Cracking Of Oil Research Articles

Weak Magnetic Internal Signal Characteristics of Pipe Welds under Internal Pressure.

Weak magnetic detection technology is an effective method to identify stress-induced damage to ferromagnetic materials, and it especially possesses great application potential in long-distance oil and gas pipeline weld crack detection. In the process of pipeline operation, due to internal pressure and external loads, local stress concentration may be generated, and partial stress concentration may lead to local cracks and expansion of the pipe. In order to improve the accuracy of magnetic signal analysis for ferromagnetic materials under internal pressure, the causes of magnetic signal generation at pipeline welds were analyzed from a microscopic perspective. The distributions of magnetic signals at pipeline welds, weld cracks, and base metal cracks under different internal pressures were numerically analyzed. The variation trends of magnetic signal characteristics, such as peak values of axial and radial components, gradient K, maximum gradient Kmax, and gradient energy factor S(K), were analyzed. In addition, experiments were carried out to verify the numerical data. It was revealed that with the elevation of internal pressure, the peak values of the axial and radial components, gradient K, maximum gradient Kmax, and gradient energy factor S(K) linearly increased. However, the magnitude and average change of S(K) were larger, which can more directly indicate variations of magnetic signals. The radial growth rate νy of S(K) was 3.24% higher than the axial growth rate νx, demonstrating that the radial component of the magnetic signal was more sensitive to variations of stress. This study provided a theoretical and experimental basis for detection of stress-induced damage to long-distance oil and gas pipelines.

Characteristics of light hydrocarbons under the superimposed influence of biodegradation and subsequent thermal maturation

Recently, several large light oil and condensate reservoirs were discovered in the Tarim and Junggar basins (China). In these superimposed petroliferous basins, the early formed palaeo-oil reservoirs experienced complex tectonic movements, resulting in complex secondary alterations (e.g., biodegradation and water washing), known to alter the chemical composition of crude oils. Thus, crude oils previously modified by biodegradation exhibit significantly different generation potential, chemical composition, and timing of generation (in terms of light oils/condensates), during subsequent thermal alteration. To elucidate the influence of biodegradation on crude oil cracking (to form light hydrocarbons), we artificially matured four crude oils of the same origin (with varying degrees of biodegradation) to various maturity levels, using programmed-temperature gold tube closed-system pyrolysis. The yields, molecular parameters, and stable carbon isotope ratios of the light hydrocarbon products derived from the matured oils were analysed and compared. The preferential removal of n-alkanes and branched alkanes during biodegradation significantly reduced the generation potential of light hydrocarbons. Under the superimposed influence of biodegradation and subsequent thermal alteration, referred to as superimposed secondary alteration (SSA), a few hydrocarbon ratios used for oil–oil correlations were severely modified. Most maturity-related light hydrocarbon parameters of the pyrolysis products derived from the biodegraded oils achieved maximum values at a lower maturity (Easy%Ro) than that observed for non-biodegraded crude oil. At 0.5–1.4 Easy%Ro, SSA caused the depletion of 13C in most light hydrocarbons, due to an increased sourcing from the biodegradation-resistant fractions of the oil. Such carbon isotopic differences decreased with increasing maturity.

Genetic relationship between the Maoping Pb-Zn deposit and paleo-oil reservoir in the northern Yunnan-Guizhou depression: Evidence from bitumen trace elements and the in-situ sulfur isotope of pyrite associated with bitumen

The coexistence of numerous Mississippi Valley-type (MVT) Pb-Zn deposits and oil/gas reservoirs in the world demonstrates that a close genetic link between them. The northern Yunnan–Guizhou depression (NYGD) is a tectonic unit containing Pb–Zn deposits, paleo-oil reservoirs and shale gas. However, previous studies on the relationship between hydrocarbon accumulation and Pb–Zn mineralization have been ignored. The Maoping Pb–Zn deposit is a large-sized MVT deposit in the NYGD where a large amount of solid bitumen (i.e., a paleo-oil reservoir) occurs, and it is an ideal area to study the relationship between hydrocarbon accumulation and lead–zinc mineralization. In this paper, the bitumen and pyrite associated with bitumen from the Xujiazhai (discovered in this study) and Xiaocaoba paleo-oil reservoirs and the Maoping Pb–Zn deposit are researched. Geological observation has revealed that bitumen occurs in dissolution pores, fractures and intercrystalline pores in dolomite of the Upper Devonian and Carboniferous. The bitumen from Xujiazhai, Maoping and Xiaocaoba with high and similar Raman equivalent reflectance (RmcRo%) indicates they are in over-mature level and may be derived from the cracking of early-accumulated crude oils. The bitumen in the Xujiazhai paleo-oil reservoir and Maoping deposit has an abundant Pb and Zn content, indicating petroleum liquids may act as the transporting agents of metallogenic metal elements, carrying them to sites where mineralization may take place. The source rocks may have provided not only the oil for paleo-oil/gas reservoirs, but also a portion of ore metals for the Pb-Zn mineralization. The bacterial sulfate reduction (BSR) and thermochemical sulfate reduction (TSR) processes were recorded by the pyrite in the paleo-oil reservoir, which was consistent with the mechanism of reduced sulfur formation in the Maoping deposit. In addition, the large negative (−27.7‰ to −5.7‰) and positive (.9‰ to 19.2‰) δ34S values of the pyrite associated with the bitumen in the paleo-oil reservoir were similar to those of the sulfide in the Maoping deposit. We believe that the formation and evolution of the paleo-oil reservoirs are closely related to the metallogenic process of the Maoping Pb–Zn deposit, and the sulfides in them have the same sulfur source and formation mechanism as reduced sulfur. BSR phenomena could occur in prior to migration of the hydrocarbons into the reservoir or low mature oil stage in paleo-oil reservoir; a small amount of H2SBSR was combined with metal ions in ancient oil reservoirs and deposits to form early subhedral, xenomorphic granular, fine-grained strawberry aggregate pyrite and/or gelatinous sphalerite. The paleo-gas reservoir formed by the evolution of the paleo-oil reservoir in the main metallogenic period potentially participated in the mineralization; that is, organic gas acted as a reducing agent and transformed SO42− in the upper Devonian Zaige Formation gypsum strata on the periphery of the Maoping lead–zinc mining area into H2STSR through TSR, providing reduced sulfur and creating the environmental conditions for mineralization. During or after the transformation of the paleo-oil reservoir to a paleo-gas reservoir, the decoupling of metals and organic complexes may have provided the ore metals for mineralization. Massive sulfide precipitation may have occurred during or after the paleo-oil reservoir cracked into the paleo-gas reservoir.

The evolution characteristics of diamondoids in coal measures and their potential application in maturity evaluation

In this study, gold tube thermal simulation experiments were carried out on the soluble components (extracts) and insoluble components (extracted coal-measure mudstones) of coal-measure mudstones, and diamondoid compounds in the pyrolysis products were quantitatively analyzed. The results showed that diamondoid compounds in the extracts and the extracted coal-measure mudstones had undergone the process of formation and decomposition during thermal evolution. Based on the quantitative composition of the extracts and the extracted coal-measure mudstones, the calculated evolution characteristics of the diamondoid compounds in the coal-measure mudstones were mainly consistent with the results of thermal simulation experiments, indicating that the formation of diamondoid compounds was primarily controlled by the original material source. Some diamondoid maturity parameters (MAI, EAI, TMAI-1) in coal-measure mudstones were consistent with the parameters of the evolution characteristics in marine shale. Therefore, the relationship between these parameters and vitrinite reflectance can be established, to calculate the maturity of marine source rocks. In addition, the evolution characteristics and some diamondoid maturity parameters in the extracts and the extracted coal- measure mudstones showed a good linear relationship, but the specific characteristics were different, which may enable the identification of kerogen cracking and secondary cracking of crude oil.

Effects of Climate Change on Geotechnical Infrastructures — state of the art

Geotechnical infrastructures, like slopes and embankments, retaining walls, foundations, engineered landfills, overburden dumps, and pavements, get continuously exposed to various environmental factors which are climate dependent. Fate/stability of these infrastructures due to extreme and abrupt change in precipitation, temperatures, humidity, and wind/airflow is quite questionable. Some of the issues related to climate change on soils include increase in infiltration rate, high pore-water pressure, decrease in effective stress, soil liquefaction, seepage failures, frost heaving, changes in soil suction potential, swelling and shrinkage in fine-grained soils, differential settlement, and damage to vegetation cover and thereby causing slope failures, waterlogged conditions, floods, soil erosion and/or internal erosion of fines, damage to landfill liners and soil covers, desertification, desiccation cracks on the ground surface, and groundwater table pollution due to contaminant migration. Therefore, studies on the impact of climate change on geotechnical infrastructures have gained attention of many researchers in the recent times. In present study, an up-to-date review of the works related to the influence of various climatic factors on geotechnical properties and thereby on geotechnical projects is carried out. Topics related to climate data downscaling using global climate models (GCM), climate change-induced slope instability, acid rains, desiccation cracking in soils with changing temperatures, impacts of dry-wet cycles and freeze-thaw cycles, and vegetation effects on soils are emphasized in this paper. Furthermore, to address the challenges, need-based research related to resilient infrastructures, thermo-hydro-mechanical models, bioremediation methods, innovative sustainable composite materials, and incorporation of climatic factors in design is highlighted and discussed.

Molecular dynamics simulation of converting waste polyethylene (PE) to chemicals and fuels under non-isothermal and isothermal conditions

Pyrolysis, one method of chemical recycling, has been an effective and clean way for processing plastic solid waste (PSW), which is a heavy burden for sustainable development. Series of molecular dynamic simulations are carried out for detailed pyrolysis of polyethylene (PE) waste using reactive force field (ReaxFF) for both non-isothermal and isothermal conditions. The results show that the PE pyrolysis at non-isothermal conditions can be divided into four stages. The last stage (post pyrolysis) is analyzed in depth, which shows decreasing of short-chain products and increasing of relatively long-chain components at high temperatures. Pyrolysis of PE at high heating rates reduces oil cracking and results in high yield of oil. The effect of reaction time depends on the pyrolysis temperature. In addition, under isothermal pyrolysis conditions, the simulated temperature range of 2500–2750 K is optimal for more recovery of C2H4 and C3H6 due to its high yield and mild influence of reaction time. Finally, detailed mechanisms of generation and consumption of C2H4 and C3H6 of PE pyrolysis are demonstrated. The regeneration of long-chain oil in the late stage of PE pyrolysis and the corresponding mechanisms are illustrated. The results in this study can be used to guide the design of systems for PSW processing with recovery of chemicals and fuels.

Green chemical production based on thermal cracking of inedible vegetable oil

This work evaluated the process for heptaldehyde, undecylenic acid, and methyl undecenoate production from castor oil, methyl ester of castor oil, and ricinoleic acid. Experiments were performed in a continuous pilot-plant scale pyrolysis reactor. Those are very important green chemical products that the thermal cracking of castor oil might produce. Transesterification of castor oil produces methyl ricinoleate, and its thermal cracking generates methyl undecenoate and heptaldehyde. The pyrolysis temperatures tested were 530?C, 545?C, 560?C, and 575?C, with residence time from 17 s to 32 s and mass flow at 400 g/h of the mixture of materials with 25% distilled water. It was observed that the temperature influenced the bio-oil yield in different degree for each material. The bio-oil was characterized by iodine index, acid number, and mass, and the contents of its compounds were obtained by GC-FID chromatography. The best result for the undecylenic acid mass yield of the desired compounds occurred at 530?C, achieving 17.8% from ricinoleic acid and 16.5% from castor oil. For the heptaldehyde, the highest production was also obtained at 530?C, with a value of 20.7% from methyl ester and 15.2% from ricinoleic acid.

Orthogonal Experimental Study on Crack Resistance of Biochar and Sisal Fiber Composite Improved Expansive Soil

Desiccation shrinkage is a key factor contributing to the engineering hazards in expansive soil. To inhibit the initiation and expansion of cracks, a composite improvement approach using biochar and sisal fibers was applied to expansive soil from Nanning, Guangxi. An orthogonal test method was employed to conduct desiccation cracking tests on the improved soil, investigating the effects of biochar and sisal fibers on crack length, crack ratio and crack width. The results indicate that different proportions of sisal fibers and biochar can effectively inhibit soil crack development. The biochar content is the primary factor affecting crack length, while sisal fibers mainly inhibit the development of crack ratio and average crack width. The optimal proportion for composite improvement approach was found to be 6‰ of 3 cm sisal fibers and 4% biochar. The study findings can provide a new approach for the expansive soil improvement and for controlling engineering problems caused by soil cracking.

Catalytic cracking of yeast-borne single-cell oil for the production of small-chain olefins over a PtSn/alumina catalyst

The ever-growing demand for sustainable energy and chemicals associated with declining fossil reserves motivates the quest for alternative feedstocks and processes.

Catalytic cracking of gas oil derived from heavy crude oil over biochar-based catalyst

Catalytic cracking of gas oil derived from heavy crude oil over biochar-based catalyst

Water retention curves and tensile strength for studying desiccation cracking of compacted clay soils

Desiccation cracking is a natural phenomenon caused by drying in near-surface earth soils subjected to constrained shrinkage. In this research, the water retention curve of two clayey soils, prepared by compaction under standard proctor conditions, are determined to study the desiccation cracking. Two techniques of suction control are applied to control the drying process and to reach the water retention curve of the soils. For the suction values higher than 4 MPa, the saline-solution method was used to impose variousrelative humidity and so, various suctions. In addition, the osmotic method was applied for the suction values between 0.5 MPa and 2 MPa. Additionally, the dynamic vapor sorption (DVS) technique is used to corroborate the water retention curves obtained with the two other techniques. The volume changes is also tracked showing significant shrinkage upon drying. To reach the tensile strength of the soil, the Braziliantest is performed on samples prepared by compaction and submitted to various suctions. According to the results, for the two tested soils, the soil with the higher plasticity index shows consistently the higher retention capacity and the larger shrinkage upon drying. Also, the obtained water retention curves exhibit a smooth transition when the suction control technique change (at suctions between 2 and 4 MPa).

Soil-atmosphere interaction: cracking of a compacted soil under the effect of a thermo-hydric stress

Reusing excavated material in geotechnical engineering reduces the carbon impact of a project. Such materials are usually placed in a compacted state in order to achieve the mechanical and hydric characteristics required to guarantee the safety of the structures. A good geotechnical knowledge of the materials is therefore necessary as well as a good anticipation of their behaviour over time. Indeed, in some situations, as in the case of waste storage, a low hydraulic conductivity is required. The use of crushed rocks rich in clays (argillite), possibly improved by adding bentonite, could be interesting. However, this addition, beneficial in terms of hydraulic conductivity, could be damaging from a mechanical point of view by the development of cracks at the interface atmosphere-compacted soil. For this purpose, samples compacted at the normal Proctor optimum are exposed to a relative humidity of 46% and a temperature of 22.5°C. The thickness, mass and surface condition (cracking) were monitored during the drying process, and measurements were taken in the thickness of the specimen after 29 hours of exposure. The results make it possible to compare the two materials at the same compaction energy. The argillite sample shows a significant shrinkage but no cracks at this scale. On the different hand, with the addition of bentonite, a significant cracking was observed and analysed. These results provide information on the hydromechanical behaviour of unsaturated fine soils at the atmosphere-compacted soil interface.

Researches on heterogeneous acid-base catalysis in Institute for sorption and problems of endoecology of the National Academy of Sciences of Ukraine

In chronological order, the reaseach results of Department of heterogeneous acid-base catalysis at Institute for sorption and endoecology problems in 2003-2023 are described. It relates to the synthesis, study and application of solid superacids WO3/ZrO2, WO3/ZrO2-SiO2, ZrO2-SiO2-Al2O3, ZrO2-SiO2-SnO2, as catalysts, in vacuum gas oil cracking, alkylation of isobutane with isobutanol, acylation toluene, oligomerization of tetrohydrofuran, acylation of methyl tert-butyl ether and other. Some study deals with a search of the correlations between of acid site strength of a catalyst and its activity, in particular, in dehydration reaction of C2-C4 alcohols, and the correlations between ability of primary and secondary alcohols to dehydrogenation and oxidation and their chemical shifts δ (R17OH) and δ (R13СОH ). For the first time, the values of Hammett's acidity function have been measured at elevated (up to 200 °C) temperatures for solid acids. In particular, for H-Y faujasite, H0 reaches superacidic value H0 at 160 °С. Since 2010, the main focus has been on the catalytic conversion of renewable raw materials, mainly bioalcohols (ethanol, glycerol) and C6 carbohydrates, into important products of organic synthesis (ethyl acetate, 1,1 diethoxyethane, n-butanol, propylene glycol, alkyl lactates, lactide, glycolide). In cooperation with “Techinservice Manufacturing Group”, new processes for obtaining ethyl acetate, 1,1 diethoxyethane, n-butanol from bioethanol and racemic lactide from glycerol were developed. Also, new technologies for obtaining propylene oxide from propylene and hydrogen peroxide (НРPОа-process), vapor phase hydrogenation of the pyrolysis C4-5 fraction, and direct high-temperature chlorination of ethylene to vinyl chloride have been developed for Kalush “Karpatnaftochim” plant. The HHPOa installation (2000 t/y) has been started at “Karpatnaftochim” in 2020.

ОЦІНЮВАННЯ ЯКОСТІ РОБОТИ КОТКА ПРИКОЧУВАЛЬНОГО ПРИЗМАТИЧНОГО «СТЕП КПП-6»

Summary The purpose of research. Evaluation of the quality of technological process performance by the «STEP KPP-6» roller according to such criteria as the intensity and degree of soil compaction, the uniformity of bottom compaction, the degree of destruction of the cracked surface of the soil, the correspondence of the values obtained during the tests to the levels of professional assessment. Research methods. Analytical review of the design, field experiment, determination of indicators by standardized methods and statistical data processing. Results. The research results proved that the prismatic «STEP KPP-6» roller stably performs the technological process of rolling with satisfactory indicators of the quality of work and can be effectively used for its intended purpose. Rolling the surface of the soil, the roller at the same time intensively acts on the bottom, compacting it, which ensures close adherence of the seed to the bottom of the seed bed to obtain uniform and friendly seedlings. The density of the soil in a layer up to 15 cm before the passage of the roller was 0.97 g/cm3, after the passage was 1.15 g/cm3, compaction was 0.18 g/cm3. With the increase in the depth of preliminary tillage after passing the roller, a sharp decrease in the degree of soil compaction is noted: from 72% (at an average depth of 5 cm) to 58% (at an average depth of 10.6 cm). It is also significant to reduce the intensity and uniformity of bottom compaction from 100% to 32% and from 24% to 10% respectively. In addition, the roller ensures the destruction and loosening of the cracked surface of the field by 88% in one pass and by up to 97% in two passes both before sowing and in the presence of seedlings of cultivated plants. Conclusions. Research has established that the «STEP KPP-6» roller has universal structural and technological solutions, meets the technological requirements of a consumer, performs the rolling process with high quality, which, along with an attractive price, puts the machine in the line of high-quality import substitution offers. The use of the «STEP KPP-6» roller is recommended before sowing after deep cultivation for sedimentation of the soil, formation of lower horizons and prevention of their drying by covering the surface with a loosened layer of soil and after sowing to ensure contact of seeds with the soil, effective at destroying the cracked soil surface without and with plants. Key words: rolling, roller, soil density, compaction, tillage depth, crust destruction, cracked soil surface.

Prediction of the displacement mechanism of the cracked soil using NXFEM and Artificial Neural Networks

Prediction of the displacement mechanism of the cracked soil using NXFEM and Artificial Neural Networks

INFLUENCE OF SURFACE CRACKS ON THE STABILITY OF CRACKED SOIL SLOPE

The slope stability is a major concern to geotechnical engineers. Traditional methods of slope stability analysis have potentially ignored the influence of surface cracks. It is also known that seasonal rainfall and seepage through crack are closely related with slope failure. First, surface cracks provide special flow channels which increase the soil permeability and decrease the soil strength. Second, water-filled cracks apply an additional active force on the slope. Finally, cracks can create a part of the critical failure surface that has no shear strength. The objective of this paper is to investigate the influence of existing cracks on the stability of a cracked soil slope in different state. The effects of crack depth, slope angle and water-filled cracks on the stability of the cracked slope are explored. The analysis was conducted using the computer modelling programs Optum G2 to analysis of slope factor of safety. The results show that with increasing of slope angle the factor of safety decreases and this problem is significant in the slope with water filled cracks. Also, Factor of safety for all of slope angles in Dry and water filled cracks states with increasing the crack depth, decrease significantly.

Application of Fractal to Evaluate the Drying Shrinkage Behavior of Soil Composites from Recycled Waste Clay Brick

Soil drying cracking is the most common natural phenomenon affecting soil stability. Due to the complexity of the geometric shapes of soil cracks during the cracking process, it has become a major problem in engineering science. The extremely irregular and complex crack networks formed in civil engineering materials can be quantitatively investigated using fractal theory. In this paper, fractal dimension is proposed to characterize the drying cracking characteristics of composite soil by adding recycled waste brick micro-powder. At the same time, the concept of the probability entropy of cracking is introduced to quantify the ordered state of crack development. Correspondingly, the endpoint value of probability entropy was solved mathematically, and the meaning of the probability entropy of cracking was clarified. In this study, the fracture fractal characteristics of composite soil mixed with different materials were first investigated. Then, five groups of composite soil-saturated muds with added recycled waste brick micro-powder of different contents were prepared in the laboratory. Using the evaporation test under constant temperature and humidity, the change rules of the fractal dimensions, probability entropy, crack ratios, and water contents of cracks during the cracking process of the soil samples were obtained. The results show that: (1) on the whole, the fractal dimensions of the soil samples added with recycled waste brick micro-powder of different contents increased over time, and the fractal dimensions of the soil samples without recycled waste brick micro-powder were obviously larger than those of the soil samples with recycled waste brick micro-powder. With the increase in the content of recycled waste brick micro-powder, the maximum fractal dimension decreased in turn. The maximum fractal dimensions of the five groups of soil samples were 1.74, 1.68, 1.62, 1.57, and 1.45. (2) The change trends of the probability entropy and fractal dimensions were similar; both of them showed an upward trend over time, and the probability entropy of the soil samples without recycled waste brick micro-powder was greater than that of the soil samples with recycled waste brick micro-powder. With the increase in the contents of recycled waste brick micro-powder, the probability entropy decreased in turn. The maximum values of the crack probability entropy of the five groups of soil samples were 0.99, 0.92, 0.87, 0.83, and 0.80. (3) Under the action of continuous evaporation, the moisture contents of the soil samples gradually decreased over time, while the crack ratios increased over time. To sum up, both from the perspective of the development process of the cracks of the soil samples and from the perspective of the final stable crack networks of the soil samples, the geometric shapes of the cracks of the soil samples without recycled waste brick micro-powder were the most complex. With the increase in the content of recycled waste brick micro-powder, the fractal characteristics of the cracks gradually changed from complex to simple.

Structural and Fractal Analysis of Soil Cracks Due to the Roots of Setaria Viridis

Soil surfaces form complex crack networks as a result of water loss and shrinkage. A crack network destroys the integrity of the soil and becomes the main factor affecting rainfall infiltration, slope instability and soil integrity. In this paper, a soil fracture network is quantified using fractal characteristics and fractal dimensions, and the soil fracture network is identified and calculated using digital image processing technology. The fracture network of silty clay with different setaria viridis root content is studied during the process of evaporation. Saturated mud is prepared by taking soil samples and collecting setaria viridis roots. The content of setaria viridis roots in each saturated mud sample is 0 g, 0.1 g, 0.2 g and 0.3 g. In the artificial climate environment simulation system, thin-layer root soil is dried by controlling the temperature and humidity to simulate dry climate conditions. During the test, the crack development process is recorded using a digital camera. The results show that when the root content is 0, 0.1 g, 0.2 g and 0.3 g, the water content values when a fissure is generated are 35.2%, 41.2%, 42% and 46.4%, and the initial fractal dimension values are 1.100, 1.106, 1.112 and 1.115, respectively. The fractal dimension value increases rapidly in the early stage of fissure generation, and it reaches the maximum value when the water content reaches 13.66%, 15.2%, 15.66% and 17.98%, respectively. According to the change law of the fractal dimension, the fractal dimension increases rapidly following the initial appearance of the fracture, and, with a continuous reduction in water content in the later stage, the fracture characteristics gradually stabilize, and the change rate of the fractal dimension becomes slow.

Healing behaviour of desiccation cracks in a clayey soil subjected to different wetting rates

Desiccation cracks initiate and propagate during the drying process and healing occurs during the wetting process. However, most of the previous studies only paid attention to the drying-induced crack propagation and the wetting-induced healing behaviour was always neglected. In this paper, a series of wetting tests were conducted on cracked soils under different wetting rates. The crack pattern evolution during wetting was recorded and quantitatively analysed. The results show that the narrow and short secondary and tertiary cracks heal earlier than the long and wide primary cracks during wetting. With the elapsed wetting time, the surface crack ratio and average crack width decrease slowly at first, then rapidly decrease and eventually stabilise. However, at the early stage of wetting, the total crack length almost remains constant. The healing of desiccation cracks in clayey soils is mainly attributed by two factors: wetting-induced swelling and disintegration. Furthermore, the healing degree of desiccation cracks become higher with increasing wetting rate. The healing of desiccation cracks with a lower wetting rate is mainly due to the wetting-induced swelling of soils. However, that with a higher wetting rate is dominated by both swelling and disintegration.

The effects of phosphate fertilizer on the growth and reproduction of Pardosa pseudoannulata and its potential mechanisms

In fields, the natural enemy spider, Pardosa pseudoannulata, plays important roles in insect pest control. Agrochemicals, such as phosphate fertilizer, disturb the ecosystem and weaken the pest control efficiency of the spider. According to the usual habitat of the spider in soil cracks, the soil-application of phosphate fertilizer was carried out to determine its effects on the growth and reproduction of P. pseudoannulata. Phosphate fertilizer treatment prolonged longevity and increased mortality in subadults. The treatment also negatively affected reproduction of P. pseudoannulata adults even with removing phosphate fertilizer stress before adult emergence, leading to a lower mating rate, fewer eggsacs and eggs per female, and fewer offsprings in the first eggsac. The transcriptomic sequencing analysis revealed the up-regulation of unigenes related to stress resistance and down-regulation of unigenes associated with protein processing and proteasomal degradation in phosphate fertilizer-treated P. pseudoannulata. Decline in proper protein processing by E3 ubiquitin-protein ligase complex and endopeptidase activity might provide a partial explanation for negative effects of phosphate fertilizer on the spider reproduction. The study put a notice on negative effects of phosphate fertilizer on beneficial arthropods, which provide a great potential in the protection of P. pseudoannulata and other predator spider species.