Moisture Characteristic Curve Research Articles

Effects of Tillage Equipment on Moisture Characteristic Curve of Dominant Paddy Soil in Guilan Province

The common method of puddling is using a conventional tiller which requires long time of soil operations.In this study, the effects of tillage equipment on moisture characteristic curve of a paddy soil were investigated. The treatments included tillage equipment (T1: conventional tiller, T2: rotary puddler, T3: cone puddler, T4: tractor mounted rotivator) and number of puddlings (P1: puddling once, P2: puddling twice, P3: three times'puddling and P4: four times'puddling). The results showed that at saturation point, tractor mounted rotivator presented the highest moisture content. At field capacity and permanent wilting point, the cone puddler showed the highest moisture value. The two newly made units held more moisture and saved water. In different tillage equipment, increasing the number of puddling reduced soil moisture. Available moisture in the soil without tillage (control) was less than in soils under rotary puddler and cone puddler.

Effect of the size of elementary soil particles on the soil moisture characteristic curve

Statistical analysis of water vapor sorption by light clayey brown forest soil and its elementary particles of different diameters has revealed extremely close correlations and linear relationships between the logarithm of total soil water potential (pressure) and the water contents in the separated particle-size fractions (due to the hydration of exchangeable cations in the diffuse layer near the surface of soil solid phase), as well as between the water content of particle-size fractions and the logarithm of their diameter (due to the differences in the specific surface area and mineralogy of these particles).

Effect of clay content of soil and salinity of irrigation water on some moisture characteristics of soil, growth and yield of beans Vicia Faba L.

A field experiment was conducted in the city of Ramadi, Anbar province - Iraq during winter season 2012-2013 to study the effect of clay content and salinity of irrigation water in some of the physical characteristics of the soil and moisture and growth and yield beans Vicia Faba L. was measured Saturated hydraulic conductivity, sorptivity, permeability, diffusivity of water, and moisture characteristic curve, as properties of water to the soil. Measured plant height and leaf area and holds the seeds, as indicators of plant growth. Saturated hydraulic conductivity, sorptivity, permeability, diffusivity of water decreased with the increased in clay content, with salt water irrigation1.08, 6.11 and 2.55 ds.m-1 led to an the values of the functions above water studied, increased values of volumetric moisture was significantly with increasing clay content of the soil with salt water irrigation has led to a lower moisture content of the soil and when any watery potential.The impact of increasing clay content of the soil in the moral growth characteristics and holds plant beans as increased plant height and leaf area and wining with increasing clay content of the soil and decreased when increasing the salinity of irrigation water.

Soil physical quality of the Indo-Gangetic plains and black soil region.

Understanding the physical quality of soil that influences its hydraulic behaviour helps in formulating appropriate water management strategies for sustainable crop production. Saturated hydraulic conductivity ( K s ) is a key factor governing the hydraulic properties of soils. K s can be estimated through various techniques. In the present article we have developed and validated the regression models to predict K s of the soils of the Indo- Gangetic Plains (IGP) and the black soil regions (BSR) under different bioclimatic systems. While particle size distribution was found to be a key factor to predict K s of the BSR soils, organic carbon was found useful for the IGP soils. Moreover, the models for K s of both soils were strengthened by putting in CaCO 3 and exchangeable sodium percentage content. It seems there is ample scope to study the interaction process for revising K s to desired levels through management practices in these two important food-growing zones. An index of soil physical quality, derived from the inflection points of the soil moisture characteristic curves could well explain the impact of management practices on soil physical quality.

Predicting the soil moisture retention curve, from soil particle size distribution and bulk density data using a packing density scaling factor

Abstract. A substantial number of models predicting the soil moisture characteristic curve (SMC) from particle size distribution (PSD) data underestimate the dry range of the SMC especially in soils with high clay and organic matter contents. In this study, we applied a continuous form of the PSD model to predict the SMC, and subsequently we developed a physically based scaling approach to reduce the model's bias at the dry range of the SMC. The soil particle packing density was considered as a metric of soil structure and used to define a soil particle packing scaling factor. This factor was subsequently integrated in the conceptual SMC prediction model. The model was tested on 82 soils, selected from the UNSODA database. The results show that the scaling approach properly estimates the SMC for all soil samples. In comparison to the original conceptual SMC model without scaling, the scaling approach improves the model estimations on average by 30%. Improvements were particularly significant for the fine- and medium-textured soils. Since the scaling approach is parsimonious and does not rely on additional empirical parameters, we conclude that this approach may be used for estimating SMC at the larger field scale from basic soil data.

Combining a Single Hydraulic Conductivity Measurement with Particle Size Distribution Data for Estimating the Full Range Partially Saturated Hydraulic Conductivity Curve

We have developed an approach for predicting the soil hydraulic conductivity curve (HCC) of soil using soil particle‐size distribution (PSD) data and one single measurement of the hydraulic conductivity in the wet range of the HCC. Unlike other models, our approach does not need a prior determination of the soil moisture characteristic curve. The development was motivated by the fact that PSD data are often available or can be inferred from soil maps and also that the hydraulic conductivity at low matric suction can be determined easily with field infiltrometer devices. The HCC prediction was good at low matric pressures, but the model performance diminished at high matric pressures. The RMSE ranged from 0.165 to 2.016, the average being 0.755 (log‐transformed hydraulic conductivity [cm d−1]). We propose to improve the accuracy of prediction models in the dry range of the HCC in future studies.

Physics of the soil medium organization part 2: pedostructure characterization through measurement and modeling of the soil moisture characteristic curves

Accurate measurement of the two soil moisture characteristic curves, namely, water retention curve (WRC) and soil shrinkage curve (SSC) is fundamental for the physical modeling of hydrostructural processes in vadose zone. This paper is the application part following the theory presented in part I about physics of soil medium organization. Two native Aridisols in the state of Qatar named locally Rodah raod´ə soil and Sabkha sab′kə soil were studied. The paper concluded two main results: the first one is about the importance of having continuous and simultaneous measurement of soil water content, water potential and volume change. Such measurement is imperative for accurate and consistent characterization of each of the two moisture characteristic curves, and consequently the hydrostructural properties of the soil medium. The second is about the simplicity, reliability, strength and uniqueness of identifying the characteristic parameters of the two curves. The results also confirmed the validity of the thermodynamic-based equations of the two characteristic curves presented in part I.

English

Coal combustion byproducts (CCBs) disposed of in unlined landfills can affect the quality of adjacent water resources. In previous studies, CCBs have been found to leach toxic heavy metals such as arsenic, mercury, and lead into groundwater. CCBs include fly ash, bottom ash, and flue-gas desulfurization product (FGD gypsum). Within a landfill, CCBs may be present at different densities associated with depth, compacted primarily from the weight of above materials. This investigation focused on determination of the unsaturated and saturated hydraulic properties of fly ash and bottom ash as a function of density and thus a function of depth within a landfill. Ash samples from a power plant in northern New Mexico were collected for laboratory analysis. Compressibility curves were developed in order to determine what densities may be experienced at a range of pressures. Saturated hydraulic conductivity was determined using falling head tests for multiple densities of each material. Moisture characteristic curves were developed from hanging column tests, pressure plate tests, dew point potentiometer measurements, and relative humidity measurements. The moisture characteristic curves were also measured at a range of densities for each material. Results indicated that the fly ash saturated hydraulic conductivity varied as a function of density for the materials tested and the density could be reasonably predicted using an equation presented. Fly ash unsaturated properties also show trends with variations in density with the variability decreasing as density increases. Fly ash in a landfill can have estimated density, unsaturated and saturated hydraulic properties as a function of depth using the methods in this paper. Bottom ash showed similar trends in compressibility with less variability with respect to the fly ash. The unsaturated and saturated hydraulic properties show some trends, though with high amounts of variability. The density of bottom ash materials in a landfill may be reasonably estimated using methods proposed in this study while unsaturated and saturated hydraulic properties have greater uncertainty.

The Effect of Superabsorbent Polymers on the Water Holding Capacity and Water Potential of Karkhe Noor Sandy Soils

Superabsorbent polymers are used in agriculture for the purpose of increasing water use efficiency in arid and semi- arid regions. In this research two kinds of superabsorbent polymers, Super AB A200 and Herbosorb were used on sandy soils of Karkhe Noor river bank near Hamidieh. The effect of 5 concentration levels of 0.3, 0.6, 0.8, 2 and 4 grams per kilogram of soil in 3 replications was studied on the parameters of soil moisture characteristic curve using RETC program and Rosetta database. It was observed that fitting of the data to the RETC model was better compared to Rosetta. Statistical analysis of the research results show that for sandy soils in these experiments there was a significant difference at one percent level for all the polymers used and the control treatment at suctions of 0.3, 1, 3, 5 and 15 bars. On the other hand for the different concentration levels of 4, 2, 0.8, 0.6 and 0.3 g/kg soil, volumetric soil moisture content showed a significant difference at one percent level. Among the superabsorbents used A200 with application rate of 4 g/kg soil resulted in the highest effect. Soil available water for plant use showed an increase compared to the control treatment. It was finally concluded that the application of 4 gram Super AB A200 and Herbosorb per kilogram soil increased soil available water about 350 and 320 percent respectively.

Effect of crop rotations with triticale (× Triticosecale Wittm.) on soil pore characteristics

Crop rotations with a high proportion of cereals, including monoculture, are typical in many countries in Europe. Although wheat is the most popular cereal as it is cultivated world-wide, in recent years a steady increase has been observed in triticale production. The objective of the study was to determine the effect of different crop rotations using triticale on soil air–water properties with a special focus on macroporosity.The following crop rotations were investigated during a long-term (2002–2010) field experiment: Norfolk crop rotation (NCR) with sugar beet, spring triticale, faba bean and winter triticale; Diculture (DCR) with spring triticale, winter triticale and oat; and Monoculture (MCR) with winter triticale and spring triticale. Undisturbed soil samples were collected in 2009 and 2010 to determine water retention parameters and morphometric characterization of soil pores. The soil moisture characteristic curve was determined in pressure chambers with ceramic plates according to Richards' method and they were expressed by the van Genuchten model. Macropore system for the investigated soil was characterized using image analysis on sections of soil samples hardened with polyester resin.The effect of the treatment applied has influenced the retention characteristics in the low water potential range, which corresponds mainly with large pores (transmission pores and fissures). The greatest differences between crops were observed in the NCR. The highest macropore volume was noticed for sugar beet. The increase in macroporosity of soil under sugar beet in the pore diameter classes ranged from 50 to 2000μm in comparison with both the spring and winter triticale. Sugar beet increases the volume of regular, irregular and elongated macropores, whereas other crops, such as faba bean, spring and winter triticale, did not significantly affect the shape of pores. Although there were some differences in size and shape of macropores, the influence of earthworm activity on soil porosity in the investigated soil was not statistically significant due to the tested crop rotations.The investigated crops in different crop rotations changed the water retention properties of the soil. The highest water retention in the range of available water was noticed for two treatments; one with spring triticale for the MCR and the second with winter triticale for the DCR. In this experiment, crop rotation had no long-term effects. The findings of the presented experiment showed that crop rotation did not play a significant role in soil structure modification. Particular crops could differ in terms of their impact on soil porosity but this effect is not permanent and is visible in the year when a particular crop is cultivated or sometimes remains until the following year.

Predicting Soil Moisture Characteristic Curves from Continuous Particle-Size Distribution Data

Soil moisture characteristic curve (SMC) is a fundamental soil property and its direct measurement is tedious and time consuming. Therefore, various indirect methods have been developed to predict SMC from particle-size distribution (PSD). However, the majority of these methods often yield intermittent SMC data because they involve estimating individual SMC points. The objectives of this study were 1) to develop a procedure to predict continuous SMC from a limited number of experimental PSD data points and 2) to evaluate model predictions through comparisons with measured values. In this study, an approach that allowed predicting SMC from the knowledge of PSD, parameterized by means of the closed-form van Genuchten model (VG), was used. Through using Mohammadi and Vanclooster (MV) model, the parameters obtained from fitting of VG to PSD data were applied to predict SMC curves. Since the residual water content (θr) could not be obtained through fitting of VG-MV integrated model to PSD data, we also examined and compared four different methods estimating θr. Results showed that the proposed equation (MV-VG integrated model) provided an excellent fit to all the PSD data and the model could adequately predict SMC as measured in forty-two soils sampled from different regions of Iran. For all soils, the method in which θr was obtained through parameter optimization procedure provided the best overall predictions of SMC. The two methods estimating θr with Campbell and Shiozawa (CS) model resulted in less accuracy than the optimization procedure. Furthermore, the proposed model underestimated the moisture content in the dry range of SMC when the value of θr was assumed to equal zero. θr could be attributed to the incomplete desorption of water coated on soil particles and the accurate estimation of θr was critical in prediction of SMC, especially for fine-textured soils at high suction heads. It could be concluded that the advantages of our approach were the continuity, robustness, and independency of model performance on soil type, allowing to improve predictions of SMC from PSD at the field and watershed scales.

Substituting Pine Wood for Pine Bark Affects Physical Properties of Nursery Substrates

Pine bark (PB) is currently imported from southern U.S. states to nursery growers in the upper midwest and northeast United States. Alternatives to PB that are regionally abundant and sustainable are needed for nursery substrates. The objective of this research was to determine the influence of pine wood (PW), which consisted of chipped and hammermilled pine trees (excluding branches and needles) on substrate physical properties when substituted partially or wholly for PB in substrates typical of Ohio. Four cooperating nursery sites, each with unique substrates comprised primarily of PB, were recruited to use PW as a substitute for 0%, 50%, or 100% of the PB fraction in their substrate. All other physical and chemical amendments used traditionally at each site were incorporated. Physical properties including particle size distribution (PSD), air space (AS), container capacity (CC), total porosity (TP), unavailable water (UAW), bulk density (Db), and moisture characteristic curves (MCC) were determined for each substrate at each cooperator site. Pine wood was generally more coarse than all but one of the PB materials used by the four cooperating sites. Amendment with PW did not have any consistent or predictable effect on AS, CC, TP, or Db of the resultant substrates. Pine wood had little identifiable effect on plotted MCC, although it reduced calculated easily available water in one substrate. It was concluded that substitution of PB with PW can result in changes to substrate physical properties that might lead to irrigation management changes, but none of these changes were considered negative or drastic enough to cause physical properties to be outside of acceptable ranges.

Moisture characteristics and their point pedotransfer functions for coarse‐textured tropical soils differing in structural degradation status

AbstractThe effect of soil structure on hydraulic pedotransfer functions (PTFs) in tropical soils with similar mineralogy and texture has not been well documented. Structurally contrasting soils from representative locations in southeastern Nigeria were analyzed for moisture retention at 0, 6, 10, 33, 100, 300 and 1500 kPa among other properties. They were grouped by depth (topsoils or subsoils) and also by their structural degradation status into low‐ and high‐stability soils, corresponding to organic matter (OM):[silt + clay] of <7.5 and >7.5%, respectively. Soil depth and structural stability influenced the soil moisture characteristic curves. The data were fitted to three tropical point PTFs, but none of them proved appropriate for predicting moisture retention in the soils. We therefore derived new ones using multiple linear stepwise regressions before and after the dataset grouping and compared their performances by means of cross‐validation. Moisture retention in the soils (sand content, 73.2–93.8%) could not be calibrated from texture and OM concentration alone, until when bulk density, total porosity and microporosity were included among the regressors. Microporosity's role was particularly outstanding at all matric potentials but the 1500 kPa. The ensuing PTFs represent a good fit for the soil moisture retention data. The two grouping strategies resulted in lower SE of the estimates in some cases, but this did not enhance the performances of the concerned PTFs. At the 1500 kPa, however, the PTF incorporating all datasets performed better than separate PTFs for topsoils/subsoils but worse than the one for high‐stability soils. Information on soil structure can therefore benefit PTF derivation for kaolinite‐dominated, coarse‐textured tropical soils at all the matric potentials considered. Copyright © 2012 John Wiley & Sons, Ltd.

Predicting the Soil Moisture Characteristic Curve from Particle Size Distribution with a Simple Conceptual Model

Indirect methods for predicting the soil moisture characteristic curve (SMC) from the particle size distribution (PSD) often rely on empirical coefficients, which limits their applicability to independent data sets. We have developed a robust simple PSD‐based conceptual SMC prediction model and evaluated the model performance through comparisons with the Haverkamp and Parlange (HP) and Arya and Paris (AP) models. Following the AP model, we divided the PSD into n size fractions where each fraction contained spherical particles whose packing state is described by a parameter. The moisture content is subsequently calculated from the PSD and measured saturated moisture content. The packing state is estimated from particle and bulk densities. The suction head is predicted based on the particle size, assuming a linear relationship between the suction head and packing state. Our results showed that the model can adequately predict the SMC as measured in 80 soils selected from the UNSODA database. It was also shown that the proposed model provides better predictions of SMC than the AP or HP models. The model underestimates the moisture content in the dry range of the SMC. We attribute this bias to the incomplete desorption of residual water coated on soil particles or water retained within nonspherical particles with high surface energy contents. We conclude that the main advantage of our model is the robustness and independency of model performance on soil type, allowing improving predictions of SMC from PSD at larger watershed scales.

Pedotransfer functions for point estimation of soil moisture characteristic curve in some Iranian soils

Soil moisture characteristic (SMC) curve is a basic soil property. Since its direct measurement is costly and time-consuming, an alternative to measurement is to estimate this property indirectly, using the more easily available soil properties. These methods are called pedotransfer functions (PTFs). Point PTFs estimate the water content of the soil at different matric potentials. For this study, twenty soil samples from the topsoils (A horizons) were selected from different locations in Fars province, South of Iran, and SMC curve of each soil was measured with the combination of hanging column for matric potentials of 0 (saturated soil moisture content), 3, 6, 9 and 12 kPa and pressure plate methods for matric potentials of 30, 100, 500, 1000 and 1500 kPa. Also, the particle size distribution curve of each soil was measured and the percentages of clay, silt and sand, and the geometric mean particle-size diameter of each soil was determined. Then, three PTFs were derived based on clay or sand fraction of the soil or geometric mean particle-size diameter, saturated soil moisture content and bulk density for point estimation of SMC curve. To evaluate the proposed PTFs another five independent soils were used. The results showed that, the PTFs for point estimation of SMC curve based on clay content were appropriate for soils with clay, silty clay and silty clay loam textures, and the PTFs based on sand content were appropriate for soils with loam and sandy loam textures. Key words: Soil moisture characteristic curve, pedotransfer functions, clay, sand, saturated soil moisture content.

Nitrogenous fertilizer effects on soil structural properties under switchgrass

Nitrogen (N) fertilization is needed to sustain the biomass yield of switchgrass ( Panicum virgatum L., Poaceae) as a biofuel feedstock and, consequently, may influence the potential for soil quality improvements through soil organic carbon (SOC) sequestration. Therefore, the objective of this study was to assess how inorganic N application to switchgrass affects soil structural properties, which may feed back to affect the sustainability of biomass production. Soil was sampled at depths of 0–5, 5–10, and 10–15 cm in April and November 2008 during the fifth year of switchgrass growth in Milan, TN. Nitrogenous fertilizer was applied as NH 4NO 3 at rates of 0, 67, and 202 kg N ha −1 y −1 beginning in the second year. Root weight density (RWD), root length density (RLD) and SOC concentration were measured under different N treatments as factors potentially influencing soil structural properties. Measured soil structural parameters included soil moisture characteristic curve (SMCC), and aggregate stability through wet-sieving. At 0–5 cm depth, spring RWD (3.8 mg cm −3) was significantly lower with 202 kg N ha −1 application compared to 0 and 67 kg N ha −1 (14.1 and 17.0 mg cm −3, respectively). Although fall RWD did not vary among N treatments, RLD under 202 kg N ha −1 (7.1 cm cm −3) was less than half of that at 0 kg N ha −1 (15.7 cm cm −3). The SOC concentration was greater in both fertilized treatments than in the unfertilized treatment. Although SMCC varied somewhat between seasons, it did not exhibit any consistent trends attributable to N application. The proportion of macroaggregates for 0–10 cm depth were significantly greater in the 0 and 67 kg N ha −1 treatments than in the 202 kg N ha −1 treatment. These data suggest that excessive N application to switchgrass could have negative impacts on soil structural properties by reducing root biomass and length, crucial determinants of soil structure despite an increase in SOC.

A New Model for Unsaturated Soil Using Skeleton Stress and Degree of Saturation as State Variables

In this paper, based on experimental results a new constitutive model, using skeleton stress and degree of saturation as independent state variables, is proposed for unsaturated soil, in which the influence of the degree of saturation can be properly described. In the model, a very simple moisture characteristics curve considering moisture hysteresis of unsaturated soil is also proposed. The moisture characteristics curve can not only be applied to secondary drying process but also primary drying process originated from slurry soil. The constitutive model is able to describe not only the behavior of unsaturated soil but also saturated soil because the skeleton stress can smoothly shift to effective stress if saturation changes from unsaturated condition to saturated condition. Meanwhile the overconsolidation, one of the main features of soils that are discussed in the models for saturated soils, is also considered together with the degree of saturation. Other mechanical features such as structure of soil and stress-induced anisotropy can be easily incorporated into the proposed model within the framework of the present research. It is known from the simulation that the main features of unsaturated soil in isotropic consolidation test and triaxial compression test under drained and exhausted condition with different confining stress and suction can be qualitatively described.

Soil aggregate properties and total available water as affected by sugar cane (Saccharum hybrid sp.) production in Mauritius

Concerns within the sugar industry of Mauritius with respect to soil degradation caused by sugar cane cropping have led to a study on soil quality. As part of this study, the effects of sugar cane production, i.e. cropping and adoption of mechanized practices, on aggregate size distribution, aggregate stability and total available water were investigated for the five major soil groups of Mauritius. These three parameters are indicative of the status of soil structure. Aggregate size distribution was determined by dry sieving, aggregate stability was derived from soil moisture characteristic curves of weathered and unweathered soil samples, and total available water was determined using ceramic pressure plate and cellulose membrane techniques. The results showed that, in general, neither soil structure nor total available water were degraded following the introduction of the sugar cane crop and the subsequent implementation of mechanized practices. A significant increase in aggregate size was observed with cropping in a rocky soil from the sub-humid zone, possibly because of changes in rooting density, with higher biomass being produced under irrigated conditions. On the other hand, aggregates were smaller in soils from the humid to super-humid zones, probably because of a lower organic matter content. Adoption of mechanized practices could also have impacted positively on aggregate properties through soil consolidation under harvester traffic. Aggregate stability decreased significantly with the adoption of mechanized practices only in the Low Humic Latosol, which has the lowest natural organic matter content. In this case, organic matter content could have been depleted with cropping below a critical threshold level. No significant difference was observed in terms of total available water. It can be concluded that sugar cane cropping has not degraded soil structure in the major soils of Mauritius but care should be taken to minimize organic matter depletion when adopting mechanized practices in the Low Humic Latosol.

Developing Moisture Characteristic Curves and Their Descriptive Functions at Low Tensions for Soilless Substrates

Moisture characteristic curves (MCC) relate the water content in a substrate to the matric potential at a given tension or height. These curves are useful for comparing the water-holding characteristics of two or more soils or soilless substrates. Most techniques for developing MCC are not well suited for measuring low tensions (0 to 100 cm H2O) in coarse substrates used in container nursery production such as those composed of bark. The objectives of this research were to compare an inexpensive modified long column method with an established method for creating low-tension MCCs and then to determine the best model for describing MCCs of bark-based soilless substrates. Three substrates composed of douglas fir (Pseudotsuga menziesii) bark alone or mixed with either peatmoss or pumice were used to compare models. Both methods described differences among the three substrates, although MCC for each method differed within a substrate type. A four-parameter log-logistic function was determined to be the simplest and most explanatory model for describing MCC of bark-based substrates.

Draining unsaturated soils with geosynthetics

ABSTRACT: The geocomposite capillary barrier drain (GCBD) comprises three layers that are, from top to bottom: a transport layer (a specially designed geotextile), a capillary barrier (a geonet), and a separator (geotextile). The GCBD was developed as a means to remove water from unsaturated soils. The transport layer removes water under negative pressures, the capillary barrier stops upward and downward unsaturated flow of water from adjacent layers, and the separator prevents underlying soil from intruding into the capillary barrier. This paper summarizes investigations and proof-of-concept studies related to the development of the GCBD, including laboratory and field studies. Capillary rise, moisture characteristic curves, and unsaturated transmissivity measurements were used to select candidate transport layers for evaluation in GCBD systems. Large-scale laboratory tests of pavement sections indicate that, when placed between a pavement base and subgrade, the GCBD will: (1) accelerate the draining and drying of the base; and (2) reduce subgrade wetting. Subsequent field studies validate these conclusions, and confirm that pavement sections with a GCBD system have lower water contents.