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Organic materials are integral to the soil carbon cycle in agricultural ecosystems, yet their specific impacts on soil organic carbon (SOC) and microbial diversity are not fully understood. In this study, we analyzed 188 data pairs from 57 published papers to assess the effects of various organic materials on SOC composition and microbial diversity across different farmlands. Our findings indicate that the addition of organic materials consistently enhances SOC composition and promotes both bacterial and fungal diversity. Notably, the particulate organic carbon (POC) fraction exhibited the most significant increase (42.35%), suggesting that POC is the primary pathway for organic carbon accumulation. Our analysis also identified the type of organic material as the leading factor influencing soil active carbon fractions and microbial diversity, with compost emerging as the most effective material for boosting soil carbon sequestration and microbial richness. Interestingly, while both dissolved organic carbon (DOC) and microbial biomass carbon (MBC) increased with organic material addition, a negative correlation between these two components was observed. This study advances our understanding of the complex interactions between organic materials, SOC components, and microbial diversity, providing valuable insights for the development of sustainable soil management practices aimed at enhancing soil carbon storage and agroecosystem health. [Display omitted] • Organic material enhanced active SOC components and microbial diversity. • Material type is a key determinant of soil carbon composition. • The main factor of SOC increase was the accumulation of POC. • MBC has a potential competition with DOC. [ABSTRACT FROM AUTHOR]

Soil structure is a dynamic property which controls a wide range of soil functions and is closely linked with soil carbon content. The carbon contents of agricultural soils are subject to several ongoing trends, including declining carbon stocks and attempts to increase the soil carbon reserves. In this study, we aimed to quantify how organic soil amendments, which have been shown to reduce long-term nutrient loads from agricultural fields, can impact soil structure. The structural impacts of a large one-time addition (8 tons carbon per hectare, three different soil amendments) of pulp and paper mill side stream sludges to a boreal clay soil were explored quantitatively in aggregate (X-ray microtomography, sample size 1–2 mm), core (water retention measurements, sample size 195 cm3) and column (macropores ≥80 µm, sample size ∼ 20 dm3) scales. Our results showed no micrometer-scale structural changes within soil aggregates despite the large number (25 aggregate per treatment) of imaged samples. However, the organic soil amendments had a statistically significant impact on the macroporosity. The macroporosity was on average 20–27 % higher compared to the control samples and visible even five years after the application of the amendments. Such change in soil structure improves soil aeration and fast infiltration of water during wet periods and extreme rain events and may thereby also reduce erosion risk by decreasing surface runoff. The increased microporosity was visible only in the column scale. No statistically significant differences were observed in the fraction of large pores in core scale water retention measurements. Probing the soil structural changes in macropore regime by X-ray tomography or developing sub-micron scale analysis methods are recommended approaches to improve our understanding of clay soil's structural changes induced by organic soil amendments. • The effect of a large single dose of organic matter on soil structure was studied. • Soil structure was investigated from aggregate to column scale. • 100 aggregates imaged with X-ray tomography. • Differences in intra-aggregate porosity were not found. • Only macropores (≥80 µm) were affected by the organic soil amendments. [ABSTRACT FROM AUTHOR]

• The performance of on-line vis-NIR for estimating soil organic carbon was evaluated. • Predictions for three datasets single field, UK with spiking, and UK were compared. • Random forest (RF) regression and spiking technique were used. • The best results obtained with the spiked UK dataset. Accurate on-line visible and near infrared (vis-NIR) spectroscopy prediction of soil organic carbon (OC) is essential for food security and environmental management. This paper aims at using on-line vis-NIR spectra coupled with random forest (RF) modelling approach for the prediction of soil organic carbon (OC), comparing between single field (SF), non-spiked UK multiple-field (NSUK) and spiked UK multiple-field (SUK) calibration models. Fresh soil samples collected from 6 fields in the UK (including two target fields) were scanned with a fibre-type vis-NIR spectrophotometer (tec5 Technology for Spectroscopy, Germany), with a spectral range of 305–2200 nm. After dividing spectra into calibration and independent validation sets, RF was run on the calibration set to develop calibration models for OC for the three studied datasets. Results showed that the model prediction performance depends on the dataset used and varies between fields. Less accurate prediction performance was obtained for the on-line prediction compared to laboratory (samples scanned in the laboratory under non-mobile measurement) prediction, and for non-spiked models compared to spiked models. The best model performance in both laboratory and on-line predictions was obtained when samples from the SF were spiked into the UK samples, with coefficients of determination (R2) values of 0.80 to 0.84 and 0.74 to 0.75, root mean square error of prediction (RMSEP) values of 0.14% and 0.17 to 0.18%, and ratio of prediction deviation (RPD) values of 2.30 to 2.5 and 1.98 to 2.04, respectively. Therefore, these results suggest that RF modelling approach when coupled with spiking provides high prediction performance of OC under both non-mobile laboratory and on-line field scanning conditions. [ABSTRACT FROM AUTHOR]

Highlights • Soil pores between 10 and 100 μm support microbial activity on aggregate exterior. • Interior aggregate microbial density is not affected by interior pore structure. • X-ray micro-CT plus SEM can delineate soil pore structure and microbial distribution. • Non-destructive plus traditional measurements help elucidate aggregate protection of SOC. Abstract Limitations of traditional measurement methods have impeded progress in understanding the role of soil aggregation in protecting soil organic carbon (SOC) from decomposition by soil microbes living in pore spaces. In this paper, we used the Scanning Electronic Microscope (SEM) and X-ray micro Computed Tomography (micro-CT) to study the relationships of the aggregate pore structure and microbial distribution in the interior and exterior of soil aggregates, and thereby gained an insight into protection of carbon within macroaggregates of an undisturbed Mollisol in northeastern China. There were close relationships between soil pore structure and distribution of soil microbes and soil organic carbon (SOC), but they were different on the exterior and interior of soil aggregate. On the exterior of macroaggregates, there were negative relationships between soil porosities, the number of pores and SOC, especially for soil pores in the 10–30 μm and 30–100 μm classes, indicating these two pore sizes are unlikely to help sequester C. In contrast, there was a positive correlation between soil pores > 100 μm and SOC. Furthermore, soil pore structure had no impact on soil microbial biomass and density or on SOC contents in the interior of soil aggregates. This study provides a new method by combining SEM with micro-CT technology for linking soil structure and soil microbial properties with C sequestration and SOC changes. [ABSTRACT FROM AUTHOR]

Complete and coherent soil profile information is important for studying soil morphological characteristics, vertical variation patterns of soil physicochemical properties, and identifying soil types. However, traditional soil survey methods use a limited number of discrete sample points at different depths as a data source to explore the correlation between soil depth and soil properties. Due to the variability of soil properties at vertical depth, there is a strong uncertainty in the conclusions drawn from the limited sample points. With the development of near-Earth remote sensing technology, the near-Earth hyperspectral imaging system can acquire hyperspectral images of soil profiles and characterize the fine texture differences and spectral variations of soil with continuous spectral curves and images, which is useful for inversion of soil properties. Soil organic carbon (SOC) is one of the important physicochemical properties to identify the genetic horizon, therefore, this paper explored the ability of visible–near-infrared (Vis-NIR) hyperspectral imaging spectroscopy to predict SOC in soil monoliths. The dataset contained five soil monoliths retrieved from the upper Yellow River, China. A random forest (RF) model was developed for predicting organic carbon, and the organic carbon content in the genetic horizon was used to establish a depth function to obtain the continuous content variation with the depth. These differences with and without depth function modeling, and the effect of three equal-spacing sampling schemes (1, 5, and 10 cm) on the depth function and the accuracy differences in five spectral statistics of the maximum (max), mean, median, mode, and minimum (min) within the image region of interest (ROI) were compared. The results indicated that (1) the depth function under the 1-cm sampling scheme predicted organic carbon the best, (2) the mode of the spectra within the ROI could yield a comparable or even a higher accuracy than that obtained with the mean, and (3) imaging spectroscopy could be used to visualize the distribution of organic carbon on soil profiles with relatively uniform morphology. These results indicated that imaging spectroscopy could be used for predicting organic carbon in undisturbed soil profiles. • Hyperspectral imaging was used to map soil organic carbon in soil profiles. • The depth function yielded optimal accuracy for predicting organic carbon, with R2 of 0.92 and RMSE of 0.73 g/kg. • The depth function under the 1-cm sampling scheme predicted organic carbon the best. • The mode of the spectra within the ROI could yield higher accuracy. [ABSTRACT FROM AUTHOR]

To accurately evaluate the effects of vegetation restoration strategies on soil carbon (C) and nitrogen (N) in erosion zones, we conducted a meta-analysis of 88 papers to analyze the dynamics of soil organic carbon (SOC) and soil total nitrogen (STN) contents under forestland and grassland restoration. The results indicated that i) vegetation restoration could reduce runoff and soil loss and increase SOC content, and forestland had a non-significant increase in STN content. ii) Vegetation restoration had the strongest soil C and N sequestration effects in the 0–20 cm soil layer and medium-textured soil. iii) Grassland restoration was more conducive to increasing the STN content and could increase the SOC and STN contents in the short term. iv) Forestland was more sustainable way to improve SOC contents compared with grassland, because its positive effects were not limited by mean annual precipitation (MAP), mean annual temperature (MAT), slope position. v) Grassland or forestland restoration could increase simultaneously both SOC and STN contents, when MAP < 800 mm, MAT < 15 °C, and at the foot position. Our findings indicate that when SOC sequestration is one of the main goals of vegetation restoration strategies, forestland restoration may be a better choice. ● The runoff and sediment reduction benefits differed little between vegetation types. ● Forestland restoration could not increase the STN content. ● Vegetation had higher SOC or STN sequestration potential in medium-textured soil. ● Grassland could increase the SOC and STN contents in a short time. [ABSTRACT FROM AUTHOR]

Maintaining or enhancing the stock of soil organic carbon (SOC) is a key factor in sustaining the soil resources of the world. The objective of this research was to study the effect of different farming systems (conventional farming with mineral fertilizers and crop specific fertilization vs. organic farming with organic fertilizers (catch crops and composted manure)) under the same 5-crop rotation (red clover, winter wheat, pea, potato, barley undersown with red clover) system on the SOC stock and the stability of SOC. The second aim was to quantify plant C inputs to the soil and to identify the relationship between C sequestration rate and C input. Data presented in this paper concerned the first rotation during 2008–2012. The main factors were farming systems: conventional and organic. Four conventional farming systems differed in the mineral nitrogen application rates used. In two organic farming systems catch crops were used with or without composted solid cattle manure. The SOC stock was determined before experiment establishment and after the first rotation. The C input into the soil was calculated based on the main product yield. The stock of SOC increased (2.57 Mg ha −1 y −1 ) considerably after the first rotation only in the organic farming systems, where the total C inputs were 1368 kg C ha −1 y −1 higher compared to the average C inputs in conventional systems. The mineral N rate did not influence the C-input but it had an effect on the properties and mineralisation of soil organic matter. The stable C fraction of SOC proportion increased in the system in which the highest rate of mineral N (20–150 kg N ha −1 y −1 depending on crop) was used and its proportion in the soil was comparable with the results obtained from organic farming systems. Thus, the intensive management with high N rates may benefit to a formation of more stabile SOC if the crop rotation used is properly elaborated. [ABSTRACT FROM AUTHOR]

Aggregate-associated soil organic carbon (SOC) controls organic carbon stabilization. The research question of this paper was: what were the effects of conversion of forest land uses to agriculture at Ranchi, India on SOC pools, soil aggregation and aggregate-associated C? The samples were taken from six different land uses viz. native forest (NF), agri-horticulture (AH), native grass land (NG), rice-wheat (RW), rice- vegetable (RV) and maize-wheat (MW) from three soil depths (0–15, 15–30 and 30–45 cm). Soil aggregation, SOC pools and aggregate-associated C were determined. Results revealed that SOC concentration in NF was 36%, 67% and 127% higher than RW, RV and MW land uses, respectively, at 0–15 cm depth. The microbial biomass carbon (MBC) was higher in NF land uses than rice-based systems in the soil surface (0–15 cm) due to less disturbance. In surface soils (0–15 cm depth) under NF, the large macroaggregates had 21% and 40% higher SOC concentration than RW and RV, respectively. Similarly, NF soil had larger small macroaggregate-associated C than RW, RV and MW systems in the 0–15 and 15–30 cm layers. This result supports that tillage and regular crop removal under arable (MW, RW and RV) systems adversely affect loss of SOC contents in the surface layers and C storage inside aggregates, both in the 0–15 and 15–30 cm soil layers at Ranchi, India. • Conversion of native forest (NF) to rice-wheat (RW) system reduced total C by 36%. • Large macroaggregates of NF had ~21% and 40% higher total C than RW system. • RW system had higher C than rice-maize (RM) in the surface (0–15 cm) soils. • NF and grassed soils had higher soil aggregation and macroaggregates than RW. [ABSTRACT FROM AUTHOR]

Understanding the spatial relationships of diffuse agricultural pollution with soil properties at a sub-basin scale is an innovative way to characterize the pollution yield. The objectives of this study was to identify the interaction of soil parameters with diffuse nitrogen (N) loading at spatial-vertical directions, which provide an optional method to assess the diffuse N pollution. The diffuse N loading of a sub-basin was simulated with the Soil and Water Assessment Tool with the consideration of land use (upland and paddy rice). Soil properties were analyzed in terms of eight parameters by employing a 1.5 km-grid soil sampling process at two depths across multiple sub-basins. The spatial soil properties were interpolated for each sub-basin. The spatial distributions of total nitrogen (TN), iron (Fe), manganese (Mn), and cadmium (Cd) exhibited the same pattern at two soil depths, but the vertical patterns of available nitrogen (AN), soil organic carbon (SOC), sulfur (S) and lead (Pb) varied. Overlaying the diffuse N loading and land use distribution, it was found that the sub-basins of upland and paddy rice were primary contributors. The diffuse N discharged from upland sub-basins was about 50% lower than that from paddy rice. The correlation analysis of soil variables with diffuse N indicated that the top layer had a stronger relationship with the diffuse N than the subsurface, which had more direct impact on the pollution. A partial least squares (PLS) regression analysis was employed to identify the key soil variables in surface layer. The analysis indicated that the metal parameters (Fe, Mn, Cd, and Pb) were the important factors for diffuse N loading. However, the TN in the paddy rice was the principal predictor. With the soil property information, the diffuse N yield from the two types of farmlands can be assessed in a simplified way. The developed method in this paper is flexible and efficient, which also is compatible with results of the SWAT model. [ABSTRACT FROM AUTHOR]

Aggregates are functional units to describe the impact of soil structural changes on physical and biogeochemical processes in soil. Both incubation and field experiments have shown that changing agricultural practices could reshape the intra-aggregate structure in a matter of days, but most such data were obtained from a single time-point and it is hence impossible to interpret that such a change was just a temporal transition or the new equilibria towards which the aggregates had evolved following the management changes. Understanding this is indispensable as intra-aggregate structure and its ability to transport substrates modulate all biogeochemical processes involved in soil carbon and nutrient cycle. This paper investigates this using soil samples archived from a reversion experiment initiated in 2008 at Rothamsted Research (UK), where parts of a plot that had been fallow since the 1950 s were converted to wheat or grass in 2008. We used X-ray Computed Tomography images, acquired at voxel size 1.5 µm, of aggregates in the archived soils to investigate the evolution of transport property of the aggregates over time, as well as its relationship with soil organic carbon (SOC). We also evaluated the development of pore connectedness following the conversion. The results show that the transport ability of the aggregates explains the SOC change much better than the porosity, and that noticeable changes in porosity of the connected pores and their ability to transport substrates did not emerge until the sixth year after the conversion. Ten years after the conversion, there was still no sign of the porosity of the connected pores and the bulk diffusion coefficient to plateau. In addition, we found the conversion to grass changed the intra-aggregate pore geometry significantly in that the bulk diffusion coefficients of their aggregates trends with their porosities in a way differing significantly from those for the bare fallow and arable treatments. All these suggest that the intra-aggregate reconfiguration following the conversion is a slow process, and that the ability of pore space to transport substrates is more important than the habitat they provide in SOC stabilisation. • Archived aggregates over a 10-year period were scanned using X-ray Computed Tomography. • Evolution of their connected pores and bulk diffusion coefficient were calculated. • Diffusion coefficient of the aggregates is positively correlated to soil organic carbon (p < 0.05). • Intra-aggregate structures did not reach new equilibria 10 years after land use changes. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) stock can be improved through the return of crop residues. However, the efficiency of C sequestered in soil (i.e., ΔSOC/ΔC input) might differ among crop systems. In this paper, we investigated the C input and SOC stabilization in paddy soil and upland soil under different long-term fertilization practices. Our objectives were to determine (i) the response of SOC stock to C input under different fertilization practices, and (ii) C sequestration efficiency in the two contrasting agroecosystems. The long-term fertilization experiment in paddy soil started in 1981, while the adjacent upland soil experiment commenced in 1986. Each experiment consists of 9 treatments: CK (no fertilization), N, P, K, NP, NK, NPK, 2NPK (double dose), and NPKOM (NPK plus organic manure). Physical SOC fractions (cPOM, silt+clay_f, fPOM, iPOM_m, silt+clay_m) were isolated by sieving, dispersion, and density flotation. Fertilization increased crop yield and C input, but it did not change the quality of SOC as revealed by CPMAS-13C NMR spectra. During the period of the experiment, SOC stock was improved by 6.7–15.3Mgha−1 in paddy soil for all fertilization practices, while in upland soil the CK, N, P, K, and NP fertilizations reduced the SOC by 1.2–3.8MgCha−1 and the other four fertilizations increased it by 0.5–7.4MgCha−1. The change in SOC was mainly ascribed to the POM fraction, whereas the two silt+clay sized fractions were independent of fertilization practice except the NPKOM treatment. At a given C input, the C sequestration efficiency was greater in paddy soil than in upland soil, which may be attributed to lower microbial activity but greater chemical (i.e., oxalate-soluble Fe) and physical stabilizations (i.e., soil structure) in paddy field. Our results indicate that paddy soil may sequester more SOC, with higher efficiency, than upland soil does. [ABSTRACT FROM AUTHOR]

Abstract: Soil plays an important role in the global carbon cycle, and carbon sequestration in soil is important for mitigating global climate change. Historically, soil erosion led to great reductions of soil organic carbon (SOC) storage in China. Fortunately, with the economic development and remarkably effective soil erosion control measures in subtropical China over the past 20 years, soil erosion has been greatly decreased. As a result, soil organic carbon sequestration has gradually increased due to the rapid recovery of vegetation in the area. However, little information exists concerning the potential of soil carbon sequestration in the area. This paper introduces a case study in Xingguo County, Jiangxi Province, China, which used to be a typical area with significant soil loss in subtropical China. This work represents a systematic investigation of the interrelations of carbon sequestration potential with soil erosion types, altitudes, soil types and soil parent materials. In this study, 284 soil samples were collected from 151 sampling sites (51 are soil profile sites) to determine soil physicochemical properties including organic carbon content. Soil organic carbon distribution maps of the surface layer (0–20cm) and whole profile (0–100cm) were compiled by linking soil types to the polygons of digital soil maps using GIS. Assuming that SOC was lost following the destruction of native vegetation, these lands hold great promise for potentially sequestering carbon again. The potential of soil carbon sequestration in the study area was estimated by subtracting the organic carbon status in eroded soils from that in non-eroded soils under undisturbed forest. Results show that the potential of SOC in the surface layer is 4.47TgC while that in the whole profile is 12.3TgC for the entire county. The greatest potential for carbon sequestration (3.72TgC) is found in severely eroded soil, while non-eroded soil has the smallest potential. Also, soil carbon sequestration potential decreases with increasing altitude. Soils at altitudes of <300m show the greatest potential (5.01TgC), while those of >800m have the smallest potential (0.25TgC). Among various soil types, red earths (Humic Acrisols) have the greatest potential of carbon sequestration (5.32TgC), and yellow earths (Ferralic Cambisols) have the smallest (0.15TgC). As for soils derived from various parent materials, soils derived from phyllite possess the greatest carbon sequestration potential, and soils from Quaternary red clays have the smallest. [Copyright &y& Elsevier]

Abstract: Intensive agricultural practices generally lead to considerable reduction of organic carbon in soils. Moreover, the use of saline water affects physical parameters such as aggregate stability, and thus, bulk density. Organic amendments have been proposed as an effective method to improve physical properties of soils. In this paper, the effect of successive biosolids (sewage sludge) amendments on aggregate stability percentage and bulk density on two degraded soils (one salinized) have been evaluated during several samplings. Different relationships between these parameters (aggregate stability and bulk density) with organic carbon, carbohydrates and exchangeable sodium percentage have been observed in these soils. The application of biosolids increased significantly the organic carbon, carbohydrates and aggregate stability percentage, resulting in a decrease of the bulk density of both soils. In the non-salinized soil, the increase in aggregate stability was related to the increase in organic carbon and carbohydrates. But in the salinized soil, the increase in aggregate stability was related to the increase in carbohydrates and specially to the decrease in exchangeable sodium percentage. In both soils, the decreases in bulk density by the organic amendments were related to the increase in aggregate stability. Application of biosolids could be a successful practice to improve soil structure in degraded soils. [Copyright &y& Elsevier]