Soil Temperature Dynamics Research Articles

Soil moisture and temperature dynamics in typical alpine ecosystems: a continuous multi-depth measurements-based analysis from the Qinghai-Tibet Plateau, China

Abstract Soil temperature and moisture are the key variables that control the overall effect of climate and topography on soil and vegetation in alpine regions. However, there has been little investigation of the potential soil temperature and moisture feedbacks on climate changes in different alpine ecosystems and their impact on vegetation change. Soil temperature and moisture at five depths were measured continuously at 10-min intervals in three typical ecosystems (Kobresia meadow (KMd), Achnatherum splendens steppe (ASSt), and Potentilla fruticosa shrub (PFSh)) of the Qinghai Lake watershed on the northeast Qinghai-Tibet Plateau, China. The findings of this study revealed that the KMd and PFSh sites had relatively low soil temperature and high soil moisture, whereas the ASSt site had relatively warm soil temperature and low soil moisture. The soil and vegetation characteristics had important effects on the infiltration process and soil moisture regime; about 47%, 87%, and 34% of the rainfall (minus interception) permeated to the soil in the KMd, PFSh, and ASSt sites, respectively. In the context of the warming climate, changes to soil moisture and temperature are likely to be the key reasons of the alpine meadow deterioration and the alpine shrub expansion in the alpine regions.

Applicability of the ecosystem type approach to model permafrost dynamics across the Alaska North Slope

AbstractThawing and freezing of Arctic soils is affected by many factors, with air temperature, vegetation, snow accumulation, and soil physical properties and soil moisture among the most important. We enhance the Geophysical Institute Permafrost Laboratory model and develop several high spatial resolution scenarios of changes in permafrost characteristics in the Alaskan Arctic in response to observed and projected climate change. The ground thermal properties of surface vegetation and soil column are upscaled using the Ecosystems of Northern Alaska map and temperature data assimilation from the shallow boreholes across the Alaska North Slope. Soil temperature dynamics are simulated by solving the 1‐D nonlinear heat equation with phase change, while the snow temperature and thickness are simulated by considering the snow accumulation, compaction, and melting processes. The model is verified by comparing with available active layer thickness at the Circumpolar Active Layer Monitoring sites, permafrost temperature, and snow depth records from existing permafrost observatories in the North Slope region.

Nitrogen leaching following clear-cutting and soil scarification at a Scots pine site – A modelling study of a fertilization experiment

Boreal forest stands fertilized with nitrogen (N) might be susceptible to elevated N leaching following clear-cutting, with consequences for water quality and soil acidification. Here, we studied a forest fertilization experiment with N, 165 Hagfors, in Sweden during the first six years (2006–2011) following clear-cutting. The N fertilization treatments were 0kgha−1 (0N) and 450kgha−1 of N (450N), supplied during 1981–1992 to a Scots pine (Pinus sylvestris L.) stand: the stand was harvested in March 2006. Following clear-cutting, disc trenching was performed and furrows (F), ridges (R) and areas in-between two furrows (IB) were created. We calculated the N leaching fluxes and ecosystem N budget during 2006–2011 as affected by previous N fertilization, disc trenching and interactions thereof, at Hagfors by the use of a process-based biogeophysical ecosystem model (CoupModel). The model was calibrated against measurements of soil water and temperature dynamics and previously reported measurements of N in soil solution, soil organic matter and vegetation biomass. Criteria for acceptance of model estimates were based on the range enclosed by the 95% confidence intervals of the mean of the field data used in calibration sampled at low frequency (1–2 occasions) and a combination of the mean error and the coefficient of the determination for variables sampled at a higher frequency (28–1921 occasions). The accepted model estimates of the mean annual leaching rates of N were 3.1 (range 1.4–22.7) and 2.4 (range 0.8–7.0) kgha−1 of Nyear−1 in the treatments 0N and 450N, respectively, without disc trenching. Disc trenching increased N leaching during the regeneration phase, more so in the 450N treatment (mean 6.1, range 1.9–16.7kgha−1 of Nyear−1) than in the 0N treatment (mean 4.6, range 1.9–12.9kgha−1 of N year−1). Overall, differences in the posterior model parameter estimates between N treatments and disc trenched treatments F, R and IB were related to the soil physical component: the differences resulted in enhanced drainage in the disc trenched treatments. We conclude that vegetation biomass N accumulation controlled soil water N leaching, and disc trenching increased N leaching from the previously N fertilized plots at Hagfors by its effects on water drainage flow and vegetation N uptake. This finding warrants more research since N fertilization followed by soil scarification in boreal forests is a practice which may increase in the future.

Spatio-temporal variation analysis of soil temperature based on wireless sensor network

Abstract: Soil temperature is a key factor for best planting dates decision-making in the large scale farming areas of northeast China because of high latitudes and frigid environment. Continuous data were collected from a wireless sensor network (WSN)-based monitoring system to exactly analyze and understand soil temperature of the whole farmland. Using the classical statistics and geo-statistics methods, real-time monitoring data were analyzed with three aspects, i.e. temporal variation, spatial variation and spatio-temporal variation. Temporal variation analysis of each sensor node showed a sinusoidal curve of daily soil temperature and gave the long-term trend of daily average soil temperature in a certain period. Spatial variation analysis provided the spatial distribution map of daily average soil temperature within a study region for a certain day. Spatio-temporal variation analysis quantified the variation process of the spatial distribution over time by the monitored classes distribution indicator (MCDI) proposed. Experimental results showed that the above variations analysis of the real-time data provide an effective approach to determine whole-farmland soil temperature. Keywords: precision agriculture, soil temperature dynamics, spatial-temporal variability, spatial variation, wireless sensor network (WSN) DOI: 10.3965/j.ijabe.20160906.1871 Citation: Liu H, Meng Z J, Wang H, Xu M. Spatio-temporal variation analysis of soil temperature based on wireless sensor network. Int J Agric & Biol Eng, 2016; 9(6): 131－138.

Evaluation of the effects of mulch on optimum sowing date and irrigation management of zero till wheat in central Punjab, India using APSIM

Machinery for sowing wheat directly into rice residues has become more common in the rice-wheat systems of the north-west Indo-Gangetic Plains of South Asia, with increasing numbers of farmers now potentially able to access the benefits of residue retention. However, surface residue retention affects soil water and temperature dynamics, thus the optimum sowing date and irrigation management for a mulched crop may vary from those of a traditional non-mulched crop. Furthermore, the effects of sowing date and irrigation management are likely to vary with soil type and seasonal conditions. Therefore, a simulation study was conducted using the APSIM model and 40 years of weather data to evaluate the effects of mulch, sowing date and irrigation management and their interactions on wheat grain yield, irrigation requirement (I) and water productivity with respect to irrigation (WPI) and evapotranspiration (WPET). The results suggest that the optimum wheat sowing date in central Punjab depends on both soil type and the presence or absence of mulch. On the sandy loam, with irrigation scheduled at 50% soil water deficit (SWD), the optimum sowing date was late October to early November for maximising yield, WPI and WPET. On the clay loam, the optimum date was about one week later. The effect of mulch on yield varied with seasonal conditions and sowing date. With irrigation at 50% SWD, mulching of wheat sown at the optimum time increased average yield by up to 0.5tha−1. The beneficial effect of mulch on yield increased to averages of 1.2–1.3tha−1 as sowing was advanced to 15 October. With irrigation at 50% SWD and 7 November sowing, mulch reduced the number of irrigations by one in almost 50% of years, a reduction of about 50mm on the sandy loam and 60mm on the clay loam. The reduction in irrigation amount was mainly due to reduced soil evaporation. Mulch reduced irrigation requirement by more as sowing was delayed, more so on the sandy loam than the clay loam soil. There was little effect of mulch on irrigation requirement for late October sowings.There were large trade-offs between irrigation input, yield, WPET and WPI on the sandy loam with regard to the optimum irrigation schedule. Maximum yield occurred with very frequent irrigation (10–20% SWD) which also had the greatest irrigation input, while WPI was highest with least frequent irrigation (70% SWD), and WPET was highest with irrigation at 40–50% SWD. This was the case with and without mulch. On the clay loam, the trade-offs were not so pronounced, as maximum yield was reached with irrigation at 50% SWD, with and without mulch. However, both WPET and WPI were maximum and irrigation input least at the lowest irrigation frequency (70% SWD). On both soils, maximum yield, WPET and WPI were higher with mulch, while irrigation input was slightly lower, but mulch had very little effect on the irrigation thresholds at which each parameter was maximised.

Development and preliminary evaluation of an integrated field scale model for perennial bioenergy grass ecosystems in lowland areas

Computer models are useful tools for evaluating environmental and economic sustainability of proposed dedicated cellulosic grass ecosystems for biofuel production. This study developed an integrated, field scale, and process-based ecosystem model (DRAINMOD-GRASS) for simulating hydrological processes, soil carbon and nitrogen cycling, and plant growth in cropping systems for producing bioenergy grasses in lowland areas. We tested the model using measurements from three replicated switchgrass (Panicum virgatum) plots located in eastern North Carolina, USA. Results showed that the model accurately predicted 5-year (2009–2013) biomass yield. Predicted daily water table depth closely matched field measurements with Nash-Sutcliffe coefficient of 0.86. The model also accurately predicted temporal dynamics of daily soil moisture and temperature with Nash-Sutcliffe coefficients of 0.7 and 0.9, respectively. Predicted seasonal changes in net N mineralization and nitrification rates were comparable to field measurements in 2011 and 2012.

Plastic mulch and nitrogen fertigation in growing vegetables modify soil temperature, water and nitrate dynamics: Experimental results and a modeling study

Plastic mulch in combination with drip irrigation present a common agricultural management technique practiced in commercial vegetable production. This management can result in various impacts on water and nutrient distribution and consequently affect nutrient dynamics in underlying soil. The aim of this work was to: (i) compare the effects of different mulching types (color) on soil temperature and (ii) crop growth; (iii) estimate the effect of plastic mulch cover (MULCH) on water and (iv) nitrate dynamics using HYDRUS-2D. The field experiment was designed in the Croatian coastal karst area on main plots with three levels of nitrogen fertilizer: 70, 140, and 210kgha−1, which were all divided in five subplots considering mulch covering with different colors types (black, brown, silver, and white) and no covering (control). Monitoring of water and nitrate dynamics was performed through lysimeters which ensured input data for HYDRUS-2D model. The experimental results showed that plastic mulch had a significant effect on soil temperature regime and crop yield. The dark color mulch (black, brown) caused higher soil temperature, which consequently enabled earlier plant development and higher yields. HYDRUS-2D simulated results showed good fitting to the field data in cumulative water and also nitrate outflow. Water flow simulations produced model efficiency of 0.84 for control (CONT) and 0.56 for MULCH systems, while nitrate simulations showed model efficiency ranging from 0.67 to 0.83 and from 0.70 to 0.93, respectively. Additional simulations exposed faster transport of nitrates below drip line in the CONT system, mostly because of the increased surface area subjected to precipitation/irrigation due to the absence of soil cover. Numerical modeling revealed large influence of plastic mulch cover on water and nutrient distribution in soil. The study suggests that under this management practice the nitrogen amounts applied via fertigation can be lowered and optimized to reduce possible negative influence on environment.

Soil temperature dynamics at the catchment scale

Temperature has a large impact on soil biogeochemical functioning. While this is well recognised there is a lack of data on the variability of soil temperature at the hillslope and catchment scale. Here we examine soil temperature for a series of nested catchments in the east of New South Wales, Australia over a twelve year period. Temperature characteristics between the three catchments were shown to be quite similar, falling into a 1°C band. Across each catchment, the larger catchments of Krui (590km2) and Merriwa (808km2) had a larger varibaility in temperature range (3.4oC and 4.9°C repectively) compared to the much smaller Stanley (175ha) sub-catchment (1.8°C), indicating that larger catchments will generally have larger variability in soil temperatures. The larger catchments also had a lapse rate of approximately 1°C per 100m elevation. Seasonal trends in soil temperature variability were observed to be quite similar between the two larger catchments, with soil temperature exhibiting greater variability for both catchments within the warmer months of the year. The similarity in soil temperature trends between Krui and Merriwa over the year is attributed to their similar size, climate, soils, and north–south orientation. All three catchments had a narrower range of temperatures during the cooler months, when Krui and Merriwa have a similar range to the soil temperatures of Stanley. The variability in soil temperature across the Stanley catchment is relatively stable throughout the year. This was attributed to its smaller size. In terms of quantifying catchment scale soil temperature from a single point, weather station sites that were located closer to the geographic centre of the catchment were shown to be less likely to over or under-estimate the average soil temperature of the catchment. The use of point-scale air temperature as a surrogate for predicting catchment soil temperature was suitable when corrections were applied. The importance of soil temperature to many ecological processes, in particular vegetation growth and soil biological activity, and therefore the soil carbon cycle and soil carbon sequestration, highlights the significance of this research.

Development and evaluation of new modelling solutions to simulate hazelnut (Corylus avellana L.) growth and development

The worldwide increase in the hazelnut demand and cultivated area are explained by the rising importance of this species for the food industry. However, no simulation models are available to support the analysis of the impact of environmental conditions and management practices on hazelnut production. This paper presents two modelling solutions to simulate hazelnut tree growth and development under potential and water-limiting conditions, partly based on generic approaches used in tree modelling and on new modules specifically developed to address hazelnut tree peculiarities. The two solutions differed in the simulation of the photosynthetic rate, in one case reproduced using a Farquhar-type model (gross photosynthesis), whereas a radiation use efficiency approach (net photosynthesis) was used in the other. The coherence of simulation outputs at leaf, organ and plant level and the models responsiveness to weather conditions was verified and discussed with literature data, and the performances of the modelling solutions were evaluated using experimental data collected between 2002 and 2013 growing seasons in Piedmont region (northern Italy). Results highlighted the reliability of both the solutions in reproducing phenological development (mean relative root mean squared error, RRMSE=8.61%), as well as the time trend of specific leaf area (RRMSE=26.32%) and leaf area index (RRMSE=18.46%). Also, the simulation of the temporal dynamics of soil water content and temperature along the soil profile led to outputs very close to observations (RRMSE=14.02% and 10.32%, respectively). The solution based on gross photosynthesis resulted slightly more accurate in reproducing the year-to-year fluctuation in yields (RRMSE=25.03%) compared to the one based on net photosynthesis (RRMSE=30.40%). These results proved the suitability of these modelling solutions to be used as simulation engines within a variety of applications, ranging from decision support systems for the management of the orchard to complex yield forecasting systems.

Local‐ and landscape‐scale impacts of clear‐cuts and climate change on surface water dissolved organic carbon in boreal forests

AbstractForest harvesting and climate change may significantly increase concentrations and fluxes of dissolved organic carbon (DOC) in boreal surface waters. However, the likely magnitude of any effect will vary depending on the landscape‐element type and spatial scale. We used a chain of hydrological, empirical, and process‐based biogeochemical models coupled to an ensemble of downscaled Regional Climate Model experiments to develop scenario storylines for local‐ and landscape‐scale effects of forest harvesting and climate change on surface water DOC concentrations and fluxes. Local‐scale runoff, soil temperature, and DOC dynamics were simulated for a range of forest and wetland landscape‐element types and at the larger landscape scale. The results indicated that climate change will likely lead to greater winter flows and earlier, smaller spring peaks. Both forest harvesting and climate change scenarios resulted in large increases in summer and autumn runoff and higher DOC fluxes. Forest harvesting effects were clearly apparent at local scales. While at the landscape scale, approximately 1 mg L−1 (or 10%) of the DOC in surface waters can be attributed to clear‐cuts, both climate change and intensified forestry can each increase DOC concentrations by another 1 mg L−1 in the future, which is less than that seen in many waterbodies recovering from acidification. These effects of forestry and climate change on surface water DOC concentrations are additive at a landscape scale but not at the local scale, where a range of landscape‐element specific responses were observed.

Infiltration of meltwater from frozen saline water located on the soil can result in reclamation of a coastal saline soil

The saline soil was irrigated by the shallow groundwater of high salinity (12 g L−1) during the air temperature below −5 °C in winter, and the saline water was frozen into saline ice on the soil expeditiously. With air temperatures increasing in spring, the saline ice melted and infiltrated into soil gradually, and the saline soil may be improved by the infiltration of the meltwater. Based on this, a field experiment was conducted to evaluate changes in saline ice during melting, seasonal dynamics of soil temperature, water, salt and sodium adsorption ratios (SAR). After the meltwater infiltrated into soil in spring, the plastic mulching (FM) and non-mulching (FN) were designed, and the control treatment (CK) did not include irrigation or mulching. The results showed that the salinity of the saline ice was reduced upon melting, and the mulching of saline ice increased the soil temperature and reduced the frozen soil layers. After infiltration of meltwater, the soil salinity and SAR were both reduced significantly (p < 0.05), and the mulching of plastic film maintained the lower level of soil salinity and SAR. During the sowing season for cotton, the soil salinity and SAR were below 4 g kg−1 and 9, respectively, in FM. And higher than 65 % of emergence rates and greater than 3.4 t ha−1 seed cotton yields were obtained in this treatment, while for the FN and CK treatments, the soil salinities were both above 8 g kg−1, which leads to yields that were not obtained.

Temporal Monitoring of the Soil Freeze-Thaw Cycles over a Snow-Covered Surface by Using Air-Launched Ground-Penetrating Radar

We tested an off-ground ground-penetrating radar (GPR) system at a fixed location over a bare agricultural field to monitor the soil freeze-thaw cycles over a snow-covered surface. The GPR system consisted of a monostatic horn antenna combined with a vector network analyzer, providing an ultra-wideband stepped-frequency continuous-wave radar. An antenna calibration experiment was performed to filter antenna and back scattered effects from the raw GPR data. Near the GPR setup, sensors were installed in the soil to monitor the dynamics of soil temperature and dielectric permittivity at different depths. The soil permittivity was retrieved via inversion of time domain GPR data focused on the surface reflection. Significant effects of soil dynamics were observed in the time-lapse GPR, temperature and dielectric permittivity measurements. In particular, five freeze and thaw events were clearly detectable, indicating that the GPR signals respond to the contrast between the dielectric permittivity of frozen and thawed soil. The GPR-derived permittivity was in good agreement with sensor observations. Overall, the off-ground nature of the GPR system permits non-invasive time-lapse observation of the soil freeze-thaw dynamics without disturbing the structure of the snow cover. The proposed method shows promise for the real-time mapping and monitoring of the shallow frozen layer at the field scale.

A parametrization of a steady periodic solution of the Fourier equation to model soil temperature dynamics

AbstractIn dry days the temperature of the upper soil layers presents a characteristic asymmetric periodic‐like pattern with a minimum in the morning and a maximum in the afternoon. In view of estimating the conductive heat component of the surface energy balance, at local, basin, and global scales, in this study we use a periodic series solution of the Fourier equation to develop a simple procedure to accurately reconstruct the soil temperature and heat flux profiles. The method is based on weighting and phasing the Fourier harmonics by means of coefficients which do not depend on the soil thermal properties but only depend on the shape of the temperature boundary condition. The proposed coefficients can be regarded to as site independent and with good approximation universal. In order to calibrate and test the procedure, measurements of soil temperature, soil heat flux, and soil water content, collected during the CividatEX Experiment (summer 2012, summer 2013, and spring and summer 2014), in Italy, were used. The method accurately reproduced the temperature observations at three measurement depths within the upper 20 cm soil layer. Once assessed the soil thermal conductivity, the method proved to be effective also in reproducing the measured soil heat flux. The procedure was furthermore validated reconstructing with good results the soil temperature dynamics measured by an independent micrometeorological station in a different environment.

Coupling boreal forest CO2, H2O and energy flows by a vertically structured forest canopy – Soil model with separate bryophyte layer

A 1-dimensional multi-layer, multi-species soil-vegetation-atmosphere transfer model APES (Atmosphere-Plant Exchange Simulator) with a separate moss layer at the forest floor was developed and evaluated for a boreal Scots pine forest situated in Hyytiälä, Southern Finland. The APES is based on biophysical principles for up-scaling CO2, H2O, heat and momentum exchange from canopy element level to a stand scale. The functional descriptions of sub-models were parametrized by literature values, previous model approaches and leaf and moss gas exchange measurements, and stand structural characteristics derived from multi-scale measurements. The model was independently tested against eddy-covariance fluxes of CO2, H2O and sensible heat measured above and within the canopy, and against soil heat flux and temperature and moisture profiles. The model was shown to well reproduce fluxes and resulting scalar gradients at diurnal and seasonal timescales. Also predictions for moss moisture content and soil moisture and temperature dynamics were acceptable considering the heterogeneity in soil hydraulic and thermal properties and uncertainties in boundary conditions.The model framework allows for (1) coupling above-ground with the soil domains through the feedbacks between soil water and vegetation mediated by the moss layer, (2) several vascular plant species or cohorts in a multi-species canopy, and (3) explicit treatment of bryophyte layer energy and water balance and bottom layer – atmosphere exchange. These features make APES well-suited for exploring feedbacks between boreal forest structure, site conditions and vegetation processes controlling ecosystem-atmosphere exchange.

Maize (Zea mays L.) yield and soil properties as affected by no tillage in the black soils of China

A four-year tillage experiment on maize was conducted in the high latitude region of Northeast of China. The main objective of this study was to investigate the effects of different field tillage practices on maize grain yield, soil physical properties, and soil water and temperature dynamics in Northeast of China. The tillage practices included moldboard plow tillage (MOT), rotary tillage (ROT), reduced tillage (RET), combined tillage (COT), and no tillage (NOT). The surface soil water content at depths of 0–20 cm was higher under NOT compared with other tillage practices, but not different at the deeper soil depths in 2011. The soil temperatures under NOT and RET were lower than those under moldboard plow tillage and ROT at depths of 5 and 15 cm, respectively, measured at 9:00 am in 2005. From the hourly dynamics of soil temperature, the differences among the tillage practices mainly appeared during the daytime (from 8:00 am to 7:00 pm). Among all the practices, the average daily soil temperature under ROT was the highest, while that under NOT was the lowest. MOT, ROT, and RET had higher soil accumulative infiltration compared with NOT and COT. The surface soil bulk density under NOT was higher than or equal to that under the other four tillage practices. The maize yields under NOT were the lowest among all the tillage practices for three years straight. Meanwhile, the yields under MOT were the highest, which were about 47%, 61%, and 38% higher than those under NOT. NOT practice is not recommended for use in spring-planted maize under the high latitude humid cool climate Mollisol region in Northeast of China.

Evaluating the Influence of Plant-Specific Physiological Parameterizations on the Partitioning of Land Surface Energy Fluxes

Abstract Plant physiological properties have a significant influence on the partitioning of radiative forcing, the spatial and temporal variability of soil water and soil temperature dynamics, and the rate of carbon fixation. Because of the direct impact on latent heat fluxes, these properties may also influence weather-generating processes, such as the evolution of the atmospheric boundary layer (ABL). In this work, crop-specific physiological characteristics, retrieved from detailed field measurements, are included in the biophysical parameterization of the Terrestrial Systems Modeling Platform (TerrSysMP). The physiological parameters for two typical European midlatitudinal crops (sugar beet and winter wheat) are validated using eddy covariance fluxes over multiple years from three measurement sites located in the North Rhine–Westphalia region of Germany. Comparison with observations and a simulation utilizing the generic crop type shows clear improvements when using the crop-specific physiological characteristics of the plant. In particular, the increase of latent heat fluxes in conjunction with decreased sensible heat fluxes as simulated by the two crops leads to an improved quantification of the diurnal energy partitioning. An independent analysis carried out using estimates of gross primary production reveals that the better agreement between observed and simulated latent heat adopting the plant-specific physiological properties largely stems from an improved simulation of the photosynthesis process. Finally, to evaluate the effects of the crop-specific parameterizations on the ABL dynamics, a series of semi-idealized land–atmosphere coupled simulations is performed by hypothesizing three cropland configurations. These numerical experiments reveal different heat and moisture budgets of the ABL using the crop-specific physiological properties, which clearly impacts the evolution of the boundary layer.

Soil freezing and thawing processes affected by the different landscapes in the middle reaches of Heihe River Basin, Gansu, China

Summary An understanding of soil freezing and thawing processes in seasonally frozen soil is important for many agricultural and environmental issues, especially under different landscapes in terms of land use and climate change. In this study, sandy soil behavior under soil freezing and thawing cycles were investigated under three typical landscapes (i.e., farmland, forest, and desert) in the middle reaches of the Heihe River Basin, Northwest China, from December 2011 to May 2012. Both Neutron Moisture Meter and Time Domain Reflectometry techniques were used to investigate the total soil water content (TSWC) and liquid soil water content (LSWC), respectively, and further based on to calculate soil ice content (SIC) and ice ratio (IR). The partition TSWC into LSWC and SIC at different depths is shown to be corresponded well with soil temperature, frost depth and groundwater dynamics, provided a vigorous basis for augmenting the limited data on soil water redistribution in seasonally frozen soils under natural conditions of different landscapes. The greatest freezing cycles were observed for the farmland, characterized with the deepest frost depths (106 cm), the highest IR (>0.9), and the largest upward heat fluxes (120 W m−2), followed by the forest, and then the desert. These differences were primarily attributed to landscape-dependent initial soil water content, soil surface cover and groundwater levels, with marginal effect being attributed to soil physical properties. Profiled water redistribution upon soil freezing and thawing was obviously observed in the moist forest, but neither in the wettest farmland or in the driest desert. The soil frozen processes had a beneficial effect on soil water conservation with reduced evaporation and seepage, and high water content maintained, which could be useful for plant germination in the following spring.

Growth, grain yield, and water use efficiency of rain-fed spring hybrid millet (Setaria italica) in plastic-mulched and unmulched fields

In order to analyze the effect of plastic mulching on water use efficiency of spring hybrid millet (Setaria italica), field experiments were conducted during the 2012 growing season, at an experimental station located in a semi-arid region of North China. Four treatments were applied: (i) plastic mulching of ridges and furrow sowing (T1), (ii) ridges and furrows without plastic mulch (T0), (iii) flat soil with plastic mulch (A1), and (iv) flat soil with no plastic mulch (A0) (control). Dynamics of soil moisture and soil temperature, together with crop growth, were monitored continuously in both mulched and unmulched fields. Changes in water consumption, soil temperature, and plant growth and development were analyzed. Results indicated that plastic mulching produced a 2–5-day advance in emergence of each growth stage. Soil temperature at 0–15cm depth increased by 1.25°C and 0.84°C under mulched treatments A1 and T1, respectively, while soil water content at a depth of 0–10cm increased by 1.42% and 1.29% in the same treatments. Leaf area index and plant height were also significantly higher in plastic-mulched treatments, except in later growth stages. Because plastic mulching improved tiller and ear numbers significantly, grain yield increased by 13.25% and 6.64%, in Al and T1 treatments, respectively. Water use efficiency at yield levels of plastic-mulched A1 and T1 plots was 24.44% and 3.6% higher than in unmulched flat and furrowed plots, respectively. Plastic mulching significantly reduced water consumption, retained soil water content, and increased soil temperature, to promote spring hybrid millet germination, and increased tiller numbers, and consequently, aboveground dry matter; it eventually significantly improved grain yield and water use efficiency. Plastic film mulching produced greater grain yield, water use efficiency, and benefits when used in flat planting patterns.

Long-term soil temperature dynamics in the Sierra Nevada, Spain

Soil temperatures play a key role on the dynamics of geomorphological processes in periglacial environments. However, little is known about soil thermal dynamics in periglacial environments of semiarid mid-latitude mountains, where seasonal frost is dominant.From September 2006 to August 2012 we have monitored soil temperatures at different depths (2, 10, 20, 50 and 100cm) in a solifluction landform located at 3005m.a.s.l. in the summit area of the Sierra Nevada (South Spain). Mean annual temperatures in the first meter of the soil ranged from 3.6 to 3.9°C while the mean annual air temperature at the nearby Veleta peak was 0.08°C. Therefore, these data point out the inexistence of widespread permafrost conditions today in this massif. Seasonal frost controls the geomorphodynamics even in the highest lands. Climate conditions have shown a large interannual variability, as it is characteristic in a high mountainous Mediterranean environment. These variations are reflected in the patterns of soil thermal dynamics. The depth and duration of the frozen layer are strongly conditioned by the thickness of the snow cover. The date of the first significant snowfalls conditioned the beginning and rhythm of freezing of the soil. Wet years resulted in a thick snow cover which insulated the ground from external climate oscillations and favored a shallow frost layer (2008–2009, 2009–2010 and 2010–2011). On the other hand, years with low precipitations promoted deeper freezing of the soil down to 60–70cm extending until late May or early June (2006–2007, 2007–2008 and 2011–2012). When snow melted a high increase of temperatures of 10–12°C in few weeks was recorded at all depths. At this time of the year, periglacial activity is enhanced due to higher water availability and the existence of freeze–thaw cycles. These were recorded mostly in spring and autumn in the first 50cm depth of the soil, ranging from 9.8days (at 2cm) to 3.7days (at 50cm).However, the inactivity of solifluction landforms suggests that the combination of present-day soil temperatures together with moisture conditions is not favorable to promote solifluction activity in the periglacial belt of the Sierra Nevada.Future climate scenarios point to a temperature increase and precipitation decrease in the area, which would entail deeper but shorter frozen soil layers. These conditions would not be favorable for active periglacial slope processes in the Sierra Nevada.

Impacts of surface soil organic content on the soil thermal dynamics of alpine meadows in permafrost regions: data from field observations

The relationship between soil organic matter and soil temperature plays an important role in our understanding of the effect of climate change on the hydrological and carbon cycles in permafrost regions. Several studies have documented that the organic horizon thickness has profound buffering effects on soil temperature for both tundra and boreal forest ecosystems. In the present study, the alpine meadow ecosystem in the middle and low-latitude permafrost region of the Qinghai–Tibet Plateau (QTP) was selected to examine the impacts of surface soil organic matter on the thermal properties of deep soil. Based on the data obtained from more than 23 observation sites, the relationship between soil organic content and soil temperature dynamics in different seasons was determined. The findings indicate a strong positive exponential (in thawing period) and linear (in freezing period) relationship between surface soil organic content (SOC) and soil temperature dynamics in deep soil layers. The higher SOC at the surface soil layer is associated with a lower rate of soil temperature variation and a later onset time for the thaw–freeze transformation. In permafrost regions of the QTP, the greater lapse rate of soil temperature per 100m of increased elevation resulted in more significant modification of the SOC and soil thermal relationship in alpine meadows than that in tundra and boreal ecosystems. The coupled soil organic matter, soil thermal and water relationships play an important role in the resilience of permafrost during climate changes.