Diurnal Variation Of Soil Temperature Research Articles

Variation characteristics of soil temperature, moisture, and heat flux in the understorey of evergreen broadleaf forest in South China

Based on observation data from the observation tower station in Zhuhai in South China from October 2015 to May 2018, the variations in soil temperature, moisture, and heat flux in the understorey of evergreen broadleaf forest are analyzed. The ground surface temperature is slightly greater than the canopy surface temperature; the soil temperature is the smallest. The seasonal variation in the soil moisture fluctuates around a relative equilibrium as the rain increases or decreases. Both ground and canopy surface temperatures have valley values before sunrise and peak values in the afternoon. The diurnal variations in soil temperature are characterized by a cosine function. With the deepening of the soil layer, the time of valley and peak lag and the amplitude of the variation in the soil temperature decrease. There is almost no diurnal variation in soil temperature at 40 cm depth or the soil heat flux at 30 cm depth. The heat fluxes at depths of 7.5 cm and 15 cm show an “S” pattern variation, with a peak at 17:30. The net radiation of the canopy surface shows a bell-shaped variation, with a peak at 12:30. The averaged soil thermal conductivities are 2.18 W·m−1·K−1, 1.22 W·m−1·K−1, and 1.26 W·m−1·K−1 for 5 ~ 10 cm, 10 ~ 20 cm, and 20 ~ 40 cm depths, respectively.

No-Tillage Promotes Wheat Seedling Growth and Grain Yield Compared with Plow–Rotary Tillage in a Rice–Wheat Rotation in the High Rainfall Region in China

Optimizing soil properties to match ecological conditions can alleviate stress damage and promote crop growth. However, the suitable soil conditions for wheat growth in an integrated rice–wheat breeding scheme under high rainfall and the mechanisms that affect yield production are not well known. Field experiments were carried out at two sites, which were all located in Jiangsu Province, China, a subtropical monsoon climate zone during two wheat growing seasons, to assess the effects of plow tillage followed by rotary tillage (PR) and no-tillage (NT) on soil physical and chemical properties, wheat seedling growth, grain yield, and spike amounts and quality. The finding indicates that with the reduction in soil mixing, soil bulk density was higher in NT than in PR, which helped to maintain moisture in dry soil. In soils with high water content, in NT, when the wheat field was subjected to waterlogging stress, the drainage decreased to deeper soil possibly due to reduced infiltration and a higher evaporation of surface water. The diurnal variation in soil temperature decreased in NT, and when the soil was cold, NT helped to insulate soils at 0–25 cm. Compared with PR, the contents of available nitrogen and phosphorus increased at 0–20 cm in NT. Root biomass and root activity of wheat seedlings at 0–20 cm were also greater in NT than in PR. Compared with PR, wheat also had more culms at the beginning of the overwintering stage, more spikes, and higher grain yield in NT, but the differences were not significant under excessive soil moisture. Therefore, the soil hydrothermal environment and spatial distributions of nutrients in NT promoted shallow root growth and tiller development in the early phase of wheat growth, which led to higher amounts of spikes per plant that resulted in high-yielding wheat crops.

Hydrothermal Effects of Freeze-Thaw in the Taklimakan Desert

The Taklimakan Desert, also known as the “Sea of Death”, is the largest desert in China and also the world’s second largest remote desert. The road crossing the Taklimakan Desert is the longest desert road in the world and has been the center of the Silk Road since ancient times. Based on field observation data (November 2013 to May 2014) collected from the Tazhong and Xiaotang stations, we studied the interannual and diurnal variations of soil temperature, soil moisture content, and surface heat fluxes during different freezing and thawing periods. The annual and daily changes of soil temperature, soil moisture content, and surface energy fluxes at different freezing and thawing stages were analyzed. We illustrated the coupling relationship between water and heat in freezing-thawing soil in the Taklimakan Desert. We established a coupling model of soil water and heat during freezing and thawing. During the soil freezing period, the soil temperatures at different depths generally trended downward. The temperature difference between the Tazhong station and the Xiaotang station was 4~8.5 °C. The freezing time of soil at 20 cm depth occurred about 11 days after that at 10 cm depth. The effect of ambient temperature on soil temperature gradually weakened with the increase of soil depth. With the occurrence of the soil freezing process, the initial soil moisture contents at 5 cm, 10 cm, 20 cm, and 40 cm depths at the Xiaotang station were 6%, 10%, 29%, and 59%, respectively, and those at the Tazhong station were 5%, 3.6%, 4.4%, and 5.8%, respectively. As the ambient temperature decreased, the freezing front continued to move downward and the liquid soil water content at each depth decreased. The desert highway is closely related to the economic development and prosperity of southern Xinjiang. Therefore, it is important to maintain and inspect the safety and applicability of freeze-thaw zones and avoid casualties from vehicles and personnel.

喀斯特地区土壤温度变化特征及其与环境因子的关系

喀斯特地区土壤温度变化特征对研究该区土壤活性及小气候变化具有重要意义。为探明喀斯特地区土壤温度变化特征及其与环境因子的关系，以喀斯特高原峡谷区四种典型土地类型（花椒地、金银花地、火龙果地、荒地）为研究对象，采用土壤含水量监测系统（ECH2O）对各样地土壤温度变化进行连续定点监测，分析土壤温度的动态变化特征及其与环境因子的关系。结果表明：10 cm处土壤温度日变幅最大，土层越深日变幅越小；土壤温度日变幅为夏季较大，秋、冬季较小。火龙果地、金银花地土壤温度日变幅明显大于花椒地、荒地；随着土层加深，土壤温度日变化出现滞后现象；不同季节土壤温度均为火龙果地 > 荒地 > 花椒地 > 金银花地。夏季土层越深，土壤温度越低；秋、冬季土层越深，土壤温度越高；土壤垂直温度变异系数表现为冬季大于夏季。相关分析表明，土壤温度与气温、太阳辐射及土壤含水量均呈显著正相关（P<0.05），土壤温度变化与容重、孔隙度、土壤质地、有机碳等土壤理化性质相关性显著。花椒地土壤温度日变幅最小，与其较高的土壤含水量和总孔隙度、容重小、土壤持水性强密切相关。综上，花椒地对土壤温度的调节效果较好，因此，在喀斯特地区生态恢复的过程中，种植花椒能在一定程度上改善土壤性质，提升土壤肥力。本研究为喀斯特地区的生态恢复提供了科学依据，为植被生态效益评价提供一定参考。;Characteristics of soil temperature variation in karst area are of great significance to the study of soil activity and microclimate change. To verify the variation characteristics of soil temperature in karst areas and its relationship with environmental factors, four typical land types including Zanthoxylum bungeanum (HJ), Hylocereus undulates (HLG), Lonicera japonica (JYH) and wasteland (HD) in the Karst plateau canyon were taken as research objects. Soil moisture monitoring system (ECH2O) was used for continuous fixed-point monitoring of different sites. The dynamic change characteristics of soil temperature at different time scales and its relationship with environmental factors were analyzed. The results showed that the daily variation of soil temperature was characterized by the sharpest diurnal variation of soil temperature appeared at 10 cm, and the deeper the soil depth, the smaller the diurnal variation. There was a great diurnal variation of soil temperature in summer but a smaller in autumn and winter. The diurnal variation of soil temperature in HL and JYH were significantly greater than that in HJ and HD as the soil depth deepens. There was a hysteresis effect in the diurnal variation of soil temperature. The daily variation of soil temperature at 10 cm and 25 cm of different land types showed a cubic function. The variation of soil temperature in different seasons was as follows:HLG > HD > HJ > JYH. The vertical variation characteristics of soil temperature was that the deeper the soil layer in summer, the lower the soil temperature was. The deeper the soil layer in autumn and winter, the higher the soil temperature. The vertical variation coefficient of soil temperature was greater in winter than in summer. There was significantly positive correlation between soil temperature with atmospheric temperature, solar radiation and soil moisture content (P<0.05). There was also a significantly close correlation between soil temperature variation with soil properties such as soil bulk density, porosity, soil texture, and organic carbon. The diurnal variation of soil temperature in HJ was the smallest, which has a close relationship with the higher soil moisture content and porosity, the better soil water holding capacity and the smaller bulk density. The soil temperature regulation capacity of HJ was the best among the four land types, therefore, the land type of HJ can improve soil properties and soil fertility to a great extent in the process of ecological restoration in karst areas. This study provides a scientific basis for ecological restoration and some reference for ecological benefits evaluation of vegetation in karst areas.

Improvement and Validation of the Common Land Model on Cropland Covered by Plastic Film in the Arid Region of China

AbstractPlastic mulch is a technology used worldwide to inhibit soil evaporation and increase crop yield. The properties of plastic film are significantly different from those of the soil. Plastic mulch not only significantly alters the physical attributes of the underlying surface, but also blocks the energy and mass exchanges between the land surface and the atmosphere. This latter situation has not been depicted in current land-surface models. This study develops a detailed new model, known as CoLM-mulch, by incorporating a plastic mulch–layer submodel and a dynamic parameterization scheme of surface albedo into the Common Land Model (CoLM) land-surface process model. The updated model elements are based on data collected from an experiment that examined land–atmosphere interaction at a plastic-film-covered cropland site in an arid region of northwestern China. Results suggest that the improved CoLM-mulch could reasonably simulate the diurnal variations of soil temperature and moisture, together with radiation, water, heat, and carbon dioxide (CO2) fluxes, on the cropland underlying a surface with a plastic film covering. The CoLM-mulch efficiency is higher, the deviations between the simulations and observations are minor, and the dynamic parameterization scheme for surface albedo is more reasonable and appropriate. Relative to CoLM simulations, the inclusion of plastic mulch with special optical properties in the model shows slight improvements in the simulations of the surface albedo and the radiation balance. By limiting the underlying soil evaporation and changing the aerodynamic resistances, plastic mulch in the model has influences on the turbulent exchanges between the atmosphere and the land surface. The soil temperature and moisture are improved by the inclusion of transparent plastic mulch in the model, which not only suppresses the CO2 generated by soil respiration, but also alters the CO2 exchange process between the canopy and the atmosphere as a result of the vegetation net assimilation controlled by the soil water and heat conditions.

Effect of Sowing Quantity on Soil Temperature and Yield of Winter Wheat under Straw Strip Mulching in Arid Region of Northwest China

In order to explore the characteristics and relationship between soil temperature and yield of winter wheat, under different sowing quantities conditions of straw mulching conventional drilling in Northwest China, this study took Lantian 26 as material, under the whole corn mulching conventional drilling in Changhe town and Pingxiang town, setting up 3 different seeding quantities of 270 kg/ha (SSMC1), 324 kg/ha (SSMC2) and 405 kg/ha (SSMC3), to study the difference of soil temperature during the growth period of winter wheat and its correlation with yield components. Results showed: the average soil temperature of 0∼25cm in two ecological zones in the whole growth period have a significant change with the increase of sowing quantities; too much seeding had a sharp drop in soil temperature; the highest temperature of SSMC in Changhe town was the middle quantity of SSMC 2; the highest temperature of SSMC in Pingxiang town was the lowest sowing quantity of SSMC1. Diurnal variation of soil temperature at all growth stages showed: with the increase of SSMC, in the morning it increased with the increase of soil depth, noon and evening reducing with the depth of the soil. The average soil temperature of SSMC2 was higher than that of in all the two ecological zones in the whole growth period of SSMC.The maximum day temperature difference of each treatment was at noon. With the increase of SSMC, the yield increase varied with two ecological zones. SSMC of the local conventional sowing quantity of 270kg/ha SSMC1 yield was the highest in Changhe Town. SSMC of the middle sowing quantity SSMC2 of 324kg/ha yield was the highest in Pingxiang town. The difference of grain number per spike was the main cause of yield difference among these 3 treatments. Correlation analysis showed: the correlation among the yield and yield components, growth index and soil temperature varied with different ecological zones; thousand kernel weight and grain number per ear (.964** and.891**) had a very significant positive correlation with the yields in Changhe Town, but thousand kernel weight and grain number per ear (.708* and.718*) had a significant positive correlation with yield in Pingxiang Town. There was a significant positive correlation between harvest index and 10cm soil temperature (.763*). But in Pingxiang Town grain number per ear and 15cm soil temperature showed a significant positive correlation (.671*); 15cm soil temperature and the average temperature of 0∼25cm soil layer in the whole growth period (-.687* and -.698*) had a significant negative correlation with the number of panicles per unit area; there was a very significant negative correlation between plant height and average temperature of 0∼25cm in the whole growth period (-.906**). Thus, the changes of soil temperature under SSMC different sowing quantity have indirect effect on the yield of winter wheat.

Soil Management in the Breede River Valley Wine Grape Region, South Africa. 2. Soil Temperature

Five soil management practices (treatments) were applied in a micro-sprinkler irrigated Chardonnay/99 Richter vineyard on a sandy clay loam soil near Robertson, commencing in April 1993 (one year after planting). The effect of the treatments on the soil temperature at a depth of 200 mm was measured on an hourly basis from April 1995 to March 1999. Differences in soil temperature between the un-mulched and mulched treatments, as measured in the grapevine rows, were negligible from late April to the end of August. From mid-September (grapevine bud break) to the end of March, the temperature of the mulched soil was, with the exception of the third week in October, lower than that of the un-mulched soil. Results indicated that soil temperatures during early spring had a slight effect on the onset of grapevine bud break. Mulching minimised the diurnal variation in soil temperature. The annual cover crop did not cause any delay in bud break and kept the soil temperatures below 25°C, with the exception of a three week period just before harvest.

Simulating the effects of soil temperature and moisture in the off-rice season on rice straw decomposition and subsequent CH4 production during the growth season in a paddy soil

To understand the effects of soil temperature and moisture on rice straw decomposition during the off-rice season and subsequent CH4 production in rice growth season, we firstly incubated a paddy soil with 13C-labeled straw addition under four temperature (±5, 5, 15, and 25 °C) and two moisture levels (60 and 100 % water-filled pore space (WFPS)) under aerobic conditions for 24 weeks and subsequently incubated those samples anaerobically at 30 °C and under submerged conditions for 4 weeks. Temperature change at ±5 °C was used to simulate the diurnal variation of soil temperature between night (−5 °C, 12 h) and day (5 °C, 12 h) during the corresponding freeze-thaw cycles. Our results showed that both increased soil temperature and moisture significantly promoted straw aerobic decomposition as observed by carbon dioxide (CO2) production, soil organic carbon (SOC) content, and its δ13C value in this incubation experiment. During the anaerobic incubation, straw-amended soil samples remarkably promoted CH4 production and CH4/total decomposed C. Both CH4 and CO2 productions in straw-amended soil samples were lowest at 25 °C and 100 % WFPS and highest at ±5 °C and 100 % WFPS, which could be attributed to a depletion of labile organic C derived from straw during the 24-week aerobic incubation. Total rates of straw C decomposition calculated from decomposed C production, SOC content, and δ13C value in the whole incubation (aerobic + anaerobic) ranged from 29.8 to 48.1, 45.0 to 64.2, and 25.7 to 35.7 %, respectively. These results imply that increasing soil temperature during the off-rice season promotes the rice straw decomposition and leads to a decrease in CH4 production during the subsequent rice growth season under conditions of northeastern Japan.

Soil Moisture Retrieval Using Ground‐Based L‐Band Passive Microwave Observations in Northeastern USA

A field experiment was performed in a grassland at the NOAA‐CREST–Soil Moisture Advanced Radiometric Testbed (CREST‐SMART) facility, which includes a mobile L‐band dual‐polarized radiometer with an in situ soil temperature and soil moisture observation network, located near Millbrook, NY. During the day‐long field campaign, intensive spatiotemporal measurements of L‐band brightness temperatures, surface temperature, soil moisture, and soil temperature at 3‐, 7‐, and 12‐cm depths were collected during three passes at 0830, 1130, and 1430 h. During the second and third passes, half of the field was irrigated. Soil roughness and water content of the short grass that remained after mowing the study area were measured. The Tau‐Omega radiative transfer model was used to assess the performance of the soil moisture retrieval using measured soil temperatures at different depths. In addition, the collected microwave observations at the three different times of the day were used to assess the impact of the diurnal variation of soil temperature on the performance of soil moisture retrieval. Obtained results showed that the root mean square error (RMSE) decreased throughout the day to reach 0.03 m3/m3 for the afternoon pass when 12‐cm soil temperature values were used in the radiative transfer model. In addition, during the three different passes, the lowest RMSE was consistently obtained when the 12‐cm soil temperature was used, which suggests that, for this investigated site, soil temperature at the 12‐cm depth can be a surrogate for soil effective temperature when L‐band microwave temperatures are used. In terms of diurnal variability, observations from the afternoon pass led to the highest agreement between observed and retrieved soil moisture values.

Variations in soil temperature at BJ site on the central Tibetan Plateau

The temporal and spatial variation in soil temperature play a significant role in energy and water cycle between land surface and atmosphere on the Tibetan Plateau. Based on the observed soil temperature data (hourly data from 1 January 2001 to 31 December 2005) obtained by GAME-Tibet, the diurnal, seasonal and interannual variations in soil temperature at BJ site (31.37° N, 91.90° E; 4509 a.s.l.) near Naqu in the central Tibetan Plateau were analyzed. Results showed that the average diurnal variation in soil temperature at 4 and 20 cm depth can be described as sinusoidal curve, which is consistent with the variation of solar radiation. However, the average diurnal variation in soil temperature under 60 cm was very weak. The average diurnal amplitude in soil temperature decreased by the exponential decay function with the increase of soil depth (R2=0.92, p<0.01). It is demonstrated that the average diurnal maximum soil temperature decreased by the exponential decay function with the increase of soil depth (R2 =0.78, p<0.01). In contrast, the average diurnal minimum soil temperature increased by the exponential grow function with increasing of soil depth (R2=0.86, p<0.01). There were a linear negative correlation between the average annual maximum Ts and soil depth (R2=0.96, p<0.01), a logarithmic function relationship between the average annual minimum soil temperature and soil depth (R2=0.92, p<0.01). The average seasonal amplitude in soil temperature followed the exponential decay function with the increase of soil depth (R2=0.98, p<0.01). The mean annual soil temperature in each layer indicated a warming trend prominently. During the study period, the mean annual soil temperature at 4, 20, 40, 60, 80, 100, 130, 160, 200 and 250 cm depth increased by 0.034, 0.041, 0.061, 0.056, 0.062, 0.050, 0.057, 0.051, 0.047 and 0.042 °C /a, respectively.

Nitrous oxide emissions from managed grassland: a comparison of eddy covariance and static chamber measurements

Abstract. Managed grasslands are known to be an important source of N2O with estimated global losses of 2.5 Tg N2O-N yr−1. Chambers are to date the most widely used method to measure N2O fluxes, but also micrometeorological methods are successfully applied. In this paper we present a comparison of N2O fluxes measured by non-steady state chambers and eddy covariance (EC) (using an ultra-sonic anemometer coupled with a tunable diode laser) from an intensively grazed and fertilised grassland site in South East Scotland. The measurements were taken after fertilisation events in 2003, 2007 and 2008. In four out of six comparison periods, a short-lived increase of N2O emissions was observed after mineral N application, returning to background level within 2–6 days. Highest fluxes were measured by both methods in July 2007 with maximum values of 1438 ng N2O-N m−2 s−1 (EC) and 651 ng N2O-N m−2 s−1 (chamber method). Negative fluxes above the detection limit were observed in all comparison periods by EC, while with chambers, the recorded negative fluxes were always below detection limit. Median and average fluxes over each period were always positive. Over all 6 comparison periods, 69% of N2O fluxes measured by EC at the time of chamber closure were within the range of the chamber measurements. N2O fluxes measured by EC during the time of chamber closure were not consistently smaller, neither larger, compared to those measured by chambers: this reflects the fact that the different techniques integrate fluxes over different spatial and temporal scales. Large fluxes measured by chambers may be representing local hotspots providing a small contribution to the flux measured by the EC method which integrates over a larger area. The spatial variability from chamber measurements was high, as shown by a coefficient of variation of up to 139%. No diurnal pattern of N2O fluxes was observed, possibly due to the small diurnal variations of soil temperature. The calculation of cumulative fluxes using different integration methods showed EC data provide generally lower estimates of N2O emissions than chambers.

Characteristics of land surface heat and water exchange under different soil freeze/thaw conditions over the central Tibetan Plateau

AbstractFreezing and thawing processes at the soil surface play an important role in determining the nature of Tibetan land and atmosphere interactions. In this study, land surface water and heat exchanges under different freezing and thawing conditions over the central Tibetan Plateau were investigated using observations from the Coordinated Enhanced Observing Period/Asia‐Australia Monsoon Project on the Tibetan Plateau, and the Simultaneous Heat and Water Model. During the freezing and thawing stages, significant diurnal variation of soil temperature resulted in a diurnal cycle of unfrozen water content at the surface. Radiation and energy components and evapotranspiration averaged over four freeze/thaw stages also changed diurnally. On average, the surface albedo (0·68) during the completely frozen stage was sharply higher than those during the freezing, thawing, and completely thawed stages due to the snow cover. The Bowen ratios were 3·1 and 2·5 in the freezing and thawing stages, respectively, but the ratio was only 0·5 in the completely thawed stage. Latent heat flux displayed distinctly better correlation with unfrozen soil water content during the freezing and thawing stages than during the completely frozen and thawed stages. This implies that the diurnal cycle of unfrozen soil water, resulting from diurnal freeze/thaw cycles at the surface, has a significant impact on latent heat flux. A surface energy imbalance problem was encountered, and the possible sources of error were analysed. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Diurnal variation of methane emissions from an alpine wetland on the eastern edge of Qinghai-Tibetan Plateau

Alpine wetland is a source for CH(4), but little is known about methane emission from such wetland, especially about its diurnal pattern. In this study we tried to probe the diurnal variation in methane emission from alpine wetland vegetation. The average methane emission rate was 9.6 +/- 3.4 mg CH(4) m(-2) h(-1). There was an apparent diurnal variation pattern in methane emission with one minor peak at 06:00 and a major one at 15:00. The sunrise peak was consistent with a two-way transport mechanism for plants (convective at daytime and diffusive at night-time). CH(4) emission was found significantly correlated with redox potentials. The afternoon peak could not be explained by diurnal variation in soil temperature, but could be attributable to changes in CH(4) oxidation and production driven by plant gas transport mechanism. The results have important implications for sampling and scaling strategies for estimating methane emission from alpine wetlands.

The effects of long-term conservation tillage, crop residues and P fertilizer on soil conditions and responses of summer and winter crops on an Andosol in Japan

A field experiment was conducted from 1983 to 1992 in Tsukuba, Japan to investigate the effects of tillage on soil conditions and crop growth in a light-colored Andosol. Three tillage methods (NT: no-tillage, RT: no-tillage for summer cropping and moldboard plowing for winter cropping, and CT: conventional rotary tillage to a depth of 15 cm) were employed in combination with crop residue application (+R, −R) and fused magnesium phosphate (FMP) fertilization (+P, −P). Under the combination of NT and +R, diurnal variation of soil temperature at a depth of 5 cm was smaller during the summer cropping season and soil temperature in the daytime was lower during the winter cropping season than under CT. Soil inorganic N concentration at a depth of 0–30 cm was +R > −R and NT > RT > CT. The early growth of summer crops was accelerated under NT in comparison with CT, and yields were higher under NT and RT in comparison with CT. On the other hand, winter crop yields were significantly reduced under NT, while they were still higher under RT in comparison with CT. Yields were higher with +R and +P application, respectively, and these effects were more pronounced in winter cropping. The positive effect of FMP fertilization was greater in combination with NT, and that of residue treatment was greater in combination with RT and NT than with CT. In conclusion, the best tillage practice for Andosols on the Kanto Plain is RT, i.e. a combination of NT for summer cropping and CT for winter cropping. The application of NT for winter cropping is not recommended, although the application of phosphate and crop residues could reduce the risk of yield reduction, because of improved soil nutrient status and moderation of diurnal soil temperature.

Retrieving soil water contents from soil temperature measurements by using linear regression

A simple linear regression method is developed to retrieve daily averaged soil water content from diurnal variations of soil temperature measured at three or more depths. The method is applied to Oklahoma Mesonet soil temperature data collected at the depths of 5, 10, and 30 cm during 11–20 June 1995. The retrieved bulk soil water contents are compared with direct measurements for one pair of nearly collocated Mesonet and ARM stations and also compared with the retrievals of a previous method at 14 enhanced Oklahoma Mesonet stations. The results show that the current method gives more persistent retrievals than the previous method. The method is also applied to Oklahoma Mesonet soil temperature data collected at the depths of 5, 25, 60, and 75 cm from the Norman site during 20–30 July 1998 and 1–31 July 2000. The retrieved soil water contents are verified by collocated soil water content measurements with rms differences smaller than the soil water observation error (0.05 m3 m−3). The retrievals are found to be moderately sensitive to random errors (±0.1 K) in the soil temperature observations and errors in the soil type specifications.

Determination of Diurnal Soil-Temperature Cycles Using Remote Sensing Data

A solution is found for the thermal conductivity equation describing the steady diurnal variation of soil temperature, which is nonuniform in depth. The solution is represented in the form of a Fourier series and is dependent on three characteristic parameters reflecting energy budget conditions at the soil surface. These parameters can be found using two remote temperature measurements with a known time for attaining a maximum value. The diurnal temperature variation retrieved on the basis of remote measurements is compared with the results of surface experiments for dry and moist soils.

Two‐Dimensional Model Simulation of 1,3‐Dichloropropene Volatilization and Transport in a Field Soil

AbstractA modeling study was conducted to simulate 1,3‐dichloropropene (1,3‐D) emission and concentration distribution in soil profiles when the chemical was applied with subsurface drip irrigation with reduced rate. The purpose was to evaluate the effect on emission reduction as compared with conventional shank injection application. To compare with field measurements, simulated scenarios included a shallow drip application at 2.5 cm, covered with a polyethylene film; a deep drip application at 20.3 em with bare soil surface; and a conventional shank injection at 30.5 cm with a regular application rate. A convective and diffusive two‐dimensional model was used to simulate the simultaneous transport of 1,3‐D in both liquid and gaseous phases. Diurnal variations of soil temperature were predicted to calculate 1,3‐D diffusion coefficient and the Henry's constant. Predicted 1,3‐D emissions compared well with field measurements for the shallow and deep drip irrigation treatments. The model simulation underpredicted 1,3‐D emission in the shank injection plot, where other transport mechanisms such as gas phase convection likely occurred during and immediately after application. Results from the modeling study indicate that computer simulation can be used effectively to study the environmental fate and transport of 1,3‐D under conditions where vapor phase diffusion and liquid phase convection are the dominant transport mechanisms. Applying 1,3‐D with subsurface drip irrigation appeared to be useful for emission reduction.

Temperature Effect on Methyl Bromide Volatilization in Soil Fumigation

Recent interest in characterizing methyl bromide emission has focused on field and laboratory measurements, which are expensive to conduct and very time consuming. Predicting methyl bromide volatilization with numerical or analytical models has been limited to idealized situations without considering environmental conditions such as diurnal temperature change. It has been found that temperature can strongly affect methyl bromide volatilization under field conditions. To quantitatively characterize temperature effect, we adopted a two-dimensional numerical model that can solve simultaneous equations of water, heat, and solute transport (including both liquid and vapor phases). Functional relationships were established between temperature and methyl bromide liquid-gas phase partition coefficient or the Henry's constant, diffusion coefficient in soil air space, and the permeability of polyethylene tarp. To test the model, soil properties and boundary conditions from Yates et al. (1996a,b,c) were used. The model prediction was completely independent of the field measurement. The model simulation by considering diurnal variations of soil temperature predicted the cumulative emission that agreed well with the measured flux density. Prediction without considering temperature missed the diurnal nature in emission flux density. Comparable results were also obtained for methyl bromide concentration in the soil profile. The key advantage of this model is its ability of describing diurnal variations in methyl bromide emission flux. Based on the temperature effect on temporal variations of methyl bromide emission, we believe that small sampling intervals are needed to determine the dynamic nature of methylbromide emission under field conditions, especially during the first 24 h after application.

CHEMICAL KINETICS OF WEATHERING IN YOUNG ANDISOLS FROM NORTHEASTERN JAPAN USING SOIL AGE NORMALIZED TO 10°C

We studied chemical kinetics of weathering in the humus horizons of young Andisols from northeastern Japan. Since there is no idealized chronosequence of Andisols, we selected eight pedons that have many similarities in the properties of parent material, soil moisture regime, vegetation, drainage, etc., but show significant differences in soil age and soil temperature. We introduced “soil age normalized to 10°C,” which was defined as the number of years a soil has been subjected to pedogenesis under mean monthly soil temperature (MMST) of 10°C throughout the year. For this calculation, temperature dependency coefficient (Q10) of Al release from volcanic glass was determined to be 1.5 by the laboratory dissolution experiment using separated glass samples. Mean monthly air temperature (MMAT) plus 1°C was employed as MMST based both on the comparison between MMST and MMAT and the determination of diurnal variations of soil temperature. Of the various elements contained in volcanic ash, Al was found to be most reliable for evaluating chemical weathering of the bulk soils, and released Al was determined by the acid oxalate method. The correlation between the soil age normalized to 10°C and acid oxalate extractable Al (Alo) showed that the chemical weathering is expressed as zero-order kinetics.

The impact of Calamagrostiscanadensis on soil thermal regimes after logging in northern Alberta

The grass Calamagrostiscanadensis (Michx.) Nutt. often forms a dense growth after logging in the boreal forest region of western Canada. Mowing treatments were applied experimentally to examine the effects of C. canadensis shoot biomass and litter on soil thermal regimes. In unmowed sites with heavy accumulations of shoot biomass and litter (768 g•m−2), thawing of soil in the spring was delayed by up to 1 month compared with sites subjected to frequent mowing. Mean soil temperature from May to August at the 10-cm depth averaged 3.8 °C warmer in mowed plots than in unmowed plots. Mowing also caused a three- to four-fold increase in the diurnal variation in soil temperature. Based on the results from different mowing treatments, it appeared that the presence of standing dead C. canadensis shoots and litter was more important than living biomass in producing cold soils. Undisturbed sites dominated by Epilobiumangustifolium L. (fireweed), which does not form a persistent litter layer, had warmer soils than unmowed C. canadensis sites. Cold soils could partly explain the poor growth of conifer seedlings that often occurs after planting in grass-dominated boreal sites.