AHFO-based soil water content sensing technology considering soil-sensor thermal contact resistance

The actively heated fiber-optic(AHFO)technology has become emerged as a research focus due to its advantages of distributed,real-time measurement and good durability.These attributes have led to the gradual application of AHFO technology to the water content measurement of in situ soil.However,all existing in situ applications of AHFO technology fail to consider the effect of soilesensor contact quality on water content measurements,limiting potential for the wider application of AHFO technology.To address this issue,the authors propose a method for determining the soilesensor thermal contact resistance based on the principle of an infinite cylindrical heat source.This is then used to establish an AHFO water content measurement technology that considers the thermal contact resistance.The reliability and validity of the new measurement technology are explored through a laboratory test and a field case study,and the spatial-temporal evolution of the soil water content in the case is revealed.The results demonstrate that method for determining the soilesensor thermal contact resistance is highly effective and applicable to all types of soils.This method requires only the moisture content,dry density,and thermal response of the in situ soil to be obtained.In the field case,the measurement error of soil water content between the AHFO method,which takes into account the thermal contact resistance,and the neutron scattering method is only 0.011.The water content of in situ soil exhibits a seasonal variation,with an increase in spring and autumn and a decrease in summer and winter.Furthermore,the response of shallow soils to precipitation and evaporation is significant.These findings contribute to the enhancement of the accuracy of the AHFO technology in the measurement of the water content of in situ soils,thereby facilitating the dissemination and utilization of this technology.

Experimental Study on the Effect of Fine-Grained Soil Content on the Freezing Strength of Aeolian Sand-Cement Interface

In cold regions,understanding the freezing strength of the interface between soil and structure is crucial for designing frost-resistant foundations.To investigate how the content of cement powder in aeolian sand affects this strength,we conducted direct shear tests under various conditions such as different fine-grained soil content,normal stress,and initial moisture content of the soil.By analyzing parameters like soil properties,and volume of ice content,and using the Mohr-Coulomb strength theory to define interface strength,we aimed to indirectly measure the cementation strength of the interface.Our findings revealed that as the particle content increased,the interface stress-strain curves became noticeably stiffer.We also observed a positive linear relationship between freezing strength and silt content,while the initial moisture content of the soil did not significantly impact the strengthening effect of fine-grained soil on freezing strength.Moreover,we discovered that as the powder content increased,the force binding the ice to the interface decreased,while the friction angle at the interface increased.However,the cohesion force at the interface remained relatively unchanged.Overall,our analysis suggests that the increase in freezing strength due to fine-grained soil content is primarily due to the heightened friction between aeolian sand and the interface.

Comparative Study on Phosphorus Contents of Soil in Karst Rocky Desertification Area during Eco-restoration Process in Guangxi Province

[Objective] The research aimed to study change law of phosphorus content of soil in karst rocky desertification region(KRD) during eco-restoration process such as Northwest Guangxi Province.[Method] The soil samples were collected from typical KRD in Pingguo County and Yizhou City.The determining quotas of different soil samples such as soil total phosphorus content and available phosphorus content were detected,in addition the soil total phosphorus content,available phosphorus content, urease activity, catalase activity and organic matter content in different soil samples were analyzed comparatively.[Result] Aspect,vegetation type and recovery time generated obviously influences on phosphorus contents in different soil samples.The concrete influence order was listed as follow: phosphorus content in soil of south slope was higher than that in soil of north slope;phosphorus content in soil where Zenia insignis Chun was planted was higher than that in soil of closed forest and that of soil where Dendrocalamus minor Var. amoen was planted,additionally,phosphorus increased with recovery time. Urease activity could be used as a monitoring index of soil fertility because it is related to the change of phosphorus content.[Conclusion] The soil of karst rocky desertification region in Northwest Guangxi Province could be recovered gradually if excessive human disturbance was stopped.If proper natural method of recovery promoted by human was taken,the recovery would reach a better result.

Effects of soil temperature and soil water content on soil respiration in three forest types in Changbai Mountain

Soil incubation experiments were conducted in lab to delineate the effect of soil temperature and soil water content on soil respirations in broad-leaved/Korean pine forest (mountain dark brown forest soil), dark coniferous forest (mountain brown coniferous forest soil) and erman's birch forest (mountain soddy forest soil) in Changbai Mountain in September 2001. The soil water content was adjusted to five different levels (9%, 21%, 30%, and 43%) by adding certain amount of water into the soil cylinders, and the soil sample was incubated at 0, 5, 15, 25 and 35°C for 24 h. The results indicated that in broad-leaved/Korean pine forest the soil respiration rate was positively correlated to soil temperature from 0 to 35°C. Soil respiration rate increased with increase of soil water content within the limits of 21% to 37%, while it decreased with soil water content when water content was over the range. The result suggested the interactive effects of temperature and water content on soil respiration. There were significant differences in soil respiration among the various forest types. The soil respiration rate was highest in broad-leaved/Korean pine forest, middle in erman's birch forest and the lowest in dark coniferous forest. The optimal soil temperature and soil water content for soil respiration was 35°C and 37% in broad-leaved/Korean pine forest, 25°C and 21% in dark coniferous forest, and 35°C and 37% in erman's birch forest. Because the forests of broad-leaved/Korean pine, dark coniferous and erman's birch are distributed at different altitudes, the soil temperature had 4–5°C variation in different forest types during the same period. Thus, the soil respiration rates measured in brown pine mountain soil were lower than those in dark brown forest and those measured in mountain grass forest soil were higher than those in brown pine mountain soil. Key words Soil temperature - Soil water content - Soil respiration - The typical forest ecosystem in Changbai Mountain CLC number S7118.51 Document code A Foundation item: This study was supported by grant from the National Natural Science Foundation of China (No. 30271068), the grant of the Knowledge Innovation Program of Chinese Academy of Sciences (KZ-CX-SW-01-01B-12) and the grant from Advanced Programs of Institute of Applied Ecology Chinese Academy of Sciences.Biography: WANG Miao (1964-), male, associate professor in Institute of Applied Ecology, Chinese Academy of Science, Shenyang 110016, P. R. China.Responsible editor: Song Funan

Effects of Land Use Patterns on Soil Heavy Metal Contents

Through sampling in farmland and analysis in laboratory,the contents and the pollution level of Cr,Cu,As,Pb,Zn in different soils were studied. The comparative result showed that the As in all soil samples are lower than the mean value of Shaanxi and whole nation,the Cr in lower half soil samples are higher than the mean value of Shaanxi and whole nation,the Cu and Zn in majority soil samples are higher than the mean value of Shaanxi and whole nation,and the Pb in all soil samples is higher than the mean value of Shaanxi and whole nation. The single factor pollution index and multi-factor pollution index method were used to evaluate the soil pollution. According to Soil Environmental Quality Standard,the studied soils were at unpolluted degrees,the soils were clear,the quality of soil adapt to the crop growth,and not affect the quality of agricultural product.

Effect of Reducing Chemical Fertilizer on Rice Yield,Output Value,Content of Soil Carbon and Nitrogen after Utilizing the Milk Vetch

A located field experiment was carried out to study the effects of different amount of chemical fertilizer usage on rice yield,economic benefits of rice,soil carbon（C） and total nitrogen（TN） under ploughing back of Chinese milk vetch for 5consecutive years.Six treatments were included in the experiment,they are CK（unfertilized）,CF（100% chemical fertilizer with the amount of N,P2O5,K2 O being150,75,120 kg/hm^2respectively）,A1（22 500 kg/hm^2 Chinese milk vetch and 100%chemical fertilizer）,A2（Chinese milk vetch and 80% nitrogen and potassium fertilizer and 100% phosphate fertilizer）,A3（Chinese milk vetch and 60% nitrogen and potassium fertilizer and 100% phosphate fertilizer）,A4（Chinese milk vetch and 40% nitrogen and potassium fertilizer and 100% phosphate fertilizer）.The results were as follows：application of fertilizer could increase the yield of rice,while Chinese milk vetch combined with fertilizer application had a much more increase effect in rice yield.Under the condition of milk vetch application with 22 500 kg/hm^2,the early rice yield of the treatment A1 was significantly increased by 7.7% compared with that of CF.And the yield of treatment A3 was basically identical to or slight increase in comparison with that of CF.Decreasing amount of fertilizers cloud improve output value of rice in the case of the utilization of Chinese milk vetch.The treatment A1 increased output value of rice by 5.92% in comparison of CF,and treatment A2 was by 4.08% in the next.Treatment A4 showed much better effect in increasing soil organic carbon and total nitrogen in the paddy soil than those of treatments applying mineral fertilizer only.There was a significant reduction on soil organic carbon and TN in treatment A2 in comparison with that of CF.In general,amount of application of milk vetch with 22 500 kg/hm^2 could replace chemical fertilizer partially,it also could improve rice yield,decrease the production cost,and raise the utilization efficiency of nutrients.

Water content and modulus relationship of a compacted unsaturated soil

In order to assess the performance of the embankment soil under various climate conditions during the period of service, the modulus behaviour of an unsaturated compacted soil is evaluated using the constant water content triaxial test. Since the water content measurement method is simple and economical and it is used widely in engineering, the soil suction is replaced by the water content and the relationship between the water content and the modulus is developed. The compacted samples are prepared with different compacted water contents, and samples with a similar water content subjected to drying or wetting procedures prior to the triaxial test are also investigated. The effect of the water content and the confining pressure on the modulus is analyzed. The results show that the modulus decreases with the increase in the water content and a power function can be proposed to quantitatively describe the relationship between the modulus and the water content in the range of the measured water content. The modulus increases with the increase in the confining pressure of the compacted soil. However, the effect of the water content on the modulus is more pronounced than that of the confining pressure. This research can be referenced for the compacted embankment soil assessment in-service period.

Characteristics of Fluoride Contents in Plants and Soils in Kaili City Under Air Pollution

Fluoride contents in plants and soils in Kaili City were measured with fluorinion as per electrode method and the related characteristics were analyzed in order to explore effects of air fluoride pollution on plant and soil.The results indicated that fluoride content in plants tended to be volatile in 135.62-1 420.97 μg/g and averaged 513.99 μg/g;fluoride content in soils changed from 240.50-340.36 μg/g and averaged 279.60 μg/g.The contents of plant and soil both exceeded background value,suggesting that plants and soils in the region have been polluted.In addition,fluoride contents differ significantly upon plants.In detail,the maximal content was in Camelliaolelfera Abel and the minimal in Camelliaolelfera Abel.The contents of fluoride in different plant species vary,as follows：shrub vine herbaceous plant arbor;evergreen plants deciduous plant;fluoride contents in plants and soils also differ in varying degrees upon research sites.

Characteristics of Soil Porosity and Changes of Soil Water Content in Eucalyptus Plantation

Objective] This study almed to investigate the characteristics of soiI total porosity （STP） and various factors affecting soiI water content （SWC） in eucalyptus pIantation （EP）, thereby providing references for soiI water utiIization in eucalyptus pIanting in the red soiI hiI y region of South China. [Method] In the same cIimatic region, soiI sampIes were coI ected from surface soiI Iayer （A）, iI uvial horizon （B） and parent material horizon （C） in the upper sIope, middIe sIope and Iower sIope of eucalyptus pIantation, native forest and pine forest, respectiveIy, to determine the soiI porosity and soiI water content and analyze changes and various infIuencing factors of soiI water content in horizontal and vertical direction. [Result] Average soiI porosity in eucalyptus pIantation, native forest and pine forest was 45.9%, 41.4%and 55.3%, respectiveIy; soiI water content in these three forest stands was 13.3%, 13.4% and 15.5%, respectiveIy. In addition, soiI water content in these three forest stands exhibited no significant differences （P＆gt;0.05） among different soiI profiIes and sIope positions, but soiI water content in surface soiI Iayer varied significantIy （P＆lt;0.05） among different forest stands; in the horizontal direction, soiI water content exerted an extremeIy significant positive correIation with total coverage. [Conclusion] Total coverage of canopy Iayer, herb and Iitter Iayer is one of the most critical fac-tors affecting the changes of soiI water content in surface soiI Iayer of forest stands.

Effects of Fertilization on Moisture Content of Soils in the Loess Hilly-gully Region

[Objective] The aim of this study was to study the influence of plants on the soil moisture content under different fertilization.[Method] Using sainfoin,sweet clover,Astragalus adsurgens,alfalfa,ryegrass,little flower,white clover as experimental material,this study explored the effects of soil moisture on the improvement of soil quality.[Result] Results showed that the soil moisture content of different plants follows as：sainfoin 〉sweet clover 〉Astragalus adsurgens 〉alfalfa perennial ryegrass 〉small crown 〉white clover,and the average moisture content reached 24.13% which was 2.45% higher than that of control group.At planting white clover,sweet clover,under the condition of 7 kinds of crops,in the treatments without fertilizer and with organic fertilizer,soil moisture content of soil in 0-20 cm grew significantly.[Conclusion] The application of organic fertilizer and growing of plants would improve soil moisture in abandoned fields,enhance the ability of soil water supply,and improve soil fertility.

Effects of Relative Soil Water Content on Antioxidant Enzyme System in Malus sieversii(Lebed.) Roem

By pot experiment under artificially simulated water stress conditions, soluble protein content, MDA content and SOD, POD, CAT and APX activities in Malus sieversfi leaves were determined to reveal the response mechanism of M. sieversii to changes of relative soil water content. According to the results, with the decrease of relative soil water content, MDA content in M. sieversii leaves increased by mem- brane lipid peroxidation. Cells resist water stress-induced membrane lipid peroxidation and clear the increased reactive oxygen species by improving soluble protein content and SOD, POD, CAT and APX activities. However, various enzymes were involved in the response to water stress under different moisture conditions. In addition, the results indicated that M. sieversii had a good adaptability to higher relative soil water contents.

Effects of Ground Mulching Treatments on Soil Moisture Content in Second-generation Seed Garden of Pinus elliottii

Different ground mulching treatments were designed to observe the effects on soil moisture content in a second-generation seed orchard of Pinus elliottii. The results showed that： （1） there were extreme differences in soil moisture content Ⅰ and soil moisture content Ⅲ, but no obvious difference in soil moisture content II was observed; and （2） the high-to-low order of soil moisture content Ⅰ under different ground mulching treatments was white film〉sawdust〉black film〉the control, and the highest value was higher than the lowest one by 26.69%; the high-to-low order of soil moisture content Ⅱ under different ground mulching treatments was white film〉black film〉sawdust〉the control, and the highest value was higher than the lowest one by 20.64%; and the high-to-low order of soil moisture content Ⅲ under different ground mulching treatments was black film〉white film〉sawdust〉the control, and the highest value was higher than the lowest one by 26.61%.

Effects of Soil Moisture Content and p H on Residual Dynamics of Chlorothalonil in Acidified Soil

[Objective] This study aimed to investigate the residual dynamics of chlorothalonil in acidified soil under different conditions of soil moisture content and pH. [Method] By simulation tests, the effects of different soil moisture content and pH on chlorothalonil residues in acidified soil were analyzed. [Result] Under different conditions of soil moisture content and pH, the residual quantity of chlorothalonil in acidified soil was reduced gradually with the extension of incubation time. To be specific, the reduction rate of chlorothalonil residues in soil was extremely high within the first three days and slightly declined at 3-7 d; after 7 d, the residual quantity of chlorothalonil in soil was reduced slowly and steadily. [Conclusion] This study provides the reference for soil environmental remediation and maintenance of a health cultivation system.

Analysis on Variation of Soil Organic Carbon and Total Nitrogen Content and Carbon Storage in the Oasis Cotton Field of Manas River Valley

Objective] The research aimed to study soil organic carbon and total ni-trogen distribution in oasis cotton farmland. [Method] With the oasis cotton field of Manas River Val ey in Tianshan Mountains as the research area and abandoned farmland as a control, the distribution characteristics of soil organic carbon and total nitrogen content in the cotton field of Manas River Val ey in the last 23 years were investigated by using geographic methods. [Result] Presenting vertical distribution, cotton soil organic carbon and total nitrogen content in Manas River Val ey de-creased with the increase of soil depth, and those in 0-30 cm soil layer was sig-nificantly higher than those in soil layer of below 30 cm, while organic carbon stor-age showed the trend of increase. Also in vertical distribution, soil organic carbon and total nitrogen decreased significantly with the increase of soil depth, and soil organic carbon content in abandoned farmland decreased month by month. Howev-er, cotton soil organic carbon storage firstly decreased and then increased in the oasis cotton field that in the early growth of cotton, soil organic carbon in the layers of 0-30 and 30-100 cm decreased to the lowest in the bloom stage, and then or-ganic carbon increased with the reproductive growth of cotton into the later stages. However, due to no input of plant litter in the abandoned farmland, the soil organic carbon storage decreased month by month. There were significantly differences be-tween oasis cotton field and abandoned farmland in organic carbon contents. [Con-clusion] The soil organic carbon content and total nitrogen content in oasis cotton field were significantly higher than those in the abandoned farmland. The soil organ-ic carbon storage increased in the layer of 0-30 cm, while there was no significant change of soil organic carbon and total nitrogen content in the layer of 30-100 cm, which was consistent with the previous study on the distribution characteristics of soil organic carbon and total nitrogen content profile.

Real-time Monitoring Scheme of Soil Moisture Content in Paddy Field

The monitoring of soil moisture content in paddy field is one of important parts and contents of regional soil moisture monitoring. But a good monitoring scheme hasn’t been established. A real-time monitoring scheme of soil moisture content in paddy field was put forward from two key links of soil moisture content monitoring and field water-layer monitoring. This scheme could meet the alternative monitoring requirements of soil moisture content in water layer and none-water layer. It had a good maneuverability and could provide references for practical work.

Spatial variability of soil water content and related factors across the Hexi Corridor of China

Soil water content(SWC) is a key factor limiting ecosystem sustainability in arid and semi-arid areas of the Hexi Corridor of China, which is characterized by an ecological environment that is vulnerable to climate change. However, there is a knowledge gap regarding the large-scale spatial distribution of SWC in this region. The specific objectives of this study were to determine the spatial distribution patterns of SWC across the Hexi Corridor and identify the factors responsible for spatial variation of SWC at a regional scale. This study collected and analyzed SWC in the 0–100 cm soil profile from 109 field sampling sites(farmland, grassland and forestland) across the Hexi Corridor in 2017. We selected 17 factors, including land use, topography(latitude, longitude, elevation, slope gradient, and slope aspect), soil properties(soil clay content, soil silt content, soil bulk density, saturated hydraulic conductivity, field capacity, and soil organic carbon content), climate factors(mean annual precipitation, potential evaporation, and aridity index), plant characteristic(vegetation coverage) and planting pattern(irrigation or rain-fed), as possible environmental variables to analyze their effects on SWC. The results showed that SWC was 0.083(±0.067) g/g in the 0–100 cm soil profile and decreased in the order of farmland, grassland and forestland. The SWC in the upper soil layers(0–20, 20–40 and 40–60 cm) had obvious difference when the mean annual precipitation differed by 200 mm. The SWC decreased from southeast to northwest following the same pattern as precipitation, and had a moderate to strong spatial dependence in a large effective range(75–378 km). The SWC showed a similar distribution and had no significant difference between soil layers in the 0–100 cm soil profile. The principal component analysis showed that the mean annual precipitation, geographical position(longitude and latitude) and soil properties(soil bulk density and soil clay content) were the main factors dominating the variance of environmental variables. A stepwise linear regression equation showed that plant characteristic(vegetation coverage) and soil properties(soil organic carbon content, field capacity and soil clay content) were the optimal factors to predict the variation of SWC. Soil clay content could be better to explain the SWC variation in the deeper soil layers compared with the other factors.

Content and densities of soil organic carbon in urban soil in different function districts of Kaifeng

Urban soil, forming along with the development of city, has unique properties of soil organic carbon. On the basis of field investigation and laboratory analysis, soil organic carbon （SOC） of Kaifeng city was studied, and the results showed that the characteristics of SOC were different not only among function districts in urban area, but also between urban area and suburbs. The order of SOC in topsoil was industrial district 〉 recreational district 〉 traffic district 〉 cultural/educational district 〉 residential/administrative district. The density of soil organic carbon （SOCD） in both topsoil and profile followed the orders of recreational district 〉 industrial district 〉 traffic district〉cultural/educational district 〉 residential/adminis-trative district, and cultural/educational district 〉 traffic district〉industrial district〉recreational district 〉 administrative/residential district, respectively. SOCD in both topsoil and profile decreased along the transection line from urban area to suburbs and urban area had 2.53-fold more SOCD in topsoil and 1.56-fold more SOCD in profile than suburbs, respectively. SOC decreased with the depth and was mainly distributed within the scope of 0-30 cm. The variances of SOC in urban area were more complicated than that in suburbs.

Relationship Between Canopy Temperature at Flowering Stage and Soil Water Content,Yield Components in Rice

The canopy temperature of rice at the flowering stage and the soil water content were investigated under different soil water treatments （the soil water contents were 24%, 55%, 90% and 175% at the flowering stage）. The canopy temperature was lower than air temperature, and the soil water content significantly influenced the canopy temperature. The lower the soil water content, the higher the canopy temperature, the less the accumulative absolute value of canopy-air temperature difference. Moreover, the maximum difference between treatments and CK in the accumulative absolute value of canopy-air temperature difference appeared at 13：00 μm. in a day, thus, it could be considered as a suitable measuring time. Under the lowest water content treatment, the peak flowering occurred in the first three days （about 70% of panicles flowered）, resulting in shortened and lightened panicle of rice. As to the CK and the high water content treatments, the peak flowering appeared in the middle of flowering duration, with longer panicle length and higher panicle weight. Results indicated the lower the soil water content, the less the filled grain number and grain yield.

Film-mulched continuous ridge-furrow planting improves soil temperature,nutrient content and enzymatic activity in a winter oilseed rape field,Northwest China

Film mulching system is a widely employed agricultural practice worldwide. However, the effects of different planting and mulching patterns on soil nutrient content and enzymatic activity have not been well documented. In this study, we examined the impact of four planting and mulching patterns（including control, flat planting without mulching; M1, flat planting with film mulching; M2, ridge-furrow planting with film mulching on both ridges and furrows; and M3, ridge-furrow planting with film mulching on continuous ridges） on the seed yield of winter oilseed rape, soil moisture, soil temperature, soil organic carbon（SOC） content, soil nutrient content, and soil enzymatic activity over three growing seasons from 2012 to 2015 in a winter oilseed rape field in the semi-arid area of Northwest China. Seed yield of winter oilseed rape, soil moisture, soil temperature, enzymatic activities, and contents of nitrate-nitrogen, available phosphorus, and available potassium were all significantly higher in mulching treatments（M1, M2 and M3） than in control treatment over the three growing seasons, whereas SOC content was significantly lower in mulching treatments than in control treatment during 2013–2014 and 2014–2015. Among the three mulching treatments（M1, M2 and M3）, the M3 treatment showed consistently higher seed yield, SOC content, nutrient contents, and enzymatic activities than the other two treatments. Seed yield of winter oilseed rape was 41.1% and 15.0% higher in M3 than in M1 and M2, respectively. SOC content and soil enzymatic activities in the top 0–20 cm soil layers and nitrate-nitrogen content in the top 0–30 cm soil layers were all significantly higher in M3 than in M1 and M2. Therefore, we advise the ridge-furrow planting with film mulching on continuous ridges（i.e., M3） as an efficient planting and mulching pattern for sustainably improving the seed yield of winter oilseed rape and preserving soil fertility in the semi-arid area of Northwest China.

Yield and Nicotine Content of Flue-Cured Tobacco as Affected by Soil Nitrogen Mineralization

Nitrogen(N)supply is the most important factor affecting yield and quality of flue-cured tobacco(FCT).A field experiment and an in situ incubation method were used to study the effects of soil N mineralization in the later stages of growth on yield and nicotine content of FCT in Fenggang and Jinsha,Guizhou Province.The yield and market value of FCT at Fenggang were much lower than those at Jinsha.However,the nicotine content of middle and upper leaves was much higher at Fenggang than at Jinsha when the same rate of fertilizer N was applied,which might be due to a higher N supply capacity at the Fenggang site.At later stages of growth(7-16 weeks after transplanting),the soil net N mineralization at Fenggang(56 kg N ha^(-1))was almost double that at Jinsha(30 kg N ha^(-1)).While soil NH_4-N and NO_3-N were almost exhausted by the plants or leached 5 weeks after transplanting,the N taken up at the later growth stages at Fenggang were mainly derived from soil N mineralization,which contributed to a high nicotine content in the upper leaves.The order of soil N contribution to N buildup in different leaves was:upper leaves>middle leaves>lower leaves.Thus,soil N mineralization at late growth stages was an important factor affecting N accumulation and therefore the nicotine content in the upper leaves.