Proportion Of Macroaggregates Research Articles

Effects of cover crops and nitrogen fertilization on soil physical properties, carbon and nitrogen fractions, and winter wheat yield in the Chinese loess plateau: A 4-year field experiment

Context or problemLone-term application of chemical fertilizers in farmland ensure adequate or profitable crop yields but may damage soil structure. Cover crops (CCs) have great potentials to improve soil quality and promote sustainable crop production. However, the combined impacts of CCs with nitrogen fertilization on soil quality and crop yields are not clear. Objective or research questionWe aimed to examine the effects of CCs combined with N fertilization rates on soil physical properties, C and N fractions in both bulk soils and aggregates, and crop yields, and to find the best management practice that improve both soil quality and crop yields synthetically. MethodsA 4-year summer CCs - winter wheat field experiment was conducted in the Loess Plateau of China. CCs with different species and combinations (CC) were soybean (SB), sudan grass (SG), a mixture of both (SS), and no cover crop (CK) and N fertilizer (NR) were applied to winter wheat at rates of 0 (N0), 60 (N60), and 120 (N120) kg N ha−1. Soil physical properties and C and N fractions in both bulk soils and aggregates were evaluated at 0–10, 10–20, and 20–40 cm soil depths. ResultsSoil total porosity (TP), saturated water content (SWC), capillary water capacity (CWC), and C and N fractions decreased while bulk density (BD) increased with the increase of soil depth. The CC, NR, and their interaction (CC×NR) had significant effects on soil BD, aggregate size distribution and stability (MWD), and C and N fractions and only CC and CC×NR had significant effects on other physical properties. The incorporation of CCs significantly increased the proportions of > 5 mm aggregates and C and N fractions in both bulk soils and aggregates, especially in 0–10 and 10–20 cm. And SB and SS improved soil other physical properties more than SG, especially in 0–10 cm, which decreased BD by 13.2% and 12.6% while increased TP by 6.5% and 8.3%, SWC by 14.3% and 15.3%, CWC by 13.9% and 14.2%, MWD by 16.6% and 14.4%, respectively, compared to CK. Additionally, soil physical properties improved more with N60 while the C and N fractions in both bulk soils and aggregates increased more with N120. However, BD increased by 2.6% and 3.3% in N60 and N120 than N0, respectively. The correlations between the proportion of macro-aggregates and soil C and N fractions at 0–10 and 10–20 cm indicated the positive effects of CCs on improving soil structure and fertility simultaneously. Aggregated-associated C and N fractions decreased firstly and then increased with the reduced aggregate sizes, and were higher in micro-aggregates than in other size classes. N60-SB increased wheat yields by 98.7% compared with N0-CK. ConclusionsOverall, the incorporation of soybean residue was the best management practice for winter wheat yield and soil fertility under the reduced N fertilization. Implications or significanceThe selection of CCs species should depend on farmland managements, and the appropriate CCs with N fertilizer rates would target the improvements in soil quality, the sequestration of soil organic carbon, and crop yields synergistically.

Biochar addition promotes soil organic carbon sequestration dominantly contributed by macro-aggregates in agricultural ecosystems of China

Soil aggregates play pivotal roles in soil organic carbon (SOC) preservation and climate change. Biochar has been widely applied in agricultural ecosystems to improve soil physicochemical properties. However, the underlying mechanisms of SOC sequestration by soil aggregation with biochar addition are not well understood at a large scale. Here, we conducted a meta-analysis of 2335 pairwise data from 45 studies to explore how soil aggregation sequestrated SOC after biochar addition in agricultural ecosystems of China. Biochar addition markedly enhanced the proportions of macro-aggregates and aggregate stability, and the production of organic binding agents positively facilitated the formation of macro-aggregates and aggregate stability. Soil aggregate-associated organic carbon (OC) indicated a significantly increasement by biochar addition, which was attributed to direct and indirect inputs of OC from biochar and organic residues, respectively. Biochar stimulated SOC sequestration dominantly contributed by macro-aggregates, and it could be interpreted by a greater improvement in proportions and OC protection of macro-aggregates. Furthermore, the SOC sequestration of soil aggregation with biochar addition was regulated by climate conditions (mean annual temperature and precipitation), biochar attributes (biochar C/N ratio and pH), experimental practices (biochar addition level and duration), and agronomic managements (land type, cropping intensity, fertilization condition, and crop type). Collectively, our synthetic analysis emphasized that biochar promoted the SOC sequestration by improving soil aggregation in agricultural ecosystems of China.

Mixed Chinese Fir Plantations Alter the C, N, and P Resource Limitations Influencing Microbial Metabolism in Soil Aggregates

Assessing the limitations of microbial metabolic resources is crucial for understanding plantation soil quality and enhancing fertility management. However, the variation of microbial resource limitations at the aggregate level in response to changes in stands remains unclear. This research explores carbon (C), nitrogen (N), and phosphorus (P) limitations affecting microbial metabolism in bulk soils and aggregates in two mixed and one pure Chinese fir stands in subtropical China, analyzing resource limitations concerning soil carbon, nutrients, and microbial indicators. The results revealed that microbes in all aggregates of the pure stands and in the micro aggregates (<0.25 mm) of the three stands were relatively limited by C and P. In contrast, microbial metabolism was more N-limited in macroaggregates (>2 mm) and small aggregates (2–0.25 mm) in the mixed stands. Additionally, in the mixed stands the proportion of soil macroaggregates increased, and that of micro aggregates decreased, resulting in a shift from C and P limitation to N limitation for bulk soil microbial metabolism. Redundancy analysis identified soil aggregate organic carbon and nutrient content as the main factors affecting microbial resource limitation, rather than their stoichiometric ratios. Pathway analysis further confirmed that soil nutrients and their stoichiometric ratios indirectly influenced soil microbe resource limitation by regulating microbial biomass, microbial respiration, and extracellular enzyme activities. Thus, the impact of mixed plantations on soil nutrients and microbial activity at the aggregate level may be crucial for maintaining land fertility and achieving sustainability.

Rice-based Climate Resilient Farming Practices Influencing the Soil Physical Parameters, Carbon Dynamics and System Productivity in Inceptisols under Coastal Agro-ecosystem

A field experiment was carried out to assess the influence of different rice establishment technique {System of Rice Intensification (SRI) and Conventional method of transplanting (CMT)}, rice-based cropping sequence {rice-groundnut-fallow (RGF) and rice-toria-greengram (RTG)}, mulching practices {No mulching (WoM) and Crop residue mulch (CRM)} and nutrient management practices{100% recommended dose of fertilizer (RDF) and 75% RDF + 25% N through FYM (INM)} on the different physical properties of the soil under changing climate at the Central Research Station, Odisha University of Agriculture and Technology, Bhubaneswar in the East and South Eastern Coastal Plain Zone of Odisha, India. The field experiment was conducted in split-plot design replicated thrice. Considerable build-up of SOC by 5.2%, 10.3% and 13.9% was observed under RTG, CRM and INM over RGF, WoM and RDF, respectively. Both CRM and INM registered higher proportion of water stable micro (14.8 %and 15.7 %) and macro-aggregates (5.2 % and 9.2 %), respectively over WoM and RDF. The CRM and INM remarkably elevated the macro-aggregate carbon by 13.9 % and 15.7 %, respectively over the initial contents (10.2 g kg-1). Additionally, the RGF and CRM recorded significantly higher REY of 9.2 t ha-1 and 9 t ha-1 over RTG and WoM treatments, respectively. Thus, SRI system along with mulching rice straw in toria and toria biomass to green gram and INM practices has been identified as the most suitable climate resilient farming practice in the coastal agro-ecosystem of Odisha, India because of its significant impact in soil physical properties including carbon storage, and thus synergizing effects for favourable soil ecosystem functioning.

Ungulate herbivores promote contrasting modifications of soil properties and organic carbon stabilization in a grazed grassland versus rewilded woodland environment

Large vertebrate herbivores are ecosystem engineers, provoking cascading effects on soil properties through modifications of plant communities as well as direct modulation of organic matter incorporated into soils. However, most studies have been carried out with domestic ungulates in grasslands, and the effects which predominate in grasslands may not be generalizable to other ecosystems. It is not well understood how trophic rewilding with wild ungulates may affect soil processes, especially in non-grassland systems albeit rewilding of natural areas is a process associated with larger trends of land abandonment, shrub encroachment or land use change. In this study we investigated ungulate herbivore exclusion in two geographically and pedo-climatically equivalent but ecologically distinct contexts: a Mediterranean grassland with domesticated herbivores, and a reforested area populated by a community of wild ungulates. In each context, long-term herbivore exclusion zones were used to understand the effect of herbivores on soil properties and particularly on soil organic carbon (SOC). Samples from the topsoil (0–5 cm) were taken inside and outside the exclosures distributed between the two contexts, and ecosystem-level effects and responses to grazing were investigated. We found that soil properties’ response to grazing depended on the ecological context in which the grazing occurred. SOC contents in the grassland increased by up to 37% with grazing, while grazing reduced SOC concentrations by 23% in the rewilded area. In both cases, grazing was also associated with significant alterations of soil microbial biomass, the microbial metabolic quotient (qCO2), and aggregate stability, but the effects were opposite: On one hand, domesticated herbivores in the grassland positively influenced carbon stabilization which was strongly associated with soil microbial processes and characteristics, and additionally the proportion of stable macroaggregates was increased. In contrast, wild ungulate herbivory in the forest ecosystem reduced SOC concentrations, accompanied by decreased microbial biomass and increased microbial maintenance costs, and stable macroaggregates were reduced. The results indicate the importance of ecological context in determining the effect of herbivores on soil properties and processes and suggest that the directionality of effects on SOC may change owing to the predominance of different mechanisms of SOC stabilization. Consequently, this study provides evidence that the management of ungulates in rangelands or forests can be associated with different outcomes as related to crucial soil properties such as SOC contents and aggregation.

Animal manures increased maize yield by promoting microbial activities and inorganic phosphorus transformation in reclaimed soil aggregates

Animal manures positively affect soil microbial activity and inorganic phosphorus (Pi) accumulation. However, how different types of manures affect microbial-driven Pi transformation at the aggregate scale is largely unclear. Here, we conducted a field experiment focused on maize cultivation in a reclamation site. Five fertilization treatments included no fertilizer (CK), chemical fertilizer (CF), chicken manure (CHM), pig manure (PM), and cow manure (CM). We examined microbial biomass, soil extracellular enzyme activities associated with carbon and phosphorus cycling, and Pi fractions (Labile-P, Moderately labile-P, and Stable-P) in three aggregate sizes (> 2 mm large macro-aggregates, 0.25–2 mm small macro-aggregates, and < 0.25 mm micro-aggregates), as well as grain yield. The results showed that manures addition significantly increased the proportion of large macro-aggregates and aggregate stability compared to chemical fertilizer. Stable-P constituted the largest proportion among the Pi fractions, accounting for 63 %–72 %. However, manures reduced Stable-P (5.4 %–10.7 %) and increased Labile-P (111 %–190 %) in Pi, especially in micro-aggregates. Both chemical fertilizer and manures increased microbial biomass and enzyme activities in aggregates, with manures causing a greater enhancement of soil microbial biomass carbon (SMBC) and C-cycling enzymes, especially under pig manure, and improving soil microbial biomass phosphorus (SMBP) and P-cycling enzymes, especially under chicken manure. Phytase, phosphatase and SMBP accounted for 81.4 %, 81.2 % and 87 % of the differences in large macro-aggregates, small macro-aggregates, and micro-aggregates, respectively. The structural equation model (SEM) demonstrated that manures facilitated the transformation of Stable-P to Labile-P by regulating aggregates and microbial activity, which consequently increased yield. In summary, manures addition, particularly chicken manure, can enhance inorganic phosphate (Pi) accumulation and transformation, thereby mitigating phosphorus (P) limitation in calcareous reclamation soils.

Long‐term biochar application promoted soil aggregate‐associated potassium availability and maize potassium uptake

AbstractBiochar is an effective ameliorator for soil quality improvement and nutrient reuse from biomass; however, the effect of biochar application on soil potassium (K) availability, plant K uptake, and the underlying mechanisms have not been well‐elucidated. To address this, the variation in the soil K forms, soil aggregate stability, and aggregate‐associated K concentration, as well as maize K uptake, were investigated in a field experiment after 9 years of biochar amendment. The treatments included no biochar and NPK fertilizer (CK); NPK fertilizer treatment (F); biochar applied annually at the rate of 2.625 t ha−1 (C1), and biochar applied annually at rate of 2.625 t ha−1 with NPK fertilizers (C1F); one‐time biochar applied with NPK fertilizers, with biochar rate of 31.5 (C2F) and 47.25 t ha−1 (C3F). The results showed that after 9 years of field application, biochar inhibited the downward K migration to the deeper layer, thus increasing water‐soluble potassium (WSK), exchangeable potassium (EK), non‐exchangeable potassium (NEK), and total potassium (TK) in 0–20 cm soil, with C1F exhibiting better performance than C2F and C3F. Biochar also increased aggregate‐associated EK, NEK, and TK pools, mainly due to an increase in the macroaggregate proportion (&gt;0.25 mm). Biochar amendment promoted maize K uptake by an average of 35.69%, the path analysis indicated that the positive effect was an outcome of the synergetic effect of the increase in surface soil WSK content and promoted macroaggregate EK pools, which was primarily attributed to biochar improved soil properties, including soil organic carbon, pH, total nitrogen, total phosphorus, and cation exchange capacity. These factors explained 76% of the variance in maize K uptake. In conclusion, biochar is an effective ameliorator for improving soil K content and availability.

Effect of alkali residue and humic acid on aggregate structure of saline‐alkali soil

AbstractHumic acid (HA) and alkali residue (AR) exert an essential impact on soil aggregate structure, but how HA and AR promote the formation of macroaggregates jointly is not clear. The aim of this research was to explore influence of alkali residue and humic acid (AHA) on the structure and stability of soil aggregates, with saline‐alkali soil in North China as an example. The morphology and structure of the soil with AHA added were detected by a scanning electron microscope, Fourier transform infrared spectroscopy, and X‐ray diffraction. Soil aggregate structure was analyzed by mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension (D), and the trend of soil colloid forming macroaggregates was evaluated by zeta potential and surface charge. The results showed that under dry and wet sieves, MWD and GMD both surged initially and then decreased with the rise of AHA content, while D had the opposite trend. With the addition of 3%, AHA, MWD, and GMD reached their peak which proves that the proportion of soil macroaggregates was the highest. In the meantime, absolute value of zeta potential was low, which illustrates that the soil colloid system was in an unstable state of condensation and microaggregates tend to transform into macroaggregates. A large number of ions such as Ca2+ and Mg2+ in AHA promoted variable charge of saline‐alkali soil, and the binding frequency of Ca2+ with negatively charged humus and soil colloid particles was increased. AHA holds great promise for improving the aggregate structure of saline‐alkali soil.

Effect of No-tillage on Soil Aggregates in Farmland：A Meta Analysis

In order to clarify the impact of no-tillage on the quality of farmland soil aggregates in China and promote the adaptive application of no-tillage practices， a Meta-analysis was conducted by collecting data from 116 published studies. The effects of no-tillage on aggregate size distribution， mean weight diameter （MWD）， and aggregate-associated C were studied. The results showed that compared with that under tillage， no-tillage significantly increased the proportion of macroaggregates （10.9%） and MWD （12.8%） and decreased the proportion of clay and silt （-15.5%） but had no significant effect on soil microaggregate and aggregate-associated C. The subgroup and Meta regression analysis showed that no-tillage significantly increased the proportion of macroaggregates in Northwest China （17.6%） and MWD in North China （15.4%）. In upland and clay loam， no-tillage increased MWD by 12.6% and 18.4%， respectively. The effect of no-tillage on increasing the proportion of macroaggregates increased with the soil pH. When straw returned， no-tillage significantly increased the proportion of macroaggregates （9.6%） and MWD （11.6%）， but no significant effect of no-tillage on aggregates was found after straw removal. Regarding test duration， short-term （ &lt; 5 a） no-tillage could significantly increase the proportion of macroaggregates， whereas long-term （ &gt; 10 a） no-tillage could improve the MWD. In different soil layers， no-tillage could only significantly improve the aggregate size distribution and MWD in topsoil （0-20 cm） but had no effect in subsoil （ &gt; 20 cm）. In summary， no-tillage could improve aggregate size distribution and stability but had no effect on aggregate-associated C. Production region， soil properties， field management methods， and other factors should be fully considered in production practice to effectively improve the quality of soil aggregates.

Effects of forest regeneration types on phosphorus fractions of soil aggregates in subtropical forest.

Soil aggregates are important for the storage and availability of phosphorus in the soil. However, how forest regeneration types affect phosphorus fractions of soil aggregates remains unclear. In this study, we examined the composition of aggregate particle size, phosphorus fractions, phosphorus sorption capacity index (PSOR), legacy phosphorus index (PLGC) and degree of phosphorus saturation by Mehlich 3 (DPSM3) in bulk soils and soil aggregates of Castanopsis carlesii secondary forest (slight disturbance), C. carlesii human-assisted regeneration forest (moderate disturbance), and Cunninghamia lanceolata plantation (severe disturbance), aiming to explore the impact of forest regeneration types on phosphorus availability and supply potential of bulk soils and soil aggregates. The results showed that forest regeneration types significantly influenced the composition of soil aggregates. The proportion of coarse macroaggregates (>2 mm) in the soil of C. carlesii secondary forest and human-assisted regeneration forest was significantly higher than that in the C. lanceolata plantation, while the proportion of silt and clay fraction (<0.053 mm) showed an opposite trend. The composition of soil aggregates significantly affected the contents of different phosphorus fractions. The contents of soil labile phosphorus fractions (PSOL and PM3) decreased as aggregate particle size decreased. The contents of soil total phosphorus (TP), total organic phosphorus (Po), mode-rately labile phosphorus fractions (PiOH and PoOH), and occluded phosphorus (POCL), as well as PSOR and PLGC, exhibited a trend of decreasing at the beginning and then increasing as particle size decreased. The contents of TP, Po, and PiOH in coarse and silt macroaggregates was significantly higher than that in fine macroaggregates (0.25-2 mm) and microaggregates (0.053-0.25 mm). Forest regeneration types significantly influenced the contents of phosphorus fractions of bulk soils and soil aggregates. The contents of TP, Po, PSOL, and PM3 in the soil of C. carlesii secondary forests was significantly higher than that in C. carlesii human-assisted regeneration forest and C. lanceolata plantation. The contents of PSOL and PM3 in different-sized aggregates of C. carlesii secondary forests were significantly higher than that in the C. lanceolata plantation. Forest regeneration types significantly influenced the composition and supply potential of phosphorus fractions in soil aggregates. The proportions of PSOL, and PM3 to TP in different-sized soil aggregates were significantly lower in C. carlesii human-assisted regeneration forest compared with C. carlesii secondary forest. PSOR and DPSM3 in different-sized soil aggregates were significantly lower in C. lanceolata plantation than that in C. carlesii secondary forest. Overall, our results indicated that natural regeneration is more favorable for maintaining soil phosphorus availability, and that forest regeneration affects soil phosphorus availa-bility and its supply potential by altering the composition of soil aggregates.

Leguminous cover orchard improves soil quality, nutrient preservation capacity, and aggregate stoichiometric balance: A 22-year homogeneous experimental site

Soil and water conservation measures, widely promoted to control soil erosion in erosive orchards, can alter soil aggregates, thereby influencing the soil quality index (SQI). However, it's still unclear how these measures affect soil aggregate nutrients, stoichiometry, and their association with SQI at a long-term timescale. This study focused on a 22-year homogeneous orchard in subtropical hilly region. Five soil and water conservation measures, namely clean tillage (CT), engineering measures (EM), tillage measures (TM), non-leguminous biological measures (NLBM), and leguminous biological measures (LBM), were implemented. Sampling depths were 0–20 cm, 20–40 cm, and 40–60 cm. The results revealed that LBM significantly enhanced SQI across the soil profile, increased the proportion of macroaggregates, and improved aggregate stability, soil organic carbon, and total nitrogen. Additionally, LBM demonstrated the highest capacity for carbon and nitrogen preservation. Soil stoichiometry revealed carbon and nitrogen limitations in the orchard soils, and leguminous cover proved effective in alleviating these limitations and maintaining the stoichiometric balance of soil aggregates. Under a long-term timescale, these measures mitigated or even surpassed the impact of soil depth on soil aggregates and SQI. The improvement of orchard SQI through the measures was primarily achieved by enhancing aggregate stability. There was no significant correlation between soil organic carbon and SQI in relation to fruit yield, ascribed to the intense competition for water and nutrients between cover plants and citrus trees. In conclusion, LBM emerges as the most beneficial soil and water conservation measure for enhancing orchard SQI, preserving nutrients, and maintaining aggregate stoichiometric balance. It holds the potential to improve orchard yield and contribute to sustainable development.

Size and concentration effects of polythene plastic residues on soil physiochemical traits and maize productivity: A three-year appraisal

Extensive studies have been conducted on the impacts of plastic film residue on crop productivity in dryland agriculture. However, the relevant results were inconsistent or even opposite, which was most probably affected by both the size and concentration of residual films. To clarify this issue, a three-year (2019–2021) field experiment was conducted to examine plastic residue landfill effects on maize productivity using three sizes (0.4 × 0.4 cm2 (small), 4 × 4 cm2 (medium), and 10 × 10 cm2 (large)) under the low and high addition concentrations in an irrigated maize field. The data indicated that medium-sized residues significantly reduced maize yield by 7.3% and 13.8% in low and high addition levels respectively, relative to non-landfill group (CK) (p < 0.05). Large and small-sized residues under low level had no significant impact on yield (p > 0.05), while high amounts of small residues turned to positively influence yield. This trend was closely correlated with soil temperature, soil moisture, key enzyme activities, macroaggregate proportion, soil organic carbon and total nitrogen contents. Structural equation modelling and relative importance analyses demonstrated soil hydrothermal (27.4%), soil nitrogen (22.0%), and physical properties (21.1%) as primary drivers. A general trend was that the sizes of residues showed evidently greater impacts than their addition levels. Moreover, medium residues showed negative effects, while large and small ones had neutral or positive effects. For the first time, our findings confirmed the size- and concentration-dependent effects of plastic residues on crop productivity and provided a novel insight into plastic film pollution assessment & management in agricultural ecosystems.

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.

Organic substitutions enhanced soil carbon stabilization and reduced carbon footprint in a vegetable farm

The strategies of substituting inorganic fertilizers with organic fertilizers have been shown to significantly impact the dynamics of soil organic carbon (SOC) combating soil degradation and climate changes in intensive vegetable production. However, the underlying mechanisms and comprehensive assessment of environmental consequences are not fully understood. We conducted a five-year field experiment in the Yangtze River Delta Alluvial Plain, China, four fertilization treatments were established at equal nitrogen (N) levels: sole mineral fertilizers (SN); organic substituting 20 % (M1N4), 50 % (M1N1), and 100 % (SM) of mineral N fertilizer with organic fertilizer. Soil carbon (C) pools, physical and chemical composition of SOC, and C footprint were measured based on soil aggregates, 13C nuclear magnetic resonance spectroscopy, and life cycle assessment to investigate the effects of organic substitution on SOC quantity, quality, and environmental implications. Our results showed a significant increase in SOC content, particularly in the M1N1 treatment. This increase was attributed to changes in soil properties, an elevation in dissolved organic C content, and improved SOC stability. Specifically, organic substitution increased the proportion of macroaggregates, content of lignin phenols, and enrichment of alkyl C groups. Based on life cycle assessment incorporating field measurements, the average C footprint ranged from 1.82 to 2.58 CO2 kg eq kg−1 vegetable in the five-year experiment, primarily influenced by transportation and fertilizer manufacturing. Partial organic substitution reduced the C footprint by 6.2–10.1 %, while the SM treatment increased it by 0.54 CO2 eq kg−1 vegetable, and the M1N1 had the lowest C footprint at 1.82 CO2 eq kg−1 vegetable. As a whole, this approach of substituting 50 % of mineral N with organic fertilizers serves as a viable strategy to bolster soil C stabilization, promote C accumulation, and mitigate the C footprint linked to intensive vegetable production in subtropical regions.

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

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

Responses of lettuce (Lactuca sativa L.) growth and soil properties to conventional non-biodegradable and new biodegradable microplastics

Residual plastic films in soils are posing a potential threat to agricultural ecosystem. However, little is known about the impacts of microplastics (MPs) derived from biodegradable and non-biodegradable plastic films on plant-soil systems. Here, we carried out a pot experiment using soil-cultivated lettuce treated by two types of MPs, degradable poly(butylene adipate-co-terephthalate) (PBAT-MPs) and non-biodegradable polyethylene (PE-MPs). MPs resulted in different degrees of reduction in shoot biomass, chlorophyll content, photosynthetic parameters, and leaf contents of nitrogen (N), phosphorus (P), and potassium (K), accelerated accumulation of hydrogen peroxide and superoxide, and increased malondialdehyde content in lettuce leaves. Moreover, MPs obviously decreased contents of total N, nitrate, ammonium, and available K in soils, and increased available P, thus altering soil nutrient availability. MPs also significantly decreased proportions of macroaggregates, and decreased soil electrical conductivity and microbial activity. PBAT-MPs had significantly greater impacts on oxidative damage, photosynthetic rate, soil aggregation, microbial activity, and soil ammonium than those of PE-MPs. Our results suggested that MPs caused oxidative damages, nutrient uptake inhibition, soil properties alteration, ultimately leading to growth reduction, and PBAT-MPs exhibited stronger impacts. Therefore, it is urgent to further study the ecological effects of MPs, especially biodegradable MPs, on soil-plant systems.

Cover cropping promotes soil carbon sequestration by enhancing microaggregate-protected and mineral-associated carbon

Cover cropping can improve soil C sequestration compared to no cover cropping, but the mechanism of C sequestration in soil aggregates and minerals needs more exploration. We explored C sequestration using C fractions in soil aggregates and minerals by cover crops in a five-year old summer cover crop – winter wheat (Triticum aestivum L.) rotation system at Changwu National Agroecology Experimental Station in the Chinese Loess Plateau. Three cover crops as soybean (Glycine max L., SB), sudangrass (Sorghum sudanense (Piper) Stapf, SG), soybean and sudangrass mixture (SS) were planted during summer fallow and incorporated into the soil two weeks prior to wheat planting each year. Soil samples at 0–10, 10–20, and 20–40 cm depths were collected at wheat harvest after 5-yr and analyzed for C fractions which were coarse particulate organic C (cPOC), intra-microaggregate fine particulate organic C (iPOC), free fine particulate organic C (fPOC), and mineral-associated organic C (MOC). The iPOC and MOC are considered as protected C against mineralization. Compared to no cover crop (CK), cover crops increased large macroaggregate proportion at 0–10 cm by 18–22 %, with SS having a greater mean-weight diameter (MWD) than other treatments. Cover crops had greater MOC, iPOC, and fPOC fractions than CK in most aggregate-size classes and the bulk soil at all depths, with SS having the greatest C fractions. The MOC was greater than any other C fractions, regardless of cover crop species. Cover cropping can enhance soil aggregation and C sequestration by increasing microaggregate-protected and mineral-associated C compared to no cover cropping, resulting in improved soil C stabilization. Cover crop mixture was more effective in promoting soil aggregate stability and C fractions than single cover crop species.

Response of Soil Aggregate Composition and Stability to Secondary Succession and Plantation of a Broad-Leaved Korean Pine Forest after Clear-Cutting and Its Causes

The composition and stability of soil aggregates are important characteristics for evaluating soil health. The objective of this study was to explore the effects of different restoration modes and secondary succession sequences of Korean pine on the stability of forest soil aggregates after clear cutting and their causes. The stability and composition of soil aggregates in 0–10 cm, 10–20 cm, and 20–40 cm were analyzed in four natural forests in the secondary succession sequence and a Pinus koraiensis plantation in the clear-cutting area of Liangshui National Nature Reserve, and the effects of forest community characteristics and cementing materials on these aggregates were explored. With the advancement of succession, the large soil water-stable aggregates and mechanical aggregates increased, and the stability increased. From the pioneer community to the top community, the proportion of macroaggregates in the soil mechanical aggregates in the 20–40 cm soil layer increased by 36%, while that in the water-stable aggregates in the 10–20 cm soil layer increased by 19%. Compared with plantation, the stability of soil aggregates in natural forests with a similar age was stronger. Water-stable aggregates were negatively correlated with bulk density, density, and porosity, and positively correlated with organic-matter-related cement. The volume of the dominant tree, litter yield, tree species diversity, biomass of various tree species, and litter biomass in the undecomposed layer were the key indicators affecting the stability of aggregates. In terms of restoration measures, natural restoration is better than plantations with a single tree species. In addition, succession makes forest soil aggregates more stable. The change of dominant tree species leads to changes in soil aggregate stability, and the effect of organic-related cementing material was stronger than that of iron oxide.

Impact of Different Land Use Practices on Size of Soil Aggregates and Its Mean Weight Diameter under Vertisols of Central India

The present study was carried out at JNKVV, Jabalpur (23010’ N latitude, 79057’ E longitudes and at elevation 393.0 meters above mean sea level). This study was carried out in 2019 that laid out in split plot design with nine main treatments of land use practices (forest land, perennial forage land, uncultivated land, aonla orchard, rice-wheat system, soybean-wheat system, guava orchard, mango orchard and citrus orchard) and three sub-plot treatments of soil depths (0-20, 20-40 and 40-60 cm) which were replicated three times. A total of 81 soil samples were subjected to determination of different size (&gt; 5.0, 2.0-5.0, 1.0-2.0, 0.50-1.0, 0.25-0.50, 0.10-0.25 and &lt;0.10 mm) water stable soil aggregates and mean weight diameter of soil aggregates. Results revealed that land use practices and soil depths significantly affect the mean weight diameter of soil aggregates, distribution of different size soil aggregates. It was noted that irrespective of soil depths, proportions of macro-aggregates (&gt;0.50 mm size) and mean weight diameter were highest under forest land and lowest in soybean-wheat system. However, number of micro-aggregates (&lt; 0.50 mm) increased with soil depths and macro-aggregates and mean weight diameter of soil aggregates were highest at 0-20 cm depth. It can be concluded that extent of soil disturbance significantly alters the proportion of macro-aggregates (&gt;0.50 mm size) and mean weight diameter of water stable soil aggregates with higher in undisturbed (forest, uncultivated and perennial forage) land uses and lower in crop lands which decreased with increase in soil depths.

Reforestation Increases the Aggregate Organic Carbon Concentration Induced by Soil Microorganisms in a Degraded Red Soil, Subtropical China.

In the process of biological carbon (C) sequestration during reforestation in degraded red soil, due to the decomposition of soil microorganisms, the interaction between soil organic carbon (SOC) and aggregates has an important effect on soil C sequestration. In this study, six common reforestation models and three soil layers were selected in a degraded red soil area of the central subtropical region to determine the composition of soil aggregates and the distribution of SOC in soil aggregates. Based on the results of the soil physicochemical properties and microbial community composition biomass, we assessed the changes in aggregate-associated organic C storage during fluctuations in the stability of the aggregates. After reforestation, the SOC stock increased by 131.28-140.00%. Compared with the three pure forests and broad-leaved mixed forests, coniferous and broad-leaved mixed forests showed the largest proportion of macroaggregates (85.48-89.37%) and higher SOC accumulation. Soil microbial biomass mainly affected the decomposition process of SOC by affecting the stability of the soil aggregates, and the effect of bacteria was more significant. Coniferous and broad-leaved mixed forests can provide more soil microorganisms and C sources than pure forest, thus promoting macroaggregate formation and stability and related organic C storage. This reforestation model has greater C sequestration potential.