Deep Soil Research Articles

Numerical Simulation of the Solute Migration Regulated by Vertical Cutoff Wall based on FEFLOW

Cutoff wall has been widely used in desalination of coastal aquifers in many coastal regions and remediation of industrial waste water pollution. In recent years, the excessive exploitation of resources in the coastal brine distribution area leads to the salinization of deep soil. At the same time, the mine water pollution caused by improper discharge of industrial waste water into the abandoned mining area is a new form of pollution in Shandong, China. However, due to the complex geological conditions of abandoned mining areas, loose collapse of overlying strata in roadway and gob layer, it is difficult to prevent and control groundwater pollution in deep gob layer. It is a major difficulty in practical engineering to evaluate the cutoff interception performance of vertical cutoff wall on the pollution of gob layer in such mining areas and optimize cutoff interception measures. In this paper, a typical polluted abandoned mining area in Shandong, China is taken as an example, and COD is used as the main simulation factor for numerical simulation. The numerical simulation results show that in the process of groundwater pollution control, the cutoff wall with appropriate thickness and hydraulic conductivity can effectively block the diffusion of solute. The horizontal transport of solute can be significantly weakened when the thickness of the cutoff wall is 90 cm and the hydraulic conductivity is 1.0×10-4 m/d. Compared with increasing the thickness, reducing the hydraulic conductivity of the cutoff wall is more effective in controlling the migration of solute in the site. When the hydraulic conductivity is reduced by an order of magnitude, the diffusion range of solute is reduced by 19.74% compared to before. Therefore, priority should be given to reducing the hydraulic conductivity of the cutoff wall in order to optimize its influence on pollutant migration.

Bare Patches Created by Plateau Pikas Contribute to Warming Permafrost on the Tibet Plateau

AbstractPlateau pikas, small mammals native to the Qinghai‐Tibet Plateau (QTP), create bare patches through burrowing. No previous assessment exists on their impact on permafrost. This study fills this gap by simulating hypothetical scenarios in the Three Rivers Headwaters Region of the QTP using the Noah‐MP model for the plant growing seasons during 2015–2018. Our findings reveal a significant increase in soil temperature in the active layer due to pika‐induced bare patches, particularly during July–August. The average temperature rise at 2.5 cm depth was 0.36°C in permafrost regions and 0.29°C in seasonally frozen ground regions during August. Minimal impact on unfrozen water content was observed, with a slight increase in deep soil layers in permafrost regions, and negligible in seasonally frozen areas. These findings underscore the previously unexplored influence of pika burrowing on permafrost temperature, suggesting a potential risk of accelerating permafrost degradation, especially in permafrost‐dominated regions.

Impacts of Deep-Rooted Apple Tree on Soil Water Balance in the Semi-Arid Loess Plateau, China

Partitioning soil water balance (SWB) is an effective approach for deciphering the impacts of vegetation change on soil hydrological processes. Growing apple trees on the Loess Plateau, China, leads to a substantial deep soil water deficit, posing a serious threat to the sustainable development of apple production. However, the impact of deep-rooted apple trees on SWB remains poorly understood. In this study, we conducted a “Paired Plot” experiment to achieve this objective by decoupling SWB components using water stable isotopes, tritium, and soil water contents from deep soil cores (up to 25 m) under apple orchards with a stand age gradient of 8–23 years. The results showed that deep soil water storage under apple orchards was notably reduced compared to nearby farmland, showing a stand age-related pattern of deep soil water deficit (R2 = 0.91). By analyzing the changing patterns of SWB components, we found that the main factor driving this deficit is the water uptake process controlled by the deep root system. This process is triggered by the increased transpiration demand of apple trees and short-term water scarcity. These findings have implications for understanding soil water dynamics, sustainable agroforestry management, and soil water resources’ protection in this region and other similar water-limited areas.

Improving cotton productivity and nitrogen use efficiency through late nitrogen fertilization: Evidence from a three-year field experiment in the Xinjiang

ContextPremature senescence is a major concern for crop production especially for high-density cotton in Xinjiang, China, when nitrogen (N) rates are reduced. This study aimed to examine the potential of late N fertilization in mitigating senescence, improving light and N use efficiency, and enhancing cotton productivity under reduced N rate. MethodsA three-year field experiment was conducted from 2019 to 2021, employing a total of 240 kg N ha-1, which was one-third lower than the traditional rate of 360 kg ha-1. Five different N application ratios based on cotton stages were tested, with N064 (0:6:4 ratio at early: middle: late growth stages) representing late N fertilization, and N262 representing traditional ratio in fertilization. The effects of N application timing-based ratios on yield components, N use efficiency, canopy photosynthesis, and root traits were evaluated. ResultsThe results showed that N064 had the highest lint yield 2727–3305 kg ha-1 (2019–2021) among all treatments over the three years. Late N fertilization (N064) resulted in significant increases in boll density (4.6–10.7%), seed cotton yield (5.8–8.1%), and N use efficiency (10.5–14.1%) when compared to traditional N262. During late peak boll-setting to boll opening stages, N064 decreased leaf area index (3.5–6.6%), canopy light interception rate (3.8–11.4%), and boll capacity of root (18.1%) compared to N262, while increasing SPAD (2.3–4.8%), diffuse non-interceptance (3.9–16.6%), canopy apparent photosynthetic rate (13.2–49.4%), root biomass (19.5%), root/shoot ratio (15.0%). N064 also resulted in a higher root surface area density in deep soil than N262. ConclusionsLate N fertigation enhanced post-flowering canopy photosynthetic production by improving the cotton root-shoot relationship and delaying root and canopy senescence, resulting in improved yields and N use efficiency. This N management strategy implemented under reduced N cultivation shows promise for sustainable cotton production in Xinjiang and similar ecological regions.

Improvement of the method of processing animal bones in the production of educational and museum exhibits

The method of processing the bones of domestic and wild animals has been improved and maximally adapted to domestic conditions. The work was carried out on the basis of the laboratory of taxidermy and museum affairs of the department of anatomy and histology named after Р. Kowalskiy Bilа Tserkva National Agrarian University. The aim of the work was the practical application of the improved method of processing the bones of domestic and wild animals for the production of museum exhibits and educational materials. For the treatment and degreasing of bones, Pervol and Gala washing powders with a whitening effect and Fairy brand dishwashing detergents used as surfactants. Precursor-free chemical paint solvents 646, 647, 650 and White Spirit have proven themselves well as solvents for intraosseous fat. At the stage of preparation and cleaning of the bones from the muscles, they were subjected to maceration in water at room temperature for 7-10 days. Degreasing of bones in solvents lasted up to 1.5 months with daily visual control and mixing. Visual control have carried out by illuminating the bones with lamps with bright light. 60% perhydrol diluted with water in a ratio of 1:4 was used as a bleaching agent. As a result of comparative testing of various means, it was established that it is better to use deep penetration soil "Artisan No. 7" with exposure of bones in it for up to 7 days as a fxing preparation. It should be noted that chemical treatment of bones using household detergents and technical solvents is quite effective and affordable, although it takes a long time. The proposed method makes it possible to produce high-quality, visually aesthetic and tactilely pleasant, absolutely odorless, uniformly white educational preparations and museum exhibits of bones with minimal fnancial costs and technical equipment. Key words: domestic, wild animals, skeleton bones odorless, solvent.

Effective strategies for reclaiming soda-saline soils: Field experimentation and practical applications in Southeast Kazakhstan

Soda-saline soils pose significant challenges to agricultural productivity, particularly in regions like the foothill plain of the Ili Alatau in southeast Kazakhstan. In this study, we examined the effectiveness of different ameliorants, including phosphogypsum, elemental sulfur, and sulfuric acid, in reclaiming soda-saline soils and enhancing crop yields. The study was conducted under real climatic and production conditions at the "Amiran" LLP farm. Using a randomized complete block design, we assessed the impact of these ameliorants on soil composition and alfalfa yield over two cutting cycles. The experiment involved the application of phosphogypsum, elemental sulfur, and sulfuric acid to designated plots within the farm, each covering an area of 15m2. Soil samples were collected before and after treatment to assess changes in soil composition and salinity. Alfalfa, a resilient perennial crop, was selected for cultivation due to its tolerance to adverse soil conditions. Our findings reveal that all tested ameliorants successfully neutralized the toxic environment of soda-saline soils, resulting in improved soil conditions and increased crop productivity. Phosphogypsum treatment led to a reduction in bicarbonate and carbonate ions, an increase in sulfate ion concentration, and improved soil structure. Elemental sulfur incubation decreased bicarbonate and carbonate ions, further reducing absorbed sodium levels and enhancing soil fertility. Sulfuric acid treatment provided rapid results in reducing alkalinity and increasing sulfate ion concentration, leading to significant improvements in soil quality and crop yield. However, the reclamation of soda-saline solonetzes presented challenges related to soil heterogeneity and poor water permeability. To address these challenges, we recommend the implementation of mechanical destruction of the solonetz soil horizon and deep soil loosening, accompanied by the addition of ameliorants. In conclusion, our study demonstrates the potential of phosphogypsum, elemental sulfur, and sulfuric acid as effective ameliorants for reclaiming soda-saline soils and improving agricultural productivity in challenging environments. By adopting recommended reclamation strategies, farmers can overcome soil limitations and achieve sustainable crop production in regions affected by soda-saline soil degradation.

Restoration Strategies in the Heidaigou Open-Pit Mine Dump Based on Water Sources and Plant Water Utilization

In this study, three typical plants capable of restoring in the Heidaigou open-pit mine dump, namely, Pinus sylvestris var. mongolica, Caragana korshinskii, and Medicago sativa, were taken as the research objects. The δ2H and δ18O values of atmospheric precipitation, soil water, stem water, and leaf water were measured using the stable isotope technique, and the distribution characteristics of the δ2H and δ18O values of different water sources were identified. The IsoSource model (version1.3.1) was used to calculate the contribution rate of different water sources to the plants, and the differences and dynamic changes in the water sources for P. sylvestris var. mongolica, C. korshinskii, and M. sativa during the rainy season were examined. Results showed that the water source of the three plants was found to be mainly soil water, and the utilization of each potential water source varied in different periods of the rainy season. In June, when SWC was sufficient, P. sylvestris var. mongolica and M. sativa primarily absorbed and utilized shallow and middle soil water, with relative utilization ratios of 55.5% and 59%, respectively, while C. korshinskii has a more balanced utilization ratio of soil water in each layer, with shallow soil water utilization at 33.7%, middle soil water at 34.2%, and deep soil water at 32.2%. In August, when SWC decreased, P. sylvestris var. mongolica, C. korshinskii, and M. sativa were all transferred to deep soil water, with utilization ratios of 75.8%, 78.8%, and 71.1%, respectively. The values showed that these three typical plants are capable of restoring can respond to external water changes through the plastic transformation of water absorption sources. Among them, C. korshinskii can flexibly use soil water in each layer, has stronger survival competitiveness in drought, and can better adapt to the fragile ecological environment of a mining dump.

Different responses of soil microbial respiration to nitrogen addition between surface and deep soil in a temperate steppe in Inner Mongolia

Different responses of soil microbial respiration to nitrogen addition between surface and deep soil in a temperate steppe in Inner Mongolia

Phosphorus fertilizer management for high yields in intensive winter wheat-summer maize rotation system: Integrating phosphorus budget and soil available phosphorus

Overuse of phosphorus (P) fertilizer in crop cultivation accelerates the consistent increase in soil P accumulation and increases the risk of P leaching from the agricultural system. The long-term implications of balanced P management on soil P availability and crop P uptake are still unknown. A three-year field experiment with six different P rates was conducted to determine the effect of a balanced P application strategy on crop yield, P uptake, soil P accumulation, and P transformation in a winter wheat-summer maize rotation system. The results found that the yield and P uptake of summer maize and wheat increased linearly with P fertilization up to 12.5 kg P ha–1, after which they stabilized, and the critical threshold is 50 kg P ha–1 for winter wheat. The soil P budget under agronomic thresholds from 2017 to 2020 was observed as –2.99 to –11.04 kg P ha−1 for maize but 15.1–24.5 kg P ha–1 for wheat. Excessive P fertilization accelerated the downward movement of soil P and stocked it in the deep soil in the form of soil labile P and moderately labile P, increasing the risk of soil P leaching. The annual application of 600 kg ha–1 P fertilizer substantially increased the total P concentration by 30%–99% from deep soil to topsoil compared to the no P treatment, while the 75 kg ha–1 and 150 kg ha–1 P fertilizer treatments did not affect soil P accumulation along the soil profile. Soil Olsen-P concentration to meet crop yield requirements is still far from meeting the critical environmental threshold of 47.6 mg kg–1 and increased slightly by an annual 2.39 mg kg–1 under the balanced P fertilization strategy. An annual negative soil P budget of 3–11 kg ha–1 for summer maize could sustain optimal yields and P use efficiency. Winter wheat cultivation required additional P application to reach the agronomic threshold, set at 15–25 kg ha–1 annually. In conclusion, balanced P fertilization can reduce soil P surplus and subsoil P stock while maintaining crop yields.

Deep soil seismic hazard assessment: analyzing the impact of local site effects by stochastic site response analysis—a comparative approach

Deep soil seismic hazard assessment: analyzing the impact of local site effects by stochastic site response analysis—a comparative approach

Influence and Mechanism of the Excavation Width on Excavation Deformations in Shanghai Soft Clay

This study investigated the influence and mechanism of the excavation width on excavation deformations in Shanghai soft clay. Based on three excavations that had different final excavation depths, dissimilar retaining structures and diverse geological conditions, 40 sets of two-dimensional numerical models with different excavation widths were employed to analyze the deformation rules affected by the excavation width. Moreover, a series of simplified models with different excavation widths were employed to analyze the effect of the excavation width on excavation deformations. The results show that under the same excavation depth, both the horizontal displacements of the retaining walls and ground surface settlements increase as the excavation width increases, but the increasing rate gradually decreases. Factors such as the unloading influence depth, the overlap degree of the passive zones, the stress state of the basal soils and the development of the relative shear stress have a significant influence on excavation deformations. With increasing excavation width, the unloading influence depth gradually deepens, the overlap area of the passive zones gradually decreases, the direction of the rotation of the major principal stress gradually reduces and the relative shear stress of the distant and deep soils gradually expands. Therefore, the constraint ability of the passive zones on excavation deformation gradually reduces and excavation deformations gradually increase.

Effects of Cultivation Years on the Distribution of Nitrogen and Base Cations in 0–7 m Soil Profiles of Plastic-Greenhouse Pepper

To clarify the migration and accumulation of nitrogen (N), magnesium (Mg), calcium (Ca), and potassium (K) in soil profiles of plastic-greenhouse vegetable fields with cultivation years, soil samples from the 0–7 m soil profiles were collected from 10 pepper greenhouses with 10 and 20 years planting history, and parallel soil samples were taken from adjacent wheat-maize fields as controls. The results showed that: (1) Compared with wheat-maize fields, the total N amount in the 0–7 m soil layers from the greenhouses increased by 6.19 ± 1.16 and 9.11 ± 3.43 t ha−1 at 10 and 20 years, respectively, accounting for about 30.4% and 17.5% of the N input. (2) The N amount that entered the environment outside the 0–7 m soil layers were 6.95 t ± 2.76 and 29.10 ± 10.14 t ha−1 after 10 and 20 years of continuous planting, accounting for approximately 34.2% and 55.9% of the N input, respectively. (3) The concentration of water-soluble Ca and Mg in the 0–7 m soil layers increased significantly with cultivation years, and correlated positively with mineral N concentration. (4) Moreover, K mainly accumulates in the form of non-exchangeable K in the surface layers (0–50 cm). Our results demonstrated that huge amounts of N migrate to the deep soil with the extension of cultivation years in plastic-greenhouse pepper production systems, accompanied by significant leaching of Ca and Mg, while K mainly accumulates in the surface layers.

The Egyptian pyramid chain was built along the now abandoned Ahramat Nile Branch

The largest pyramid field in Egypt is clustered along a narrow desert strip, yet no convincing explanation as to why these pyramids are concentrated in this specific locality has been given so far. Here we use radar satellite imagery, in conjunction with geophysical data and deep soil coring, to investigate the subsurface structure and sedimentology in the Nile Valley next to these pyramids. We identify segments of a major extinct Nile branch, which we name The Ahramat Branch, running at the foothills of the Western Desert Plateau, where the majority of the pyramids lie. Many of the pyramids, dating to the Old and Middle Kingdoms, have causeways that lead to the branch and terminate with Valley Temples which may have acted as river harbors along it in the past. We suggest that The Ahramat Branch played a role in the monuments’ construction and that it was simultaneously active and used as a transportation waterway for workmen and building materials to the pyramids’ sites.

Influence of Bioformulations on Productivity, Profitability and Quality in Soybean under Rainfed Condition of Northern Transition Zone of Karnataka

Background: Soybean [Glycine max (L.) Merrill] is the most important major oilseed crop among the edible oil seed crops. It has emerged as a potential protein as well as oilseed crop worldwide. The average productivity of soybean is low due to less importance and mostly grown under rain-fed condition without using bio-fertilizers (novel bio-formulations). Hence the current study was carried out to enhance the productivity and profitability of soybean under rainfed condition. Methods: The present investigation was carried out at AICRP on Soybean, Main Agricultural Research Station, University of Agricultural Sciences, Dharwad with medium deep black soil under rainfed condition. The experiment was executed in a Randomized Block Design with three replications and seven treatments. The influence of bioformulations on growth, yield parameters, yield, economics, quality and nutrient status of soybean (DSb 21) was carried out during kharif 2021-22 and 2022-23. Result: The pooled data of two years concluded that, application of 100% RDF alone (T2) was recorded significantly higher dry matter production (79.2 g plant-1), pods per plant (64.0), seed index (14.41 g), seed yield (2,797 kg ha-1) and straw yield (4,340 kg ha-1) and similarly higher uptake of nitrogen (103.74 kg ha-1), phosphorus (17.54 kg ha-1) and potassium (91.40 kg ha-1) in soybean crop followed by next best treatment with application of 75 per cent RDF + Rhizobium + MDSR14 + 12c (76.6 g plant-1, 61.6, 14.19 g, 2,631, 4,170, 100.12, 16.73 and 86.64 kg ha-1 respectively) (T7) as compared to other treatments. Further, higher net returns (Rs.1,13,015 ha-1) and benefit cost ratio (4.73) was also obtained in T7. Therefore, the application of 75 per cent RDF + Rhizobium + MDSR14 + 12c can be recommended for eco-friendly, economically viable, environmentally sound and sustainability in nature, besides improving the physico chemical properties of soil and in turn higher productivity and profitability under medium deep black soil in Northern Transition zone of Karnataka (India).

Deep soil desiccation hinders nitrate leaching to groundwater in the global largest apple cultivation area

Massive use of N fertilizer in apple orchards aids China’s Loess Plateau (CLP) to become the largest region of apple production in the world, but it also leads to substantial nitrate accumulation in the vadose zone, posing a potential environmental risk. However, a holistic understanding of the spatial patterns and controls of soil nitrate in the vadose zone of apple orchards remains understudied, which is unfavorable for the formulation of a science-based N application strategy. To this end, we collected a total of 2852 paired data across apple orchards on the CLP from 52 published literature and 1000 paired data from our field sampling. We found that residual nitrate accumulation primarily occurred in the top 4–8.8 m soil layer, and it varied according to mean annual precipitation (MAP) and stand age; the accumulation peaked in sites with MAP of 500–600 mm and declined with a decrease in MAP; and among various stand ages, the highest nitrate content was observed in the 25-yr-old orchard. It was found that MAP and N fertilizer application amounts dominated nitrate accumulation in the soil. Furthermore, the desiccation index of the soil layer below the maximum cumulative depth was identified as the main factor influencing soil nitrate maximum accumulation depth . This means that deep soil desiccation hinders nitrate leaching towards deeper layers and reduces the risk of groundwater contamination. The findings here may provide insights into sustainable nitrogen and water management in apple orchards on the CLP and potentially in other similar regions.

Hydraulic conductivity of cement and fly ash stabilised clay mixes – Application to soil mixing techniques for seepage barrier construction

In-situ ground improvement techniques, namely, deep soil mixing, jet grouting, cutter soil mixing, and mass stabilisation are often utilized to improve the strength of soft grounds, and construct seepage barriers. Due to economic and environmental concerns, there is a global shift towards using industrial wastes such as fly ash (FA) from conventional binders such as ordinary Portland cement and lime. There is a plethora of literature on unconfined compressive strength (UCS) of cement-treated clays, and clays treated with fly ash-cement mixes with alkali activator (FCAA) binders. However, much remains unclear about the hydraulic conductivity of the FCAA-treated clays as low permeable hydraulic barrier systems. In this paper, the hydraulic conductivities of cement-treated and FCAA-treated clays are studied both quantitatively and qualitatively for different binder-content, FA:cement ratios, curing periods, and effective confining stress. The hydraulic conductivity of treated clay is measured by performing a series of accelerated permeability tests using a custom-fabricated triaxial system. The trends obtained from the measured hydraulic conductivity values are explained from the observations of X-ray diffraction analysis and scanning electron microscopy analysis. Results showed that the values of hydraulic conductivity for cement-treated clay were mostly higher than those of untreated clay. On the contrary, the hydraulic conductivities for the FCAA clay mixes were comparable to, or even lower than those for the untreated clay. The hydraulic conductivity reduced with the increase in effective confining stress; the influence of effective confining stress, however, became less substantial for 28 days curing period and higher cement-content (40 and 50 %). The relationships between the hydraulic conductivity, UCS, and water-binder (w/b) ratios were also determined for both cement-treated and FCAA-treated clays. The exponential function was found suitable to express the relationship between hydraulic conductivity and UCS of treated clays. In contrast, a strong logarithmic relationship was obtained for measured values of hydraulic conductivity and adopted w/b ratios. The results shall serve as a guide to adopting suitable binder-content or target UCS for achieving design hydraulic conductivity in ground improvement projects that involve cement and/or FCAA-treatment of clays.

Water use and yield response of rainfed safflower (Carthamus tinctorius L.) in Vertisols with varying soil depths

AbstractSafflower (Carthamus tinctorius L.) is an edible oilseed crop mainly cultivated in marginal lands. This study evaluates safflower crop water requirements to understand its feasibility to cultivate under rainfed ecosystem through a field experiment undertaken at the International Crops Research Institute for the Semiarid Tropics research farm, India. Eight improved and stress‐tolerant safflower cultivars (five spiny and three non‐spiny) were evaluated in Vertisols at three soil depths, that is, shallow: <0.60 m, medium: 0.60–1.20 m, and deep:1.20–1.80 m, over 3 years (2009–2012). Wet, normal, and deficit rainfall years were experienced during 2009/2010, 2010/2011, and 2011/2012, respectively. Soil moisture, crop yield, and growth parameters were measured, and field‐scale hydrology was captured through a calibrated one‐dimensional water balance model. Safflower responded to available residual soil moisture which varied with soil depth and rainfall received in different years. Total crop water use was 300–320 mm during the postrainy season, of which about 70% was extracted in deep Vertisols and 55% in medium Vertisols through residual soil moisture. In addition, 30% of water requirement was met through postrainy season rainfall. Safflower grown in shallow Vertisols could only meet 40% of crop water requirement. Spiny cultivar NARI‐H‐15 grown in deep soil recorded a maximum yield of 1890 kg ha−1 in the wet year. Seed yield from spiny cultivars grown in deep and medium soils was nearly similar (1500–1600 kg ha−1) during wet and normal years; a significant reduction in yield (>50%) occurred in shallow soils and also during a rainfall deficit year. Spiny cultivars produced 10%–50% higher seed yield compared to non‐spiny cultivars. Growing safflower in medium and deep Vertisols provides opportunities for crop intensification.

Impact of Physical Interventions, Phosphorus Fertilization, and the Utilization of Soil Amendments on the Absorption of Cadmium by Lettuce Grown in a Solar-Powered Greenhouse.

This study aimed to evaluate the effects of physical measures and the applications of phosphorus fertilizer and soil conditioner on the growth of lettuce (Lactuca sativa) and its uptake of cadmium (Cd). In a solar greenhouse that contained soil enriched with cadmium (Cd) (1.75 ± 0.41 mg/kg) with lettuce used as a test plant, field experimental methods were utilized to explore the influence of physical measures, such as deep plowing and soil covering, and the applications of phosphorus fertilizer, including diammonium phosphate (DAP), calcium magnesium phosphate (CMP), and calcium superphosphate (SSP), and soil conditioners, such as biochar, attapulgite clay, and nano-hydroxyapatite, on the uptake of Cd in lettuce. The results indicated that the concentrations of Cd in the aboveground parts of lettuce were 1.49 ± 0.45, 1.26 ± 0.02, 1.00 ± 0.21, and 0.24 ± 0.13 mg/kg when the soil was plowed 30, 40, and 50 cm deep, respectively, and when the soil was covered with 15 cm, this resulted in reductions of 27.5%, 38.3%, 51.4%, and 88.4%, respectively, compared with the control treatment that entailed plowing to 15 cm. When 75, 150, and 225 kg/ha of phosphorus pentoxide (P2O5) were applied compared with the lack of application, the contents of Cd in the aboveground parts of lettuce increased by 2.0%, 54.5%, and 73.7%, respectively, when DAP was applied; by 52.5%, 48.5%, and 8.1%, respectively, when CMP was applied; and by 13.1%, 61.6%, and 90.9%, respectively, when SSP was applied. When the amounts of biochar applied were 0, 2, 4, 6, 8, 10, and 12 t/ha, the contents of Cd in the aboveground parts of lettuce were 1.36 ± 0.27, 1.47 ± 0.56, 1.80 ± 0.73, 1.96 ± 0.12, 1.89 ± 0.52, 1.44 ± 0.30, and 1.10 ± 0.27 mg/kg, respectively. Under concentrations of 0, 40, 80, 120, 160, and 200 kg/ha, the application of nano-hydroxyapatite resulted in Cd contents of 1.34 ± 0.56, 1.47 ± 0.10, 1.60 ± 0.44, 1.70 ± 0.21, 1.31 ± 0.09, and 1.51 ± 0.34 mg/kg, respectively. The concentrations of Cd in the aboveground parts of lettuce treated with attapulgite clay were 1.44 ± 0.48, 1.88 ± 0.67, 2.10 ± 0.80, 2.24 ± 0.75, 1.78 ± 0.41, and 1.88 ± 0.48 mg/kg, respectively. In summary, under the conditions in this study, deep plowing and soil covering measures can reduce the concentration of Cd in the aboveground parts of lettuce. The application of phosphorus fertilizer increased the concentration of Cd in the aboveground parts of lettuce. The application of higher amounts of DAP and SSP led to greater concentrations of Cd in the aboveground parts of lettuce. The application of higher amounts of CMP caused a lower concentration of Cd in the aboveground parts of lettuce. When biochar, attapulgite clay, and nano-hydroxyapatite were applied, the concentration of Cd in the aboveground parts of lettuce increased in parallel with the increase in the concentration of application when low amounts were applied. In contrast, when high amounts were applied, the concentration of Cd in the aboveground parts of lettuce began to decrease.

Effects of the freeze–thaw process on sources and pathways of subsurface flow in an alpine hillslope on the northeastern Qinghai-Tibet Plateau

The impact of the freeze–thaw process on the active layer is reflected in the changed subsurface flow (SSF) process in cold alpine regions. Identifying sources and pathways of SSF in the freeze–thaw process is critical but difficult, and the related dominant factors and mechanisms are still unknown. In this paper, the effective identification and analysis of SSF are promoted based on field sampling data from the thawing (June) to freezing (September) period of 2022 in the Qinghai Lake basin on the northeastern Qinghai-Tibetan Plateau. By the proposed method with a high sampling frequency and refined sampling spatial scale, the sources and pathways of SSF are clearly identified. The results are as follows: (1) The soil temperature is considered the most fundamental factor affecting the SSF pathways, it influences water infiltration to the deep layer and the effect is extended to the saprolite and weathered bedrock layers. (2) Thawing promotes water to infiltrating into deep layer. 30 cm soil water contributes the most to SSF (2 %–86 %) in the thawing period, while the contribution difference of the water from the 30 cm, 60 cm, and 90 cm layers is small (ranging from 32 %–33 %, 24 %–26 %, and 32 %–35 %, respectively) in the thawed period. (3) Meanwhile, the soil water from different slope positions contribute differently to SSF, and the SSF from deep soil layer is transit in prolong paths and depths. It is caused by the out-of-sync water transit process in the hillslope. With continuing climate warming, we propose that the differences in the water sources of SSF across soil layers may decrease, while the differences in the transit processes of SSF across soil layers may increase.

Response of Soil Moisture to Four Rainfall Regimes and Tillage Measures under Natural Rainfall in Red Soil Region, Southern China

Investigating the effects of natural rainfall on the soil moisture for sloping farmland is extremely important for comprehending a variety of hydrological processes. Rainfall regimes can elicit different responses to soil moisture at the depth of soil layers, and the responses may differ depending on the landscape position of the sloping farmland. This paper utilized the surface runoff natural rainfall and soil moisture measured on sloping farmland with conventional tillage and contour tillage in the red soil area of China to investigate the influence of natural rainfall events on soil moisture content and to evaluate if the response results were consistent across the four rainfall regimes. Natural rainfall events were classified into different four regimes in line with rainfall duration, rainfall amount, and the maximum 30 min rainfall intensity (I30) by the k-means clustering method, including advanced, intermediate, uniform and delayed regimes. The result showed that the advanced regime was the predominant one in the study area, which represented 45.9% of the total rainfall events. The rainfall regimes influenced the surface runoff coefficient and runoff depth on sloping farmland for conventional and contour tillage, with the uniform regime generating the highest runoff coefficient (5.20% and 5.82%) and runoff depth (2.00% and 2.05%), respectively. For the conventional tillage, soil moisture at a depth of 0–20 cm increased appreciably when the rainfall amount was larger than 20 mm and larger than 30 mm for the advanced regime. For the contour tillage, soil moisture in 20–40 cm layer increased for the advanced regime when the rainfall amount was larger than 15 mm and 30 mm, while the values were modified with rainfall duration and the antecedent dry day (ADD). A longer rainfall duration had a more obvious effect on soil moisture increasing in deep soil. At a depth of 20 cm, the ADD showed an appreciably positive correlation with the increment in soil moisture, which means that a brief ADD produces a compounding effect for a natural rainfall event. The present results underline the complexity of the effect of the rainfall events on soil moisture under two tillage measures for different rainfall regimes and suggest that the advanced regime significantly affects the distinction of soil moisture and the contour tillage can effectively reduce soil water loss and enhance water storage on the sloping farmland with red soil, presenting a theoretical basis for local soil and water conservation research and sloping farmland conservation tillage management.