Soil Temperature Distribution Research Articles

Experimental study on the movement of oil spill under freeze-thaw action

Oil leakages cause environmental pollution, economic losses, and even engineering safety accidents. In cold regions, researchers urgently investigate the movement of oil spill in soils exposed to freeze-thaw cycles. In this study, a series of laboratory model experiments were carried out on the migration of oil leakage under freeze-thaw action, and the distributions of soil temperature, unfrozen water content, and displacement were analyzed. The results showed that under freeze-thaw action, liquid water in soils migrated to the freezing front and accumulated. After the pipe cracked, oil pollutants first gathered at one side of the leak hole, and then moved around. The pipe wall temperature affected the soil temperature field, and the thermal influence range below and transverse the pipe wall (35cm–40cm) was larger than that above the pipe wall (8cm) owing to the soil surface temperature. The leaked oil's temperature would make the temperature of the surrounding soil rise. Oil would inhibit the cooling of the soils. Besides, oil migration was significantly affected by gravity and water flow patterns. The freeze-thaw action would affect the migration of the oil, which was mainly manifested as inhibiting the diffusion and movement of oil when soils were frozen. Unfrozen water transport caused by freeze-thaw cycles would also inhibit oil migration. The research results would provide a scientific reference for understanding the relationship between the movement of oil pollutants, water, and soil temperature, and for the establishment of a water-heat-mass transport model in frozen soils.

Performance analysis of ground source heat pump systems for constant temperature and humidity air conditioning in industrial buildings: a case study

Abstract The ground source heat pump (GSHP) system has gained widespread popularity for its provision of efficient and environmentally sustainable cooling and heating solutions for buildings. While the performance of GSHP systems has raised significant concerns, research predominantly focuses on residential and office buildings, leaving a gap in understanding their applicability in industrial settings with constant temperature and humidity air conditioning needs. This study aims to address this gap by evaluating the performance of a hybrid ground source heat pump (HGSHP) system implemented within a cigarette factory located in the hot summer and cold winter (HSCW) of China. Through a comprehensive analysis of operational data and long-term monitoring under three cooling conditions, essential parameters including water temperature characteristics, indoor temperature and humidity, system efficiency, power consumption, and soil temperature distribution were examined. The findings revealed that the weighted average coefficient of performance (COP) of the heat pumps (COPhp) and the whole system (COPsys) was decreased from 5.05 to 4.32 and 3.32 to 2.89, respectively. A positive correlation was observed between low cooling load high energy consumption, and low COP. The inlet temperature of the condenser exhibited a declining trend, which was attributed to the intermittent operation of condensation heat recovery. Furthermore, a comprehensive analysis of indoor temperature and humidity distribution within the controlled room was presented and found that almost all the rooms serviced by this system meet the specified design requirements. This research contributes to an enhanced understanding of the viability of HGSHP systems in industrial settings and provides valuable references for improving their energy efficiency and overall performance.

Factors Affecting Soil Bulk Density: A Conceptual Model

Soil bulk density is an important aspect of soil properties, and it can affect agroecology as in diversity, synergies, efficiency, recycling, and resilience. Diversity as in soil low in bulk density allows greater penetration of plant roots allow better access of water and nutrients. The synergistic effect of adequate supply of soil moisture content in forming moderately low soil bulk density for deeper plant roots for better access to water and nutrients. Agroecology efficiency reduces the need of external inputs to reduce environmental impact related to the resulted excessive pollution and wastage. Ultimately, an improved soil bulk density may increase the overall agroecosystem resilience and output, thus, improving the efficiency. Recycling in agroecology involved mass recycling and heat circulation as in nutrient, water, and waste reduction. A high soil bulk density will impede the recycling process the soil. Resilience as in drought resistance is for soil not too loosely packed that cannot hold water or too compacted until flooding water occurs at the surface and too little water infiltrates the soil. In addition, soil bulk density can affect the estimation of soil moisture content and temperature distribution. The ability to understand the factors that influence changes in soil bulk density would improve the predictive ability of the current model. The current study conducts a review on factors affecting the soil bulk density that is divided into soil physical, chemical, biological, environmental, and management practices. A cumulative of more than 50 factors are discussed in the review on how it affects the change in soil bulk density. The current review illustrates the conceptual relation of these factors on soil bulk density. Also, the result of the current work can be used to support future endeavour by turning the conceptual relation into quantifiable predictive model.

Influence of extraction and injection conditions on the performance of thermal-enhanced soil vapor extraction

Thermal-enhanced soil vapor extraction (T-SVE) is an in-situ remedial technique that can address the limitations of contaminant mass transfer and soil permeability. The relative humidity of the injected air, heating temperature of the thermal well, extraction pressure, and extraction mode are important design parameters of a T-SVE system that determine the temporal and spatial distributions of soil temperature and removal rate. Using a thermal–hydraulic–chemical coupled model with the interphase mass transfer of contaminants and water evaporation/condensation, this study investigated the effects of relative humidity, heating temperature, extraction pressure, and extraction mode on T-SVE performance. The results showed that with an increase in relative humidity, the heating temperature of the contaminated soil significantly improved; however, the removal rate of contaminants decreased, particularly in the late stage of remediation. Considering the heating temperature of the thermal well, a critical air relative humidity value that significantly affects the removal rate of contaminants was observed. The heating temperature of the thermal well must be considered in engineering design; however, the evaluation of the relative humidity of the air cannot be ignored.

Application of computer technology to numerical simulation of hydrothermal variation of subgrade enhanced by seepage drainage geoglage under freeze-thaw cycle

In seasonal frozen soil areas, engineering problems are common due to the high water content of subgrade soil. In view of this phenomenon, a new type of percolating drainage geogrid (SDG) is proposed for cooling and drainage. The changes of soil temperature and moisture at different time points were analyzed through computer simulation laboratory model test, and the changes and distribution of soil temperature and moisture under freeze-thaw conditions were obtained. The temperature and moisture changes and their distribution obtained by computer modeling agree with the experimental results. By optimizing the soil materials of the model samples, the changes of temperature and moisture with time under freeze-thaw conditions were more significant. Therefore, it can be inferred that, without changing the configuration of the percolation drain grid, the cooling drainage performance of the percolation drain grid can be improved under the same conditions by changing the heat transfer coefficient or the macroporous filling material. It provides theoretical support and data guarantee for the reinforcement of subgrade percolation and drainage grid in cold area.

Visualized Experimental Study of Soil Temperature Distribution around Submarine Buried Offshore Pipeline Based on Transparent Soil

The temperature distribution around the offshore burial pipeline is an important factor affecting its safety design and economic operation. The traditional test method cannot obtain the continuous temperature distribution of soil owing to the constraints of placing measurement sensors in soil. The transparent soil model test is an alternative method to realize the visualization research of soil temperature. In this paper, a relationship between the temperature of transparent soil and pixel intensity was first established. Then, the transparent soil test and numerical simulation, considering the natural convection, were carried out to study the temperature distribution around the submarine pipeline during start-up and stable operation. The influence of buried depth and pipeline diameter was analyzed. The results suggest that the continuous temperature distribution can be obtained visually by using a transparent soil test, and the observed heating zone of influence extended to a radial distance of 2.6 pipe diameters. The numerical analysis results show that the influence zone of the temperature of pipeline is a distance of four pipeline diameters at a temperature difference of 45 °C. The buried depth and pipeline diameter have little influence on the influence zone. In addition, the contour curves of soil temperature around the pipeline with different diameter are similar in shape. With the decrease in the buried depth of pipeline, the temperature gradient of soil around the pipeline decreases, which is caused by the natural convection.

The Effect of Sowing Date on the Growth and Yield of Soybeans Cultivated in North-Eastern Poland

Soybean yields are influenced by numerous factors, including environmental conditions, location, and agricultural practices. Sowing date affects plant growth, development, and yields, and it plays a particularly important role in soybean cultivation. The optimal sowing date should be selected based on soil temperature, precipitation, and rainfall distribution in a given region. The aim of this study was to determine the effect of various sowing dates (I—early, II—optimal, III—late) on the time from sowing to emergence of soybean seedlings, length of the growing season, morphological traits of soybean plants, yield components, and seed yields of soybeans grown in north-eastern Poland. Sowing date considerably affected the time from sowing to the emergence of soybean seedlings and seed yields. In north-eastern Poland, soybeans should be sown in the first half of May to minimize the risk of ground frost damage, which can occur even in late May. Sowing date also influenced soybean yields. In north-eastern Poland (Region of Warmia and Mazury), yields were maximized when soybeans were sown late (in mid-May), which was decisively influenced by climatic conditions, mainly temperature. The linear regression analysis revealed that the length of the growing season was correlated with the seed yields of soybeans sown on different dates.

Can Drip Irrigation without Film Mulching Be Favorable for Potato Growth in Eastern China?

The main measures to improve potato cultivation in eastern China are film mulching and drip irrigation. However, the film can cause soil pollution and inhibit plant growth because of non-degradable polyethylene, which is the main component of the film. Whether drip irrigation without mulching can improve potato yield needs to be fully explored. Field experiments were conducted at the Special Potato Experimental Station, China Agricultural University, Rizhao City, Shandong Province, China, in 2019 and 2020 to investigate the effects of mulching and soil wetted percentage on soil water and temperature distribution, as well as potato growth. In 2019, three treatments with soil wetted percentage of 50% were set up: black plastic film mulching (BMP2), transparent plastic film mulching (TMP2), and no mulching (NMP2). In 2020, soil wetted percentage treatments were added to the existing mulching treatments: no mulching without irrigation (NMP0) and no mulching with soil wetted percentage of 25% (NMP1), 50% (NMP2), and 75% (NMP3); black plastic film mulching without irrigation (BMP0) and black plastic mulching with 50% soil wetted percentage (BMP2); and transparent plastic film mulching with no irrigation (TMP0) and transparent plastic film mulching with 50% soil wetted percentage (TMP2). The results indicated that mulching did not have a significant effect (p < 0.05) on soil temperature, potato growth, and yield. Irrigation reduced soil temperature by a range of 0.4 to 3.0 °C during the high air temperature season. Irrigation significantly increased potato plant height, stem thickness, and yield. The potato yield under the irrigation treatment could be 16.0–24.9% greater than that under the non-irrigation treatment. The highest irrigation water use efficiency (IWUE) was achieved at soil wetted percentage P1 and P2, which were beneficial for water saving. The NMP1 and NMP2 treatments had 83.4% and 81.0% significantly higher IWUE than NMP3 treatment. Considering environmental protection, resource conservation, and economic efficiency, drip irrigation without mulching under soil wetted percentage P2 was suitable for potato cultivation in eastern China.

Investigation of earth air heat exchangers functioning in arid locations using Matlab/Simulink

This study presents a MATLAB/Simulink model to predict the distribution of soil temperatures and design Earth-to-Air Heat Exchangers (EAHEs) efficiently. It compares four EAHE configurations, including single-pipe, multi-pipe, multiple-single pipes (MS-pipes), and twisted-single pipes (TS-pipes) systems. The presented model is validated with reliable results and allows for easy modifications to obtain the final design. Results show that MS-pipe EAHE is the better in terms of pressure losses and good in terms cooling potential. The study proves that the installation of the EAHEs in Kufa, Iraq, is highly efficient, achieving cooling potential of 1626 W in August and 129.8 W in March. Additionally, the study highlights the influence of the geometric configuration of EAHEs on both their flow behavior and thermal efficiency, presenting an equation for comparing pipe lengths at different soil depths. This study fills the knowledge gap in the use of MATLAB simulation for designing EAHEs and estimating soil temperatures distribution and it compares four EAHEs configurations.

Effect of Plastic Film Colours and Perforations on Energy Distribution, Soil Temperature, and Evaporation

Plastic film mulching is a commonly used agricultural measure in arid/cold regions to improve crop growth. Despite previous studies on the impact of film mulching on soil water/heat status and crop growth, it is not clear how plastic film colours and perforations affect energy distribution, soil temperature, and evaporation. Six sets of column experiments were performed with three plastic film colours: transparent (T), black (B), and silver-grey (G), and two perforation ratios: 4.49% and 21.44%, to monitor soil evaporation and soil/film mulching temperature. Using these two main control factors, a soil–mulch–atmosphere system (SMAS) model was established to simulate soil evaporation and energy distribution. The simulations of soil evaporation compared well with the measurements. The available net energy was positively related to the perforation ratio and transmittance of the plastic film, which further influenced soil temperature and altered energy distribution. Both simulated and measured results gave the following order for transpiration with the plastic films: T > B > G. The SMAS model was more accurate when a mulch with weak light transmittance covered the field. Moreover, by comparing simulated evaporation mass loss with and without considering heat conduction between the plastic mulch and the soil surface, Csm, we found that it is feasible to exclude Csm. However, Csm is indispensable in the SMAS model for understanding the mechanism of plastic film mulching in agroecosystems, particularly at night.

Effects of Topography on Radial Growth of Tree Species with Different Mycorrhizal Types

In the dynamic monitoring fixed sample plot of 25 ha of coniferous broad-leaved mixed forest in the temperate zone of Northeast China, we used the data from two surveys (2013 and 2018) and microtopography data of the sample plot, and the mycorrhizal type data of tree species to explore whether the different microtopography types and single terrain factors will affect the radial growth of tree species with different mycorrhizal types on a regional scale. We studied the adaptability of tree species with different mycorrhizal types in the north end of Changbai Mountain and the south slope of Laoyeling mountain, and which provided basis for further revealing the response mechanism of tree species with different mycorrhizal types to the microtopography in this area. We found that: the tree species with different mycorrhizal types have higher radial growth rates on gentle slopes than on steep slopes. Tree species on sunny slopes have higher growth rates and survival rates than tree species of the same mycorrhizal type on shady slopes. The quantity and radial growth of AM (Arbuscular mycorrhiza) type, EcM (Ectomycorrhiza) type, and ErM (Ericoid mycorrhiza) type tree species were significantly positively correlated with different microtopography types. The quantity and radial growth of AM type tree species and EcM type tree species were significantly positively correlated with slope. The quantity of AM type tree species, EcM type tree species and the radial growth of EcM type tree species were significantly negatively correlated with slope aspect. The quantity and radial growth of ErM type tree species and radial growth of EcM type tree species the were significantly positively correlated with slope position. We believe that the reasons for these conclusions may be caused by the differences in soil temperature, humidity, and water distribution caused by different slopes.

Numerical Investigation of the Long-Term Load Shifting Behaviors within the Borehole Heat Exchanger Array System

In the process of development and utilization of a large-scale borehole heat exchanger (BHE) array system, the phenomenon of load shifting within BHE array can be observed. In this paper, OpenGeoSys software coupled with TESPy toolkit is used to establish a comprehensive numerical model of BHE system (without depicting the heat pump part), and the behaviors of load shifting between BHEs with different design parameters are studied. The results show that the outlet temperature of single BHE and BHE array is generally rising, and the soil temperature around the BHE has accumulated unbalanced heat. The soil temperature near the BHEs array fluctuates more obviously than the single BHE system, and the distribution is uneven. At the end of the 15th year, the soil temperature near the center BHE increased by 2 °C compared with the initial soil temperature, which was more favorable in winter, but was not conducive to the performance improvement in summer. Further analysis by changing the inter-borehole spacing shows that with the increase of the inter-borehole spacing, the load shifting behaviors are gradually weakened, and the maximum shifted load of the central BHE is linear with the change of the inter-borehole spacing. After changing the layout methods, we observe that the more intensive the layout is, the more load shifting behavior is, and the unbalanced rate of soil temperature distribution around the linear layout is lower than other layouts. With the increase in the number of BHEs, the load shifting behaviors are further enhanced. By analyzing the proportion of shifted load amount relative to the average value, it is found that the system will take a longer time to reach heat balance with the increase of BHEs’ number. A shutdown of part of BHEs for a certain period of time will help to improve the long-term operational efficiency of the large-scale shallow ground source heat pump (GSHP) system.

Optimal Drip Fertigation Regimes Improved Soil Micro-Environment, Root Growth and Grain Yield of Spring Maize in Arid Northwest China

Understanding the spatial distributions of soil water, temperature and nutrients as well as their effects on maize growth and grain yield is vital for optimizing drip fertigation regimes. In this study, a 2 year field experiment was conducted on drip-fertigated spring maize with plastic mulching in arid northwestern China in 2015 and 2016. Four irrigation levels were set: as I60 (60% ETc; ETc is crop evapotranspiration), I75 (75% ETc), I90 (90% ETc) and I105 (105% ETc) in 2015; and as I60 (60% ETc), I80 (80% ETc), I100 (100% ETc) and I120 (120% ETc) in 2016. Two fertilization rates of N-P2O5-K2O were set: as F180 (180-90-90) and F240 (240-120-120). The results showed that the average soil water content in the deeper soil layer (80–120 cm) increased with the increase in irrigation level, and the lowest average soil water content in the 0–80 cm soil layer occurred under I95 in 2015 and under I100 in 2016. The irrigation level more significantly influenced the soil temperature at 5 cm than at the other depths. With the decrease in the irrigation level and progression of the growth period, the soil temperature increased. The soil nitrate nitrogen content in the root zone decreased with increasing irrigation level. The largest soil nitrate nitrogen content at the 0–100 cm depth occurred under I60 in both 2015 and 2016. Significant differences were observed for root length density in the 0–20 cm soil layer at various lateral locations. In deeper (60–100 cm) soil layers, the root length density under I75 (2015) and I80 (2016) was greater than at other depths. Grain yield, water use efficiency (WUE) and partial factor productivity (PFP) increased with the increase in irrigation level in 2015, while it increased and then decreased in 2016. I105F180 achieved the maximum grain yield (18.81 t ha−1), WUE (3.32 kg m−3), and PFP (52.26 kg kg−1) in 2015, while I100F180 achieved the maximum grain yield (20.51 t ha−1), WUE (3.99 kg m−3), and PFP (57.02 kg kg−1) in 2016. The optimal drip fertigation regimes for spring maize in arid northwest China were recommended as 90–100% ETc and 180-90-90 (N-P2O5-K2O) kg hm−2.

Surface water-groundwater interaction affects soil temperature distributions and variations in salt marshes

Soil temperature is an important environmental factor affecting biogeochemical processes in salt marshes and further wetland ecological functions. This study conducted field investigation and numerical simulations to examine temperature distributions and variations in a creek-marsh section subjected to estuarine and meteorological forcing conditions. The results showed that periodic tidal inundation induced water and heat exchange across sediment-water interfaces and thus modified diurnal temperature variations in shallow soil layers caused by meteorological fluctuations. The combination of periodic tidal inundation and sediment-atmosphere heat exchange led to the formation of three characteristic soil temperature zones along the creek-marsh section: a high-elevation marsh zone with diurnal temperature variations influenced by meteorological fluctuations, a near-creek zone where tide-induced porewater circulations regulated soil temperatures, and a low-elevation and sloping zone where sediment-atmosphere heat exchange decreased with the reduced marsh elevation. Sensitivity analyses demonstrated that a larger hydraulic conductivity facilitated the porewater circulation and heat transport in the near-creek zone, enhancing temperature fluctuations. An increased soil thermal conductivity intensified vertical heat exchange across sediment-water-atmosphere interfaces and increased the effect of estuarine and meteorological conditions on soil temperature. This study highlights the importance of surface water-groundwater interaction on temperature variations and helps to understand thermodynamics-dependent biogeochemical processes in salt marshes.

Earth-to-air Heat Exchanger for Cooling Applications in a Hot and Dry Climate: Numerical and Experimental Study

Shallow geothermal energy, by an earth-to-air heat exchanger (EAHE), is utilized to cool buildings with minimal energy usage. Significant parameters affecting the heat exchanger's performance must be investigated to obtain a suitable design. Shallow geothermal energy, by an earth-to-air heat exchanger (EAHE), is utilized to cool buildings with minimal energy usage. Significant parameters affecting the heat exchanger's performance must be investigated to obtain a suitable design. This article numerically and experimentally investigates the effect of pipe diameter, pipe length, inlet air temperature, soil temperature, airflow velocity, and soil thermal conductivity on the performance of the heat exchanger under hot and dry climate conditions. The soil temperature distribution was measured from the surface to a depth of 7 m in the city of Karbala (center of Iraq) in the summer season. The experimental test for EAHE was carried out in water-saturated soil and ambient air temperatures of 41 ºC, 45 ºC, and 49.5 ºC at four different velocities. The percentage drop in the EAHE outlet air temperature at 9 m/s was 28.3%, 25.5%, and 19.5%, respectively. Also, the three-dimensional model was created, and the simulation results were compared with the experimental results, which were in good agreement. An equation for the outlet air temperature was found as a function of pipe diameter and length, ambient air temperature, soil temperature around the pipe, and soil thermal conductivity. The resulted equation were compared with the current experimental results and experimental results of reported data inliterature. As a result, a very good agreement was observed. The results showed that the parameter L (length of the pipe) causes the strongest nonlinear behavior in the equation. For the cases considered, at diameters 75 and 100 mm, an approximate linear behavior for the length required to achieve a specific outlet temperature was observed. It can be concluded from the results that changing the soil type from dry one (k=0.5 W/m K) to saturated one (case of Karbala city, k=1.5 W/m K) resulted about 25% reduction in the length of the pipe. Also, the results showed that at an air velocity of 7m/s, the length required to obtain 26 ºC at the outlet of EAHE is 62.1 m which is 55% higher than the case of 29 ºC (39.9m).

Effect of freeze–thaw process on heat transfer and water migration between soil water and groundwater

Understanding the mechanisms of water migration and heat transfer in frozen soil is essential for the selection of water resource management measures and determination of irrigation schemes for winters. However, the dynamics of the groundwater level and temperature caused by freezing and thawing and their impact on soil water redistribution remain unclear. In this field study, the mechanisms of water migration and heat transfer in the soil during the freeze–thaw period under the combined action of the surface temperature change (upper boundary) and groundwater level fluctuation (lower boundary) were comprehensively considered with the theory and method of heat transfer, freeze–thaw characteristic curves of soil, and water balance model. The results showed that: (1) The soil temperature distribution and groundwater temperature dynamics can be interpreted intuitively by the soil temperature gradient and accumulated heat storage. (2) The freeze–thaw characteristic curves of soil indicated that the soil temperature dynamics caused a phase transition of the soil water. This further changed the soil water potential and permeability by 1–2 magnitudes and 1–5 magnitudes, respectively, which affected the direction and quantity of water migration. (3) The water balance quantitatively revealed the controlling effect of groundwater level changes caused by freezing and thawing on soil moisture dynamics. About 20% of the ice in the frozen layer was formed by the upward recharge of the groundwater during the freezing period. In the thawing period, most of this water returned to the groundwater (84%), while the rest (16%) increased the soil water content. These results systematically explain the mechanisms of heat transfer and water migration between the soil water and the groundwater during the freeze–thaw period, providing a theoretical reference for agricultural water management in seasonally frozen regions.

Analytic model for calculation of soil temperature and heat balance of bare soil surface in solar greenhouse

This study establishes a soil temperature model of a solar greenhouse, which takes into account the soil water evaporation, solar radiation, thermal radiation and convective heat transfer on the soil surface. The model is utilized to obtain the mathematical function of soil temperature distribution according to solar radiation and air temperature in a solar greenhouse. The model is validated in two greenhouses with and without plants. Based on the model, the heat gain and loss of solar greenhouse soil are calculated. The results show that the heat accumulated by the greenhouse soil is mainly by absorbing solar radiation during the day and the heat lost by the greenhouse soil is mainly by water evaporation during the day and thermal radiation at night. Then, according to the small convective heat transfer between soil and air in the solar greenhouse, the solar-air temperature calculation equation is simplified, so that the simplified model can predict the soil temperature based on solar radiation and outdoor air temperature, which provides an important soil boundary condition for the solar greenhouse thermal model and CFD prediction. Finally, the evaporation coefficient is proposed to characterize the effect of water evaporation intensity on the soil temperature in a solar greenhouse. In this case, the average soil temperature increases by about 2℃ for every 0.1 decrease in evaporation coefficient.

Temperature Distributions in Geogrid-Reinforced Soil Retaining Walls Subjected to Seasonal Freeze–Thaw Cycles

Temperature Distributions in Geogrid-Reinforced Soil Retaining Walls Subjected to Seasonal Freeze–Thaw Cycles

Determination of the coefficient of effective thermal diffusivity of soil under natural changes in environmental conditions

An experimental setup and a data processing technique have been developed to obtain the soil temperature distribution in depth and in time. The results of measuring the soil temperature during 2021 in the city of Ramenskoye, Moscow Region at depths from 0 to 1.475 m are obtained and presented. An analytical solution of the problem of heat transfer in the soil based on the superposition principle is shown and verified. The coefficient of effective thermal diffusivity of soil a = 0.99 · 10−6 m2/s was determined indirectly in a passive experiment. Conclusions are drawn about the coincidence with the results of the experiment of the asymptotic nature of the dependence of the analytical solution for determining the amplitude of soil temperature fluctuations on depth and linear for the phase. An analytical solution is presented to obtain the temperature distribution in the soil with the known law of temperature fluctuations on the surface and the coefficient of effective thermal diffusivity.

Modelling Soil Water, Salt and Heat Dynamics under Partially Mulched Conditions with Drip Irrigation, Using HYDRUS-2D

Drip irrigation under mulch is a widely used technique in the arid region of northwest China. The partially mulched soil and the bare strips between mulched areas may complicate the migration of water, salt, and heat in soils, and cause lateral salt accumulation on bare soil surfaces. For investigating hydrothermal dynamics and salt distribution patterns under such circumstances, tank experiments with drip irrigation under plastic film on partially mulched soil were conducted under two intensities of drip irrigation (i.e., low (W1) and high (W2)) with the same total irrigation amount. The spatial distributions of soil water, temperature, and electrical conductivity were monitored accordingly. The two-dimensional (2D) model of soil water, salt, and heat transport under drip irrigation and partially mulched soil conditions was established using HYDRUS-2D, and kinetic adsorption during salt migration was considered. The results of the experiments showed that the uneven distribution of the hydrothermal state led to the accumulation of salt on the un-mulched soil surface. Water migrated from where the dripper was located, and heat accumulated mainly in the mulched soil. HYDRUS-2D matched reasonably well with the observed data, with an R2 higher than 0.54. Under the partially mulched conditions, lower intensity of drip irrigation (W1) show higher desalination efficiency in root zones, with less even lateral salt distribution. Scenario simulations further demonstrated that a larger total irrigation amount would result in a larger desalination zone, and drip irrigations with appropriate incremental intensity could improve salt leaching in the root zone with increased lateral migration of water.