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Soil biological activity (i.e. mineralized carbon (C) (Cmin)) is a crucial property to evaluate soil health and its changes due to soil use. In the southeastern Buenos Aires province (SEB) there is scarce information about how agriculture ecological intensification (IEA) affects soil global biological activity and the potentially mineralized C (C0) to improve the comprehension of the mechanisms that regulate soil C dynamics. It would be relevant to determine the adequate incubation time at which the determination of Cmin can predict C0 in soils from the SEB. Moreover, the Cmin determined in early incubation days has been proposed as a quick alternative to estimate C0. It has been hypothesized that it is necessary to run longer incubations to correctly evaluate C0 of soils of the SEB and that the CO2 emitted during short incubation periods is a good estimator of C0. Soil samples were taken (0-5 and 5-20 cm) from a long-term experiment on crop-pasture rotations on Mollisols at Balcarce with different levels of IEA under conventional tillage and no-tillage (SD). Total (COT), particulate (COP) and associated organic C were determined, as it was the Cmin from aerobic incubations under controlled conditions at 2, 4, 6, 10, 16, 22, 28, and 63 days. The C0 was estimated from the Cmin at 22, 28, and 63 days. The Cmin and C0 showed similar patterns among cropping systems. The estimations of C0 from the Cmin at 63 days were the most trustable (mean of C0 466,9 and 517,8 mg C kg-1 from Cmin(28) and Cmin(63), respectively). Furthermore, the Cmin at a few days of incubation showed high correlation coefficients with C0 (r between 0.68 and 0.92 at 0-20 cm for 2 to 10 incubation days) and therefore short incubations would be promising to estimate C0. [ABSTRACT FROM AUTHOR]

Periodic oxygen (O2) limitation in humid terrestrial soils likely influences microbial composition, but whether communities share similar responses in disparate environments remains unclear. To test if specific microbial taxa share consistent responses to anoxia in radically different soils, we incubated a rainforest Oxisol and cropland Mollisol under cyclic, time-varying anoxic/oxic cycles in the laboratory. Both soils are known to experience anoxic periods of days to weeks under field conditions; our incubation treatments consisted of anoxic periods of 0, 2, 4, 8, or 12 d followed by 4 d of oxic conditions, repeated for a total of 384 d. Taxa measured by 16S rRNA gene sequences after 48 d and 384 d of experimental treatments varied strongly with increasing anoxic period duration, and responses to anoxia often differed between soils at multiple taxonomic levels. Only 19% of the 30,356 operational taxonomic units (OTUs) occurred in both soils, and most OTUs did not respond consistently to O2 treatments. However, the OTUs present in both soils were disproportionally abundant, comprising 50% of sequences, and they often had a similar response to anoxic period duration in both soils (p < 0.0001). Overall, 67 OTUs, 36 families, 15 orders, 10 classes, and two phyla had significant and directionally consistent (positive or negative) responses to anoxic period duration in both soils. Prominent OTUs and taxonomic groups increasing with anoxic period duration in both soils included actinomycetes (Micromonosporaceae), numerous Ruminococcaceae , possible metal reducers (Anaeromyxobacter) or oxidizers (Candidatus Koribacter), methanogens (Methanomicrobia), and methanotrophs (Methylocystaceae). OTUs decreasing with anoxic duration in both soils included nitrifiers (Nitrospira) and ubiquitous unidentified Bradyrhizobiaceae and Micromonosporaceae. Even within the same genus, different OTUs occasionally showed strong positive or negative responses to anoxic duration (e.g., Dactylosporangium in the Actinobacteria), highlighting a potential for adaptation or niche partitioning in variable-O2 environments. Overall, brief anoxic periods impacted the abundance of certain microbial taxa in predictable ways, suggesting that microbial community data may partially reflect and integrate spatiotemporal differences in O2 availability within and among soils. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) mineralization plays an important role in global climate change. Temperature affects SOC mineralization, and its effect can be limited by the substrate available. However, knowledge of the effects of temperature and substrate quality on SOC mineralization in the Mollisols of Northeast China is still lacking. In this study, based on a spatial transplant experiment, we conducted a 73-day incubation to examine the effects of temperature on SOC mineralization and its temperature sensitivity under different carbon levels. We found that the SOC content, incubation temperature and their interaction had significant effects on SOC mineralization. A higher SOC content and higher incubation temperature resulted in higher SOC mineralization. The temperature sensitivity of SOC mineralization was affected by the substrate quality. The temperature sensitivity of SOC mineralization, showed a downward trend during the incubation period, and the range of variation in the Q10 declined with the increment in the SOC content. The study suggested that there was a higher SOC mineralization in high levels of substrate carbon when the temperature increased. Further, SOC mineralization under higher SOC contents was more sensitive to temperature changes. Our study provides vital information for SOC turnover and the CO2 sequestration capacity under global warming in the Mollisols of Northeast China and other black soil regions of the world. [ABSTRACT FROM AUTHOR]

A full understanding of the nature of sorption/desorption reactions of Zn in soils is crucial for the interpretation and prediction of its chemical behavior in soils. Therefore, to identify the kinetics of zinc (Zn) adsorption in selected common diagnostic horizons of soils in southwestern Iran, 30 ml of solutions containing 10 mg Zn/L was added to 3 g of each of mollic, calcic, and salic diagnostic horizons (in triplicate) and at specified times (5 to 2880 minutes) the residual concentration of Zn in the supernatant was measured by an atomic absorption spectrometer. The results indicated that the Zn adsorption process in the soils studied was a three-stage process. Accordingly, by end of the first step (120 minutes from the beginning of the experiment) 65.7, 57.8, and 26.7% of the total amount of Zn was adsorbed in mollic, calcic and salic horizons, respectively. The Zn adsorption capacity of mollic, calcic, and salic diagnostic horizons were 58.20, 63.57, and 79.50 mg g−1, respectively. Excellent agreement was found between the pseudo-second-order kinetic model and the experimental data (R2 ≈ 0.994–0.999). The Zn sorption/desorption isotherms were also derived with 0.1 M Ca (NO3)2 solutions containing varying concentrations of Zn (0 to 10 mg L−1) for 24 h. Accordingly, comparing with the Langmuir model (0.888 < R2 sorption < 0.956; 0.896 < R2 desorption < 0.984), Freundlich isotherm model (0.987 < R2 sorption < 0.999; 0.963 < R2 desorption < 0.994) could better explain Zn sorption/desorption data in the soils studied. The Zn adsorption data on all three soils followed an L-shaped isotherm. Besides, Zn adsorption isotherms showed greater values than desorption isotherms, suggesting that the Zn adsorption process is irreversible. Results obtained from hysteresis calculations indicated that the desorption of freshly sorbed Zn was less hysteretic in calcic and mollic horizons relative to salic horizon. This suggests low mobility and leaching potential of freshly sorbed Zn can be expected from these soils. [ABSTRACT FROM AUTHOR]

Artificial ecological corridors (AECs) are internationally approved ecological restoration and climate mitigation strategies. The width and recovery time indices of AECs directly affect the restoration efficiency of degraded soil nutrients. However, there is a lack of comprehensive and quantitative evaluation research on the construction factors of AECs from the perspective of soil fertility improvement. This research aimed to examine the critical ecological corridor construction factors affecting Mollisols' eco-chemometrics and give a scientific scope. We collected 55 Mollisol samples at different restoration years (0–35 years) and different distances (0–280 m) from the AEC of the Ashi River, a typical Mollisol restoration area in Harbin, and the cold regions of China. We measured the distances, restoration years, soil thickness, pH, electrical conductivity (EC), cation exchange capacity (CEC), soil total organic carbon (SOC), soil total organic matter (SOM), dry matter content (DMC), and the proportion of nitrogen (TN), phosphorus (TP) and potassium (TK). The results are as follows: (1) Within the AEC, there were significant differences in soil stoichiometric characteristics in different restoration years and locations; after restoration for 10–35 years, the soil stoichiometric characteristics reach or exceed the reference value of Mollisols. (2) It is feasible to restore large-scale degraded Mollisols through ecological corridors. In this recovery process, the soil nutrients first decreased, then increased, and finally reached and exceeded the reference value of normal Mollisols. (3) Soil nutrient accumulation was related to ecological corridor width and recovery time. The recommended unilateral width of the ecological corridor based on Mollisols' CEC and SOC indices for restoration is 175–225 m, and the restoration period is 22.7–35 years based on Mollisols' EC and SOC indices for restoration. This study demonstrated the change mechanism of Mollisols in AECs based on recovery time and location, and provided the basis for the Chinese government to formulate policies for Mollisol remediation. [ABSTRACT FROM AUTHOR]

Degradation of microplastics (MPs) by both physicochemical and biological processes in the natural environment is determined by the enzymes inside the soil, and which was severely influenced by crop growth and straw amendment (SA). However, it is still unclear how crop growth and SA influence degradation of MPs in soils. In this study, both catalase and sucrase were measured, and the stereomicroscope combined with microscopic infrared spectroscopy and scanning electron microscope (SEM) was used to detect the morphology and quantity of low-density polyethylene microplastic (LDPE-MP) and low-density polypropylene microplastic (LDPP-MP), after crop growth (maize and soybean, with and without SA, 1 and 2% MP) in an outdoor pot experiment, in the Mollisols. The results showed that the growth of the crops changed the morphology, functional groups (e.g., methylene, carbonyl), total mass, and abundance ratio of MPs of different sizes. These were possibly caused by enzymes that were significantly influenced by crop types, abundance, and types of MPs in the soils. Maize growth decreased the mass of LDPE-MP and LDPP-MP by 28.7 and 32.7%, respectively, and 2% (w/w) of LDPP-MP addition in soil decreased mass of 9%, which was higher than that in 1% (w/w) LDPP-MP addition in soil. Soybean growth with SA decreased the mass of LDPE-MP and LDPP-MP by 36.6 and 20.7%, respectively, than the control treatment (CK). Compared with CK, both crop growth and SA changed the abundance of MPs of different sizes and decreased the mean size of MPs. The LDPE-MP could be more easily degraded by enzymes in the soils compared to LDPP-MP when the MP size was smaller with surface roughness. Generally, both maize and soybean growth can accelerate MP change in soils, and MP change process was mainly determined by SA, MP types, and the dose effect of MP. [ABSTRACT FROM AUTHOR]

In agroecosystems, effective straw return modes are one of the key practices for increasing soil fertility and carbon (C) availability. Although they improve soil quality, there is currently little information available regarding the influence of distinct straw return modes with respect to potential soil organic carbon (SOC) sequestration. In this study, we established a five-year (2015–2019) field experiment in Mollisols of Northeast China, which included four straw return modes, plow tillage with straw return as the control (PTS), rotary tillage with straw return (RTS), rotary tillage with straw strip return (RSS), and plow tillage with straw strip return (PSS), to investigate the impact on soil physicochemical properties, aggregates, and C sequestration. The results reveal that RSS effectively improved the soil physicochemical properties. Such responses increased the contents of SOC, fulvic acid carbon (FAC), and humin carbon (HMC) in all soil layers (0–30 cm). The proportion of macroaggregates was higher in RSS, whereas the proportion of silt/clay was the lowest at depths of 0–20 cm; consequently, the mean weight diameter (MWD) and geometric mean diameter (GMD) of RSS were higher at depths of 0–20 cm due to the improved physical soil structure. In the 0–10 cm and 20–30 cm layers, the highest humic acid carbon (HAC) concentrations associated with all aggregate sizes were found for RSS, in contrast to 10–20 cm, which had increased HMC. Structural equation modeling (SEM) revealed that C transformation was mainly mediated through silt/clay-associated FAC, HMC, and SOC, ultimately determining HAC (81%) and HMC (85%) as the primary humus fractions for SOC sequestration. Therefore, this study shows that RSS is the suitable straw return mode for effectively improving soil quality, aggregate stability, and C sequestration in Mollisols of Northeast China. [ABSTRACT FROM AUTHOR]

To better understand the mechanism of nitrogen (N) distribution, absorption, utilization and loss in fertilizer under different tillage practices, a study was conducted to quantitatively explore the fate of fertilizer N in the soil–plant–atmosphere using the 15N labelling technique under the long-term conservation tillage experiment in Northeast China. The test crop used was corn. This study compared the residual amount of 15N fertilizer in soil, the content of 15N fertilizer N in particle organic nitrogen (PON), light fraction organic matter nitrogen (LFOMN) and heavy fraction organic matter N (HFOMN) under different tillage practices. In addition, N uptake, utilization and distribution by corn, the emission of N2O and the gas loss of fertilizer N, and the fertilizer N utilization rate were also taken into account. The results showed that no tillage (NT) had a significantly lower amount of residual 15N fertilizer than a moldboard plow (MP) (p < 0.05). In general, the content under NT at the 0–30 cm soil layer was 7.85% lower than that of MP. NT led to significantly greater PON and LFOMN of soil organic N compared to MP (p < 0.05). 15N from N uptake, fertilizer absorption and utilization under NT were significantly higher than that under MP (p < 0.05), the soil N absorbed by plants under NT or MP was greater than 70%. The distribution of 15N from N fertilizer in each corn part increases in this order: seed > leave > sheath > stem > bract > ear; about 57.91–64.92% of 15N is distributed in the grain. NT resulted in significantly lower average and cumulative N2O emissions than those from MP based on the static closed chamber approach (p < 0.05). The average and cumulative emissions of soil fertilizer 15N-N2O under MP were also significantly greater than that of NT. Among the N2O emissions, 15.3% and 22.98% came from fertilizer N under NT and MP, respectively. On average, 0.1–0.16% of fertilizer N was lost in the form of N2O. There was a significant difference in fertilizer utilization between NT and MP, and NT was 4.23% larger than MP (p < 0.05). These one year findings suggest that NT plays a positive role in improving the N absorption and utilization of fertilizer in a Chinese mollisol and long-term effects need to be further studied. [ABSTRACT FROM AUTHOR]

Tillage has been reported to induce seasonal changes of organic carbon (Cmicro) and nitrogen (Nmicro) in the biomass of microorganisms. Soil microorganisms execute such ecosystem functions as it is an immediate sink of labile biophil elements; it is an agent of a conversion, catalysis and synthesis of humus substances; it transforms soil contaminants into nonhazardous wastes and it participates in soil aggregation and pedogenesis as a whole. However, the seasonal turnover of microorganisms on arable lands in temperate ecosystems has not been studied at a relevant level. Hence, we are aimed at studying the dynamics of such soil microbial biomass patterns as Cmicro, Nmicro, microbial index (MI = (Cmicro/CTOC)·100%) and CO2-C emissions against the background of 9 years of tillage and 22 years of abandoned (Ab) and fallow (F) usage. Our study was conducted on a long-term experimental site on a Mollisol in Northeast China. The maximum Cmicro and Nmicro contents were recorded at the beginning of the growing season at the 0–10-cm layer and mid-July at the 20–40-cm layer, while the minimum content was during August–October. The Cmicro content ranged from 577.79 to 381.79 mg−1 kg−1 using Ab in the spring to 229.53 to 272.86 mg−1 kg−1 in the autumn using CT (conventional tillage) and F in the 0–10- and 10–20-cm layers, respectively. The amplitude of Nmicro content changes were several times lower as compared with the Cmicro. The smallest quartile range (IQR0.25–0.75) of such changes was shown when using the following treatments: no till (NT) and Ab in the 0–10-, NT and F in the 10–20- and CT in the 20–40-cm layer. The widest Cmicro:Nmicro ratio was recorded at F and CT in the 0–20- and CT and rotational tillage (Rot) in the 20–40-cm layer. The MI dynamics were similar to the trends of Cmicro and Nmicro and changed from 0.72 ± 0.168 to 2.00 ± 0.030%. The highest share of Cmicro in CTOC was at Ab (1.82 ± 1.85%) and NT (1.66 ± 1.52 %) in the 0–10-, Ab (1.23 ± 1.27%) and NT (1.29 ± 1.32%) in the 10–20- and Ab (1.19 ± 1.09%) and F (1.11 ± 1.077%) in the 20–40-cm layer, correspondingly. The Pearson's correlation coefficient between Cmicro and CTOC increased from the upper 0–10- to the lower 20–40-cm layer; it was "strong" and "high" between Cmicro and CTOC. Different uses of Mollisol affected the amplitude of the Cmicro and Nmicro seasonal changes, but it did not change their trend. Our results suggest the key role of Ab and NT technologies in Cmicro accumulation in the total organic carbon (TOC). [ABSTRACT FROM AUTHOR]

Purpose: The interaction between soil microbial and nutrient characteristics is still under debate, and the long-term fertilization experiment provides a good research platform. Methods: The microbial activity (reflected by the soil respiration rate and extracellular enzyme activities) and functional diversity (based on the Biolog EcoPlate method) of a fluvo-aquic soil fertilized with organic manure and/or chemical fertilizers for 36 years were examined. The treatments included a control without fertilization (CK), inorganic N fertilizer (N), NP fertilizers (NP), and NPK fertilizers (NPK), and organic manure (M), organic manure + inorganic N fertilizer (MN), organic manure + inorganic NP fertilizers (MNP), and organic manure + inorganic NPK fertilizers (MNPK) treated soils. Results: Microbial respiration rate of the organic manure-treated soil was 64.39% higher than that of the untreated soils. The β-glucosidase, N-acetyl-glucosaminidase, β-xylosidase, and β-cellobiosidase activities of organic manure-treated soils were 80.44%, 152.25%, 35.23%, and 126.03% higher than those of untreated soils, respectively. Additionally, the average well color development (AWCD) value of organic manure-treated soils was 23.82% higher than that of untreated soils. M treatment exhibited the highest microbial diversity and microbial utilization capacity of carbon sources; however, organic + inorganic fertilizers tended to reduce soil functional diversity compared to that of M treatment. Long-term nutrient deficiencies negatively affected the microbial utilization capacity of carbon sources, as indicated by the low AWCD value, Shannon richness, and Simpson indices of CK soils. Multiple stepwise regression analysis showed that P availability and P-related stoichiometric ratio played more important roles in determining microbial activity and functional diversity than C, N, and K in fluvo-aquic soils. Conclusion: This study suggested that organic manure had greatest promoting effect on soil metabolic activity, and NPK balanced fertilization had higher microbial activity than NPK unbalanced fertilization. Generally, P availability and stoichiometry are pivotal in determining microbial activity and functional diversity. [ABSTRACT FROM AUTHOR]

Soil water and temperature are important factors to reflect variations in soil heat and water flows especially for tillage systems. The objective of this study was to evaluate the performance of the CoupModel in predicting the effect of tillage practices on soil water and heat processes for conventional tillage (CT) and no-tillage (NT) systems with straw mulching on semi-arid and high-latitude Mollisols of northeast China. This model was calibrated and evaluated in a three-year tillage experiment from 2009 to 2011 in a field experiment station, using field measurements of daily soil temperature and water storage in profiles for CT and NT separately. The results showed that under the model, soil temperatures were well simulated at 0–90 cm soil depths for CT, as indicated by R2 ≥ 0.97, the nRMSE = 27.5–38.7% and −1.02 °C ≤ ME ≤ −0.31 °C, and soil water storage at 0–130 cm soil depth (R2 = 0.01–0.06, the nRMSE = 19.6–37.1%, 13.3 mm ≤ ME ≤ 28.2 mm) was simulated with more uncertainty. "Moderate to good agreements" were achieved for NT. In general, the temporal and spatial variations of soil temperature and water for NT were well simulated by CoupModel. Although NT decreased soil evaporation—thus improving soil water content, especially in the root zone soil—and lowered the soil frozen depths, it reduced the soil temperatures, which could influence crop growth. It was concluded that the CoupModel proved to be a functional tool to predict soil heat and water processes for CT and NT systems in high-latitude seasonal frost conditions of Mollisols in China to estimate the soil temperature, water, energy balance, and frost depth dynamics in relatively complex systems that combined plant dynamics with tillage and/or no tillage covered with straw mulching in the soil surface. [ABSTRACT FROM AUTHOR]

In the northeast plains of China, the intensive utilization of agricultural soils has been a persistent issue, and finding ways to utilize soil resources efficiently and sustainably through a scientifically-driven management system has become a crucial challenge for agricultural production. Conservation tillage is a crucial technology for sustainable agriculture. Currently, plow and rotary tillage are the dominant methods used in Mollisols, but there is limited information on the effects of different conservation tillage practices in this region. The objective of this study was to investigate the short-term impact of tillage and sowing methods on soil physical properties and corn plant growth and to examine the relationship between soil physical properties and plant characteristics during various stages of growth. This study consisted of four tillage and sowing methods: plow tillage and precision seeder sowing (PTS), rotary tillage and precision seeder sowing (RTS), no-tillage and no-tillage seeder sowing (NTS), and no-tillage and precise sowing in stubble field (STS) (all four treatments involved total straw return). The results indicated that the soil penetration resistance (SPR) in the 10–40 cm soil layer under the PTS treatment was significantly lower (by 11.9% to 18%) compared to the other treatments (p < 0.05). On average, the soil moisture content in the NTS treatment was 2.7% and 1.4% higher than that of the PTS and RTS treatments. Additionally, soil temperature was 5.6% to 8.6% lower under the STS treatment compared to the other treatments during late corn growth. The RTS treatment also significantly reduced the bulk density of surface soil. High SPR impeded early crop growth but did not impact mid-crop development, while low soil temperature was one of the main factors affecting late corn growth and development as temperatures decreased. Based on the comparisons, we found that the short-term implementation of conservation tillage did not result in a significant decrease in corn yield. We believe that the short-term implementation of NTS tillage sowing practices in Mollisol regions is a feasible option.

Soil organic matter (SOM) decreases after the conversion of native grasslands to croplands and increases after the conversion of croplands to plantations. However, the reasons for loss and/or accumulation of SOM fractions remain unclear. Hence, we investigated SOM fraction quantity and quality of soils from cropland (CL), a plantation (PL) converted from cropland, and native grassland (NG) all converted from the black soil (Mollisols) region of China. Results showed that: (1) across all sites, coarse particulate organic matter (cPOM), fine particulate organic matter (fPOM), and mineral‐associated organic matter (mSOM) formed successively, and the mSOM carbon (C) content accounted for more than 70% of the bulk SOM C content. (2) The cPOM C contents in CL and NG were similar, but the fPOM and mSOM C contents in CL were only 11.35% and 52.95% of those in NG, respectively. The C contents of cPOM, fPOM, and mSOM in PL were 53.77%, 27.72%, and 72.80% of those in NG, respectively. (3) The accumulation of mSOM was affected by the quantity of fPOM, but had no obvious relationship with the quality of fPOM. However, the accumulation of fPOM was affected by both quantity and quality of cPOM. In general, promoting the accumulation of fPOM may increase the mSOM and SOM contents of CL, and increasing cPOM may be a feasible way to increase the SOM content of PL. The study provides a fundamental reference for promoting SOM accumulation of croplands and plantations in the black soil region. [ABSTRACT FROM AUTHOR]

Intensive crop production on grassland-derived Mollisols has liberated massive amounts of carbon (C) to the atmosphere. Whether minimizing soil disturbance, diversifying crop rotations, or re-establishing perennial grasslands and integrating livestock can slow or reverse this trend remains highly uncertain. We investigated how these management practices affected soil organic carbon (SOC) accrual and distribution between particulate (POM) and mineral-associated (MAOM) organic matter in a 29-y-old field experiment in the North Central United States and assessed how soil microbial traits were related to these changes. Compared to conventional continuous maize monocropping with annual tillage, systems with reduced tillage, diversified crop rotations with cover crops and legumes, or manure addition did not increase total SOC storage or MAOM-C, whereas perennial pastures managed with rotational grazing accumulated more SOC and MAOM-C (18 to 29% higher) than all annual cropping systems after 29 y of management. These results align with a meta-analysis of data from published studies comparing the efficacy of soil health management practices in annual cropping systems on Mollisols worldwide. Incorporating legumes and manure into annual cropping systems enhanced POM-C, microbial biomass, and microbial C-use efficiency but did not significantly increase microbial necromass accumulation, MAOM-C, or total SOC storage. Diverse, rotationally grazed pasture management has the potential to increase persistent soil C on Mollisols, highlighting the key role of well-managed grasslands in climate-smart agriculture. [ABSTRACT FROM AUTHOR]

Corn stover is a global resource used in many industrial sectors including bioenergy, fuel, and livestock operations. However, stover removal can negatively impact soil nutrient availability, especially nitrogen (N) and phosphorus (P), biological activity, and soil health. We evaluated the effects of corn stover management combined with N and P fertilization on soil quality, using soil chemical (nitrate, ammonium and Bray-1 P) and biological parameters (β-glucosidase, alkaline phosphatase, arylsulfatase activities and fluorescein diacetate hydrolysis—FDA). The experiment was performed on a Mollisol (Typic Endoaquoll) in a continuous corn system from 2013 to 2015 in Minnesota, USA. The treatments tested included six N rates (0 to 200 kg N ha−1), five P rates (0 to 100 kg P2O5 ha−1), and two residue management strategies (residue removed or incorporated) totalling 60 treatments. Corn stover management significantly impacted soil mineral-N forms and enzyme activity. In general, plots where residue was incorporated were found to have high NH4+ and enzyme activity compared to plots where residue was removed. In contrast, fields where residue was removed showed higher NO3− than plots where residue was incorporated. Residue management had little effect on soil available P. Soil enzyme activity was affected by both nutrient and residue management. In most cases, activity of the enzymes measured in plots where residue was removed frequently showed a positive response to added N and P. In contrast, soil enzyme responses to applied N and P in plots where residue was incorporated were less evident. Soil available nutrients tended to decrease in plots where residue was removed compared with plots where residue was incorporated. In conclusion, stover removal was found to have significant potential to change soil chemical and biological properties and caution should be taken when significant amounts of stover are removed from continuous corn fields. The residue removal could decrease different enzymes related to C-cycle (β-glucosidase) and soil microbial activity (FDA) over continuous cropping seasons, impairing soil health. [ABSTRACT FROM AUTHOR]

Evaluating soil quality is of vital importance to strategize fertilization and management practices for sustaining agricultural productivity. Five fertilization practices were carried out for 6 years under corn-soybean rotation in Mollisols of Northeast China. Two soil quality index models of Nemoro quality index (NQI) and integrated quality index (IQI), and two indicator selection approaches of total data set (TDS) and minimum data set (MDS) were applied for evaluating changes in soil quality index. NQI-MDS, NQI-TDS, IQI-MDS, and IQI-TDS approaches all indicated that six-year crop straw returning and dairy manure application under corn-soybean rotation increase soil quality index at 0–30 cm soil depth. Depended on soil-depth, IQI-MDS is the most suitable soil quality model for evaluating soil quality at 0–10 cm and 10–20 cm, and NQI-MDS at 20–30 cm soil depth. Soil quality index in IQI-MDS at 0–10 cm soil depth is the method to evaluate soybean yield. Integrating crop yield and soil quality index, the six-year organic amendments, especially dairy manure application is the most suitable management practice in promoting soil biochemical, chemical and physical properties under corn-soybean rotation in Mollisols. [ABSTRACT FROM AUTHOR]

Soil penetration resistance (SPR) is one of the major indicators of soil physical properties. Crop residue managements, tillage practices and their interactions exert significant effects on the SPR. However, rare information is available in the sloping farmland of Mollisols. Field experiments were conducted to investigate the variations of the SPR as affected by crop residue managements and tillage practices on the sloping land in Northeast China from 2015 to 2019. The split-plot experiment was arranged with two crop residue managements (removed, REM and retained, RET), and three tillage practices (no tillage, NT; rotary tillage, RT; plow tillage, PT). SPR data in 0-80 cm soil depth was measured at the end of harvest of maize monoculture. Results showed that the two crop residue managements induced significant variations in the SPR at 0-15 cm, 15-30 cm and 0-80 cm soil depths under NT, RT, and PT treatments, respectively. In comparison with RET treatment, the average values of the SPR under REM treatment were 10.9% and 8.9% higher in 45-60 cm and 60-80 cm soil depths, respectively. The average values of the SPR under PT treatment were 12.4% and 14.1% lower in 0-15 cm soil depth, and 23.9% and 10.4% lower in 15-30 cm soil depth than those under NT and RT treatments. However, the average value of the SPR under PT treatment was 11.2% and 22.0% higher in 60-80 cm soil depth than those under NT and RT treatments, respectively. The SPR generally decreased with the slope position declined in the deeper soil depth (except for the NT+RET treatment). The findings from this research can provide a scientific reference for the establishment of rational cultivation and the sustainable development of productivity on the sloping land of Mollisols in cold regions. [ABSTRACT FROM AUTHOR]

Innovative agricultural technologies such as organic fertilization have provided long and short-term benefits as far as sustainable soil management is concerned. In this study, five treatments were applied: cow manure (CM), chicken manure (JM), poplar tree leaves (TL), maize straw (MZ), and control (CK). The aim was to evaluate the long-term effects of applying organic materials on soil chemical and electrochemical properties. The highest pH and EC were recorded in JM and CM respectively. The highest cation exchange capacity (CEC) and specific surface area (SSA), were recorded in treatment TL while the application of organic materials increased the CEC and SSA by 24.9-85.5% and 6.9-52.4% respectively. The surface charge characteristics were significantly improved by the organic treatments compared with CK (P<0.05). The application of organic materials increased the surface charge potential (φ0) by 28-35.9% and the surface charge density (σ0) by 21.42-35.71%. Moreover, the electric field strength (E0) and surface charge number (SCN) were increased by 16.6-27.8% and 21.7-94.9% respectively. The soil chemical and electrochemical properties decreased along the soil profile with the exception of pH and EC, which increased with depth. The granulometric properties of organic matter and other physical attributes affected the chemical and electrochemical properties of the soil. The surface charge characteristics were significantly positively correlated with each other and the soil chemical properties as shown by the correlation analysis. The application of organic materials especially treatment TL is recommended as it had a more advantageous effect on enhancing the surface charge characteristics and could improve the quality of agricultural soils. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is used to enhance agricultural productivity. Organic acids increase the release of inorganic phosphorus (Pi) into soil solutions and thereby improve phosphorus utilization in soils; however, the effects of both organic acids and the soil organic matter contents on Pi release are poorly understood. To assess the importance of these factors in determining phosphorus availability, the release of soil Pi fractions (i.e. aluminium‐bound phosphorus (Al‐P), iron‐bound phosphorus (Fe‐P), occluded phosphorus (O‐P) and calcium‐bound phosphorus (Ca‐P)) was evaluated on addition of organic acids (citric, oxalic and malic acids) to soils from Mollisols region that had different organic matter contents and received phosphorus fertilizer. Biochemically produced humic acid was used to modify soil organic matter contents. Among Pi fractions, the Fe‐P fraction had the highest concentration in all the soils with different organic matter contents. In the presence of organic acids, the release of Pi fractions decreased as the soil organic matter increased. Among the fractions, Al‐P had the highest release, followed by Fe‐P. Comparison among various organic acids revealed that oxalic acid was the most effective for Pi release. Path analysis showed that Al‐P release had larger direct‐path and indirect‐path coefficients, which implied that Al‐P release had the largest contribution to total Pi (TPi) release. We concluded that the effectiveness of organic acids in improving soil phosphorus availability was most pronounced in soils with low organic matter contents, but further field‐scale research is needed to confirm this. Al‐P was the most effective source of inorganic phosphorus in Mollisols. [ABSTRACT FROM AUTHOR]

The genesis of this study is in response to the United States (US) Fish and Wildlife Service (USFWS) listing of the monarch butterfly (Danaus plexippus plexippus) on 17 December 2020 in the US Federal Register as a candidate species under the Endangered Species Act of 1973. Annual censuses have identified that the eastern and western North American monarch migratory populations have been generally declining over the last 20 yr due to a myriad of environmental factors. Monarch reproduction at the larval stage is dependent on the presence of milkweed (Asclepias) plant species. The United States Department of Agriculture‐Natural Resources Conservation Service (USDA‐NRCS) National Resource Inventory rangeland data set (~23,400 on‐site samples; 2032 sites with milkweed presence) was used to evaluate milkweed species densities, geolocations, and environmental gradients. Twenty‐two milkweed species were identified on rangelands across 17 sampled US western states, with seven species comprising 65.5% of milkweed frequency of occurrence. The most dominant milkweed species on non‐federal rangelands were Asclepias viridis, A. syriaca, A. verticillata, and A. speciosa (constancy >10% where milkweed was present). Asclepias speciosa was the dominant species from the standpoint of total plant density for the data set, whereas A. viridis was the most frequently occurring species. Total milkweed density estimates based on low, midpoint, and high estimates were 1.3, 4.1, and 6.9 B plants on 13.2 M ha. Seven US states (Kansas, Texas, Nebraska, South Dakota, North Dakota, Oklahoma, and Montana) contained 88.8% of the total estimated ha with milkweed presence. In the Central Great Plains, Northwestern Great Plains, Nebraska Sand Hills, and Flint Hills, Southwestern Tablelands, High Plains, Northwestern Glaciated Plains, and Cross Timbers, Omernik level III ecoregions contained 76.7% of the estimated milkweed plants. Milkweed species density was highest at latitude N35‐40 with decreasing populations toward south (N25‐30) and north (N45‐50) latitudes. Milkweed species densities were greatest at longitude W‐95‐100 and decreased toward the western US with lowest population numbers at W‐120‐125. Analysis of environmental variables showed milkweed species dominance on mollisols, non‐saline sites, neutral pH, well‐drained soils, loam and sandy loam soil textures, and sites with soil organic matter at 1.5–3%. Disturbance gradients and habitat dynamics relating to ecological condition and rangeland health differed among the dominant milkweed species identified in this study. [ABSTRACT FROM AUTHOR]

Maintaining nitrogen (N) balance and inhibiting N leaching loss in the soil-crop system is crucial to maintaining yield and reducing the environmental pollution. This study investigated the effects of soil NO3--N content and accumulation, eggplant yield, N leaching and balance response to biochar addition, including regular fertilisation and irrigation (W + F), biochar addition with regular fertilisation and irrigation (W + F + B), and biochar addition with 20% fertilisation and irrigation reduction (0.8W + 0.8F + B) treatments. Compared with W + F, W + F + B and 0.8W + 0.8F + B increased soil NO3--N content in 0-40 cm and soil NO3--N accumulation in 0-20 cm, and raised harvest index, N surplus and balance. Simultaneously, 0.8W + 0.8F + B compared to W + F enhanced N use efficiency and N partial factor productivity, conversely, it decreased N dry matter production efficiency, N surplus and balance. Stepwise regression analysis demonstrated that the effect of NO3--N leaching lasted in 60 cm under biochar addition in the first year, and lasted in 20 cm without biochar application in the next year. Altogether, biochar addition with 20% fertilisation and irrigation reduction is the most suitable management strategy to decrease N surplus and leaching, and maintain eggplant N uptake in a two-year cycle system on greenhouse vegetables in Mollisols. [ABSTRACT FROM AUTHOR]

The soil-borne disease caused by Fusarium graminearum seriously affects the corn quality. Straw can greatly improve soil quality, but the effect is limited by its nature and environmental factors. This study explored the impact of straw-JF-1(biocontrol bacteria) combination on soil environment and soil disease resistance. The results showed that the combined treatment increased the proportion of soil large and small macro-aggregates by 22.50 and 3.84%, with soil organic carbon (SOC) content by 16.18 and 16.95%, respectively. Compared to treatment with returning straw to the field alone, the straw-JF-1 combination increased the soil content of humic acid, fulvic acid, and humin by 14.06, 5.50, and 4.37%, respectively. Moreover, A metagenomics showed that returning straw to the field alone increased the abundance of disease-causing fungi (Fusarium and Plectosphaerella), however, the straw-JF-1 combination significantly suppressed this phenomenon as well as improved the abundance of probiotic microorganisms such as Sphingomonas, Mortierella, Bacillus, and Pseudomonas. Functional analysis indicated that the combination of straw and JF-1 improved some bacterial functions, including inorganic ion transport and metabolism, post-translational modification/protein turnover/chaperones and function unknown, fungal functions associated with plant and animal pathogens were effectively inhibited. Pot experiments showed that the straw-JF-1 combination effectively inhibited the Fusarium graminearum induced damage to maize seedlings. Therefore, the combination of straw and JF-1 could be a practical method for soil management. [ABSTRACT FROM AUTHOR]

Background: Urban flood susceptibility evaluation (FSE) can utilize empirical and rational procedures to focus on the urban flood evaluation using physical coefficients and land-use change ratios. The main aim of the present paper was to evaluate a flood susceptibility model in the southern watersheds of Mashhad city, in Iran, for 2010, 2020, and 2030. The construction of the model depended on the utilization of some global datasets to estimate the runoff coefficients of the watersheds, peak flood discharges, and flood susceptibility evaluations. Results and conclusions: Based on the climatic precipitation and urban sprawl variation, our results revealed the mean values of the runoff coefficient (Cr) from 0.50 (2010) to 0.65 (2030), where the highest values of Cr (> 0.70) belonged to the watersheds with real estate cover, soil unit of the Mollisols, and the slope ranges over 5–15%. The averagely cumulative flood discharges were estimated from 2.04 m3/s (2010) to 5.76 m3/s (2030), revealing an increase of the flood susceptibility equal 3.2 times with at least requirement of an outlet cross-section by > 46 m2 in 2030. The ROC curves for the model validity explained AUC values averagely over 0.8, exposing the very good performance of the model and excellent sensitivity. [ABSTRACT FROM AUTHOR]

The degradation of black soil is a serious problem with the decrease in soil organic matter (SOM) content in northeast China, and animal manure as a reservoir of antibiotic resistance genes (ARGs) is commonly amended into soil to sustain or increase the SOM content. However, the potential effect of SOM content on soil resistome remains unclear. Here, a soil microcosm experiment was established to explore the temporal succession of antibiotic resistance genes (ARGs) and bacterial communities in three black soils with distinct difference in SOM contents following application of poultry manure using high-throughput qPCR (HT-qPCR) and MiSeq sequencing. A total of 151 ARGs and 8 mobile genetic elements (MGEs) were detected across all samples. Relative abundance of ARGs negatively correlated with SOM content. Manure-derived ARGs had much higher diversity and absolute abundance in the low SOM soils. The ARG composition and bacterial community structure were significantly different in three soils. A random forest model showed that SOM content was a better predictor of ARG pattern than bacterial diversity and abundance. Structural equation modeling indicated that the negative effects of SOM content on ARG patterns was accomplished by the shift of bacterial communities such as the bacterial diversity and abundance. Our study demonstrated that SOM content could play an important role in the dissemination of ARGs originated from animal manures, these findings provide a possible strategy for the suppression of the spread of ARGs in black soils by increasing SOM content.

Black soil rich in organic matter is one of the most fertile soils in Northeast China, one of the four largest black soil regions in the world. However, the structure and function of black soil have seriously deteriorated after long-term cultivation in recent years. Much effort has been made to ensure the sustainable development of black soil. However, most previous studies were focused on the soil structure and nutrients in the year of the experiment. In this study, a systematic investigation was performed on the soil structure and function during the whole growth period of crops, thereby elaborating the dynamic evolution after the long-term conservation tillage. A field test was also conducted in the Hailun Monitoring and Research Station of Soil and Water Conservation, Chinese Academy of Sciences (47°26′N, 126°38′E), located at the Hailun City, Heilongjiang Province, the center of the typical Mollisols zone in Northeast China. Taking the corn-soybean rotation black soil as the research object, four tillage treatments were set (conservation tillage: NT (No-tillage with straw returning), RT (Reduced-tillage); traditional tillage: MT (Moldboard-tillage), Rot (Rotary-tillage)) during the different growth periods of soybean (SS (seedling stage), FlS (flowering stage), FiS (filling stage), and MS (maturity stage)). Some parameters were measured, including the soil bulk density, porosity, water status, and water-stable aggregate content in response to tillage. Once the soybean matured, the soil samples were collected to quantitatively characterize the soil organic carbon in the vertical direction of different tillage treatments, and the soil moisture infiltration rate in the plow layer. The results showed that: 1) The NT improved to stabilize the soil structure. The soil bulk density under the NT system was more stable than the other three treatments. The soil surface field capacity under the NT treatment was 4.56% ~ 23.07% higher than that of conventional tillage during the whole growth period of soybean. The NT treatment increased the content of large aggregates on the soil surface by 62.10%, and the Average Weight Diameter (MWD) reached 0.48 mm, higher than the rest. The NT also improved the soil water infiltration, where the initial infiltration rate was 1.26 to 1.63 times that of the rest treatments. 2) The NT significantly increased the accumulation of soil surface organic carbon. Specifically, the organic carbon content of soil surface under the NT treatment was 32.60%, 30.28%, and 25.79% higher than MT, RT, and Rot treatments, respectively. 3) The NT maintained the soil productivity. In short, the long-term no-tillage with the straw returning significantly determined the soil structure and organic carbon accumulation. The NT treatment performed better the structure and organic carbon accumulation in the lower layer soil, thereby promoting the sustainable development of black soil. This finding can provide a strong theoretical basis to explore the long-term effects of conservation tillage in the black soil area of Northeast China. [ABSTRACT FROM AUTHOR]

The study area was located in the North of Iraq. Five sites were selected that have formed from the limestone parent material. One pedon dug in each site and was divided into a number of horizons. Thirty-five soil samples were collected for physical and chemical analyses. The climate of study sites were similar to the Mediterranean Sea climate which is hot dry in summer and cool humid in winter. The mean of annual precipitation, varies from one site to another. Studied soils classified as Mollisols, Inceptisols, Vertisols, and Aridisols. Study soils were relatively high clay content and its content at the surface horizons is lower than it at subsurface horizons, and soil texture was ranged between clayey to loamy, the high value for clay content indicates to soil development. Fine clay/Coarse clay ratio showed that the pathway of fine clay similar to the pathway of total clay. CEC values increased with increasing clay. Organic matter was high in the surface horizons and decrease with depth. The following pedogenic processes occurred in study soils loss, gain, leaching, illuviation, eluviation, alkalization, humification, lessivage, desalinization, calcification, decomposition, and synthesis. [ABSTRACT FROM AUTHOR]

Improving soil productivity is the best way to increase grain production by 1% annually for feeding the rising population within the next 20 years in China. Nevertheless, how soybean yield and seed quality are affected by improving soil quality via consecutive manure addition are still unclear. A 7‐year consecutive cattle manure addition experiment was conducted under a soybean [Glycine max (Merrill.) L.] and maize (Zea mays L.) rotation in Mollisols. Treatments were as follows: CK: the non‐fertilizer control; CF: chemical fertilizer (NPK); CFM1: CF + 15 Mg ha−1 cattle manure; CFM2: CF + 30 Mg ha−1 cattle manure. The results showed CFM1 significantly increased soybean yield by 22%–105% and 21%–86% compared to CK and CF during 2014–2018. The consecutive cattle manure addition significantly increased the proportion of macro‐aggregates (1–0.25 mm) but decreased the proportion of micro‐aggregates (0.25–0.053 mm) and slit (<0.053 mm). The SOC storage in the large (>1 mm) and small macro‐aggregates (1–0.25 mm) was higher (by 24%–156%) under cattle manure addition than that under CK and CF. The soil productivity was enhanced by cattle manure addition because of the increase in soil available nutrients, that is, NH4+‐N and NO3−‐N, and Olsen‐P, all of which had positive correlations with the yield increase. At least 36% of soybean yield variation under CFM1 could be attributed to the indirect effect of pH value on increasing soil available nutrients concentrations. The cattle manure addition increased soybean seed oil concentration but decreased protein concentration. However, there were no differences in yield and quality between CFM1 and CFM2 after 7‐year of the treatment. It suggests that cattle manure addition at 15 Mg ha−1 is a practical approach to improve Mollisols' productivity and SOC stability. [ABSTRACT FROM AUTHOR]

BACKGROUND: The conversion of arable land to grassland and/or forested land is a common strategy of restoration because the development of plant communities can inhibit the erosion of soil, increase biodiversity and improve associated ecosystem services. The vertical profiles of microbial communities, however, have not been well characterized and their variability after land conversion is not well understood. We assessed the effects of the conversion of arable land (AL) to grassland (GL) and forested land (FL) on bacterial communities as old as 29 years in 0–200‐cm profiles of a Chinese Mollisol. RESULTS: The soil in AL has been a stable ecosystem and changes in the assembly of soil microbiomes tended to be larger in the topsoil. The soil properties and microbial biodiversity of arable land were larger following revegetation and reforestation. The conversion caused a more complex coupling among microbes, and negative interactions and average connectivity were stronger in the 0–20‐cm layers in GL and in the 20–60‐cm layers in FL. The land use dramatically influenced the assembly of the microbial communities more in GL than AL and FL. The bacterial diversity was an important component of soil multinutrient cycling in the profiles and microbial functions were not as affected by changes in land use. CONCLUSION: The spatial variation of the microbiomes provided critical information on below‐ground soil ecology and the ability of the soil to provide crucial ecosystem services. © 2021 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The continuous planting of soybeans leads to soil acidification, aggravation of soil-borne diseases, reduction in soil enzyme activity, and accumulation of toxins in the soil. Microorganisms in the rhizosphere play a very important role in maintaining the sustainability of the soil ecosystem and plant health. In this study, two soybean genotypes, one bred for continuous cropping and the other not, were grown in a Mollisol in northeast China under continuous cropping for 7 and 36years in comparison with soybean–maize rotation, and microbial communities in the rhizosphere composition were assessed using high-throughput sequencing technology. The results showed that short- or long-term continuous cropping had no significant effect on the rhizosphere soil bacterial alpha diversity. Short-term continuous planting increased the number of soybean cyst nematode (Heterodera glycines), while long-term continuous planting reduced these numbers. There were less soybean cyst nematodes in the rhizosphere of the tolerant genotypes than sensitive genotypes. In addition, continuous cropping significantly increased the potential beneficial bacterial populations, such as Pseudoxanthomonas , Nitrospira , and Streptomyces compared to rotation and short-term continuous cropping, suggesting that long-term continuous cropping of soybean shifts the microbial community toward a healthy crop rotation system. Soybean genotypes that are tolerant to soybean might recruit some microorganisms that enhance the resistance of soybeans to long-term continuous cropping. Moreover, the network of the two genotypes responded differently to continuous cropping. The tolerant genotype responded positively to continuous cropping, while for the sensitive genotype, topology analyses on the instability of microbial community in the rhizosphere suggested that short periods of continuous planting can have a detrimental effect on microbial community stability, although this effect could be alleviated with increasing periods of continuous planting. [ABSTRACT FROM AUTHOR]

Straw incorporation is an effective measure for increasing soil organic carbon (SOC) thereby improving soil quality and crop productivity. However, quantitative assessments of the transformation and distribution of exogenous carbon (C) in soil aggregates under various field fertilization practices have been lacking. In this study, we collected topsoil samples (0–20 cm) from three fertilization treatments (no fertilization control, CK; inorganic fertilizer, IF; inorganic fertilizer plus manure, IFM) at a 29-year long-term Mollisol experiment in Northeast China. We then mixed the soil samples with 13C-labeled maize straw (δ13C = 246.9‰), referred as CKS, IFS, and IFMS, and incubated them in-situ for 360 days. Initial and incubated soil samples were separated into four aggregate fractions (> 2, 1–2, 0.25–1, and < 0.25 mm) using the dry-sieving method, which counted 18%, 17%, 45%, and 21% (averages from the three initial soil samples), respectively. Organic C content was highest in 0.25–1 mm aggregate (6.9–9.6 g kg−1) prior to incubation, followed by > 2 mm aggregates (2.2–5.8 g kg−1), 1–2 mm aggregates (2.4–4.6 g kg−1), and < 0.25 mm aggregates (3.3–4.5 g kg−1). After 360-day incubation with straw incorporation, organic C content was 2.3–4.5 g kg−1, 2.9–5.0 g kg−1, 7.2–11 g kg−1 and 1.8–3.0 g kg−1 in > 2, 1–2, 0.25–1, and < 0.25 mm aggregates, respectively, with the highest in the IFMS treatment. Straw-derived C content was 0.02–0.05 g kg−1, 0.03–0.04 g kg−1, 0.11–0.13 g kg−1, and 0.05–0.10 g kg−1 in > 2, 1–2, 0.25–1, and < 0.25 mm aggregates, respectively. The relative distribution of straw-derived C was highest (40–49%) in 0.25–1 mm aggregate, followed by < 0.25 mm aggregates (21–31%), 1–2 mm aggregates (13–15%), and > 2 mm aggregates (9.4–16%). During the incubation, the relative distribution of straw-derived C exhibited a decrease in > 2 mm and 1–2 mm aggregates, but an increase in the < 0.25 mm aggregate. At the end of incubation, the relative distribution of straw-derived C showed a decrease in the 0.25–1 mm aggregate but an increase in the < 0.25 mm aggregate under the IFMS treatment. This study indicates that more straw-derived C would be accumulated in smaller aggregates over longer period in Mollisols, and combined inorganic and organic fertilization is an effective measure for C sequestration in Northeast China. [ABSTRACT FROM AUTHOR]

Mollisols are of major importance for food security worldwide but are increasingly degraded by soil erosion. Mollisols in Northeast China have been converted into agricultural use only since the 19th century, but gullies are widely distributed. Gully erosion history, rates, and causes in this region remained unclear. We chose a study area with landforms and land‐use history typical for the central Mollisol region of Northeast China to estimate the initiation years and rates of gully erosion from 1968 to 2018 using aerial and satellite imageries. The outlet fan deposits of a large gully system were dated by Cesium‐137 (137Cs) and artifacts. Local farmers were interviewed to verify the results. Gully volumes were measured by a structure‐from‐motion technique using photos taken from an unmanned aerial vehicle. Our results showed that gully systems had already appeared on the steep slopes and along unpaved roads in 1968. They had become larger and more complex in 2018 by the upslope retreat of the main gullies and side gully formation. Gully incision started in the 1950s and 1960s when the original grassland and forest were completely converted into arable land. From 1968 to 2018, the gully density increased from 1.2 to 2.3 km km−2 and the gully heads retreated at speeds from 1.5 to 2.5 m yr−1. The soil loss from gully erosion ranged from 25.7 to 44.7 Mg yr−1 ha−1. These data demonstrate the severity of gully erosion in the Mollisol region of Northeast China and underline the importance of appropriate countermeasures. [ABSTRACT FROM AUTHOR]

Purpose: Exploring how organic amendments influence carbon sequestration by affecting particulate organic carbon (POC) and determining the optimum amendment for protecting and restoring mollisol and increasing yields. Methods: Differences of POC properties and maize yields in 3-year soils amended with organic material of different origins were studied. POC was separated by a wet sieving method, and the structure was analyzed by 13C NMR spectroscopy. Results: We found that SOC accumulation in soils amended with plant origin organic materials resulted from increasing organic fractions other than POC, while that in soils amended with animal origin materials resulted from increasing POC. The proportion of POC net variation in SOC net variation was significantly negatively correlated with SOC (p < 0.01). POC, mainly composed of alkyl C and alkoxyl C (more than 68%), had its stability more accurately evaluated through combined analysis of the carbonyl C content and alkyl C/alkoxyl C ratio. The addition of organic materials improved POC stability by increasing the alkyl C/alkoxyl C ratio and decreasing the carbonyl C content. Maize yields were positively correlated with SOC content and POC stability (p < 0.01), which increased by at least 2012 kg ha−1 with the addition of organic materials. Conclusion: Increasing more stable POC will promote the carbon sink. The order of the stability of POC in mollisol amended with organic materials of different origins was woody plant material > herb material > livestock dung > poultry dung. The woody plant material was the optimum organic amendment for mollisol, enhanced POC stability, and promoted SOC sequestration while increasing the yield. [ABSTRACT FROM AUTHOR]

Cover crops (CC) may offer a compelling strategy to increase the availability of nutrients, such as phosphorus (P), in agroecosystems where continuous extractive agriculture has resulted in a depletion of soil fertility. Our objective was to analyse the long-term effect of CC incorporation in soybean-based crop sequences on: i) organic and inorganic P fractions (P inorg and P org), ii) extractable inorganic P (P Bray), and iii) biochemical soil properties associated with P mineralization (monophosphatase activity and P org in the coarse fraction (P org -CF)) in soils with contrasting P availability and under different edaphoclimatic conditions. A factorial design was performed evaluating two sequences (continuous soybean (Sb) or CC/Sb) and two fertilization treatments (with or without P fertilization, +P and 0 P, respectively). In general, the long-term annual implementation of CC tended to decrease inorganic P fractions (P inorg and P Bray), and the magnitude of this effect was more marked when P availability was low (0 P). However, in treatments where P was applied, the use of CC did not modify P Bray. The effect of CC on organic P fractions was greater than that of P fertilization. Increases of up to 63 kg P org ha−1 were determined when including CC, whose magnitude was unrelated with soil texture. Cover crops also increased P org -CF and monophosphatase activity. Our results demonstrate that, despite decreasing inorganic P fractions, CC have beneficial effects on biochemical variables associated with P mineralization, which is an essential process for crops nutrition. • We studied cover crops (CC) and fertilization effects on P fractions. • The CC tended to decrease inorganic P, especially in low P availability conditions. • The CC had a greater effect on organic P fractions than P fertilization. • Monophosphatases and organic P in the coarse fraction increased in CC treatments. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) volatilization, a critical pathway of nitrogen (N) loss in agroecosystems, is closely regulated by ammonium (NH 4 +-N) availability and associated NH 4 +-N transformation dynamics in soil. To determine the effect of no-tillage and crop stover retention on soil internal gross N transformation and further NH 3 volatilization in the long-term conservation tillage (CT) agroecosystem, a combination of 15N-tracing field monitoring and paired 15N-labeled incubation experiments was simultaneously conducted on a 9-year maize cropping system in the Mollisol of Northeast China. Three treatments were set up: traditional ridge tillage (RT), no-tillage with maize stover removal (NT0), and no-tillage with full harvest (ca. 7500 kg ha−1 yr−1) maize stover mulching (NTS). It was found that NH 3 volatilization in the experimental Mollisol primarily occurred within 7 days after fertilization. Given that the paired gross NH 4 +-N transformation dynamics were considered in terms of the mutual production-consumption processes, the low fertilizer-derived NH 3 volatilization was mainly attributed to a high gross N transformation rate combined with a low net N transformation rate for all treated plots, indicating that there was a rapid internal NH 4 +-N turnover in the studied Mollisols. Additionally, no-tillage with maize stover mulching considerably reduced NH 3 emissions by 17% compared with RT treatment, and the inhibitory effect was primarily owing to the synchronized stimulation of biotic mineralization-immobilization and abiotic adsorption-release turnover in the CT agroecosystem. These findings suggest that long-term no-tillage with maize stover mulching could be a sustainable management strategy for improving soil NH 4 +-N retention and mitigating NH 3 losses in the Mollisol of Northeast China. • NH 3 volatilization potential was highly regulated by gross N transformation dynamics. • There was a rapid internal NH 4 +-N turnover in the studied Mollisols. • Low risk of NH 3 volatilization loss was observed in cropland of Northeast China. • Stover mulching in no-tillage farming accelerated both biotic-abiotic NH 4 +-N turnover. • No-tillage with stover mulching favored effective NH 3 mitigation in agroecosystems. [ABSTRACT FROM AUTHOR]

• SOC stabilization in conservation tillage primarily occurs in mineral-associated OC. • Amorphous iron (Fe) was positively correlated with SOC sequestration. • The formation of organo-Fe complexes improved aggregate stability. • The aromatic-C/aliphatic-C ratio was increased under conservation tillage. • Conservation tillage promoted soil aggregation and enhanced SOC chemical stability. Conservation tillage practices, which involve minimal or no soil disturbance and crop residue retention, are known to help preserve soil organic carbon (SOC). However, the mechanisms underlying the minerals-mediated chemical and physical stabilization of SOC remain unclear. Here, a long-term field experiment was initiated in 2012 to investigate the effects of tillage managements on the contents and chemical composition of SOC density fractions, iron oxides transformation and aggregate stability in Mollisols. We utilized three treatments: conventional tillage (CT) without crop residue, reduced tillage (RT) and no tillage (NT) with straw mulching. Compared to CT, RT and NT significantly increased SOC content by 13.6 % and 17.9 % in the 0–20 cm soil layer due to an increase in the aromatic compound contents. Furthermore, NT and RT increased the mean weight diameter by 17.7 % and 10.7 %, respectively, indicating increased aggregate stability compared to CT. Additionally, the contents of amorphous iron oxides (Feo) and complex iron oxides (Fep) increased under NT and RT by 10.6–14.4 % and 12.7–41.1 %, respectively, in bulk soil and silt + clay fractions within macroaggregates (>0.25 mm). The contents of Feo and Fep were strongly positively correlated with aggregate stability (p < 0.001, r2 = 0.64), and promote the physical protection of SOC. Both NT and RT enhanced the aromatic-C content and aromatic-C/aliphatic-C ratio by 13.6 %–24.6 % and 16.5 %–38.9 % in macroaggregates compared with CT. Moreover, the aromatic-C/aliphatic-C ratio increased with increasing Feo plus Fep contents (p < 0.001, r2 = 0.73), which led to an increased in the recalcitrant-C proportion, and this shift was benefit for the accumulation of mineral-associated OC. These results indicate that long-term conservation tillage can augment the accessibility of Fe for binding C, possibly by forming organo-Fe complexes, which subsequently improve soil aggregation, and thus promoted the chemical stability and long-term sequestration of SOC in Mollisols of Northeast China. [ABSTRACT FROM AUTHOR]

Increased atmospheric carbon dioxide (CO 2) concentrations cause climate change, affecting the stability of agricultural ecosystems. Soil nitrification and denitrification, which are fundamental N cycling processes, determine soil N availability for plants, nitrous oxide (N 2 O) emissions, and N flow in ecosystems. However, the responses of specific nitrifying and denitrifying soil microorganisms to increased CO 2 levels remain unknown. In this study, four soybean [ Glycine max (L.) Merr.] varieties (Xiaohuangjin [XHJ], Suinong 14 [SN14], Mufeng 5 [MF5], and Dongsheng 1 [DS1]) were planted in open-top chambers containing Mollisols under ambient CO 2 (aCO 2 , 410 ppm) and elevated CO 2 (eCO 2 , 550 ppm) conditions. The abundance, composition, and potential activity of ammonia mono‑oxygenase subunit A gene (amoA) of ammonia oxidise bacteria (AOB) and nitrite reductase S gene (nirS)-type denitrifiers under increased atmospheric CO 2 levels were investigated. The results showed that eCO 2 decreased the nitrification potential in XHJ and MF5 rhizospheres, whereas increasing it in the SN14 rhizosphere. Denitrification potential decreased in the rhizosphere of all soybean cultivars, except XHJ, under eCO 2 conditions. The decreased nitrification and denitrification potentials imply that eCO 2 conditions may slow N 2 O emission. Principal co-ordinate analysis revealed that the composition of amoA and nirS communities was not altered by eCO 2 , but rather by the presence of different soybean cultivars. The eCO 2 -induced variations in the nitrification and denitrification potentials of microbes in the rhizosphere among different cultivars can affect the N cycle and should be considered in future soybean breeding programmes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Substantial effluxes of C and Se occur in the cold-region cultivated Mollisols. • Organic-bound Se acts as a direct source of volatile Se species. • Anaerobic respiration contributes greatly to CO 2 , CH 4 and methyl selenide fluxes. • The findings inform scientific management of C and Se resources in agriculture. Mollisols rich in natural organic matter are a significant sink of carbon (C) and selenium (Se). Climate warming and agricultural expansion to the cold Mollisol regions may enhance soil respiration and biogeochemical cycles, posing a growing risk of soil C and Se loss. Through field-mimicking incubation experiments with uncultivated and cultivated soils from the Mollisol regions of northeastern China, this research shows that soil respiration remained significant even during cold seasons and caused co-emission of greenhouse gases (CO 2 and CH 4) and methylated Se. Such stimulus effects were generally stronger in the cultivated soils, with maximum emission rates of 7.45 g/m2/d C and 1.42 μg/m2/d Se. For all soil types, the greatest co-emission of CO 2 and dimethyl selenide occurred at 25 % soil moisture, whereas measurable CH 4 emission was observed at 40 % soil moisture with higher percentages of dimethyl diselenide volatilization. Molecular characterization with three-dimensional fluorescence and ultra-high resolution mass spectrometry suggests that CO 2 emission is sensitive to the availability of microbial protein-like substances and free energy from organic carbon biodegradation under variable moisture conditions. Predominant Se binding to biodegradable organic matter resulted in high dependence of Se volatilization on rates of greenhouse gas emissions. These findings together highlight the importance of dynamic organic carbon quality for soil respiration and consequent Mollisol Se loss risk, with implications for science-based management of C and Se resources in agricultural lands to combat with Se deficiency. [ABSTRACT FROM AUTHOR]

The Soil Science Society of Poland has elected chernozem to be the Soil of the Year 2019. Although chernozems cover less than 2% of Poland, they have high importance for agriculture due to their productivity and play a specific scientific role for understanding of soil development and functioning in an environment. Chernozems are also crucial for the reconstruction of Neolithic agriculture development and human impacts on soil and landscape. This introductory paper presents (a) a specific definition of chernozem in Poland, connected with a separate distinction of black earths and colluvial chernozemic soils; (b) a review of the present and former classification schemes for chernozems in Poland and their correlation with international soil classification systems (WRB and Soil Taxonomy); (c) the spatial distribution of chernozems in Poland, their agricultural evaluation and threats for chernozems’ quality and future existence related to intense land use.

The morphology and properties of heavily eroded soils found in chernozems in the upland landscape of the Proszowice Plateau (southern part of Poland) was presented. The issue of classification of these soils was also discussed. Taking into account the terrain context, it should have been assumed that these soils were formed as a result of strong erosion (truncation) of chernozems. These (post-chernozem) soils were relatively young, in which only the development of humus horizon can be documented. However, the accumulation of humus was hampered by constantly intense erosion processes. Evidence of the occurrence of the illuviation process as well as formation of cambic horizon is not visible macroscopically and microscopically. These soils are often classified as weakly developed soils though despite the poor development of the soil profile, they are characterized by potentially high productivity, which results both from the properties of their parent material (texture, porosity) and from their youthfulness (carbonate content both in fine earths and in nodules, high pH in whole profile). Therefore, the name proposed in Polish Soil Classification, 6th edition (‘pararędzina’) seems to be justified. These soils would be classified as Entisols according to USDA Soil Taxonomy and as Regosols according to WRB.

Land-use change and specifically a change in the type of vegetation cover affects soil morphology, chemistry, biology, and nutrient regimes. Numerous studies have documented that in land-use conversions from agricultural land to forest, or from plantations to restored natural savanna most soil attributes and functions undergo changes. The purpose of the present study was to evaluate the changes brought about by afforestation of degraded croplands and to understand the impact of forest vegetation on soil evolution in a semiarid region where soils originally co-evolved with a savanna biotope. We used long-term experiments (>40 years) of five tree species: Pinus halepensis (PH), Pinus halepensis inoculated with ecto-mycorrhiza at planting (PM), Pinus pinea (PP), Eucalyptus spp. (E), and Gleditsia triacanthos (G) and compared these to an agricultural soil (A) at the same site near Santa Rosa, La Pampa in the semiarid center of Argentina. Soil profiles were described, and samples taken for chemical and physical analyses of soil properties [organic matter (OM), pH, cation exchange capacity (CEC) and exchangeable cations, particle size distribution (texture), aggregate stability (MWD), bulk density (BD), porosity (TP), and water holding capacity (WHC)]. We found a strong effect of tree species on soil profile morphology, even taxonomy, and on all studied variables. PM and G had highest OM, CEC, neutral pH, higher TP, WHC, while PH, PP, and E had acid pH, lower base saturation, OM, TP, and WHC. The effect of tree species on the soil profile was noticeable a depth of about 40 cm, comprising the A and AC, but not the C horizons. The results showed that to obtain reasonable results of OM sequestration under forest systems, tree species should be chosen to include legumes to improve C/N stoichiometry for C fixation, or inoculation with mycorrhiza to promote microbial transformation of forest litter.

BACKGROUND: Phosphorus (P) is an essential mineral nutrient for crop growth and development. Much remains unknown regarding the content and distribution of P forms in different soil aggregates as affected by tillage practices. A 3-year field experiment was conducted to investigate the effects of no-tillage (NT), rotary tillage (RT), subsoiling (SS), and deep tillage (DT) on soil aggregate distribution pattern, aggregate-associated P content, and to understand the conversion trend. RESULTS: Tillage has the potential to accelerate the processes in transforming macro-aggregates (> 0.25 mm) into microaggregates (< 0.25 mm). Greatest aggregate stability was attained under RT. Total phosphorus (TP) and available phosphorus (AP) under NT were increased by 21.1-82.0% in contrast to other tillage treatments. The NT had high content in inorganic phosphorus (IP), aluminum phosphorus (Al-P), and iron phosphorus (Fe-P) with 416.7, 107.9, and 99.1 mg·kg-1 on average, respectively. Aggregates with a size dimension of < 2 mm were more sensitive than other sizes of aggregates. IP was evenly distributed throughout all aggregates, ranging from 336.3 to 430.6 mg kg-1. No differences in organic phosphorus (OP) were found in all tillage treatments, while NT promoted the transformation of labile OP to IP. The AP and OP were generally more abundant in aggregates of 2 to 0.25 mm and < 0.25 mm. CONCLUSION: Short-term NT can improve soil structure and increase P reserves, thus, enhancing the conversion of P from being scarce to available. [ABSTRACT FROM AUTHOR]

A field micro-plot experiment with nitrogen isotope (15 N) labelling was performed to study the impacts of the timing of aside-dressed Napplication on urea-15 N in amaize-soil system. The treatments comprised three application timings, each of which consisted of the identical total rate of N, i.e. 280kg ha−1. In all treatments, 40% of the Nwas used theday prior to sowing, and the rest was used either at the jointing stage (V6) (N1), at the bell stage (V12) (N2) or at the tasselling stage (VT) (N3). The results indicated that the grain yields increased in both the N1 and N2 treatments compared with the N3 treatment. Asplit application of Nat the bell stage significantly raised the percentage of Nderived from fertilizer N(Ndff) compared to the two other side-dressed Napplication timings. The 15 N recovery efficiencies for the N2 and N1 treatments were 10% greater than the N3 treatment. The possible Nlosses in the N2 treatment were lower than those in the other treatments. Therefore, Nside-dressing at the bell stage is an alternative and sustainable management strategy for maize production and NUE in spring maize cropping systems. [ABSTRACT FROM AUTHOR]

Understanding the influence of tillage and fertilizer management on soil physical properties, and their roles in soil stoichiometry are critical for estimating the ecological implications of agricultural management. The study investigated the 3-yr effects of tillage and fertilizer management on soil physical properties, nutrients, and stoichiometry. The study included two tillage methods: rotary tillage (R) and deep tillage (D), with three fertilizer management: chemical fertilizer (N), chemical fertilizer + straw returning (S), chemical fertilizer + straw returning + organic fertilizer (M). Samples were collected at three depths: 0–15, 15–30, 30–50 cm. Results indicated that treatment effects were better at depth 0–30 cm than at 30–50 cm. The D significantly increased the soil C: N but decreases the C: P because nutrient fixation state was broken. The M had more effect on soil nutrient concentrations and stoichiometry. Effects of tillage and bulk density were positively correlated with soil nutrient concentrations, while moisture content and compactness were positively correlated with the soil stoichiometric ratio. Fertilizer management is the main factor to control soil nutrient and stoichiometry while using organic fertilizer under deep tillage can improve nutrients and maintain the stability of Mollisols ecosystem. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) plays an important role in preserving soil fertility. Assessing how topographic factors (slope gradient, slope length, slope shape, and slope position) and their interactions influence the SOC dynamics in the surface soil of longitudinal ridges of sloping farmland is very important for Mollisols protection in Northeast China. The SOC contents and variations were quantified within classes of topographic factors. A total of 39 soil samples were collected at the same sampling points in 13 typical Mollisol sloping farmland in 2004 and 2016. The results indicated that the average annual decrease rate of SOC from 2004 to 2016 was 5.64‰. The SOC stocks were significantly affected by slope gradient, slope length, and slope shape, but only affected by the interaction between slope gradient and slope position. In addition, the SOC stocks decreased with increasing slope gradient (p < 0.05). The variation in SOC stocks during 12 years showed a decreasing trend with increasing slope length (p < 0.05). The straight slopes had higher variation in SOC stocks than concave and convex slopes (p > 0.05); the footslope had higher SOC content than the upper and middle slope (p > 0.05), corresponding to the soil erosion and deposition along the slope. Our findings could offer suggestions for future landscape management. [ABSTRACT FROM AUTHOR]

Biochar can affect soil microbial abundance and community structure due to its excellent physiochemical properties. Our previous study of soil bacterial community discovered that the relative abundance of Acidobacteria was significantly influenced by biochar. In this study, we further investigated the effect of biochar on acidobacterial community composition generated with Acidobacteria-specific primers ACIDO/342 R using Illumina MiSeq sequencing in the same black soil samples after 3 years of biochar application. The qPCR results showed that biochar addition increased the acidobacterial abundance, especially at the rates of 4% and 8%. There were 18 acidobacterial subgroups detected, and Gp4 and Gp6 were the most abundant subgroups. The relative abundance of Gp4 was positively correlated with soil total potassium and negatively correlated with soil pH, while Gp6 was on the opposite. Biochar addition did not influence the α-diversity but altered the acidobacterial community composition. Redundancy analysis revealed that changes in the soil acidobacterial community compositions were closely associated with soil properties, such as pH, total potassium and available potassium. Given that these soil properties were highly correlated with biochar addition, which suggested that the long-term impacts of biochar on the soil acidobacterial community were indirectly driven by changes in soil properties. [ABSTRACT FROM AUTHOR]

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This document is a corrigendum for an article titled "Effects of varied nutrient regimes on soil health and long-term productivity in a rice-wheat system: insights from a 29-year study in the mollisols of the Himalayan Tarai region." The corrigendum acknowledges an error in the author list, where D. K. Singh was erroneously excluded. The corrected author list and author contributions section are provided. The authors apologize for the error and state that it does not change the scientific conclusions of the article. [Extracted from the article]