Soil-air Interface Research Articles

Visualizing NH3 emission and the local O2 and pH microenvironment of soil upon manure application using optical sensors

The application of fertilizers and manure on fields is the largest source of ammonia (NH3) in the atmosphere.·NH3 emission from agriculture has negative environmental consequences and is largely controlled by the chemical microenvironment and the respective biological activity of the soil. While gas phase and bulk measurements can describe the emission on a large scale, those measurements fail to unravel the local processes and spatial heterogeneity at the soil air interface. We report a two dimensional (2D) imaging approach capable of visualizing three of the most important chemical parameters associated with NH3 emission from soil. Besides the released NH3 itself also O2 and pH microenvironments are imaged using reversible optodes in real-time with a spatial resolution of <100 µm. This combined optode approach utilizes a specifically developed NH3 optode with a limit of detection of 2.11 ppm and a large working range (0–1800 ppm) ideally suited for studying NH3 volatilization from soil. This NH3 optode will contribute to a better understanding of the driving factors for NH3 emission on a microscale and has the potential to become a valuable tool in studying NH3 dynamics.

Advances in heat‐pulse methods: Measuring near‐surface soil water content

AbstractSoil water content (θ) influences physical, chemical, and biological processes in the soil. Near‐surface θ (&lt;1‐cm depth) is particularly important for surface energy partitioning, but few techniques are available for near‐surface in situ θ measurements. Heat‐pulse sensors can be used to determine the soil volumetric heat capacity, which is linearly related to θ. Here we describe the principles and procedures of determining near‐surface in situ θ with a heat pulse sensor. The main limitations and potential errors associated with the method are also presented. When ambient soil temperature drift and the soil–air interface effects are addressed, the error in the heat‐pulse‐determined θ is greatly reduced. For an example, data series with θ data determined by gravimetric initial θ and heat‐pulse‐based change in θ (Δθ), results agree well with gravimetric θ values, yielding a coefficient of determination of 0.95. We conclude that heat‐pulse sensors are useful tools for continuously and nondestructively determining near‐surface θ of non‐shrink–swell soils.

A Review on Airborne Microbes: The Characteristics of Sources, Pathogenicity and Geography

Microbes are widespread and have been much more studied in recent years. In this review, we describe detailed information on airborne microbes that commonly originate from soil and water through liquid–air and soil–air interface. The common bacteria and fungi in the atmosphere are the phyla of Firmicutes, Proteobacteria, Bacteroides, Actinobacteria, Cyanobacteria and Ascomycota, Basidiomycota, Chytridiomycota, Rozellomycota that include most pathogens leading to several health problems. In addition, the stability of microbial community structure in bioaerosols could be affected by many factors and some special weather conditions like dust events even can transport foreign pathogens to other regions, affecting human health. Such environments are common for a particular place and affect the nature and interaction of airborne microbes with them. For instance, meteorological factors, haze and foggy days greatly influence the concentration and abundance of airborne microbes. However, as microorganisms in the atmosphere are attached on particulate matters (PM), the high concentration of chemical pollutants in PM tends to restrain the growth of microbes, especially gathering atmospheric pollutants in heavy haze days. Moreover, moderate haze concentration and/or common chemical components could provide suitable microenvironments and nutrition for airborne microorganism survival. In summary, the study reviews much information and characteristics of airborne microbes for further study.

A new model for simulation of collection and conveyance sections of Qanat

In this paper, a new numerical model has been developed for simulation of Qanat-aquifer system. This model employs quasi-3D mixed-form of Richards’ equation and 1D fully-hydrodynamic form of Saint-Venant equations to simulate subsurface and overland flow, respectively. In order to handle non-orthogonal grids, subsurface flow module benefits from coordinate transformation technique. Using the above-mentioned governing equations, the presented model is able to simulate water flow inside both collection and conveyance sections of the gallery as well as dynamics of groundwater and vadose zone from impermeable bed rock to the soil-air interface. Since measured data corresponding to the hydraulics of Qanats is scarce, the overland and subsurface modules have been validated with analytical, numerical and experimental benchmarks in the literature. Subsequently, the model was employed to simulate ten different hypothetical aquifer-Qanat systems with different properties including the depth of groundwater aquifer, roughness of the gallery and saturated hydraulic conductivity of the gallery-aquifer boundary and the influence of each the parameters was monitored on the outflow rate at the appearance point of each Qanat. Furthermore, the advance of water inside two initially dry galleries were simulated at different time levels up to steady state. Eventually, the streamlines have been shown at the steady state for two Qanat-aquifer systems. Although, the presented study sheds light on some aspects of Qanat-aquifer hydraulics, the validation of the presented model with in-lab or on-field data remains ongoing for the future researches.

Greenhouse gas emissions from riparian zone cropland in a tributary bay of the Three Gorges Reservoir, China.

BackgroundA huge reservoir was formed by the Three Gorges Dam in China, which also formed a riparian zone along the bank of the reservoir. In the period of low water-level, the riparian zone in tributary bays of the Three Gorges Reservoir (TGR) was always unordered cultivated, owing to its gentle slope and high soil fertility. This land-use practice creates high potential of generating greenhouse gas (GHG) emissions with periodic water level fluctuation.MethodsTo evaluate potential GHG emissions from the soil-air interface, the static opaque chamber method was adopted to evaluate the effect of elevations (180 m, 175 m, 170 m and 165 m) and land use types (dry lands, paddy fields and grass fields) from April to September in 2015 and 2016.ResultsThe results showed that carbon dioxide (CO2) was the main contributor of GHG emission in riparian zone most likely because of high organic carbon from residues. Furthermore, high soil water content in paddy fields resulted in significantly higher methane (CH4) flux than that in dry lands and grass fields. Compared to grass fields, anthropogenic activities in croplands were attributed with a decrease of soil total carbon and GHG emissions. However, inundation duration of different elevations was found to have no significant effect on CH4 and CO2 emissions in the riparian zone, and the mean nitrous oxide (N2O) flux from dry lands at an elevation of 165 m was significantly higher than that of other elevations likely because of tillage and manure application. The high N2O fluxes produced from tillage and fertilizer suggested that, in order to potentially mitigate GHG emissions from the riparian zone, more attention must be paid to the farming practices in dry lands at low elevations (below 165 m) in the riparian zone. Understanding factors that contribute to GHG emissions will help guide ecological restoration of riparian zones in the TGR.

Subsurface MIMO: A Beamforming Design in Internet of Underground Things for Digital Agriculture Applications

In underground (UG) multiple-input and multiple-output (MIMO), transmit beamforming is used to focus energy in the desired direction. There are three different paths in the underground soil medium through which the waves propagate to reach the receiver. When the UG receiver receives a desired data stream only from the desired path, then the UG MIMO channel becomes a three-path (lateral, direct, and reflected) interference channel. Accordingly, the capacity region of the UG MIMO three-path interference channel, and the degrees of freedom (multiplexing gain of this MIMO channel) requires careful modeling. Therefore, expressions are required for the degrees of freedom of the UG MIMO interference channel. The underground receiver needs to perfectly cancel the interference from the three different components of the EM waves propagating in the soil medium. This concept is based upon reducing the interference of the undesired components to a minimum level at the UG receiver using the receive beamforming. In this paper, underground environment-aware MIMO using transmit and receive beamforming has been developed. The optimal transmit and receive beamforming, combining vectors under minimal intercomponent interference constraints, are derived. It is shown that UG MIMO performs best when all three components of the wireless UG channel are leveraged for beamforming. The environment-aware UG MIMO technique leads to three-fold performance improvements and paves the way for design and development of next-generation sensor-guided irrigation systems in the field of digital agriculture. Based on the analysis of underground radio-wave propagation in subsurface radio channels, a phased-array antenna design is presented that uses water content information and beam-steering mechanisms to improve efficiency and communication range of wireless underground communications. It is shown that the subsurface beamforming using phased-array antennas improves wireless underground communications by using the array element optimization and soil–air interface refraction adjustment schemes. This design is useful for subsurface communication system where sophisticated sensors and software systems are used as data collection tools that measure, record, and manage spatial and temporal data in the field of digital agriculture.

A Theoretical Model of Underground Dipole Antennas for Communications in Internet of Underground Things

The realization of Internet of underground things (IOUT) relies on the establishment of reliable communication links, where the antenna becomes a major design component due to the significant impacts of soil. In this paper, a theoretical model is developed to capture the impacts of the change of soil moisture on the return loss, resonant frequency, and bandwidth (BW) of a buried dipole antenna. Experiments are conducted in silty clay loam, sandy, and silt loam soil, to characterize the effects of soil, in an indoor testbed and field testbeds. It is shown that at subsurface burial depths (0.1–0.4 m), the change in soil moisture impacts communication by resulting in a shift in the resonant frequency of the antenna. Simulations are done to validate the theoretical and measured results. This model allows system engineers to predict the underground antenna resonance and also helps to design an efficient communication system in IOUT. Accordingly, a wideband planar antenna is designed for an agricultural IOUT application. Empirical evaluations show that an antenna designed considering both the dispersion of soil and the reflection from the soil–air interface can improve communication distances by up to five times compared to antennas that are designed based on only the wavelength change in soil.

Carbon isotopic signature of interstitial soil gases reveals the potential role of ecosystems in mitigating geogenic greenhouse gas emissions: Case studies from hydrothermal systems in Italy

Volcanic and hydrothermal areas largely contribute to the natural emission of greenhouse gases to the atmosphere, although large uncertainties in estimating their global output still remain. Nevertheless, CO2 and CH4 discharged from hydrothermal fluid reservoirs may support active soil microbial communities. Such secondary processes can control and reduce the flux of these gases to the atmosphere. In order to evaluate the effects deriving from the presence of microbial activity, chemical and carbon (in CO2 and CH4) isotopic composition of interstitial soil gases, as well as diffuse CO2 fluxes, of three hydrothermal systems from Italy were investigated, i.e. (i) Solfatara crater (Campi Flegrei), (ii) Monterotondo Marittimo (Larderello geothermal field) and (iii) Baia di Levante in Vulcano Island (Aeolian Archipelago), where soil CO2 fluxes up to 2400, 1920 and 346 g m−2 day−1 were measured, respectively. Despite the large supply of hydrothermal fluids, 13CO2 enrichments were observed in interstitial soil gases with respect to the fumarolic gas discharges, pointing to the occurrence of autotrophic CO2 fixation processes during the migration of deep-sourced fluids towards the soil-air interface. On the other hand, (i) the δ13C-CH4 values (up to ~48‰ vs. V-PDB higher than those measured at the fumarolic emissions) of the interstitial soil gases and (ii) the comparison of the CO2/CH4 ratios between soil gases and fumarolic emissions suggested that the deep-sourced CH4 was partly consumed by methanotrophic activity, as supported by isotope fractionation modeling. These findings confirmed the key role that methanotrophs play in mitigating the release of geogenic greenhouse gases from volcanic and hydrothermal environments.

Summary of Advances in Heat‐Pulse Methods: Measuring Near‐Surface Soil Water Content

Core Ideas Describes the method for determining near‐surface water content with heat pulse sensors. Temperature data prior to a heat‐pulse are used to reduce ambient temperature effects. The PILS–ABC model is used to minimize errors because of the soil–air interface. Surface layer soil water content is important for evaporation, surface energy balance, seed germination, residue decomposition, microbial activity, and many other biological, chemical, and physical processes. The standard method (i.e., the gravimetric method) for measuring soil water content requires destructive sampling and is unsuitable for continuous measurement. Techniques such as neutron thermalization and time domain reflectometry suffer relatively large errors in measuring soil water content near the surface. In a recent Methods of Soil Analysis article, the authors present the principles and procedures for using a heat‐pulse sensor to determine near‐surface soil water content.

A Two-Year Study on Mercury Fluxes from the Soil under Different Vegetation Cover in a Subtropical Region, South China

In order to reveal the mercury (Hg) emission and exchange characteristics at the soil–air interface under different vegetation cover types, the evergreen broad-leaf forest, shrub forest, grass, and bare lands of Simian Mountain National Nature Reserve were selected as the sampling sites. The gaseous elementary mercury (GEM) fluxes at the soil–air interface under the four vegetation covers were continuously monitored for two years, and the effect of temperature and solar radiation on GEM fluxes were also investigated. Results showed that the GEM fluxes at the soil–air interface under different vegetation cover types had significant difference (p &lt; 0.05). The bare land had the maximum GEM flux (15.32 ± 10.44 ng·m−2·h−1), followed by grass land (14.73 ± 18.84 ng·m−2·h−1), and shrub forest (12.83 ± 10.22 ng·m−2·h−1), and the evergreen broad-leaf forest had the lowest value (11.23 ± 11.13 ng·m−2·h−1). The GEM fluxes at the soil–air interface under different vegetation cover types showed similar regularity in seasonal variation, which mean that the GEM fluxes in summer were higher than that in winter. In addition, the GEM fluxes at the soil–air interface under the four vegetation covers in Mt. Simian had obvious diurnal variations.

Model of the 2 × 25 kV high speed railway supply system taking into account the soil-air interface

This paper deals with the modelling of the 2×25kV – 50Hz high speed railway supply system. The proposed approach extends the traditional multi-conductor transmission line approach typically used for high speed railway systems, which is based on the assumption of overhead conductors. More specifically, this approach models the system by considering the presence of both overhead and buried conductors. Analytical formulations to calculate self and mutual line parameters are used. A numerical simulation allows evidencing the different results when the simplified and the detailed modelling approaches are adopted. A sensitivity analysis to point out the influence of the finitely conductive ground is also proposed.

A High‐Resolution Surface Mapping Procedure for Soil Cores Using Computed Tomography Scanning Data

Core Ideas Reliable surface representation is important for porosity analysis inside soil cores. High‐resolution soil surface maps are drawn from computed tomography scanning data. The moving‐window procedure presented here deals with artifacts and soil cavities. High‐resolution mapping of the soil surface provides insight regarding gas and water transport at the soil–atmosphere interface and biogeochemical reactions occurring in soil pores connected to the atmosphere. A new procedure for high‐resolution soil mapping was tested in undisturbed cores (15‐cm diameter) with images constructed from X‐ray computed tomography (CT) scanning. Our procedure includes detecting boundaries at the soil–air interface, edge cleaning, and removal of artifacts by use of a moving window with optimized size. We tested the procedure on three undisturbed soil cores from an agricultural field: (i) without introduced earthworms vs. in which earthworms of (ii) smaller (Aporrectodea turgida Eisen) or (iii) larger (Lumbricus terrestris L.) size were introduced and resided for 28 d. Soil surface maps were produced at a scale of 0.35‐ by 0.35‐mm pixels, with gray tones reflecting lower to higher elevation. This work has implications for describing pore connectivity and interpreting greenhouse gas fluxes from the soil.

Changes in soil characteristics and C dynamics after mangrove clearing (Vietnam)

Of the blue carbon sinks, mangroves have one of the highest organic matter (OM) storage capacities in their soil due to low mineralization processes resulting from waterlogging. However, mangroves are disappearing worldwide because of demographic increases. In addition to the loss of CO2 fixation, mangrove clearing can strongly affect soil characteristics and C storage. The objectives of the present study were to quantify the evolution of soil quality, carbon stocks and carbon fluxes after mangrove clearing. Sediment cores to assess physico-chemical properties were collected and in situ CO2 fluxes were measured at the soil-air interface in a mangrove of Northern Vietnam. We compared a Kandelia candel mangrove forest with a nearby zone that had been cleared two years before the study. Significant decrease of clay content and an increase in bulk density for the upper 35cm in the cleared zone were observed. Soil organic carbon (OC) content in the upper 35cm decreased by >65% two years after clearing. The quantity and the quality of the carbon changed, with lower carbon to nitrogen ratios, indicating a more decomposed OM, a higher content of dissolved organic carbon, and a higher content of inorganic carbon (three times higher). This highlights the efficiency of mineralization processes following clearing. Due to the rapid decrease in the soil carbon content, CO2 fluxes at sediment interface were >50% lower in the cleared zone. Taking into account carbonate precipitation after OC mineralization, the mangrove soil lost ~10MgOCha−1yr−1 mostly as CO2 to the atmosphere and possibly as dissolved forms towards adjacent ecosystems. The impacts on the carbon cycle of mangrove clearing as shown by the switch from a C sink to a C source highlight the importance of maintaining these ecosystems, particularly in a context of climate change.

Comparison of ET partitioning and crop coefficients between partial plastic mulched and non-mulched maize fields

The ratio of evaporation to evapotranspiration (E/ET) and crop coefficients (Kc) are important parameters for evaluating the water-saving potentials of agronomic technologies and they may vary with different practices of dryland cultivation. This study synchronously investigated changes of E/ET and Kc for three years using two eddy covariance systems and multi-microlysimeters under two cultivation methods—conventional flat planting without mulching (CK) and a furrow-ridge system with plastic film partially mulching (MFR)—on the semiarid Loess Plateau of China. Due to an increase of vapor diffusion resistance at the soil-air interface partially mulched by plastic film, the average E and ET of MFR were lower than those of CK by 38.1% and 9.3%, respectively, for the three growing seasons. Thus, the average E/ET in MFR decreased by 11.2 percentage points compared with CK. E/ET showed a significant logistic function with the green leaf area index (GLAI) under both treatments during the three growing seasons. The seasonal Kc varied with GLAI following a step function curve for both treatments, and was linearly correlated to GLAI with significance levels when GLAI was below the thresholds of 3.0 and 3.2–3.4 for CK and MFR, respectively. Maximum Kc values were 1.01±0.05 and 0.91±0.09 for CK and MFR, respectively, at the middle crop growth stage. These results suggest that MFR can significantly reduce E/ET and maximum Kc, which help to improve yield and water use efficiency in rainfed spring maize fields. Consequently, MFR enhanced the average grain yield and crop water use efficiency by 12.5% and 24.6%, which amounted to 11527kg/ha and 3.36kg/m3, respectively. Therefore, MFR promoted crop water productivity and is an effective approach to solve water crises in dryland regions.

Improved representations of coupled soil–canopy processes in the CABLE land surface model (Subversion revision 3432)

Abstract. CABLE is a global land surface model, which has been used extensively in offline and coupled simulations. While CABLE performs well in comparison with other land surface models, results are impacted by decoupling of transpiration and photosynthesis fluxes under drying soil conditions, often leading to implausibly high water use efficiencies. Here, we present a solution to this problem, ensuring that modelled transpiration is always consistent with modelled photosynthesis, while introducing a parsimonious single-parameter drought response function which is coupled to root water uptake. We further improve CABLE's simulation of coupled soil–canopy processes by introducing an alternative hydrology model with a physically accurate representation of coupled energy and water fluxes at the soil–air interface, including a more realistic formulation of transfer under atmospherically stable conditions within the canopy and in the presence of leaf litter. The effects of these model developments are assessed using data from 18 stations from the global eddy covariance FLUXNET database, selected to span a large climatic range. Marked improvements are demonstrated, with root mean squared errors for monthly latent heat fluxes and water use efficiencies being reduced by 40 %. Results highlight the important roles of deep soil moisture in mediating drought response and litter in dampening soil evaporation.

Mercury dynamics and mass balance in a subtropical forest, southwestern China

Abstract. The mid-subtropical forest area in southwest China was affected by anthropogenic mercury (Hg) emissions over the past 3 decades. We quantified mercury dynamics on the forest field and measured fluxes and pools of Hg in litterfall, throughfall, stream water and forest soil in an evergreen broadleaved forest field in southwestern China. Total Hg (THg) input by the throughfall and litterfall was assessed at 32.2 and 42.9 µg m−2 yr−1, respectively, which was remarkably higher than those observed from other forest fields in the background of North America and Europe. Hg fluxes across the soil–air interface (18.6 mg m−2 yr−1) and runoff and/or stream flow (7.2 µg m−2 yr−1) were regarded as the dominant ways for THg export from the forest field. The forest field hosts an enormous amount of atmospheric Hg, and its reserves is estimated to be 25 341 µg m2. The ratio of output to input Hg fluxes (0.34) is higher compared with other study sites. The higher output / input ratio may represent an important ecological risk for the downstream aquatic ecosystems, even if the forest field could be an effective sink of Hg.

A quantum cascade laser infrared spectrometer for CO2 stable isotope analysis: Field implementation at a hydrocarbon contaminated site under bio-remediation

Real-time methods to monitor stable isotope ratios of CO2 are needed to identify biogeochemical origins of CO2 emissions from the soil–air interface. An isotope ratio infra-red spectrometer (IRIS) has been developed to measure CO2 mixing ratio with δ13C isotopic signature, in addition to mixing ratios of other greenhouse gases (CH4, N2O). The original aspects of the instrument as well as its precision and accuracy for the determination of the isotopic signature δ13C of CO2 are discussed. A first application to biodegradation of hydrocarbons is presented, tested on a hydrocarbon contaminated site under aerobic bio-treatment. CO2 flux measurements using closed chamber method is combined with the determination of the isotopic signature δ13C of the CO2 emission to propose a non-intrusive method to monitor in situ biodegradation of hydrocarbons. In the contaminated area, high CO2 emissions have been measured with an isotopic signature δ13C suggesting that CO2 comes from petroleum hydrocarbon biodegradation. This first field implementation shows that rapid and accurate measurement of isotopic signature of CO2 emissions is particularly useful in assessing the contribution of contaminant degradation to the measured CO2 efflux and is promising as a monitoring tool for aerobic bio-treatment.

The effect of addition of a wettable biochar on soil water repellency

SummaryThe potential of biochar to ameliorate soil water repellency has not been widely studied. Previous studies have focused on the potential for biochar to induce or exacerbate existing water repellency rather than alleviate it. This study investigates the effect of adding wettable biochar to water‐repellent soil by comparing the water drop penetration times (WDPTs) of a control and biochar‐amended soil. The potential of wettable biochar to act as a physical amendment to water‐repellent soil was evaluated by mixing coarsely‐ground biochar (CGB, particle size range 250–2000 µm) or finely‐ground biochar (FGB, particle size range &lt; 250 µm) with one strongly and one severely naturally water‐repellent soil in various quantities, and then measuring the WDPT for each mixture. When biochar particles did not fall within the size range of existing soil particles, an initial increase in both mean WDPT (WDPTM) and variation in WDPT was observed with small additions of biochar. These effects possibly result from increased surface roughness and inhibition of infiltration by the suspension of drops above the average soil–air interface at a few hydrophobic points. Both CGB and FGB reduced soil water repellency, FGB more effectively than CGB. The addition of 10% w/w FGB reduced soil WDPT by 50%, and 25% FGB eliminated repellency. Direct absorption of water by biochar and an increase in soil surface area in contact with water are the predominant physical mechanisms involved. This exploratory study suggests biochar has the potential to amend water‐repellent soil.

Evaluation of VOC fluxes at the soil-air interface using different flux chambers and a quasi-analytical approach

Dense nonaqueous-phase liquids (DNAPLs) spilled on the soil migrate vertically depending upon gravity and capillary forces through the unsaturated zone of the porous aquifer, forming a vapour plume. These volatile organic compounds (VOCs) can be transferred by advection-diffusion to the groundwater or to the atmosphere. Evaluating DNAPL vapour fluxes at the soil-air interface is one of the key challenges in the remediation of contaminated sites. This work discusses the results of a large-scale vapour plume experiment with a well-defined trichloroethylene (TCE) spill, including a sequential raising and lowering of the water table, where the TCE vapour fluxes at the soil surface were experimentally quantified in two ways: (i) directly, with measurements at the soil-air interface using different flux chambers at various operational modes under both transient and steady-state conditions of the vapour plume, and (ii) indirectly, using a quasi-analytical approach based on soil gas measurements. It was shown that upward displacement of the water-air front during the controlled raising of the water table (approximately 10 cm h−1) increased the TCE vapour flux measured at the soil surface by factors of 4 to 10. Under steady-state transport conditions, TCE vapour fluxes measured using five types of flux chambers and three operational modes were similar. The effects of the flux chamber geometry, the accumulation of TCE vapours in the chamber headspace or the air recirculation at a low flow rate on the measured TCE vapour fluxes were low. At steady-state transport conditions, TCE vapour fluxes measured with the flux chambers and estimated using the quasi-analytical approach were of the same order of magnitude. However, under transient conditions of the vapour plume, the TCE vapour flux predicted by the quasi-analytical approach greatly underestimated or overestimated the real TCE vapour flux at the soil-air interface.

Thermal Property Measurement Errors with Heat‐Pulse Sensors Positioned near a Soil–Air Interface

Heat‐pulse sensor measurements analyzed with pulsed infinite line source (PILS) theory have been widely used to measure soil properties. The PILS theory assumes that the measured soil medium is uniform and infinite. When the sensors are positioned near the soil surface, the effects of the heterogeneity associated with the soil–air interface should not be ignored. In 1999, Philip and Kluitenberg (PK99) proposed an analytical solution using an instantaneous heating model to analyze the effects of the soil–air interface on soil thermal property measurements with heat‐pulse sensors. The purpose of this study is to test the PK99 instantaneous heat source solution under controlled laboratory conditions. Soil thermal properties including volumetric heat capacity, thermal diffusivity, and thermal conductivity were measured with a commercially available dual‐needle heat‐pulse sensor buried at different depths beneath the soil surface. Three soil materials, sand, loamy sand, and sandy clay loam, were tested at both air‐dry and saturated moisture conditions. With shallow sensor burial, measured thermal properties were underestimated by up to 50%, similar to the predicted thermal properties from the PK99 analytical solution, due to the effects of the soil–air interface. Using PK99 to adjust thermal property values obtained from shallow sensors has potential to improve estimates of water content, evaporation, and other soil measurements derived from heat‐pulse sensors.