Soil Temperature Regimes Research Articles

Cyanobacteria and moss biocrusts increase evaporation by regulating surface soil moisture and temperature on the northern Loess Plateau, China

Soil evaporation is a three-stage process and plays a vital role in soil physical, chemical, and biological processes, as well as global climate change. As an important living skin, biocrusts strongly influence most soil properties and support fundamental ecosystem functions. Although there are many studies concerning biocrust effects on surface soil hydrological processes, it still remains unclear how biocrusts impact soil evaporation and their potential effects on the water budget in drylands. In this study, we selected aeolian sandy soil (bare soil) and three types of biocrusts, specifically cyanobacteria (cyano), cyanobacteria and moss mixed crusts (cyano-moss), and moss crusts (moss), on the northern Chinese Loess Plateau. By utilizing weighing micro-lysimeters in simulated and ∼4 months in-situ field evaporation experiments, we investigated all evaporation stages containing stages I–II and III, as well as the soil evaporation rate (E) of all treatments. The soil moisture (θ) and temperature (T) at 2 cm and 10 cm depths were also measured in field. Our results showed that biocrust types strongly influenced E in the ranked order of moss > cyano-moss > cyano > bare soil. The cumulative evaporation amount (Ec) of all types of biocrusts was significantly higher than that of bare soil in simulated experiments. Particularly, moss increased Ec by 15.7% compared with bare soil. The results of in-situ field measurements illustrated that the E of cyano, cyano-moss, and moss was increased by 42.4%, 55.5%, and 46.9%, respectively, compared with the bare soil, and these increasing effects became more pronounced after rainfall events. Additionally, all types of biocrusts markedly increased θ and decreased T at 0–10 cm depth of soil, but cyano and cyano-moss increased T (by up to 5.7 °C) at 2 cm depth during the non-rainfall periods. The increasing effects of biocrusts on E were reasonably attributed to their higher contents of fine particles and organic matter, as well as their higher field capacity in contrast to bare soil. All these regulations of biocrusts on soil properties further reshaped soil water and temperature regimes and finally changed soil evaporation. In conclusion, biocrusts may greatly intensify surface soil water loss due to their higher E. However, their greater θ and lower T in comparison to bare soil may partially offset these negative effects in return, and they may have feedback impacts on surface soil water and heat balances in drylands.

Application of georadiolocation to assess the influence of the highway on the depth of permafrost in polygonal swamps of the North of Western Siberia

The results of the application of geo-radar profiling for the study of soils and underlying rocks of polygonal bogs of the Pur-Taz interfluve (North of Western Siberia), functioning in natural and anthropogenic disturbed conditions, are presented. The research area belongs to the southern tundra with a predominantly continuous distribution of permafrost rocks. The construction of highways in the North of Russia is one of the main factors of anthropogenic impact on the tundra geosystems of the cryolithozone, affecting the temperature regimes of soils and the depth of permafrost. The features of spatial differentiation of the depth of occurrence of permafrost rocks on the site of polygonal swamps intersected by a federal highway were determined by the methods of geo-radar profiling. Georadiolactic profiling made it possible to determine the configuration of the depth of the permafrost roof both in natural and anthropogenic disturbed areas of polygonal swamps. The maximum lowering of the permafrost roof is determined at the base of the road embankment and does not exceed a depth of three meters. Despite the deep occurrence of the MMP roof under the road embankment, the thickness of the thawed buried peat horizons here is similar to that of the seasonally shallow layer of undisturbed peat polygons. The features of spatial differentiation of the depth of the permafrost roof in the polygonal swamps intersected by the bulk highway in the North of Western Siberia are similar to those characteristic of regions with a continuous low-temperature cryolithozone. The method of manual probing of the permafrost roof was used to verify the results of geo-radar profiling within undisturbed areas.

Proposed changes to the soil family taxon within the Canadian System of Soil Classification

The soil family was developed in the 1960s as the fourth level of taxa within the hierarchical structure of the Canadian System of Soil Classification. The original aim of the soil family category was to provide a framework for checking and establishing limits for soil series while providing a link between the series and the subgroup level. Its intended use was to define and group numerous soil series based on soil characteristics important for the purpose of applying appropriate management practices. In the current Canadian System of Soil Classification, taxa at the family level represent subdivisions of the subgroups. Classification of mineral soils at the family level is based on properties of the parent materials which include particle size; soil mineralogy; reaction (soil pH); calcareousness; depth to bedrock and permafrost; as well as climactic factors: soil temperature and soil moisture regimes. The soil family particle-size classes were originally intended as a compromise between both agronomic and engineering influences; however, the resulting product has limited functionality because of differences in definitions between engineering and agronomic grain sizes and non-alignment with soil textural classes. Consequently, classification and use of the family taxon have largely been ignored. Some adjustments to the family taxon for mineral soils and terric layers in organic soils are proposed including realignment of classes in the current family particle-size triangle to follow the divisions of the soil textural classes. Minor adjustments to mineralogy classes and depth to bedrock are also proposed.

The importance of permafrost in the steady and fast increase in net primary production of the grassland on the Qinghai–Tibet Plateau

Permafrost affects soil water and soil temperature regimes; however, its effects on net primary production (NPP) remain unknown. Here, we examined temporal-spatial changes in grassland NPP during 2000–2018 in permafrost and permafrost-free areas on the Qinghai–Tibetan Plateau using the random forest (RF) and radial basis function artificial neural network (RBF-ANN). Our results indicated that the areas that showed increasing, decreasing, and non-significant trends for NPP accounted for 13.88%, 1.90%, and 84.22% of the permafrost area, respectively. For the permafrost-free areas, these NPP trends accounted for 22.25%, 2.68%, and 75.07% of the permafrost-free area, respectively. The mean NPP in the permafrost regions showed a faster and steadier (1.520 g C/m2/yr, p < 0.05) increase than in non-permafrost regions (1.224 g C/m2/yr, p < 0.05). The Biome-BGC model confirmed that these spatial NPP patterns could be attributed to differences in soil water and soil temperature between permafrost and permafrost-free areas. Both the soil temperature and soil water content in permafrost sites exhibited relatively lower variance than in permafrost-free sites. Although many factors may be attributed to these patterns, our results suggest that there is a possibility that the relatively stable change in permafrost NPP can be explained by the fact that permafrost can regulate soil water and temperature regimes. Therefore, climate warming can increase NPP in cold regions, and permafrost degradation may destabilize the grassland ecosystem, which may cause NPP values to exhibit greater interannual changes in the future.

Microbial “hotspots” of organic matter decomposition in temperate peatlands are driven by local spatial heterogeneity in abiotic conditions and not by vegetation structure

Climate change is triggering rapid shifts in plant communities and alterations in soil abiotic conditions in peatlands, with cascading effects on belowground decomposers and ecosystem C turnover. However, elucidating the dominant causal relationships between plant communities, soil biota and C fluxes in these vulnerable ecosystems requires a better understanding of the spatio-temporal variability of abiotic and biotic drivers. In this study we investigated the effects of biotic (plant functional types, PFTs) and abiotic factors (soil temperature and soil moisture) in determining dynamic patterns of soil microbial community structure and C cycling. Four representative temperate peatland habitats were selected based on their peat forming vegetation – an Atlantic wet heathland, two active blanket bogs with herbaceous plants (Molinia caerulea and Eriophorum angustifolium), and a transition mire dominated by Sphagnum mosses located along an altitudinal gradient to include the natural variations in soil temperature and water content regimes. We found that peat microbial communities were more strongly linked to local abiotic conditions than to the dominant above-ground vegetation. Aerobic conditions and warmer temperatures accelerated fungal driven decomposition and CO2 emissions under shrubs, whereas decreases in Gram−negative bacteria promoted increased C losses under Molinia. These findings suggest that small spatial differences in abiotic conditions can create local “hotspots” of organic matter decomposition. We propose that temperate peatlands should be considered as ‘ecosystem sentinels’ for climate change, acting as early-warning indicators of climate-carbon feedbacks.

Soil carbon and nitrogen stock of the Japanese agricultural land estimated by the national soil monitoring database (2015–2018)

ABSTRACT Estimation of the soil organic carbon (SOC) stock based on the monitoring data is important to validate the carbon model estimates and provide the initial values of SOC stock to the model. The Japanese National Greenhouse Gas Inventory Report (NIR) has applied the RothC model since 2015 to report changes in SOC in agricultural land. This study estimated soil carbon and nitrogen stocks and C:N ratio of top 30 cm arable land in Japan using the 2015–2018 database of the national soil monitoring project. Estimates based on the stationary monitoring data from the top 30 cm of the soil layer arethe first public release. We modified categorization of the soil temperature regime and soil-type classification for estimation, expecting to mitigate the underestimation and overestimation of SOC stock in the areas of soil temperature 15–17°C and more than 17°C, respectively, and to optimize the soil classification to 16 fewer types to allow an appropriate estimation even in the current situation of decreasing number of survey sites. Statistical analysis to see the effects of land use and soil temperature on SOC stock, TN stock, and C:N ratio showed that soil types other than Andosols had an inverse temperature-dependent trend for all variables, while Andosols had an unclear trend in soil temperature, supporting existing studies. Also, when Lowland soils (Fluvisols or Anthrosols in the World Reference Base) were surrounded by Andosols, redeposition of volcanic ash could affect the temperature trend in SOC stock for Lowland soils. The distribution map of the SOC stock and C:N ratio across Japan visually showed a high value in the Andosols distribution areas and a temperature-dependent trend at the distribution areas of the other soil types. The total SOC stock estimated in this study was 176±12.8 TgC in paddy field, 100±8.6 TgC in upland field, 25±1.7 TgC in orchard, 78±8.9 TgC in grassland, and 379±17.9 TgC in total, the standard deviations of which were much smaller than those of the mean values for each land use calculated by the simple average method.

The influence of climatic and topographic parameters on the distribution of forest communities of the Ufa plateau

The purpose of this study was to analyse the influence of climatic and topographic parameters on the distribution of forest communities (on the alliance level) on the Ufa plateau. In order to characterize the features of the forest vegetation habitats of six alliances, topographic parameters were calculated using the digital elevation model SRTM-3, and bioclimatic variables Bioclim (CHELSA). Cluster analysis using climatic characteristics showed that the main factors in the differentiation of alliances are the amount of precipitation in January and in the winter quarter. The amount of precipitation determines the depth of soil freezing and the sufficiency of soil moisture in the initial period of the seasonal development of trees. These factors are the main ones in differentiating the habitats of the communities of the suballiance Tilio cordatae-Pinenion sylvestris from the habitats of the other forest communities. The amount of precipitation in the summer quarter is the next most important climatic parameter, differentiating the habitats of communities. Cluster analysis using topographic parameters showed that the main factors of differentiation of the habitats of the alliances are the profile and plan curvature, slope steepness and aspect. These factors determine the accumulation of soil, moisture and the temperature regime of soils.

Soil temperature field and dynamics of freezing-thawing processes in the south of the Vitim Plateau (Transbaikal region)

The results of geographic and stationary studies of temperature, water and permafrost regimes and soil properties in the south of the Vitim Plateau (Transbaikal region) are discussed. Instrumental data on soil temperature regimes indicate the dynamics of soil freezing–thawing processes and attest to changes in the thawing depth of permafrost-affected soils. The revealed spatiotemporal patterns of soil freezing/thawing reflect the distribution of heat and cold (permafrost) in the soils of the studied cryoarid landscapes. Seasonal, annual and long-term differences in the soil temperature field cause a great heterogeneity of soil toposequences with contrasting soils on the north– and south–facing slopes. An increase in the soil thawing depth has been observed over the past 50 years. In the relatively wet and cold 1970–1990 years, its rate varied from 1.0 to 1.5 cm/year with higher values typical for Haplic Chernozems under meadow-steppe vegetation, and lower values for Phaeozems under forest vegetation. Over the recent 25 years, the rate of the increase in the soil thawing depth for the same soils has intensified by 2.5– 3.0 times in relation to aridization and climate warming.

Landscape-climatic features of the reforestation dynamics pyrogenically transformed geosystems of the Tunkinskaya depression

In order to identify the features of the dynamics of the soil temperature regime during the post-fire restoration of the subtaiga light-coniferous geosystems of the Tunkinskaya depression, a study of the demutation processes in the pine forests of the Badar urochishche was conducted. Our research is based on the data of observations initiated after the fire that took place in 2010. The model key areas were selected at intact landscape complexes that did not experience pyrogenic influence, as well as the territory subjected to forest fires. Comparing the dominant composition of secondary succession biocenoses with natural plant communities in the background key area, indicators of the prospects for successful reforestation were identified. The analysis of 10-year data on the observation of the soil temperature regime from the surface to a depth of 3.2 m was carried out at the selected sites. The differences between the soil temperatures in the disturbed and natural sites, which vary during a year were revealed. During the observation period, a decrease in microclimatic differences was observed with the regeneration of vegetation cover, which indicates the restoration of the temperature regime in the pyrogenic-disturbed area.

Modeling the thermic soil temperature regime boundary of the eastern United States

AbstractWithin U.S. soil taxonomy,soil temperature regimes (STRs) are recognized and incorporated in the classification and mapping of soils. Although knowledge of STR can inform crop selection, yield estimates, and nutrient management decisions, detailed and current maps of STRs derived from measured data are not available for most of the United States. Soil temperature measurements at the prescribed depth of 50 cm were summarized for 69 Soil Climate Analysis Network (SCAN) stations in the eastern United States. Mean annual soil temperature (MAST) was calculated for the 2005–2015 period from monthly averages calculated from daily soil temperature observations. A prediction equation for MAST was developed using mean annual air temperature (MAAT) from the PRISM (Parameter‐elevation Regressions on Independent Slopes Model) group as a predictor: MAST = 2.49 + (0.91 × MAAT). The adjusted r2 was .96 with a RMSE of 0.74 °C and mean absolute error of 0.59 °C based on 10‐fold cross‐validation. Orographic influence is incorporated in PRISM MAAT, yielding a simple model. The MAST surfaces were calculated by applying the prediction equation to MAAT grids for the 1895–2015 period. The yearly MAST surfaces allow estimation of STR over time and for various summary periods including the 1895–2015 record, 30‐yr normal, and probabilities based on individual years for the 1895–2015 period. Based on this investigation, the mesic–thermic STR boundary occurs north of the presently recognized location, is dynamic, and is supported by existing native plant communities associated with thermic STR.

Thinning decreased soil respiration differently in two dryland Mediterranean forests with contrasted soil temperature and humidity regimes

The effects of a thinning treatment on soil respiration (Rs) were analysed in two dryland forest types with a Mediterranean climate in east Spain: a dry subhumid holm oak forest (Quercus ilex subsp. ballota) in La Hunde; a semiarid postfire regenerated Aleppo pine (Pinus halepensis) forest in Sierra Calderona. Two twin plots were established at each site: one was thinned and the other was the control. Rs, soil humidity and temperature were measured regularly in the field at nine points per plot distributed into three blocks along the slope for 3 years at HU and for 2 years at CA after forest treatment. Soil heterotrophic activity was measured in laboratory on soil samples obtained bimonthly from December 2012 to June 2013 at the HU site. Seasonal Rs distribution gave low values in winter, began to increase in spring before lowering as soil dried in summer. This scenario indicates that with a semiarid climate, soil respiration is controlled by both soil humidity and soil temperature. Throughout the study period, the mean Rs value in the HU C plot was 13% higher than at HU T, and was 26% higher at CA C than the corresponding CA T plot value, being the differences significantly higher in control plots during active growing periods. Soil microclimatic variables explain the biggest proportion of variability for Rs: soil temperature explained 24.1% of total variability for Rs in the dry subhumid forest; soil humidity accounted for 24.6% of total variability for Rs in the semiarid forest. As Mediterranean climates are characterised by wide interannual variability, Rs showed considerable variability over the years, which can mask the effect caused by thinning treatment.

Influences of local hydroclimatology and teleconnections on Florida's precipitation and temperature variability

AbstractUnderstanding the influences of local hydroclimatology and two large‐scale oceanic‐atmospheric oscillations (i.e., Atlantic Multidecadal Oscillation (AMO) and El Niño‐Southern Oscillation (ENSO)) on seasonal precipitation (P) and temperature (T) relationships for a tropical region (i.e., Florida) is the focus of this study. The warm and cool phases of AMO and ENSO are initially identified using sea surface temperatures (SSTs). The associations of SSTs and regional minimum, maximum and average surface air temperatures (SATs) with precipitation are then evaluated. The seasonal variations in P‐SATs and P‐SSTs associations considering AMO and ENSO phases for sites in (1) two soil temperature regimes (i.e., thermic and hyperthermic); (2) urban and non‐urban regions; and (3) regions with and without water bodies, are analysed using two monthly datasets. The analyses are carried out using trend tests, two association measures, nonparametric and parametric statistical hypothesis tests and kernel density estimates. Decreasing (increasing) trend in precipitation (SATs) is noted in the recent multi‐decadal period (1985–2019) compared to the previous one (1950–1984) indicating a progression towards warmer and drier climatic conditions across Florida. Spatially and temporally non‐uniform variations in the associations of precipitation with SATs and SSTs are noted. Strong positive (weak negative) P–T associations are noted during the wet (dry) season for both AMO phases and El Niño, while significant (positive) P–T associations are observed across southern Florida during La Niña in the dry season. The seasonal influences are predominant in governing the P–T relationship over the regions with and without water bodies; however, considerable variations between El Niño and La Niña are noted during the dry season. The climate variability influences on P–T correlations for hyperthermic and thermic soil zones are found to be insignificant (significant) during the wet (dry) season. Nonparametric clustering is performed to identify the spatial clusters exhibiting homogeneous P–T relationships considering seasonal and climate variability influences.

Soil Temperature in Disturbed Ecosystems of Central Siberia: Remote Sensing Data and Numerical Simulation

We investigated changes in the temperature regime of post-fire and post-technogenic cryogenic soils of Central Siberia using remote sensing data and results of numerical simulation. We have selected the time series of satellite data for two variants of plots with disturbed vegetation and on-ground cover: natural ecosystems of post-fire plots and post-technogenic plots with reclamation as well as dumps without reclamation. Surface thermal anomalies and temperature in soil horizons were evaluated from remote data and numerical simulation and compared with summarized experimental data. We estimated the influence of soil profile disturbances on the temperature anomalies forming on the surface and in soil horizons based on the results of heat transfer modeling in the soil profile. According to remote sensing data, within 20 years, the thermal insulation properties of the vegetation cover restore in the post-fire areas, and the relative temperature anomaly reaches the level of background values. In post-technogenic plots, conditions are more “contrast” comparing to the background, and the process of the thermal regime restoration takes a longer time (&gt;60 years). Forming “neo-technogenic ecosystems” are distinct in special thermal regimes of soils that differ from the background ones both in reclamated and in non-reclamated plots. An assumption was made of the changes in the moisture content regime as the main factor causing the long-term existence of thermal anomalies in the upper soil horizons of disturbed plots. In addition, we discussed the formation of transition zones (“ecotones”) along the periphery of the disturbed plots due to horizontal heat transfer.

The effect of temperature fields on soil and plant cover formation in arid ecosystems of the Uvs Nuur basin

Introduction of remote and automated methods into the practice of soil and ecological studies urges for development of the methodological basis for combined analyses of surface and satellite data. The aim of the study was to explore the possibility to identify and typologise the structural and functional borders of soil cover using temperature fields, obtained by combined analysis of the temperature time series obtained by field and remote temperature monitoring. The functional relationships that are expressed within geosystems as the flux of energy and matter are reflected in soil temperature regimes, hydrophysical soil properties and plant cover biological productivity, which were studied in the arid ecosystems of the Uvs Nuur depression in Tuva, Russia. The quantitative characteristic of the temperature fields of the psammophytic soils were obtained, and the effect of hydrothermal conditions and soil hydrophysical properties on above- and belowground phytomass stocks of the sand massif Zuger-Els revealed and discussed.

Numerical modeling of the thermal performance of soil containing microencapsulated PCM

Phase change material (PCM) can be used with soil as an alternative type of thermal regulation of the subgrade, since it has an ability to accumulate and generate heat during the phase change. This paper evaluates the position of PCM microcapsules in the soil by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The SEM image processing method includes an integrated approach to transferring a color pixel image into a numerical matrix, followed by noise removal and precise determination of the position and size of microcapsules. Based on these data, a macroscale model of the soil volumetric unit with the inclusion of the microencapsulated phase change material (mPCM) was created, which made it possible to estimate the temperature of the mixture at a changing external temperature, as well as the nature of the effect of mPCM on the soil temperature regime. Through the analysis of many points in the model, the following results were obtained: 1) mPCM not only reduces the peak temperatures of its own volume, but it also softens the peak temperatures of the surrounding soil, 2) with a decrease in the external temperature, there is a tendency to a decrease in the temperature change rate as the model temperature approaches the phase change temperature range, 3) in the second cycle of changing the outside temperature, the effect of mPCM on peak temperatures is greater than in the first cycle due to the cumulative effect of decreasing the temperature change from cycle to cycle. PCM materials release/absorb a large amount of latent heat during hardening/melting, which can be useful in solving problems associated with seasonal freezing and thawing of pavements.

Assessment of the road transport infrastructure facility functionality loss risk resulting from climate change

The cause of a road bridge functionality loss risk in the conditions of climate changes in the Arctic is a decrease in its load-bearing capacity as a result of permafrost soil degradation. Modeling of the soil temperature regime of the bridge piling in Yakutsk for 2 years was performed and the minimum load-bearing capacity of the bridge piling was determined for this period. It was assumed that the average annual air temperature increased by 2 degrees Celsius in combination with an increase in the contrast between summer and winter temperatures. The obtained value of the climate risk level (438 units) allows to continue operating the facility without implementing engineering and technical measures aimed at stabilizing the soil temperature regime.

Geotechnical monitoring bearing capacity boring pile foundations of bridge during permafrost degradation

The construction and operation of bridge foundations in permafrost conditions is associated with many problems, the most urgent of which is the degradation of the frozen state of soils due to the effect of solar radiation on the thawing process. Thawing of permafrost soils of the base significantly affects structures, the design of which does not provide for thorough protection from natural factors - first of all, these are railway bridges. The changing climate has a destructive effect on permafrost soils, which is destructive for infrastructure facilities operated in the permafrost zone. The aim of the given work is to increase the efficiency of systems that regulate the temperature regime of permafrost soils of the bridges foundations which are located on railways in permafrost regions.

Effect of plastic film mulching on maize productivity and nitrogen use efficiency under organic farming in South Korea

Winter cover crop cultivation and its biomass recycling as green manure (GM) were accepted as an ideal nutrient management practice in temperate organic farming fields. Since its biomass growth was boosted with air temperature rising from late Spring to early Summer, this stage overlapped with cash crops' seeding or transplanting. Thus, organic farmers were suffering from low crop productivity, due to delayed mineralization of incorporated biomass. To accelerate the mineralization of biomass nutrients and control weeds, plastic film mulching (PM) was broadly utilized in organic farming fields of temperate-monsoon climate region. However, the effect of PM on increasing nutrient use efficiency was not properly quantified in GM amended soil. To determine the effect of PM on crop productivity and nutrient use efficiency in GM amended soils, PM and no-mulching treatments were installed under different levels of GM biomass amended soils (0, 25, 50 and 100% of harvested aboveground biomass). The biomass productivity of barley and hairy vetch mixture as cover crop and biomass nitrogen productivity were dramatically increased from the mid May to the early June. PM significantly improved soil temperature and moisture regimes during maize cropping seasons, and then increased inorganic N (NH4+ and NO3−) contents in soils. These improved soil properties under PM highly increased maize productivity and nitrogen use efficiency (NUE). Comparing with no-mulching, as GM application level was increased, the effect of PM on increasing maize productivity became greater, but its effect on increasing NUE became smaller. In conclusion, PM could be very useful tool to improve productivity and NUE of cash crop maize in organic cropping fields, in which the harvesting time of GM biomass might be sustained to increase GM biomass productivity.

Changing the hierarchical placement of soil moisture regimes in Soil Taxonomy

AbstractSoil moisture and temperature are incorporated into Soil Taxonomy through the broad classes of moisture and temperature regimes. Although both are important variables in soil formation and land use, soil temperature regime (STR) is typically applied at the family level, whereas soil moisture regime (SMR) is applied at the suborder level. In this paper, we are questioning whether moving SMR to the family level will create a classification system that is more efficient and provide more information to the user at higher categories. The pros and cons of moving ustic, xeric, and udic SMRs from suborder to family category are discussed. To explore this potential change, we used Shannon diversity (ΔH) as an index of the information gain moving from order to suborder when classifying a soil. The analysis indicated a relatively small ΔH for most of the country considering current suborder classes. The proposed group of suborders, characterized by diagnostic horizons instead of SMR, conveyed a considerably larger ΔH supporting a substantial gain in information if the change was incorporated into Soil Taxonomy. The proposed change also has the potential to reduce the number of subgroup taxa by nearly 50%, without losing any of the current information within each taxa. Counterarguments for the change are that SMRs have soil genesis connotations and provide a way to group similar soils on broad‐scale maps. A change in the hierarchy of SMRs within Soil Taxonomy could deemphasize the relevance of soil moisture to soil genesis, morphology, and ecology.

Near-infrared spectroscopy: Alternative method for assessment of stable carbon isotopes in various soil profiles in Chile

The role of soil in the global carbon cycle and carbon–climate feedback mechanisms has attracted considerable interest in recent decades. Consequently, development of simple, rapid, and inexpensive methods to support the studies on carbon dynamics in soil is of interest. Near-infrared spectroscopy (NIRS) has emerged as a rapid and cost-effective method for measurements of soil properties. The aim of this study was to develop and validate a predictive model for δ13C values using NIRS in various soil profiles across Chile. Eleven sites were selected in the range of 30° to 50° S. These sites represent different soil moisture and soil temperature regimes, clay mineralogies, parent materials, and climates; in addition, they have prairie vegetation and contain C3-type vegetation. Air-dried soil samples were scanned in the NIR range at a resolution of 4 cm−1. The carbon isotopic composition, expressed as δ13C relative to the Vienna Pee Dee Belemnite standard, was analysed using an elemental analyser–isotope ratio mass spectrometer system. A prediction model for δ13C values based on NIRS data was developed through a partial least-squares regression (PLS) model using ten latent variables. A second model was generated using a random forest (RF) approach. The model performances were acceptable. The RF model provided the best results. The values of the root mean square error of prediction for the validation runs for δ13C obtained using the PLS and RF models were 1.38‰, and 1.15‰, respectively. These model performances indicate that NIRS can be used to predict δ13C for the selected dataset. The results of this study support the use of NIRS as a predictive method in soil analyses and as a nondestructive waste-free method for studies on carbon dynamics in soil.