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Increasing soil organic carbon (SOC) aims to increase and maintain soil quality for sustainable crop production and to achieve carbon removal targets. Agronomic practices are therefore needed to reduce carbon losses and increase SOC stocks, especially in deep soil layers, which promote long-term storage. Regenerative agriculture is an approach aimed at increasing soil quality for sustainable production and therefore should be suitable for achieving the required goals under organic farming conditions. We analysed SOC content down to a depth of 1 m and calculated the SOC stock based on bulk density after ten years of regenerative farming practices, i.e., reduced tillage, dead organic mulch, and high-quality yard waste compost application, in two organic field trials set up one year apart in Central Germany and we calculated the carbon (C) and nitrogen (N) input to the soil from organic amendments and from main crops and cover crops by applying C allocation factors for crop residues, roots, and rhizodeposition. C derived from crops was the main carbon input source over ten years. Increasing C input promoted an increase in the cumulative SOC stock down to 1 m. We observed greater SOC stocks dominated by topsoil changes with reduced tillage and compost application and with the combination of all practices (+ 16%) than in the control with conventional ploughing and no external carbon input while none of the farming practices affected the subsoil SOC stock. Mulch application had no effect at all on SOC stocks. Crop biomass contributed most C input. Farming practices, especially the combination of reduced tillage and compost application, enhanced topsoil SOC stocks and N but not subsoil C storage. Other farming practices and crop rotation adjustments must be identified to increase crop production as well as subsoil SOC stocks and promoting long-term C storage, e.g., by fostering deep-rooting crops and cover crops.

Understanding soil organic carbon fractions in southern India is crucial for enhancing soil health, crop productivity, and sustainable land management. It is majorly affected by cropping systems, nitrogen levels, irrigation management, etc. Therefore, the present study aimed to investigate the effects of varying nitrogen doses [N 1 : No nitrogen, N 2 :100% of recommended dose of N (RDN), and N 3 : 200% RDN] and different cropping systems (fieldbean, finger millet, and maize) on aggregate-associated soil organic carbon and its fractions, as well as their impact on aggregate stability under rainfed and irrigated conditions. Aggregates were separated into different classes and analyzed for organic carbon and its fractions (dissolved organic carbon, microbial biomass carbon, potassium permanganate oxidizable carbon, and non-labile organic carbon). Applying 200% RDN enhanced total organic carbon (TOC) and its fractions. Conversely, aggregate stability was not influenced by N levels as determined by mean weight diameter and tensile strength. Macroaggregates (> 250 μm) had higher total organic carbon and their fractions than microaggregates (< 250 μm). The effect of the cropping systems was significant and the maize cropping system had the highest content of TOC and other fractions, followed by fieldbean and finger millet cropping systems. Mean weight diameter (MWD) was significantly higher in finger millet-grown soils. The impact of nitrogen fertilizer and cropping systems on aggregate-associated organic carbon was more pronounced in irrigated than rainfed conditions, indicating the potential for carbon sequestration under irrigated conditions. Thus, the optimum level of nitrogen and the type of cropping system adopted influence the distribution pattern of aggregate-associated organic carbon, along with its fractions that play a pivotal role in carbon accumulation and stabilization.

In conservation agriculture, conservation tillage potentially influences the physical, chemical, and biological quality of the soil. Although the effects of conservation agriculture on the soil’s physical properties have been studied in conventional management systems, studies on organic farming systems, especially concerning long-term changes, are scarce. This study summarizes the results of physical and mechanical soil parameters obtained over the initial 10 years of different conservation management treatments (plowing versus reduced tillage with and without compost application) in an organic field trial conducted in central Germany. Moreover, as a research objective, the effects of soil conservation measures on soil’s physical quality were evaluated. Differences in the soil’s physical quality during treatments were mainly detected in the topsoil. At a depth of 0.10–0.24 m, the total porosity and air capacity were lower, and the bulk density was higher in the reduced-tillage systems, compared to those of the plowed treatments. Additionally, the soil’s mechanical stability (precompression stress) was higher at a depth of 0.10 m for reduced-tillage systems combined with compost application. In addition, the soil’s aggregate stability was enhanced in the reduced-tillage systems (higher mean weight diameter, as determined via wet sieving). Overall, the reduced-tillage treatments did not exceed the critical physical values of the soil, nor affect the functionality of the soil (saturated hydraulic conductivity), thereby demonstrating its feasibility as a sustainable technique for organic farming. Future studies should include measures to ameliorate compaction zones in reduced-tillage treatments, e.g., by applying subsoiling techniques in combination with deep-rooting crops to prevent limited rooting space resulting from the high mechanical impedance, especially under dry soil conditions.

Modeling peatland hydraulic processes in cold regions requires defining near-surface hydraulic parameters. The current study aims to determine the soil freezing and water characteristic curve parameters for organic soils from peatland-dominated permafrost mires. The three research objectives are as follows: (i) Setting up an in situ soil freezing characteristic curve experiment by installing sensors for measuring volumetric water content and temperature in Storflaket mire, Abisko region, Sweden; (ii) Conducting laboratory evaporation experiments and inverse numerical modeling to determine soil water characteristic curve parameters and comparing three soil water characteristic curve models to the laboratory data; (iii) Deriving a relationship between soil freezing and water characteristic curves and optimizing this equation with sensor data from (i). A long-lasting in situ volumetric water content station has been successfully set up in sub-Arctic Sweden. The soil water characteristic curve experiments showed that bimodality also exists for the investigated peat soils. The optimization results of the bimodal relationship showed excellent agreement with the soil freezing cycle measurements. To the best of our knowledge, this is one of the first studies to establish and test bimodality for frozen peat soils. The estimated hydraulic parameters could be used to better simulate permafrost dynamics in peat soils.

Over the last few decades, due to increase in grazing intensity, animal trampling has led to soil structure deterioration in Inner Mongolia, China. We investigated two different steppe ecosystems: Leymus chinensis (LCh, characterized by relatively higher precipitation) and Stipa grandis (SG) and two grazing intensities: ungrazed since 1979 (UG79) and grazed (continuously grazed, CG, at the Stipa grandis site and winter grazed, WG, at Leymus chinensis). Soil mechanical and hydraulic properties of semiarid steppe soils from each site and treatment were determined for soil aggregates and disturbed and bulk soil samples from different depths (4-8, 18-22, 30-34 and 56-60 cm for disturbed and bulk samples and 0-15 cm for the aggregates). Grazing causes a significant increase in tensile strength of aggregates and in the precompression stress of the bulk soil as well as a decrease in air and saturated hydraulic conductivity, irrespective of the vegetation type. Furthermore, exclusion from grazing led to more pronounced recovery of soil strength and pore continuity and hydraulic conductivity at the LCh site but it also depended on the moisture conditions of the sites. Under wetter conditions as well as after repeated freezing and thawing the soil strength declined.

Long-term monitoring of soil properties reveals site-specific ecosystem shifts in soil processes due to land use and climate changes. This paper aims to study the effects of physical landscape changes associated with grazing on soil thermal and moisture regime at the plot scale in a semiarid Leymus chinensis steppe of Inner Mongolia, China. The investigated sites were subjected to three grazing intensities: ungrazed since 1979 (UG79), moderately grazed only in winter time (WG), and heavily grazed (HG). At each plot, we recorded the soil moisture and temperature over a 6-year period that spanned between June 2004 and September 2009 and experienced a large range in precipitation (162 to 362 mm). Based on these monitoring data, we divided a year into four hydric periods: (1) growing period (late April to August); (2) transitional period from summer to winter (September-October); (3) winter time (November-first March); and (4) transitional period from winter to summer (March-April). In general, soil moisture in grazed sites was lower than in the ungrazed site, particularly for the 30-50 cm soil layer. Seasonal fluctuation of the soil moisture, due to variable precipitation and atmospheric demands, was most significant in the topsoil (0-10 cm) and was less pronounced in deeper soil. Regardless of hydric seasons, soil moisture was significantly influenced by grazing intensity, whereas soil temperature was slightly influenced. With increasing grazing intensity, soil water storage decreased remarkably. Consequently, grazing reduced plant available water and therefore grassland productivity, which are linked to a great extent with the trampling-induced soil structure change and soil moisture regime.

Numerous methods are available for sampling, extracting, and detecting microplastics (MP; 0.001–5 mm) in soil. However, previous studies mostly focused on pristine MP and changing surface properties due to ageing (e.g. surface photooxidation) that will impact transport in soils are not considered. This study primarily aimed at MP recovery from soil by density separation, focusing on the impact of UV-aging on recovery rates while monitoring MP surface properties to avoid analytical artifacts. Thus, we mixed sandy loam and silt loam topsoil with both, pristine and UV-aged polyethylene terephthalate (PET) and polystyrene (PS) MP, produced from PET bottles and PS plates in three size classes. MP particles were recovered by density separation, using oversaturated NaCl and NaI, solutions, followed by H 2 O 2 -treatment to oxidise soil organic matter. Recovery rates were determined gravimetrically after filtration of the supernatant. MP surface properties were characterised by FTIR, Nile red staining, contact angle (CA), and XPS analysis before and after recovery. Recovery rates averaged 81.0%, ranging from 56.5% to 89.7%, with no defined differences between MP type, size, and variant (pristine, UV-aged). Before recovery, FTIR analysis revealed an increase in carbonyl groups, Nile red staining showed a darker colour, CA was significantly decreased, and XPS indicated an increase in surface O/C ratio for UV-aged MP. After recovery, FTIR and Nile red analysis showed no changes, CA of UV-aged MP, however, was found to be increased, probably due to H 2 O 2 -treatment that may have removed the oxidised surface layer. In summary, the separation procedure applied was found to successfully recover pristine and UV-aged MP from both, sand and silt soil, regardless of MP type tested (PET, PS).

Accurate simulation of soil water and heat transfer is critical to understand surface hydrology under cold conditions. Using an extended freezing code in HYDRUS-1D (freezing module), this study was conducted: (1) to evaluate the freezing module using field data collected in a grazed steppe of Inner Mongolia; and (2) to further simulate grazing effects on frozen soil hydrological processes. The experimental data consisted of soil water and temperature profiles measured during freeze-thaw cycles from 2005 to 2006 in two plots (ungrazed since 1979 (UG79) and winter grazing (WG)). To check the sensitivity of the freezing module, a model without a freezing scheme (normal module) was used for comparison. We found that while the normal module can only simulate soil water and heat transfer under unfrozen conditions, the freezing module can simulate well under both frozen and unfrozen conditions. The freezing module can reasonably compute water phase change and, therefore, substantially improved the simulation of the evolution of liquid water and temperature in frozen soil. It overestimated liquid water content during spring snowmelt and, thus, underestimated surface runoff from underlying frozen soil layers. Furthermore, the weak prediction of soil moisture at the WG site, compared with the UG79 site, might relate to the less than ideal parameterization of soil hydraulic properties. Our results confirmed that the freezing module was able to accurately predict behaviors of soil freezing and thawing, as well as the effects of land management. We suggest that detailed knowledge of the soil-atmosphere processes is needed to improve the surface runoff algorithm in the frozen soil module.

Soil structure controls soil hydraulic properties and is linked to soil aggregation processes. The aggregation processes of Oxisols are controlled mainly by clay mineralogy and biological activity. Computed microtomography (µCT) may be a tool for improving the knowledge of the hydraulic properties of these soils. Thus, this study brings an advance in the use of 3D image analysis to better comprehend the water behavior in tropical soils. In this work, three Oxisols were studied with the objective to (i) characterize the soil water retention curve (SWRC), the corresponding pore size frequency, and the saturated hydraulic conductivity (Ksat); (ii) use µCT to obtain, based on 3D images of soil structure and pore size distribution; and (iii) correlating parameters from SWRCs, Ksat, and µCT with other physical-hydric, chemical, and mineralogical attributes. Rhodic Haplustox—P1, Anionic Acrustox—P2, and Typic Hapludox—P3 were the three studied Oxisols. The differences among the SWRCs were related to the microgranular and block type’s structure morphology, which modified the soil pore space. The pore size frequency was calculated from SWRCs for pores with diameters of 87 ± 2 μm in P1, 134 ± 11μm in P2, and 175 ± 18 μm in P3. Pore size distribution from µCT was determined for the range of 20–100 µm, mainly with the highest percentages: 12 ± 1.09% for P1 and 12 ± 1.4% for P2. Pore connectivity was assessed from images by calculating Euler Numbers (EN), with the differences related to the biggest pore (ENbigpore): P1 (−44,223 ± 10,096) and P2 (−44,621 ± 12,573) showed more connected pores (ENbigpore) in comparison to P3 (−11,597 ± 6935). The parameter ENbigpore was decisive in understanding the water retention and conduction processes of the studied soils. The better-connected pore space increased Ksat in P1 (220 ± 0.05 mm h−1) and P2 (189 ± 0.1 mm h−1) in comparison to P3 (20 ± 0.3 mm h−1) and modified the shape of SWRCs.

The aim of this paper is to clarify the effect of soil management and thus also of soil aggregation on physical and chemical properties of structured soils both on a bulk soil scale, for single aggregates, as well as for homogenized material. Aggregate formation and aggregate strength depend on swelling and shrinkage processes and on biological activity and kinds of organic exudates as well as on the intensity, number and time of swelling and drying events. Thus, soil management like conventional or conservation tillage alter not only the mechanical strength but also the pore continuity and the hydraulic, gas and heat fluxes, and also alter the accessibility of exchange places for nutrients and for carbon storage (global change aspects). The possibility to predict physical properties on these various scales depends on the rigidity of the pore system. In general this rigidity depends on the above-mentioned physical and chemical processes both with respect to intensity and frequency, which again are linked to the soil management systems.