Initial Soil Moisture Content Research Articles

Boundary Condition and Soil Attribute Impacts on Anionic Surfactant Mobility in Unsaturated Soil

AbstractSurfactant mobility in unsaturated soil will impact the effectiveness and efficiency of using these compounds for in situ environmental remediation above the water table. For this reason, transient unsaturated column tests were used to study the influence of boundary conditions and soil attributes on anionic surfactant transport. In these tests, aqueous surfactant solutions were injected into the inlet of horizontally mounted soil columns. Two commercial anionic surfactants were used, an alkyl ether sulfate (AES) and a linear alkylbenzene sulfonate (LAS).The overall study was divided into two parts. First, boundary condition effects including injected surfactant solution concentration, initial moisture content, and surfactant application rate were investigated. Increasing the injection solution concentration increased anionic surfactant mobility in the column while changes in the initial soil moisture content and surfactant application rate had no significant impact. Second, the impacts of soil attributes such as texture, dominant exchangeable cation, and resident organic matter were measured. With respect to texture, mobility was found to be greater in a sandy soil as compared with two loamy soils. Both surfactants, especially LAS, were found to be more mobile in a Na+ dominated soil rather than one dominated by Ca−2.The absence of soil organic matter increased LAS mobility.

Infiltration in cracking clay soils as affected by initial soil moisture content

Infiltration in cracking clay soils as affected by initial soil moisture content

Potato Production in Wide Beds Compared to Conventional Rows

Regional growers have expressed an interest in the feasibility of producing potatoes on wide beds. Using wide beds decreases compaction and may increase water available to the crop due to the elimination of postplanting cultivation, or hilling, required in conventional rows. The middle row of wide beds may have cooler soil temperatures than the other rows in the bed. In addition, wide beds allowed for a planting density 1.5-times greater than conventional rows, which could significantly increase yields. Potatoes, `Atlantic', were planted mid-March into conventional rows on 38-inch centers and 6-foot 4-inch-wide beds, each bed with three rows. Plots were 50 feet long. Initial soil moisture contents in the middle of the bed, the outer rows of the bed and the conventional rows were not significantly different. Initial soil temperature data suggests that fluctuations in temperature are greatest in the conventional rows and least in the middle row of the wide beds. Soil temperature and soil moisture are reported. Marketable yields from wide beds are compared to marketable yields from conventional rows. Influence on potato size distribution and quality factors also are reported.

Towards a continuous operational system to estimate the root-zone soil moisture from intermittent remotely sensed surface moisture

A study has been carried out to develop and evaluate a system to estimate soil moisture content in the root-zone using active microwaves from the European Remote Sensing Satellite, ERS-1, to measure moisture content in the top 10 cm of the soil profile. Two permanent grass sites in the UK with contrasting soil types, clayey and sandy, were selected for this study. The system consists of an initialization phase, which provides surface and root-zone moisture contents as initial values for the dynamic phase of a soil water balance model. The initial value of surface moisture can be either a remotely sensed or a measured value. The surface moisture value for a given day is in turn used to derive the initial value of the root-zone moisture for the same day. This can be obtained either from an empirical relationship for drying or wetting conditions, or during drying conditions alone. Both types of relationship have been established for each of the sites, with strong coefficient of determination, R 2. The two-layer soil dynamic model requires as input daily rainfall, evapotranspiration and three soil physical parameters—soil moisture at field capacity, wilting point and a pseudo-diffusivity coefficient. The first layer represents the remotely sensed layer, taken as 0–10 cm, and the second represents the root-zone, taken as 0–50 cm, for both sites. The model has been run for 1992 and 1993. The model was not initialized by remote sensing data owing to an insufficient number of microwave backscatter-surface moisture data pairs to produce a relationship with good R 2. It is hoped that the continuing collection of data will improve the relationships. Initial soil moisture contents of both layers were considered to be at field capacity, which is usually the case during winter time. The dynamic model, which offers a good balance between accurate description of the processes and minimum input of data, proved capable of simulating both surface and root-zone moisture content. Despite the fact that the two phases of the system have been tested using ground-truth measurements, it has the potential to produce continuous surface and root-zone moisture contents using intermittent remotely sensed surface moisture to initialize or update the model. Therefore, further tests with remote sensing data and entirely independent soil moisture data sets (under collection) are still required. At present, the system has been tested on two soil types and one vegetation cover, namely permanent grass. For a wider use of the system at a regional scale, further developments are planned to account for more soil types and land covers.

Stress tolerance and burrowing behaviour in the southern African millipedeAlloporus uncinates

Laboratory experiments were carried out to assess the tolerance and behaviour of the southern African spirostreptid millipedeAlloporus uncinates(Attems) to moisture and temperature stress. Rates of water loss in dry air were 0–026 mg H20 cm‐2hour‐1for females and 0021 for males and remained relatively constant with an increase in temperature from 20 to 30°C but at higher temperatures there was a rapid increase in water loss, especially for females. In dry laboratory conditions at 30°C all individuals died within 30 days, whilst at 20°C at least 90% of individuals survived this period. Aggregation appeared to have no significant effect on survivorship but small body size conferred a survivorship advantage. Females burrowed earlier and to a greater depth than males, and initial moisture content of soil had a significant effect on mean burrow depth.Alloporus uncinatus, like other spirostreptid millipedes, appears to have considerable tolerance to dry conditions but the wide geographic and habitat range of this species may mean that the intensity of selection for tolerance to moisture stress may vary.

Effects of rock fragments on physical degradation of cultivated soils by rainfall

To understand better the role of rock fragments in soil and water conservation processes, the effects of rock fragments in maintaining a favourable soil structure and thus also in preventing physical degradation of tilled soils was studied. Laboratory experiments were conducted to investigate the effects of rock fragment content, rock fragment size, initial soil moisture content of the fine earth and surface rock fragment cover on soil subsidence by rainfall (i.e. change in bulk density by one or more cycles of wetting and drying). A total of 15 rainfall simulations (cumulative rainfall, 192.5 mm; mean intensity, 70 mm h −1) were carried out. Before and after each rainfall application the surface elevation of a 19-cm thick plough layer was measured with a laser microrelief meter. In all experiments, the bulk density of the fine earth increased with applied rainfall volume to reach a maximum value at about 200 mm of cumulative rainfall. From the experimental results it was concluded that the subsidence rate decreased sharply for soils containing more than 0.50 kg kg −1 rock fragments, irrespective of rock fragment size. Fine earth bulk densities were negatively related to rock fragment content beyond a threshold value of 0.30 kg kg −1 for small rock fragments (1.7–2.7 cm) and 0.50 kg kg −1 for large rock fragments (7.7 cm). Initial soil moisture content influenced subsidence only in the initial stage of the experiments, when some swelling occurred in the dry soils. Surface rock fragment cover had no significant effect on subsidence of the plough layer. Therefore, subsidence of the plough layer in these experiments appears to be mainly due to changing soil strength upon drainage rather than the result of direct transfer of kinetic energy from falling drops. The relative increase in porosity of the fine earth as well as the absolute increase in macroporosity with rock fragment content will cause deeper penetration of rainfall into the soil, resulting in water conservation. Therefore, crushing of large rock fragments into smaller ones is to be preferred over removal of rock fragments from the plough layer.

ROOT DISTRIBUTION, WATER USE, AND NUTRIENT UPTAKE OF MILLET AND GRAIN SORGHUM ON WEST AFRICAN SOILS

Field experiments were carried out in three Sahelian agroecosystems (Kala Pate, N'Dounga, and Chikal) to compare the rooting systems and water and nutrient extraction of millet and sorghum under different levels of water, fertilization, and plant density. Initial soil moisture content was so low (<0.04 m3 m-3) that crop rooting was limited by the maximum depth of the wetting front. Soil acidity (pH 4.5) and aluminum and manganese toxicities reduced the effective crop rooting depth to less than 45 cm at Kala Pate. Millet utilized water more efficiently under less favorable soil conditions, but in most cases it extracted less nutrients and utilized rainfall less efficiently than sorghum. Results from this study suggest that root penetration of both crops was controlled by the seasonal wetting front and soil pH. These factors were most limiting for efficient nutrient and water use. Inputs of water and fertilizer significantly increased rainfall use efficiency and nutrient uptake by both crops.

Evaluation of Philip's infiltration equation for cultivated upland terraces in Indonesia

The effect of traditional soil management practices (ridge tillage) on the parameters and applicability of Philip's infiltration equation was evaluated during the rainy season (1987) in an upland area located in the Samin watershed, Indonesia, about 800 m above mean sea level. A double ring infiltrometer was used. Sortivity ( S) was determined by fitting field data, using the equation S = I t 1 2 at an elapsed time of 5 min, where I and t represent cumulative infiltration (cm) and time, respectively. Traditional tillage treatments significantly influenced the spatial variability of the sorptivity and soil surface saturated conductivity ( K s). The relationship between S and clay content, and initial soil moisture content, was weak. The non-tilled or older tilled areas exhibited mostly matrix K s and more recent tilled areas exhibited macroporosity. Equating a second parameter ( A) in the Philip's equation with the K s yielded a fair agreement of calculated cumulative infiltration with the experimental data. However, extra care was required in choosing the constant A in the case of newly cultivated areas. Averaging parameters S and A on the basis of tillage treatment gave a reasonable representation of the cumulative infiltration in the experimental area. The error varied from 17.7% to 33.2%. Excellent fit of calculated values of cumulative infiltration with the experimental data for individual measurement was obtained by evaluating parameters S and A using multiple linear regression analysis. Averaging the values of S and A resulted in a slightly more accurate predicted value than the previous method, with an error variation of 16.2–31.5%. Further, the sorptivity obtained from the multiple linear regression approach and the previous equation mentioned were highly correlated ( r = 0.96).

Transformation and movement of urea in soil as influenced by water application rate, moisture management regime, and initial moisture content

Abstract Laboratory experiments were conducted to study the influence of water application rate (2.5, 5.0, 7.5, and 10.0 cm), moisture management regime (i.e., frequency of water application), and initial soil moisture content (25, 50, 75, and 100% of field capacity) on the transformation and movement of urea in soil columns. In general, moisture content and the amounts of urea and NH4 +‐N decreased with depth and time at all water application rates. Whereas approximately 79 to 82% of the added urea was hydrolyzed within 48 h, there was no nitrification of the urea‐derived NH4 + within this time period. The application of 1.0, 2.5, 5.0, and 10.0 cm of water resulted in the percolation of water to depths of 33, 36, 39, and 42 cm, respectively. Moisture management had a significant effect on the distribution of N‐species in the soil columns. Increasing the frequency of water additions from one (10.0 cm added on day 1) to ten (additions of 1.0 cm day‐1 for 10 days) resulted in an increase in the amount of urea‐derived NH4 + in the surface layers of the soil, but a decrease in the amount of NO3 ‐‐N in these layers. The initial moisture content of the soil had a considerable effect on the movement of urea. The movement of urea and urea‐derived N into the soil increased with increasing initial soil moisture content, but was restricted to the upper 7 cm of the soil columns. At all soil moisture contents, 60 to 65% of the urea‐derived N was recovered in the top 2 cm of the soil column. In general, the recovery of urea‐derived N from the soil ranged from about 78 to 85%.

Partitioning solute transport between infiltration and overland flow under rainfall

Solute transport from soil to overland flow is an important source of nonpoint pollution and was investigated through tracer studies in the laboratory and at an outdoor laboratory catchment. The depth of surface water interaction with soil, defined as the mixing zone is a useful value for approximate estimation of potential solute transport into surface water under rainfall. It was measured in the laboratory for a noninfiltration case (0.90 to 1.0 cm) and estimated through mass balance modeling for an infiltration case (0.52 and 0.73 cm). At an outdoor laboratory catchment, mixing zones were calculated through calibration of a numerical model that describes unsteady, uniform, infiltration and chemical transport. Overland flow was simulated using kinematic wave theory. Mixing zone depths ranged from 0.47 to 1.02 cm and were a linear function of rainfall intensity. Also, the fraction of solute present in the mixing zone at the time of ponding which was extracted into overland flow was a linear function of the initial soil moisture content. A steady state analytical approximation of the solute transport model was also developed which overpredicted solute transport into overland flow by 1 to 60%.

Infiltration experiments on loess soils and their implications for modelling surface runoff and soil erosion

Infiltration parameters such as infiltration rate, the infiltration control zone depth and the initial soil moisture content, used in the Holtan/Overton equation, have a strong impact on the output of the erosion model ‘ANSWERS’. Therefore, infiltration was measured accurately and spatial and temporal variability were taken into account. 72 infiltration experiments on three types of loess soils under simulated rain show that the Holtan/Overton equation describes infiltration correctly. Both Philip's equation and the Green-Ampt model yield similar results. Because the infiltration parameters show a “within-unit” variance which is larger than the “between-unit” variance, no differences in infiltration characteristics between the three loess soil types could be detected statistically. To evaluate the consequences of the large spatial variability of infiltration, stochastic methods must be used in combination with a distributed hydrologic model. Consecutive simulated rainstorms applied to the same samples show the influence of temporal variability in infiltration behaviour. This type of variability is attributed to the formation of surface crusts. The influence of crust formation on Holtan infiltration can be expressed in terms of a change in infiltration control zone depth. Assuming a relation between crusting and cumulative kinetic energy of rain, the temporal variability of infiltration behaviour was successfully modelled, yielding an empirical relation between control zone depth and cumulative kinetic energy of rain. However, a more physically based hydrologic sub-model of the influence of crusting on infiltration during the growing season is needed.

Time‐dependency of runoff velocity and erosion the effect of the initial soil moisture profile

AbstractThe paper reports on experiments carried out to evaluate the effect of the initial soil moisture profile on temporal variations in runoff erosion rate. The moisture profile was varied by applying infrared heating to the soil sample surface over various time periods, while runoff erosivity was varied by varying the slope of the flume. The experiment confirms that dry loamy soils are very erodible: on a slope length of only 4.3 m long sediment concentrations are near transporting capacity in case of a dry soil sample. It appears that temporal variations in sediment concentrations can be well simulated using a simple relationship between runoff erosion resistance and initial soil moisture content, thereby implicitly assuming that the effect of initial moisture content is persistent over the whole duration of the experiment. The implications of these findings with respect to the modelling of sediment output from larger catchments and the design of experiments on rill erodibility are discussed.The experiments also show that, under the present circumstances, mean velocities in the rills appear to be independent of slope. This finding may be of importance with respect to overland flow routing and deterministic erosion modelling.

The impact of 20 years' absence of earthworms and three levels of N fertilizer on a grassland soil environment

Replicated plots of a sward sown to perennial ryegrass ( Lolium perenne) growing at Hurley on a soil of the Griston series were given 188, 376 or 752 kg N fertilizer ha −1 year −1 for a period of 20 years. Half of each plot at the lowest and highest application rate of N fertilizer was treated frequently with the pesticide phorate, which kept those halves almost free of earthworms and other invertebrates. Measurements of several soil parameters were made during at the end of the 20-year period. The pesticide treatment, i.e. absence of earthworms, dramatically increased soil bulk density, shear strength, penetrability and depth of leaf litter, but greately reduced soil organic matter content, initial infiltration rate, pH and soil moisture content. Increasing the level of nitrogen fertilizer increased soil shear strength and penetrability, but had little or no significant effect on the other parameters measured. The soil profile was examined in detail to a depth of 1.5 m at the junction of a low-N-level pesticide-treated sub-plot and an untreated sub-plot. The main changes in the soil profile attributable to the pesticide treatment were confined to the topsoil. The leaf litter layer (F horizon) on the treated plot was pronounced and some 2–3 cm deep. The topsoil on treated plots had a more developed coarse angular blocky structure and was more brittle. There was no visible earthworm activity in the treated plot.

MODELING AMMONIA VOLATILIZATION FROM LOAMY SAND SOIL TREATED WITH LIQUID UREA

ABSTRACT Laboratory experiments were conducted to measure amounts of ammonia volatilized from loamy sand soil using an airflow technique. A composite rotatable statistical design was used to define the relationship between ammonia volatilization (Z, kg-N/ha) and temperature (C), soil pH, initial soil moisture content (MC, g water/100 g dry soil), urea application rate (R, 7-N/ha), and urea application depth (D, cm). Soil samples were treated to adjust the sample parameters (i.e., soil pH). Each soil sample was placed in a small container and the containers were placed in an environmentally controlled room. Air was passed through each container and the ammonia volatilized from the soil in the container was trapped in an acid bath. The acid baths were analyzed periodically to determine the amount of ammonia released by the soil. Curves defining the release of ammonia with time were plotted from the results. Using regression techniques, a response surface was developed that defined accumulated ammonia volatilization over a 15-day period as a function of the independent variables. The response surface is defined by the following equation.

Influence of different initial soil moisture contents on the distribution and population dynamics of introduced Rhizobium leguminosarum biovar Trifolii

Data on bacterial distribution in soil were obtained with a method of washing and thoroughly shaking of the soil. Bacterial cells attached to or enclosed in different size groups of soil particles or aggregates were separated and enumerated on plates containing selective media. Soil portions of a loamy sand and a silt loam with different initial moisture contents were inoculated with Rhizobium leguminosarum biovar trifolii. Results of this experiment indicated that the initial moisture content influenced the distribution of the inoculated rhizobial cells. Differences in distribution were still found after prolonged incubation periods, suggesting a lack of transport and migration of the rhizobial cells. It was shown that rhizobial cells survived better in soils with a lower, than in soils with a higher initial moisture content. Rhizobial cells attached to or enclosed in soil particles or aggregates larger than approx. 50μm had a more favourable microhabitat than unattached cells or cells attached to smaller particles.

Effect of initial soil moisture content on the vertical infiltration process — A guide to the problem of runoff-ratio and loss

Initial soil moisture content plays an important role in hydrologic processes. In this paper, the relationships among the initial soil suction (an index of the soil-moisture content), total amount of rainfall, rainfall intensity, runoff loss, runoff ratio and lag between rainfall and runoff occurrence are examined with a simplified one-dimensional analog of the infiltration process based on a cylindrical lysimeter with artificial rainfalls. It is conclusively shown that the loss of infiltrated rainfall is uniquely correlated with the initial soil-moisture content measured by tensiometers and is independent of the total amount of rainfall as well as of the rainfall intensity, if it does not exceed the infiltration rate of the soil. Consequently, the runoff ratio is a function of the initial soil-moisture content and total rainfall, but not a function of the rainfall intensity. The nondimensional propagation velocity of the wetting front or inversely the nondimensional lag of runoff occurrence defined by T★ 1 = T 1r H ( T 1 = lag between rainfall and runoff; r = infiltration rate, in this case, rainfall intensity; and H = depth of the lysimeter or distance from the surface to the less pervious layer) is also well correlated with the initial soil moisture. These results are further proven and extended through the use of numerical experiments, solving the Richards equation of unsaturated infiltration. An approximate analytical solution has been derived for the runoff ratio and rainfall loss.

Effects of Frost Action on Soil Aggregate Stability

ABSTRACT Arainfall simulator study was conducted on three Minnesota soils to examine the effects of soil type, initial soil moisture content at the time of freezing, rate of freezing, number of freeze-thaw cycles, and energy of raindrop impact on soil aggregate stability. For all three soils, the effect of raindrop impact energy was more pronounced than the effect of freezing and thawing on the disruption of soil aggregates. The rate of freezing had little or no significant effect on aggregate stability. While freezing, in general, resulted in a breakdown of soil aggregates, there were certain optimum soil moisture levels at which aggregate disruption as a result of frost action was minimized or reversed. The effect of number of freeze-thaw cycles on aggregate stability of the three soils tested was not consistent. Regression equations that relate the mean weight diameter of soil aggregates to these factors are presented.

Factors affecting the efficiency of urea for pot-grown ryegrass

Urea can be an inefficient nitrogen source, compared with ammonium nitrate, on calcareous soils (Ernst &amp; Massey, 1960) and under dry conditions (Murphy, 1978) as a result of ammonia volatilization. However, the interaction between factors which can affect the performance of urea is not clearly understood. The risk of ammonia volatilization would appear to be higher on light soils with a low cation exchange capacity than on heavier soils (Fenn &amp; Hossner, 1985). Field trials in the Netherlands indicated that a minimum of 5 mm of rain must fall within 2 days of application to give good dry-matter yields with urea (Van Burg, Dilz &amp; Prins, 1982). In addition ammonia volatilization has been affected by initial soil moisture content in some studies (Fenn &amp; Escarzaga, 1977) but not in others (Gasser, 1964).

Fate of spilled xylene as influenced by soil moisture content

Barrel size undisturbed monoliths of Weswood silt loam soil (Fluventic Ustochrept) were collected, instrumented, equilibrated at desired moisture contents, and treated with xylene by spilling it on the soil surface. Volatilization of xylene was measured using a chamber equipped with a granular activated carbon (GAC) vapor trap. Leachate was collected daily under − 33 kPa tension with a GAC vapor trap between each collection bottle and the vacuum source. Residual xylene was determined by collecting soil samples at the end of the leaching period and analyzing them for xylene. Degradation was estimated as the xylene applied less the sum of the xylene which remained, leached, and volatilized. Most of the observed volatilization occurred immediately after application and was greatest from the driest soil. An application rate of 7.2 × 10−2 m depth of xylene at the intermediate moisture content resulted in four times more volatilization than occurred from the 3.6 × 10−2 m application. Xylene appeared in the leachate collected at a depth of 0.78 m from all treatments within 12 hr after the xylene was applied. Initial soil moisture content greatly influenced the amount which passed through the soil. An average of 34% and less than 0.5% of the applied xylene moved through the wettest and driest soils, respectively. Doubling the xylene application depth resulted in a 10 to 17-fold increase in the amount of xylene in the leachate. Vapor traps in line with soil pore liquid samplers were essential, since for some treatments, an average of 95.1% of the xylene collected in the leachate was recovered from the vapor trap. The xylene which remained in the soil after 67 days ranged from 6.7 to 12.8%. Estimated degradation rates ranged from 45.7 to 137.8 g day−1 with the greatest degradation occurring in the soil with the highest application rate and the least degradation in the wettest soil with the lowest application rate.

The time scale of the soil hydrology using a simple water budget model

AbstractA simple water budget model is used to get a characteristic time scale of the soil hydrology, which is defined as the time scale for the onset of agricultural droughts. Assuming that there is no rain, our estimation requires as input the knowledge of the initial soil moisture content and an evaluation of the potential evaporation. Two applications at a global scale are shown. In a first case an initially saturated soil is considered to get an estimation of the time needed by a climate model to adjust realistically to initial errors in the soil moisture distribution. In a second case climatological values are used as initial conditions to get a measure of the sensitivity of the hydrological cycle to the atmospheric forcing.