to CF soil, CF + MM and CF + ML soil displayed a significant increase in MWD, GMD, and aggregate-associated TN, AN, NO3−-N, NH4+-N, AIN, AAN, ASN, and AMN contents and stocks, especially CF + MM soil. Organic N was more sensitive to the response of aggregate size and stand type than mineral N. Redundancy analysis and Pearson’s correlation analysis indicated that the 0.25–1 mm aggregate proportion was the main controlling factor for the variations in soil N content and storage. Overall, this study contributed significantly to the promotion of the sustainable use of soil resources and reference information for the scientific management and sustainable development of Chinese fir forests.

Effects of acid rain and root exclusion on soil organic carbon in Cunninghamia lanceolata and Michelia macclurei plantations.

Acid rain is one of most serious environment problems in China. The types of acid rain have gradually transformed from sulfuric acid rain (SAR) to mixed acid rain (MAR) and nitric acid rain (NAR) in recent years. Roots are one source of soil organic carbon and play an important role in the formation of soil aggregates. However, the changes in acid rain type and the effect of root removal on soil organic carbon in forest ecosystems are poorly understood. In this study, we removed roots and simulated acid rain with different types (SO42-:NO3- ratio of 4:1, 1:1, and 1:4) for three years in Cunninghamia lanceolata (CP) and Michelia macclurei (MP) plantations to analyze the changes of soil organic carbon and physical properties and to measure the size and mean weight diameter (MWD) of aggregates. Results showed that root removal in C. lanceolata and M. macclurei remarkably reduced soil organic carbon pool by 16.7 % and 21.5%, and soil recalcitrant carbon by 13.5% and 20.0%, respectively. Root removal substantially decreased the MWD and proportion and organic carbon content of soil macroaggregates in M. macclurei, but not in C. lanceolata. Acid rain did not affect soil organic carbon pool and soil aggregate structures. Our results indicated that roots promote soil organic carbon stabilization and that their contribution to the stability of soil organic carbon varies with forest types. Moreover, soil organic carbon stabilization is not affected by different types of acid rain in the short term.

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.

Effect of Long-Term Organic Cropping Systems on Physico-Chemical Properties of the Soils of Indian Punjab

Organic farming is gaining momentum because of awareness among consumers for quality food. The long term effects of organic cropping systems on soil quality yet not have been studies in details. Therefore the present study the long term effect of five cropping systems viz. Poplar (Populus deltoids) + turmeric (Curcuma longa), sugarcane (Saccharum officinarum Linn )+ bottle gourd (Lagenaria siceraria) - broccoli (Brassica oleracea), basmati rice (Oryza sativa) - wheat (Triticum aestivum), sugarcane fodder and maize (Zea mays) + summer moong (Vigna radiate) - wheat on soil physico-chemical properties was studied at Bhagat Puran Singh Natural Agriculture Farm and Research Centre, Amritsar, Punjab (31.5730 N, 75.0660 E). The depth wise soil samples from these cropping systems were collected after rabi (2018-19) and kharif (2019) seasons. Poplar + turmeric cropping system has significantly higher soil organic carbon(SOC), soil carbon stock(SOCS), soil aggregate associated carbon(AAC), water stable soil aggregates (WSA) and mean weight diameter(MWD) of soil than other cropping systems. Sugarcane fodder cropping system has significantly higher soil pH than other cropping systems while basmati rice - wheat cropping system has significantly lower electrical conductivity (EC) and higher soil bulk density (BD) compared to other cropping systems. In the top soil (0-7.5 and 7.5-15 cm depths) SOC, SOCS, AAS, EC, WSA and MWD were significantly higher than subsurface layers (15-22.5 cm and 22.5-30 cm depth) whereas soil pH and BD were significantly lower in surface soil than subsurface soil.

Response of sediment transport capacity to soil properties and hydraulic parameters in the typical agricultural regions of the Loess Plateau

The sediment transport capacity by overland flow (Tc) is a key parameter in process-based soil erosion models and Tc variation is sensitive to changes in soil properties. This study was undertaken to investigate Tc variations with respect to soil properties and establish a universal relationship to predict Tc. The test soils were collected from typical agricultural regions (Guanzhong basin—Yangling (YL), Weibei Dry plateau—Chunhua (CH), Hilly and gully region—Ansai (AS), Ago-pastoral transition zone along the Great Wall—Yuyang (YY), and Weiriver floodplain—Weicheng (WC)) of the Loess Plateau, and subjected to 36 different combinations of slope gradients (S, 5.24–44.52 %) and flow discharge (q, 0.00033–0.00125 m2 s−1) in a hydraulic flume. The results showed that the mean Tc values for WC were 2.15, 1.38, 1.32, and 1.16 times greater than those for YL, CH, AS, and YY, respectively. Tc significantly decreased with clay content (C), mean weight diameter (MWD), and soil organic matter content (SOM). Tc for different soil types increased with S and q as a binary power function, and Tc variation was more sensitive to S than to q. Stream power (w) was the most appropriate hydraulic variable to express Tc for different soils. Tc for different soil types could be satisfactorily simulated using a quaternary power function of S, q, C, and MWD (R2 = 0.94; NSE = 0.94) or a ternary power function of w, C, and MWD (R2 = 0.94; NSE = 0.94). The new Tc equation can reflect the effect of soil properties on it and facilitate the development of a process-based soil erosion model.

Short-term cultivation limiting soil aggregate stability and macronutrient accumulation associated with glomalin-related soil protein in Eucalyptus urophylla × Eucalyptus grandis plantations

The relationship between glomalin-related soil protein (GRSP) and soil aggregation has been a hot topic of research for its close link to soil stability and quality. However, the short-term cultivation of Eucalyptus poses serious threats to soil stability and nutrient stocks, and the effects of GRSP on soil aggregate stability and macronutrient accumulation remain unclear. The aim is to clarify the potential mechanisms affecting soil aggregate stability and macronutrient accumulation in short-term Eucalyptus plantations. Five Eucalyptus urophylla × Eucalyptus grandis plantations with different cultivation periods (1–5 years) in this study were investigated, and a native evergreen broadleaf forest (0 year) was selected as control. The mean weight diameter index increased in the first 3 years and then significantly decreased during 5 years cultivation of Eucalyptus. Soil organic carbon (SOC) and total nitrogen also decreased after planting Eucalyptus for 3 years, but variation in total phosphorus was not obvious. The relative abundance of Glomeraceae and Claroideoglomeraceae decreased in the 5-year-old Eucalyptus plantations and was positively correlated with GRSP content. In pathway modeling, nutrient-acquisition enzyme activities positively affected GRSP and macronutrient content. Total GRSP (T-GRSP) had higher total effects than easily extractable GRSP on soil aggregate stability, and positively correlated with SOC in macroaggregates. Both T-GRSP and SOC had positive and direct effects on soil aggregate stability. Variance partitioning analysis further explained the contribution of GRSP and SOC to aggregate stability, particularly in >2 and 2–0.25 mm macroaggregates. Our results suggested that GRSP was directly associated with SOC content and soil aggregate stability, and was a potential key factor affecting soil aggregate stability in Eucalyptus plantations. Improving T-GRSP and SOC are efficient approaches for preventing the gradual deterioration of soil aggregate stability. Short-term cultivation should be carefully used in Eucalyptus plantations, and a new cultivation period is needed.

The Effect of Organic Waste Applications on Soil Aggregation and Soil Organic Carbon Fractions

ABSTRACT In this study, organic wastes obtained from different sources (Olive Oil Solid Waste-OSW, vermicompost-VC, farmyard manure- FYM) were applied in different doses (0, 1, 2, 3%) and the aggregation status of the soils and soil organic carbon (SOC) fractions (organic carbon-OC, activated carbon-AC, microbial biomass carbon-MBC) were investigated. In this study, unlike other studies, the contribution of organic materials to SOC fractions and which of these fractions have a significant relationship on aggregation have been revealed. In the study, the aggregate stability (AS) and mean weight diameter (MWD) properties of the soils increased by 12% and 8% compared to the control with 3% organic waste application. It was determined that OSW and FYM were more effective than VC on aggregate development of soils. In addition, statistically significant differences were found with organic material application on SOC fractions. The highest increase was detected in the microbial biomass carbon content (69%) compared to the control. While a high positive correlation was determined between aggregate stability and carbon fractions, the relationship between C fractions and AS was listed as organic carbon > microbial biomass carbon > activated carbon (r: 0.96, 0.94, 0.68; p < .05). The effects of organic wastes applied at 2 and 3% dose levels, the obtained AS, MWD, and OC contents showed significant variability depending on the differences in the wastes. As a result of the study, it was evaluated that organic waste application was effective in the aggregate development of soils. In addition, it was determined that the most effective SOC fraction in increasing the aggregate stability of soils was OC. On the other hand, it was determined that the more unstable activated carbon contributed to the increase of AS at lower levels.

Is adding biochar be better than crop straw for improving soil aggregates stability and organic carbon contents in film mulched fields in semiarid regions? –Evidence of 5-year field experiment

Plastic film mulching is used widely to increase crop yields in semiarid areas, but improving the soil fertility in film mulched fields is also important for achieving sustainable high yields in northwest of China. In this study, a completely randomized two–factor field design experiment was conducted in Pengyang, Ningxia, China during 2017–2021. In order to investigate the effects of plastic film mulching with straw/biochar addition on the soil aggregate characteristics, organic carbon content, and maize yield. Six treatments were established as follows: control (C), straw (S), biochar (B), plastic film mulching (F), plastic film mulching with added straw (FS) or biochar (FB). After 5 years of continuous production, each straw and biochar addition treatments significantly improved the soil aggregate distribution and stability, and the average aggregate content >0.25 mm increased significantly by 47.32%. Compared with the treatments without plastic film mulching, the mean weight diameter and geometric mean diameter of the soil particles increased by 9.19% and 4.15%, respectively, under the plastic film mulching treatments. The organic carbon content of the 0–60 cm soil layer increased significantly under each straw and biochar addition treatment compared with the without straw. The aggregate organic carbon contents under each treatment increased as the aggregate particle size increased, where the straw and biochar addition treatments significantly increased the organic carbon content of the aggregates, whereas the contents decreased under the plastic film mulching treatments. The contributions of the soil aggregates >0.25 mm to the organic carbon contents of the 0–60 cm soil layer were significantly higher under FS (37.63%) and FB (56.45%) than F. Structural equation modeling showed that straw/biochar added, plastic film mulching, and a greater soil organic carbon content could significantly promote yield increases, where the straw and biochar addition treatments significantly increased the average maize by 14.6% on average. In conclusion, carbon input as straw, especially biochar, had a positive effect on improving the soil organic carbon content and maize yield under plastic film mulching farmland in a semiarid region.

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

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

Soil aggregate stability and its response to overland runoff–sediment transport in karst peak–cluster depressions

Karst peak–cluster depressions are ecologically fragile, and slope runoff is a cause of severe soil erosions. However, the runoff–sediment pattern and influencing factors of typical lithologies slope erosion are still unclear. This study investigated the soil aggregate stability of limestone and dolomite and their effects on interrill erosion using rainfall tests. The dolomite soil aggregates were smooth with fine, tightly arranged particles. The limestone soil aggregates were rough with regularly shaped flocculent granular bodies. Soil aggregates of limestone had a higher microporosity than that of dolomite. The contents of macroaggregate with a particle size > 0.25 mm (WSA0.25) were significantly higher in limestone soils than in dolomite soils (P < 0.05). The mean weight diameter (MWD) trend was consistent with the WSA0.25 value. The MWD value for forest soil of limestone was the highest among all soil types, 5.65 mm. With the Le Bissonais (LB) method, the MWD values followed the order of limestone > dolomite soils. The organic matter, Ca and Mg contents were highly significantly correlated with the aggregate stability (P < 0.01). During rainfall, the trend for soil runoff rates mainly indicated three stages: 0 ∼ 10 min, rapidly increasing; 10 ∼ 30 min, fluctuating; and 30 ∼ 60 min, essentially stable. The stable runoff rates of limestone soils were lower than that of dolomite soils. At a slope of 10°, the soil loss rate of dolomite forest was 0.16 g/(min·m2) higher than that of limestone. The sediment concentrations of dolomite soils were higher than those of limestone soils. The sediment aggregates were dominated by macroaggregates. The content of macroaggregates in dolomite soils ranged from 49.54% to 64.84% at 30 min of runoff and ranged from 51.60% to 69.88% in limestone soils. In general, limestone soils experienced less erosion than dolomite soils because of the difference in soil aggregate stability. The results of this study could provide a theoretical reference for karst rocky desertification management and ecological restoration.

Mean‐weight diameter of aggregation as affected by initial screen size of two fine‐textured soils

AbstractSoil aggregation is considered a key indicator of soil health to protect soil against erosion, enhance organic C storage, and offer habitat for soil organisms. Various methods to assess aggregation may change interpretations of management, and therefore should be cross‐calibrated. We assessed the impact of initial sieve opening size (8 or 4.75 mm) prior to determination of dry‐stable and water‐stable mean‐weight diameter (MWD) from two fine‐textured soils—a Rhodic Hapludox from São Paulo, Brazil and a Rhodic Kanhapludult from North Carolina, United States. Both soils were subjected to management expected to alter surface soil conditions. As expected, initial sieving through 8 mm led to greater dry‐stable MWD (3.37 ± 0.60 mm) than initial sieving through 4.75 mm (1.94 ± 0.28 mm). However, soil stability index (water‐stable MWD/dry‐stable MWD) was not affected by initial sieve size opening (0.56 ± 0.13 mm mm−1 under both initial sieve openings). Management interpretations were consistent with both approaches as well, and in particular to detect the strong depth effect on water‐stable MWD (i.e., declining with depth). Water‐stable macroaggregates had 32% ± 25% greater C concentration than microaggregates; similarly under both initial sieving conditions. Soil stability index when initially sieved through 4.75 mm was highly associated with aggregate stability of 1–2‐mm sized dry aggregates, which is a more common procedure. We conclude that passing soil through a screen with 4.75‐mm openings to conduct a diversity of soil analyses can be appropriate for obtaining reasonable estimates of and interpretations about surface soil aggregation.