Search

Environmental awareness about soil and water conservation in agroecosystems has shifted behaviors toward favoring conservation practices in agricultural management. Interest in conservation tillage and cover cropping has increased, but some regions encounter major challenges with adjusting management to accommodate these practices while optimizing crop production. In an Ultisol in the North Carolina Piedmont, a long-term corn (Zea mays) and soybean (Glycine max) rotation with tillage intensities ranging from no-till to moldboard plowing in a randomized complete block design was used to assess changes in physical soil properties after introducing wheat (Triticum aestivum) as a winter cover crop. Cover crop biomass was measured along with volumetric water content (VWC) and bulk density (BD) at 0–15 cm, water retention (WR), water-stable aggregation (WSA), and soil organic carbon (SOC) at 0–7.5 cm, and penetration resistance (PR) at 0–45 cm. No differences in VWC or WR could be solely attributed to cover cropping, but no-till with cover cropping had the highest macroporosity where there was no vehicle traffic. Vehicle traffic had a stronger effect on soil compaction (BD and PR) than cover cropping regardless of tillage. Conservation tillage increased WSA and SOC when compared to plow tillage, but three seasons of a wheat cover crop did not significantly change these properties, possibly because wheat produced low biomass each year (750–1900 kg ha−1). Wheat had minimal effect on physical soil properties in the short term, and potential for improvement with long-term optimal cover crop management in this region requires further assessment. [ABSTRACT FROM AUTHOR]

Miscanthus is a perennial grass that can yield substantial amounts of biomass in land areas considered marginal. In the Coastal Plain region of North Carolina, marginal lands are typically located in coarse‐textured soils with low nutrient retention and water‐holding capacity, and high erosivity potential. Little is known about miscanthus water use under these conditions. We conducted a study to better understand the efficiency with which miscanthus uses natural resources such as water and radiant energy to produce harvestable dry biomass in comparison to corn, a typical commodity crop grown in the region. We hypothesized that under non‐limiting soil water conditions, miscanthus would have greater available energy and water use rates owing to its greater leaf area, thus leading to greater agronomic yields. Conversely, these effects would be negated under drought conditions. Our measurements showed that miscanthus intercepted more radiant energy than corn, which led to greater albedo (by 0.05), lower net radiation (by 4% or 0.4 MJ m−2 day−1), and lower soil heat flux (by 69% or 1.0 MJ m−2 day−1) than corn on average. Consequently, miscanthus had greater available energy (by 7% or 0.6 MJ m−2 day−1) and water use rates (by 14% or 0.5 mm day−1) than corn throughout the growing season on average, which partially confirmed our hypothesis. Greater water use rates and radiation interception by miscanthus did not translate to greater water‐use (1.5 g kg−1 vs. 1.6 g kg−1) and radiation‐use (0.9 g MJ−1 vs. 1.1 g MJ−1) efficiencies than corn. Compared to literature values, our data indicated that water and radiation availability were not limiting at our study site. Thus, it is likely that marginal land features present at the Coastal Plain region such as low soil fertility and high air temperatures throughout the growing season may constrain agronomic yields even if soil water and radiant energy are non‐limiting. [ABSTRACT FROM AUTHOR]

Vegetation is an important component of stormwater control measures, as vegetation can reduce erosion and runoff. While grass is typically used in stormwater control measures, wildflowers can be planted to reduce maintenance and improve pollinator habitat. Previous studies have established that tillage followed by establishment of a vigorous vegetation stand can increase infiltration relative to compacted soils. Compost can also improve soil physical properties and fertility. The goal of this study was to evaluate potential improvements in infiltration using tillage together with compost and either grass or wildflowers. Wildflowers or grass were planted on tilled soil with or without compost at three sites in North Carolina. Bulk density, infiltration rate, root mass density, and penetration resistance were measured every 6 months over a 30‐month period. A subset of plots received wheel traffic from a mower. Compost application reduced bulk density compared to tillage alone. Compost improved infiltration at two sites (46%–50%). Wildflowers improved infiltration at all sites (30%–43%) compared to grass. Few differences were observed in root mass and penetration resistance. Mower traffic reduced soil improvements more in grassed plots than wildflower plots due to higher mowing frequency. Results suggest compost and/or wildflowers together with tillage (at establishment) provide viable options to improve soil conditions and infiltration rate in construction impacted soils. [ABSTRACT FROM AUTHOR]

Miscanthus is a productive perennial grass that is suitable as a bioenergy crop in "marginal" lands (e.g., eroded soils) with low water holding capacity. However, little is known about the impact of miscanthus residues on vapor transport and soil water budgets. Laboratory experiments were conducted to measure the vapor conductance through miscanthus residues and its effect on soil water evaporation. The ranges for the length, width, and thickness of residue elements were 0.5–9.0, 0.1–0.5, and 0.1–0.5 cm, respectively. Average residue areal, bulk, and skeletal densities were 0.88 kg m−2, 24 kg m−3, and 1006 kg m−3, respectively, giving a porosity of 0.98 m3 m−3. A power function described the decrease in conductance with increasing residue load. The corresponding conductance for a residue load of 0.88 kg m−2 was 1.6 mm s−1. During the first days of a 60‐day drying experiment, cumulative evaporation showed logarithmic decay with increasing residue load. Conversely, cumulative evaporation during the last days of the study showed little difference between treatments. Measurements indicated that there is a "critical" residue load (∼1.0 kg m−2) beyond which evaporation no longer decreases appreciably when the soil is under the stage 1 evaporation regime. Results suggest that soil water conservation in marginal lands may be accomplished by maintaining moderate amounts of bioenergy grass residue covering the soil. Determining "critical" loads for different residue types is a knowledge gap that merits further research. Core Ideas: Residues had skeletal density of 1006 kg m−3 and porosity of 0.98 m3 m−3.Residue conductance to water vapor decreased with increased areal density.Evaporation decreased with increased residue load during the first 15 days of drying.After 60 days of drying, treatments showed little difference in cumulative evaporation. [ABSTRACT FROM AUTHOR]

The most common method for in situ measurement of saturated hydraulic conductivity (Ksat) of the vadose zone is the constant head well permeameter method. Our general objective is to provide an empirical method for determining volume of water required for measuring Ksat using this procedure. For one-dimensional infiltration, steady state reaches as time (t) → ∞. For three-dimensional water flow from a cylindrical hole under a constant depth of water, however, steady state reaches rather quickly when a saturated bulb forms around the hole. To reach a quasi-steady state for measuring Ksat, we assume an adequate volume of water is needed to form the saturated bulb around the hole and increase the water content outside of the saturated bulb within a bulb-shaped volume of soil, hereafter, referred to as wetted soil volume. We determined the dimensions of the saturated bulb using the Glover model that is used for calculating Ksat. We then used the values to determine the volume of the saturated and wetted bulbs around the hole. The volume of water needed to reach a quasi-steady state depends on the difference between the soil saturated and antecedent water content (Δθ). Based on our analysis, between 2 and 5 L of water is needed to measure Ksat when Δθ varies between 0.1 and 0.4 m3 m−3, respectively. [ABSTRACT FROM AUTHOR]

There has been widespread interest in using compost to improve the hydrologic functions of degraded soils at construction sites for reducing runoff and increasing infiltration. The objective of this study was to determine the effects of compost amendment rate on saturated hydraulic conductivity (Ks) and water retention in order to identify target compost rates for enhancing soil hydrologic functions. Samples were prepared with three soil textures (sandy loam, silt loam, and sandy clay loam), amended with compost at 0%, 10%, 20%, 30%, 40%, and 50%. All soils were tested at a porosity of 0.5 m3/m3, and the sandy loam was further tested at high (0.55 m3/m3) and low (0.4 m3/m3) porosities. The Ks and water retention data were then used to model infiltration with HYDRUS‐1D. With increasing compost amendment rate, Ks and water retention of the mixtures generally increased at the medium porosity level, with more compost needed in heavier soils. As porosity decreased in the sandy loam soil, the amount of compost needed to improve Ks rose from 20% to 50%. Water distribution in pore fractions (gravitational, plant‐available, and unavailable water) depended on texture, with only the highest compost rates increasing plant‐available water in one soil. Results suggest soil texture should be taken into consideration when choosing a compost rate in order to achieve soil improvement goals. Hydrologic benefits may be limited even at a high rate of compost amendment if soil is compacted. [ABSTRACT FROM AUTHOR]

Providing adequate water for crops is a key consideration for agricultural resiliency. Climate change is expected to exert substantial pressure on crop water supplies through increased rainfall variability and increased evaporative demand. The temporal and spatial variability of these climate change impacts, in combination with many feedbacks, at times operating at different scales, makes identifying specific, yet broadly applicable "one‐size‐fits‐all" soil management solutions challenging. Adaptations that work well in one location may represent a poor management choice in another. Considering the local combinations of climate, soils, and crop production systems is fundamental for identifying appropriate strategies. Nonetheless, some broadly applicable soil management pathways for increasing soil water availability can be identified: (i) maximizing rainfall capture, (ii) maximizing soil water storage capacity (intensity × volume), and (iii) suppressing unproductive evaporative water losses, particularly during intervals when leaf area of the primary crop is low. Selecting climate, soil, and production‐system‐appropriate tillage and surface cover management practices is among the most relevant considerations for improving soil water availability. Maintaining surface cover favors evaporation suppression and increased capture of precipitation. Tillage choices affect internal soil water storage through impacts on soil properties that influence storage intensity and by altering the volume of soil available for root growth, as well as through effects on surface cover. Promoted management practices aimed at improving soil water availability for increased agricultural resiliency must be practically feasible and cost‐effective in order to support their broad adoption, and such constraints should be an important consideration in their development. Core Ideas: Climate change is expected to increase rainfall variability and evaporative demand.Evapotranspiration responses to elevated CO2 and temperature are complex due to many feedback mechanisms.Soil management to conserve water enhances resiliency, but strategies are site and region dependent.Resilience is enhanced by increasing rainfall capture and water storage in soils.Resilience is enhanced by reducing soil water evaporation. [ABSTRACT FROM AUTHOR]

Turfgrass managers have suspected that runoff-independent movement of herbicides and fertilizers is partially responsible for uneven turfgrass quality in sloped areas. We hypothesized that subsurface lateral solute transport might explain this phenomenon especially in areas with abrupt textural changes between surface and subsurface horizons. A study was conducted to track solute transport using bromide (Br−), a conservative tracer, as a proxy of turfgrass soil inputs. Field data confirmed the subsurface lateral movement of Br− following the soil slope direction, which advanced along the boundary between soil horizons over time. A model based on field data indicated that subsurface lateral movement is a mechanism that can transport fertilizers and herbicides away from the application area after they have been incorporated within the soil, and those solutes could accumulate and resurface downslope. Our results demonstrate that subsurface lateral transport of solutes, commonly ignored in risk assessment, can be an important process for off-target movement of fertilizers and pesticides within soils and turfgrass systems in sloped urban and recreational landscapes. [ABSTRACT FROM AUTHOR]

Soil particle density (ρs) is often assumed as 2.65 g cm−3 (density of quartz). The objectives of this study were to compare the use of different gases for determining ρs in a gas pycnometer and relate measured ρs to soil particle size distributions. The ρs of 36 natural soil samples representing 12 USDA textural classes, fine glass beads, crushed granite rock, kaolinite, and bentonite were measured by a commercial gas pycnometer using He, N2, and dry air. The ρs of 30 of the soil samples, glass beads, and crushed rock were also determined with a water pycnometer. The ρs of 36 soil samples determined by He and 30 samples determined by water had narrow ranges with averages of 2.65 and 2.59 g cm−3, respectively. The ρs determined by air and N2 had much wider ranges with averages of 2.93 and 2.97 g cm−3, respectively. There was a near 1:1 relationship between ρs of all samples determined by air and N2 with a highly significant (p <.001) correlation coefficient (r =.99). The average ratio of ρs determined by He and water was 1.03, but the correlation coefficient for their relationship was only.416. Although the relationship between ρs determined by He and either air or N2 was relatively strong (r <.61), the regression coefficient was <.17. There was a strong relationship between soil clay content and ρs determined by N2 or air but a weaker, yet statistically significant (p <.05) relationship when using He. Core Ideas: Average particle density of soils belonging to 12 textural classes determined by helium was 2.65 g cm−3.Average particle density measured by air and nitrogen were 2.93 and 2.97 g cm‐3, respectively.Helium, nitrogen, or air can be used to measure particle density of coarse‐textured soils.Only helium should be used to measure particle density of medium‐ and fine‐textured soils. [ABSTRACT FROM AUTHOR]

One of the United Nations Sustainable Development Goal's (SDGs) aims is to enhance access to clean energy. In addition, other SDGs are directly related to the restoration of degraded soils to improve on-farm productivity and land management. Integrating Short Rotation Woody Crops (SRWC) for bioenergy into conventional agriculture provides opportunities for sustainable domestic energy production, rural economic development/diversification, and restoration of soil health and biodiversity. Extensive research efforts have been carried out on the development of SRWC for bioenergy, biofuels, and bioproducts. Recently, broader objectives that include multiple ecosystem services, such as carbon sequestration, and land mine reclamation are being explored. Yet, limited research is available on the benefits of establishing SRWC on degraded agricultural lands in the southeastern U.S. thereby contributing to environmental goals. This paper presents a literature review to (1) synthesize the patterns and trends in SWRC bioenergy production; (2) highlight the benefits of integrating short rotation woody crops into row crop agriculture; and (3) identify emerging technologies for efficiently managing the integrated system, while identifying research gaps. Our findings show that integrating SRWC into agricultural systems can potentially improve the climate of agricultural landscapes and enhance regional and national carbon stocks in terrestrial systems. [ABSTRACT FROM AUTHOR]

Growers use cover crops to provide nutrients for crops and build soil organic matter (SOM). Termination methods may alter the effects of cover crops on soil labile C and N. We examined how two cover crops and three termination methods affected soil microbes, soil aggregates, and C and N pools in an organic grain system. We compared crimson clover (Trifolium incarnatum L.) (CC), hairy vetch (Vicia villosa Roth) (HV), and a control together with disking, mowing, or a roller‐crimper for effects on hot‐water‐extractable carbohydrates, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), potentially mineralizable C and N, and aggregation (quantified by mean weight diameter [MWD]). Disking comprised flail mowing plots and then cultivating. Roller‐crimping occurred via a roller with blades. Vetch soil contained 14% higher MBC than no cover crop pretermination, possibly because of enhanced rhizodeposition. Planting CC resulted in 44% higher MBC than no cover crop a week after termination, likely due to its higher biomass C/N ratio. Disking decreased MWD relative to flail mowing in no cover crop soils at 4 wk after termination across both years at 0‐to‐5‐cm depth. In addition, MWD was lower under CC than under no cover crop for both the flail mowed and roller‐crimped treatments at 4 wk after termination across both years from 0 to 5 cm. This is possibly due to enhanced desiccation of the soil in bare plots after termination. Our results indicate that quantity and quality of biomass of different legume species, rather than termination methods, dominated effects on labile C. Core Ideas: Disking lowered aggregation in no cover crop control plots vs. flail‐mowing.Hairy vetch raised mineralizable N vs. crimson clover or no cover crop, even before termination.Mowing cover crops did not increase soil microbial activity compared with rolling. [ABSTRACT FROM AUTHOR]

This document is an editorial from the Vadose Zone Journal, announcing a special section on soil physics in agricultural production, water resources, and waste management. The special section includes nine papers, some of which focus on African scenarios. The papers cover topics such as catchment hydrology, modeling of hydrological processes, uncertainty in modeling and measuring vadose zone hydrological processes, and nutrient dynamics. The special section aims to advance soil physics knowledge and its practical applications in agricultural and environmental management. The editorial also acknowledges the contributions of the authors and the legacy of Don and Betty Kirkham, who supported the 2022 Kirkham conference where the research was presented. [Extracted from the article]

Infiltration rate measurements are used to assess soil health and develop land management practices to address runoff from precipitation and irrigation. Differences in observed infiltration rates determined by available methods can be attributed to both the technique and soil property differences. The primary objective of this study was to compare two methods for measuring steady infiltration rate: the Cornell sprinkle infiltrometer (single‐ring) method (CSI), and the double‐ring infiltrometer method (DRI). Measurements were made at four sites using four replications of 13 sets of conditions (52 total paired measurements). The relationship between CSI and DRI measurements was significant (p <.001) and strong (R2 =.71). For 8 of 13 conditions, there was no difference between CSI and DRI steady infiltration rates. Variability in measurements was high (CVs ranged from 0.04 to 1.18) but similar for both methods. Both CSI and DRI results were strongly related to saturated hydraulic conductivity of the surface soil layer determined using a laboratory constant head method on intact soil cores. Overall, results suggest that estimates of steady infiltration rate determined by the CSI and standard DRI methods are comparable. Core Ideas: Cornell sprinkle and double‐ring infiltrometer measurements were compared.Results for the methods were strongly related and similar over a range of conditions.Both methods had large variability in replicate infiltration measurements.Infiltration rates were strongly related to surface saturated hydraulic conductivity. [ABSTRACT FROM AUTHOR]

Crops grown for bioenergy purposes are a potential alternative to traditional row crops and pasture–hay systems in the North Carolina (NC) Piedmont, but there is limited information available about their biomass yields and water requirements in this region. The goal of this study was to evaluate biomass yield and water‐use efficiency of switchgrass (Panicum virgatum L.), giant miscanthus (Miscanthus × giganteus Greef et Deu.), biomass sorghum (Sorghum bicolor spp.), silage corn (Zea mays L.) and tall fescue (Lolium arundinacea Schreb.). The perennial systems were established in 2012 while annuals were planted each spring. Crop water use was evaluated for the 2016 and 2017 growing seasons using a water balance approach. Giant miscanthus had the highest 2‐yr average biomass yield (29.1 ± 0.8 Mg ha–1) followed by corn (23.6 ± 0.6 Mg ha–1) and biomass sorghum (22.0 ± 1.8 Mg ha–1). Switchgrass and tall fescue had the lowest biomass yields, 14.2 ± 1.9 and 12.5 ± 1.2 Mg ha–1, respectively. Fescue had the highest season‐long water use in both years of the study. Perennial grasses giant miscanthus and switchgrass had similar seasonal water use, but giant miscanthus had higher water‐use efficiency due to greater biomass yields. The annual crops corn and sorghum used less water than the perennial systems because of their shorter growing season, and, consequently, had higher water‐use efficiencies. This information can aid growers when making management decisions about converting land into bioenergy crops. Core Ideas: Miscanthus had the highest biomass yields, followed by corn and sorghum.Annual crops used less water than perennials due to a shorter growing season.High water‐use efficiency (WUE) of annual crops was due to high biomass yields and low cumulative evapotranspiration.Miscanthus WUE was comparable to that of corn and sorghum. [ABSTRACT FROM AUTHOR]

Aims: Seed germination is one of the most important processes in plant biology and ecology because it determines the timing and magnitude of seedling emergence events every growing season influencing community dynamics. Our aim was to determine whether polyethylene glycol (PEG) solutions simulate soil water potential accurately and recreate germination responses to soil water availability. Methods: In this study, we compared seed germination of four plant species in PEG and four soils with different textures under six water potentials under controlled laboratory conditions. Results: Total seed germination for all species significantly differed between soil and PEG under the same water potentials, as well as among soil water potentials for each of PEG and soil materials. Due to the inconsistent total germination associated with soil water potential, we evaluated unsaturated soil hydraulic conductivity (Kh) as a predictor of germination. The germination of all species followed the same response to Kh. Germination rate (GR50) was more directly related to water potential than total germination, but Kh provided a more robust description of GR50 across species and soils than PEG-osmotic potentials. Conclusions: Our findings showed that Kh is a more informative variable to predict both total seed germination and germination rate in soil, and caution must be used when considering results obtained using PEG solutions to infer germination behavior under field conditions. [ABSTRACT FROM AUTHOR]

Ice content (θi) is a critical parameter affecting soil thermal, mechanical, and hydraulic properties in cold regions. Few techniques are available for accurately determining θi in laboratory samples and in situ. A combined heat‐pulse and time domain reflectometry (thermo‐TDR) sensor, which measures soil thermal properties and electrical properties simultaneously, can be used to estimate θi. The thermo‐TDR method determines θi by using a heat‐capacity‐based (C‐based) approach or a thermal‐conductivity‐based (λ‐based) approach. Here, we describe the principles and procedures of such approaches. The C‐based thermo‐TDR approach is simple to use and provides reasonable θi values at temperatures below −5°C, but it fails at higher temperatures. The λ‐based approach, which solves for θi from thermo‐TDR measurements with an iterative method, gives more accurate θi estimates than does the C‐based approach and extends the thermo‐TDR measurement range to temperatures near the freezing point of water. Therefore, the λ‐based thermo‐TDR method is preferred for determining θi in partially frozen soils. [ABSTRACT FROM AUTHOR]

Soil thermal conductivity (λ) is an important thermal property for environmental, agricultural, and engineering heat transfer applications. Existing λ models for frozen soils are complicated to use because they require estimates of both liquid water content and ice content. This study introduces a new approach to estimate λ of partially frozen soils from air‐filled porosity (na), which can be determined by using an oven‐drying method. A λ and na relationship was established based on measurements for 28 partially frozen soils. A strong exponential relationship between λ and na was found (with R2 of 0.82). Independent tests on 10 partially frozen soils showed that the exponential λ–na model produced reliable λ estimates with a RMSE of 0.319 W m−1 K−1, which was smaller than those of two widely used λ models for partially frozen soils. The λ–na model is easier to use than existing models, because it requires fewer parameters. Note that the λ‐na model ignores the effect of temperature on λ of frozen soils and is most applicable to soil at temperatures of at least −4 °C. [ABSTRACT FROM AUTHOR]

Soil thermal properties play important roles in dynamic heat and mass transfer processes, and they vary with soil water content (θ) and bulk density (ρb). Both θ and ρb change with time, particularly in recently tilled soil. However, few studies have addressed the full extent of soil thermal property changes with θ and ρb. The objective of this study is to examine how changes in ρb with time after tillage impact soil thermal properties (volumetric heat capacity, Cv, thermal diffusivity, k, and thermal conductivity, λ). The study provides thermal property values as functions of θ and ρb and of air content (nair) on undisturbed soil cores obtained at selected times following tillage. Heat pulse probe measurements of thermal properties were obtained on each soil core at saturated, partially saturated (θ at pressure head of −50 kPa) and oven‐dry conditions. Generally, k and λ increased with increasing ρb at the three water conditions. The Cv increased as ρb increased in the oven‐dry and unsaturated conditions and decreased as ρb increased in the saturated condition. For a given θ, a larger ρb was associated with larger thermal property values, especially for λ. The figures of Cv, k and λ versus θ and ρb, as well as Cv, k and λ versus nair, represented the range of soil conditions following tillage. Trends in the relationships of thermal property values with θ and ρb were described by 3‐D surfaces, whereas each thermal property had a linear relationship with nair. Clearly, recently tilled soil thermal property values were quite dynamic temporally due to varying θ and ρb. The dynamic soil thermal property values should be considered in soil heat and mass transfer models either as 3‐D functions of θ and ρb or as linear functions of nair. Highlights: Thermal property values for a range of θ and ρb were measured on undisturbed soil cores.Freshly tilled soil thermal property values were quite dynamic temporally.The thermal property values of a tilled soil were described as 3‐D surfaces with θ and ρb.The thermal property values of a tilled soil varied linearly with nair. [ABSTRACT FROM AUTHOR]

Core Ideas Soil health indicator sensitivity to management is not consistent. Core Ideas Predictability of corn yields based on soil health indicators is too variable. Core Ideas CASH overall soil health index is not predictive of long‐term corn yields Core Ideas Variability in soil health indicator response is likely due to physiographic differences. Core Ideas Soil health assessment should be correlated to quantifiable agroecological outcomes. --> We published data showing that current soil health indicator (SHI) assessments do not consistently detect differences in a range of soil management practices implemented in North Carolina soils. Van Es and Karlen reanalyzed our data and asserted that it validates SHI correlation to crop yields and sensitivity to management as measured by the Comprehensive Assessment of Soil Health (CASH). We respond to van Es and Karlen with a more representative analysis of our data showing that individual SHI measurements are not predictive of crop yield from the 30‐yr North Carolina agronomic trial. Regressions for aggregate stability (r2 = 0.07) and P (r2 = 0.18) show that neither SHI sufficiently predicts corn yield for this dataset and show no obvious pattern based on tillage intensity. Relationships between corn (Zea mays L.) yield and most biological SHI had r2 ≤ 0.18, with only soil protein being moderately predictive of corn yield (r2 = 0.45). The CASH index to assess overall soil health by integrating physical, chemical, and biological SHI measurements into a single value of soil health is also not predictive of corn yield in the trial (r2 = 0.12). It is possible that current sampling and analytical procedures for assessing soil health do not consistently detect differences in productivity from soils with regional differences in land and ecological resources. We believe that calibrating SHI assessments to quantifiable agroecological outcomes instead of statistical rankings will reduce bias across regions and create a more inclusive framework for quantifying soil health. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) provides many beneficial soil ecosystem services for sustainable soil management, but it is unclear how results from different methods of measuring SOM should be compared when making soil management decisions. To compare different methods, we used 84 soil samples from longterm agronomic trials in the coastal plain, piedmont, and mountain regions of North Carolina. Coastal plain and mountain trials included combinations of tillage and management (conventional vs. organic), whereas piedmont trials were configured to evaluate tillage intensity. The methods used to measure SOM were Walkley-Black (WB), mass loss on ignition (LOI), automated dry combustion (ADC), and humic matter (HM) colorimetry. Correlations among LOI, WB, and ADC were significant (p < 0.0001) for SOM measured from the total population of soils, but variability due to location implied that HM had no correlation to other methods. For measures of soil organic carbon compared to SOM, the WB results were biased high compared to ADC, and ADC was more strongly correlated to LOI than WB. When using the methods to evaluate the effects of agronomic management on SOM, results varied for different methods and locations. Conservation management did not consistently accumulate more SOM than other soil management practices, and no method consistently differentiated soils based on management. Variation in the composition of SOM measured using conventional methods may be causing discrepancies in reported changes in SOM content over time. To avoid confusion about how agronomic management affects SOM, assessments should limit comparisons to methodologies with similar measurement protocols. [ABSTRACT FROM AUTHOR]

Core Ideas: Surface energy balance was quantified with micro‐Bowen ratio instrumentation.Surface energy balance was similar over native topsoil and soils treated with thermal desorption.Thermal desorption did not alter soil temperature dynamics or evaporation.A mix of topsoil and thermal desorption–treated soil matched surface energy balance of topsoil best. Remediation efforts to reduce contaminant concentrations in soils often alter soil properties. Since these alterations can affect the capacity of soil to function, their extent and magnitude may dictate future land use. This study addresses the suitability of soils for agricultural production after remediation of petroleum hydrocarbons using ex situ thermal desorption by quantifying the daytime surface energy balance prior to the growing season. The energy balance was quantified using micro‐Bowen ratio instrumentation to compare non‐contaminated topsoil (A) to both subsoil materials treated by thermal desorption (TD) and a 1:1 mixture (v/v) of TD and A (TDA). Despite differences in soil characteristics, the net radiation, soil heat flux, latent heat flux, and sensible heat flux were each similar among the three reclamation conditions over a period of 18 d. The fluctuations in these fluxes between the three conditions were attributed to natural variability, and they were not large enough to induce apparent inconsistencies in soil temperature dynamics or evaporative losses. Overall, these findings suggest the surface energy balance in thermal desorption–treated soils is similar to that of the native topsoil and that using a mixture of treated soils with native topsoil may even be a better representation of pre‐disturbance conditions. [ABSTRACT FROM AUTHOR]

Abstract: Soil bulk density (ρb) is commonly treated as static in studies of land surface dynamics. Magnitudes of errors associated with this assumption are largely unknown. Our objectives were to (a) quantify ρb effects on soil hydrologic and thermal properties and (b) evaluate effects of ρb on surface energy balance and heat and water transfer. We evaluated 6 soil properties, volumetric heat capacity, thermal conductivity, soil thermal diffusivity, water retention characteristics, hydraulic conductivity, and vapour diffusivity, over a range of ρb, using a combination of 6 models. Thermal conductivity, water retention, hydraulic conductivity, and vapour diffusivity were most sensitive to ρb, each changing by fractions greater than the associated fractional changes in ρb. A 10% change in ρb led to 10–11% change in thermal conductivity, 6–11% change in saturated and residual water content, 49–54% change in saturated hydraulic conductivity, and 80% change in vapour diffusivity. Subsequently, 3 field seasons were simulated with a numerical model (HYDRUS‐1D) for a range of ρb values. When ρb increased 25% (from 1.2 to 1.5 Mg m−3), soil temperature variation decreased by 2.1 °C in shallow layers and increased by 1 °C in subsurface layers. Surface water content differed by 0.02 m3 m−3 for various ρb values during drying events but differences mostly disappeared in the subsurface. Matric potential varied by >100 m of water. Surface energy balance showed clear trends with ρb. Latent heat flux decreased 6%, sensible heat flux increased 9%, and magnitude of ground heat flux varied by 18% (with a 25% ρb increase). Transient ρb impacted surface conditions and fluxes, and clearly, it warrants consideration in field and modelling investigations. [ABSTRACT FROM AUTHOR]

Bioenergy crops are potential alternatives to traditional rowcrop and pasture/hay systems. A trial comparing effects of bioenergy to traditional production on soil properties was established in 2012 under no-till in the North Carolina Piedmont. Five cropping systems included: giant miscanthus (Miscanthus × giganteus), switchgrass (Panicum virgatum L.), biomass sorghum (Sorghum bicolor spp.), tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.], and corn (Zea mays L.)/ wheat (Triticum aestivum L.)/soybean (Glycine max L.) rotation. Soil samples were collected before and 3 yr after trial establishment. Sorghum produced average yield of 21.5 Mg ha-1 in 2012 to 2015. Miscanthus and switchgrass reached yield plateaus of 21 and 15 Mg ha-1, respectively, and removed significantly less N, P, and K than other crops, due to their rhizome systems and lower fertilizer requirements. They did not, however, demonstrate advantages over annual crops in soil physical properties. Soils under miscanthus and switchgrass had the least macropores and lowest saturated hydraulic conductivity. Summed to 30-cm soil depth, miscanthus maintained similar soil organic C as with tall fescue (58.6 vs. 55.0 Mg C ha-1), whereas soil organic C under sorghum and switchgrass were lowest (average of 49.5 Mg ha-1). Microbial biomass soil C under miscanthus (0-12-cm depth) was significantly greater than under annual crops. Negative effects of switchgrass on soil physical properties and organic C and N might have been due to tillage required for establishment. Typical bioenergy crops do not appear to have major negative or positive effects on soil properties in the North Carolina Piedmont. [ABSTRACT FROM AUTHOR]

Recent soil tests evaluating "soil health" on a broad scale may not properly consider the intrinsic limitations of soil properties and have not been assessed in regionally unique soil conditions. To evaluate three soil tests in North Carolina, we used long-term agronomic management trials from three distinct physiographic regions: mountain (22 yr), piedmont (32 yr) and coastal plain (17 yr). Mountain and coastal plain trials included combinations of organic or chemical management with or without tillage; the piedmont trial included nine different tillage treatments. Soil samples were collected and submitted for analysis as recommended by the North Carolina Department of Agriculture and Consumer Services, Haney soil health test (HSHT) and Cornell comprehensive assessment of soil health (CASH). Plant nutrient concentrations varied but were still sufficient for crops. The CASH physical soil indicators, such as surface hardness and aggregate stability, were not statistically different, regardless of tillage intensity or management. Biological soil indicators (e.g., CO2 respiration) responded differently to management, but this differentiation was inconsistent among locations and tests. Despite many years of conservation management, the CASH results described mountain soils as "low" or "very low" soil health for all but no-till organic management, which received a "medium" score. The HSHT results considered soil from all but moldboard plowing (piedmont) to be in good health. Finally, there was no correlation between soil health tests and crop yields from North Carolina soils. Soil health tests should be calibrated to better differentiate among soil management effects that vary depending on intrinsic soil limitations. [ABSTRACT FROM AUTHOR]

Accurate measurement of soil temperature gradients is important for the estimation of soil heat flux and latent heat flux, both major components of the surface energy balance. Soil temperature gradients are commonly measured using heat-pulse sensors equipped with thermistors. In this study, individual thermistors showed absolute temperature differences on the order of 0.2°C when placed under uniform temperature conditions. These differences compromised measurement of soil temperature gradients over small depth increments and/or conditions with relatively minor variation in temperatures. An in situ calibration approach was found to reduce the uncertainty between thermistors to about 0.05°C in a vineyard under arid conditions. In situ calibration results were similar to laboratory results before and after field deployment for temperatures ranging between 4 and 60°C. Thermistor offsets were found to change very little over a 5-yr period, indicating that pre- or post-laboratory calibration could be sufficient. The in situ approach can be useful when calibration prior to field deployment is unavailable and/or sensor failure prevents post-field calibration. [ABSTRACT FROM AUTHOR]

Soil water characteristics (SWC) is a common requirement in studies of soil physics and hydrology, and modeling this property is preferred because experimental measurements are error-prone, time-consuming, and costly. However, unknown empirical parameters in SWC models remain a source of uncertainty. This study proposes a formulation for computing pore radii and SWCs from routinely available particle-size distribution (PSD), bulk density, and particle density data, without the need for incorporating unknown empirical parameters. The proposed model emerged from combining attributes of natural-packed soil structure with those of a counterpart hypothetical structure consisting of spherical particles, and has the form rin = √ 0.0717 Φwi/ρb)/ni4/3Ri where rin is the pore radius for a given fraction of particles on the PSD curve, F is the porosity, wi is the fraction solid mass, ρwb is the bulk density, ni is the number of spherical particles that can be formed using the fraction solid mass, and Ri is the mean particle radius for the fraction. The model was applied to calculate SWC for 41 soils consisting of loam, clay, sandy loam, and sand textures. Root mean square residuals (RMSRs) of log-transformed pressure heads were calculated to assess goodness of agreement between experimental pressure heads and those predicted by the non-empirical model of this study and the empirical model of Arya et al. The distribution of RMSR values (log10 ∣h∣, cm) showed a range from 0.021 to 1.309. When viewed in conjunction with plotted SWC curves, results showed reasonable to excellent agreement with experimental data in about 75% of the cases. Barring a few exceptions, predictions of the proposed model also agreed well with predictions of the empirical model of Arya et al. [ABSTRACT FROM AUTHOR]

A dry surface layer (DSL) forms when wet soil is exposed to the sun; development of a DSL coincides with a shift between surface and subsurface evaporation. There remains debate as to when this shift from surface to sub-surface evaporation occurs relative to the timing of the shift between potential and falling-rate evaporation. We performed a field experiment to investigate the onset of subsurface evaporation, development of the DSL, and the extent of the evaporation zone. Our objective was to determine the timing of the onset of subsurface evaporation with respect to decline in evaporation rates. We estimated total (surface plus subsurface) and subsurface soil evaporation rates using microlysimeter (water mass balance) and sensible heat balance (SHB) approaches, respectively, for a bare loamy sand soil under natural wetting and drying cycles. Results showed that the onset of subsurface evaporation coincided with the beginning of falling-rate evaporation. The evaporation zone extended into the subsurface when evaporation rates fell below the potential rate but were still as high as 50% of potential evaporation. Over a 5-d drying event, estimated evaporation zones were as deep as 4 to 9 mm, and the estimated DSL had a maximum depth of approximately 6 mm. A low soil water content-dependent albedo was observed when evaporation occurred at potential rates, but albedo increased as evaporation rates declined. Data from the intensive observation period suggest that this increase in albedo corresponded to formation of a DSL and onset of subsurface evaporation. Overall, surface drying and formation of a DSL appeared to be a dominant process for this coarse-texture soil exposed to ambient boundary conditions, even as evaporation rates remained relatively high (0.3 mm h-1). [ABSTRACT FROM AUTHOR]

The effect of soil wettability on coupled heat and water transfer in soil is not well understood. The objective of this work was to determine the effect of soil wettability on coupled heat and water transfer for two wettable soils and their artificially hydrophobized counterparts. Closed soil cells instrumented with heat-pulse sensors provided in situ measurements of soil temperature, soil volumetric water content (θ), soil thermal conductivity (λ), and soil thermal diffusivity (α). Nonlinear temperature distributions developed in response to the 150°C m-1 temperature gradients applied to the soil cells for both the wettable and hydrophobized soils due to soil moisture redistribution. Hydrophobized sand and silt loam soils had different responses relative to their wettable counterparts. Soil moisture redistribution was similar in the wettable and hydrophobized sand soils. Net water transfer was reduced by 56% in the hydrophobized silt loam compared with the wettable silt loam. Reduced net water transfer in the hydrophobized silt loam indicated that water vapor transfer must have been lower in the hydrophobized silt loam than in the wettable silt loam. Diffusive pathways for water vapor may increase due to hydrophobicity. In both the wettable and hydrophobized soils, l and a decreased in the warm regions and increased in the cold regions of the soil cells due to soil moisture redistribution. Wettability is a function of water content, and relative to wettable soil, water redistribution in hydrophobized soil is reduced only when the water content is small enough for the soil to behave as hydrophobic. If the water content is large enough for a hydrophobized soil to behave as wettable, water redistribution is similar to that in a wettable soil. [ABSTRACT FROM AUTHOR]

Given the ever‐present threat of drought and the knowledge that water availability is the strongest limiting factor in vegetation growth, it is important to characterize the effect of water limitations on agricultural production. In this study, a small field plot technique for controlling soil moisture content suitable for physiological research in moist, humid areas was tested. We characterized the effect of water stress on total leaf conductance (gl) for two distinct determinate soybean [Glycine max (L.) Merr.] genotypes. Based on these findings, a model of gl as a function of plant age and soil moisture content was formulated and validated. The dependency of gl on plant age was well represented by a parabolic function that increased throughout the vegetative period, peaked around anthesis, and decreased throughout the reproductive period and senescence. A sigmoidal function explained the relation of gl to plant‐available soil water content. This new empirical model effectively quantifies the response of gl to plant‐available soil water and plant age with a functional form similar to the abscisic acid related Tardieu–Davies model. [ABSTRACT FROM AUTHOR]

Spence, Porchè L., Deanna L. Osmond, Wesley Childres, Joshua L. Heitman, and Wayne P. Robarge, 2012. Effects of Lawn Maintenance on Nutrient Losses Via Overland Flow During Natural Rainfall Events. Journal of the American Water Resources Association (JAWRA) 48(5): 909-924. DOI: 10.1111/j.1752-1688.2012.00658.x Abstract: A sampling system was used to evaluate the effect of residential lawn management on nutrient losses via overland flow generated during natural rainfall events from three residential landscapes: a high maintenance fescue lawn (HMFL), a low maintenance fescue lawn (LMFL), and a mixed forested residential landscape (FRL). A sampling system was located in designated areas within each landscape such that 100% of the runoff follows natural flow paths to the outlet ports and collects in sterile Nalgene® B3 media bags (Thermo Fisher Scientific, Rochester, NY). A rainfall event was defined as producing ≥2.54 mm of water. A total of 87 rainfall events occurred during a 20-month monitoring period. The total runoff volume collected from the LMFL was higher than from the HMFL and FRL, but on average <1% of the total rainfall was collected from the three landscapes. Mean nitrate concentrations from each lawn did not exceed 0.6 mg N/l. Nutrient unit area losses from the HMFL, LMFL, and FRL were 1,000 times less than fertilizer and throughfall inputs, which were due to the presence of well-structured soils (low bulk densities) with high infiltration rates. This study demonstrated that the frequency of runoff, total runoff volumes, and nutrient losses during natural rainfall events are lower from highly maintained (i.e., irrigation, fertilizer application, and reseeding) densely uniform manicured lawns than low maintenance lawns and forested residential landscapes. [ABSTRACT FROM AUTHOR]

The soil water retention curve (SWRC) is a key tool for understanding the fundamental relationship between soil moisture content and its associated energy. The objective of this study was to measure soil water retention including hysteresis at the dry end of the SWRC and to examine the effect of wettability on the SWRCs of two wettable soils and their hydrophobized counterparts. Two conditions, wettable and hydrophobic, were measured for each soil. The method used to measure the SWRCs was vapor equilibration over salt solutions of known osmotic potentials. Free water in the form of individual droplets was found to be present at the surface of the unwashed hydrophobic soils due to decreases in the osmotic potential during the hydrophobizing process. Water droplets did not form on the hydrophilic and washed hydrophobic soils. Soil wettability was found to affect soil water retention in relatively dry soil. The hydrophilic soils used in this study exhibited significant hysteresis in the water potential range of -2.3 to -19.2 MPa. Soil wettability and hysteresis should be considered when studying water sorption and desorption in relatively dry soil. [ABSTRACT FROM AUTHOR]

Urban development exposes and compacts the subsoil, resulting in reduced infiltration, which often leads to problems with establishing vegetation, increased erosion, and increased runoff volumes. Compost incorporation into these soils can potentially enhance soil physical properties, vegetation establishment, and pollutant removal. The goal of this field study was to determine the efficacy of compost as a soil improvement measure to reduce runoff volume, improve runoff quality, and increase vegetation establishment on a disturbed sandy clay subsoil representing post-development conditions. Two sources of compost were tested: (1) a certified yard waste product at 10%, 30%, and 50% by volume, and (2) an uncertified yard waste product at 30% by volume, both compared to a tilled, no-compost control. Treatment plots were established at Lake Wheeler Road Field Laboratory in Raleigh, NC, and observed for one year. Tilling alone may have been sufficient to reduce runoff quantity as few differences were found between tilled and compost amended plots. Runoff water quality also did not differ according to compost addition. However, the certified compost increased biomass production proportionally to the amount added and compared to the uncertified compost at the same rate. The improved vegetation establishment with compost is important for long-term erosion control and ecosystem services. The results of this study suggest (1) tilling is a viable option to achieve high infiltration rates and reduce runoff volumes, (2) compost incorporation does not reduce nor improve water quality, and (3) compost may yield more robust vegetation establishment. [ABSTRACT FROM AUTHOR]

Particles in a substrate create a network of pore pathways for water to move through, with size and shape determining the efficacy of these channels. Reduced particle size diversity can lead to increased leachate, poor substrate hydration, and an inefficient irrigation practice. This research examined the hydration characteristics of three greenhouse substrate components at three preconditioned initial moisture contents using subirrigation under five different irrigation durations and three water depths (2 mm, 20 mm, and 35 mm). Sphagnum peatmoss, coconut coir, and aged pine bark were tested at 67%, 50%, and 33% initial moisture (by weight). The objectives were to determine the impact of varying irrigation event durations (5, 10, 20, 30, 60 min) over a 60-min period, and the further influence of water depth and initial moisture, on the water capture abilities of peat, coir, and pine bark. The number of irrigation events depended on the irrigation event time of that experimental unit divided by the total time of 60 min, varying from 12, 6, 3, 2, and 1 event. Hydration efficiency was influenced by initial moisture content (IMC), water depth, pulsing duration, and inherent substrate characteristics (hydrophobicity/hydrophilicity). Initial MC had the largest impact on peat, regardless of water level or irrigation duration. Lower IMCs increased the hydrophobic response of peat, further reducing the amount of water the substrate was able to absorb. Pine bark had a 5–10% decrease in initial hydration between 67%, 50%, and 33% IMC, while coir's hydrophilic nature reduced any IMC affects. At 50% IMC or less, coir had the highest volumetric water content (VWC) across all substrates, pulsing durations, and water depths. Water depth was found to increase initial hydration and final hydration 6–8% across all substrates. These three materials had altered and varied water capture responses depending on the combination of treatments employed. This work demonstrated the effects of intensity and exposure on substrates and the need for more integrated research for improving water use efficiency on container crops. [ABSTRACT FROM AUTHOR]

Plant water availability in soilless substrates is an important management consideration to maximize water efficiency for containerized crops. Changes in the characteristics (i.e., shrink) of these substrates at low water potential (<−1.0 MPa) when using a conventional pressure plate-base can reduce hydraulic connectivity between the plate and the substrate sample resulting in inaccurate measures of water retention. Soilless substrate components Sphagnum peatmoss, coconut coir, aged pine bark, shredded pine wood, pine wood chips, and two substrate composites were tested to determine the range of volumetric water content (VWC) of surface-bound water at water potentials between −1.0 to −2.0 MPa. Substrate water potentials were measured utilizing dewpoint hygrometry. The VWC for all components or composites was between 5% and 14%. These results were considerably lower compared to previous research (25% to 35% VWC) utilizing conventional pressure plate extraction techniques. This suggests that pressure plate measurements may overestimate this surface-bound water which is generally considered unavailable for plant uptake. This would result in underestimating available water by as much as 50%. [ABSTRACT FROM AUTHOR]

Substrate wettability is an important factor in determining effective and efficient irrigation techniques for container-grown crops. Reduced substrate wettability can lead to lower substrate water capture, excessive leaching and poor plant growth. This research examined substrate water capture using surface and subirrigation under three initial moisture contents (IMC). Sphagnum peat moss, coconut coir, and pine bark were tested at IMCs of 67% 50%, and 33%. Substrate water capture was influenced by both IMC and irrigation technique. Surface irrigation increased the water capture of coir and peat, regardless of IMC, whereas IMC influenced pine bark water capture more than irrigation method. Surface-irrigated coir at or above 50% IMC provided the greatest water capture across all treatments. The first irrigation had the highest capture rate compared to all other events combined. Container capacities of pine bark and coir were unaffected by IMC and irrigation type, but the CC of peat was less by ~ 40% volumetrically under low IMC conditions. Coir, had the greatest ability to capture water, followed by pine bark and peat, respectively. Moisture content, irrigation type and component selection all influence the water capture efficiency of a container substrate. [ABSTRACT FROM AUTHOR]

Soil ice content is an important component for winter soil hydrology. The sensible heat balance (SHB) method using measurements from heat pulse probes (HPPs) is a possible way to determine transient soil ice content. In a previous study, in situ soil ice content estimates with the SHB method were inaccurate, due to thermal conductivity errors and the use of relatively long time steps for calculations. The objective of this study is to reexamine the SHB method for soil ice content determination. A soil freezing and thawing laboratory experiment was performed with soil columns and heat exchangers. Transient soil ice contents in the soil columns during soil freezing and thawing were determined with the SHB method. The SHB method was able to determine dynamic changes in soil ice contents during initial freezing and final thawing for soil temperatures between -5 and 0°C when latent heat values associated with ice formation or with thawing were relatively large. During an extended freezing period, when soil temperatures were below -5°C, the small associated latent heat fluxes were below the sensitivity of the SHB method, and the SHB method did not provide accurate estimates of ice contents with time. However, the soil ice contents during the extended freezing period could be estimated well from changes in volumetric heat capacity (C) determined with HPP. Thus, combining the SHB method for initial freezing and final thawing, with a change in C method for extended freezing periods, allowed determination of dynamic soil ice contents for the entire range of freezing and thawing soil temperatures investigated. HPPs were able to measure soil ice contents. [ABSTRACT FROM AUTHOR]

Feasibility of the sensible heat balance (SHB) method for determining in situ soil ice content with heat pulse (HP) sensors was evaluated using field measurements. The required accuracy of HP sensor measurements for SHB was further assessed with a sensitivity analysis. Improving accuracy of thermal conductivity measurements and using short time steps are necessary to accurately estimate ice contents with the SHB method. Soil ice content impacts winter vadose zone hydrology. It may be possible to estimate changes in soil ice content with a sensible heat balance (SHB) method, using measurements from heat pulse (HP) sensors. Feasibility of the SHB method is unknown because of difficulties in measuring soil thermal properties in partially frozen soils. The objectives of this study were (i) to examine the SHB method for determining in situ ice content, and (ii) to evaluate the required accuracy of HP sensors for use in the SHB method. Heat pulse sensors were installed in a bare field to measure soil temperatures and thermal properties during freezing and thawing events. In situ soil ice contents were determined at 60-min intervals with SHB theory. Sensitivity of the SHB method to temperature, heat capacity, thermal conductivity, and time step size was analyzed based on numerically produced soil freezing and thawing events. The in situ ice contents determined with the SHB method were sometimes unrealistically large or even negative. Thermal conductivity accuracy and time step size were the key factors contributing to SHB errors, while temperature and heat capacity accuracy had less influence. Ice content estimated with a 15-min SHB time step was more accurate than that estimated with a 60-min time step. Sensitivity analysis indicated that measurement errors in soil temperature and thermal conductivity should be less than ±0.05°C and ±20%, respectively, but the error in the soil heat capacity could vary by ±50%. Thus, improving the accuracy of thermal conductivity measurements and using short time steps are required to accurately estimate soil ice contents with the SHB method. [ABSTRACT FROM AUTHOR]

The applicability of the sensible heat balance (SHB) concept for estimating soil freezing and thawing rates was tested in a numerical modeling study. Results indicated that the SHB method was suitable for estimating soil freezing and thawing rates at depths below 24 mm. Application of the method requires accurate estimates of soil thermal properties. Agronomy Dep., Iowa State Univ., Ames, IA 50011; Soil Science Dep., North Carolina State Univ., Raleigh, NC 27695 USDA-ARS, Northwest Watershed Research center, Boise, ID 83712 In situ determination of soil freezing and thawing is difficult despite its importance for many environmental processes. A sensible heat balance (SHB) method using a sequence of heat pulse probes has been shown to accurately measure water evaporation in subsurface soil, and it has the potential to measure soil freezing and thawing. Determination of soil freezing and thawing may be more challenging than evaporation, however, because the latent heat of fusion is smaller than the latent heat of vaporization. Furthermore, convective heat flow associated with liquid water flow and occurrence of evaporation or condensation during freezing and thawing may cause inaccurate estimation of freezing and thawing with the SHB method. The objective of this study was to examine the applicability of the SHB concept to soil freezing and thawing. Soil freezing and thawing events were simulated with the simultaneous heat and water (SHAW) model. Ice contents were estimated by applying the SHB concept to numerical data produced by the SHAW model. Close agreement between the SHB-estimated and the SHAW-simulated ice contents were observed at depths below 24 mm. The main cause of inaccuracies with the SHB method was poor estimation of heat conduction at the 12-mm depth, possibly due to simplifications of temporal or vertical distributions of temperature and thermal conductivity. The effects of convective heat flow and concurrent evaporation or condensation and freezing or thawing on the SHB method were small. The results indicate that the SHB method is conceptually suitable for estimating soil freezing and thawing. Independent, accurate estimates of thermal properties must be available to effectively use the SHB method to determine in situ soil freezing and thawing. [ABSTRACT FROM AUTHOR]