Soil Aggregates Research Articles

Decade-long effects of integrated farming systems on soil aggregation and carbon dynamics in sub-tropical Eastern Indo-Gangetic plains

Integrated farming system (IFS) aims to diversify the agricultural landscapes by incorporating different components to meet the multifarious needs of the burgeoning population. The present study was undertaken to understand the impact of different cropping systems on soil organic carbon (SOC) stock, aggregate distribution, and aggregate associated organic carbon (AAOC) in 2-IFS models of varying sizes (0.4 and 0.8 ha) established during 2008–2009. After 10 years of the study, the fodder system registered the greatest TOC and carbon stocks across IFS models, with surface soil (0–15 cm) accumulating 17 and 13% higher TOC and C stock, respectively, in 0.4 and 0.8 ha models. In 0–15 cm, macroaggregates (Ma) represented the highest proportion (75–76%) in both models. Among cropping systems, the fodder system recorded the highest large macroaggregates in both IFS models. Within 0–30 cm depth, small macroaggregates are mostly found in the perennial system (fodder, guava+turmeric, and lemon intercropping system), indicating the potential to improve the aggregate stability over the seasonal (shorter duration) system. In general, micro aggregate (Mi) fraction was pre-dominant in sub-surface soil (17.35%). The maximum AAOC was found in Ma compared to Mi fractions, with approximately 67 and 63% of total carbon associated with Ma in 0.4 and 0.8 ha IFS models, respectively. Interestingly, the 0.8 ha IFS model had higher TOC (~11%) and carbon stock (~12%) than the 0.4 ha model, but AAOC did not show a similar result, indicating the influence of cropping systems on AAOC. The study indicated that the fodder-based production system had better performance in terms of soil physical health and increased aggregate stability and content of soil carbon. This is indicative of the advantages of perennial-based systems over seasonal- or annual-based cropping systems for soil sustainability in Eastern Indo-Gangetic Plains.

Changes in Soil Aggregate Carbon Components and Responses to Plant Input during Vegetation Restoration in the Loess Plateau, China.

Vegetation restoration is an effective measure to cope with global climate change and promote soil carbon sequestration. However, during vegetation restoration, the turnover and properties of carbon within various aggregates change. The effects of plant source carbon input on surface soil and subsurface soil may be different. Thus, the characteristics of carbon components in aggregates are affected. Therefore, the research object of this study is the Robinia pseudoacacia forest located in 16-47a of the Loess Plateau, and compared with farmland. The change characteristics of organic carbon functional groups in 0-20 cm, 20-40 cm, and 40-60 cm soil layers were analyzed by Fourier near infrared spectroscopy, and the relationship between the chemical structure of organic carbon and the content of organic carbon components in soil aggregates was clarified, and the mechanism affecting the distribution of organic carbon components in soil aggregates was revealed in the process of vegetation restoration. The results show the following: (1) The stability of surface aggregates is sensitive, while that of deep aggregates is weak. Vegetation restoration increased the surface soil organic carbon content by 1.97~3.78 g·kg-1. (2) After vegetation restoration, the relative contents of polysaccharide functional groups in >0.25 mm aggregates were significantly reduced, while the relative contents of aromatic and aliphatic functional groups of organic carbon were significantly increased. The opposite is true for aggregates smaller than 0.25 mm. (3) With the increase in soil depth, the effect of litter on organic carbon gradually decreased, while the effect of root input on the accumulation of inert carbon in deep soil was more lasting.

Old-growth Ficus trees provide soil water and carbon storage to urban greenspaces in a Brazilian metropolis

Urban flooding has been considered one of the most severe natural disasters around the world, and urban greenspaces can provide important flood regulation ecosystem services. In Belo Horizonte (Brazil), the woody vegetation, especially the old-growth Ficus trees, appears to protect an urban park against the flooding of the Arrudas river. Thus, we compared the soil water content, soil water-holding capacity, soil aggregation and porosity among a highly permeable urban park planted with herbaceous and woody species, including Ficus, a semi-permeable parking lot with only Ficus and an impermeable site without trees (Disturbed Site-DS). The soil water content and water holding capacity of the urban park did not differ from that of the Ficus site, but it was lower than DS. These results were correlated with soil organic matter (SOM) content, soil aggregation and porosity, suggesting that Ficus trees play an important role in the hydrological cycle. To understand how the Fiscus species provide such soil permeability, we compared the aboveground plant biomass, soil fertility and soil carbon sequestration (total soil carbon, soil organic matter, humic and fulvic acids and soil isotopic δ13 C) in plots with Ficus and without this species within the park as well as in a preserved urban forest and a disturbed square. The outstanding plant biomass produced by Ficus species explained the high soil carbon sequestration, particularly in humic organic matter, favouring soil aggregation, porosity and water retention. Therefore, Ficus species may be considered an exceptional C-sequestering species, contributing for soil stabilization and the hydrological cycle in urban greenspaces.

Stronger aggregation reduces temperature sensitivity of soil organic carbon decomposition in croplands

AbstractThe temperature sensitivity (Q10) of soil organic C (SOC) decomposition is an important parameter to predict C dynamics under climate change. Given that SOC is mainly protected by aggregates and minerals, differentiating the Q10 of the two C fractions helps to explain bulk soil C dynamics. In the present study, we collected agricultural soils from adjacent paddy and upland areas in mid‐temperate (Mollisols) and subtropic (Ultisols) regions of China. We employed density fractionation to separate aggregate‐protected and free mineral‐associated C fractions of soil samples and determined the Q10 of SOC and the two C fractions at 15 and 25°C incubated conditions. Results showed that the Q10 of SOC for Mollisols were lower than that for Ultisols, with an exception of aggregates in upland soils. Aggregate‐protected C had lower Q10 than free mineral‐associated C, except in the upland Mollisols. The Q10 of SOC was negatively correlated with the proportion of C protected in aggregates, whereas it was positively correlated with the proportions of mass or C of free minerals. Given that the mass and C proportion of aggregates in bulk soils of Mollisols were 271% and 80% higher than of Ultisols, respectively, the SOC of Mollisols exhibited lower Q10 than Ultisols. Therefore, stronger soil aggregation and higher proportion of aggregate‐protected C contributed to the lower temperature sensitivity of SOC in Mollisols. Consequently, agricultural practices aimed at promoting soil aggregation will alleviate SOC loss under future global warming scenarios.

Afforestation Promotes Soil Organic Carbon and Soil Microbial Residual Carbon Accrual in a Seasonally Flooded Marshland

This study aimed to delve deeper into the alterations in the microbial residual carbon (MRC) accumulation in the Yangtze River’s wetland ecosystems as a consequence of afforestation and to evaluate their impact on soil organic carbon (SOC). The hypothesis posited that afforestation could foster soil aggregation by augmenting arbuscular mycorrhizal fungi (AMF) hyphae and glomalin-related soil protein (GRSP) in deep soil, thereby suppressing the proliferation of genes pivotal to microbial residue decomposition and enhancing MRC accumulation. We collected soil samples at 0–20, 20–40, 40–60, 60–80 and 80–100 cm respectively. Metagenomic sequencing, the quantification of soil amino sugars and MRC, soil aggregate distribution profiling and the measurement of AMF mycelium length density alongside GRSP levels were analyzed. Our findings showed that afforestation notably elevated the concentration of soil amino sugars and the levels of total and fungal MRC, with increases ranging from 53%–80% and 82%–135%, respectively, across the five soil depths examined, in stark contrast to the eroded, non-afforested control. The role of MRC in the SOC was observed to escalate with increasing soil depth, with afforestation markedly amplifying this contribution within the 40–60 cm, 60–80 cm and 80–100 cm soil layers. The study concludes that the SOC content in the deeper soil horizons post-afforestation witnessed a significant rise, paralleled by a substantial increase in both total and fungal MRC, which exhibited a robust positive correlation with the SOC levels. This underscores the pivotal role that amino sugar accumulation from microbial residues plays in the retention of SOC in the deeper soil layers of afforested regions, challenging the conventional wisdom that plant residues are recalcitrant to decomposition within forested SOC matrices.

Stability and heavy metals accumulation of soil aggregates under different land uses in the southwest coastal Bangladesh

Agricultural soil contamination is increasing day-by-day and becoming a major problem over the globe. Trace elements accumulation in the bulk soil is frequently documented, however, there is no precise mechanism of their distribution in the different soil aggregates level. We collected twelve composite soil samples from banana fields, fallow land, rice cultivated with pond water (rice field-I), and rice cultivated with rain water (rice field-II). We separated soil samples into four different size of aggregates (4-2, 2–0.25, 0.25–0.053, <0.053-mm) and then, aggregate stability (MWD), soil organic carbon (SOC), and heavy metals content (Pb, Cd, Cr, As, Fe, Mn, Zn, Ni, Co, Cu) in the soil samples were measured with different techniques. Results showed that MWD was higher in the rice-based land use, which was significantly contributed by SOC (p < 0.001). The concentration of Pb, As, Cd, Fe, and Mn were increased, while Cu and Zn concentration were reduced with increasing aggregate size (p < 0.05). In contrast, aggregate size did not influence on Ni and Co accumulation (p > 0.05). Moreover, macroaggregate acted as an accumulator for Fe, Mn, and As, while all the aggregate fractions acted as accumulators for Cu and Zn. Our study indicated that MWD, SOC, aggregate size and composition, and metal species were the controlling factors of trace elements accumulation and distribution in the various sizes of soil aggregates.

Enhancement of soil ecological remediation using a hydrogel material constructed by freeze–thaw driving force

Composite polymer materials as soil improvers are developed to enhance soil cohesion and aggregate stability. However, the improved soil still struggles to overcome the reduction in strength caused by day-to-day freeze–thaw (FT) cycle in the plateau area with large temperature difference. In this study, the natural power of FT cycle was used to drive the crosslinking of poly (vinyl alcohol) (PVA) and sodium alginate (SA) to form the interpenetrating networks of PVA-SA hydrogel. Then, this hydrogel was applied to stabilize the soil. The characterizations by FTIR, TGA, SEM and XRD indicated that the PVA-SA hydrogel had a porous, multi-channel and multi-chamber structure. Under the action of FT driving force, a series of studies including physical, chemical, water retention, direct shear, permeability, and aggregate stability were carried out on the soil with hydrogel applied. Compared to the control group, the data indicated that the cohesion of soil is significantly improved to 80 kPa. And the saturated hydraulic conductivity of the soil was reduced to 1/45 of the pre-modification rate, which had a positive impact on the water retention of the soil. What’s more, the results revealed that the PVA-SA hydrogel had effects on the aggregate stability, the submerged soil with added PVA-SA hydrogel still had no sign of disintegration and its mass percentage was greater than 99 % after 70 days. In a word, this composite material can effectively improve the cohesion and aggregate stability of the soil with the help of natural driving forces, which is potential to be used as remediation material for the plant layer in ecological restoration process.

Divergent responses of aggregate breakdown by slaking to nitrogen forms in solution for contrasting soil types

Aggregate stability strongly affects many soil processes and is critical to maintain sustainable agriculture. Aggregate breakdown is controlled by the interaction between soil intrinsic properties and solution characteristics. Nitrogen fertilization including different forms is well known to influence aggregate stability; however, relative to their long-term effects, there is little recognition on the rapid response of aggregate breakdown to nitrogen solutions. This study aimed to examine the effects of nitrogen form and concentration on aggregate stability for different types of soils. Aggregate breakdown against slaking of three soil types (Phaeozem, Luvisol, and Acrisol) and three horizons (organo-mineral (A), illuvium (B), and parent material horizons (C)) was determined subjected to nitrogen solutions of three forms (CO(NH2)2, NH4+, NO3–) and five concentrations (0.05 ∼ 1.0 mol/L). Among nitrogen forms, urea solution almost had non-significant effect irrespective of soil type and horizon (p > 0.05); for NH4+ and NO3– solutions, aggregate stability showed little variations (MWD of 0.19 ∼ 0.26 mm) with electrolyte concentration for Phaeozem in B and C horizons, overall increased for Luvisol and Phaeozem in A horizon, and decreased first and then reached a steady state for Acrisol. The effects of nitrogen forms on aggregate breakdown were dependent on soil aggregation status or cementing agents (mainly organic matter, clay mineralogy). Electrolyte nitrogen solutions (NH4+ and NO3–) inhibited aggregate breakdown mainly through reducing electrostatic repulsive forces for moderately developed soils rich in swelling clays, and promoted aggregate breakdown by both weakening particle cohesion and enhancing compression pressure of entrapped air for highly developed soils rich in non-swelling clays and Fe/Al oxides. These results facilitate an improvement of fertilizer management and irrigation to improve soil quality on different soil types.

Thermal desorption remediation effects on soil biogeochemical properties and plant performance: Global Meta-analysis

Soil contamination remains a global problem, and numerous studies have been published for investigating soil remediation. Thermal desorption remediation (TDR) can significantly reduce the contaminants in the soil within a short time and consequently has been used worldwide. However, the soil properties respond to TDR differently and are dependent on the experimental set-up. The causative mechanisms of these differences are yet to be fully elucidated. A statistical meta-analysis was thus undertaken to evaluate the TDR treatment effects on soil properties and plant performance. This review pointed out that soil clay was reduced by 54.2%, while soil sand content was enhanced by 15.2% after TDR. This might be due to the release of cementing agents from clay minerals that resulted in the formation of soil aggregates. Soil electrical conductivity enhanced by 69.5% after TDR, which might be due to the heating-induced loss of structural hydroxyl groups and the consequent liberation of ions. The treatment of TDR leads to the reduction of plant germination rate, length, and biomass by 19.4%, 44.8%, and 20.2%, respectively, compared to that of control soil. This might be due to the residue of contaminants and the loss of soil fertility during the thermal process that inhibited plant germination and growth. Soil pH and sulfate content increased with heating temperature increased, while soil enzyme activities decreased with thermal temperature increased. Overall, the results suggested that TDR treatment has inhibited plant growth as well as ecological restoration.

Crop straw incorporation increases the soil carbon stock by improving the soil aggregate structure without stimulating soil heterotrophic respiration

Crop straw incorporation increases the soil carbon stock by improving the soil aggregate structure without stimulating soil heterotrophic respiration

Smooth vetch covering alters soil aggregate microbial metabolic limitations in citrus orchards

Green manure covering alters the supply-demand relationship between soil resources and microorganisms by improving soil structure and increasing carbon inputs. However, it remain unclear how soil microorganism respond to the imbalance between resources and demands at the aggregate scale. The present study analyzed the stoichiometric ratios of organic carbon, nitrogen, and phosphorus nutrients, microbial extracellular enzyme activities, and biomass in large macroaggregates (LMA, 2–8 mm), small macroaggregates (SMA, 0.25–2 mm), and microaggregates (MIA, < 0.25 mm) under smooth vetch covering. The relationship between microbial carbon use efficiency and nutrient restriction in soil aggregates was elucidated and the alteration was revealed in microbial metabolic pathways and carbon sequestration functions within soil aggregates under green manure covering. The results showed that: (1) Smooth vetch covering significantly increased the C: N resource imbalance (ln(MBC: MBN)/ln(SOC: TN)) in soil aggregates from 0.50 to 0.69, and thus increased the nitrogen requirement of soil aggregates. However, the N:P resource imbalance (ln(MBN: MBP)/ln(TN: TP)) decreased from 2.25 to 1.78, especially in microaggregates. (2) To mitigate the limitation imposed by nitrogen availability at the aggregate level, microorganisms have ramped up the activity of C- (46.72 %–98.64 %), N- (2.32 %–121.00 %), and P- acquiring enzymes (119.11 %–187.78 %). Nevertheless, the spatial heterogeneity inherent in soil aggregates, characterized by varying particle sizes, has led to a pivotal shift in microbial nutrient limitation. As soil aggregate size diminishes, the primary constraint on microbial activity transitions from nitrogen limitation to phosphorus limitation, reflecting the dynamic interplay between soil structure and nutrient availability. (3) In addition, smooth vetch covering increased the microbial carbon use efficiency of soil aggregates, and it increased with the increase of the particle size of soil aggregates: LMA (178.80 %) > SMA (147.23 %) > MIA (9.99 %). Microorganisms allocated more energy to generate biomass instead of obtaining limiting nutrient elements. These results indicate that smooth vetch covering could increase the organic carbon content of soil aggregates. In addition, in order to adapt to nutrient imbalance, soil aggregates microorganisms choose a “egoistic” metabolic pathway, which alleviates nutrient limitation and assimilated more energy and nutrients into their own biomass and reduces the release of organic carbon. It is evident that integrating Vicia villosa Roth var. glabresens Koch as a ‘green manure’ in orchards serves a dual purpose: it mitigates the environmental impact of chemical fertilizers while simultaneously promoting soil carbon sequestration. This approach offers a robust theoretical framework for achieving the harmonious integration of ecological sustainability and economic viability in economic forestry, such as citrus orchards.

Poly-γ-glutamic acid enhanced the yield and photosynthesis of soybeans by adjusting soil aggregates and water distribution.

Poly-γ-glutamic acid (γ-PGA) is employed extensively in agriculture to enhance soil water retention; however, the underlying mechanism by which γ-PGA improves soil structure and soybean productivity in arid regions remains poorly understood. A micro-scale field experiment was conducted in the arid region of northwest China, employing five concentrations of γ-PGA to investigate its impacts on soybean yield, photosynthesis, and water-use efficiency, as well as soil aggregates and water distribution. The five levels of γ-PGA were 0 (CK), 10 (P1), 20 (P2), 40 (P3), and 80 kg ha-1 (P4). The results demonstrated that the application of γ-PGA significantly improved soybean yield, photosynthesis, and chlorophyll content. It resulted in a decrease in soil aggregate content with a maximumdiameter of less than 0.053 mm and an increase in the stability of soil aggregates in the uppermost layer of the soil (0-30 cm). The application of γ-PGA significantly increased soil water content, particularly in the uppermost layer of the soil, and effectively reduced water consumption and improving water use efficiency in soybeans. Overall, the P3 treatment exhibited the most pronounced improvement of soybean yield, photosynthesis, water-use efficiency, as well as distribution of soil aggregates and water. The correlation matrix heatmap also revealed a strong correlation between improvement of soybean yield or photosynthesis at various γ-PGA application levels and the enhancement of soil stability or soil water content. The multivariate regression analysis revealed that an optimal application level of 46 kg ha-1 γ-PGA could enhance effectively both yield and water use efficiency of soybean in the arid region of northwest China. © 2024 Society of Chemical Industry.

Long-term straw return increases fungal residual contribution to soil microaggregate nitrogen pool: An eco-enzymatic stoichiometric study

Straw return is a widespread agricultural practice for improving cropland nitrogen (N) stocks. However, the contribution of microbial N to the soil aggregate N pool and the underlying microbial metabolic regulation mechanisms remain uncertain. This study was based on a 13-year field experiment with rice (Oryza sativa L.) and wheat (Triticum aestivum L.) rotation, using only a chemical fertilizer alone (CF) as the control. We analyzed the effects of the chemical fertilizer combined with (CS, 9500 kg ha−1 y−1) and wheat (4000 kg ha−1 y−1) straw on microbial derived-N, microbial carbon (C) and N limitations. We also assessed microbial N use efficiency (NUE) in various aggregates of ferric lixisols (0–20 cm). Rotary tillage reached a depth of 20 cm. The CS significantly increased microbial-derived N concentrations in soil aggregates and enhanced the contribution of fungal residual N to the N pool in aggregates < 0.25 mm, but did not affect those > 0.25 mm. Conversely, the bacterial contribution to the N pool was not affected by CS. Meanwhile, CS significantly increased the soil organic C and microbial biomass in the aggregates. The results of our eco-enzymatic stoichiometric model revealed that the CS significantly alleviated microbial C limitations and increased microbial NUE in soil aggregates. Structural equation modeling further revealed that the microbial biomass and soil organic C contents are key drivers of the microbial C limitation. The increased contribution of fungal residual N to the N pools in < aggregates 0.25 mm was attributed to improved microbial NUE resulting from the straw, without altering net N mineralization rates or β-1,4-N-acetylglucosidase activity. Our findings suggest that straw return promotes microbial-derived N production and sequestration by alleviating microbial C limitation. The strategies governing these microbial-derived N responses in aggregates to straw return might vary. This might be valuable for designing cropland management practices to improve N storage.

Contrasting effects of iron oxides on soil organic carbon accumulation in paddy and upland fields under long-term fertilization

Active iron oxides, especially poorly crystalline forms, benefit soil organic carbon (SOC) accumulation via directly bounding and indirectly promoting aggregation. However, it remains unclear on the impacts of active iron oxides on SOC accumulation in paddy and upland soils under long-term fertilization regimes. Here, we attempted to clarify the underlying mechanisms of amorphous (FeO) and organically complexed (FeP) iron oxides mediating SOC accumulation in paddy and upland soils based on two long-term fertilization experiments (both including no fertilization [CK]; chemical nitrogen, phosphorus and potassium [NPK] and NPK plus manure [NPKM] treatments). Results showed that compared to upland soil, Fe-bound organic carbon (Fe-bound OC) content in paddy soil, occupying 21–30% of SOC, was 77% higher on average, due to larger amounts of FeO (+31%) and FeP (+224%). The FeO and FeP were positively related to mean weight diameter (MWD) of soil aggregates across paddy and upland soils. Compared to NPK treatment, NPKM treatment strongly increased FeO (+41%), FeP (+60%) and associated Fe-bound OC (+19%) in paddy soil, and increased FeO (+17%) and FeP (+25%) while decreasing Fe-bound OC (−9%) in upland soil. These combined findings indicated the importance of poorly crystalline iron oxides facilitating Fe-bound OC formation and its contribution to SOC accumulation in paddy soil rather than upland soil. Moreover, long-term manure amendment could enhance SOC accumulation by increasing Fe-bound OC and aggregation stability in paddy soil and enhancing physical protection in upland soil, largely attributed to increased poorly crystalline iron oxides. Overall, these results highlight the potential mechanisms through which active iron oxides regulate SOC accumulation and guide fertilization management in paddy and upland soils.

Decomposer faecal food web and C sequestration in soil. Can near infrared spectroscopy describe transfers and transformations from fresh organic inputs to protected forms in soil aggregates?

This study sought to characterize the transfer of agricultural organic inputs by macrofauna to the biogenic aggregate compartments of the soil and test the existence of a faecal food web process based on coprophagic feeding behaviours. In an experimental plantain crop field of Colombia, we applied the agroecological FBO (Fertilisation Bio Organique ®) technology, a nucleation technique which consists in planting perennial plants in 1.0 x 0.4 × 0.4 m deep trenches where low- and high-quality organic materials are added in a specific design, and endogeic earthworms are inoculated. We evaluated the effectiveness of Near Infrared Spectroscopy (NIRS) to track this flow of organic matter through different natural stages of decomposition represented by soil macroaggregates produced by soil macroinvertebrates as faecal pellets and casts. After one year, great part of the organic inputs had been either mineralized or incorporated into macroaggregates of different sizes and origins. Using NIRS and physicochemical laboratory analyses, we assessed the quality and quantity of organic matter in the different types of aggregates separated manually according to their origin: large biogenic aggregates (LBA), medium sized biogenic aggregates (MBA) and small biogenic aggregates (SBA); physical aggregates (PA), root aggregates (RA) and residual soil (RS).Earlier studies had shown that these structures were presumably formed by the activity of macroinvertebrates of three different functional groups, Diplopoda and Isopoda litter transformers for SBA, epidendogeic earthworms for MBA and mesohumic endogeic earthworms for LBA, organized in a feeding succession.A Coinertia analysis between showed significant covariation among the two sets of physico chemical (22 variables) and NIR spectral (100 different wavelength absorbances) characterization of 135 samples representative of the three classes of biogenic macroaggregates, physical aggregates and residual non macroaggregated soil, (RV = 0.55; p < 0.001). This analysis clearly separated biogenic structures and ranked them according to their size, from small SBA to medium sized MBA and large LBA. Physical PA aggregates and RS residual soil were projected close to the LBAs in the coinertia factorial plan. Multiple combinatorial data analysis CDA, associated 5 specific wavelength absorbance ranges with aggregate types and residual soil. Along the sequence from small to large biogenic aggregates, residual soil and physical aggregates, wavelengths associated to easily decomposed substrates (in ranges 1708–1716 nm; 1796–1948 and 2164–2316 nm) had progressively decreasing absorbances. Substrates associated to slowly decomposing aromatic, alkane and phenolic substrates either increased (1420–1436) or decreased (1284–1380) along this sequence.These results are compatible with the hypothesis of a progressive transformation and transfer of organic residues first into small biogenic aggregates that are presumably faecal pellets of Isopoda and Diplopoda, then to medium sized biogenic aggregates identified as casts of epiendogeic earthworms and finally to large biogenic aggregates expected to be the casts of the large endogeic earthworms present in these soils. A definitive verification of the hypothesis and the involvement of specific macroinvertebrates will require direct experimentation in controlled laboratory conditions.

Cover cropping enhanced soil aggregation and associated carbon and nitrogen storage in semi-arid silage cropping systems

Wind and water erosion in arid and semi-arid regions significantly degraded soil, reduced soil organic carbon (SOC) storage, and exacerbated the impact of climate change on agricultural productivity. Cover cropping is one of the approaches to improve soil health and reduce climate change impacts, yet its impacts on soil aggregation and associated SOC and nitrogen (N) storage in water-limited environments are poorly understood. This study aimed to evaluate soil aggregate dynamics and aggregate-associated SOC and soil total N in irrigated silage sorghum [Sorghum bicolor L. (Moench)] − corn (Zea mays L.) rotations with various cover crop mixtures: grasses + brassicas + legumes (GBL), grasses + brassicas (GB), grasses + legumes (GL), and no cover crops (NCC). Results showed in the second year of the study that, at 0–0.1 m depth, mean weight diameter and geometric mean diameter of dry aggregates were 22–23 % and 6 % greater, respectively, with cover crops than NCC. At the same depth, cover crop treatments had 15–17 %, 15–16 %, and 13 % greater SOC in 0.25–2, 0.053–0.25, and < 0.053 mm aggregate classes, respectively, compared to NCC. Similarly, at 0–0.1 m depth, N in < 0.053 mm fraction was 8–10 % greater with cover crops than without. In the fourth year of the study, water-stable aggregates (WSA) percent did not differ among treatments, but WSA-associated SOC was 31–37 % and 12–16 % greater with cover crops at 0–0.1 and 0.1–0.2 m depths, respectively, than without. The WSA-associated N at 0–0.1 m was 21–33 % greater with cover crops than without. Despite the inconsistencies in soil aggregate stability results, cover crop-integrated silage systems showed greater SOC and N within aggregate classes and water stable aggregates. This insight is crucial for advancing sustainability in silage production systems, particularly in the context of increasing climate change and variability in erosion-prone soils of arid and semi-arid regions.

Carbon in soil macroaggregates under coffee agroforestry systems: Modeling the effect of edaphic fauna and residue input

Crop diversification tends to favor the soil fauna community, soil aggregation, and consequently soil organic carbon (SOC) stock. Understanding the association between these attributes can help in understanding the dynamics of physical protection of soil organic matter. In this context, our study aimed to answer: (1) how does the edaphic macrofauna community and soil carbon and aggregate classes respond to two types of coffee agroforestry systems (coffee with Grevillea robusta and coffee with banana) and how these responses differ from native ecosystem; (2) how and to what extent are soil aggregation regulated by the complex structural interactions of plant residue input, SOC, and the soil faunal community? The work was conducted in the municipality of Planalto, state of Bahia, Brazil. Three systems were evaluated: agroforestry system of Coffee arabica L. with Grevillea robusta (CG); agroforestry system of Coffee arabica with Musa spp. (CB); and native forest (NF). Four plots were delimited in each system, in which dry fractionation of the soil was performed to obtain aggregates of classes >6, 6–4, 4–2 and < 2 mm. The macrofauna was sampled using the Tropical Soil Biology and Fertility Program method. The labile and total carbon of the soil and aggregates were determined and the carbon management indices were calculated. The CG and CB presented a greater amount of larger size aggregates (> 6, 6–4 and 4–2 mm) than the NF. The CB system provided more favorable conditions for the soil macrofauna. Despite this, both coffee agroforestry systems favored the occurrence of Oligochaeta. The CG was more favorable to maintain labile fractions of organic matter than the CB. The edaphic fauna show a close relationship with the formation of carbon aggregates and stabilization which was directly influenced by continuous input of plant residues in diverse coffee growing systems.

Mulching drive changes in soil microbial community assembly processes and networks across aggregate fractions

Soil microbial community assembly processes and networks in croplands have been widely explored; however, their dynamics and how they regulate winter wheat yield across distinct soil aggregate fractions under the combined effects of mulching and soil horizons have not been comprehensively understood. Therefore, based on a 9-y field experiment, the responses of soil bacterial and fungal community assembly processes and interkingdom association networks to mulching were specifically investigated at the soil aggregation level. Soil properties and microbial biomass were separated into distinct mulching in the topsoil (0–10 cm), and soil water content was considered the most critical factor. The soil bacterial community was affected mainly by mulching and soil horizon compared with the fungal community in microaggregates (<0.25 mm). Notably, the bacterial community displayed more robust stochastic processes than the fungal one, and microbial interkingdom association networks were more complex and stable in micro-than macroaggregates. Soil potential carbon mineralization, pH, and total nitrogen were the dominant properties regulating winter wheat grain yield in combination with microbial community composition, assembly processes, and networks in each soil aggregate class. Wheat yield decreased under straw mulching and was mainly regulated by bacterial community composition and assembly processes. Thus, this study enhanced our understanding of the regulations for wheat yield, which could facilitate soil microbial community management at the aggregation level for sustainable crop production in mulching conservation agroecosystems.

Long-term evolution of soil quality in citrus orchard terrace system: A whole life cycle perspective

Terracing is widely recognized as an effective strategy for mitigating soil erosion and preserving soil quality. This study aimed to evaluate the variations in soil aggregate C, N, and P composition, as well as the soil quality index (SQI), in subtropical citrus orchards of different plantation ages (PA) and across various terrace positions (TP). Surface soil samples (0–20 cm) were collected from four TP categories: terrace wall (TW), slub ditch (SD), under grove (UG), and between grove (BG), across varying PA (5, 15, 25, 35, and 45 years). The results showed the C, N, and P concentrations in most soil aggregates, along with the SQI of the slub ditch and under grove, increased significantly with plantation age. Compared to the 5-year-old plantations, the SQI of the slub ditch and under grove increased by 84 % and 66 % at 45 years, respectively. The aggregate stability and SQI of BG generally trended upwards but declined at 25 and 35 years. By 45 years, the SQI of the terrace wall was significantly lower than that of other positions, being 58 %, 61 %, and 39 % lower compared to the slub ditch, under grove, and between grove, respectively. Additionally, the C/P and N/P ratios of the terrace wall were higher than those of other positions, indicating phosphorus limitation in TW. Path analysis revealed plantation ages had greater effects on SQI. Aggregate stability and soil properties showed significant positive impacts on SQI. Overall, as plantation age increased, the differences in SQI among the slub ditch, under grove, and between grove decreased, while the terrace wall exhibited the weakest erosion resistance. Therefore, efforts should be made to restore the ecological function of the terrace wall, such as by colonizing it with moss. Additionally, reasonable tillage plans, including appropriate fertilization, should be formulated to enhance orchard soil quality.

Oil palm agroforestry systems store more carbon and nitrogen in soil aggregates than monoculture in the Amazon

Oil palm agroforestry systems store more carbon and nitrogen in soil aggregates than monoculture in the Amazon