Experimental investigation into the salinity effect on the physicomechanical properties of carbonate saline soil

For engineering structures with saline soil as a filling material,such as channel slope,road subgrade,etc.,the rich soluble salt in the soil is an important potential factor affecting their safety performance.This study examines the Atterberg limits,shear strength,and compressibility of carbonate saline soil samples with different NaHCO3 contents in Northeast China.The mechanism underlying the influence of salt content on soil macroscopic properties was investigated based on a volumetric flask test,a mercury intrusion porosimetry(MIP)test,and a scanning electron microscopic(SEM)test.The results demonstrated that when NaHCO3 contents were lower than the threshold value of 1.5%,the bound water film adsorbed on the surface of clay particles thickened continuously,and correspondingly,the Atterberg limits and plasticity index increased rapidly as the increase of sodium ion content.Meanwhile,the bonding force between particles was weakened,the dispersion of large aggregates was enhanced,and the soil structure became looser.Macroscopically,the compressibility increased and the shear strength(mainly cohesion)decreased by 28.64%.However,when the NaHCO3 content exceeded the threshold value of 1.5%,the salt gradually approached solubility and filled the pores between particles in the form of crystals,resulting in a decrease in soil porosity.The cementation effect generated by salt crystals increased the bonding force between soil particles,leading to a decrease in plasticity index and an improvement in soil mechanical properties.Moreover,this work provides valuable suggestions and theoretical guidance for the scientific utilization of carbonate saline soil in backfill engineering projects.

Remote sensing of soil degradation:Pro gress andperspective

Soils constitute one of the most critical natural resources and maintaining their health is vital for agricultural development and ecological sustainability,providing many essential ecosystem services.Driven by climatic variations and anthropogenic activities,soil degradation has become a global issue that seriously threatens the ecological environment and food security.Remote sensing(RS)technologies have been widely used to investigate soil degradation as it is highly efficient,time-saving,and broad-scope.This review encompasses recent advances and the state-of-the-art of ground,proximal,and novel Rs techniques in soil degradation-related studies.We reviewed the RS-related indicators that could be used for monitoring soil degradation-related properties.The direct indicators(mineral composition,organic matter,surface roughness,and moisture content of soil)and indirect proxies(vegetation condition and land use/land cover change)for evaluating soil degradation were comprehensively summarized.The results suggest that these above indicators are effective for monitoring soil degradation,however,no indicators system has been established for soil degradation monitoring to date.We also discussed the RS's mechanisms,data,and methods for identifying specific soil degradation-related phenomena(e.g.,soil erosion,salinization,desertification,and contamination).We investigated the potential relations between soil degradation and Sustainable Development Goals(SDGs)and also discussed the challenges and prospective use of RS for assessing soil degradation.To further advance and optimize technology,analysis and retrieval methods,we identify critical future research needs and directions:(1)multi-scale analysis of soil degradation;(2)availability of RS data;(3)soil degradation process modelling and prediction;(4)shared soil degradation dataset;(5)decision support systems;and(6)rehabilitation of degraded soil resource and the contribution of RS technology.Because it is difficult to monitor or measure all soil properties in the large scale,remotely sensed characterization of soil properties related to soil degradation is particularly important.Although it is not a silver bullet,RS provides unique benefits for soil degradation-related studies from regional to global scales.

Effects of reclaimed water irrigation and nitrogen fertilization on the chemical properties and microbial community of soil

The ecological effect of reclaimed water irrigation and fertilizer application on the soil environment is receiving more attention.Soil microbial activity and nitrogen（N）levels are important indicators of the effect of reclaimed water irrigation on environment.This study evaluated soil physicochemical properties and microbial community structure in soils irrigated with reclaimed water and receiving varied amounts of N fertilizer.The results indicated that the reclaimed water irrigation increased soil electrical conductivity（EC）and soil water content（SWC）.The N treatment has highly significant effect on the ACE,Chao,Shannon（H）and Coverage indices.Based on a 16S ribosomal RNA（16S rRNA）sequence analysis,the Proteobacteria,Gemmatimonadetes and Bacteroidetes were more abundant in soil irrigated with reclaimed water than in soil irrigated with clean water.Stronger clustering of microbial communities using either clean or reclaimed water for irrigation indicated that the type of irrigation water may have a greater influence on the structure of soil microbial community than N fertilizer treatment.Based on a canonical correspondence analysis（CCA）between the species of soil microbes and the chemical properties of the soil,which indicated that nitrate N（NO3-–-N）and total phosphorus（TP）had significant impact on abundance of Verrucomicrobia and Gemmatimonadetes,meanwhile the p H and organic matter（OM）had impact on abundance of Firmicutes and Actinobacteria significantly.It was beneficial to the improvement of soil bacterial activity and fertility under 120 mg kg^-1 N with reclaimed water irrigation.

Influence of tourist disturbance on soil properties, plant communities, and surface water quality in the Tianchi scenic area of Xinjiang, China

The impact of tourist disturbance on the environment has become a focal issue of environmental science, ecology, and travel management studies. To assess the influence of tourist disturbance on soils and plants in the Tianchi scenic area of Xinjiang, China, we compared soil properties and plant community characteristics at 0, 5, 10, and 20 m from the tourist trail within areas at three different altitudes, where the intensities of tourist disturbance are distinct. Surface water quality was also studied at three different levels relative to the Tianchi Lake. The results showed that tourist disturbance significantly increased soil pH within 10 m from the trail and soil bulk density on the edge of the trail, but significantly reduced soil organic matter and total nitrogen contents within 5 m from the trail. The number of tree seedlings on the edge of the trail and the shrub coverage and height of herbaceous plants within 5 m from the trail significantly decreased due to tourist disturbance. Changes in herbaceous plant diversity differed by soil zones. In the high altitude region, tourist disturbance led to a remarkable increase in the herbaceous plant diversity on the edge of the trail, while in the low altitude region, tourist disturbance had a low impact on the diversity of herbaceous plants. In addition, tourist activities polluted the surface water, significantly reducing water quality. Thus, current tourist activities have a significant negative impact on the ecological environment in the Tianchi scenic area.

The Response of Vegetation Biomass to Soil Properties along Degradation Gradients of Alpine Meadow at Zoige Plateau

Alpine grassland of the Tibetan Plateau has undergone severe degradation, even desertification. However, several questions remain to be answered, especially the response mechanisms of vegetation biomass to soil properties. In this study, an experiment on degradation gradients was conducted in an alpine meadow at the Zoige Plateau in 2017. Both vegetation characteristics and soil properties were observed during the peak season of plant growth. The classification and regression tree model(CART) and structural equation modelling(SEM) were applied to screen the main factors that govern the vegetation dynamics and explore the interaction of these screened factors. Both aboveground biomass(AGB) and belowground biomass(BGB) experienced a remarkable decrease along the degradation gradients. All soil properties experienced significant variations along the degradation gradients at the 0.05 significance level. Soil physical and chemical properties explained 54.78% of the variation in vegetation biomass along the degradation gradients. AGB was mainly influenced by soil water content(SWC), soil bulk density(SBD), soil organic carbon(SOC), soil total nitrogen(STN), and pH. Soil available nitrogen(SAN), SOC and p H, had significant influence on BGB. Most soil properties had positive effects on AGB and BGB, while SBD and p H had a slightly negative effect on AGB and BGB. The correlations of SWC with AGB and BGB were relatively less significant than those of other soil properties. Our results highlighted that the soil properties played important roles in regulating vegetation dynamics along the degradation gradients and that SWC is not the main factor limiting plant growth in the humid Zoige region. Our results can provide guidance for the restoration and improvement of degraded alpine grasslands on the Tibetan Plateau.

Re-Examining Field-Surveyed Variations in Elevation and Soil Properties with a 1-m Resolution LiDAR-Generated DEM

This article presents a 2017 LiDAR-DEM guided 1-m resolution examination of field-surveyed elevation and soil property variations (5 × 5 m spacings) conducted in 1977 across a hummocky New Brunswick field used for potato production. This examination revealed that the field incurred minor elevation differences likely due to upslope erosion as revealed through increasing Sand % and CF % with increasing elevation, and increasing Silt % along low-lying areas. Soil moisture, field capacity, permanent wilting and nitrate nitrogen (NO3-N) also increased at downslope locations. Directly as well as indirectly, soil pH, ammonium nitrogen (NH4-N), Caesium137 (Cs137) and Mehlich-3 extracted Ca, Mg, K, Fe, Mn, Cu, and Zn were likewise affected by topographic location. Factor analyzing these variables led to: 1) a Soil Loss Factor that captured 24% of the textural variations;2) a Soil-Cropping Factor accounting for 16% of the N, P, K, Ca, Mg, Mn variations;3) a Soil Organic Matter (SOM) Factor relating 9% of the in-field variations for SOM, Fe, Zn, Cu to via organo-metal complexation and low NO3-N retention. Many of the topographic variations increased or decreased with the metric DEM-projected depth-to-water index (DTW) index. This index was set to 0 along DEM-derived flow channels with minimum upslope flow-accumulation areas of 0.1, 0.25, 0.5, 1 or 4 ha. Among these, the DTW > 4 ha threshold was useful for reproducing the textural variations, while the DTW > 0.25 ha threshold assisted in capturing trends pertaining to moisture retention and elemental concentrations.

Tillage and Rice-Wheat Cropping Sequence Influences on Some Soil Physical Properties and Wheat Yield under Water Deficit Conditions

Adopting a better tillage system not only improves the soil health and crop productivity but also improves the environment. A field experiment was conducted to investigate the effects of tillage and irrigation management on wheat (Triticum aestivum L.) production in a post-rice (Oryza sativa L.) management system on silty clay loam soil (acidic Alfisol) for 2003-2006. Four irrigation levels (RF: rainfed;I1: irrigation at crown root initiation (CRI);I2: irrigation at CRI + flowering;I3: irrigation at CRI + tillering + flowering), and two tillage systems (ZT: zero tillage and CT: conventional tillage) were tested. Zero tillage compared to CT, resulted in higher bulk density (1.34 vs 1.23 Mg –3), lower total porosity (48.7 vs 52.9%), higher penetration resistance (1.51 vs 1.37 MPa), lower saturated hydraulic conductivity (1.60 vs 92.0 mm h–1), lower infiltration rate (9.40 vs 36.6 mm h–1) and higher volumetric available water capacity (7.9 vs 7.5%) in the surface 0.15 m soil layer. Irrigation levels significantly affected crop water use, wheat yield, and water use efficiency (WUE). Average total water use was 461, 491, 534 and 580 mm under RF, I1, I2 and I3 treatments, respectively. Grain and straw yield of wheat were statistically the same under ZT and CT during 2003-2004;the values, averaged over four irrigation levels were 2.10 and 2.38 Mg a–1 for grain, and 3.46 and 3.67 Mg a–1 for straw, respectively. Grain yield declined by 22%, 11% and 8% of I3 (2.32 Mg ha–1) with RF, I1 and I2 treatments, respectively, under ZT;and by 13%, 8% and 5% of I3 (2.61 Mg ha–1) with RF, I1 and I2 treatments under CT. Average values of WUE were 4.33 kg ha–1 m–1 and 2.35 m3–1 grain for the ZT and CT treatments. Wheat yield increased with increased irrigation levels for all the cropping seasons. Results from this study concluded that ZT system was better compared to the CT system even with lower yields due to lower input costs for this treatment.

Impact of Short Term Irrigation with Different Water Types on Some Chemical and Physical Soil Properties

The concern of this study is determine the quality of soil when irrigation used treated water and wastewater in comparison with soil irrigated with tap water on some chemical and physical soil properties. The experiment components were three trials carried out under greenhouse conditions, 10 pots for each trial. The first trial irrigated with tap water, the second trial irrigated by treated water and the third trial irrigated with wastewater. The experiment conducted to study the impact of water types on some soil physical and chemical properties. The experiment included important analysis for water and soil before and after irrigation. The results showed that the values for electrical conductivity (EC) were 0.850, 308 and 324 μs/cm for the treated soil with tap water, treated water and wastewater, respectively. The variation of pH values seems to be approximately constant between the different of water used. The percent of organic matter (OM) in soils receiving treated water and wastewater 4.7% and 5.2% respectively were higher than values in soil treated with tap water 3%. The same trend was in organic carbon (OC) in soils receiving treated water and wastewater 58.5% and 89% respectively, while soil treated with tap water showed the lowest value 27.7%. Soil particle density (SPD) increased significantly in both water treatments were the values was 2 g/cm3 in tap water but increased value 2.8 g/cm3 and 3.3 g/cm3 in treated water and wastewater used respectively. The Bulk Density (BD) values range 1.1 g/cm3 in soil irrigated with tap water 1.5 g/cm3 in soil irrigated with treated water and 1.85 g/cm3 in soil irrigated with treated water. The results of soil analysis before and after planting showed that most of the values increased for the physical and chemical soil properties.

Structure of Vegetables Farming and Farmer’s Perception of Soil and Water Degradation in Two Periurban Areas in Yaounde Cameroon

Vegetable farming is an activity sensitive to the dynamism of the population and to the level of intensification in the use of soil resources. A study was conducted in the peri-urban zones of Yaoundé to present the socioeconomic characteristics of vegetable farming and the farmers’ perception of soil and water degradation as a result of this activity. A semi-structured questionnaire was administered to this purpose in 2016 in two vegetable farming sites in Yaoundé, namely Nkolbisson and Nkolondom III. Results showed that most vegetable farmers from both sites (around 75%) lack training in agriculture while 74 and 90 didn’t benefit from training on management of pesticides. Spreading and landfilling of amendments are the two most popular ways of applying fertilizers. In fact, while the majority (35.4%) of these fertilizers is applied at planting time, the minority (4.9%) is applied several months before planting. Besides young plots are more exploited (52.4% and 30%) compared to older ones (2.4% and 5%) in Nkolondom III and Nkolbisson respectively, as they are more responsive to fertilizer application. As consequence, high rates of fertilizers are applied to the oldest farms. As for irrigation water, it is altogether polluted. Base on the above, the farmers’ perception of degradation is seen through the degradation of soils properties with time in the order of 14.3% to 60% and 15% to 44% at Nkolbisson and Nkolondom III respectively resulting in a gradual decrease of crop production (up to 50%). It is also seen through the polluted produce obtained from irrigation and cleaning water.

The Effect of Land Use Change on Soil and Water Quality in Northern Iran

Rapid urbanization has led to extensive land-use changes,particularly in developing countries.This research is aimed to investigate the role of land use and its effect on soil and water quality in Ziarat watershed focusing on four land uses:forest,pasture,cultivated and urban development.Soil samples were taken from a depth of 0-30 cm on each land use and were analyzed by completely randomized split-plot design in two geographical directions.Results showed that bulk density(BD),electrical conductivity(EC),pH,calcium carbonate equivalent(CCE),and soil particle density(DS) of the soil samples in pastures,cultivated and urban areas increased and the mean weight diameter(MWD),soil porosity(F),organic carbons(OC),total nitrogen(TN),exchangeable cations(Ca 2+,Mg 2+,K +,Na +),cation exchange capacity(CEC) and soil microbial respirations(SMR) decreased,respectively in comparison with the forest soils.For water quality evaluations,sodium adsorption ratio(SAR),electrical conductivity(EC),pH,total dissolved solids(TDS),bicarbonate(HCO 3),chloride(Cl),total hardness(TH),calcium(Ca 2+),potassium(K +),sodium(Na +) and magnesium(Mg 2+) were investigated in two areas:Nahrkhoran and Abgir stations.Results showed that the concentration of TDS,EC and HCO 3 in Naharkhoran station is higher than that in Abgir station.On the other hand,the concentration of TDS,EC and HCO 3 in Abgir station are the relatively higher due to its location.Total hardness had the same trend during the study years except in the last three years;however,TH showed an increase of 25% TH in Naharkhoran for the last two years.Cl,K + and SAR in Naharkhoran station increased by 61%,22%,78% and 56% respectively,in comparison with Abgir station.This study demonstrated that the trend of soil degradation and mismanagement of land use may increase the frequency of urban floods and human health problems.

Effect of vegetation on soil water retention and storage in a semi-arid alpine forest catchment

The runoff generated from mountainous regions is recognized as the main water source for inland river basins in arid environments. Thus, the mechanisms by which catchments retain water in soils are to be understood. The water storage capacity of soil depends on its depth and capacity to retain water under gravita- tional drainage and evapotranspiration. The latter can be studied through soil water retention curve （SWRC）, which is closely related to soil properties such as texture, bulk density, porosity, soil organic carbon conteMt, and so on. The present study represented SWRCs using HYDRUS-1D. In the present study, we measured pl^ysical and hydraulic properties of soil samples collected from Sabina przewalskii forest （south-facing slope with highest solar radiation）, shrubs （west-facing slope with medium radiation）, and Picea crassifolia forest （north-facing slope with lowest radiation）, and analyzed the differences in soil water storage capacity of these soil samples. Soil water content of those three vegetation covers were also measured to validate the soil water storage capacity and to analyze the relationship between soil organic matter content and soil water content. Statistical analysis showed that different vegetation covers could lead to different soil bulk densities and differences in soil water retention on the three slope aspects. Sand content, porosity, and organic carbon content of the P. crassifolia forest were rela- tively greater compared with those of the S. przewalskii forest and shrubs. However, silt content and soil bulk density were relatively smaller than those in the S. przewalskii forest and shrubs. In addition, there was a sig- nificant linear positive relationship between averaged soil water content and soil organic matter content （P〈0.0001）. However, this relationship is not significant in the P. crassifolia forest. As depicted in the SWRCs, the water storage capacity of the soil was 39.14% and 37.38% higher in the P. crassifolia forest than in the S. przewalskii forest and shrubs, respectively, at a similar soil depth.

Prediction of soil–water characteristic curve for Malan loess in Loess Plateau of China

To predict the soil-water characteristic curve(i.e.SWCC)of natural and remoulded Malan loess from soil physical properties,one-point methods for determining the SWCC that are much simpler than experimental methods are proposed.The predicted SWCC is presented in the form of the BRUTSAERT equation,in which the four model parameters can be estimated from soil physical properties using the best correlations obtained in the present study along with one measured data point.The proposed one-point methods are validated using the measured SWCC data reported in the literature.The results of validation studies suggest that the proposed one-point methods can provide reasonable prediction of the SWCC for natural and remoulded Malan loess.The measured data point should be within the transition zone;the measured suction is suggested between25to100kPa for natural loess,while between100to500kPa for remoulded loess.

Relationship Between Soil and Water Conservation Practices and Soil Conditions in Low Mountain and Hilly Region of Northeast China

The soil and water conservation practices of ecological restoration(ER),fish scale pit(FP),furrow and ridge tillage across the slope(FR),shrub strips(SS),and vegetation-covered ridge(VR)are characteristic of the Jixing small watershed of the low mountain and hilly region of Jilin Province,Northeast China.This study aims to elucidate the effects of soil and water conservation practices on soil conditions after the short-term implementation of practices.Soil samples were collected from five soil and water conservation sites(ER,FP,FR,SS,and VR)and two controls(BL and CT)to investigate their properties.To evaluate the influence of soil and water conservation practices on soil quality,an integrated quantitative index,soil quality index(QI),was developed to compare the soil quality under the different soil and water conservation practices.The results show that not all soil and water conservation practices can improve the soil conditions and not all soil properties,especially soil organic carbon(SOC),can be recovered under soil and water conservation practice in short-term.Moreover,the QI in the five soil and water conservation practices and two controls was in the following order:ER>VR>BL>FR>CT>SS>FP.ER exhibited a higher soil quality value on a slope scale.In the low mountain and hilly region of Northeast China,ER is a better choice than the conversion of farmlands to planted grasslands and woodlands early in the soil and water conservation program.

Degradation leads to dramatic decrease in topsoil but not subsoil root biomass in an alpine meadow on the Tibetan Plateau, China

Understanding the effects of degradation on belowground biomass(BGB)is essential for assessment of carbon budget of the alpine meadow ecosystem on the Tibetan Plateau,China.This ecosystem has been undergoing serious degradation owing to climate change and anthropogenic activities.This study examined the response of the vertical distribution of plant BGB to degradation and explored the underlying mechanisms in an alpine meadow on the Tibetan Plateau.A field survey was conducted in an alpine meadow with seven sequential degrees of degradation in the Zoige Plateau on the Tibetan Plateau during the peak growing season of 2018.We measured aboveground biomass(AGB),BGB,soil water content(SWC),soil bulk density(SBD),soil compaction(SCOM),soil organic carbon(SOC),soil total nitrogen(STN),soil total phosphorus(STP),soil available nitrogen(SAN),and soil available phosphorus(STP)in the 0-30 cm soil layers.Our results show that degradation dramatically decreased the BGB in the 0-10 cm soil layer(BGB0-10)but slightly increased the subsoil BGB.The main reason may be that the physical-chemical properties of surface soil were more sensitive to degradation than those of subsoil,as indicated by the remarked positive associations of the trade-off value of BGB0-10 with SWC,SCOM,SOC,STN,SAN,and STP,as well as the negative correlation between the trade-off value of BGB0-10 and SBD in the soil layer of 0-10 cm.In addition,an increase in the proportion of forbs with increasing degradation degree directly affected the BGB vertical distribution.The findings suggest that the decrease in the trade-off value of BGB0-10 in response to degradation might be an adaptive strategy for the degradation-induced drought and infertile soil conditions.This study can provide theoretical support for assessing the effects of degradation on the carbon budget and sustainable development in the alpine meadow ecosystem on the Tibetan Plateau as well as other similar ecosystems in the world.

Effects of degradation succession of alpine wetland on soil organic carbon and total nitrogen in the Yellow River source zone,west China

Wetland is an important carbon pool,and the degradation of wetlands causes the loss of organic carbon and total nitrogen.This study aims to explore how wetland degradation succession affects soil organic carbon(SOC)and total nitrogen(TN)contents in alpine wetland.A field survey of 180 soilsampling profiles was conducted in an alpine wetland that has been classified into three degradation succession stages.The SOC and TN contents of soil layers from 0 to 200 cm depth were studied,including their distribution characteristics and the relationship between microtopography.The results showed that SOC and TN of different degradation succession gradients followed the ranked order of Non Degradation(ND)>Light Degradation(LD)>Heavy Degradation(HD).SWC was positively correlated with SOC and TN(p<0.05).As the degree of degradation succession worsened,SOC and TN became more sensitive to the SWC.Microtopography was closely related to the degree of wetland degradation succession,SWC,SOC and TN,especially in the topsoil(0-30 cm).This result showed that SWC was an important indicator of SOC/TN in alpine wetland.It is highly recommended to strengthen water injection into the wetland as a means of effective restoration to reverse alpine meadow back to marsh alpine wetland.

Unraveling the hydraulic properties of loess for landslide prediction:A study on variations in loess landslides in Lanzhou,Dingxi,and Tianshui,China

Loess has distinctive characteristics,leading to frequent landslide disasters and posing serious threats to the lives and properties of local re sidents.The involvement of water repre sents a critical factor in inducing loess landslides.This study focuses on three neighboring cities sequentially situated on the Loess Plateau along the direction of aeolian deposition of loess,namely Lanzhou,Dingxi,and Tianshui,which are densely populated and prone to landslide disasters.The variations in hydraulic properties,including water retention capacity and permeability,are investigated through Soil Water Characteristic Curve(SWCC)test and hydraulic conductivity test.The experimental findings revealed that Tianshui loess exhibited the highest water retention capacity,followed by Dingxi loess,while Lanzhou loess demonstrated the lowest water retention capacity.Contrastingly,the results for the saturated permeability coefficient were found to be the opposite:Tianshui loess showed the lowest permeability,whereas Lanzhou loess displayed the highest permeability.These results are supported and analyzed by scanning electron microscopy(SEM)observation.In addition,the water retention capacity is mathematically expressed using the van Genuchten model and extended to predict unsaturated hydraulic properties of loess.The experimental results exhibit a strong accordance with one another and align with the regional distribution patterns of disasters.

Variation of soil organic carbon and bulk density during afforestation regulates soil hydraulic properties

Grain to Green program on arable land has been conducted for decades in semi-arid regions of North China.However,it remains uncertain how afforestation practices affect soil hydraulic properties(SHP).Two afforestation types,i.e.shrubland(SL)and woodland(WL),and the adjacent cropland(CL)were investigated to determine afforestation effects on SHP in this area.Disturbed and undisturbed soil cores were collected in three experimental sites.Soil field capacity(FC),wilting point(WP),and available water capacity(AWC)increased in SL compared to the CL.Soil saturated water content,however,decreased significantly in both SL and WL.Correlation and redundancy analysis identified that bulk density(BD)and soil organic carbon(SOC)were the main factors regulating SHP across different land uses.Lower saturated water contents in afforestation sites were likely driven by the higher BD,compared to the adjacent cropland.FC,WP,and AWC were positively correlated to SOC content.While afforestation may not increase the saturated water content of a landscape,our results indicate that it can improve soil water retention and could be an effective practice for soil and water conservation.

Effects of Carboxymethylcelluloses (CMC) on Some Hydraulic Properties of Sandy Soil

The property of hydrophilic polymers capable absorbing huge volumes of water led to many practical applications of these new materials in arid regions for improving the water retention in sandy soils. Effects of four carboxymethylcelluloses （CMC） mixed at various rates with the sandy soil, on the water-holding capacity and hydraulic conductivity （Ks） when leached with distilled water （simulating rain）, tap water, and saline water were evaluated. The maximum water absorption of CMCs ranged between 80 and 100 kg. kg^-1 of polymer; however, the absorbent swelling capacity decreased significantly with increasing the salt concentration in the solution. The water absorption capacity of CMCs decreased significantly when incorporated in the sandy soil compared to that of the absorbent alone. Application of CMC increased significantly the available water content up to 3 ± 0.5 times. All soils treated with CMCs showed a significant lower in Ks compared to the control soil. Meanwhile, Ks was found increased with increasing the salt concentration in the leaching solution. This understanding of characteristics of the absorbents and the interactions among absorbents, soil, and irrigation water quality would be of help in water management of sandy soil

Suitability of Soil Water Retention Characteristic Models (SWRC) in Regions and Soil Depth

Soil Water Retention Characteristics (SWRC) models have been widely used in many applications. Presently, there are many models in the literature and many more still being developed so much so that it is confusing which model to prefer. The current choice of the appropriate model to use has not been well guided by any incisive research on the predictive performance of these models. Consequently, SWRC model applications have been largely moved by convenience. This study used a global dataset to evaluate 12 commonly used SWRC models. The measured data onto which the models were evaluated was grouped into different soil depths and different regions of the world. The evaluation used correlation, Nash-Sutcliffe efficiency, and residual standard error statistics to choose the best overall performing model and models for each category. It gives an indication of the type of SWRC models to use in different regions of the world and depths of sampling. The suitability of the models to regions showed that the Fredlund and Xing model had the best performance in subsoils in Africa;Omuto in Southern Asia;and van Genuchten in subsoils of the other regions. It is recommended that many more models be tested using the procedures in this study so that benchmarks can be established on SWRC model selection suitable for various regions.

Effects of Spatial Information of Soil Physical Properties on Hydrological Modeling Based on a Distributed Hydrological Model

The spatial distribution of soil physical properties is essential for modeling and understanding hydrological processes. In this study, the different spatial information (the conventional soil types map-based spatial information (STMB) versus refined spatial information map (RSIM)) of soil physical properties, including field capacity, soil porosity and saturated hydraulic conductivity are used respectively as input data for Water Flow Model for Lake Catchment (WATLAC) to determine their effectiveness in simulating hydrological processes and to expound the effects on model performance in terms of estimating groundwater recharge, soil evaporation, runoff generation as well as partitioning of surface and subsurface water flow. The results show that: 1) the simulated stream flow hydrographs based on the STMB and RSIM soil data reproduce the observed hydrographs well. There is no significant increase in model accuracy as more precise soil physical properties information being used, but WATLAC model using the RSIM soil data could predict more runoff volume and reduce the relative runoff depth errors; 2) the groundwater recharges have a consistent trend for both cases, while the STMB soil data tend to produce higher groundwater recharges than the RSIM soil data. In addition, the spatial distribution of annual groundwater recharge is significantly affected by the spatial distribution of soil physical properties; 3) the soil evaporation simulated using the STMB and RSIM soil data are similar to each other, and the spatial distribution patterns are also insensitive to the spatial information of soil physical properties; and 4) although the different spatial information of soil physical properties does not cause apparent difference in overall stream flow, the partitioning of surface and subsurface water flow is distinct. The implications of this study are that the refined spatial information of soil physical properties does not necessarily contribute to a more accurate prediction of stream flow, and the selection of appropriate soil physical property data needs to consider the scale of watersheds and the level of accuracy required.