Silty Clay Soil Research Articles

EVALUATION OF SOAKED AND UNSOAKED CBR VALUES OF SOIL BASED ON THE COMPACTION CHARACTERISTICS

Subgrade of a pavement should be strong enough to give adequate support to the pavement and for supporting and distributing the wheel loads. The design and behaviour of a flexible pavement depends mainly on the stability of the subgrade soil, which can be increased by compacting the soil at optimum moisture content (OMC) thus achieving maximum dry density (MDD). In this study, Modified Proctor Compaction Test (MPCT) was conducted by giving 5 different number of blows per layer so as to establish a relationship of compaction energy with OMC & MDD. Also, OMC and MDD are one of the most important parameters influencing California Bearing Ratio (CBR) test. CBR is a penetration test used for evaluating the mechanical strength of subgrade soil and for determining the thickness of the pavement required. Determination of soaked and unsoaked CBR value for a soil is time consuming and a laborious process. Hence in this paper an attempt has been made to arrive at regression equations to correlate soaked and unsoaked CBR values for the silty clay (CL) soil with the compaction characteristics, so that based on OMC and MDD, CBR value of soil can be predicted thus avoiding the time consuming process of conducting CBR tests. The soil sample used in this project was a disturbed sample collected from Thiruporur District in Chennai.

Arsenic Retention on Technosols Prepared with Nanoparticles and Ferric Soil from Mine Drainage Water

Mining activities generate a large amount of solid waste and acid drains that contain heavy metals in high concentrations. In wastewater of gold mines from Southern Ecuador (Portovelo), arsenic concentrations between 4.8 and 27.5 μg/L have been detected. In this context, the objective of this study is to prepare a technosol, which was used in the capture of arsenic dissolved in the acid drains. Technosol was elaborated using a clay-silty soil (iron-rich soil), collected in the mining area, and iron nanoparticles synthetized with the extract of orange peel. The technosol was experimentally characterized using adsorption isotherms and uptake kinetics. Besides, a mathematical model was developed using Vensim® to scale the process and predict the dynamic behavior of the adsorbent. Results indicate that adsorption behavior of technosol can be fitted to Langmuir isotherms (R2 > 0.9), with 95% of adsorption of As from an input of 4.5 mg/L. The model will be useful to predict the time needed to remedy contaminated water and the duration of the adsorbent (until its saturation).

Effect of biochar application method on nitrogen leaching and hydraulic conductivity in a silty clay soil

Biochar is anticipated to be an effective option for mitigating nitrogen (N) leaching and improving the hydraulic characteristics of soil, particularly sandy soil. However, little attention has been paid to understanding the effect of biochar on N leaching and hydraulic conductivity (K) in fine-textured soil. Additionally, whether different biochar application methods have different effects on N leaching and K remains unclear. Therefore, our objective in this study is to determine the effects of biochar with different application methods on nitrate/ammonium leaching and K in silty clay soil. The three biochar application patterns were as follows: A, biochar was mixed into 0–10 cm of surface soil; B, biochar was mixed into 10–20 cm of subsurface soil; and C, biochar was mixed evenly into 0–20 cm of plow layer soil. In addition, biochar was added at three rates, namely, 1%, 2% and 4% (mass ratios), and a soil column without biochar addition served as the control (CK). Our results demonstrated that the choice of biochar application method significantly influenced N leaching and soil K and balance between the soil K and N leaching, particularly for nitrate. Additionally, the leaching of N in silty clay soil occurred mainly in nitrate form. Compared with the CK, all 1% biochar treatments increased nitrate leaching (except C1%, which showed no differences from the CK) and tended to decrease K. However, all 4% biochar treatments increased nitrate leaching due to a high K. All 2% biochar treatments significantly reduced nitrate leaching by 8.3–17.0%, and B2% significantly increased the saturated hydraulic conductivity (Ksat) of soil by 20.9%. Hence, the mixing of biochar at a rate of 2% into the subsurface soil effectively mitigated N leaching and increased K in silty clay soil. These findings could have some implications for the field application of biochar. For instance, the combination of subsurface biochar application with that of fertilizer to roots in orchards or with deep tillage in fields, which would mimic the B2% model, would yield multiple benefits, including lower costs.

Sunflower response to Boron supply when grown in a silty clay soil

Abstract The objective of this study is to identify the requirements and the response of sunflower to boron (B) supply when grown in a silty caly soil. Two native soils B contents have been prospected. The soil “1” contains 0.66 mg kg−1 of B and soil “2” contains 0.19 mg kg−1 of B (Hot water extraction). For soil “1”, six levels of B supply (0, 2, 5, 10, 15 and 20 mg kg−1) were tested during 2015 season. For soil “2”, six B rates (0, 0.2, 0.5, 1, 5 and 10 mg kg−1) were tested during 2016 season. B was applied in the sodium form (Na2B8O13·4H2O). The experiments were conducted in containers. The results showed the absence of B symptoms deficiency on sunflower grown in the both studied soils. The kernels B content at harvest was around 20 mg kg−1 for all B rates. The kernels yield components (Kernels dry weight, 1000 kernels weight and number of kernels per head) and the contents of kernels on oil and on protein did not show any enhancement with B application. However, B supply higher than or equal to 5 mg kg−1 and 10 mg kg−1 in soil “1” and in soil “2”, respectively, induced phytotoxicity symptoms without affecting growth, biomass and oil production.

Effects of tillage and liming on macropore networks derived from X‐ray tomography images of a silty clay soil

AbstractSoil structure influences water infiltration, aeration and root growth and, thereby, also the conditions for sustainable crop production. Our objective was to quantify the effects of different soil management methods and land uses on the topsoil structure of a silty clay soil. We sampled 32 intact soil columns (18 cm high, 12.7 cm diameter) from an experimental silty clay field with four treatments: conventional tillage (CT), conventional tillage followed by liming (CTL), reduced tillage (RT) and unfertilized fallow (UF). The columns were analysed using 3‐D X‐ray tomography. The samples were taken in autumn after harvest, 7 yr after quick lime was applied to the CTL plots. Despite a relatively large number of replicates per treatment (8, 8, 8 and 6 (two UF samples were excluded), respectively), there were no significant differences between any of the investigated macropore network properties related to tilled treatments. The UF treatment, in contrast, exhibited more vertically oriented macropores, which were also better connected compared to the other treatments. This confirms previous findings that tillage may disrupt the vertical continuity of macropore clusters. The impact of liming on soil pore network properties may have been limited to pores smaller than the resolution in our X‐ray images. It is also possible that the effects of lime on soil structure were limited to a few years which means that any effect would have diminished by the time of this study. These matters should be further investigated in follow‐up studies to understand better the potential of lime amendments to clay soil.

Modeled climate change impacts on subirrigated maize relative yield in northwest Ohio

Subirrigation is employed to supply water to crop root zones via subsurface drainage systems, which are typically installed for the purpose of excess soil water removal. Crop yield increases due to subirrigation have been demonstrated in numerous studies, but there is limited information regarding yield under future climate conditions when growing season conditions are expected to be drier in the U.S. Corn Belt. DRAINMOD was calibrated and validated for three locations with different soil series in northwest Ohio and used to investigate maize relative yield differences between subirrigation and free subsurface drainage for historic (1984–2013) and future (2041–2070) climate conditions. For historic conditions, the mean maize relative yield increased by 27% with subirrigation on the Nappanee loam soil, but had minimal effect on the Paulding clay and Hoytville silty clay soils. Maize relative yield under free subsurface drainage is predicted to decrease in the future, causing the relative yield difference between free subsurface drainage and subirrigation practices to nearly double from 9% to 16% between the historic and future periods. Consequently, the subirrigation practice can potentially mitigate adverse future climate change impacts on maize yield in northwest Ohio.

Maize productivity, heavy metals uptake and their availability in contaminated clay and sandy alkaline soils as affected by inorganic and organic amendments

Contamination of arid and semi-arid ecosystems by toxic heavy metals is a serious concern due to its impact on growth and productivity of crop and health risk through food chain. Therefore, the aims of this investigation were to study the impact of inorganic (i.e. nano hydroxyapatite, NHA and polyacrylamide, PAM) and organic (i.e. sugar beet factory lime, SBFL and biochar, BI) soil amendments on maize productivity grown in contaminated silty clay (i.e. fluvial, lacustrine) and sandy (i.e. marine) alkaline soils. In addition, the effect of those amendments on the content of heavy metals in plant organs and their fractions in alkaline soils at harvest as well as human health risk assessment were investigated. Application of amendments, particularly SBFL, followed by NHA and BI resulted in an improvement for maize growth and its productivity in comparison to PAM application and untreated soil. However, application of NHA significantly reduced the mobile fraction of Cd, Pb and Ni in soil and consequently in different maize organs, followed by application of SBFL and BI in comparison to untreated soil or soil treated with PAM. Additionally, transfer factors and health risk of metals were lesser when NHA and SBFL were applied into soil than those obtained from application of PAM. In conclusion, applications of NHA, SBFL and BI into contaminated alkaline soils with toxic heavy metals can be considered a vital option for ameliorating such soils from the view of environment and sustainable management in terms of heavy metals immobilization and reducing the metals content in plant organs.

A Study of Some Physical Properties of Two Different Soil Textures Planted with Conocarpus Trees (Conocarpuslancifolius. Engl)


 
 
 
 This research has been conducted to study the effect of Conocarpus trees and their roots on some of soilphysical properties. The soil physical properties are moisture content , bulk density , total porosity , mean weight diameter (dry sieveing) and soil penetration resistance . Some soil samples are collected from two locations :the first location is Agric. College research, Garmat Ali, stations , Basra university , and the second location isZuwber province farm . The soil texture of the first location is silty clay which is classified as fine clay mixed Calcarioushy perthermictypictorrifluvent, while the soil texture of the second location is sandy loam. This soil is classified with in species Entisol and under species psamments and high group , underhigh group and family (Typictorripsamments, Calcarious Mixed Hyperthermic). The soil samples are collected from two soil depths( 0 – 30 and 30 – 60) from both locations are planted with Conocarpus trees, their ages ranged between 4 to 5 years . The trees height is 2.5 – 3.0 m . Another soil samples are also collected from unplanted soil with Conocarpus trees. The results reveated that the silty clay soil is significantly surpassed the sandy loam soil in moisture content and mean weight diameter by a percentage of 68.76% and 32.91% respectively . Whereas, the bulk density and soil penetration resistance decreased , while the total porosity of the silty clay soil as compared with sandy loam soil .For unplanted soil, moisture content, the bulk density and the soil penetration resistance are increased as compared with planted soil . The soil depth (30 – 60)cm is surpassed soil depth of ( 0- 30)cm in giving higher values of moisture content andbulk density whereas it does not significantly affect the mean weight diameter and soil penetration resistance .
 
 
 

Temperature response of ammonia and greenhouse gas emission from manure amended silty clay soil

ABSTRACTSoil temperature plays an important role in organic matter decomposition, thus likely to affect ammonia and gaseous emission from land application of manure. An incubation experiment was conducted to quantify ammonia and greenhouse gas (GHG) (N2O, CO2 and CH4) emissions from manure and urea applied at 215 kg N ha−1 to Fargo-Ryan silty clay soil. Soil (250 g) amended with solid beef manure (SM), straw-bedded solid beef manure (BM), urea only (UO), and control (CT) were incubated at 5, 10, 15, and 25 °C for 31 days at constant 60% water holding capacity (WHC). The cumulative GHGs and NH3 emission generally increased with temperature and highest emission observed at 25 °C. Across temperature levels, 0.11–1.3% and 0.1–0.7% of the total N was lost as N2O and NH3, respectively. Cumulative CO2 emission from manure was higher than UO and CT at all temperatures (P < 0.05). Methane accounted for <0.1% of the total C (CO2 + CH4) emission across temperatures. The Q10 values (temperature sensitivity coefficient) derived from Arrhenius and exponential models ranged 1.5–3.7 for N2O, 1.4–6.4 for CO2, 1.6–5.8 for CH4, and 1.4–5.0 for NH3. Our results demonstrated that temperature significantly influences NH3 and GHG emissions irrespective of soil amendment but the magnitude of emission varied with soil nutrient availability and substrate quality. Overall, the highest temperature resulted in the highest emission of NH3 and GHGs.

Development and Comparison of Soil Water Release Curves for Three Soils in the Red River Valley

Core Ideas Soil water release curve is important but difficult to measure. HYPROP and WP4 are used to develop the soil water release curves for three soils. HYPROP and WP4 provided a good and simple way to measure soil water release curves. A soil water release curve (SWRC) describes the critical and soil‐specific relationship between soil water content and matric potential. In this study, soil moisture and corresponding matric potentials were measured using (1) a new method by HYPROP and WP4 dewpoint potentiometer, and, (2) the traditional method by hanging water column, Tempe cell, and pressure plate. The SWRCs were developed for Fargo silty clay, Glyndon silty loam, and Hecla sandy loam soils by using the van Genuchten model. The goodness of fit between the fitted SWRC and the measured data agreed well with R2 between 0.91 and 0.98. The comparison for the fitted SWRCs showed that the SWRCs for Hecla sandy loam soil provided the best agreement while Glyndon silty loam soil had the best match in terms of slope and shape. The SWRCs for Fargo silty clay soil did not provide a good match between the two methods. The difference in water content between the two fitted SWRCs was less than 2% for Glyndon silty loam and Hecla sandy loam soils. However, Fargo silty clay had a 4.5 to 5% difference for 66% of the measurements, possibly due to the different bulk densities caused by shrinkage and swelling nature of the clay soil. Since the best fitted van Genuchten parameters were within the reference range that was acceptable for the same type of soils, the HYPROP and WP4 can be used to develop SWRCs that are comparable to the traditional laboratory methods for the three soils in the Red River Valley.

Research of Consolidation of Water-Saturated Silty-Clay Soils with Vertical Drainage

В статье рассматриваются вопросы изучения процессов консолидации водонасыщенных пылевато-глинистых грунтов. Перед исследователями ставилась задача оценки эффективности работы ленточных дрен в водонасыщенных пылевато-глинистых грунтах и определения оптимального расстояния между дренами. Методика проведения полевого эксперимента основывалась на положении о необходимости максимально возможного сохранения природной структуры грунта при установке в нем аппаратуры для исследований. Принят бесконтактный способ определения послойных деформаций грунта с помощью глубинных кольцевых марок и методы определения напряжений мессдозами и датчиками порового давления, которые устанавливались в пробуренные в массиве грунта скважины. Оборудование контрольно-измерительной аппаратурой полигонов с разным шагом дрен, а затем проведение наблюдений на них в сочетании с наблюдениями на полигоне без дрен позволяет оценить эффективность работы ленточных дрен в данных грунтах и определить оптимальное расстояние между дренами.

Effect of using Modified Subsoiler-Moldboard Plow on Some of the Soil properties and Broad Bean (Vicia faba L.) Growth and Yield Parameters

Field experiments were conducted in silty clay soil, to study the effect of using the modified subsoiler-moldboard plow (MSMP) on some soil properties (bulk density, penetration resistance and electrical conductivity) and on some of broad bean growth and yield parameters (emergency rate, plant height, frock number, pods number per plant, seeds number per pods, weight of 1000 seeds, and total yield). The experiment parameters were three depths of subsoiler as a part of MSMP (30,40 and 50cm) and two depths of moldboard as a part of MSMP (20 and 30cm). The results showed that increasing the subsoiler depth from 30 to 40 cm resulted in redusing the bulk density and electrical conductivity of the soil by 2.70 and 8.29%, respectively, while increased the growth and yield parameters by 10.17, 14.29, 33.43, 7.37, 21.46, 27.31 and 45%, respectively. Increasing the subsoiler depth from 40 to 50cm decreased the soil bulk density and electrical conductivity by 1.85 and 0.60% respectively, whereas the growth and yield parameters increased by 10.22, 37.50, 49.89, 93.13 35.34, 33.34 and 117.67% respectively. The increase of the moldboard depths from 20 to 30cm leaded to increase the growth and yield parameters by 23.16%, 24.70%, 67.46%, 57.51%, 34.38%, 20.33% and 68.16% respectively. The subsoiler and moldboard depths (50 and 30cm) gave the highest emergence rate, plant height, weight of 1000 seeds and yield by 71.61%, 109.42%, 111.01% and 407.46% compared with the shallow depths of subsoiler and moldboard plow depths (30 and 20cm respectively). The results revealed that the values of the soil properties decreased by 12.50%, 60.31% and 40.86%, respectively after tillage, whereas they increased by 17.35%, 250.68% and 169.09%, respectively before harvest.

English

A laboratory study was conducted to determine the potassium (K) adsorption characteristics of five soils under enset (Ensete ventricosom cheesman) farming system in Sidama. Potassium adsorption isotherms were constructed by equilibrating 5 g soil samples with 5 levels of K (0 to 78mg/L) as KCl in 10 mmoles/L CaCl2 solutions. Suspensions were shaken for half an hour. Adsorption data were fitted to Freundlich, Langmuir and Temkin adsorption equations. On an average, amount of K adsorbed ranged from 29.2 to 67.82% of added K. Significant positive relationship existed among percent K adsorbed, CEC, percent clay and pH. Langmuir equation gave a better fit of equilibrium K adsorption data for sandy clay loam and silty clay loam soils, while Freundlich equation gave a better fit for clay and loam soils. Furthermore, Temkin isotherm gave a better fit of equilibrium K adsorption data for clay loam soil. Sandy clay loam and loam soils had low 1/n values. The n values on the other hand indicated that the sorption is favorable only for these soils. The Freundlich adsorption capacity, kf were found low as compared to available soil potassium. The negative values of Langmuir isotherm maximum monolayer coverage capacity (a) for clay loam and clay soils agreed with the absence of best fit to the model. Sandy clay loam and silty clay loam which indicated best fit had high monolayer coverage. Value of Temkin isotherm equilibrium binding constant (AT) was high for clay loam soil and this was manifested by high coefficient of determination. Low values of constant related to heat of sorption (B) were determined for sandy clay loam and loam whilst clay loam, silty clay loam and clay soils indicated high binding energy (B). Key words: Sorption isotherm, Freundlich, Langmuir, Temkin model, monolayer coverage, equilibrium binding constant, heat of sorption. &nbsp

Properties and microstructure of cementing material made with waste silty clay soil

The compressive, splitting tensile and immersion strength, drying shrinkage and microstructure of the cementing material made with waste silty clay soil from waterway regulation engineering were investigated in this paper. Cement (11.0–24.0 wt.%), fly ash (4.6–9.2 wt.%) and gypsum (1.9–3.8 wt.%) at different proportions were used in the mixtures. Results show that the specimen addition of appropriate cement, fly ash and gypsum presents excellent mechanical properties and water resistance and low drying shrinkage. The microstructure observation indicates that there are quite a lot of hydrate products in matrix which verifies the formation of cementing compounds. The results obtained suggest that there is potential to manufacture cementing material with silty clay soil in substitution of ordinary concrete to use in hydraulic engineering.

Shallow water table effects on water, sediment, and pesticide transport in vegetative filter strips – Part 2: model coupling, application, factor importance, and uncertainty

Abstract. Vegetative filter strips are often used for protecting surface waters from pollution transferred by surface runoff in agricultural watersheds. In Europe, they are often prescribed along the stream banks, where a seasonal shallow water table (WT) could decrease the buffer zone efficiency. In spite of this potentially important effect, there are no systematic experimental or theoretical studies on the effect of this soil boundary condition on the VFS efficiency. In the companion paper (Muñoz-Carpena et al., 2018), we developed a physically based numerical algorithm (SWINGO) that allows the representation of soil infiltration with a shallow water table. Here we present the dynamic coupling of SWINGO with VFSMOD, an overland flow and transport mathematical model to study the WT influence on VFS efficiency in terms of reductions of overland flow, sediment, and pesticide transport. This new version of VFSMOD was applied to two contrasted benchmark field studies in France (sandy-loam soil in a Mediterranean semicontinental climate, and silty clay in a temperate oceanic climate), where limited testing of the model with field data on one of the sites showed promising results. The application showed that for the conditions of the studies, VFS efficiency decreases markedly when the water table is 0 to 1.5 m from the surface. In order to evaluate the relative importance of WT among other input factors controlling VFS efficiency, global sensitivity and uncertainty analysis (GSA) was applied on the benchmark studies. The most important factors found for VFS overland flow reduction were saturated hydraulic conductivity and WT depth, added to sediment characteristics and VFS dimensions for sediment and pesticide reductions. The relative importance of WT varied as a function of soil type (most important at the silty-clay soil) and hydraulic loading (rainfall + incoming runoff) at each site. The presence of WT introduced more complex responses dominated by strong interactions in the modeled system response, reducing the typical predominance of saturated hydraulic conductivity on infiltration under deep water table conditions. This study demonstrates that when present, the WT should be considered as a key hydrologic factor in buffer design and evaluation as a water quality mitigation practice.

Mineralization of organic carbon and nitrogen in semi-arid soils under organic and inorganic fertilization

Abstract Although compost is added to soils to improve their nutritive status and properties; yet upon its decomposition, considerable amounts of CO2 might be emitted to the atmosphere causing hazardous environmental risks. Investigating the mineralization of compost applied to a sandy soil and a silty clay one of low organic-C content in the green house for 90 days under soil moisture contents of 75 or 100% of FC was considered. Efflux rate of CO2 decreased considerably for one day in the sandy soil after application of the compost; beyond which showed an almost constant rate. In the silty clay soil, the efflux rate decreased obviously to achieve non detectable value 3 days later. Even in soils amended with mineral N-fertilizer, CO2 emissions were valued while decreased with time. By the end of the incubation time, the rate of C-mineralization was significantly higher in the sandy soil compared with the silty clay one. Increasing soil moisture content from 70 to 100% of the field capacity led to further increases in rates of CO2 efflux as well as org-C mineralization. The amount of N mineralized in the sandy soil was 1.7 times higher than its content in the silt clay one at the FC and 1.1 times in case of 70% of FC. In conclusion, a reversible equilibrated process between decomposition of soil organic matter and buildup of more stable organic components might exist at the same time.

Release of Ammonia and Greenhouse Gases along Moisture Gradient from Manure and Urea Applied Fargo Silty Clay Soil

Abstract. Greenhouse gas (GHG) [nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4)] emission and ammonia (NH3) volatilization from organic and commercial fertilizers are likely related to soil moisture levels. Effect of soil moisture [(30%, 60%, and 90% water-holding capacity (WHC)] on emissions from urea and manure treated (215 kg ha-1) Fargo-Ryan silty clay soil was studied under laboratory conditions. Soils (250 g) amended with solid beef manure (SM), straw-bedded solid beef manure (BM), urea (UR), and control (CT) were incubated for 28 days at 22±1°C, to determine GHGs (N2O, CO2, and CH4) emission and NH3 volatilization loss. The cumulative emission of N2O-N, CO2-C, and CH4-C ranged from 27 to 4402 µg N2O-N kg-1, 272 to 2030 mg CO2-C kg-1, and 10.1 to 1389 µg CH4-C kg-1 soil, respectively. The daily fluxes and cumulative emissions of N2O and CO2 generally followed the decreasing order of 30% &amp;lt; 90% &amp;lt; 60% of WHC. At 60% WHC, 1.01% of the total applied N was lost as N2O from urea treated soil. Carbon dioxide emission from manure treated soil (SM and BM) was up to two times the emission from UR treated soils. The Fargo clay soils showed higher CH4 emission at 90% WHC level. The cumulative NH3 volatilization loss from soil ranged from 29.4 to 1250.5 µg NH3-N kg-1, with the highest loss from UR amended soils at 30% WHC. These results suggest that gaseous emissions from manure and urea application under laboratory study are influenced by moisture levels of Fargo-Ryan silty clay soil. Keywords: Beef manure, Greenhouse gas, Soil water, Urea, Water holding capacity.

Hydrophysical Database for Brazilian Soils (HYBRAS) and Pedotransfer Functions for Water Retention

Core Ideas We propose a Hydrophysical Database for Brazilian Soils (HYBRAS). Data in HYBRAS comprise 445 soil profiles, with 1075 samples of Brazilian soils. We compared the accuracy of water retention estimates based on climate‐based PTFs. In general, the Brazilian PTFs performed better than the temperate models for HYBRAS. Model performance differed due to clay content and mineralogical properties. Soil water retention data are fundamental in soil modeling studies. Temperate pedotransfer functions (PTFs) have been commonly used to estimate water retention of Brazilian soils, mainly because of the lack of soil data for Brazil. However, these PTFs may not be suitable for tropical or subtropical conditions such as those found in Brazil. The objective of this study was to establish a dedicated Hydrophysical Database for Brazilian Soils (HYBRAS) suitable for PTF development. Data present in HYBRAS comprise 445 soil profiles with 1075 samples and are representative of a wide range of Brazilian soils. The data are organized in a relational structure of tables that cover general site descriptions, land cover, and hydrophysical and chemical measurement methods. Raw data (e.g., water retention points covering the 0–15,000‐cm suction range) and derived data are included in the tables. Another objective of this study was to use the database to compare the accuracy of water retention estimates based on PTFs developed for Brazilian and temperate regions. In general, the Brazilian PTFs performed better than the temperate models, especially for weathered (Ferralsols, Acrisols, and Nitisols) fine‐textured (clay, sandy clay, clay loam, silty clay loam, and silty clay) soils. Silt content was not a successful criterion for distinguishing performance of Brazilian and temperate PTFs for Brazilian weathered soils. The water retention of weathered soils was shown to differ from that of temperate soils due to differences in pore structure resulting from their clay content and mineralogical nature, thus confirming results reported in the literature.

Influence of lime stabilization on shear strength parameters of silty clay soil

Lime soil stabilization is a well-known and often used method. One of the methods of landslide stability improvement is changing soil with materials that have better physical and mechanical characteristics. In most of the methods for determining slope stability, the main input data are internal friction angle and cohesion. The main objective of this paper was to find out if the sampled silty clay soil was suitable for lime stabilization, and to get the values of shear strength parameters from soil samples with and without added lime. The results showed that by increasing lime content, internal friction angle rises, while cohesion values decrease, as well as deformations, all the way to 15% of lime by mass. The changes in internal friction angle, cohesion and deformations were most noticeable between 0 and 5% of added lime. Samples that endured the largest pressures were those containing 10% of lime.

The effects of projected climate and climate extremes on a winter and summer crop in the southeast USA

In this study, we explored how changing climate conditions in the 20th and 21st century affect summer and winter crop yields the southeast United States. An ensemble of 10 global circulation models (GCMs) were utilized and the uncertainties associated to their estimates were calculated. The objectives of this study were to utilize historical and projected climate data to (i) analyse historical and projected precipitation and temperature separately for a winter and a summer crop; (ii) evaluate how these climate factors impact the crop yield and the water use; (iii) quantify for the two crops, and for vegetative vs. reproductive stages, the impacts of climate extremes on crop yield and water use. The daily weather data for both historical and projected periods were obtained from the Multivariate Adaptive Constructed Analogs (MACA) downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) datasets. A series of 16 climate extremes indices mostly selected from the Expert Team on Climate Change Detection and Indices (ETCCDI) was calculated using the MACA downscaled CMIP5 data. The Decision Support System for Agrotechnology Transfer (DSSAT) model was used to simulate the effects of climate on a summer crop (maize, using the CERES-Maize model) and a winter crop (wheat, using the CERES-Wheat model) crop on a silty-clay and on a sandy soil during the historical baseline (1950–1999) and the projected (2006–2055) periods. Overall, the decadal crop-specific growing season temperature trend showed warming of the southeast with little variability across the climate models for the baseline and an increase uncertainty for future conditions. For each 1°C the simulated maize yield would decrease by 4.6% across the different climate projections, while wheat would be reduced by 3.8%. Water use efficiency decreased under future projections by 2.7% on a silty-clay soil, independently of the winter/summer crop, but on a sandy soil the decrease was 4% for maize and 1.7% for wheat. The impacts of projected temperature and rainfall change will be different for a winter than for a summer crop depending on the type of soil on which the crop is grown.