Aggregate Stability Index Research Articles

Saline Water Irrigation Changed the Stability of Soil Aggregates and Crop Yields in a Winter Wheat–Summer Maize Rotation System

Irrigation using saline water is extensively used in areas of agricultural production where freshwater is scarce. However, saline water irrigation adversely impacts soil’s physicochemical characteristics and crop productivity. In this study, we established irrigation water with five salinity levels (ECiw, 1.3, 3.4, 7.1, 10.6, 14.1 dS·m−1) to investigate how these salinity levels influenced grain yields as well as soil salinity, alkalinity, sodicity, and aggregate stability in the 0~20 cm soil layer of a wheat and maize rotation field (in 2022–2023). Tukey’s test, entropy-weighted TOPSIS, and the least squares method were used to analyze the significance analysis, comprehensively evaluate the soil aggregate stability and soil index comprehensive score (SICS), and achieve linear fitting, respectively. The results showed that when ECiw > 3.4 dS·m−1, there was a significant increase in the soil salinity, pH, and sodium adsorption ratio. When ECiw > 7.1 dS·m−1, a significant reduction in soil aggregate stability was observed. When ECiw ≤ 3.4 dS·m−1, there was no significant reduction in the grain yields of wheat and maize. Furthermore, the annual grain yields of wheat and maize decreased by 5% and 10%, respectively, resulting in a change in ECiw values from 2.98 to 4.24 dS·m−1, based on the linear regression analysis of SICS and ECiw, as well as the annual grain yields and SICS. Under uniform irrigation conditions, the soil salinity, alkalinity, and sodicity were lower, and soil aggregate indexes were more stable at the maturity stage of maize.

Vegetation restoration changed the soil aggregate stability and aggregate carbon stabilization pathway according to δ13C signatures

Vegetation restoration can increase soil organic carbon (SOC) sequestration through the physical protection of soil aggregates. However, the soil aggregate stability and C flow pathway associated with long-term plantation restoration have not yet been fully characterized. Here, we conducted a study on Robinia pseudoacacia plantations at different recovery stages, studied the distribution and stability of aggregates, analysed the aggregate-associated organic carbon (OC) content and δ13C value, and quantified the aggregate C flow pathway. The results revealed that vegetation restoration increased the proportion of large macroaggregates (LMAs) and decreased the proportion of small macroaggregates (SMAs), with no changes observed in the proportion of microaggregates (MIAs) or silt + clay (SC) at 0–20 cm. The indices of aggregate stability, namely, the mean weight diameter (MWD), geometric mean diameter (GMD) and structural stability index (SSI), increased under vegetation restoration at 0–20 cm, with maximum values of 3.83 mm, 2.88 mm, and 2.00 %, respectively, at 35 years of age (35Y). The OC content of the LMAs increased from 10.96 to 21.64 g kg−1 and from 7.27 to 10.05 g kg−1 in the 0–20 cm and 20–40 cm layers, respectively. LMAs and SMAs had the greatest contributions to SOC accumulation in the 0–20 cm and 20–40 cm layers, respectively. The δ13C value increased with decreasing aggregate size. The C flow pathway was from macroaggregates to MIAs or SC. Compared with abandoned farmland, vegetation restoration decreased the aggregate C flow intensity in the 0–20 cm layer. The soil aggregate stability and aggregate-associated OC content decreased with increasing soil depth, but the soil δ13C value exhibited the opposite trend. Vegetation restoration regulated soil aggregate stability by influencing the fine root biomass (FRB) and SOC content. In summary, our analysis offers a valuable reference for the controlling effect of aggregation on C stability influenced by vegetation restoration.

Water holding capacity, aggregation, respiration, and chemical character of acid soil amended rice straw biochar enriched with different volumes of liquid extract (sap) of Kappapychus alvarezii

The quality of acidic soil is determined by organic C content produced from rice straw biochar in agriculture. In this context, liquid extract from Kappapychus alvarezii (K-sap) is used as a biochar enrichment agent. Therefore, this research aimed to (i) analyze the character of K-sap enriched rice straw biochar with different volumes, as well as (ii) evaluate the impact on soil water holding capacity, size class distribution, aggregate stability index, respiration rate, and acidic soil chemical characters. The treatment tested was the volume of K-sap kg-1 biochar, namely (i) without biochar, (ii) 0 mL, (iii) 500 mL, (iv) 1,000 mL, and (v) 1,500 mL. Each treatment was repeated three times and placed according to a randomized block design procedure. The area covered by K-sap, pore size, and amorphous degree increased while the pore volume of the biochar surface decreased. The addition of 1,000 mL of K-sap kg-1 biochar released a new peak number associated with the aliphatic and aromatic groups. The K-sap enriched biochar increased the proportion of soil aggregate size of 1-2 mm, water holding capacity, carbon storage, pH, total N, available P and K, exchangeable base cations as well as base saturation. Meanwhile, the concentration of Al3+ and H+ were decreased in the acidic soil solution. The results showed that the performance of rice straw biochar, K-sap volumes, soil chemical quality, water holding capacity, and ability to store carbon of the acidic soil was improved by adding K-sap volume.

Soil aggregate stability index independent from pre-stress aggregate size distribution: A test from soils affected by the water level fluctuation in the Three Gorges Reservoir, China

Soil aggregate stability measurement is essential to determine soil health status under various conditions. The Mean Weight Diameter (MWD) is the most applied index to express aggregate stability particularly for wet and dry sieving. However, the MWD could generally present results affected by pre-stress aggregate size distribution when remained aggregates after stress are considered for calculation. Therefore, the objective of the present study was to eliminate the similarities between the MWD results and pre-stress aggregate size distribution, which largely affects treatments differentiation. Samples from 145-160 m (lower), 160–169 m (middle), and 169–175 m (upper) elevations differently affected by the Water Level Fluctuation in Three Gorges Reservoir (TGR) and control (>175 m) were exposed to wet shaking stress. Aggregates remained at each sieve opening, aggregates disintegrated/passed through the sieve opening, and small macroaggregates and microaggregates accumulated were recorded. These aggregates were used to determine and compare two indexes (1) using remained aggregates (MWD) and (2) using disintegrated/accumulated aggregates (MWDd/a) based on the differences among treatments. The results for both pre-stress aggregates and remained aggregates after stress were showed consistent significant differences (p < 0.05) between upper and control elevations. This gives indication that aggregates remained after stress strongly depend on pre-stress aggregate size distribution. As the MWD was calculated from remained aggregates, the identified difference between upper and control elevations for this index could also confirm its dependence to pre-stress aggregates distribution. Contrary, disintegrated and accumulated aggregates showed non-significant differences between upper and control elevations. This non-significant and significant differences between upper and control elevations for disintegrated and pre-stress aggregates suggest a non-dependence condition. Similarly, the upper and control elevations showed no significant differences in MWDd/a. This substantially informs that this index is independent from pre-stress aggregates distribution because it was entirely calculated from disintegrated aggregates. Higher aggregate stability was indicated by high MWD, with values ranging from 1.41 to 6.24 mm. On the other hand, higher stability was expressed by lower values of the MWDd/a, with the values varying between 3.87 and 0.5 mm. Overall, the present study evidenced the major advantage of considering the disintegrated/accumulated than remained aggregates in calculating unbiased MWD index for aggregate stability.

Aggregate Stability Indices of a Typic Hapludult under Different Land-Use Types and Varying Depths at Umuahia

Aggregate Stability Indices of a Typic Hapludult under Different Land-Use Types and Varying Depths at Umuahia

Studi Fisika Tanah pada Budi Daya Tembakau (Nicotiana tabacum L) di Berbagai Kemiringan Lahan

The percentage of slope classes on a land has an impact on changes in soil physics. The purpose of this study is to evaluate the physical properties of soil planted with tobacco on various slopes in Kenagarian Situjuah Batua, Situjuah Limo Nagari District, Lima Puluh Kota Regency. The method used in this study was a survey; samples were taken purposively based on slope classes at slopes 8-15%, 15–25%, and 25–45% at depths of 0–20 cm and 20–40 cm. From each slope 3 repetitions were taken. The results showed that there were changes in soil physics properties in each slope class with the dominant texture of sandy clay loam. Organic matter was classified as high to low (18.77–3.63%), low soil buld density (0.66–0.34 g/cm3), and total pore space was classified as high (75.27–86.87%). The permeability of the soil was classified as very fast to somewhat slow (34.88–0.78 cm/h), and the aggregate stability index was somewhat steady to less steady (60.89–45.98%). It is recommended that tobacco farmers to make terrracing and cut the length of the slope so that it does not lose organic matter. Keywords: soil physical properties, slope level, tobacco plantation

Influence of cover crops on soil aggregate stability, size distribution and related factors in a no-till field

Soil aggregation plays an essential role in maintaining soil structure. A three-year field experiment was undertaken to explore the effects of cover crops on soil aggregate stability indices (mean weight diameter, water-stable aggregates greater than 0.25 mm, and soil erodibility factor), size distribution and their correlations with nine soil physical and chemical properties (soil bulk density, pH, organic carbon, total nitrogen, C/N, calcium, phosphorus, potassium, and cation exchange capacity) at 0–5 and 5–10 cm depths in a Marietta silt loam soil in a no-till field, Northeastern Mississippi. The cover crop treatments included elbon rye (Secale cereale L.), daikon radish (Raphanus sativus ssp. acanthiformis), Austrian winter field peas (Lathyrus hirsutus), and their mixture. The samples were wet-sieved to five size classes of aggregates (> 2, 2–1, 1–0.5, 0.5–0.25, and < 0.25 mm). Results showed that the < 0.25 mm aggregates dominated (50.95–78.02 %) soil aggregate size distribution at 0–5 and 5–10 cm depths. The rye plot soil displayed the greatest values for mean weight diameter (0.58 mm) in the two soil depths. Soil water-stable aggregates greater than 0.25 mm value under peas was significantly higher by 68.61 % compared to the no cover crop treatment at 0–5 cm depth, while soil erodibility factor did not change significantly. Mean weight diameter, water-stable aggregates greater than 0.25 mm, soil erodibility factor, 1–0.5 mm aggregates, and < 0.25 mm aggregates were significantly correlated with soil organic carbon, pH, bulk density, phosphorus, and potassium. The dominant factors driving changes in three aggregate stability indices and size fractions (excluding 2–1 mm aggregates) were bulk density and pH. Furthermore, high pH restricted soil aggregate stability and size distribution. This study demonstrated the positive impact of cover crops, specifically peas and rye, on soil aggregate stability and size distribution. This study will provide valuable information for future research on soil stabilization in crop production management systems.

Conservative farming systems and their effects on soil organic carbon and structural quality

Pesticides-free integrated farming systems emerge as a viable option to promote environmental protection, due to the diversification of the agroecosystem, making the soil productive and resilient. However, there is a lack of information about the influence of integration farming systems on the relationship between soil physical quality and organic matter. The objective was to determine soil organic carbon fractions, and soil structural attributes in conservative single and integrated farming systems, to verify the potential of these farming systems to increase soil organic carbon stocks and improve soil structural quality. The experiment was carried out at a pesticide-free agricultural systems. Soil samples were collected in three layers (0–0.05, 0.05–0.10, and 0.10–0.20 m) of five farming systems (Cropland - C, Livestock - L, Forestry - F, Livestock-Forestry – LF, and Crop-Livestock-Forestry - CLF) in the randomized block design. Sampling was carried out in two transects of 25 m each, collecting five samples per transect, totaling 10 samples per layer. The following soil attributes were determined: soil organic carbon (SOC), particulate organic carbon (POC), mineral-associated organic carbon (MAOC), soil organic carbon stocks (Cst), visual evaluation of soil structure (VESS), tensile strength of aggregates (TS), soil friability, weighted mean diameter (WMD), geometric mean diameter (GMD) and the aggregate stability index (ASI). At 0–0.05 m, the SOC content was up to 12% higher in the Cropland system compared to other farming systems, while at 0.05–0.10 m and 0.10–0.20 m of depth, the difference was higher, around 27% between Cropland and other farming systems. For the VESS, Cropland had the lowest score (1.35), while the higher scores were in the Forestry, and CLF systems (2.25, 2.24, respectively). Both soil organic carbon and soil physical quality were greater in all farming systems. The particulate organic carbon and weighted mean diameter were efficiently to promote changes in soil carbon inputs and structural changes. The single and integrated farming systems promoted an increase in soil organic carbon, by a rate of 3.02, 1.81, 2.17, 1.78, and 2.01 Mg ha−1 yr−1, respectively for Cropland, Livestock, Forestry, LF, and CLF. The pesticide-free farming systems, under conservative practices, were very promising in showing the increase of SOC, POC and MAOC, supporting the soil physical quality, and cooperating with the soil health.

Cover crops and poultry litter impact on soil structural stability in dryland soybean production in southeastern United States

AbstractThis study explored the efficacy of soil aggregate indices in quantifying soil structural development, utilizing 5‐year field experiment data from the Southeastern United States. The experiment utilized a split‐plot design with cover crops (native vegetation as control, cereal rye (Secale cereale L.), winter wheat (Triticum aestivum), hairy vetch (Vicia villosa), and mustard (Brassica rapa) plus cereal rye as the main factor and fertilizer source (no fertilizer as control, inorganic fertilizer with phosphorus, potassium, and elemental sulfur, and poultry litter) as the secondary factor. Aggregate size fractions were determined using the wet‐sieving method, and aggregate stability index (ASI), mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension (FD) were calculated to assess soil structural stability. Main effects results indicated that cereal rye (55.11%) and poultry litter (50.97%) exhibited the highest ASI values. The highest MWD, GMD, and FD were observed under mustard plus cereal rye (1.187 mm), cereal rye (0.462 mm), and hairy vetch (2.573), respectively. Principal component analysis revealed that cover crops significantly improved soil aggregate structure and stability, overcoming limitations of sole fertilization practices. Regression analysis suggested that ASI, MWD, and GWD positively correlated with soil organic carbon, whereas FD negatively correlated with MWD, GMD, and ASI. Principal component analysis exhibited that FD decreased with increasing soil organic carbon, ASI, MWD, and GMD, demonstrating that lower FD values indicate enhanced soil aggregation and structure. Assessed indices, FD included, effectively gauged soil structural stability. These metrics should be prioritized in managerial decisions to support soil productivity and health in agricultural systems.

Effects of Straw Returning on Soil Aggregates and Its Organic Carbon and Nitrogen Retention under Different Mechanized Tillage Modes in Typical Hilly Regions of Southwest China

Tillage modes and straw returning influence soil aggregate stability and the distribution of organic carbon (C) and nitrogen (N) in aggregates of different particle sizes. In the typical hilly regions of southwest China, the predominant soil type is purple soil, characterized by heavy texture and high stickiness, with relatively lower soil fertility compared to other soil types. The improper use of fertilizers and field management practices further exacerbates soil compaction. However, abundant straw resources in the region provide an opportunity for comprehensive straw utilization. The effective utilization of straw resources is of significant importance for stabilizing agricultural ecological balance, improving resource utilization efficiency, and alleviating ecological pressure. Previously, most studies have focused on the impact of different mechanized tillage systems on the physical and chemical properties of soil in hilly areas, while research on the preservation of water-stable aggregates’ organic C and N content remains limited. In this study, the soil properties of fields under a winter pea–summer corn rotation for two years were studied with regards to the effects of straw returning on its water-stable aggregate distribution, macroaggregate content (R0.25), mean weight diameter (MWD), geometric mean diameter (GMD), and the organic C and N content in soil aggregates of different particle sizes and at different depths. The effects of five different tillage modes were assessed, namely rotary tillage with straw mixed retention (RTM), conventional tillage with straw burial retention (CTB), no-tillage with straw covered retention (NTC), subsoiling with straw covered retention (STC), and no-tillage without straw retention (NT). Based on the study results, under different tillage modes, straw returning effectively enhanced the soil organic carbon (SOC) and total nitrogen (TN) reserves at the plow layer (0–30 cm), SOC increased by 17.2% to 88%, and TN increased by 8.6% to 85.9%. At the same time, the content of 0.25–2 mm aggregates increased under the straw-return treatments under different tillage patterns. The NT treatment had the lowest R0.25 and MWD and GMD values for soil aggregates at different depths, which were significantly different (p &lt; 0.05) from the other treatment modes. The correlation coefficients between SOC and soil aggregate stability indices ranged from 0.68 to 0.90, with most of them showing highly significant positive correlations (p &lt; 0.01). In conclusion, straw returning under different tillage systems has improved soil aggregate stability and promoted soil structure stability. Specifically, the STC treatment has shown more pronounced effects on soil improvement in the upper soil layer of the hilly regions in southwest China, while the RTM treatment is beneficial for improving the lower soil layer. Therefore, the comprehensive experimental results indicate that the combination of STC and RTM treatments represents the most promising mechanized tillage and straw returning practices for the hilly regions in southwest China.

Variable rate phosphorus fertilizer recommendations for rainfed wheat

A uniform application of phosphorus (P) fertilizers to spatially variable soils often results in under-fertilization in low P-localities and over-fertilization in high P-localities. This study aimed to evaluate the variable rate applicability of P fertilizers on a 300-ha sloping landscape under rainfed winter wheat cultivation for over 70 years. The soils were sampled (155 samples) using a random spatial sampling technique based on visual differences in soil color and topographic factors. Plant available soil P content (Pav) and other variables of soil samples were analyzed. The spatial variability of Pav was evaluated and the area was divided into three uniform zones (low, medium, high) for fertilizer P application based on the spatial variation of Pav. The values of Pav showed moderate variablity (CV= 21.3%). The fertilizer recommended by the Ministry of Agriculture and Forestry (MAF) was calculated for five identically-sized sub-regions. The results showed that P fertilizer rates calculated for all five sub-regions based on MAF were identical, suggesting that the MAF was insensitive to spatial variability of Pav in the study soils. Both semivariograms and surface maps of soil properties indicated a strong spatial association between Pav and each of plant available water content (PAWC) and aggregate stability index (ASI), suggesting that yield limitation casued by PAWC should be considered in a variable P-application program in the study area. A more comprehensive study is needed to evaluate the efficiency and cost-benefit economics of variable P application in the study soils.

The Use of Biofilm Biofertilizer to Increase Smart Farming System in Mustard Yield and Improve Soil Physical Properties of Vertisols

Soil serves as the growing medium and source of nutrients for plants. Vertisol soil, however, does bring with it some flaws particularly its physical characteristics. The application of organic fertilizer decomposed with Biofilm biofertilizer, thus, isexpected to improve the physical characteristics of soil and yield of mustard. The aim of the research is to study the effect of the dose of organic fertilizer decomposed by Biofilm biofertilizer to the betterment of Vertisol soil physical characteristics and the mustard yield. The experiment was completed in a field with Randomized Complete Block Design consisting of a single treatment factor in the form of Biofilm biofertilizer. The data obtained from the series of observations was analyzed based on the F test with 95% confidence level followed by Duncan’s Multiple Range Test (DMRT). The variables of the observations involve the mustard plant yield and the soil physical characteristics. The study shows that the application of the organic fertilizer decomposed by Biofilm bio-fertilizer provides significant effects towards the improvement of the vertisol soil’s physical characteristics and the increase in mustard plant yield. The dose 21 tons/ha results in the highest increase in the mustard plant production and the best improvement of the vertisol soil physical characteristics. Organic fertilizer decomposed by Biofilm bio-fertilizer 21 tons/ha helps in developing permeability as much as 685.71%; aggregate stability index 201.6%; organic material 20.74%; and porosity 122.38%. Also, organic fertilizer decomposed by Biofilm bio-fertilizer 21 tons/ha can boost the mustard plant production as much as 4.25 tons/ha compared to the absence of organic fertilizer decomposed by Biofilm bio-fertilizer.

Using a novel vector length stability index (VLSI) to evaluate soil aggregate stability: A preliminary study

Soil aggregate stability is an important soil characteristic which can represent the improvement of soil structure after revegetation. Due to the high heterogeneity of soil, large-scale sampling is usually necessary to estimate the spatial variation of aggregate stability across landscapes. Although there are many methods and corresponding indices for analysis of aggregate stability, many of them are not suitable for investigations with a large number of samples due to time-consuming experimental practices. To avoid unnecessary costs of time and labor in the long-term land degradation and restoration monitoring across large regional scales, simple indices of aggregate stability would help monitoring across large regional scales. For this reason, we introduced a new, simple, and normalized index, the vector length stability index (VLSI) and its weighted form (wVLSI) to describe soil aggregate stability. The VLSI shares key information of aggregate size distribution with mean weight diameter (MWD), but it is naturally normalized and dimensionless. This new index was tentatively tested to describe soil aggregate stability of the 0–30 cm soil layers under artificial plantations, natural grassland, abandoned farmland, and farmland in production in a small watershed located in the Loess Plateau of China. The results showed that the aggregate stability of the 0–20 cm layers in abandoned farmland could be recovered near to the condition under artificial plantations just after 2-year abandonment, but the aggregate stability hardly changed in the 20–30 cm layer. The aggregate stability of the 0–10 cm layer in natural recovered grassland is close to that in top soil layers under artificial plantations, but the stability in the 10–30 layers appeared as low as that in farmland. Because of its simple form and low data requirements, the VLSI could be an alternative efficient tool for soil aggregate stability evaluation when a large number of samples are needed.

Monitoring soil quality of different land use systems: a case study in Suha watershed, northwestern highlands of Ethiopia

The problem of soil quality degradation has been becoming more severe in the highlands of Ethiopia due to soil erosion; land use and land cover change, and poor land management. The level of soil quality degradation was not well known and documented in the study area and the results of this study could provide new information to improve soil conditions. The present study was conducted to evaluate soil quality in terms of its physical and chemical fertility under different land use types in the Suha watershed, northwestern highlands of Ethiopia. A total of 27 composite surface soil samples (0–30 cm) were collected from adjacently located land-uses in three replications from two elevation gradients. Standard procedures were followed to analyze selected soil physical and chemical quality indicators. The differences in the mean values of the parameters were tested using a two-way analysis of variance. In addition, Soil Quality Degradation Index was evaluated to see the direction and magnitude of change in soil quality indicators. The analysis of variance results revealed that soil quality indicators such as index of soil aggregate stability, organic carbon (OC), total nitrogen (TN), and C:N ratio were significantly decreased in the cultivated land use system compared to other land use systems. On the other hand, the content of available Phosphorus was significantly higher in the cultivated land. Soil quality deterioration index values were highly negative for SOC (− 71.3%) and TN (− 67.7%) in the cultivated land, followed by grazing land (SOM = − 35.5% and TN = − 27.7%). Aggregated Soil Quality Index values also indicated that the status of soil quality under cultivated fields is rated as low, grazing land as optimal, and forest land as high. Generally, results indicated that land use and cover changes had adverse effects on soil quality indicators. Hence, soil management strategies, mainly Integrated Soil Fertility Management which integrates soil and water conservation strategies, are required to alleviate the problem of soil quality deterioration and improve agricultural productivity.

Spatial changes of soil structural properties and organic carbon storage of arable farmland at Umuahia, Abia State

Precision agriculture requires that spatial changes of soil structural properties and soil organic carbon (SOC) accumulation be established for effective soil management. A research was carried out to ascertain the spatial variation of soil structural properties and organic carbon accumulation of an arable farmland at Umuahia. The experiment was conducted by delineating the land into three (3) portions. Three auger and core soil samples each were randomly collected from each portion, and this gave nine (9) observational points which were georeferenced. The soil samples were prepared and analysed in a laboratory for determination of parameters. The data generated were analysed for spatial variation using a GIS software package. The highest SOC accumulation of 26.46 ton / ha was obtained at the extreme north and northwestern regions of the land, while the lowest SOC accumulation of 19.71 ton / ha was obtained at extreme southeastern region of the land. The entire central area to the north western portion of the land had lowest bulk density (BD) of 1.33 kg / m3, while the southward to the north eastern portions of the land had the highest BD of 1.37 kg / m3. The highest hydraulic conductivity of 4.75 cm / mins was observed at the south western portion. The southward and extreme north eastern portions of the land had the highest mean weight diameter (MWD) of 0.95 mm, while the lowest MWD of 0.75 mm was observed at the central areaand extended to the north western portions of the land. There were also spatial changes in the total porosity, and micro aggregate stability indices across the land area. Suitable agronomic practices need to be adopted within the various portions of the land in managing the soil.

Tree species identity affects nutrient accumulation and stoichiometric in soil aggregates in mixed plantations of subtropical China

The conversion of monocultural to mixed plantations is an increasing and widespread practice worldwide to improve forest productivity and soil fertility. Although tree species identity can affect soil ecological processes, there is still limited research on how it affects soil aggregate stability and nutrient variability. Here, we investigated the variation of 0–100 cm aggregate stability index (percent of aggregate destruction, PAD; fractal dimension, D; geometric mean diameter, GMD; mean weight diameter, MWD), associated carbon (C), nitrogen (N), phosphorus (P), and stoichiometry in mixed plantations from coniferous trees (Pinus massoniana Lamb.) and a variety of individual broadleaved trees (Camellia oleifera Abel, Manglietia chingii Dandy, Cercidiphyllum japonicum Sieb. et Zucc., Michelia maudiae Dunn, and Bretschneidera sinensis Hemsl.). We discovered that compared to coniferous plantations, most mixed plantations significantly improved the mechanical and water stability of topsoil aggregates. Deep-rooted tree species (e.g., Michelia maudiae Dunn) favored the development of subsoil macro-aggregates to improve aggregate water stability (e.g., PAD = 46.10, MWD = 1.23, GMD = 0.49, D = 2.81). Mixed planting led to the enrichment of soil C, N, and P in microaggregate, which increased by at least 37.14, 20.24, and 61.11 %, respectively. The reduced C:P and N:P in soil aggregates indicate that soil P limitation may be alleviated. Furthermore, tree species and soil depth indirectly affected aggregate stability to regulate the accumulation of C, N, and P. Overall, we emphasize the necessity of selecting tree species combinations with complementary ecological niches in mixed plantations to improve soil stability and support forest productivity.

Impact of agro-geotextiles on soil aggregation and organic carbon sequestration under a conservation-tilled maize-based cropping system in the Indian Himalayas

Although agro-geotextile (AGT) emplacement shows potential to mitigate soil loss and, thus, increase carbon sequestration, comprehensive information is scanty on the impact of using agro-geotextiles on soil organic carbon (SOC) sequestration, aggregate-associated C, and soil loss in the foothills of the Indian Himalayan Region. We evaluated the impacts of Arundo donax AGT in different configurations on SOC sequestration, aggregate stability, and carbon management index (CMI) since 2017 under maize-based cropping systems on a 4% land slope, where eight treatment procedures were adopted. The results revealed that A. donax placement at 0.5-m vertical-interval pea–wheat (M + AD10G0.5-P-W) treatment had ∼23% increase in SOC stock (27.87 Mg·ha−1) compared to the maize–wheat (M-W) system in the 0–30-cm soil layer. M + AD10G0.5-P-W and maize–pea–wheat treatments under bench terracing (M-P-W)BT had similar impacts on SOC stocks in that layer after 5 years of cropping. The total SOC values in bulk soils, macroaggregates, and microaggregates were ∼24, 20, and 31% higher, respectively, in plots under M + AD10G0.5-P-W treatment than M-W in the topsoil (0–5 cm). The inclusion of post-rainy season vegetable pea in the maize–wheat cropping system, along with AGT application and crop residue management, generated additional biomass and enhanced CMI by ∼60% in the plots under M + AD10G0.5-P-W treatment over M-W, although M + AD10G0.5-P-W and (M-P-W)BT had similar effects in the topsoil. In the 5–15-cm layer, there was no significant effect of soil conservation practices on CMI values. Under the M + AD10G0.5-P-W treatment, the annual mean soil loss decreased by ∼92% over M-W treatment. We observed that CMI, proportion of macroaggregates, aggregate-associated C, labile C, total SOC concentration (thus, SOC accumulation rate), and mean annual C input were strongly correlated with the mean annual soil loss from 2017 to 2021. The study revealed that the emplacement of an A. donax mat and incorporation of a legume in a cropping system (M-W), conservation tillage, and crop residue retention not only prevented soil loss but also enhanced C sequestration compared to farmers’ practice (M-W) in the Indian Himalayas. The significance of this study is soil conservation, recycling of residues and weeds, and climate change adaptation and mitigation, as well as increasing farmers’ income.

A new method for disentangling the coupling effect of slaking and mechanical breakdown on aggregate stability: Validation on splash erosion

Aggregate breakdown strongly influences soil erosion process, during which slaking and mechanical breakdown are two dominant breakdown mechanisms. Despite of many methods on aggregate stability, there is a paucity of satisfactory one to disentangle how these two mechanisms interact in aggregate breakdown. Herein, on the basis of Le Bissonnais method (1996) including three treatments (i.e., fast wetting (FW), stirring after pre-wetting (WS), and slow wetting (SW)), a new treatment of water-stirring after fast wetting (SF) was proposed in order to evaluate the coupling effect of slaking and mechanical breakdown on aggregate stability. The coupling effect of slaking and mechanical breakdown was larger to a varying extent than their individual effects, and its difference with slaking showed a unimodal variation with increased aggregate stability. This new method can partition the unique and shared effects of these two breakdown mechanisms; the shared effect (0–77%) decreased logarithmically with increased aggregate stability; the unique effect of slaking (16–52%) showed a unimodal variation and much larger than that of mechanical breakdown (0–17%). As validated by previously published splash erosion data over a wide range of soils (including various soil types, land uses, textures and parent materials), the proposed aggregate stability indices in this new method showed better performance in predicting splash erosion compared to existing ones (e.g., RSI×RMI and RSI/RMI). Collectively, this new method facilitates a systematic understanding on aggregate breakdown mechanisms and exhibits great superiority in aggregate stability measurement and erosion prediction.

Land management affects soil structural stability: Multi-index principal component analyses of treatment interactions

Soil structure mediates soil functioning and can be influenced by agricultural management practices (cropping intensity, tillage, and nitrogen source). This study evaluated the effectiveness of multiple soil aggregate indices to quantify soil structural development using long-term data from three locations within the central Great Plains: Alternative Crop Rotation (ACR) and Long-Term Tillage (LTT) near Akron, Colorado, and Knorr-Holden (KH) near Mitchell, Nebraska. Tillage treatments include no-tillage (NT), reduced tillage (RT), conventional tillage (CT), and moldboard plow (MP). Commercial mineral fertilizer (F) was used as a nitrogen source in ACR and LTT sites while manure (M) plus F treatments were used in KH. Soil aggregate size classes were measured in the laboratory, and aggregate stability index (ASI), mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension (FD) were calculated to evaluate soil aggregation using linear regression and principal component analysis (PCA). At 0–15 cm, intensive tillage treatments (CT and MP) in ACR and LTT, reduced (P < 0.05) ASI by 46.7%, MWD by 21.0% and GMD by 8.4% and increased FD by 0.77% compared with NT and RT treatments. The addition of manure increased (P < 0.05) ASI by 72.2%, MWD by 65.6%, GMD by 32.8%, and reduced FD by 5.5% compared with tillage treatments in ACR and LTT. The PCA indicated clear effects of M on aggregate structure and stability, indicating that manure addition could compensate for the tillage operations in sustaining soil structural stability. Explanatory variables FD and ASI were orthogonal across the three sites, while FD was negatively correlated with MWD and GWD; thus, FD provides information not captured by ASI and complements MWD and GWD. The evaluated indices, including FD, are effective in measuring soil aggregation and structural stability and should be considered further in management decisions to sustain soil resources and enhance economic returns. The methods developed here can be applied to any site where soils are sampled and analyzed for aggregates.

Strong links between aggregate stability, soil carbon stocks and microbial community composition across management practices in a Chinese dryland cropping system

Increasing soil carbon (C) stocks and improving soil structure are critical challenges in semi-arid agroecosystems. Conservation tillage has been widely applied to promote aggregate stability, enhance soil organic C (SOC) storage, and conjointly influence microbial community composition. However, the relation among soil microbial groups, aggregate stability and SOC stocks under management practices remains unclear. We conducted a 17-year field experiment in a spring maize cropping system on the Loess Plateau of northwest China, comparing three types of management: conventional tillage with residue removal (CT-RR), reduced tillage with residue incorporation (RT-RI) and no-tillage with residue mulching (NT-RM). We evaluated aggregate stability index (ASI), SOC stocks and microbial community composition at 0–10 and 10–25 cm. The results showed that RT-RI and NT-RM significantly increased ASI by 11% and 16% relative to CT-RR in the 0–10 cm layer; RT-RI significantly increased ASI by 13% relative to CT-RR in the 10–25 cm layer (p < 0.05). The RT-RI increased the SOC concentrations and SOC stocks of macroaggregates (>250 μm), which harbor most of the total SOC stocks in bulk soil. Both RT-RI and NT-RM increased total microbial biomass and biomass of six microbial groups (i.e., gram-negative bacteria (GN), gram-positive bacteria (GP), total bacteria (B), total fungi (F), arbuscular mycorrhizal fungi (AMF) and saprophytic fungi (SF)) at 0–10 cm, and RT-RI increased the above groups at 10–25 cm. Across a range of microbial community indicators, we found strong positive relationships between SOC and GN, ASI and AMF in bulk soil. A random forest analysis indicated that GN and F were the best microbial predictors of SOC concentrations and overall aggregate stability, whereas AMF/SF was the best predictor of SOC concentrations within aggregates and the stability of individual aggregate size classes. These results demonstrated a strong link between aggregate stability, SOC dynamics and microbial community composition, and suggest that conservation tillage increases both soil aggregation and SOC storage, thus providing sustainability and technical feasibility for the development of dryland agroecosystems.