Differences In Soil Temperature Research Articles

Effect of strip tillage widths on soil moisture, soil temperature and soil structure in northeast China

Strip tillage is an effective tillage technique, which included the strip seedbed tilled area (ST-IR) and the straw-covered area between the seedbeds (ST-BR). However, soil hydrothermal conditions and soil disturbance varies with strip tillage widths, which might affect crop growth and yields. Therefore, this study explored the effect of strip tillage width on the soil hydrothermal conditions and soil structure of ST-IR and ST-BR, to determine the optimal strip tillage width. A field experiment with three replicates was conducted to analyze soil moisture and soil temperature variation and to clarify the difference of soil structure in the IR and BR. Three strip tillage widths, 20 cm (ST20), 30 cm (ST30), and 40 cm (ST40), were examined in this study. Soil temperature in both the ST-IR and ST-BR increased as the strip tillage width increased, and the average soil temperature of ST30-IR and ST40-IR in the seedling stage was 2.11°C and 2.62°C higher than that of ST20-IR, respectively. Moreover, the daily soil temperature range in both the IR and BR was greater for ST40 than for ST20 and ST30 in the seedling stage; soil temperature differences in other crop growth stages were small. No significant difference in soil temperature was observed between ST30-IR and ST40-IR. Conversely, soil moisture was greater in ST20-IR and ST30-IR than in ST40-IR; soil moisture was also greater in ST30-BR and ST40-BR than in ST20-BR during the monitoring period. Soil moisture in ST40-IR and ST20-BR increased and decreased more rapidly during rainfall events than in the other treatments. Moreover, soil temperature was higher in the ST-IR than in the ST-BR for all 3 strip tillage widths, and the opposite results were observed for soil moisture. In addition, strip tillage widths had no significant differences on soil structure. In conclusion, a 30 cm strip tillage width had higher soil temperature and remained more soil moisture than other strip tillage widths, so this strip tillage width is thus recommended for use by farmers in Northeast China.

Development of inter-grid-cell lateral unsaturated and saturated flow model in the E3SM Land Model (v2.0)

Abstract. The lateral transport of water in the subsurface is important in modulating terrestrial water energy distribution. Although a few land surface models have recently included lateral saturated flow within and across grid cells, it is not a default configuration in the Climate Model Intercomparison Project version 6 experiments. In this work, we developed the lateral subsurface flow model within both unsaturated and saturated zones in the Energy Exascale Earth System Model (E3SM) Land Model version 2 (ELMv2.0). The new model, called ELMlat, was benchmarked against PFLOTRAN, a 3D subsurface flow and transport model, for three idealized hillslopes that included a convergent hillslope, divergent hillslope, and tilted V-shaped hillslope with variably saturated initial conditions. ELMlat showed comparable performance against PFLOTRAN in terms of capturing the dynamics of soil moisture and groundwater table for the three benchmark hillslope problems. Specifically, the mean absolute errors (MAEs) of the soil moisture in the top 10 layers between ELMlat and PFLOTRAN were within 1 %±3 %, and the MAEs of water table depth were within ±0.2 m. Next, ELMlat was applied to the Little Washita experimental watershed to assess its prediction of groundwater table, soil moisture, and soil temperature. The spatial pattern of simulated groundwater table depth agreed well with the global groundwater table benchmark dataset generated from a global model calibrated with long-term observations. The effects of lateral groundwater flow on the energy flux partitioning were more prominent in lowland areas with shallower groundwater tables, where the difference in simulated annual surface soil temperature could reach 0.3–0.4 ∘C between ELMv2.0 and ELMlat. Incorporating lateral subsurface flow in ELM improves the representation of the subsurface hydrology, which will provide a good basis for future large-scale applications.

Influence of thermal soil regimes on the forest fires frequencies

This paper focuses on the possible impact of the thermal soil regime on the occurrence of forest fires in the Zajecar administrative district in Eastern Serbia. The study uses data on soil temperature from the Republic Hydrometeorological Service of the Republic of Serbia and the ERA5-Land gridded reanalysis dataset for monthly temperature and volumetric soil water of the soil level 1 (0-7 cm), and soil level 2 (7-28 cm) with horizontal resolution of 0.1? (approximately 12 km ? 12 km) during the period of 2009-2021. Differences in soil temperature at depths of 2 cm, 5 cm, 10 cm, and 20 cm at the meteorological station in Zajecar for the periods 1961-1990 and 2009-2021 are observed. By analyzing the data on the registered number of forest fires for the period 2009-2021, pronounced oscillations in the dynamics of forest fires can be observed. The minimum number of forest fires (0) is registered in 2014, when the maximum of soil moisture in the soil levels 1 and 2 is observed. A high number of forest fires corresponds to high soil temperatures in 2012 and 2017. Soils drier and hotter than the average are registered in 47.0% of all months with the fire occurrences. About 50% of fires occurred in dry and hot soils during 2012 and 2017. This percentage was zero in 2014, when there were no fires.

Dynamics and variability of microclimate in an unmanaged mountain forest after a bark beetle outbreak

Forest disturbances alter hydrological, energy, and microclimatic characteristics and their extents vary with the landscape characteristics of the terrain. We evaluated changes in evapotranspiration and latent heat rate in an unmanaged, central European mountain forest (Norway spruce) after a bark beetle-induced mortality of >75 % trees, and the spatial variability in microclimate during its natural regeneration. We observed that (1) the annual mean incident solar radiation to the treeless plots was 8.2 MJ m−2 day−1 (95 W m−2), being reduced by ∼45 % compared to its theoretical flux by high average cloudiness (70.6%) and short daily sunshine (4.3 hour day−1). The observed energy input to the forest floor beneath survived canopies (1.2 MJ m−2 day−1) was an order of magnitude lower than solar radiation to the canopy surface. (2) The mean annual evapotranspiration and the average annual latent heat rate decreased by 155 mm yr−1 and 385 MJ m−2 yr−1 (12 W m−2), respectively, after tree dieback. (3) The soil and air temperatures at individual plots correlated positively with the incident solar radiation and negatively with elevation. Mean soil and air temperatures exhibited similar lapse rates of 5.9–8.0 °C km−1 during the growing season (May-October). The energy input (positive relationship) and elevation (negative relationship) explained 74–83 % of the between-plot variability in mean soil and air temperatures and 51–77 % of their daily amplitudes during the growing season. (4) On sunny days, the observed soil and air temperatures were significantly lower (by ∼50 and 15 %, respectively) than ground surface temperature based on thermal satellite data (Landsat-8). The ground surface temperature explained 80–92 % of the observed variability in the soil and air temperatures. (5) The between-plot differences in daily soil and air temperatures and their amplitudes were from 24 to 70 % explained by solar radiation (positive correlation) and relative air humidity and wind speed (negative correlations).

Response of CO2 and CH4 emissions from Arctic tundra soils to a multifactorial manipulation of water table, temperature and thaw depth

Significant uncertainties persist concerning how Arctic soil tundra carbon emission responds to environmental changes. In this study, 24 cores were sampled from drier (high centre polygons and rims) and wetter (low centre polygons and troughs) permafrost tundra ecosystems. We examined how soil CO2 and CH4 fluxes responded to laboratory-based manipulations of soil temperature (and associated thaw depth) and water table depth, representing current and projected conditions in the Arctic. Similar soil CO2 respiration rates occurred in both the drier and the wetter sites, suggesting that a significant proportion of soil CO2 emission occurs via anaerobic respiration under water-saturated conditions in these Arctic tundra ecosystems. In the absence of vegetation, soil CO2 respiration rates decreased sharply within the first 7 weeks of the experiment, while CH4 emissions remained stable for the entire 26 weeks of the experiment. These patterns suggest that soil CO2 emission is more related to plant input than CH4 production and emission. The stable and substantial CH4 emission observed over the entire course of the experiment suggests that temperature limitations, rather than labile carbon limitations, play a predominant role in CH4 production in deeper soil layers. This is likely due to the presence of a substantial source of labile carbon in these carbon-rich soils. The small soil temperature difference (a median difference of 1 °C) and a more substantial thaw depth difference (a median difference of 6 cm) between the high and low temperature treatments resulted in a non-significant difference between soil CO2 and CH4 emissions. Although hydrology continued to be the primary factor influencing CH4 emissions, these emissions remained low in the drier ecosystem, even with a water table at the surface. This result suggests the potential absence of a methanogenic microbial community in high-centre polygon and rim ecosystems. Overall, our results suggest that the temperature increases reported for these Arctic regions are not responsible for increases in carbon losses. Instead, it is the changes in hydrology that exert significant control over soil CO2 and CH4 emissions.

Short-term effect of different returning methods of maize straw on the temperature of black soil plough layer

Clarifying the effect of different maize straw returning methods on soil temperature is crucial for optimizing the management of farmland straw and the efficient utilization of heat resources in the black soil region of Northeast China. To investigate the impacts of straw returning methods on soil temperature, we conducted a field experiment with four treatments during 2018 and 2020, including plough tillage with straw returning (PTSR), rotary tillage with straw returning (RTSR), no-tillage with straw returning (NTSR), and a control treatment of conventional ridge tillage without straw returning (CT). We measured soil temperature and water content at the 5 cm, 15 cm and 30 cm soil layer, and the straw coverage rate during the 3-year maize growth period. We further analyzed the differences of soil temperature in different soil layer under different treatments, accumulated soil temperature and growing degree-days (GDD) above 10 ℃, daily dynamics of soil temperature, the production efficiency of air accumulated temperature among different treatments, and explored factors causing the difference of soil temperature and the production efficiency of air accumulated temperature. Our results showed that different treatments mainly affected soil temperature from the sowing to emergence stage (S-VE) of maize. The daily average soil temperature showed a trend of CT>PTSR>RTSR>NTSR. The differences of soil temperature under different treatments showed a decreasing trend as growth process advanced and soil depth increased. Compared with the CT treatment, soil temperature at 5 cm depth was decreased by 0.86, 1.84 and 3.50 ℃ for PTSR, RTSR, and NTSR treatments, respectively. NTSR significantly reduced the accumulated temperature of ≥10 ℃ in different soil layers and GDD. The accumulated temperature ≥ 10 ℃ at the 5, 15, and 30 cm soil layers decreased by 216.2, 222.7, and 165.1 ℃·d, and the GDD decreased by 201.9, 138.7 and 123.9 ℃·d, respectively. In addition, production efficiency of air accumulated temperature decreased by 9.7% to 15.6% for NTSR. Conclusively, PTSR and RTSR had significant impacts on topsoil temperature during the maize growing period from sowing to emergence, but did not affect the accumulated soil temperature and the production efficiency of air accumulated temperature. However, NTSR significantly reduced topsoil temperature and production efficiency of air accumulated temperature.

DEVELOPMENT OF A DIGITAL MODEL OF A PIPELINE IN PERMAFROST SOILS

The work is devoted to the study of the stress-strain state of a pipeline laid in permafrost soils. The essence of the study is the development and verification of a tool for assessing the stress-strain state of a pipeline when changing the properties of the soil around the pipeline.
 The purpose of this study is to develop a computer model that takes into account the dependence of the mechanical properties of permafrost soils on temperature when calculating the stress-strain state of the pipeline during the destruction of thermal insulation.
 Research objectives:
 1. development of a coupled thermal and mechanical model of a pipeline in permafrost soil in application software;
 2. adding to the calculation model the dependence of soil properties on temperature;
 3. adding to the calculation model a change in the volume of soil due to freezing of liquid in the soil. Adding properties of heaving soil.
 The introduction deals with digital and analytical coupled thermal, mechanical and hydraulic models. The choice of a software package for modeling processes is substantiated, and the relevance of such modeling is also shown.
 The simulation of the pipeline defrosting process is carried out using the ANSYS software, which is based on the finite element method. The article shows the developed model of the pipeline, as well as the details of setting up such a model for thermal mechanical calculation. Features such as specifying loads and boundary conditions by steps, as well as setting the relationship of these steps are given.
 Based on the results of the thermal calculation, it was revealed that the depth of thawing in case of violation of thermal insulation for given boundary conditions varies from three to five meters from the daytime surface of the soil. With such a spread of the boundaries of the thawing halo, the pipeline deflection varies from 0 to 300 mm, while the equivalent stresses increase from 10 to 140 MPa.
 To improve the model, a method is proposed for setting the properties of soil heaving using the soil linear expansion coefficient. An experimental bench is proposed for determining the values of this coefficient depending on soil moisture and temperature difference.

Mathematical Modeling of Seepage–Temperature Field for Earth Dam Using Experimental Test

Monitoring the seepage field is essential to characterize the operation of the earth dam. However, conventional seepage monitoring typically involves the use of a piezometer tube or pressure sensor for point distribution. A mathematical model incorporating the feedback of the temperature field on the seepage field was proposed based on experimental test observations. First, a theoretical analysis of the mathematical model is conducted, which includes examining the relationship between the variation of temperature field and factors, such as hydraulic gradient, water and soil temperature difference, hydraulic conductivity, thermal conductivity, specific heat, and time. Second, a homogeneous earth dam model is constructed in the laboratory with a distributed temperature sensor system to obtain synchronous information of the seepage–temperature field. Finally, the parameters of the mathematical model are quantified using observations from experimental tests, demonstrating good agreement between calculated and measured values. The experimental results indicate the feasibility of inferring seepage field monitoring information from the temperature field and elucidation of the interaction mechanism of the coupled fields. The quantitative mathematical model of the temperature field feedback on the seepage field is validated for its applicability in earth dams.

Improving maize growth and development simulation by integrating temperature compensatory effect under plastic film mulching into the AquaCrop model

Temperature compensatory effect, which quantifies the increase in cumulative air temperature from soil temperature increase caused by mulching, provides an effective method for incorporating soil temperature into crop models. In this study, compensated temperature was integrated into the AquaCrop model to investigate the capability of the compensatory effect to improve assessment of the promotion of maize growth and development by plastic film mulching (PM). A three-year experiment was conducted from 2014 to 2016 with two maize varieties (spring and summer) and two mulching conditions (PM and non-mulching (NM)), and the AquaCrop model was employed to reproduce crop growth and yield responses to changes in NM, PM, and compensated PM. A marked difference in soil temperature between NM and PM was observed before 50 days after sowing (DAS) during three growing seasons. During sowing–emergence and emergence–tasseling, the increase in air temperature was proportional to the compensatory coefficient, with spring maize showing a higher compensatory temperature than summer maize. Simulation results for canopy cover (CC) were generally in good agreement with the measurements, whereas predictions of aboveground biomass and grain yield under PM indicated large underestimates from 60 DAS to the end of maturity. Simulations of spring maize biomass and yield showed general increase based on temperature compensation, accompanied by improvement in modeling accuracy, with RMSEs decreasing from 2.5 to 1.6 t ha−1 and from 4.1 t to 3.4 t ha−1. Improvement in biomass and yield simulation was less pronounced for summer than for spring maize, implying that crops grown during low-temperature periods would benefit more from the compensatory effect. This study demonstrated the effectiveness of the temperature compensatory effect to improve the performance of the AquaCrop model in simulating maize growth under PM practices.

Topography and canopy cover influence soil organic carbon composition and distribution across a forested hillslope in the discontinuous permafrost zone

AbstractTopography and canopy cover influence ground temperature in warming permafrost landscapes, yet soil temperature heterogeneity introduced by mesotopographic slope positions, microtopographic differences in vegetation cover, and the subsequent impact of contrasting temperature conditions on soil organic carbon (SOC) dynamics are understudied. Buffering of permafrost‐affected soils against warming air temperatures in boreal forests can reflect surface soil characteristics (e.g., thickness of organic material) as well as the degree and type of canopy cover (e.g., open cover vs. closed cover). Both landscape and soil properties interact to determine meso‐ and microscale heterogeneity of ground warming. We sampled a hillslope catena transect in a discontinuous permafrost zone near Fairbanks, Alaska, to test the small‐scale (1 to 3 m) impacts of slope position and cover type on soil organic matter composition. Mineral active layer samples were collected from backslope, low backslope, and footslope positions at depths spanning 19 to 60 cm. We examined soil mineralogical composition, soil moisture, total carbon and nitrogen content, and organic mat thickness in conjunction with an assessment of SOC composition using Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). Soils in the footslope position had a higher relative contribution of lignin‐like compounds, whereas backslope soils had more aliphatic and condensed aromatic compounds as determined using FT‐ICR‐MS. The effect of open versus closed tree canopy cover varied with the slope position. On the backslope, we found higher oxidation of molecules under open cover than closed cover, indicating an effect of warmer soil temperature on decomposition. Little to no effect of the canopy was observed in soils at the footslope position, which we attributed, in part, to the strong impact of soil moisture content in SOC dynamics in the water‐gathering footslope position. The thin organic mat under open cover on the backslope position may have contributed to differences in soil temperature and thus SOC oxidation under open and closed canopies. Here, the thinner organic mat did not appear to buffer the underlying soil against warm season air temperatures and thus increased SOC decomposition as indicated by the higher oxidation of SOC molecules and a lower contribution of simple molecules under open cover than the closed canopy sites. Our findings suggest that the role of canopy cover in SOC dynamics varies as a function of landscape position and soil properties, namely, organic mat thickness and soil moisture. Condition‐specific heterogeneity of SOC composition under open and closed canopy cover highlights the protective effect of canopy cover for soils on backslope positions.

Measurements and statistical analysis of CO2 efflux and related parameters from crop and forested lands

The LULUCF sector (land use, land use change and forestry) can act as a carbon dioxide (CO2) sink, either by increasing the removal of greenhouse gasses from the atmosphere or by reducing their current emissions. This paper intends to analyze the results of the CO2 monitoring methodology by the chamber method in order to estimate the effect of different land use cover and management techniques. For this purpose, seasonal CO2 efflux field measurements were conducted in two types of ecosystems (forested land and wheat crop) located in the adjacent area of Bucharest. CO2 efflux was analysed for each land cover in relation to the physical characteristics of the soil, respectively soil temperatures and humidity, but also together with the main weather parameters. The measurements were performed simultaneously in both land covers at relevant time intervals. The difference in measured values between the two ecosystems was recorded but the results of the statistical analysis showed a lack of differences in the correlation between the CO2 efflux. This indicates that the CO2 efflux can be affected by particular elements of the environment which facilitates differences in soil temperature and humidity in the same weather conditions.

Spatiotemporal variation in soil methane uptake in a cool-temperate immature deciduous forest

Atmospheric methane (CH4) concentration has been increasing recently, contributing to global warming. As natural sinks, forest soils are expected to mitigate the atmospheric CH4 rise. However, it had been difficult to measure soil CH4 flux continuously and accurately because of the limited stability and precision of CH4 analyzers in the field. In this study, we measured hourly CH4 flux with plant roots (Root) and without roots (Trench) during the growing season in a regenerating deciduous forest using an automated chamber system with an up-to-date analyzer. Combined with a Random Forest (RF) approach, we studied the spatiotemporal variation and control of soil CH4 uptake rates. The results showed that the soil was a CH4 sink throughout the experimental period, and the existence of roots significantly enhanced CH4 uptake, mainly through improving soil aeration. The CH4 uptake rate varied seasonally according to the variations in soil gaseous diffusion caused by soil moisture and temperature differences. In addition, soil CH4 uptake showed a significant spatial variation, mainly resulting from spatial difference in soil porosity, soil carbon and nitrogen contents, and fine root biomass. The RF models showed high performance in soil CH4 flux prediction using the soil O2 diffusion coefficient and soil temperature as explanatory variables. The performance of RF models using ordinary variables of soil water content or water-filled pore space (WFPS) was equal to or slightly better than that of models using the diffusion coefficient. The higher importance of ambient CH4 concentration in Trench chambers indicates an increase in soil CH4 uptake at higher CH4 concentrations, which is predicted in the future. Although there are limitations, we believe that a machine learning approach, such as RF, using a large amount of continuous data with high temporal resolution, has great potential for investigating the dynamic variation in soil CH4 flux.

Environmental effects of a management method used after fire on development of temperate Scots pine ecosystem: a 15-year study from Poland

Due to the ongoing climate changes, temperate forests are increasingly exposed to fires. However, until now the functioning of post-fire temperate forest ecosystems with regard to used forest management method has been weakly recognized. Here, we examined three variants of forest restoration after fire (two variants of natural regeneration with no soil preparation—NR, and artificial restoration by planting following soil preparation—AR) regarding their environmental consequences in development of post-fire Scots pine (Pinus sylvestris) ecosystem. The study was conducted using a 15-year timespan in a long-term research site located in the Cierpiszewo area (N Poland) being one of the biggest post-fire grounds in European temperate forests in last decades. We focused on soil and microclimatic variables as well as on growth dynamics of post-fire pines generation. We found that the restoration rates of soil organic matter, carbon and most studied nutritional elements stocks were higher in NR plots than in AR. This could be primarily linked to the higher (p < 0.05) density of pines in naturally regenerated plots, and the subsequent faster organic horizon reconstruction after fire. The difference in tree density also involved regular differences in air and soil temperature among plots: consistently higher in AR than in both NR plots. In turn, lower water uptake by trees in AR implied that soil moisture was constantly the highest in this plot. Our study delivers strong arguments to pay more attention to restore post-fire forest areas with the use of natural regeneration with no soil preparation.

Alley cropping tree lines alter temperature and light quantity and influence daily growth rates of grassland

AbstractTrees alter microclimate and radiation budget in alley cropping systems, which in turn change physiological processes of the grassland component. The influence of the trees on grassland growth depends on the climate zone as well as possibly on weather conditions during the respective growth interval. The proportion of shade‐tolerant species in the grassland further modifies the tree effect on grassland growth, as well as the number of annual harvests. We studied the effect of distance and orientation relative to the tree line (tree line in the South‐West vs. North‐East) on growth rates of the adjacent grassland with two cutting frequencies (frequent vs. infrequent) in an alley cropping system with grassland of two different vegetation compositions (diverse vs. grass‐clover) and willow clones. Microclimate parameters and radiation were measured at the points where growth rates were determined to better characterize the effect of position relative to the tree line. Growth rates differed significantly (p &lt; 0.05) depending on the distance to the trees and annual biomass accumulation amounted to 389 ± 13.5 g m−2 in the center vs. 321 ± 10.0 g m−2 with trees in the North‐East vs. 292 ± 9.2 g m−2 with trees in the South‐West of the transect position. Lower growth rates occurred at positions with lower light quantities close to the trees, namely the position with the trees adjacent in the South‐West. Temperature and relative humidity differences between the distances were significantly (p &lt; 0.05) affected by distance to the tree line, but differences in neither soil nor air temperatures between the distances affected growth rates. Vegetation composition mediates the influence of the trees: the difference between positions was more pronounced in the diverse vegetation composition with higher productivities in the center between the alleys, but also with higher overall sward productivity.

Drivers of soil temperature variation in alpine lichen heaths and shrub vegetation during the summer

ABSTRACT Lichen heaths are decreasing in abundance in alpine and Arctic areas because of an increased competition with shrubs. This shift in vegetation might have important consequences for the soil temperature. The aim of this study is to find the drivers of the variation in soil temperature below lichen heaths and shrubs. Moreover, we want to gain more insight in the variability of the soil temperature below lichen heaths. We measured the soil temperature in thirty lichen plots and fifteen shrub plots in an alpine area in southern Norway during July and August 2019. We applied several treatments to study the drivers behind the variation in soil temperature between lichen heaths and shrub vegetation. We found that the average soil temperature was 1.45°C higher below lichen heaths than below shrub vegetation. Moreover, we measured a difference in soil temperature of 1.66°C between north- and south-facing lichen heaths, which contributes to the small-scale spatial variability in soil temperature below lichen heaths. Based on our experiments, we conclude that the buffering capacity of the litter layer below shrubs and shading of the soil by the shrub canopy lead to a lower soil temperature below shrubs compared to lichen heaths during the summer.

On the correlation between thermal imagery and fugitive CH4 emissions from MSW landfills

Landfill gas (LFG) is related to the biochemical processes generating heat and releasing CH4, CO2, and other gases in lower concentrations, which result in environmental impacts and risk of local explosion. Thermal infrared imagery (TIR) is employed to detect CH4 leakage as a risk control approach. However, the challenge for LFG leakage detection using TIR is establishing a relation between the gas flux and the ground temperature. This study evaluates the problem of a heated gas flowing through a porous medium column where the upward surface exchanges heat by radiation and convection to the environment. A heat transfer model that considers the upward LFG flow is proposed, and a sensibility analysis is developed to relate the flux to the ground temperature level in the condition of non-income solar radiation. An explicit equation to predict CH4 fugitive flow as a function of temperature anomalies of the ground was presented for the first time. The results show that the predicted ground surface temperatures are consistent with the literature’s experimental observations. Moreover, the model was complementarily applied to a Brazilian landfill, with in situ TIR measurements in an area with a slightly fractured cover. In this field observation, the predicted CH4 flux was around 9025 g m−2 d−1. Model limitations concerning the soil homogeneity, the transient variation of atmospheric conditions or local pressure, and soil temperature difference in low-flux conditions (related to TIR-cameras accuracy) require further validation. Results could help landfill monitoring in conditions of a high-temperature ground anomaly in dry seasons.

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

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

No-tillage with straw mulching promotes wheat production via regulating soil drying-wetting status and reducing soil-air temperature variation at arid regions

Straw returning is a technical measure of crop production widely adopted in arid and water-deficient areas. However, the mechanism by which straw returning drives spatio-temporal changes in soil moisture and temperature to improve crop productivity remains unclear. So, a three-year field experiment was conducted with four various straw returning treatments for wheat production: 1) no-tillage with straw mulching (NTSM), 2) no-tillage with straw standing (NTSS), 3) conventional tillage with straw incorporation (CTS), and 4) conventional tillage without straw returning (CT, control). The spatio-temporal variations of soil moisture content and soil temperature were assessed. It will provide the basis for selecting the appropriate way of straw returning to increase wheat yield and clarifying its hydrothermal regulation mechanism. NTSM and NTSS were effective in maintaining soil moisture and regulating soil temperature, and had a greater effect on grain increase, than CTS and CT. Meanwhile, NTSM had a relatively higher yield than NTSS through better regulation of soil hydrothermal characteristics. NTSM had higher soil moisture content in the 0–120 cm depth by 9.8–10.2%, 6.7–8.2%, 6.5–10.2%, and 6.9–7.4% at sowing to jointing, jointing to booting, booting to early-filling, and early-filling to maturing stages of wheat, respectively. NTSM decreased evapotranspiration modulus coefficient (ETMC) and evapotranspiration intensity (ETI) at jointing to early-filling stage of wheat, but increased both indexes from early-filing to maturing stage of wheat, which is helpful to adjust the contradiction of soil moisture demand for wheat in different growth stages. Additionally, NTSM had 9.8–10.2%, 6.7–8.2%, 6.5–10.2%, and 6.9–7.4% lower soil temperature in the 5–25 cm depth than CT, at the four aforementioned wheat growth stages, respectively. The difference of soil temperature was mainly reflected at the 5–15 cm depth by analyzing the difference on soil temperature in various soil depths. The treatment on NTSM had little variation and stabilized soil temperature, according to the difference between air and average soil temperature of 5–15 cm depth. NTSM allowed wheat to grow a suitable thermal environment across their growth period, which is a significant regulatory mechanism for wheat to maintain better growth and development. Thereby, NTSM boosted wheat grain yield by 18.6–27.3% as compared to CT. Collectively, the NTSM treatment had better effect on regulating soil drying-wetting status and reducing soil-air temperature variation, which could be used as a recommended measure to improve wheat productivity at arid conditions.

Response of soil bacterial communities in wheat rhizosphere to straw mulching and N fertilization.

Straw mulching and N fertilization are effective in augmenting crop yields. Since their combined effects on wheat rhizosphere bacterial communities remain largely unknown, our aim was to assess how the bacterial communities respond to these agricultural measures. We studied wheat rhizosphere microbiomes in a split-plot design experiment with maize straw mulching (0 and 8,000 kg straw ha-1) as the main-plot treatment and N fertilization (0, 120 and 180 kg N ha-1) as the sub-plot treatment. Bacterial communities in the rhizosphere were analyzed using 16S rRNA gene amplicon sequencing and quantitative PCR. Most of the differences in soil physicochemical properties and rhizosphere bacterial communities were detected between the straw mulching (SM) and no straw mulching (NSM) treatments. The contents of soil organic C (SOC), total N (TN), NH4 +-N, available N (AN), available P (AP) and available K (AK) were higher with than without mulching. Straw mulching led to greater abundance, diversity and richness of the rhizosphere bacterial communities. The differences in bacterial community composition were related to differences in soil temperature and SOC, AP and AK contents. Straw mulching altered the soil physiochemical properties, leading to greater bacterial diversity and richness of the rhizosphere bacterial communities, likely mostly due to the increase in SOC content that provided an effective C source for the bacteria. The relative abundance of Proteobacteria was high in all treatments and most of the differentially abundant OTUs were proteobacterial. Multiple OTUs assigned to Acidobacteria, Chloroflexi and Actinobacteria were enriched in the SM treatment. Putative plant growth promoters were enriched both in the SM and NSM treatments. These findings indicate potential strategies for the agricultural management of soil microbiomes.

Quantification and machine learning based N2O–N and CO2–C emissions predictions from a decomposing rye cover crop

AbstractCover crops improve soil health and reduce the risk of soil erosion. However, their impact on the carbon dioxide equivalence (CO2e) is unknown. Therefore, the objective of this 2‐yr study was to quantify the effect of cover crop‐induced differences in soil moisture, temperature, organic C, and microorganisms on CO2e, and to develop machine learning algorithms that predict daily N2O–N and CO2–C emissions. The prediction models tested were multiple linear regression, partial least square regression, support vector machine, random forest (RF), and artificial neural network. Models’ performance was accessed using R2, RMSE and mean of absolute value of error. Rye (Secale cereale L.) was dormant seeded in mid‐October, and in the following spring it was terminated at corn's (Zea mays L.) V4 growth stage. Soil temperature, moisture, and N2O–N and CO2–C emissions were measured near continuously from soil thaw to harvest in 2019 and 2020. Prior to termination, the cover crop decreased N2O–N emissions by 34% (p = .05), and over the entire season, N2O–N emissions from cover crop and no cover crop treatments were similar (p = .71). Based on N2O–N and CO2–C emissions over the entire season and the estimated fixed cover crop‐C remaining in the soil, the partial CO2e were −1,061 and 496 kg CO2e ha–1 in the cover crop and no cover crop treatments, respectively. The RF algorithm explained more of the daily N2O–N (73%) and CO2–C (85%) emissions variability during validation than the other models. Across models, the most important variables were temperature and the amount of cover crop‐C added to the soil.