Surface Soil Layer Research Articles

Machine learning soil-environmental impacts on agroecosystems for relating microbial biomass to soil carbon sequestration

Background and AimsStoring carbon (C) within soils is significant for maintaining soil-health and reinforces the feedback loop of C loss from soils as CO2 to the atmosphere. Seasonal variation with increased temperatures and inconsistent precipitation as climate change consequences also affect the soil C-sequestration process globally. Soil-health management practices (SHMPs) such as cover crops, crop residues and manures increase organic components as well as soil-organic C (SOC) pool in an agroecosystem. While, soil microbial-biomass (SMB) which is considered as a soil-health metric to understand microbial community response, is still not modelled to relate with SOC and seasonal impacts to identify suitable SHMPs. MethodsCover crops followed by 100% residue addition and combinations of manure +organic-fertilizer were the SHMPs for a winter-wheat system in our field study. Seasonal data regarding SOC, nitrogen, SMB-C and labile-C content of soils were used to machine-learn the system and understand the influence of different drivers on SMB-C. ResultsThe test models based on ‘Multivariate Linear Regression’ could explain 70% of the variability and predicted seasonal-variation as a dominant variant followed by SHMPs and soil-moisture. AdaBoost and Random Forest Models performed better than others if ‘Ensemble Learning’ was used. ‘Feature Importance’ predicted labile-C and aboveground-biomass as the two most important drivers impacting SMB-C. ConclusionsEnsemble Learning’ method of Machine-Learning could be successfully implied to understand the SMB-C in an agroecosystem and set benchmark-strategies for soil-health improvement. 50% manure+ 50% fertilizer with crop-residue could be recommended for maximum labile-C and SOC in surface soil-layers.

Soil warming decreased dissolved organic carbon quantity and quality in subtropical forests.

Soil dissolved organic carbon (DOC) is the most active part in forest soil carbon pool, the responses of which to climate warming has profound effects on forest carbon cycling. Based on a manipulative soil warming experiment in subtropical evergreen broad-leaved forests, we collected soil solutions in situ and used ultraviolet-visible, infrared and three-dimensional fluorescence spectroscopy analyses to explore the effects of soil warming (+4 ℃, 1 year) on soil DOC quantity and quality along the soil profile. The results showed that soil DOC flux remained constant along the soil profile. Soil DOC mainly included two humic-like fractions and one microbial metabolite. Warming significantly decreased soil DOC flux and the abundance of aromatic and hydrophobic components, and increased the amount of low molecular weight carbohydrates. Furthermore, soil warming increased the relative proportion of humic-like fractions in the surface soil layer (0-10 cm) and microbial metabolite in the deep soil layer (30-40 cm), indicating that warming might accelerate microbial turnover in the deep layer. Overall, soil warming not only decreased soil DOC content, but also simplified the composition of soil DOC in subtropical evergreen broad-leaved forests.

Behavior of Pile Group Constructed on Clayey Soil under El-Centro Seismic

Over the past decades, pile foundations used to support buildings through a transfer of superstructure loads into more stable soil strata than surface soil layers. Buildings are exposed to seismic force, pile undergoes more stress through the significant vibration of the surrounding soil in addition to the static stresses of buildings. The investigation of the behavior of pile foundations under the influence of earthquakes is still limited or not well described. Further, this paper presents a theoretical study to evaluate the vertical settlement and horizontal displacement of piles embedded in clay and silty soil of Baqubah soil under the effect of the acceleration time history of the 1940 El-Centro earthquake. The study was carried out by using the commercial finite element software PLAXIS 3D. A three-dimensional analysis of the soil-pile foundation for four multi-story buildings is performed with different diameters (0.5, 0.7, and 1) m for the corner, exterior, and interior pile, respectively. The linear elastic model for pile foundation and the Mohr-Coulomb model for soil layers were used in this numerical analysis. The research showed that vertical settlement and horizontal displacement increase as the duration of the earthquake increases, and horizontal displacement with values smaller than vertical displacement. Also, the results showed the vertical settlement is similar for different diameters, in contrast to the horizontal displacement, which was of different values with a range between (3% to 22%) when the diameter increased from 0.5m, 0.7m, and 1m. Also, it can be observed that values increased with the direction of the earthquake from the right to the left side of the pile-soil system with a range of (12% to 32%).

Long-term tillage and irrigation effects on aggregation and soil organic carbon stabilization mechanisms

Sustainable soil management practices are required in agriculture to enhance carbon sequestration and restore soil functions. Here, the aim was to investigate the effect of different tillage practices combined with or without irrigation on (i) soil organic carbon (SOC) content, (ii) fungal biomass and their relationships with aggregate size classes in the soil surface layer; further, (iii) the concept of soil particle saturation with SOC was tested to evaluate if a threshold was reached in a 14 year-experiment. Our hypothesis was that long-term irrigation, intensive tillage and their combination, would negatively affect soil aggregation and SOC stabilization. The experiment has started in 2003 on a research farm in Canterbury, New Zealand. The present work focused on two contrasting tillage practices –intensive tillage with 20–25 cm ploughing (IT) and direct drill (DD)– combined with sprinkler-irrigated and non-irrigated (hereafter called Rainfed) conditions in a split-plot experimental design. Soil samples (0–5 cm layer) were analyzed for pore size distribution, specific surface area and microbial biomass. Further, wet sieving was used to isolate large macroaggregates (LM, > 2000 μm), small macroaggregates (SM, 250–2000 μm), microaggregates (m, 53–250 μm), particle sized silt + clay fractions (s+c, < 53 μm) and Fine20 particles (<20 μm), followed by the analysis of aggregate morphology and SOC quantification in them. Results showed that both DD and Rainfed management increased total SOC content of the bulk soil. Only the LM fraction and the SOC therein (OC-LM) increased significantly in DD compared to IT, while m and s+c fractions and OC-m and OC-s+c did not differ between treatments. Macroaggregate breakdown processes and measured SOC therein had likely not reached steady-state conditions, as suggested by the lack of any SOC differences in the aggregate size classes < 250 µm. In contrast, the Fines20:SOC ratio differentiated between soils that had reached (i.e., DD) or not reached (i.e., IT) the saturation threshold. Finally, it was observed that a higher fungal:bacteria (F:B) ratio was generally accompanied by a greater LM fraction and mean weight aggregate diameter, highlighting the importance of fungi in the formation of LM. These results suggested that our hypothesis of detrimental effects on soil aggregation and SOC accumulation of both tillage and irrigation was not fully demonstrated yet. A longer study period would be required to better understand the effects of such practices of SOC storage.

Grazing Regulates Changes in Soil Microbial Communities in Plant-Soil Systems

Soil microorganisms promote material transformation and energy flow in the entire ecological environment and play a key role in the stability and development of grassland ecosystems. Studies on the impacts of grazing on the soil microbial community and the establishment of a reasonable grazing intensity are crucial to improve our knowledge of the mechanisms underlying grassland degradation and to accurately assess the influence of grazing management on grassland functions and the nutrient cycle. Based on the grassland grazing control experimental platform, we compared the structure and diversity characteristics of soil microbial communities under six grazing intensities (0.00, 0.23, 0.34, 0.46, 0.69, and 0.92 AU ha−1) (1 AU = 500 kg of adult cattle) on the Hulunbuir Leymus chinensis meadow steppe. The results showed that soil microbial biomass carbon (MBC) and nitrogen (MBN) decreased with increasing soil depth. The 0–10 cm soil layer of G0.34 had the highest MBC and MBN, and the G0.92 treatment had the lowest MBC and MBN. Heavy grazing significantly decreased the MBC and MBN contents in the soil surface layer. The soil bacterial diversity under light grazing treatment (0.23 AU ha−1) was higher than that under heavy grazing, and the fungal diversity under the no-grazing treatment was higher than that under the grazing treatment. Overgrazing reduced the bacterial species in the soil. The plant belowground biomass significantly (p = 0.039) influenced the bacterial community structure, and the soil pH (p = 0.032), total nitrogen (p = 0.011), and litter (p = 0.007) significantly influenced the fungal community. The effects of grazing on microbial communities were primarily driven by vegetation productivity, litter mass, and soil geophysical and chemical characteristics. This study deepened our understanding of the impacts of grazing practices on soil microbial communities on the meadow steppe, suggesting that moderate-disturbance grazing can promote the sustainable development of grassland vegetation-soil microorganisms.

The role of conventional tillage in agricultural soil erosion

Conventional tillage refers to the tillage process, especially the spring and autumn plowing process in which all the soil surface layer is disturbed, generally tilling approximately 20 cm deep. Conventional tillage is still widely used in sloping land, which leads to serious soil erosion and land degradation. The effect of tillage on soil erosion is defined by Tillage factor (T) in the model. The purpose of this study is to analyze the effect of conventional tillage on soil erosion and to calculate the value of the conventional tillage Factor T. The values of the conventional tillage factor (T value) were calculated for different soil and water conservation zones in China by collecting published literature and plot measurements from unpublished monitoring sites. The results showed that (1) the tillage factors of conventional tillage in China ranged from 0.27 to 0.55, with the largest being the North earth-stony region, the smallest being the Qinghai-Tibet plateau region, and the other six regions, namely, the Northeastern mollisol, the Northern wind erosion, the Northwest Loess Plateau, the South red soil, the Southwestern purple soil and the Southwestern karst region, were 0.34, 0.28, 0.53, 0.37, 0.35 and 0.29, respectively. In the regional soil erosion evaluation, the values can be taken by each of the eight main erosion type regions. (2) In the water erosion area except for the northeast, there is an obvious northsouth difference in the distribution of the T value, showing a decreasing trend from north to south. In practical use, the T value of the corresponding latitude area can be determined according to the Equation T = 0.2351φ- 0.02225, where φ is the latitude (°). (3) The T values of contour tillage, no-till, and monopoly tillage measures are significantly lower than the T values of conventional tillage, which have significant soil and water conservation benefits. The study initially determined the conventional tillage T values for each water conservation subzone, which can provide basic parameters for soil loss prediction on sloping land.

Establishing Critical Leaf Nutrient Concentrations and Identification of Yield Limiting Nutrients for Precise Nutrient Prescriptions of Oil Palm (Elaeis guineensis Jacq) Plantations

African oil palm (Elaeis guineensis Jacq.) is a bulk feeder of nutrients. In this study, we aimed at devising strategies for efficient nutrient management in the oil palm plantations of the Krishna River basin located in Andhra Pradesh, India by assessing soil fertility status, establishing optimal leaf nutrient concentrations and identifying yield restrictive nutrients. In total, 67 oil palm plantations were surveyed from this area in 2020, soil samples were collected and analysed for different soil properties, including pH, EC, SOC, available P, K, S, exchangeable Ca and Mg, and hot water-soluble boron (HWB) in surface (from 0–20 cm depth), subsurface (from 20–40 cm depth) and deep (from 40–60 cm depth) soil layers. As per DRIS (Diagnosis and Recommendation Integrated System) indices estimated in this study, the order of requirement of nutrients is Nitrogen (N) &gt; B &gt; K &gt; P &gt; Mg for this area. Optimum leaf nutrient concentrations ranged between 2.07–4.29%, 0.13–0.27%, 0.52–0.94%, 0.44–0.76% and 44.97–102.70 mg/kg for N, P, K, Mg and B, respectively. In surveyed plantations, about 15, 6, 16, 9 and 12 percent of leaf samples had less than optimum concentration of N, P, K, Mg and B respectively. Nitrogen and Boron are the major yield limiting factors in this region. Leaf nutrient concentrations need to be maintained at the optimum ranges as estimated above for higher productivity in the Krishna basin area.

Latitudinal and Altitudinal Patterns and Influencing Factors of Soil Humus Carbon in the Low-Latitude Plateau Regions

The composition of forest soil organic matter is an important part of the global carbon cycle, which is effective by temperature and moisture. As we all know, the temperature and moisture in the low-latitude plateau regions are very sensitive to changes in latitude and altitude. However, the composition of soil organic matter response to changes in latitude and altitude in the low-latitude plateau regions is unknown. In this study, the effects of latitude (21–29° N) and altitude (500–4000 m) on soil organic carbon (SOC) and humic acid carbon (HAC), fulvic acid carbon (FAC), and humin carbon (HMC) in forest surface soil (0–10 cm) were investigated. The results showed that the contents of soil organic carbon and humus increased with the increase in altitude and latitude. The effect of altitude on the composition of organic matter was significant only at 23° N to 25° N. The composition of organic matter is not only regulated by mean annual temperature (MAT) and soil moisture content (SMC) but also affected by soil pH, carbon to nitrogen ratio (C/N), and powder. The soil surface layer (0–10 cm) carbon sequestration capacity in high-latitude and high-altitude areas is stronger than that in low-latitude and low-altitude areas. As a consequence, in today’s response to global climate change, the high carbon sequestration capacity of high latitude and high altitude areas should be given attention and protection.

Vertical organization of microbial communities in Salineta hypersaline wetland, Spain.

Microbial communities inhabiting hypersaline wetlands, well adapted to the environmental fluctuations due to flooding and desiccation events, play a key role in the biogeochemical cycles, ensuring ecosystem service. To better understand the ecosystem functioning, we studied soil microbial communities of Salineta wetland (NE Spain) in dry and wet seasons in three different landscape stations representing situations characteristic of ephemeral saline lakes: S1 soil usually submerged, S2 soil intermittently flooded, and S3 soil with halophytes. Microbial community composition was determined according to different redox layers by 16S rRNA gene barcoding. We observed reversed redox gradient, negative at the surface and positive in depth, which was identified by PERMANOVA as the main factor explaining microbial distribution. The Pseudomonadota, Gemmatimonadota, Bacteroidota, Desulfobacterota, and Halobacteriota phyla were dominant in all stations. Linear discriminant analysis effect size (LEfSe) revealed that the upper soil surface layer was characterized by the predominance of operational taxonomic units (OTUs) affiliated to strictly or facultative anaerobic halophilic bacteria and archaea while the subsurface soil layer was dominated by an OTU affiliated to Roseibaca, an aerobic alkali-tolerant bacterium. In addition, the potential functional capabilities, inferred by PICRUSt2 analysis, involved in carbon, nitrogen, and sulfur cycles were similar in all samples, irrespective of the redox stratification, suggesting functional redundancy. Our findings show microbial community changes according to water flooding conditions, which represent useful information for biomonitoring and management of these wetlands whose extreme aridity and salinity conditions are exposed to irreversible changes due to human activities.

Soil Organic Matter and Nutrient Levels in Outdoor Runs in Organic Laying Farms.

To evaluate the nutrient load due to the grazing of laying hens in outdoor runs, monitoring of soil characteristics was conducted in three Italian organic farms. For each farm, soil samples were taken from three increasing distances from the hen house and two depths, and different chemical parameters were evaluated. The comparison among the results from the different distances shows that N-NO3 and Olsen P are the most affected parameters by hen feces: both present high values with a statistically significant difference in the area close to the poultry house and for the most superficial layer. Even TKN and TOC show significant differences between the concentrations of the first layer (more concentrated) and those of the second layer (less concentrated). In general, the surface soil layer closest to the chicken house is the portion of the outdoor run most affected by chicken droppings and represents the most critical point in terms of potential environmental impact. Therefore, it is necessary to intensify the management of the outdoor run with tools that can facilitate the grazing of animals and with vegetation that can absorb nutrients by limiting leaching and runoff.

Potassium Simulation Using HYDRUS-1D with Satellite-Derived Meteorological Data under Boro Rice Cultivation

Potassium (K) is a critical nutrient for crops, as it is a major constituent in fertilizer formulations. With increasing concentrations of K in agricultural soil, it is necessary to understand its movement and retention in the soil. Sub-surface modeling is an alternative method to overcome the exhausting and uneconomical methods to study and determine the actual concentration of K in soil. HYDRUS-1D is considered an effective finite-element model which is suitable for sub-surface modeling. This model requires the input of ground-station meteorological (GM) data taken at a daily timestep for the simulation period. It can be a limiting factor in the absence of ground stations. The study compares K predictions in surface and sub-surface soil layers under Boro rice cultivation obtained with the usage of different meteorological datasets. Thus, the main hypothesis of the study was to validate that, in the absence of GM data, satellite-based meteorological data could be utilized for simulating the K concentration in soil. The two meteorological datasets that are considered in the study included the GM and satellite-derived NASA-Power (NP) meteorological datasets. The usage of a satellite meteorological product at a field scale may help in applying the method to other regions where GM data is not available. The numerical model results were validated with field experiments from four experimental fields which included varied K doses. The concentration in soil was assessed at the regular depths (0–5, 5–10, 10–15, 15–30, 30–45 and 45–60 cm), and at various stages of crop growth, from bare soil and sowing, to the tillering stages. The concentration of K was measured in the laboratory and also simulated through the optimized model. The modeled values were compared with measured values statistically using relative root mean square error (RMSER) and Nash–Sutcliffe modeling efficiency (E) for simulating K concentration in the soil for the Boro rice cropping pattern with both GM data and NP data. The model was found most suitable for the 0–30 cm depth on all days and for all treatment variations.

Zeolite as a Tool to Recycle Nitrogen and Phosphorus in Paddy Fields under Straw Returning Conditions

Excess nitrogen (N) caused by straw returning to paddy fields undergoing flooding irrigation deteriorates the water quality. The purpose of this research was to use both simulated field and pot experiments to explore a new approach using zeolite to recycle this excess N. The results from simulated field experiments in stagnant water showed N adsorption with different zeolite applications (25, 50, 75, 100, 125, and 150 g L−1). Pot experiments revealed how straw and reused zeolite applications affected the concentrations of ammonia N (NH4+-N), nitrate N (NO3−-N), total N (TN), and total phosphorus (TP) in the surface water and soil layers of the paddy field. Zeolite showed a strong ability to adsorb NH4+-N in wastewater, even in a simulated drainage ditch (100 g L−1 zeolite adsorbed 74% NH4+-N). The zeolite recycled from the drainage ditch was still able to reduce N concentration caused by straw decomposition in the surface water. Zeolite adsorption reduced the peak values of NH4+-N, TN, and TP by 30%, 19%, and 5%, respectively. Based on these findings and conventional field designs, the use of 20 t ha−1 zeolite in the field is effective for recycling N and P. This research provides a sustainable development method to mitigate the water quality deterioration caused by straw returning to the field.

Soil depth as a driver of microbial and carbon dynamics in a planted forest (Pinus radiata) pumice soil

Abstract. Forest soils are fundamental in regulating the global carbon (C) cycle; their capacity to accumulate large stores of C means they form a vital role in mitigating the effects of climate change. Understanding the processes that regulate forest soil C dynamics and stabilisation is important to maximise the capacity and longevity of C sequestration. Compared with surface soil layers, little is known about soil C dynamics in subsoil layers, sensu those below 30 cm depth. This knowledge gap creates large uncertainties when estimating the distribution of global soil C stocks and assessing the vulnerability of soil C reserves to climate change. This study aimed to dive deep into the subsoils of Puruki Experimental Forest (New Zealand) and characterise the changes in soil C dynamics and the soil microbiome down to 1 m soil depth. ITS and 16S rRNA sequencing and quantitative real-time PCR were used to measure changes in soil microbial diversity, composition, and abundance. Stable (δ13C) and radioactive (14C) C analyses were performed to assess depth-driven changes in the stability and age of soil C. Our research identified large declines in microbial diversity and abundance with soil depth, alongside significant structural shifts in community membership. Importantly, we conservatively estimate that more than 35 % of soil C stocks are present in subsoil layers below 30 cm. Although the age of soil C steadily increased with depth, reaching a mean radiocarbon age of 1571 yr BP (years before present) in the deepest soil layers, the stability of soil C varied between different subsoil depth increments. These research findings highlight the importance of quantifying subsoil C stocks for accurate C accounting. By performing a broad range of analytical measures, this research has comprehensively characterised the abiotic and biotic properties of a subsoil environment – a frequently understudied but significant component of forest ecosystems.

Spatiotemporal evolution of global long-term patterns of soil moisture

Surface soil moisture (SM) is essential for existence of biotic lifeform and geophysical processes. However, with increasing global warming due to climatic changes, its spatiotemporal evolution is uncertain and largely unknown. In this study we detected long-term (40 years; 1981–2020) SM patterns of global vegetated areas through spatial timeseries clustering using the state-of-the-art ERA5-Land dataset. In addition, we also analyzed long-term patterns of precipitation (P), evapotranspiration (bare soil evaporation (BSe) and vegetation transpiration (VT)), and normalized difference vegetation index (NDVI). Our results indicate that surface SM (0–7 cm depth) of about 48 % and 9 % of the global vegetated area is showing drying and wetting pattern over the past 40 years, respectively. The detected soil drying, and wetting patterns were largely consistent across different soil depth, with 90 % and 80 % pattern similarity of surface soil layer with 2nd soil layer (7–28 cm) and 3rd soil layer (28–100 cm), respectively. About 80 % of areas with drying soil pattern also showed increasing evapotranspiration and/or decreasing precipitation. Specifically, decreasing P, increasing BSe and VT pattern were detected for 11 % of the soil drying pattern area. Similarly, increasing BSe and VT pattern, only decreasing P and only increasing VT pattern were detected for 17 %, 25 % and 12 % of soil drying areas, respectively. Both decreasing precipitation and increasing evapotranspiration patterns showed about 40 % similarity with decreasing soil moisture patterns. Across different landcover types, broadleaved forests, and cropland areas showed largest drying pattern. Under the future global warming scenario, the global soil water is expected to decrease as evapotranspiration would increase with inconsistent trend of global precipitation change. Our findings are of utmost importance for global soil water resource conservation and management.

Linkages between the molecular composition of dissolved organic matter and soil microbial community in a boreal forest during freeze-thaw cycles.

Soil dissolved organic matter (DOM) plays a vital role in biogeochemical processes. Global warming leads to increased freeze-thaw cycles (FTCs) in boreal forest soils, which can change DOM production and consumption. However, the interactions between the chemical composition of DOM molecules and the microbial communities that drive C decomposition in the context of freeze-thaw are poorly understood. Here, a FTCs incubation experiment was conducted. Combined with pyrolysis gas chromatography-mass spectrometry and high-throughput sequencing techniques, the relationships between DOM chemodiversity and microbial community structure were assessed. Results indicated that both low-frequency (2FTCs) and high-frequency freeze-thaw cycles (6FTCs) significantly increased soil dissolved organic carbon (DOC) contents in the surface (0-10 cm) and subsurface (50-60 cm) soil layers. In the topsoil, FTCs significantly reduced the relative abundance of aromatic compounds, but increased the relative proportions of alkanes, phenols, fatty acid methyl esters (Me) and polysaccharides in the DOM. In the subsuface soil layer, only the relative abundance of Me in the 6FTCs treatment increased significantly. The response of bacterial communities to FTCs was more sensitive than that of fungi, among which only the relative abundance of Gammaproteobacteria increased by FTCs. Moreover, the relative abundance of these taxa was positively correlated with the increment of DOC. Co-occurrence networks confirmed DOM-bacterial interactions, implying that specific microorganisms degrade specific substrates. At class level, Gammaproteobacteria were significantly positively correlated with labile C (polysaccharides and alkanes), whereas other bacterial classes such as Actinobacteria, Alphaproteobacteria, and Thermoleophilia were significantly positively correlated with aromatic compounds in the topsoil. Collectively, FTCs tended to activate DOM and enhance its biodegradability of DOM, potentially hampering DOC accumulation and C sequestration. These findings highlight the potential of DOM molecular mechanisms to regulate the functional states of soil bacterial communities under increased FTCs.

Productivity and Quality Sugarcane Broth at Different Soil Management

The quality of sugarcane broth can be affected by soil management. In compacted soils the productivity is reduced, and the raw material is poor. This research aimed to evaluate productivity and quality of sugarcane for four soil management types: (CT) heavy harrow + light harrow; (CTI) Subsoiler + light harrow; (MT) Subsoiler and (NT) no soil movement. The variables investigated were resistance to soil penetration (SPR), the chemical raw material quality (broth) and crop yield. In crop rows, SPR did not reach severe levels up to 0.3 m for sugarcane root development. However, below this layer, MT, NT, and CTI reached SPR limiting values of 2.50, 2.35 and 1.95 MPa, respectively. In inter-crop rows, compaction was concentrated in soil surface layers (0–0.3 m). In addition, all adopted managements presented SPR above the critical value (2 MPa). The soil preparation forms qualitatively affected the sugarcane broth, showing higher fiber and protein contents in NT, MT, and CT. The PS, Brix, TRS, and Pol were not affected by soil management. Still, higher absolute values were found in the NT, indicating an increase in broth quality when applying conservation management. The highest yields were obtained by reduced tillage (MT), surpassing the lowest yield management (NT) with an increase of 10.5 Mg ha−1.

Analysis of soil water potential characteristics of wheat croplands and apple orchards in an agroforestry ecosystem based on the van Genuchten model

Due to intense droughts and water shortages, soil water deficit limits agricultural production in arid and semiarid areas, such as China’s Loess Plateau region. Yet the effects of different cover crops on soil water in these areas have received insufficient attention. This study was conducted in the Weibei rainfed highland to investigate soil water potential dynamics in an agroforestry ecosystem comprising winter wheat (<i>Triticum aestivum</i> L.) and apple (<i>Malus domestica</i>) trees over the apple growth period (March to September of 2020). Soil water characteristic curves (SWCCs) of cropland topsoil (0 to 40 cm), orchard topsoil (0 to 40 cm), dark loessial subsoil (40 to 80 cm), and loess parent material (80 to 150 cm) were determined using the centrifuge method and water vapor equilibrium method. The van Genuchten model was used to fit SWCCs and then convert volumetric soil water content monitored in field plots to soil water potential. A quantitative analysis was conducted to evaluate soil water stress in wheat croplands and apple orchards. The model performed well in fitting SWCCs for all tested soils, yielding a robust accuracy (<i>R</i>² &gt; 0.96). Compared to apple trees, wheat was more threatened by drought. From mid-March to early July, the 0 to 100 cm soil layers of croplands all exhibited high water stress with matric suction pF &gt; 3.98, and unavailable water occurred in the 0 to 20 cm and 0 to 80 cm soil layers in late March to late April and mid-May to mid-July, respectively. Drought threat in apple orchards increased with an increase in tree age. In young orchards (&lt;10 y), high water stress was found only in surface soil layers (0 to 20 cm) in mid-March to late April and late May to early July, which spread to a depth of 70 cm in early June to early July. In mature orchards (10 to 20 y), high water stress was similarly observed in the surface soil layers in mid-March to early May and late May to early July, which extended to the 80 cm depth in late May to early July. In old orchards (&gt;20 y), high water stress initially emerged in the surface soil layers in early April to mid-April and then reached the 70 cm depth in late May to mid-July, whereas unavailable water occurred in the 0 to 60 cm soil layers in mid-June to mid-July. The results indicated that soil water stress zones with low water potential were formed intermittently at different soil depths of apple orchards depending on tree age and growth stage. However, compared to wheat croplands, apple orchards were less influenced by drought stress, so that converting croplands to orchards could alleviate drought threats in the Weibei area.

Identification and Evolution of Soil Organic Carbon Density Caused by Coastal Rapid Siltation Based on Imaging Spectroscopy

This study aimed to investigate the feasibility of using imaging spectroscopy (IS) to predict soil organic carbon density (SOCD) either directly or indirectly through soil organic carbon (SOC). Three methods, partial least square regression (PLSR), support vector machine (SVM), and random forest (RF), were utilized to calibrate the models and map the SOCD. The results showed that direct prediction was better than indirect prediction and the best model SVM had high R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.94 and 0.93 for calibration and validation, respectively. The measured SOCD was mainly concentrated in the surface soil layer from 0 to 40 cm, and the deeper layer tended to be gentle. The continuous depth variation trend of SOCD in the topsoil (0-40 cm) was relatively close to the measured values, while in the deeper layers (below 40 cm), it was much higher than the measured values. The study also found that the best fitting function of measured SOC stocks over time varied from linear to power and then to logarithmic with increasing depth, indicating less efficient accumulation of SOC in deep soil compared to topsoil, resulting in an overall decrease in SOC accumulation rate across soil depth. The best temporal functions for the predicted values differed from the measured values at each depth, but the changing trends of the three functions were basically consistent. It suggests that IS technology has the potential to quantitatively reveal the process of coastal soil evolution and offers a new insight for the rapid monitoring of soil property changes.

Results of determining the agrotechnical indicators of a flat cutter for fine tillage

In modern conditions, most soils are exposed to erosion processes. In this regard, it is necessary to control the amount of dust particles in the surface layer of the soil. Fine tillage with flat-cutting working bodies solves this issue by creating a finely cloddy soil structure of the upper fertile layer. The article considers the developed original design of a flat cutter for fine tillage. The results of experimental studies on the determination of agrotechnical indicators for the treated background and untreated stubble background are presented. In the course of the research, such indicators were established as: the average actual working depth, the standard deviation of the working depth from the given one, the coefficient of variation in the working depth, crumbling of the soil by the working bodies, the moisture content inside the reservoir, the number of erosion-dangerous particles in the surface soil layer. As a result of the research, it was found that the flat cutter qualitatively performs the specified depth of tillage with an acceptable deviation, the ridge size is in the range of 3.6-3.9 cm, which is allowed by agrotechnical requirements, the number of lumps up to 25 mm in size after the passage of the working body is 82-85% . With shallow tillage with a flat cutter, the removal of wet layers to the soil surface is not observed. The flat cutter can function qualitatively on an untreated stubble background as part of a combined unit that is not equipped with disk working bodies.

三峡库区典型茶园土壤水分对不同降雨模式的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 三峡库区典型茶园土壤水分对不同降雨模式的响应 DOI: 10.5846/stxb202201240232 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（42077065）；国家自然科学基金项目（U224022） Response of soil moisture in typical tea gardens to different rainfall regimes in the Three Gorges Reservoir Area Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤水分是坡面产流和生物地球化学过程的关键控制因素。降水事件可以通过引起土壤剖面不同深度的土壤水分响应，从而影响流域中的径流路径、产流机制和土壤侵蚀过程等。基于三峡库区典型分布的茶园为对象，通过长期定点、高频的气象和水分数据观测，研究不同降雨模式下茶园不同土层深度（0-10、10-20、20-30、30-40cm）土壤水分的时空变化特征，分析茶园不同深度土壤在雨季的水分动态变化规律和对不同降雨模式的响应特征。结果表明：（1）研究区内的降雨和土壤水分含量均表现出明显的季节性特征。降雨在7月达到最大值，土壤水分含量则在8月达到峰值。表明降雨是影响土壤水分含量变化的重要因子，土壤水分对降雨有着明显的响应过程。（2）在相同降雨条件下，土壤含水量具有明显的垂直梯度变化。随着土层深度的增加，土壤水分对降雨的响应逐渐呈现出滞后现象。表层土壤（0-20cm）对降雨的响应较为迅速且幅度更加明显，深层土壤（30-40cm）水分含量变化相对稳定，并且对降雨的响应时间更加滞缓。随着土层深度的增加，土壤水分含量的变化幅度逐渐趋于平稳。（3）土壤水分含量对不同的降雨模式表现出显著差异。在较大雨强条件下，土壤水分变化出现了上升期、平台期及退水期。在小雨强短历时的降雨中，降雨对土壤水分的影响主要表现在土壤表层（0-10cm）。在降雨初期，降雨强度越大，土壤水分入渗越快，土壤的响应深度越深。研究三峡库区典型分布的茶园在不同降雨模式下的土壤水分变化特征，为三峡库区坡地的降水资源优化配置和园地面源污染防控提供理论依据，对区域水土流失治理以及面源污染物防控具有重要意义。 Abstract:Soil moisture is a key control factor for slope runoff generation and biogeochemical processes. Rainfall events can affect runoff paths, runoff mechanisms, and soil erosion processes in watersheds by causing soil moisture responses at different depths in the soil profile. Based on the typical tea gardens in the Three Gorges Reservoir Area, through long-term, fixed-point and high-frequency meteorological and moisture data observations, the temporal and spatial variation characteristics of soil moisture in different soil depths (0-10, 10-20, 20-30 and 30-40cm) of tea gardens under different rainfall regimes was studied, and the dynamic variation of soil moisture in the rainy season at different depths of tea gardens and the response characteristics to different rainfall regimes were analyzed. The results showed that:(1) The rainfall and soil moisture content in the study area showed obvious seasonal characteristics. Rainfall peaked in July and soil moisture levels peaked in August. It showed that rainfall was an important factor affecting the change of soil moisture content, and soil moisture had an obvious response process to rainfall. (2) Under the same rainfall conditions, soil water content had obvious vertical gradient changes. With the increase of soil depth, the response of soil moisture to rainfall gradually showed a hysteresis phenomenon. The topsoil (0-20cm) responds to rainfall more rapidly and the amplitude was more obvious, the change of water content in the deep soil (30-40cm) was relatively stable, and the response time to rainfall was more sluggish. With the increase of soil depth, the variation range of soil moisture content gradually became stable. (3) The soil moisture content showed significant differences with different rainfall regimes. Under the condition of high rainfall intensity, soil moisture changes appeared in the rising period, the plateau period and the retreating period. In the rainfall with small rainfall intensity and short duration, the effect of rainfall on soil moisture was mainly manifested in the soil surface layer (0-10cm). The greater the rainfall intensity, the faster the soil moisture infiltration, and the deeper the soil response depth were exhibited in the early stage of rainfall. Studying the characteristics of soil moisture variation characteristics in typical tea gardens in the Three Gorges Reservoir area under different rainfall patterns will provide a theoretical basis for the optimal allocation of precipitation resources and the prevention and controlling of ground source pollution in the gardens, which is of great significance to regional soil erosion control and the prevention and control of non-point source pollution. 参考文献 相似文献 引证文献