Near-surface Soil Research Articles

Thermal conductivity contrast effect of organic soils and its environmental implications

Thermal conduction control is important for retarding permafrost degradation and mitigating of frost geohazards. Similar to a thermodiode, high thermal conductivity contrast (HTCC) materials can serve as good thermal insulators. A preferred HTCC material for ground cooling is larger in thermal resistance in summer and smaller in winter. Because of contrasting thermal conductivity under frozen and thawed states, organic soil is blessed with such a property. This study quantified and reported the HTCC effects on a range of soil organic matter concentrations (SOMC) and soil moisture saturation degree (SMSD). Using the COMSOL, influences of different SOMC and SMSD on ground temperatures were simulated and compared with laboratory-measured properties. Simulation results demonstrated that with constant SMSD at 20% throughout the year, the thermal insulation effect was strengthened with increasing SOMC. A better insulating effect was judged by lower annual amplitudes and smaller depths of zero annual amplitude of ground temperatures. In case of low SMSD in summer (20%) and high SMSD in winter (60–80%), the HTCC effect of soil is enhanced with increasing SOMC. This enhancement was evidenced by increased thermal offsets and decreased maximum summer and average near-surface soil temperatures. With constant SOMC and increasing SMSD, the rising HTCC effect gradually cools the ground. An integral analysis indicates that the higher the SOMC and SMSD in winter, the larger the thermal offset and the lower the ground temperature, i.e., the greater the HTCC effect of organic soil. This study may provide geocryological bases for engineering and environmental applications in cold regions.

Measuring Soil Moisture With Refracted GPS Signals

In the last 20 years, the reflected signal of Global Navigation Satellite System (GNSS) has been used for remotely sensing a series of geophysical parameters, resulting in two GNSS based remotely sensing techniques: GNSS reflectometry (GNSS-R) and GNSS interferometric reflectometry (GNSS-IR). In this letter, the refracted GNSS signal is first proposed to estimate near-surface soil moisture (SM). Amplitude of the refracted GNSS signal will attenuate when penetrated into soil due to refraction and propagation of the signal in the soil. Amplitude attenuation degree of the refracted signal is quantified as the amplitude ratio (AR) of the direct GNSS signal to the refracted signal. Two low-cost navigational GNSS chips and right-hand circularly polarized (RHCP) antennas are used to collect the refracted and direct GNSS signal in an experimental campaign, respectively. To simplify the modeling, the AR at elevation angle of 20° is used to develop the model to describe the relationship between SM, AR, and soil temperature (ST) in the letter; and the AR and ST observation can be converted into SM accurately with a 2nd-order polynomial. The modeled SMs are strongly correlated with the sensor-based ones with correlation coefficient of 0.947 and root-mean-square error (RMSE) of 0.013 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (or, 1.3%) when SM is between 0.272 and 0.489 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The study also suggests that, based on the proposed method, the low-cost GNSS instrument can be treated as a new type of sensor monitoring SM in a cost-effective way.

Cover Crop Effects on Near-Surface Soil Aggregate Stability in the Southern Mississippi Valley Loess (MLRA 134)

The use of cover crops (CC) during the agricultural fallow period has been shown to help alleviate soil compaction and provide stabilizing effects against soil erosion. These benefits are particularly important as many of the silty, loess-derived soils of the major land resource area (MLRA) 134, the Southern Mississippi Valley Loess, have large erosion potentials. This study evaluated the effects of CC and no-cover crop (NCC) treatments on a selection of silt-loam soils in MLRA 134. Treatments were implemented during Fall 2018 and Fall 2019 and consisted of a range of CC species. Soil samples from the top 10 cm were collected to evaluate a suite of soil properties. Soil texture, pH, soil organic matter, and Mehlich-3 extractable Mg, Na, and Ca were unaffected (P > 0.05) by CC treatment. Total water-stable aggregate concentration was unaffected (P > 0.05) by CC treatment and soil depth (i.e., 0 - 5 and 5 - 10 cm). Soil bulk density was greater (P •cm−3) than under CC treatment (1.24 g•cm−3). Water-stable aggregate concentration was unaffected (P > 0.05) by CC treatment and soil depth, but was 21.5 times greater (P •g−1) than in the > 4-mm (0.05 g•g−1) size class. Study results indicate that, even among sites with large variability, CC can have consistent, short-term, positive effects on soil properties, but a long-term commitment to continuous, annual cover crops is necessary for the full realization of potential benefits.

Inter-Comparison of Proximal Near-Surface Soil Moisture Measurement Techniques

Precision agriculture is experiencing substantial development through the improved availability of cost-effective instruments for data collection. This includes ground-based proximal sensing technologies that are able to compete with satellite and aircraft observation systems, due to low operational costs, high operational flexibility, and high spatial resolution. This article was therefore designed to compare the performance of multiple sensing systems mounted on a smart buggy platform. A number of proximal sensing technologies were then evaluated and intercompared for their accuracy in retrieving high resolution near-surface soil moisture. The sensors tested included an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> -band microwave radiometer (ELBARA III), a global navigation satellite system reflectometer sensor (LARGO), and an electromagnetic induction sensor (EM38). Data were collected during the fifth Soil Moisture Active Passive Experiment (SMAPEx-5) in Yanco, NSW, Australia, in September 2015. Observations from each sensor were converted to surface soil moisture values which were in turn evaluated against reference measurements obtained by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> soil moisture measurements. The sensing technologies tested here have been individually assessed by many other studies, but within different regions and environments including surface condition, local weather, observing height, size of footprint, etc. Consequently, this article has used a single platform to intercompare the different sensors to be evaluated concurrently. Results from this article indicated that the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> -band microwave radiometer achieved the best performance in retrieving surface soil moisture. The average RMSE and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> were found to be 0.055 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 0.68 for ELBARA III, 0.084 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 0.51 for LARGO, and 0.090 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 0.32 for the EM38.

Understanding of flow liquefaction phenomena in Palu City from shear wave velocity profiles

On 28 September 2018, a strong earthquake (Mw 7.5) struck Donggala Regency triggering flow liquefaction (locally termedNalodo) phenomena in two residential areas in Palu City. Mitigating such an earthquake collateral hazard requires understanding the geological condition controlling such liquefaction. This paper presents a geophysical study to clarify the geological condition controlling theNalodophenomena in Palu City. The objectives of this study were to estimate shear wave velocity (Vs) profiles in theNalodoand non-Nalodosites and evaluate liquefaction potential based on the shear wave velocity profiles. The study involved a series of array microtremor surveys in twoNalodosites and three non-Nalodosites in Palu City. The results show thatVsgenerally increases with depth but varies from one site to another. Based on theVsprofiles, a thick soil layer withVsof less than 175 m/s is present from the ground surface in the Balaroa and Petobo sites. Contrary, this soil layer is detected at a deeper depth in the non-Nalodosites. Based on the liquefaction potential analysis, the near-surface soil layers in the Balaroa and Petobo sites are clearly liquefiable for all the PGA values used in this study. Although deeper soil layers can also be liquefied, no liquefaction occurred in non-Nalodosites because a thick medium soil layer exists near the surface. Thus, a thick soil layer withVsof less than 175 m/s near the ground surface controls theNalodophenomena in Palu City. Further studies to clarify other factors controlling flow liquefaction are recommended.

Spatial mapping of soil moisture in an agricultural farm through geostatistical approach

Spatio temporal changes in near-surface soil moisture (NSSM; 0–5 cm) were captured over the research farm (242 ha) at ICAR-Indian Agricultural Research Institute, New Delhi during rabi (winter) season by applying geostatistical techniques. Ranges of NSSM have been different on different days, and was not related to either bulk density or clay content of the surface layer. Even the best-fitting semi-variogram models were different with an average root mean square error of 6.8 over the study period. The minimum separation distance between two sampling points was ~6 m, and nearly 50% variability could be explained by the nugget indicating small scale variations of soil moisture. Spatial variability maps of NSSM were prepared using ordinary kriging wherein a few distinct wetness zones were apparent. Sub-surface soil moisture (SSSM) was correlated with NSSM till 40 cm depth, making plausibility of root-zone soil moisture mapping from surface measurements. The kriged maps will help in scheduling irrigation and deciding sowing dates over a large farm with limited number of in-situ point observations.

Improvement in Modeling Soil Dielectric Properties During Freeze-Thaw Transitions

Soil freeze-thaw cycles have a profound impact on heat and water fluxes at the land-atmosphere interface and transport in soils. Microwave remote sensing is a widely used technique to detect near-surface soil freeze/thaw states due to significant changes in dielectric properties associated with water phase transitions in soils, where uncertainty remains. This letter proposes a new parameterization scheme for the estimation of unfrozen water content to improve the modeling of soil dielectric properties during freeze-thaw transitions. Predictions from the new model referred to as Zhang-Zhao&#x2019;s model were compared with dielectric measurements during thawing processes of soil samples collected from Baoding (silty clay soil), Zhangjiakou (loamy sandy soil), and Zhengzhou (clay loam soil) in China. The mean biases of the predictions were 3.25 (4.44 and 2.07 for the thawed value and frozen value, respectively) and 1.54 (2.22 and 0.88 for the thawed value and frozen value, respectively) for the real part and imaginary part, respectively. The model-predicted soil complex relative permittivity (CRP) was highly correlated with measurements, with correlation coefficients ranging from 0.7944 to 0.9865. The normalized root mean square errors of the predictions were 13.72&#x0025; (real part) and 25.41&#x0025; (imaginary part).

Ground motion of the Ms7.0 Jiuzhaigou earthquake

Abstract Eighty-eight free-field strong ground motion observation datasets obtained by the National Strong Motion Observation Network System of China for the Jiuzhaigou Ms7.0 earthquake were used to study the characteristics of the strong ground motion and the site response. In this study, we calculated the VS30 of the near field station and compared the observed values of the horizontal peak acceleration and peak velocity with the CB2014 ground motion prediction models developed by Campbell et al. (2014). The results indicate that the observed values of the horizontal peak acceleration and peak velocity of the Jiuzhaigou earthquake are both smaller than the predicted values obtained from the ground motion prediction equations. By regressing the spatial variation curves of the D SR (5–95%) and D SR (5–75%) ground motion durations, and comparing them with Bommer’s (2009) ground motion duration prediction curve, it was found that the duration of the Jiuzhaigou earthquake was greater than that obtained from the global empirical prediction equation. The scope of the source duration corresponding to the D SR (5–75%) duration is 2.76–4.28 s, and the scope of the source duration corresponding to the D SR (5–95%) duration is 8.88–10.36 s, which are close to the peak time and completion time of the seismic moment release during the source rupture process. The linear elastic acceleration response spectra of 11 stations within 100 km of the fault were calculated for comparison with the design spectrum. It was concluded that the range of the predominant period of the response spectrum was 0.05–0.26 s, which is less than the natural vibration period of the local multistory building. However, the response spectrum value recorded by station 51JZZ is greater than the design spectrum of the 8° rare earthquake and the observation values of the nearby strong ground motion stations. Through analysis of the H/V spectrum ratio and the case of station 51JZZ, which is closest to the epicenter, this phenomenon was concluded to be related to the magnification effect of the near-surface soil layer and the nonlinear response of the site under the action of strong earthquakes.

Evaluating the impact of midwestern cropping systems on soil health and soil carbon dynamics

Crop producers are becoming more interested in improving the health of their soils. The effects of cropping practices on soil health have been studied extensively, but much uncertainty remains. This study investigated the impacts of standard midwestern US agronomic practices on soil health indicators. The Soil Management Assessment Framework was used to quantify soil quality index (SQI) scores for each system. Corn–soybean (<i>Zea mays</i> L.–<i>Glycine max</i> L.) rotations received 168 kg N ha^–1 applied prior to corn. Treatments were the following: spring-applied urea ammonium nitrogen (SU168), fall-applied manure (FM) in no-till (NT) for 2 years (FM168NT2), FM with 10 years of NT and cereal rye (<i>Secale cereale</i>) cover crop (FM168NT10+R), and FM with 38 years of NT management (FM168NT38). Continuous corn (CC) treatments had FM applied annually at 224 kg N ha^–1 with eight years of stover removal (FM224CC-S) and with no stover removal (FM224CC). Soil cores were taken to a depth of 15 cm in the spring of 2017 and analyzed for total carbon (TC), total nitrogen (TN), water-stable aggregates (WSA), bulk density (BD), and potentially mineralizable nitrogen (PMN). Results showed that FM168NT38 and FM224CC had significantly greater TC and TN than other treatments. There were minimal treatment differences in total WSA &gt; 0.212 mm. No significant differences in PMN were found. Bulk density levels were significantly higher in NT treatments. The FM224CC and FM224CC-S treatments had the highest SQI scores, and FM168NT10+R had the lowest SQI score due to having higher BD and lower TC. Results suggest that the effect of cropping practices on some near-surface soil health indicators may be small and difficult to quantify. This study also demonstrated the need to adjust management to minimize compaction and maximize yield and soil health in cover-cropped systems. The study also monitored soil TC levels to a depth of 120 cm from 2007 through 2017. The rate of change in TC over time at a given depth did not differ between treatments. Total C levels did not change significantly to a depth of 15 cm. Significant increases in TC were found in all treatments except FM224CC-S at 30 to 60 cm and 90 to 120 cm depths, and in all treatments at 60 to 90 cm depth. These results suggest that C accumulation deep in the soil profile may be typical in midwestern cropping systems. Deep sampling to ≥100 cm is needed to capture the complete picture of soil C dynamics to assess soil C accumulation potential.

Towards standardized nuclear reactors: Seismic isolation and the cost impact of the earthquake load case

Nuclear energy has a key role to play in global decarbonization. Impediments to the widespread deployment of reactors are their projected high capital cost and levelized cost of energy, and time required to analyze, design, license, construct, and commission them. The earthquake load case is a key cost driver for a new build nuclear plant, because near-surface soils and seismic hazard are different at each site, requiring site-specific analysis, design, engineering, qualification, licensing, and regulatory review, essentially making every design First-of-a-Kind (FoaK). To enable deployment at the scale needed for deep decarbonization, the cost and time impact of the seismic load case must be significantly mitigated, and plants must be standardized. Seismic base isolation has been proven to considerably reduce the earthquake response of structures and equipment but has yet to be applied to a nuclear power plant in the United States, in part because the financial impacts, positive or negative, are not known. Because there are no recent non-proprietary data to characterize the influence of the seismic load case on capital cost, it is difficult to confidently quantify the financial benefits of seismic isolation.Scheme-level designs of two fundamentally different advanced reactor buildings were developed to assemble cost data on the influence of the seismic load case. Both buildings were equipped with three bespoke pieces of safety-related equipment and analyzed for incremented levels of earthquake shaking to quantify the seismic penalty on equipment, in terms of vessel weights and horizontal accelerations. Using analysis results, a questionnaire was developed and transmitted to nuclear utilities, reactor developers, engineers, and equipment suppliers to collect cost data on engineering and fabrication costs for these unique pieces of safety-class equipment. Synthesis of the cost data showed that the seismic load case significantly affects the capital cost (sum of engineering and fabrication cost) of safety-class equipment, with engineering costs being comparable to fabrication costs. Standardization of safety-class equipment is made possible by seismic isolation, that is, equipment designed for minimal seismic robustness can resist earthquake shaking at a site of much higher seismic hazard. The average reduction in the capital cost of the safety-related equipment, enabled by seismic isolation, is a factor of two for FoaK equipment and a factor of five for standardized equipment.

Environment-Monitoring IoT Devices Powered by a TEG Which Converts Thermal Flux between Air and Near-Surface Soil into Electrical Energy.

Energy harvesting has an essential role in the development of reliable devices for environmental wireless sensor networks (EWSN) in the Internet of Things (IoT), without considering the need to replace discharged batteries. Thermoelectric energy is a renewable energy source that can be exploited in order to efficiently charge a battery. The paper presents a simulation of an environment monitoring device powered by a thermoelectric generator (TEG) that harvests energy from the temperature difference between air and soil. The simulation represents a mathematical description of an EWSN, which consists of a sensor model powered by a DC/DC boost converter via a TEG and a load, which simulates data transmission, a control algorithm and data collection. The results section provides a detailed description of the harvested energy parameters and properties and their possibilities for use. The harvested energy allows supplying the load with an average power of 129.04 W and maximum power of 752.27 W. The first part of the results section examines the process of temperature differences and the daily amount of harvested energy. The second part of the results section provides a comprehensive analysis of various settings for the EWSN device’s operational period and sleep consumption. The study investigates the device’s number of operational cycles, quantity of energy used, discharge time, failures and overheads.

Nitrogen Cycling and Biosignatures in a Hyperarid Mars Analog Environment.

The hyperarid Atacama Desert is a unique Mars-analog environment with a large near-surface soil nitrate reservoir due to the lack of rainfall leaching for millennia. We investigated nitrogen (N) cycling and organic matter dynamics in this nitrate-rich terrestrial environment by analyzing the concentrations and isotopic compositions of nitrate, organic C, and organic N, coupled with microbial pathway-enzyme inferences, across a naturally occurring rainfall gradient. Nitrate deposits in sites with an annual precipitation of <10 mm carry atmospheric δ15N, δ18O, and Δ17O signatures, while these values are overprinted by biological cycling in sites with >15 mm annual precipitation. Metagenomic analyses suggest that the Atacama Desert harbors a unique biological nitrogen cycle driven by nitrifier denitrification, nitric oxide dioxygenase-driven alternative nitrification, and organic N loss pathways. Nitrate assimilation is the only nitrate consumption pathway available in the driest sites, although some hyperarid sites also support organisms with ammonia lyase- and nitric oxide synthase-driven organic N loss. Nitrifier denitrification is enhanced in the “transition zone” desert environments, which are generally hyperarid but see occasional large rainfall events, and shifts to nitric oxide dioxygenase-driven alternative nitrifications in wetter arid sites. Since extremophilic microorganisms tend to exploit all reachable nutrients, both N and O isotope fractionations during N transformations are reduced. These results suggest that N cycling on the more recent dry Mars might be dominated by nitrate assimilation that cycles atmospheric nitrate and exchanges water O during intermittent wetting, resulting stable isotope biosignatures could shift away from martian atmospheric nitrate endmember. Early wetter Mars could nurture putative life that metabolized nitrate with traceable paleoenvironmental isotopic markers similar to microbial denitrification and nitrification stored in deep subsurface.

Recent Trends in Greenhouse Gases Levels in the Soils of the Coconino National Forest

We have taken near-surface soil measurements of the gases CO2 , CH4 , H2 O and isoprene in several regions of the Coconino National Forest, Arizona, USA. Sets of measurements were taken both prior to the start of the seasonal monsoon season, in addition to while the monsoon season was underway. We have also compared the current monsoon season readings with readings taken at the same locations four years prior. For CO2, the relative level in the pristine forest soil is just under 3.7 percent lower than that measured in 2017, while the CO2 relative levels for the thinned and logged sites are lower by 13.5 and 5.4 percent, respectively. Even accounting for small increases in forest vegetation, these lower readings appear to be correlated to lower overall soil H2 O concentrations. The pristine CH4 relative concentration in 2021 is 9.6% higher and the thinned CH4 level is 19% higher. For the logged region, the measured methane level is over 70% lower than in 2017, but still approximately triple the methane level as seen in the other forest areas. We conclude that this result also may also be correlated to lower measured H2 O levels in the soils.

Nitrogen transport in a tundra landscape: the effects of early and late growing season lateral N inputs on arctic soil and plant N pools and N2O fluxes

Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used 15N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N2O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic.

How does deep-band fertilizer placement reduce N2O emissions and increase maize yields?

It is unclear how deep-band fertilizer placement influences N2O emission and maize (Zea mays L.) yield, and the production and diffusion of N2O within the soil profile under deep-band fertilizer placement treatments. Thus, we conducted a field experiment in 2019–2020 with spring maize to study the effects of different fertilization depths of 5 cm (D5), 15 cm (D15), 25 cm (D25), and 35 cm (D35) on N2O emissions. The N2O concentration in the fertilized soil profile was measured to calculate the N2O diffusion and production rates, and the surface N2O emissions were measured simultaneously. The results showed that the availability of NO3–-N in the soil was the main factor related to N2O production and emissions, and N2O emissions were strongly related to the production and diffusion of N2O in the 0–20 cm soil layer. Deep-band fertilizer placement significantly reduced surface N2O emissions, and the N2O production and diffusion rates in the 0–20 cm soil profile. The cumulative N2O diffusion in the 0–20 cm layer accounted for 79.2%, 73.7%, 58.2%, and 48.6% of those in 0–40 cm soil depth under D5, D15, D25, and D35, respectively. Compared with D5, D25 and D35 significantly reduced the N2O emissions by 30.8% and 59.3%, respectively, N2O-N emission factors by 41.6% and 80.0%, and yield-scaled N2O-N by 39.3% and 58.2%. D25 also increased the maize yield by 13.8% and obtained the highest nitrogen use efficiency (NUE, 43.6%), whereas D35 had negative effects on the maize yield and NUE. Therefore, deep-band fertilizer placement reduced the N2O production rate and diffusion flux in the near-surface soil layer by decreasing the NO3–-N content in the 0–20 cm soil layer. Thus, the location where N2O was produced transferred to the deeper soil layer to reduce surface N2O emissions. The recommended fertilization depth of 25 cm can reduce N2O emissions and significantly enhance the maize yield, N uptake, biomass, and NUE.

Direct estimation of shear-wave velocity profiles from surface wave investigation of geotechnical sites

Surface wave methods have been developed as a commonly used non-invasive tool for shear-wave velocity (Vs) profiling of near-surface soil and rock formations. Inversion is a key step to back-calculate the Vsprofile from dispersion curves; however, the non-linear and ill-posed nature of the problem sometimes yields non-unique Vsprofiles. To overcome these challenges, a new method was developed to circumvent inversion and directly estimate Vsprofiles from the fundamental mode dispersion trend for sites with Vsgradually increasing with depth. This method is developed based on the relationship between the phase velocity of surface waves at a given frequency with the time-averaged shear-wave velocity within a depth of one-half wavelength. Three field sites and three simulated sites covering shallow, medium and deep locations with gradually increasing Vswith depth are employed to verify the feasibility of the proposed methodology. Results indicate that the method can efficiently give a reasonable and realistic estimation of Vsprofiles. The goal of this method is to provide an alternative to obtain Vsprofiles with high certainty and low computational cost for surface wave testing, but not necessarily to find a ‘better’ profile than inversion or to locate each layer interface.

Cover crop effects on soil temperature in a clay loam soil in southwestern Ontario

Although it is well established that soil temperature has substantial effects on the agri-environmental performance of crop production, little is known of soil temperatures under living cover crops. Consequently, soil temperatures under a crimson clover and white clover mix, hairy vetch, and red clover were measured for a cool, humid Brookston clay loam under a corn–soybean–winter wheat/cover crop rotation. Measurements were collected from August (after cover crop seeding) to the following May (before cover crop termination) at 15, 30, 45, and 60 cm depths during 2018–2019 and 2019–2020. Average soil temperatures (August–May) were not affected by cover crop species at any depth, or by air temperature at 60 cm depth. During winter, soil temperatures at 15, 30, and 45 cm depths were greater under cover crops than under a no cover crop control (CK), with maximum increase occurring at 15 cm on 31 January 2019 (2.5–5.7 °C) and on 23 January 2020 (0.8–1.9 °C). In spring, soil temperatures under standing cover crops were cooler than the CK by 0.1–3.0 °C at 15 cm depth, by 0–2.4 °C at the 30 and 45 cm depths, and by 0–1.8 °C at 60 cm depth. In addition, springtime soil temperature at 15 cm depth decreased by about 0.24 °C for every 1 Mg·ha−1 increase in live cover crop biomass. Relative to bare soil, cover crops increased near-surface soil temperature during winter but decreased near-surface soil temperature during spring. These temperature changes may have both positive and negative effects on the agri-environmental performance of crop production.

Memory of land surface and subsurface temperature (LST/SUBT) initial anomalies over Tibetan Plateau in different land models

This study applies three widely used land models (SSiB, CLM, and Noah-MP) coupled in a regional climate model to quantitatively assess their skill in preserving the imposed ± 5 °C anomalies on the initial land surface and subsurface temperature (LST/SUBT) and generating the 2-m air temperature (T2m) anomalies over Tibetan Plateau (TP) during May–August. The memory of the LST/SUBT initial anomalies (surface/soil memory) is defined as the first time when time series of the differences in daily LST/SUBT cross the zero line during the simulation, with the unit of days. The memory of the T2m anomalies (T2m memory) is defined in the same way. The ensemble results indicate that the simulated soil memory generally increases with soil depth, which is consistent with the results based on the observations with statistic methods. And the soil memory is found to change rapidly with depth above ~ 0.6–0.7 m and vary slowly below it. The land models have fairly long soil memories, with the regional mean 1.0-m soil memory generally longer than 60 days. However, they have short T2m memory, with the regional means generally below 20 days. This may bring a big challenge to use the LST/SUBT approach on the sub-seasonal to seasonal (S2S) prediction. Comparison between the three land models shows that CLM and Noah-MP have longer soil memory at the deeper layers (> ~ 0.05 m) while SSiB has longer T2m/surface memories and near-surface ( $$\le$$ ~ 0.05 m) soil memory. As a result, it is difficult to say which land model is optimal for the application of the LST/SUBT approach on the S2S prediction. The T2m/surface/soil memories are various over TP, distinct among the land models, and different between the + 5 °C and − 5 °C experiment, which can be explained by both changes in the surface heat fluxes and variances in the hydrological processes over the plateau.

Effects of gravel cover on the near-surface airflow field and soil wind erosion

Gravel cover is a traditional farming practice to improve soil properties and advance soil productivity. In arid areas, gravel cover can directly affect the near-surface airflow field to inhibit the soil wind erosion rate (q). The effectiveness of gravel cover in wind erosion control has been recognized in practice, but there are few reports about experimental data. This study aimed to identify the mechanism under which gravel changes the near-surface airflow field and q. The wind profiles at different positions around gravel roughness elements and q were measured under five inlet friction wind velocities (u*∞), five gravel sizes (D) and five gravel coverages (GC) in a large wind tunnel, and an equation of q was established. The results showed significant differences among the wind profiles due to the effects of u*∞, D and GC. Although the wind profile at any position did not represent the average state of the rough surface, the average wind profile of the different positions did. When the density of gravel roughness elements increased, the near-surface airflow changed from isolated-roughness flow to wake interference flow and skimming flow, which directly affected the spatial pattern and the rate of wind erosion. The equation of q established in this study not only integrated the effects of variables on the q, including D, GC, the average friction wind velocity (u*¯) and threshold friction wind velocity (u*t), but also represented the behavior of wind erosion being aggravated by gravel cover when GC ≤ 10 % and D ≥ 3.15 cm. This study can contribute to an understanding of the structural change to the near-surface airflow field and to the prediction of q on gravel-covered surfaces, which provides guidance information for rational utilization of gravel-covered fields in arid areas.

Wheat stubble height effects on soil water capture and retention during long fallow

A 4-yr study was conducted in a dry Mediterranean region of the Inland Pacific Northwest USA (PNW) to measure winter wheat (WW) (Triticum aestivum L.) stubble height and orientation effects on overwinter precipitation capture in the soil and subsequent water retention during ensuing dry summer months. The stubble was left standing and undisturbed during the 13-mo fallow periods. Stubble-height treatments were:(i) short (8 cm), (ii) medium (25 cm), and (iii) tall (75 cm). An additional treatment: (iv) mow tall stubble in mid-June, was included in the final two years. Soil water measurements were obtained at the beginning, middle, and end of fallow in 15-cm increments to a depth of 180 cm. Additionally, seed-zone water content was measured at the end of fallow in 2-cm increments to a depth of 26 cm. Near-surface soil temperature was measured from June-August. On average, tall- and medium-height stubble captured 34 and 32 mm (p = 0.002) more overwinter precipitation, respectively, than short stubble and these values were particularly pronounced (91 and 79 mm greater than short stubble) during a winter of heavy snow drifting. However, from mid-April until late August, the tall stubble lost an average of 91 mm of soil water compared to 70 and 59 mm in the medium and short stubble treatments (p < 0.001). Mowing tall stubble in mid-June before the hot, dry summer did not improved water retention. Continuous soil temperatures at 3, 7, 15, 25, and 40-cm depths measured electronically from June-August were coolest with the short, mowed, medium, and tall stubble, respectively, with frequent significant differences of > 1 °C among treatments. We speculate that soil in the tall treatment was warmest and lost the most over-summer water because all stubble was standing and offered less soil shading than the other treatments. At the end of fallow, medium and tall stubble averaged 14 and 8 mm greater soil water, respectively, than the short treatment (p = 0.027). Short stubble was a disadvantage for overwinter precipitation capture but was equal or better than the other treatments for retaining soil water from April to late August; presumably because this treatment had the most residue lying flat on the soil surface for shading. These findings offer opportunity to improve current models for soil water dynamics during fallow by incorporating stubble height. For combined soil water retention and farm management factors, medium-height WW stubble is the best fallow option for farmers in the PNW drylands.