Higher Soil Organic Carbon Content Research Articles

Numerical modeling of PFAS movement through the vadose zone: Influence of plant water uptake and soil organic carbon distribution

In this study, we investigated the effects of soil organic carbon (SOC) distribution and water uptake by plant roots on PFAS movement in the vadose zone with a deep groundwater table under temperate, humid climate conditions. Two series of numerical simulations were performed with the HYDRUS computer code, representing the leaching of historical PFOS contamination and the infiltration of water contaminated with PFOA, respectively. We considered soil profiles with three distributions of SOC (no SOC, realistic SOC distribution decreasing with depth, and uniform SOC equal to the content measured in topsoil), three root distributions (bare soil, grassland, and forest), and three soil textures (sand, sandy loam, and loam). The SOC distribution had a profound impact on the velocity of PFOS movement. The apparent retardation factor for realistic SOC distribution was twice as large as for the scenario with no SOC and more than three times smaller than for the scenario with uniformly high SOC content. We also showed that the root distribution in soil profoundly impacts the simulations of PFAS migration through soil. Including the root zone significantly slows down the movement of PFAS, primarily due to increased evapotranspiration and reduced downward water flux. Another effect of water uptake by plant roots is an increase of PFAS concentrations in soil water (evapo-concentration). The evapo-concentration and the slowdown of PFAS movement due to root water uptake are more significant in fine-textured soils than in sand.

Determining environmental drivers of global mud snail invasions using climate and hydroclimate models

AbstractClimate change and invasive species represent two intertwined global environmental challenges profoundly affecting freshwater ecosystems. This study uses Ecological Niche Modeling along with risk screening to delve into the preferences and potential distribution of Potamopyrgus antipodarum, an invasive species, in relation to climate zones and habitat types, shedding light on the critical importance of coastal wetlands and high soil organic carbon content in shaping habitat suitability. Our findings underscore that P. antipodarum exhibits a distinct affinity for cool temperate, moist climates, as well as temperate floodplain rivers, wetlands, and coastal areas. Notably, coastal wetlands, endowed with elevated soil organic carbon levels, emerged as pivotal habitats for this species. Projections indicated a significant expansion in North America, potentially extending into South America. Türkiye reveals an intriguing alignment between its habitat and the natural distribution areas of P. antipodarum, presenting potential for habitat contraction while still retaining a broader range compared to other regions. These potential expansions were predominantly driven by climate suitability, playing a pivotal role in the invasiveness of P. antipodarum, with anticipated future climate regimes exerting substantial influence on its dispersal capabilities.

A Properly Chosen Rate of NPK Fertilizers Has a Positive Effect on C Sequestration in Sandy Soils in the Conditions of a Changing Climate

Abstract Soil organic carbon (SOC) plays a significant role in climate change. Its content can be modified by soil management practices, however, the effect of mineral fertilization on SOC is not clear. For this reason, a long-term effect of gradually increasing rates of NPK fertilizers on changes in soil organic carbon (SOC) in bulk soil and in water-stable aggregates (WSA) in soils with sandy loam and loamy sand texture at two experimental sites (Skierniewice, Poland, and Dražovce, Slovakia) was quantified. In both sites, soil samples were collected from the following treatments: NF – no fertilization, NPK1 and NPK2 – 1st level and 2nd level of NPK fertilization, respectively. The results showed that 100-year long application of NPK1 increased total carbon (TC) and SOC content by 24%, while NPK2 decreased it by 5% compared to NF at the Skierniewice site. The content of water-stable macroaggregates (WSAma) increased because of NPK application. In NPK1, the content of WSAma was higher and the content of water-stable microaggregates (WSAmi) was lower than in NPK2 or NF. However, as a result of NPK application, the content of agronomically favorable WSAma in size fraction 0.5–3 mm was reduced by 8 and 24% in NPK1 and NPK2, respectively, compared to NF. Overall, SOC in WSAma was lower than in bulk soil. The SOC in WSAma in NF, NPK1 and NPK2 treatments was 6.51, 7.77 and 5.89 g.kg−1, respectively. Similar tendency of SOC in WSAma 0.5–3 mm was observed (NF: 6.12 g.kg−1, NPK1: 7.35 g.kg−1, and NPK2: 6.88 g.kg−1). The SOC in WSAmi in NF, NPK1 and NPK2 was 8.33, 7.39 and 7.24 g.kg−1, respectively. At Dražovce site, TC content decreased significantly due to the graded rates of NPK, not because of SOC mineralization but as a result of carbonate dissolution for a period of 14 years. The carbonate content decreased from 20 g.kg−1 in NF to 6.5 g.kg-1 in NPK1 and 3.0 g.kg-1 in NPK2, while SOC did not change significantly: (NF: 23.8 g.kg−1, NPK1: 25.9 g.kg−1, and NPK2: 23.4 g.kg−1). In NPK1, the WSAma content was reduced significantly when compared to NPK2 and NF treatments. No significant difference was observed between NF and NPK2. On the contrary, the content of WSAma 0.5–3 mm significantly increased when compared to NF and NPK1. No difference was observed between NF and NPK1. Lower SOC content was found in WSA than in the bulk soil. Overall, higher SOC content was observed in WSAma when compared with WSAmi. The application of NPK1 and NPK2 increased SOC in WSAma as well as in WSAma 0.5–3 mm. The effect was more significant in NPK1 than NPK2 treatments when compared to NF.

No tillage and leguminous cover crop improve soil quality in a typical rainfed Mediterranean system

Soil and crop management influence soil organic carbon (SOC), chemical composition, and overall soil quality. In a Mediterranean region, a study initiated in 1994 examined the long-term effects of conventional tillage (CT) versus no-tillage (NT) practices. Initially focusing on continuous durum wheat cultivation until 2009, the experiment later introduced a two-year rotation of durum wheat and Vicia faba L. cover crops in half of the CT and NT fields. SOC was monitored from 2008 to 2018, while microbial biomass (as dsDNA), soluble nitrogen (N), and enzyme activities (EAs) were monitored from 2011 to 2014 to evaluate the rotation's impact.
 Between 2009 and 2018, CT yields were on average 15% higher than NT, especially during high rainfall years. NT significantly increased SOC content in the 0-30 cm soil layer, along with higher levels of soluble N, dsDNA, and EAs at 0-10 cm depth. NT led to a 23% and 10% increase in SOC stock and SOC stock per equivalent soil mass respectively compared to CT. EAs increased by over 50% under NT, indicating enhanced biological activity. The SOC increase due to NT was limited to the top 10 cm, with a decrease at deeper depths (up to 50 cm). Introducing cover crops over four years did not yield significant impacts, suggesting the need for a longer period to observe noticeable effects.
 Overall, adopting NT practices resulted in higher SOC concentration, enhanced soil biological activity, and improved biogeochemical cycles, emphasizing the positive impact of no-tillage on soil health and sustainability.

Spatial variation of soil organic carbon under major rubber planting regions in China

AbstractUnderstanding the dynamic relationships between soil organic carbon (SOC) and stand age are essential to quantify and predict the terrestrial carbon sequestration potential. However, the spatial patterns in the response of rubber plantation SOC to stand age and their driving factors remain unclear. Based on SOC and its components measurement at different soil depths (0–40 cm) in rubber plantations under five different age classes (0–5, 5–10, 10–20, 20–30, and >30 years) in three major rubber cultivation regions in China, distribution pattern and controlling factors of SOC were investigated. We found that SOC and its components showed significant spatial variability vertically with soil depth and laterally across sampling sites. SOC contents in three major rubber cultivation regions range from 4.48 to 20.13 g kg−1 at a depth of 0–40 cm. Among the sampling sites, Jinghong had the highest SOC content at a depth of 0–10 cm (20.13 g kg−1). On a large‐scale, the relationship between SOC and stand age in rubber plantations did not show a consistent pattern among different sampling sites. Additionally, annual rainfall, soil moisture content, and soil pH had a stronger impact on SOC in rubber plantations compared to stand age. The results indicated that the spatial variability of SOC in rubber plantations with stand age could be influenced by specific soil properties and climate‐related variables at each sampling site. This study emphasized the significance of conducting multi‐site, multi‐scale studies to enhance our understanding of SOC dynamics and its influencing factors, and help to more accurately predict the dynamic changes of soil carbon storage in rubber plantations.

Organic Carbon Sources in Surface Sediments on the Northern South China Sea

AbstractThe burial of organic carbon (OC) in marine sediments regulates CO2 content in the atmosphere. However, the OC sources and their effect on the OC preservation in sediments of the continental marginal sea remain elusive. Here, we survey the abundance, stable carbon and radiocarbon isotopes of OC, as well as mineral surface area and grain size in surface sediments from the shelf to the abyssal plain of the South China Sea. We found that the marine OC comprises the 63 ± 9% and 78 ± 14% of sedimentary OC off South China and Luzon, respectively. The petrogenic OC contributing to sedimentary OC in these sites is generally higher than that of soil OC (22 ± 10% vs. 12 ± 6%). The sedimentary OC off Taiwan is predominantly derived from petrogenic OC, accounting for 57 ± 10%, with remaining consisting of marine OC (36 ± 10%) and soil OC (6 ± 1%). High soil OC contents are found in fine sediments on the inner shelf off South China, and high petrogenic OC contents occur in fine sediments off Taiwan. Marine OC contents are high in fine sediments on the middle shelf and upper slope off South China, but low in coarse sediments on the outer shelf and upper slope, and fine sediments on the lower slope and abyssal plain. The OC sources, mineral surface area, and oxygen exposure time of OC together control the preservation of OC in sediments with their relative importance differing on varying depositional settings of this sea.

Changes in the Soil Organic Carbon of Grasslands in the High Andes of Peru after Their Conversion to Croplands and Their Environmental Controls

The high-Andean grasslands of Peru provide a wide range of goods and services, not only locally, but also regionally and globally. However, land-use change and global warming are threatening these ecosystems, of which soil organic carbon (SOC) is a key element affecting their sustainability. In this study, we have analyzed the variation of SOC stocks to a depth of 20 cm in 16 paired cropland and grassland sites located in the Sullccapallcca stream micro-watershed (elevation > 3600 m.a.s.l., Ayacucho, Peru). We have also analyzed the environmental controls on the SOC stocks and their variation with land-use change. We found that the studied high-Andean grasslands store high SOC contents (247 Tn SOC ha−1), whose spatial variability was partially explained by the slope of the terrain (r2 = 0.26, p < 0.05). Despite the higher NDVI, the conversion of these grasslands into croplands decreased the SOC stock by 39 Tn SOC ha−1 on average, a decrease that was more pronounced when the initial SOC content of the grassland was higher (r2 = 0.60, p < 0.05). This study provides the first evidence of the effects of land-use change on the SOC in the region, although the mechanisms involved still need to be investigated.

Effects of Conservation Tillage Method, Phosphorus Level, and Variety on Soil Organic Carbon and Cowpea Performance at Minna in Nigeria’s Southern Guinea Savanna

The study was carried out at the Teaching and Research Farm of the Federal University of Technology Minna, Gidan Kwano Campus in Latitude 9° 41' N, Longitude 6° 31' E, and Altitude 258.5 m above sea level. This study was conducted across 2 seasons within the cropping season of 2017 to determine the effects of tillage method, phosphorus level, and cowpea variety on soil organic carbon and cowpea performance in Minna. The experiment was therefore a 3x3x3 factorial arrangement in a split-plot design with tillage methods (zero, reduced, and manual ridging) and cowpea varieties (IT93K-452-1, IT99K-573-1-1, and IT90K-277-2) forming the main plot while phosphorus levels (0 P kg ha-1, 30 P kg ha-1, and 60 P kg ha-1) formed the sub-plot with 3 replicates. Results obtained revealed that soil organic carbon was not significantly affected by tillage method and phosphorus level alone, regardless of the planting season. Cowpea variety alone significantly affected organic carbon only in the late planting season. Zero tillage, 60 kg P ha-1, and IT93K-452-1 produced the highest soil organic carbon content, respectively. In the early season, N fixed was highest (0.98 g plant-1) when cowpea was fertilized with 60 Kg P ha-1 under zero tillage. The closest to this value (0.92 g plant-1) was recorded in the late season when 60 kg P ha-1 was supplied to cowpea under manual tillage. Regardless of the planting season and varietal difference, cowpea recorded the highest N fixed when fertilized with 60 kg P ha-1. Across varieties, cowpea fixed more N under zero tillage than the other tillage methods, especially in the early season. In the late season, only IT90K-277-2 fixed N (0.49 g plant-1) under zero tillage that was statistically not different from the highest N fixed due to manual tillage of soil under the cultivation of IT93K-452-1 and IT99K-573-1-1 (0.62 g plant-1, respectively). In the early season, IT99K-573-1-1 cultivated under zero tillage produced the highest grain yield (404.11 kg ha-1). Fodder yield followed a different trend compared to grain yield. In the early planting season, cowpea fertilized with 60 kg P ha-1 produced the highest fodder yield, while in the late season, the application of 30 kg P ha-1 produced the highest fodder yield. Regardless of the planting season, grain yield was highest when IT99K-573-1-1 was fertilized with 60 kg P ha-1. Averagely, soil organic carbon content, N fixed, and grain yield values were highest during the late planting than the early planting season. The reverse was, however, the case for fodder yield, seedling emergence, root length, root, and shoot biomass, respectively. For the best performance in cowpea production, farmers are encouraged to plant IT99K-573-1-1 on zero-tilled soil with phosphorus application at the rate of 60 kg ha-1. IT90K-277-2, which is the most genetically stable variety across seasons, will be most ideal in controlling negative climate change and should therefore be considered for further investigations.

Investigating Soil Water Retention and Water Content in Retrogressive Thaw Slumps in the Qinghai-Tibet Plateau, China

Retrogressive thaw slumps (RTSs) are becoming more common on the Qinghai-Tibet Plateau as permafrost thaws, but the hydraulic properties of thaw slumps have not been extensively studied. To fill this knowledge gap, we used the “space-for-time substitution method” to differentiate three stages of RTSs: original grassland, collapsing, and collapsed. Our study included on-site investigations, measurements in the laboratory, and measured and simulated analyses of soil water retention curves and estimated hydrological properties. Our findings show that the measurements and simulated analyses of soil water retention were highly consistent across RTSs, indicating the accuracy of the Van Genuchten model in reproducing soil hydraulic parameters for different stages of RTSs. The original grassland stage had the highest soil water retention and content due to its high soil organic carbon (SOC) content and fine-textured micropores. In contrast, the collapsed stage had higher soil water retention and content compared to the collapsing stage, primarily due to increased proportions of soil micropores, SOC content, and lower bulk density (BD). From original grassland stage to collapsed stage, there were significant changes on the structure of each RTS site, which resulted in a decrease in SOC content and an increase in BD in general. However, the absence of soil structure and compaction led to the subsequent accumulation of organic matter, increasing SOC content. Changes in field capacity, permanent wilting point, and soil micropore distribution aligned with variations in SOC content and water content. These findings highlight the importance of managing SOC content and water content to mitigate the adverse effects of freeze-thaw cycles on soil structure and stability at different thaw collapse stages of RTSs. Effective management strategies may include incorporating organic matter, reducing soil compaction, and maintaining optimal water content. Further research is needed to determine the most suitable management practices for different soil types and environmental conditions.

Seasonal dynamics of soil CO2 emissions from different semi-arid land-use systems

ABSTRACT Soil carbon dioxide (CO2) fluxes are a critical component in understanding carbon sequestration. In sub-Saharan Africa, empirically measured CO2 emissions data from diverse land-use systems is limited. Soil CO2 emission rates were measured in the Limpopo Province, South Africa for 12 months at two-week intervals in natural systems (forest and shrubland) and commercially managed orchards (avocado and citrus) to establish seasonal dynamics of soil CO2 emissions across these land-use systems. The results showed a variation in emission rates with the variation depending on the season. In the spring and winter, soil CO2 emission rates in citrus were four times higher than in the shrubland due to higher moisture levels. However, in the summer season, the forest emission rates were 40% higher than in citrus due to higher soil organic carbon content. Organic carbon stocks were higher in the forest (1.19 kg/m2) compared to the other land uses. This study revealed differences in soil CO2 emission rates among land-use systems, with the cumulative amount of CO2 emitted over a 12-month period following the order: forest (39.3 tons/ha) > citrus (36.1 tons/ha) > shrubland (28.1 tons/ha) > avocado (26.9 tons/ha). Thus, understanding the emission patterns from various ecosystems can inform strategies for mitigating greenhouse gas emissions.

Collaborative Utilization of Sentinel-1/2 and DEM Data for Mapping the Soil Organic Carbon in Forested Areas Based on the Random Forest

Optical remote sensing data are widely used for constructing soil organic carbon (SOC) mapping models. However, it is challenging to map SOC in forested areas because atmospheric water vapor affects the results derived from optical remote sensing data. To address this issue, we utilized Sentinel-1, Sentinel-2, and digital elevation model (DEM) data to obtain a comprehensive feature set (including S1-based textural indices, S2-based spectral indices, and DEM-derived indices) to map the SOC content in forested areas. The features set were the predictor variables, and the measured SOC content was the dependent variable. The random forest algorithm was used to establish the SOC model. The ratio of performance to inter-quartile range (RPIQ) was 2.92 when the S2-based spectral indices were used as predictor variables. When the comprehensive feature set was utilized as the model input, the model achieved an RPIQ of 4.13 (R2 = 0.91, root mean square error (RMSE) = 9.18), representing a 41.44% improvement in model accuracy. The average SOC content in the Greater Khingan Mountains was 43.75 g kg−1. The northern and southwestern parts had higher SOC contents (>54.93 g kg−1), while the southeastern and northwestern parts had lower contents (<39.83 g kg−1). This discrepancy was primarily attributed to agricultural activities. The results indicate that using a comprehensive feature set and the random forest algorithm is a reliable approach for estimating the spatial distribution of the SOC content in forested areas and is suitable for forest ecology and carbon management studies.

Soil buffering capacity enhances maize yield resilience amidst climate perturbations

CONTEXTMaize production in China is facing a multitude of challenges such as climate change, increasing demand, and limited cropland availability. Soil properties, beyond supporting crop growth and development, can play a critical role in buffering the impacts of climate crisis on crop yields. However, little information is known about such buffering capacities and their spatial distributions of soil properties in buffering the impacts of climate perturbations on maize yields in China's maize belt (CMB). OBJECTIVEThe objective of this study was to identify the responses of different regions within the CMB to climate perturbations in terms of maize yields, as well as their spatial differences and magnitudes. Additionally, we aimed to quantify the capacities of soil properties in buffering the impacts of climate perturbations. METHODSWe quantified the impacts of climate perturbations (climate fluctuations deviating from the mean state) on maize yields using the APSIM across the China's maize belt. We then used the random forest model to interpret the buffering effects of typical soil properties to the adverse impacts of climate perturbations. RESULTS AND CONCLUSIONSOur results reveal that temperature variability was the predominant climatic perturbation affecting maize yields, with rising temperature leading to significant yield losses in most regions. Perturbations in solar radiation and precipitation exhibited relatively stronger positive yield impacts only in areas with inadequate solar radiation and dry conditions, respectively. Notably, soil properties explained ∼40% to ∼70% of the spatial variations for the impacts of climate perturbations. Soils with high soil organic carbon content (SOC) can significantly reduce the negative impacts of temperature increase, highlighting the crucial buffering effect of SOC in response to global warming. Soil texture, field capacity and bulk density were also critical soil buffering properties for interpreting the spatial patterns of the impacts of climate perturbations. SIGNIFICANCEOur results underscore the importance of soil quality improvement to ensure stable food production, which is an effective strategy for enhancing agricultural system resilience amidst future climate crises.

Selective uneven enrichment of soil organic carbon among different-sized sediments under a rain-induced overland flow: 13C stable isotope evidence

Soil organic carbon (SOC) enrichment varies among sediments of different sizes during rain-induced overland flow erosion. This selective transport of SOC is complex in conjunction with the exposure of labile and stable organic carbon (OC), accompanied by heterogeneous aggregate disintegration under raindrop effects. Utilizing the variations in δ13C values of SOC fractions, we traced this selective transport, linking it to aggregate-wrapped SOC changes during erosion. A modified soil pan facilitated the simultaneous monitoring of splash and sheet erosion via artificially simulated rainfall, with control over the intensity and slope. Aggregate composition, SOC distribution, and δ13C values in the erosion samples were analyzed. The results indicated that distinct sorting existed within the aggregate fragments. Along with SOC variation among different sediment sizes, the proportions of clay and fine silt within sediment aggregates increased as a function of slope and rainfall intensity, whereas particulate OC within aggregates decreased. The SOC enrichment ratios (ERocs) and δ13C values in splash-eroded sediments were positively correlated with those in sheet-eroded sediments. The ERocs in splash-eroded sediments were lower than those in sheet-eroded sediments, but δ13C values were the opposite. Moreover, δ13C values of SOC enriched in sediment particles of all sizes from aggregate stripping were lower than those of the original soil. This indicates that raindrop hits promote heavy C loss during sheet erosion, which is different for mineral-associated and particulate OC. As the slope and rainfall intensity increased, δ13C values for all sediment sizes decreased over the course of erosion. Interestingly, the highest δ13C values were observed under a rainfall intensity of 60 mm h−1, whereas the highest SOC concentrations were noted on a 5° slope. These observations suggest divergent mechanisms affect δ13C values and SOC concentrations in eroded sediments. All these results verified that selective sorting existed for the light SOC fraction. Finally, the internal selective transport of one SOC fraction may explain the enhanced mineralization and reaggregation capacity of the deposited sediments.

Addition of Exogenous Organic Ameliorants Mediates Soil Bacteriome and Microbial Community Carbon Source Utilization Pattern in Coastal Saline–Alkaline Soil

Knowledge regarding how abiotic and biotic environmental factors operate in soil microbiome reassembly remains rudimentary in coastal saline–alkaline soils amended by different organic ameliorants. In this study, field trials were conducted to investigate the impacts and underlying mechanisms of sewage sludge (S) and sludge-based vermicompost (V) at the application amounts of 0, 50, and 100 t ha−1 on soil physicochemical characteristics, carbon source utilization pattern, and bacteriome in coastal saline–alkaline soils. Results revealed that impacts of the organic ameliorants on soil’s physicochemical and microbial attributes were highly dependent upon the carbon types and amounts applied. Unsurprisingly, applying sewage sludge and vermicompost significantly alleviated environmental constraints, such as saline–alkaline stress and nutrient deficiency, with lower pH, salinity, and higher soil organic carbon content observed in organics-amended soils. Specifically, higher microbial substrate metabolic activity, but lower diversity was observed in saline–alkaline soils amended by organic ameliorants. In addition, reassembled bacteriomes harboring distinguishable core and unique community profiles were observed in reclaimed soils as compared to unamended saline–alkaline soil. Procrustes analysis showed that the soil microbial utilization pattern of carbon sources was significantly related to the alterations in their physicochemical property and bacterial core microbiome. Additionally, Redundancy Analysis (RDA) revealed that soil core bacteriome reassembly was dominated by the integrated impacts of soil salinity, successively followed by carbohydrates, amino acids, polymers, pH, soil organic carbon (SOC), and available nitrogen (AN). Overall, this study provides a comprehensive understanding of soil abiotic and biotic determinants in bacteriome assembly in coastal saline–alkaline soil remediation mediated by organic ameliorants.

Short-term effects of brassica cover crops on soil quality indicators in organic production in high tunnels

The use of cover crops is aimed at sustaining soil health and productivity in the context of agricultural intensification and accompanying soil degradation. While cover crops have been extensively studied in field production systems, limited research has been conducted concerning their application in high-tunnel vegetable production. This study aimed to assess the effects of turnip (Brassica napus subsp. napobrassica (L.) Jafri) and swede Brassica rapa subsp. Rapifera Metzg) cover crops (CCs) on soil physicochemical and biological properties in an organic high tunnel system in southern Poland in 2017–2019. The planting sequence was as follows: winter cover crops/pumpkin/romaine lettuce/broad bean/chilli pepper. Soil analyses included measurements of bulk density, water capacity, soil aggregation, soil organic carbon (SOC), available soil nutrients, as well as microbial abundance and diversity. Rape crops produced a higher aboveground dry biomass (4.11 t ha−1) than swede (2.85 t ha−1), and the N content in their biomass was 101 kg N ha−1 and 75 kg N ha−1, respectively. The results presented that CC residue significantly contributed to soil organic carbon stock, retention of plant-available nitrogen, and improvement of soil physical properties, especially wet aggregate stability. Soils with the highest SOC concentrations were associated with the highest bacterial and fungal abundance. The most significant number of mesophilic bacteria was detected in the soil where turnip was grown as a cover crop (7.6 × 107 cfu g−1 DM soil). Moreover, a higher abundance of the tested nitrogen cycle bacteria was found in the soils after CC cultivation compared to the control soils, particularly bacteria reducing NH4 +-N and NO₃⁻-N. These findings highlight the importance of cover crop management practices in high tunnels, as they influence the composition of the total bacterial community and the abundance of N-cycling microbial guilds.

Carbon Storage Potential of Soil in Diverse Terrestrial Ecosystems

Soil is one of the largest carbon reservoirs sequestering more carbon than vegetation and atmosphere. Due to the enormous potential of soil to sequester atmospheric CO2, it becomes a feasible option to alleviate the current and impending effects of changing climate. Soil is a vulnerable resource globally because it is highly susceptible to global environmental problems such as land degradation, biodiversity loss, and climate change. Therefore, protecting and monitoring worldwide soil carbon pools is a complicated challenge. Soil organic carbon (SOC) is a vital factor affecting soil health since it is a major component of SOM and contributes to food production. This review attempts to summarize the information on carbon sequestration, storage, and carbon pools in the major terrestrial ecosystems and underpin soil carbon responses under climate change and mitigation strategies. Topography, pedogenic, and climatic factors mainly affect carbon input and stabilization. Humid conditions and low temperature favor high soil organic carbon content. Whereas warmer and drier regions have low SOC stocks. Tropical peatlands and mangrove ecosystems have the highest SOC stock. The soil of drylands stores 95% of the global Soil Inorganic Carbon (SIC) stock. Grasslands include rangelands, shrublands, pasturelands, and croplands. They hold about 1/5th of the world’s total soil carbon stocks.

The deep soil water dynamics and its environmental controls after long-term revegetation

The increase in the extreme drought trend, reduction in soil erosion, and acceleration of deep soil desiccation are renewing interests in soil water dynamics and its environmental controls after long-term (>30 years) grass and shrub revegetation on the Chinese Loess Plateau (CLP). However, inconsistent findings have been reported on soil water dynamics in these typical land uses due to the multi-dependent environmental controls. The objectives of this study are to identify the spatial variability of soil water dynamics and its controls in a small watershed. For this purpose, spatiotemporal soil water storage in 1 m interval to a depth of 5 m was decomposed into a temporal mean (i.e., time-stable pattern) and temporal anomaly (Atn), which varies over time and is related to soil water dynamics. Atn was then decomposed into a space-invariant temporal anomaly (i.e., spatial mean of Atn) and a space-variant temporal anomaly (Rtn), which reflects the spatial variability of soil water dynamics. The Rtn was further decomposed using the empirical orthogonal function (EOF) to identify its major controls. Results showed that soil water dynamics (gain and loss) decreased from grassland to abandoned cropland followed by shrubland after long-term revegetation. The hot spots in deep soil water dynamics (2–5 m) were identified in layered soils with an overlying sand layer and underlying silt layer, and grassland with the coexistence of tree-shrub-grass and high deep soil organic carbon (SOC) content. 50–70% of the total variations of Rtn were explained by the first two spatial patterns (EOFs). Silt and SOC content controlled EOF1 of Rtn at 0–2 and 2–5 m, respectively. Plant canopy and soil profile properties (e.g., layered soils with an overlying sand layer and underlying silt layer) controlled EOF2 of Rtn at 0–1 and 2–5 m, respectively. The EOF analysis suggests that silt and SOC dominated soil water storage capacity, plant canopy regulated water flux, and variations of hydraulic properties in soil profiles may jointly drive spatial variability of soil water dynamics.

A global insight on sensitivity of nitrate leaching to drainage in arable cropping systems

Nitrate (NO3–) leaching leads to widespread deterioration of water quality. NO3– leaching can be regulated by both biochemical and hydrological processes. However, the extent to which drainage accounts for the variation in NO3– leaching and the sensitivity of NO3– leaching to drainage remain unclear, particularly at the global scale. This raises uncertainties in prioritizing the regulation of hydrological (e.g., drainage) processes for reduced NO3– leaching. A global meta-analysis was conducted for arable cropping systems to test two hypotheses: (1) Global variations in NO3– leaching are explained more by drainage and associated influencing factors (e.g., water input); (2) NO3– leaching is more sensitive to the changes in drainage under conditions with lower risks of preferential flow. In this meta-analysis, the average NO3– leaching loss from arable cropping systems was 22.2 kg N ha−1 year−1. Water input, followed by N input, were the most influential in explaining global variations in NO3– leaching. Compared with NO3– concentration, drainage and associated influencing factors explained more of the global variations in NO3– leaching losses. NO3– leaching was more sensitive to drainage in soils with finer texture and higher soil organic carbon content, in regions with low to medium mean annual temperature (<15 ℃) and medium mean annual precipitation (600–1000 mm), where water input during the measurement period was low (<2 mm day−1), nitrogen fertilizer rates were high (>200 kg N ha−1), and where conservation tillage systems (no-tillage or non-inversion tillage) were adopted. Therefore, more attention should be given to avoiding excessive water application in soils characterized by low risk of preferential flow. Preferential flow reduces the chance for drainage water to interact with NO3– in the soil matrix, particularly in areas with high N inputs. While this study has successfully tested our hypotheses, it further highlights the importance of water input management for mitigating global NO3– leaching risks, particularly under environments and changing climate conditions more conducive to drainage events.

Soil organic carbon changes under selected agroforestry cocoa systems in Ghana

Given the pressing issue of climate change, there is a clear need for long-term and reliable soil organic carbon (SOC) data. This data should be complemented by insights into agricultural management practices, with a particular emphasis on agroforestry systems. Unfortunately, such comprehensive data remains in short supply. We report SOC and bulk density changes in the soil (≤ 60 cm depth) of Ghanaian agroforestry cocoa systems sampled along a chronosequence of farm fields established 3, 15, 18, 30 and 45 years after forest conversion. Additionally, we assessed changes in SOC and bulk density from agroforestry cocoa systems fifteen years after similar data was collected from the same fields. The 45-year-old plot significantly had higher (p < 0.05) SOC concentration, comparable to the pre-conversion forest. Cocoa trees aged 18 and above had higher SOC concentrations than the forest at the 20–60 cm depth. The SOC stocks initially declined by 18% (12 Mg ha−1) after forest conversion in the three-year-old cocoa farm but increased considerably thereafter to 121 Mg C ha−1 after 45 years of cocoa production. The 45-year-old cocoa plantation had more than twice the SOC stocks observed in the forest at the 20–60 cm depth. A 15-year period comparison of agroforestry cocoa systems revealed proportional increases in SOC stocks, with the exception of minor declines observed within specific age groups at the 0–10 cm depth. Mean bulk densities did not exceed the critical value of 1.6 g cm−3 above soil conditions considered unsuitable for plant growth. Soil bulk densities generally increased with depth, and agroforestry cocoa systems had significantly (p < 0.05) denser soils compared to the forest. Our study provides compelling long-term empirical evidence emphasizing the importance of agroforestry cocoa systems on SOC storage and reinforces their role as a sustainable and climate-smart approach to agriculture.

Improved thermal conductivity parameterization of SHAW model in permafrost regions on the Qinghai-Tibet Plateau

Soil thermal conductivity is critical for determining the hydrological and energy transfer processes in permafrost regions and simulating hydrological and thermal dynamic processes with land surface models. In this study, improved thermal conductivity parameterizations of the Simultaneous Heat and Water model (SHAW) were assessed using observation data from permafrost regions on the Qinghai-Tibet Plateau (QTP). The results indicated that the SHAW could precisely describe soil hydrological and thermal processes at the Tanggula (TGL) site. In general, the performances of Johansen's, Luo's, and the ORCHIDEE-MICT model's soil organic matter (SOM) parameterizations were superior to the original De Vries's parameterization. The SOM parameterization performed the best. The root mean square error (RMSE) of the active layer's soil temperature was 0.42 °C lower than that of the original parameterization at the Xidatan (XDT) site and 0.2 °C lower at the TGL site. In particular, the RMSE of the soil temperature at 3 m depth at TGL was 0.8 °C lower than that of the original parameterization. The average Nash-Sutcliffe Efficiency (NSE) for simulating the active layer soil temperature using the SOM parameterization was 0.915 at TGL site and 0.806 at XDT site. While De Vries parameterization yielded average NSE values of 0.771 and 0.627 for soil temperature simulations at the two sites, respectively. The results indicate that the soil organic carbon cannot be ignored in the simulation of hydrological and thermal processes in permafrost areas with a high soil organic carbon content. Notably, the simulated soil temperatures during the freezing period and the soil liquid water content during the thawing period improved significantly after modifying the thermal conductivity parameterization of SHAW. Therefore, the revised SHAW more accurately reflects the water and heat transfer processes of permafrost and can be used to analyze land-atmosphere interactions.