Proportion Of Macroaggregates Research Articles

СТРУКТУРНО-АГРЕГАТНЫЙ СОСТАВ РАЗНОВОЗРАСТНЫХ ЗАЛЕЖНЫХ ОСУШЕННЫХ ПОЧВ ЕВРЕЙСКОЙ АВТОНОМНОЙ ОБЛАСТИ

Involving new virgin soils in agricultural use requires huge capital investments and significant labor resources. The secondary return to agricultural use of fallow reclaimed lands not used in agriculture can become a less costly method of increasing the area of agricultural arable land. In the Middle Amur Lowland, the issues of environmental assessment of fallow drained soils, re-involved in agricultural use, remain poorly studied and practically there are no materials devoted to this issue. To study the ecological state of abandoned drained soils in the Jewish Autonomous region, the authors were carrying out a field research from July to September 2022. The studies showed that drained soils of agrocenoses after being out of agricultural use enter a complex process of self-healing. In fallow soils, the density of the top layer of soil decreases, which has a beneficial effect on the structure of the soil. With the fallow age increasing in drained meadow sod-gley soils, a decrease in the structure coefficient is observed to values close to the lower limit of “good” structure. In brown 20-year-old fallow mountain-forest soils it is observed a noticeable increase in the proportion of macro aggregates, including agronomically valuable ones, which indicates an improvement in the agronomic properties of fallow soils. The condition of the examined different age meadow gley soils deposits, which form the regional arable fund basis, makes it possible to classify them as suitable for agricultural use.

Distribution of soil physical and hydraulic properties between erosion and deposition topographies in five small catchments from north to south on the Loess Plateau of China

Soil erosion, the most widespread form of soil degradation worldwide, has been acknowledged to cause onsite soil physical deterioration. However, the off-site impact of erosion on the soil physical and hydraulic properties of deposited sediments remains unclear, especially at catchment or larger scales. Here, we measured soil physical and hydraulic properties in erosion topography (hillslopes) and deposition topography (check dams) at 0–2 m depth in five eroding catchments across China's Loess Plateau. Results indicated that the deposition zone exhibited a higher clay content (+13%) at the southern sites with a finer texture and a higher erosion modulus, while the same zone exhibited a higher sand content (+25%) at the northern sites with a coarser texture and a higher extreme rainfall erosivity. The deposition zone exhibited a higher bulk density (+9%) and a lower saturated hydraulic conductivity (-13%), field capacity (−9%), and porosity (-5%) than those of the erosion zone, which was strengthened by a higher mean annual precipitation. Soil macroaggregate proportion and mean weight diameter of aggregates were significantly lower in the deposition zone (14.36% and 0.69 mm, respectively) than those in the erosion zone (15.71% and 0.75 mm, respectively), and the differences were larger at sites with higher rainfall erosivity levels and in surface 20 cm soils. However, sediment reaggregation occurred due to the accumulation of binding agents such as clay and organic carbon at sites with lower rainfall erosivity levels. The spatial heterogeneities of sediment physical and hydraulic properties were greater than or similar to those of soils in the erosion zone. Results of our study highlight the dependence of variations in soil physical and hydraulic properties driven by erosion and deposition on erosion factors, which contributes to a better understanding of the hydrology cycle and carbon stability in erosion and deposition topographies.

Moss-dominated biocrust-based biodiversity enhances carbon sequestration via water interception and plant-soil-microbe interactions

We investigated a nature-based solution (NbS) via incorporating biocrust into alfalfa-maize intercropping system to test carbon sequestration in seriously eroded agricultural soils. Field investigation showed that the NbS (moss-dominated biocrust+ intercropping) massively lowered surface soil erosion by 94.5% and soil carbon (C)and nitrogen (N)loss by 94.7 and 96.8% respectively, while promoting rainwater interception by 82.2% relative to bare land (CK). There generally existed positive interactions between biocrust and cropping in the integrated standing biodiversity system. Enhanced plant biomass input into soils substantially promoted soil fungal community diversity and abundance under NbS (p<0.05). This enabled NbS to evidently improve soil macroaggregate proportion and mean weight diameter. Critically, topsoil carbon storage was increased by 2.5 and 10.7%, compared with CK and pure intercropping (p<0.05). Conclusively, the standing diversity under such NbS fostered soil C sequestration via water interception and plant-soil-microbe interactions in degraded agricultural soils.

Soil aggregate development and associated microbial metabolic limitations alter grassland carbon storage following livestock removal

Natural restoration of degraded grasslands following livestock removal changed soil nutrient and carbon concentrations, soil aggregate distributions, and patterns of extracellular enzyme activities. Here, we used an ecoenzymatic stoichiometry model to quantify microbial resource limitations in semiarid grassland soil aggregates at 0, 11, 26, and 36 years after livestock removal and linked these limitations to microbial carbon use efficiency (CUE), which was estimated from stoichiometry theory (CUEST). Overall, livestock removal altered the size distribution of soil aggregates, increased microbial resources and stimulated extracellular enzyme activities. Long-term livestock removal increased the proportion of small macroaggregates (2–0.25 mm). Microbial carbon (C) and phosphorus (P) limitations in soil aggregates declined to minimum levels at 26 years following livestock removal and then increased after 36 years, with an opposite trend for CUEST. Additionally, the greatest resource limitations to microorganisms were found in smaller aggregates (<2 mm) under long-term livestock removal. Random forest and structural equation models revealed that soil abiotic factors, especially total nitrogen and pH, were key determinants of microbial resource limitation in soil aggregates. Moreover, microbial C and P limitations had significant direct effects on the CUEST. Thus, increasing microbial metabolic limitations after long-term livestock removal could reduce microbial C turnover, potentially reducing soil C sequestration. Overall, this study revealed that livestock removal altered soil aggregate development as well as the allocation of resources in aggregates and consequent microbial resource limitations, providing information that may be useful for developing grassland management strategies to enhance C sequestration.

Contributions of mycorrhizal fungi to soil aggregate formation during subalpine forest succession

Although soil structure is essential for land sustainability, resilience, and fertility, the biological factors of aggregate formation and dynamics, especially the role of mycorrhizal fungi, are still unclear. Soils from a secondary succession, grasslands → shrublands → secondary forests → primary forests in subalpine regions, were sampled to compare the contribution of mycorrhizal fungal communities to the aggregate structure. Four aggregate size classes (>2000 and 250–2000 µm, large and small macroaggregates, respectively; 53–250 µm microaggregates; and < 53 µm silt and clay fraction) were related to microbial community structure, root biomass, and morphology, mycorrhizal infection rate, and external mycorrhizal hyphae. The proportion of large macroaggregates increased by 10 %, while small macroaggregates decreased by 9 % during vegetation succession, increasing the mean weight diameter by 17 %. The Shannon–Wiener and Chaos indexes of arbuscular mycorrhizal fungi (AMF) in grassland soil were three times and in shrubland, they were 24 times higher than in the primary spruce forests. The Simpson index of AMF had a positive linear relationship with soil structure. The mycorrhizal hyphal density was maximal in primary forests and could explain the aggregate size distribution before the arboreous layer developed. In contrast, dissolved organic carbon (DOC) and the diameter of the mycorrhizal hyphal contributed to the distribution of aggregates during later succession stages. Thus, biological aggregation mechanisms in the studied subalpine region followed ecosystem succession, with the mycorrhizal fungal communities being the crucial factor affecting the soil structure mainly during grassland and shrubland succession (AMF stage). In contrast, during the ECM stage, the contribution of DOC to aggregate formation became more critical.

In situ degradation of low-density polyethylene film in irrigation maize field: Thickness-dependent effect

Thickness of low-density polyethylene (LDPE) film might determine its mechanical strength, clean production and soil health. Yet, this issue is little understood. In situ aging effects were evaluated in LDPE films with the thickness of 0.006 mm, 0.008 mm, 0.010 mm and 0.015 mm in maize field. The data showed that maximum tensile force (TFmax), maximum tensile strength (TSmax) and elongation at break (EAB) were massively lowered with increasing thickness after aging. The greatest and lowest reduction magnitude of EAB was 27.6 % and 11.2 % in 0.006 mm and 0.015 mm films respectively. Also, the melting point (Tm) and crystallinity (Xc) under Differential Scanning Calorimeter (DSC) tended to decline with the increasing thickness. Moreover, the peak intensity of crystalline regions tended to transfer and concentrate on the amorphous regions, and such tendency became more pronounced in the thin films. Interestingly, there existed a pronounced distinct thickness-dependent effects on soil bulk density (SBD) and soil water-stable aggregate proportion. Thick plastic film mulching increased SBD but reduced the proportion of macroaggregates (mainly referred to 0.015 mm and 0.010 mm). In addition, thick film mulching slightly reduced the levels of soil organic carbon (SOC) and total nitrogen (TN), but significantly promoted the contents of soil labile C and N. Particularly, it significantly promoted above- & under-ground biomass of maize across two growing seasons (p < 0.05). To sum up, thickening LDPE film may act as a promising solution to improve LDPE film residue recycling, while benefiting for higher productivity. However, thick film mulching may cause a certain adverse impact on soil structure, and further investigations would be needed in the future.

Particulate and mineral-associated organic carbon fractions reveal the roles of soil aggregates under different land-use types in a karst faulted basin of China

Soil aggregation has been recognized as the main mechanism of organic carbon (C; OC) stabilization, and OC dynamics within aggregates are closely linked to soil OC (SOC) sequestration. To unravel the roles of different-sized aggregates and the associated OC fractions in SOC accumulation, SOC stocks (SOCS), aggregate distributions, and OC fractions within aggregates were measured under five typical land-use types (cropland, grassland, shrubland, plantation forest, and natural forest) in a karst faulted basin, China. Land-use type had distinct effects on SOCS in the topsoil (0–10 cm) and along the soil profile (0–60 cm), and the primary factors influencing SOCS varied with the soil horizons. Plantation forest had the highest SOCS (51.2 Mg C ha−1) in the topsoil, whereas the SOCS in shrubland (182.7 Mg C ha−1) was distinctively higher than those of other land-use types across the soil profile. Soil microbial biomass C and mean weight diameter were the major factors driving SOCS variation in the topsoil layer and the entire soil profile, respectively. OC content within macroaggregates (>0.25 mm) was significantly positively correlated with the SOC content of bulk soil, whereas only the mass proportion of large macroaggregates (>2 mm) showed a positive relationship with SOC. Additionally, mineral-associated OC (MAOC) was the dominant fraction of SOC and was abundant in macroaggregates. However, particulate OC (POC) within aggregates was relatively enriched in the topsoil and microaggregates. Considering the decomposition and distribution characteristics of OC fractions in different-sized aggregates, we suggest that the POC/MAOC ratios of macro- and microaggregates could respectively reflect aggregate capacity to sequestrate MAOC and POC across different land-use types. Overall, shrubland is the optimal land-use type for rocky desertification control in the karst fault basin, due to the protection of POC and MAOC within different-sized aggregates.

Appropriate N addition improves soil aggregate stability through AMF and glomalin‐related soil proteins in a semiarid agroecosystem

AbstractSoil aggregation and structural stability play a crucial role in soil organic carbon (SOC) sequestration. However, the underlying mechanisms of arbuscular mycorrhizal fungi (AMF) and glomalin‐related soil protein (GRSP) responses to N addition and their impacts on soil aggregation and organic carbon stability remain unclear. Hence, a 16‐year field N addition experiment on winter wheat (Triticum aestivum L.) was conducted to investigate the effects on the stability of soil structure and SOC fractions via AMF and GRSP. Overall, N addition increased the soil aggregate mean weight diameter (MWD), which exhibited an increase in the proportion of large macroaggregates and a decrease in the proportion of silt‐clay fractions. Appropriate N (180 kg N ha−1) input increased SOC stability and total SOC stock, while excessive N (360 kg N ha−1) input increased labile organic carbon fractions, and active C index and decreased the C stock. The concentrations of SOC, total GRSP (T‐GRSP), and easily extractable GRSP (EE‐GRSP) showed the largest increases in small macroaggregates, and GRSP was significantly correlated with SOC, recalcitrant organic carbon, and MWD (p &lt; 0.05). These results indicated that appropriate N addition promoted AMF to secrete GRSP, which in turn favoured large macroaggregation and enhanced the physical protection of SOC. Meanwhile, the increased GRSP stimulated the accumulation of recalcitrant C, thus improving soil organic carbon stability and carbon sequestration capacity. The study suggested that appropriate N addition (180 kg N ha−1) should be used to improve the carbon sequestration potential of farmland on the Loess Plateau.

Effect of soybean–wheat rotation on soil aggregation, organic nitrogen and net nitrogen mineralization characteristics: a four-year field study

ABSTRACT Long-term, excessive application of synthetic N fertilizers will reduce soil aggregate stability and N supply capacity in corn–wheat (Zea mays L. – Triticum aestivum L.) rotation. This study aimed to determine the effects of soybean (Glycine max L.) on soil aggregation, soil organic N (SON) and net amount of N mineralization (NANM) in wheat season compared with corn. Three rotation systems, corn–wheat (C-W), soybean–wheat (S-W) and soybean inoculated with Rhizobium-wheat (SR-W) were established in 2017. In wet screening, compared with C-W rotation, the mass proportions of large macro-aggregates (LM%) + small macro-aggregates (SM%) at 0–20 cm was increased by 51.9% and 16.6% under S-W and SR-W rotations, respectively, and was increased by 50.6% and 59.8%, respectively, in the 20–40 cm. The proportions of LM + SM-associated N (LMN% + SMN%), ammonium N (AN) and amino acid N (AAN) were higher under the S-W and SR-W rotations. Furthermore, the NANM of S-W and SR-W rotations increased by 34.1% and 28.6% compared with C-W rotation, respectively, and the non-N benefits of soybean played an important role. In conclusion, the improvement degree of soil aggregation by soybean is an important factor affecting soil N mineralization in wheat season.

Aggregate-associated carbon compositions explain the variation of carbon sequestration in soils after long-term planting of different tea varieties

Strategies to increase carbon (C) sequestration in tea plantation soils are pertinent to mitigating global climate change, but little is known about the variation in C sequestration in soils planted with different tea varieties. In the current study, we collected 0–20 and 20–40 cm layer soil samples from a tea plantation planted with four tea varieties (Chuancha No.3 (CC3), Chuanmu No. 217 (CM217), Chuannong Huangyazao (CN), and C. sinensis ‘Fuding Dabaicha’ (FD)). Soil organic carbon (SOC) stock and composition in the bulk soil and aggregate fractions, as well as the SOC stability index (SI), were investigated. Both SOC stock and composition in the bulk soil or aggregate fractions were variable among the soils after planting different tea varieties. Overall, the highest SOC stock (0–40 cm) was observed in FD soil, followed by CN, CC3, and CM217 soil. This difference was dominated by the SOC stock associated with macroaggregates, and the highest macroaggregate-associated SOC stock was detected in FD soil in both soil layers. Moreover, FD soil showed the highest proportion of macroaggregates in both soil layers, accumulated the greatest recalcitrant organic carbon (ROC) and further contributed to the highest SI values of SOC associated with most aggregate fractions. In contrast, CN topsoil (0–20 cm) accumulated the greatest labile organic carbon (LOC) in most aggregate fractions, which had a positive correlation with the amount of C return by pruning litter. Ultimately, long-term planting of FD promoted macroaggregate formation, and ROC accumulation in aggregates greatly contributed to maintaining high C sequestration in the tea plantation soils and showed a high potential for future C budgets; in contrast, the tea plantation soil planted with CN could be a potential C source because of high C return.

The effects of co-utilizing green manure and rice straw on soil aggregates and soil carbon stability in a paddy soil in southern China

The co-utilization of green manure (GM) and rice straw (RS) in paddy fields has been widely applied as an effective practice in southern China. However, its effects on soil aggregate and soil organic carbon (SOC) stability remain unclear. In the present study, the effect of GM, RS, and co-utilization of GM and RS on particle size distribution of soil aggregates and SOC density fractions were measured in a field experiment. The experiment included six treatments, i.e., winter fallow (WF) without RS return (Ctrl), WF with 50% RS return (1/2RS), WF with 100% RS return (RS), GM without RS return (GM), GM with 50% RS return (GM1/2RS) and GM with 100% RS return (GMRS). The results showed that the proportion of small macro-aggregates (0.25–2 mm) and the mean weight diameter (MWD) of aggregates in the GMRS treatment was greater (by 18.9 and 3.41%, respectively) than in the RS treatment, while the proportion of silt+clay particles (<0.053 mm) was lower (by 14.4%). The concentration of SOC in microaggregates (0.053–0.25 mm) and silt+clay particles was higher in the GMRS treatment than in GM and RS treatments individually. The concentration and proportion of free light organic carbon (fLOC) in aggregates of various particle sizes and bulk soil was greater in the GMRS treatment than the RS treatment, whereas the concentration and proportion of mineral-associated organic carbon in small macroaggregates, microaggregates, and bulk was lower in the GMRS treatment than in the RS treatment. The proportion of intra-aggregate particulate organic carbon (iPOC) was greater in the GMRS treatment than in GM treatment. The GMRS treatment had strong positive effects on iPOC in small macroaggregates, suggesting that SOC was transferred from fLOC to iPOC. In conclusion, co-utilizing green manure and rice straw cultivated the SOC pool by increasing the concentration of fLOC and improved soil carbon stability by promoting the sequestration of organic carbon in iPOC as a form of physical protection.

Assessing the Impacts of Fertilization Regimes on Soil Aggregate Dynamics in Northeast China

Determining the effects of fertilization regimes on soil aggregates, carbon (C) and nitrogen (N) distribution, and pH is essential for improving soil structure and soil organic carbon (SOC) accumulation to help in proper soil fertility management. Based on a 41-year field fertilization experiment conducted on dark brown soil in northeast China, we examined the soil aggregate size distribution and associated C, N, and pH to provide a scientific basis for elucidation of the mechanisms underlying the effects of fertilization treatments on soil structure and fertility. Six different fertilization treatments included no fertilizer (CK), low-dose chemical fertilizer (NP), moderate-dose chemical fertilizer (2NP), high-dose chemical fertilizer (4NP), normal-dose organic fertilizer (M), and normal-dose organic fertilizer plus moderate-dose chemical fertilizer (M+2NP). Our findings showed that compared to CK, M and M+2NP significantly increased the proportion of macroaggregates by 40% and 28%, respectively, whereas 4NP significantly decreased it by 19%. The mean weight diameter (MWD) and geometric mean diameter (GMD) under M and M+2NP were significantly higher than that under CK, at 12–21% and 24–36%, respectively. The fractal dimension (D) value of M+2NP was significantly lower than those of 2NP and 4NP by 4% and 5%, respectively. Soil pH under the M treatment was highest, followed by M+2NP. Soil pH under 2NP and 4NP more significantly decreased, by 0.1 and 0.2 units, than under M treatment. Soil pH values were correlated with the proportion of soil macroaggregates, MWD, and GWD, respectively (p &lt; 0.05). Relative to CK, M and M+2NP increased the contents and stocks of SOC (by 40–49% and 89–93%, respectively) and total N (59–68% and 119–123%, respectively). Furthermore, the contents and stocks of aggregate-associated SOC and total N decreased following the order: NP &gt; 2NP &gt; 4NP. Overall, the long-term application of organic fertilization regimes (M and M+2NP) effectively improved soil aggregation as well as SOC accumulation and decreased soil acidification in dark brown soil in northeast China.

Soil macroaggregation drives sequestration of organic carbon and nitrogen with three-year grass-clover leys in arable rotations

Conventional arable cropping with annual crops established by ploughing and harrowing degrades larger soil aggregates that contribute to storing soil organic carbon (SOC). The urgent need to increase SOC content of arable soils to improve their functioning and sequester atmospheric CO2 has motivated studies into the effects of reintroducing leys into long-term conventional arable fields. However, effects of short-term leys on total SOC accumulation have been equivocal. As soil aggregation may be important for carbon storage, we investigated the effects of arable-to-ley conversion on cambisol soil after three years of ley, on concentrations and stocks of SOC, nitrogen and their distributions in different sized water-stable aggregates. These values were benchmarked against soil from beneath hedgerow margins. SOC stocks (0–7 cm depth) rose from 20.3 to 22.6 Mg ha−1 in the arable-to-ley conversion, compared to 30 Mg ha−1 in hedgerows, but this 2.3 Mg ha−1 difference (or 0.77 Mg C ha−1 yr−1) was not significant). However, the proportion of large macroaggregates (> 2000 μm) increased 5.4-fold in the arable-to-ley conversion, recovering to similar abundance as hedgerow soils, driving near parallel increases in SOC and nitrogen within large macroaggregates (5.1 and 5.7-fold respectively). The total SOC (0–7 cm depth) stored in large macroaggregates increased from 2.0 to 9.6 Mg ha−1 in the arable-to-ley conversion, which no longer differed significantly from the 12.1 Mg ha−1 under hedgerows. The carbon therefore accumulated three times faster, at 2.53 Mg C ha−1 yr−1, in the large macroaggregates compared to the bulk soil. These findings highlight the value of monitoring large macroaggregate-bound SOC as a key early indicator of shifts in soil quality in response to change in field management, and the benefits of leys in soil aggregation, carbon accumulation, and soil functioning, providing justification for fiscal incentives that encourage wider use of leys in arable rotations.

Soil depth determine the ecological stoichiometry of soil aggregates after returning ancient rice terraces to forest

Soil carbon-nitrogen-phosphorus (CNP) ecological stoichiometry is an effective means of reflecting soil nutrient status, transformations, and limitations, but the effect of returning ancient rice terraces to forest on soil CNP stoichiometry is still unclear at the aggregate scale in the subtropical hilly areas of southern China. This study explored how the CNP content and stoichiometry of soil water-stable aggregates responded after returning ancient rice terraces to forest in the soil layer depth of 0–60 cm in subtropical hilly areas. The results showed that the stability, soil organic carbon (SOC), total nitrogen (TN), C/P, and N/P ratios of soil aggregates decreased significantly with soil depth in ancient rice terraces, Chinese fir (Cunninghamia lanceolata), and moso bamboo (Phyllostachys pubescens). The proportion of macroaggregates decreased gradually and the proportion of microaggregates increased significantly after the soil depth increased. Returning ancient rice terraces to Chinese fir was more conducive to increasing the SOC, TN, C/P, and N/P ratios of soil aggregates, which may be related to plant litter biomass. Eta squared analysis showed that soil depth had a greater impact on soil aggregate stability (34 %, 38 %, and 46 %), CNP content (34 %–45 %), and stoichiometry (34 %–57 %) than land use types and their interactions. These findings indicated that returning ancient rice terraces to Chinese fir and moso bamboo can significantly alter soil water-stable aggregate stability, CNP content, and stoichiometry, and soil depth plays an extremely important role in changing them. Future research should focus on the ecological impacts of soil depth on agroforestry ecosystems.

Compost amendment maintains soil structure and carbon storage by increasing available carbon and microbial biomass in agricultural soil – A six-year field study

Soil organic amendments in agricultural production can benefit crop production and a wide range of soil properties, including soil aggregation. Soil aggregate formation is largely driven by microbial activities, and can in-turn influence microbial communities by generating distinct microbial habitats, as well as associated impacts on water and nutrient dynamics. We investigated the long-term effects of two fertilizer management strategies (poultry manure compost vs. mineral fertilizer) and biochar amendment (0 vs. 10 t ha−1 walnut shell biochar, 900 °C pyrolysis temperature, by-product of gasification) on soil aggregation, soil organic C, and microbial community dynamics in water-stable aggregate fractions in corn-tomato rotations. Using wet-sieving, soils (0–15 cm) were divided into four size fractions: large macroaggregates (2000–8000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm) and silt and clay (<53 μm) for calculation of mean weight diameter in both 2014 and 2018. The total C and microbial community composition and abundance within each fraction were evaluated in 2018. Across all treatments, six years of continuous compost application maintained soil aggregate stability and C storage by increasing soil microbial biomass and associated dissolved organic C. Bacterial and fungal populations under compost treatments were significantly higher than under mineral fertilizer treatments based on 16S rRNA gene copy number and internal transcribed spacer (ITS) abundance, which likely contributed to the formation and maintenance of macroaggregates in compost treatments. Interestingly, continuous application of manure compost may increase microbial available C sources by increasing the abundance of bacteria with the potential to degrade aromatic C as predicted from 16S sequences. Soil under the mineral fertilizer treatment showed decreases in the proportion of large macroaggregates, bulk soil C, and aggregate-associated C storage compared to the compost treatment. The application of highly recalcitrant walnut shell biochar had limited long-term impacts on soil aggregation and C dynamics, likely due to its lack of microbially-available C and limited interaction with the soil environment. Our results indicate that continuous compost inputs maintained soil structure and associated physical stabilization of SOM by enlarging soil microbial available C pool, higher soil microbial biomass, and increasing aggregate formation. The soil aggregate structure, in-turn, generated diverse habitats and altered soil microbial communities. Compost inputs, in addition to or in partial replacement of mineral fertilizer inputs, can provide valuable microbial-driven ecosystem services, such as carbon storage and soil structure, while still providing fertility for crop growth.

Nitrogen addition decreases soil aggregation but enhances soil organic carbon stability in a temperate forest

Soil aggregates and the stability of their associated soil organic carbon (SOC) are important factors mediating soil carbon (C) sequestration and soil functions. However, the response of SOC stability to nitrogen (N) deposition is highly divergent, and the combined influences of N deposition and soil aggregates on SOC stability are poorly understood. The mechanisms underlying these influences were explored in a six-year field N-addition experiment covering a wide range of soil aggregates, root morphologies, soil properties and several SOC stability indices (represented by heterotrophic respiration and δ13C or δ15N) in a deciduous broad-leaved forest in Northeast China. The results showed that N addition significantly decreased the proportion of large macroaggregates (2–8 mm), reducing the soil aggregate mean weight diameter (MWD) by 10.0–17.2 %, which was negatively correlated with root length density (RLD) and root weight density (RWD). Organic C stability in soil aggregates was enhanced by N addition, as indicated by the decrease in the decomposition rate of organic C and the increase in the δ13C values but not the C content in microaggregates within macroaggregates (mM) or δ15N values. Furthermore, the promotion of mineral-associated organic C formation after N addition was detected by stable isotopic mixed model analysis (SIMM), indicating increased C protection by minerals. With the use of a structural equation model (SEM), the variation in the C stability of large macroaggregates (2–8 mm) was explained by the changes in fine roots, MWD and N availability but not those in small macroaggregates (0.25–2 mm) due to the instability of large macroaggregates. These results demonstrate that N addition may enhance soil C stability in all the soil aggregate sizes by promoting mineral sorption of C, with the C stability in large macroaggregates being more vulnerable to multiple environmental changes than that in small macroaggregates. Therefore, the soil C stability response to N deposition in the temperate forests of Northeast China could be modulated by soil aggregate sizes and may cause negative feedbacks to global warming.

Effect of reduced tillage and mulching on soil health in Sesbania alley cropping based rainfed food - fodder systems

ABSTRACT An experiment was laid out in split-plot design with 3-Sesbania alley-based rainfed food-ufodder systems [Sesbania+(fodder sorghum–chickpea), Sesbania+(fodder sorghum–barley) and Sesbania+(fodder sorghum–mustard)] in main-plots and 6-reduced tillage and Sesbania mulching combinations in sub-plots to assess their impact on soil health. Minimum tillage (MT) during rainy season followed by zero tillage (ZT) during winter season along with mulch (MT-ZT+mulch) resulted in higher proportion of soil macro-aggregate, increased infiltration rate by 27.4%, hydraulic conductivity by 14.9% and water holding capacity by 5.9% (v/v) over conventional tillage (CT) during rainy season followed by conventional tillage during winter season without mulch (CT-CT without mulch). The MT-ZT+mulch had the highest soil organic carbon (7.3 g kg–1), microbial biomass carbon (226 mg kg–1 soil), SOC stock (14.9 Mg ha−1), carbon sequestration rate (1.72 Mg ha−1 year−1), soil quality index (SQI, 1.09) and enhanced the available soil N, P and K by 45.1, 47.2 and 22.2%, respectively, over CT-CT without mulching. The Sesbania alley + (fodder sorghum–mustard) cropping system had adverse effect on soil health while inclusion of chickpea in the system improved soil health and recorded the highest SQI (0.97).

Soil macroaggregates determine soil organic carbon in the natural grasslands of the Loess Plateau

Soil aggregates are generally thought to be the nucleus of all carbon sequestration mechanisms. However, the Loess Plateau, a typical region where a fragile ecosystem has gradually recovered, has high variability in soil aggregates due to differences in climate and soil properties; thus, the driving mechanism of soil aggregates to changes in soil organic carbon (SOC) content remain unclear. To determine the dominant mechanisms affecting SOC content, we performed a large-scale investigation of the aggregate size fractions, aggregate-associated OC, OC in bulk soil, and environmental factors of the natural grasslands across a climatic gradient (semi-arid to semi-humid) on the Loess Plateau. The results showed that the proportion of macroaggregates (MA) decreased but that of microaggregates (MI) increased in the soil from south to north on the Loess Plateau. MA content decreased with soil depth, whereas MI and the silt + clay fraction (SC) contents increased with soil depth. In addition, aggregate-associated OC decreased with soil depth. The contribution rate of macroaggregate-associated OCwf (MAFC) to OC in bulk soil from south to north in the Loess Plateau showed a trend of decreasing first and then increasing, and the contribution rates were 73.77 % (Fufeng), 62.29 % (Huangling), 32.78 % (Suide), 28.31 % (Shenmu), and 47.62 % (Dalad Banner), respectively. For the entire Loess Plateau, MAFC contributed the most to SOC in different soil layers and the contribution rates were 64.68 % (0–5 cm), 49.54 % (5–10 cm), 44.43 % (10–20 cm), and 37.23 % (20–30 cm), respectively. Across the considered depths and sites, the MA, MAFC, and OC content of MA had significantly (p < 0.05) positive direct effects on the OC in bulk soil. Furthermore, MAFC was mainly dependent on the OC content and proportion of MA. Therefore, these results indicated that the proportion of MA and OC content within MA dominated the OC dynamics in bulk soil in the Loess Plateau.

Litter Inputs Control the Pattern of Soil Aggregate-Associated Organic Carbon and Enzyme Activities in Three Typical Subtropical Forests

Soil extracellular enzyme activities among aggregate fractions are critical to short-term microbial activity and long–term carbon dynamics in forest ecosystems, but little is known regarding the effects of forest types on the soil enzyme activities in different soil aggregate fractions. Three typical subtropical forest types (Broadleaved forest, Moso bamboo forest and Chinese fir forest) were selected, and undisturbed soil samples (0–15 cm) were collected. We investigated the effects of forest types on aggregate stability (mean weight diameter, geometric mean diameter and fractal dimension), aggregate–associated organic carbon (OC) and the functionality of five enzymes (cellobiohydrolase, β-glucosidase, β-xylosidase, N–acetylglucosaminidase, leucine aminopeptidase) of different aggregate fractions (&gt;2 mm, 0.25–2 mm, 0.053–0.25 mm and &lt;0.053 mm). The results showed that the proportion of macro-aggregates, aggregate stability and macro–aggregates associated–carbon content and storage were higher in broadleaved and Moso bamboo forests than in Chinese fir forests, indicating that forest types influence the distribution of total soil OC among aggregate fraction classes and would delay the loss of OC in broadleaved and Moso bamboo forests. We also found that the extracellular enzymes were higher in aggregates of broadleaved forests and Moso bamboo forests. SEM (structural equation model) analysis also supported significantly positive relationships between litter quantity and aggregate enzyme activity, and indirect impact of litter quantity and litter C/N ratio together with soil organic carbon (SOC) and soil aggregate organic C content (SAOCC) on aggregate enzyme activity. The results of this study indicate that forest types showed large impact on aggregate-associated OC and enzyme activities, and the litter input of different forest types is the main control on enzyme activity among different aggregate fractions, and thus may play an important role in adjusting the sink capacity and stability of SOC.

Improving soil aggregates stability and soil organic carbon sequestration by no-till and legume-based crop rotations in the North China Plain

Conservation agriculture (CA) has been adopted worldwide on about 200 Mha to enhance soil organic carbon (SOC) for mitigating climate change. However, as a crucial mechanism to sequester SOC, how the protection of aggregates responds to the interaction between no-till and crop rotations (two principles of CA) remains unknown. Thus, a field experiment with six treatments [e.g., no-till or rotary tillage under the maize-wheat-soybean-wheat system (NT-MWSW, RT-MWSW), no-till or rotary tillage under the maize-wheat system (NT-MW, RT-MW), and no-till or rotary tillage under the soybean-wheat system (NT-SW, RT-SW)] was conducted from June 2018 to June 2021 in the North China Plain (NCP) to assess their effects on aggregation and SOC. Results indicated that macroaggregates (> 0.25 mm) were the main contributors to the soil carbon (C) pool, comprised 64.7–87.3 % of aggregates, and encompassed 64.9–73.1 % of the SOC stock. NT increased not only the proportion of macroaggregates but also aggregate stability (i.e., mean weight diameter and geometric mean diameter). Significant positive effects from legumes were observed under NT. SW increased by 13.6 % macroaggregate-associated SOC under NT in 0–20 cm compared to that under MW. Additionally, the conversion rate of straw C input under NT-SW was higher than that in other treatments, augmenting it by 9.4–21.9 %. This may be attributed to the higher macroaggregate total nitrogen (increased by 1.7–15.9 %) in 0–10 cm under legume-based crop rotations compared to that under MW, resulting in lower C: N ratios, which promoted the decomposition of straw. Furthermore, the total potential mineralization of macroaggregates under NT legume-based crop rotations was 3.0–16.0 % higher than that of MW. Thus, a legume-based NT system can significantly improve soil macro-aggregation, increase the conversion rate of straw C input, and reduce C loss, which can be a viable practice to enhance SOC sequestration capacity under CA in the NCP.