Soil Structural Stability Research Articles

Evaluation of the effects of long‐term maize–peanut intercropping on soil aggregate stability based on different methods

AbstractIntercropping is an effective measure to increase crop yield and improve soil structure. The soil aggregate is the basic unit of soil structure, and its stability is affected by intercropping system. To study the effects of intercropping system on soil aggregate stability, the particle size distribution and stability characteristics of soil aggregates under three planting patterns of maize only (SM), peanut only (SP) and maize intercropped with peanut (M‐P) were evaluated by dry sieving (mainly used to determine the mechanical stability of soil aggregates), wet sieving (mainly used to determine the water stability of soil aggregates) and Le Bissonnais (mainly used to distinguish different decomposition mechanisms of soil aggregates) (including slow wetting (SW), wet stirring (WS) and fast wetting (FW) tests) methods. The results showed that the particle size distribution of soil aggregates was mainly the >2 mm fraction in the dry sieving test, the 1–0.5 mm and <0.053 mm fractions in the wet sieving test, the >2 mm fraction in the SW test, the >2 mm and 2–1 mm fractions in the WS test and the 1–0.5 mm and 0.5–0.25 mm fractions in the FW test. The mean weight diameter (MWD), geometric mean diameter (GMD) and R0.25 of soil aggregates in the three determination methods were all ranked as SP < SM < M‐P, indicating that intercropping could increase the proportion of large aggregates and improve the stability of soil aggregates. In the three tests using the Le Bissonnais method, the MWD order was FW < WS < SW, indicating that the soil aggregates in this area were the most sensitive to slaking effects and the least sensitive to mechanical breakdown, and intercropping could reduce the sensitivity of soil aggregates to slaking effects and mechanical breakdown. In addition, the MWD of dry sieving was significantly positively correlated with the MWD of SW and WS, and the MWD of wet sieving was significantly positively correlated with the MWD of FW. The results of this study could provide a reference for better understanding of farmland soil structure and aggregate stability under intercropping system in the North China Plain.

Biochar a promising amendment to mitigate the drought stress in plants: review and future prospective

Drought stress (DS) is one of the most destructive abiotic stresses that negatively affects plant growth, and yield. The intensity of DS is continuously increasing due rapid of water sources, less rainfall, and an increase in global warming. The world’s population is increasing at an alarming rate which needs a substantial increase in crop production to meet global food needs. Therefore, in this context, we must have to increase crop production in the scenarios of rapid climate change and increasing intensity of abiotic stresses. Globally, different measures are used to mitigate the adverse impacts of DS, recently biochar (BC) has emerged as an excellent soil amendment to mitigate the toxic effects of DS and improve crop production. The application maintains membrane integrity, plant water relations, nutrient homeostasis, photosynthetic performance, hormonal balance and osmolytes accumulation, and gene expression thereby improving plant performance under DS. Moreover, BC application under DS also improves soil organic matter, water holding capacity, soil structure stability, and activity of beneficial microbes which can improve the plant performance under DS. In the present review different mechanisms through which BC mitigates the adverse impacts of DS on plants are discussed. This review provides new suggestions on the role of BC in mitigating the adverse impacts of DS.

Short Crop Rotation under No-Till Improves Crop Productivity and Soil Quality in Salt Affected Areas

Soil productivity and crop yield were examined in response to legume-based short crop rotation under conventional (CT) and no-till (NT) tillage practices in saline meadow-alluvial soils of the arid region in Bukhara, Uzbekistan. Compared with the CT treatment, crop yield was consistently higher under NT, i.e., winter wheat 9.63%, millet 9.9%, chickpea 3.8%, and maize 10.7% at the first experiment cycle during 2019–2021. A further crop productivity increase was observed at the second experiment cycle during 2021–2023 under NT when compared to CT, i.e., winter wheat 17.7%, millet 31.2%, chickpea 19.6%, and maize 19.1%. An increase in total phyto residue by 20.9% and root residue by 25% under NT compared to CT contributed to the improvement in soil structure and played a vital role in the sustained improvement of crop yields. In turn, the increased residue retention under NT facilitated soil porosity, structural stability, and water retention, thereby improving soil quality and organic matter content. Soil salinity more significantly decreased under NT than in CT, reducing salinity buildup by 18.9% at the 0–25 cm and 32.9% at the 75–100 cm soil profiles compared to CT. The total forms N and P were significantly increased under NT when compared to CT, while the efficiency of the applied crop rotation was essential. This study showed the essential role of the NT method with legume-based intensive cropping in the maintenance of soil health and crop yield, thereby touching on recent advances in agro-biotechnology and the sustainable land management of drylands.

Impact of typical land use type on the stability and content of carbon and nitrogen of soil aggregates in western Hubei

AbstractIn order to investigate the characteristics of soil structural stability and the factors influencing it under typical land use types in the karst region of western Hubei, soil samples were collected from five land use types (natural mixed forest [NF], cypress forest [CF], stone dike terrace [ST], stone dike forest [SF], and abandoned land [AL]) in Xialaoxi to analyze the particle size distribution of aggregates, structural stability, and the distribution characteristics of carbon, nitrogen, and extracellular enzyme contents. The results showed that the aggregates of NF, CF, SF, and AL were dominated by >2‐mm aggregates, while ST showed mostly 2–0.25‐mm aggregates. The mean weight diameter (EMWD) and the geometric mean diameter (EGMD) of mechanical aggregates showed a trend of CF > NF > SF > AL > ST, whereas the erodibility factor K showed an opposite trend. The total organic carbon (TOC), labile organic carbon (LOC), and total nitrogen (TN) contents of aggregates of each particle size were significantly higher in NF and CF than in ST and AL under the five land types. The content of available nitrogen (AN) was highest in NF and ST. The content of carbon and nitrogen and extracellular hydrolases (β‐glucosidase [BG], cellulose disaccharide hydrolase [CBH], β‐N‐acetyl‐aminoglucosidase [NAG], and leucine aminopeptidase [LAP]) in soil aggregates were mainly concentrated in <0.25–0.053‐mm aggregates. The variation in carbon and nitrogen abundance of each particle size agglomerate mainly originated from the LAP content of that particle size agglomerate and showed significant correlation. The partial least squares path models (PLS‐PM) showed that the main influences on the stability of soil aggregates in small watersheds were land use types, soil physical properties, carbon and nitrogen abundance, and extracellular enzyme activity. In conclusion, the structural stability of soil aggregates in Xialaoxi watershed is the result of the interaction between human disturbance and soil nutrient self‐cycling. In general, NF and CF have better soil aggregate stability and are conducive to soil carbon and nitrogen accumulation, whereas for later development and management of SF, ST, and AL sample plots, scientific cultivation means should be adopted, and attention should be paid to long‐term carbon and nitrogen accumulation and conservation.

Crop diversification promotes soil aggregation and carbon accumulation in global agroecosystems: A meta-analysis

Soil aggregation contributes to the stability of soil structure and the sequestration of soil organic carbon (SOC), making it an important indicator of soil health in agroecosystems. Crop diversification is considered a rational management practice for promoting sustainable agriculture. However, the complexity of cropping systems and crop species across different regions limits our comprehensive understanding of soil aggregation and associated carbon (C) content under crop diversification. Therefore, we conducted a meta-analysis by integrating 1924 observations from three diversification strategies (cover crops, crop rotation, and intercropping) in global agroecosystems to explore the effects of crop diversification on soil aggregates and associated C content. The results showed that compared to monoculture, crop diversification significantly increased the mean weight diameter and bulk soil C by 7.5% and 3.3%, respectively. Furthermore, there was a significant increase in the proportion of macroaggregates and their associated C content by 5.0% and 12.5%, while there was a significant decrease in the proportion of microaggregates as well as silt-clay fractions along with their associated C under crop diversification. Through further analysis, we identified several important factors that influence changes in soil aggregation and C content induced by crop diversification including climatic conditions, soil properties, crop species, and agronomic practices at the experimental sites. Interestingly, no significant differences were found among the three cropping systems (cover crops, crop rotation, and intercropping), while the effects induced by crop diversifications showed relatively consistent results for monoculture crops as well as additive crops and crop diversity. Moreover, the impact of crop diversification on soil aggregates and associated C content is influenced by soil properties such as pH and SOC. In general, our findings demonstrate that crop diversification promotes soil aggregation and enhances SOC levels in agroecosystems worldwide.

Assessment of the soil structure stability focusing on the high-energy moisture characteristic curve in pasture and arable land uses in semi-arid areas, northeastern Iran

Assessment of the soil structure stability focusing on the high-energy moisture characteristic curve in pasture and arable land uses in semi-arid areas, northeastern Iran

The QuantiSlakeTest, measuring soil structural stability by dynamic weighing of undisturbed samples immersed in water

Abstract. We evaluated the performance of a new, simple test to evaluate soil structural stability. The QuantiSlakeTest (QST) consists in a quantitative approach of the slake test, a dynamic weighing of a dried structured soil sample once immersed in water. The objective of this work was threefold: we aimed to (i) derive indicators from QST curves to evaluate soil structural stability, (ii) establish the relationship between soil properties and QST indicators, and (iii) assess how QST indicators respond to contrasting soil management practices. To reach these goals, we sampled the soil of 35 plots from three long-term field trials in the silt loam region of Belgium dealing respectively with contrasting organic matter inputs, tillage and P–K fertilisation. For each plot, indicators calculated from QST curves (e.g. total relative mass loss, disaggregation speed and time to meet a threshold values of mass loss) were compared to the results of the three tests of Le Bissonnais (1996), used as a reference method for the measurement of soil aggregate stability. Shortly after immersion in water, soil mass increases due to the rapid replacement of air by water in soil porosity. Then soil mass reaches a maximum before decreasing, once mass loss by disaggregation exceeds mass gain by air loss. Our results confirmed that the early mass loss under water is mainly related to slaking, whereas after a longer time period, clay dispersion and differential swelling become the dominant processes of soil disaggregation. The overall soil structural stability was positively correlated to the soil organic carbon (SOC) content and negatively correlated to the clay content of soil. Consequently, the SOC : clay ratio was closely related to QST indicators. Nevertheless, for a similar mean annual carbon (C) input, green manure and crop residues were more efficient in decreasing clay dispersivity and differential swelling, whereas farmyard manure promoted SOC storage and was more efficient against slaking. QST curves had a strong discriminating power between reduced tillage and ploughing regardless of the indicator, as reduced tillage increases both total SOC content and root biomass in the topsoil. The QST has several advantages. It (i) is rapid to run, (ii) does not require expensive equipment or consumables, and (iii) provides a high density of information on both specific mechanisms of soil disaggregation and the overall soil structural stability. As an open-access programme for QST data management is currently under development, the test has a strong potential for adoption by a widespread community of end users.

Spatial variations in soil erodibility induced by rock outcropping on sloping cropland in the karst region of Southwest China

Sloping croplands in karst areas of Southwest China usually contain a multitude of rock outcrops with diameters larger than 25 cm. Rock outcrops and spatial location have substantial effects on soil properties and thus likely affect soil erodibility. Moreover, rock outcropping is a indicator of rocky desertification and has an important impact on soil erosion and soil formation processes. However, the potential effects of spatial location and rock outcrops on the soil erodibility of sloping cropland in karst areas are still unclear. This study was performed to explore the variations in soil erodibility reflected by saturated hydraulic conductivity (KS), mean weight diameter (MWD), soil structural stability (SSI), soil erodibility factor (K) and soil organic carbon content (SOC) at three spatial locations in sloping cropland with rock outcrops on the karst hillside. The results showed that the soil erodibility indicators KS, MWD, SSI and SOC declined with increasing soil depth for all tested sites. SSI and SOC were predominant factors contributing to the variation in soil erodibility, which were 34.9 % and 35.1 % at the upper spatial location, 31.4 % and 30.9 % at the middle spatial location, and 32.1 % and 32.6 % at the lower spatial location, respectively. There were significant variations in the K factor between the sloping cropland with rock outcrops and the control group. The variations in soil erodibility indicators with rock outcrops and spatial locations were attributed to the changes in soil particle distribution, soil bulk density and SOC. There was a significant linear correlation between the K factor and spatial location, slope gradient, coverage and height of rock outcrops. These results indicated that rock outcrops and their characteristics can reduce soil erosion intensity by redistributing precipitation and runoff, thus further affecting infiltration and soil erodibility. These findings are helpful to comprehend the processes and mechanisms of the spatial variation in soil erosion on sloping cropland with rock outcrops.

The Effects of Partial Substitution of Fertilizer Using Different Organic Materials on Soil Nutrient Condition, Aggregate Stability and Enzyme Activity in a Tea Plantation.

Fertilization plays a crucial role in enhancing tea production. However, it has been demonstrated that the long-term single application of chemical fertilizer will reduce soil nutrient content and the formation of soil aggregates, which is not conducive to the sustainable development of soil and agriculture. Many studies have shown that partial substitution of chemical fertilizer with organic fertilizer can improve soil physicochemical properties and soil nutrient content. This study compared the effects of different organic materials as substitutes for chemical fertilizer. We partially replaced chemical fertilizer with rabbit manure, wine lees and rapeseed cake, amounting to 30% of the total annual nitrogen application in the field experiment, and we set nine different fertilization methods to assess and analyze the soil nutrient condition, aggregate stability and enzyme activity. The results showed that the experimental soil aggregate mean weight diameter (MWD) and geometric mean diameter (GMD) were significantly increased compared with control (p < 0.05); the aforementioned fertilization methods also decreased the soil aggregate fractal dimension (D), disruption rate (PAD), average weight-specific surface area (MWSSA) and soil erodibility factor (K). The application of the fertilizer containing organic materials and microbial agent increased soil organic carbon (SOC) by 20.7% to 22.6% and total nitrogen (TN) by 34.6% to 38.1%; it also significantly promoted sucrase, urease and protease activities in all aggregate sizes (p < 0.05) and increased the 2-5 mm aggregate content. The correlation coefficients between the SOC and the enzyme activities were 0.18-0.95, and most of them showed an extremely significant positive correlation (p < 0.01). In conclusion, the application of fertilizers containing organic materials and microbial agents can improve soil aggregate stability, aggregate enzyme activity and soil structural stability.

Spatial variation in soil aggregate stability and erodibility at different slope positions in four hilly regions of northeast China

The spatial heterogeneity of erosion can affect soil properties in agricultural areas, which can in turn alter the soil aggregate stability and erodibility. However, it remains elusive how aggregate stability and soil erodibility vary at different positions in the Mollisol region of northeast China, and how soil properties drive these variations. This study selected different slope positions across a latitudinal gradient in four hilly regions from cold temperate (Jiusan, JS; Keshan, KS) to middle temperate (Hailun, HL; Binxian, BX) areas in northeast China. The spatial variations of soil properties, geometric mean diameter (GMD), mean weight diameter (MWD), soil erodibility (K), and soil structural stability index (SSI) were calculated at topsoils (0–20 cm) and subsoils (20–40 cm). Total nitrogen (TN) and soil organic carbon (SOC) decreased with increasing latitudes, and gradually declined and finally rose with decreasing slope positions. MWD, GMD, and SSI were the highest in JS, and first obviously decreased from the top position to lower position, and then increased at the bottom position. The K followed an order of BX > HL > KS > JS, and decreased in the bottom position compared with that in the middle and lower positions across the four regions, which could be ascribed to the new aggregate formation promoted by fine soil particle deposition at the slope bottom. Redundancy analysis and variance decomposition analysis indicated that SOC, TN, and bulk density had higher vector values, and region (interpretation rate = 57.97 %) had the greatest influence on aggregate stability and soil erodibility. Available potassium (AK), saturated conductivity (KS), SOC, TN and soil texture were the main factors driving the variation of MWD and K. These findings highlight the spatial variations in soil aggregate stability and erodibility in Mollisol regions, providing a scientific basis for soil restoration in eroded farmland.

Fe‐modified biochar improved the stability of soil aggregates and organic carbon: Evidence from enzymatic activity and microbial composition

AbstractBiochar modifications are used to improve soil organic carbon (SOC) content, while its effects on soil structure stability and carbon (C) mineralization are less known especially in saline–alkaline soils. A 5 years field experiment was arranged with organic amendments addition in the Yellow River Delta, including (i) NPK, only 255, 56, and 190 kg ha−1 N, P, and K each year, (ii) RS, NPK + rice straw, (iii) BC, NPK + straw‐derived biochar, and (iv) FeBC, NPK + biochar modified with ferric chloride. Relative to NPK treatment, the mean weight diameter was significantly increased with organic amendments addition, which was the highest in FeBC treatment. Meanwhile, SOC content in the soil added with organic amendment was increased by 2%–18%. Compared with the RS and BC, FeBC addition increased the content of stable humin (HU), crystalline Fe oxides (Fed), and amorphous Fe oxides (Feo). There was a positive correlation between HU and Feo/Fed, indicating HU and Fe oxides might form organic mineral complexes to limit SOC biodegradation. While the mineralization rate of SOC in FeBC treatment was decreased by more than 30.4% than that in BC treatment. This might be due to the decrease of soil β‐glucosidase and cellobiohydrolase activities, as well as the abundance of Gammaproteobacteria and Actinobacteria. These results were the mechanism of soil enzyme activity and bacterial community regulating C stability. Therefore, Fe‐modified biochar is a better organic amendment to improve the stability of aggregates structure and SOC in saline–alkaline paddy soil.

Soil management effects on soil organic matter properties and carbon sequestration (SOMPACS)

SOMPACS is a project recommended by EJP SOIL for funding under the 1st External Call "Towards Healthy, Resilient and Sustainable Agricultural Soils". The goal of this project is to assess management practices that enrich organic matter pools that are resilient to rapid microbial decomposition. The project started in 2022 as a consortium of 12 research institutions from Poland, Germany, Ireland, Lithuania, UK, Italy and USA for a period of three years. Soil and vegetation samples from eight long-term experiments that differ in soil management practices (i.e., conventional vs. no-tillage; mineral vs. organic fertilization; with and without catch crop; and arable land vs. undisturbed grassland) are investigated. Study sites include: 22- and 54-year long experiments in Lithuania; 26-year long experiment in Italy; 30- and 40-year long experiments in Ireland; 30- and 46- and 100-year long experiments in Poland; and 178-year long Broadbalk experiment in Great Britain. Additional experimentation includes assessing the impact of root growth promoting amendments (commercially available humic substances, biochar and biogas digestate) on stable organic matter pools. In parallel with soil sampling, plant productivity are measured in all field experiments. This investigation is couples fields studies with small-scale experimental plots and laboratory incubations under controlled conditions. In addition to assessing basic soil properties, the following state-of-the-art analyses are conducted: SOM composition and stability by Py-GC-MS; fractionation of aggregate size classes and C pools of increasing physicochemical protection; isotopic analysis of δ13C and δ15N performed on different SOM pools; microbiological properties (community-level physiological profiling, selected functional genes involved in C and N cycles, microbiome and mycobiome analyses by next-generation sequencing, genetic diversity using terminal restriction fragment length polymorphism); enzymatic activity; soil water retention and soil water repellency; mineral composition of clay fraction; (8) soil structure stability. SOM composition and stability by Py-GC-MS; fractionation of aggregate size classes and C pools of increasing physicochemical protection; isotopic analysis of δ13C and δ15N performed on different SOM pools; microbiological properties (community-level physiological profiling, selected functional genes involved in C and N cycles, microbiome and mycobiome analyses by next-generation sequencing, genetic diversity using terminal restriction fragment length polymorphism); enzymatic activity; soil water retention and soil water repellency; mineral composition of clay fraction; (8) soil structure stability. The most resistant SOM pool (humin) are isolated by different methods (isolation vs. extraction) and examined for chemical composition and structure, using spectrometric and spectroscopic techniques (mass spectrometry, NMR, FTIR, EPR, UV-Vis-NIR, fluorescence). The carbon stocks in the soil profile will be evaluated and the carbon extractable in cold water will be determined to assess the potential carbon leaching and microbial availability. Additionally, in-field soil carbon dioxide (CO2) fluxes from selected experiments is monitored. Thus far, soil samples (0-100 cm depth) were collected and the humin fraction from surface A horizon was isolated for spectroscopic studies. Crop yield and vegetation productivity was also assessed. The research was financed by NCBR (EJPSOIL/I/78/SOMPACS/2022).

Straw Inputs Improve Soil Hydrophobicity and Enhance Organic Carbon Mineralization

The mechanism of the influence of soil water repellency (SWR) and agglomeration stability on soil organic carbon (SOC) mineralization has not been thoroughly studied following different methods of returning straw to the field. The research background in this study was ordinary black soil, and the addition of straw was accomplished via straw mixing (CT), straw mulching (CM), straw deep burying (CD), and straw tripling deep burial (CE). A 120-day long-term incubation test was used to measure the contact angle between water droplets and soil, the particle size distribution of aggregates and their organic carbon (OC) content, organic carbon pool (OCP) content, OC contribution, and soil CO2-C release, the extent of SWR and the direct effect of agglomerates on SOC mineralization were assessed under different straw return methods. The results revealed that the water-droplet–soil contact angle (CA) was much greater and the rate of CA decline was significantly lower in the CD treatment compared to the CT, CM, and CE treatments, the rate of water droplet penetration on the soil surface was slower, and the SWR was improved. The CD treatment significantly increased the content of macroaggregates and their OCP content, and also significantly increased the content of microaggregates’ OC. The CO2-C emission rate and cumulative emissions were enhanced by adding the same amount of straw, with the most significant enhancement in the deep straw treatment. The cumulative CO2-C emission rate and SOC mineralization significantly increased with increases in SWR, macroaggregates content, and microaggregates OC content, but significantly decreased with increases in macroaggregates’ OC content, according to principal component analysis and Pearson’s correlation analysis. These results highlight the extent of SWR and the direct effect of agglomerate particle size distribution and OC content on SOC mineralization under different straw return methods. This will help to consolidate soil structural stability and nutrient management to support productivity and SOC sequestration in different agricultural systems.

The Impact of Tillage and Crop Residue Incorporation Systems on Agrophysical Soil Properties.

A long-term field experiment has been ongoing since 1999 at the Experimental Station of Vytautas Magnus University's Agriculture Academy. According to the latest edition of the International Soil Classification System, the soil in the experimental field can be classified as Planosol, with a silty medium-loam texture at a depth of 0-20 cm and a silty light-loam texture at a depth of 20-40 cm. Studies were carried out on winter wheat crops in 2014, 2017, and 2023. This research aimed to assess how different long-term tillage systems impact soil shear strength and aggregate stability, their interconnection, and the effect of crop residues on soil stability. The treatments were arranged using a split-plot design. In a two-factor field experiment, straw was removed from one part of the experimental field, while the entire straw yield was chopped and spread at harvest in the other part (Factor A). The subplot factor (Factor B) included three different tillage systems: conventional deep ploughing, cover cropping for green manure with no tillage, and no tillage. The soil samples were analyzed at the Laboratory of Agrobiology at Vytautas Magnus University's Agriculture Academy. The findings indicated that the long-term application of reduced tillage significantly increased the soil shear strength. Shallower tillage depths led to a higher soil shear strength, while the effect of spreading plant residues was relatively lower. The long-term tillage of different intensities, spreading plant residues, and catch crop cultivation for green manure did not significantly affect the soil structure. However, the soil structural stability was found to be highly dependent on soil tillage. Cover cropping for green manure with no tillage and no tillage alone positively affected the soil aggregate stability in the upper 0-10 cm and 10-25 cm layers. The correlation-regression analysis showed that, in the top 0-10 cm and 10-25 soil layers, there were moderate to strong correlations between the soil structural stability, soil shear strength, and the effect of crop residues on soil stability.

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.

Impact of land use type and slope position on the erodibility of karst hillslopes in Southwest China

Land use type and slope position have a considerable impact on soil properties and thus likely influence soil erodibility. Soil erosion on karst hillslopes in South China is still serious due to the high intensity of human activities and fragile ecological environment. Nevertheless, the potential effects of land use type and slope position on soil erodibility indicators in karst areas are still unclear. This study was conducted to investigate the spatial variations in soil erodibility indicators, namely, the saturated hydraulic conductivity (KS), mean weight diameter (MWD), soil structural stability (SSI), soil erodibility K factor, soil organic carbon content (SOC), and a comprehensive soil erodibility index (CSEI) for three typical land uses and three slope positions on a karst hillslope. The results showed that KS, MWD, SSI, K factor, SOC and CSEI varied significantly with land use type and slope position. The measured KS, MWD, SSI, K factor and SOC at the nine tested sites displayed a similar trend with soil depth. SOC, MWD and SSI contributed more to the CSEI, with contributions of 27.9%, 25.9% and 25.9%, respectively. KS and K factor contributed less to the CSEI, with contributions of 17.7% and 2.5%, respectively. Woodland is most susceptible to erosion on upper, cropland on middle and grassland on lower slope positions according to the values of CSEI. There were significant positive correlations among sand content, bulk density and CSEI, and there were significant negative correlations among clay content, silt content, root mass density, SOC and CSEI. The changes in soil properties and soil erodibility indicators with land use type and slope position led to the differences in the CSEI. The results provide valuable information for policymakers to select appropriate land use types to mitigate soil erosion and thus improve the healthy development of the ecological environment on karst slopes. Moreover, the results have crucial implications for understanding the mechanism of the spatial variation in soil erosion of karst hillslopes in Southwest China.

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

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

Effect of soil compaction and cover crop management on soil physical quality, biomass production and corn and soybean yield

ABSTRACT No-till with cover crop (CC) has been marketed to growers as a sustainable way to increase soil quality and crop yields. Our goal was to better understand the effect of CC management strategies on crop yield and mitigation of soil compaction. The compaction treatments were: four (C4) and eight (C8) wheel passes of a tractor, and without additional compaction (C0). CCs in autumn/winter were Italian ryegrass (IR) hay, IR as CC, and mix of IR and forage radish as CC. In the spring/summer, corn and soybean were cultivated. The reduction of hydraulic conductivity (0–6 cm depth) after first season in the IR hay was 74.9% in C4 and 96.2% in C8 comparted with C0. Overall, harvested CC has limited capacity to respond to compaction, decreasing root growth (root biomass of 2191, 2753, and 3744 kg ha−1, IR hay, IR CC, and mix, respectively). Further, the negative effects of compaction on crop yield were modest, probably because of the low axle loads and contact stresses; high inherent structural stability of Oxisols; and permanent no-till and CC roots which favored soil structure stability. Future works should use higher axle loads and surface stresses and a control treatment without CC.

Aggregate-Breaking Mechanism Response to Polyacrylamide Application of Purple Soils in Southwestern China Using Le Bissonnais Method

Polyacrylamide (PAM) is a water-soluble polymer with strong cohesiveness and a strong water absorption capacity, and it has been widely used to modify soil structural stability. However, little information is available on the impact of PAM application on the aggregate-breaking process of purple soils in hilly areas of southwestern China. Therefore, the current study aimed to examine the influence of PAM application on the aggregate stability of purple soil in terms of different breakdown mechanisms at different hillslope locations. Three disruptive tests employing the Le Bissonnais method (FW, fast-wetting sieving; SW, slow-wetting sieving; and WS, wet-stirring sieving) were used to determine the mean weight diameter (MWD), geometric mean diameter (GMD), and mass fractal dimension (D) of the soil aggregates, and soil erodibility factor (K) was calculated as an index of soil anti-erodibility. Overall, the major aggregate-breaking mechanism for purple soils was the following: SW (differential swelling) &gt; WS (mechanical breakdown) &gt; FW (slaking). The content of water-stable aggregates (&gt;0.25 mm) obviously rose after PAM application, with the most significant influences shown under FW. A significant difference in MWD was observed between PAM application and without polyacrylamide application (CK) under WS (p &lt; 0.05). However, there was a significant difference in GMD between PAM and CK (p &lt; 0.05) under FW and SW. In comparison with CK, D value in PAM under FW and SW was significantly reduced, mainly at the slope locations of 0 and 20 m. A descending order of FW, WS, and SW was found on the basis of K value at different slope locations. These findings contribute to improved understanding of proper application of soil amendments to control soil and water loss in purple soils.

Rapid increase in soil organic carbon and structural stability in a sandy loam soil following conversion from long-term arable to semi-natural grassland irrespective of initial soil conditions

Converting arable land to semi-natural grassland has the potential to restore soil structural stability (SSS) and increase soil organic carbon (SOC) storage. However, the effect of the initial soil C level and conditions on the changes following introduction of grassland is poorly understood. We quantified changes in SSS and SOC in topsoil from the Askov straw disposal and cover cropping experiment initiated in 1981 in Denmark before and after its conversion to semi-natural grassland in 2020. Due to different straw input and cover crop use in the arable phase, the grass was established on soils with different initial conditions (11.9–17.9 g C kg−1 oven-dry soil). Soils sampled in 2019 and 2021 from plots subjected to different treatments in the arable phase were analyzed for clay dispersibility measured on two macro-aggregate sizes (ClayDis 1–2 mm and ClayDis 8–16 mm), wet stability of aggregates (WSA) and SOC. Irrespective of initial soil conditions, introduction of semi-natural grassland resulted in a rapid increase in SOC, a decline in ClayDis 1–2 mm and no change in WSA. The relative change in ClayDis 1–2 mm was larger than the change in SOC, and the slope for the relationship between SOC and ClayDis 1–2 mm decreased after conversion to grassland. Based on these observations, we suggest that the additional driver in play was aggregate-binding and -bonding agents being persistent due to the absence of tillage following the conversion to grassland. Notably, changes in SOC and SSS were similar regardless of initial soil conditions, which may be related to a similar productivity in the semi-natural grassland and soil C saturation.