Initial Soil Moisture Content Research Articles

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.

Application of Soil Conditioner Solutions to Soil Columns to Increase Water Stability of Aggregates1

Soil aggregate stabilization by water-soluble anionic polymers (soil conditioners) applied by drip irrigation was studied in columns containing silt loam and clay aggregates. Soil conditioners moved during irrigation to depths similar to the wetting front depth (30 cm) and increased aggregate water stability. Conditioning depth was controlled mainly by convective flow through the soil profile. Distribution of conditioner macromolecules, which affects the size of water-stable aggregates, was controlled by both convective flow into aggregates and molecular diffusion. Conditioning depth and mean diameter of water-stable aggregates were found to depend on initial aggregate size, initial soil moisture content, application flux rate, polymer molecular weight, solution concentration, and total applied volume. Conditioning effect was more apparent in silt loam than in clay loam. Best conditioning results were obtained for silt loam aggregates at a moisture content somewhat lower than field capacity, treated with polymers of molecular weight >75 000 at concentrations >4 g L−1 applied at a small flux rate of 1.5 × 10−3 cm s−1 (50 mm h−1). Conditioners of molecular weight <75 000 acted better than those of molecular weight >75 000 in increasing water stability of aggregates in the surface layer.

Air Encapsulation: I. Measurement in a Field Soil

AbstractEncapsulated air is an important component of shallow water table fluctuations. Our objective was to measure the quantity and persistence of encapsulated air in a field setting. Using sprinkling rates of either 3.5 × 10−6 or 3.8 × 10−5 m s−1, we brought the water table in a field soil from a depth of 1.5 m to the surface on several occasions. Moisture contents during and after sprinkling were monitored with a neutron probe. Twice following sprinkling, the water table was maintained at the surface for more than 20 d, during which time we continued to monitor moisture contents. With the water table at the surface, differences between the porosity and the measured moisture content were attributed to encapsulated air. Encapsulated air contents ranged from 1.1 to 6.3% of the bulk soil volume, depending on the rate of sprinkling, soil depth, and initial soil moisture content. During ponding, encapsulated air persisted at the 0.3m depth for up to 28 d. The results indicate that encapsulated air is measurable in a field situation and that its quantity and persistence should be considered in analyzing the results of similar field experiments.

Transport of Cadmium by Organic Solvents Through Soil

AbstractSolutions of 0, 50, and 100% 2‐propanol and ethylene glycol in water containing 1 mM Cd were perfused through soil columns of river sand, Anthony sl (coarse‐loamy, mixed [calcareous], thermic Typic Torrifluvents), or Davidson c (clayey, kaolinitic, thermic Rhodic Paleudults) at two initial soil moisture contents (air dry and water saturated) to determine if organic solvents have the potential to alter the rate of Cd movement through soils as compared with water alone. Soils adsorbed less Cd from ethylene glycol than from water. Cadmium breakthrough was rapid and Anthony sl and river sand adsorbed &lt;6 µmol Cd g−1 when leached with Cd‐enriched 2‐propanol. The 2‐propanol increased Cd adsorption compared to water in the Davidson c. Cadmium adsorption increased with increasing 2‐propanol concentration in the Davidson c but decreased with increasing 2‐propanol concentration in the River Sand and Anthony sl. No consistent trends occurred with increasing ethylene glycol concentration. Davidson c and river sand adsorbed significantly more Cd at 95% confidence levels from 2‐propanol when initially air dry, while Anthony sl adsorbed more Cd when initially water saturated. Initial soil moisture content did not significantly affect ethylene glycol transport of Cd at the 95% confidence level.

Effect of Environmental Factors on Ammonia Volatilization from a Urea-Fertilized Soil

A greenhouse experiment using 15N followed by wind tunnel experiments using a micrometeorological technique were conducted to identify some of the factors that contribute most significantly to ammonia (NH3) volatilization in a simulated semiarid environment following application of urea. An Aridic Calciustolls with high urease activity was subjected to a variety of initial soil moisture contents, rainfall patterns, wind speeds, air-humidity, and urea application methods. Losses of broadcast urea-N in the greenhouse at 42-d harvest, presumably due to NH3 volatilization, were reduced from 40% with a first rain of 1 cm (7 d after fertilizer application) to 13% with a first rain of 4 cm. Nitrogen losses were increased by 8% when initial soil moisture was increased from 21% (≅ permanent wilting point or PWP) to 31%. Wind tunnel experiments verified that nitrogen can be conserved either by heavy initial rain events (showing no NH3 volatilization with application of 2.5 cm rain immediately after urea application) or by banding of urea at a depth of 2.5 cm. Losses were maximized by maintaining adequate moisture in the topsoil for urea hydrolysis without inducing leaching, either by humidifying the air between 80 and 95% or by applications of 8 mm rain every 3 d. Increasing wind velocity from 1.7 to 3.4 ms−1 reduced NH3 loss from 19 to 7.5%, likely due to more rapid drying of the soil surface.

Water percolation in a tropical alfisol under conventional plowing and no-till systems of management

Field studies were conducted to investigate percolation and redistribution of water in a gravelly Alfisol under conventional and no-tillage systems. Five cm of water tagged with chloride was applied to the soil surface by sprinkling and flood irrigation. Soil samples for water and chloride determinations were obtained immediately after infiltration and at 5, 24 and 48 h after infiltration initiation. Depending on the mean initial soil moisture content ( θ i ) and method of water application, mean infiltration rate ranged from 4.6 to 42.9 cm h −1 for plowed compared to a range of 15 to 120 cm h −1 for the no-till treatment. In the conventionally plowed soil at θ i = 0.077 cm 3 cm −3 , water penetrated toa depth of 30 cm immediately after infiltration for both sprinkling and flood application. Within 5 h of infiltration initiation, the profile was wetted to 80 cm depth and most of the applied water was retained in the 0–80 cm layer. Samples obtained at subsequent times did not indicate appreciable additional percolation. At θ i = 0.195 cm 3 cm −3 , however, water penetrated to 80 cm depth immediately after infiltration and about 57% of the applied water was retained for sprinkling as well as flood application. At 24 h, retentions were reduced to 17 and 25% for sprinkling and flood application, respectively. Similar results were obtained in no-till fallow or no-till soil cultivated to maize. Percolation in soil under both systems was rapid during the first 5 h after infiltration initiation but decreased rapidly afterwards. After 24 h, however, soil under no-till had more mean water content over the 0–80 cm depth than conventionally plowed treatment. Chloride profile indicated that a large percentage of the added water percolated beyond 80 cm depth without displacing the initially present water. More chloride recovery than water in profiles at high θ i also indicated some adsorption of chloride in these soils. Adsorption seemed more in the no-till system than in tilled soil.

Factors Affecting Ammonia Volatilization from Sewage Sludge Applied to Soil in a Laboratory Study

AbstractA forced‐air polyvinyl chloride (PVC) cylinder manifold chamber was used to collect ammonia (NH3) volatilized from sewage sludges applied to soil in the laboratory. A series of experiments were conducted in which the effect on NH3 volatilization of a single variable was studied. The reference control conditions were: Columbus, Ohio anaerobically digested liquid sewage sludge applied at 5 Mg ha−1 (dry wt) to a Crosby silt loam soil (pH 6.7) at 0.01 MPa initial moisture tension. The soil was bare and the sludge was unincorporated during the 24‐h study period. Air temperature was 26 ± 2°C. The variable conditions were: (i) initial soil moisture (0, 0.01, 1.5 MPa and air‐dry); (ii) time of incorporation (0.25, 1, 3, 6, 12, and 24 h after sludge application); (iii) soil pH (5.1, 6.7, 7.5); (iv) sludge type (anaerobically digested Columbus liquid sludge, partially dewatered Columbus anaerobic sludge, aerobically digested Medina liquid sludge, lime stabilized primary Ashland sludge, and composted primary Columbus sludge); (v) temperature (12.8, 18.3, 26.7°C); and (vi) vegetative cover [bare, grass sod (Poa pratensis), wheat straw (Triticum aestivum)].Initial soil moisture contents ≤1.5 MPa tension increased NH3 volatilization compared with air‐dry soil. Volatilization increased linearly with time elapsed before sludge incorporation. Ammonia loss was greater from soil at pH 7.5 than at pH 6.7 or 5.1. There was significantly greater loss of NH3 from the lime‐stabilized sludge (pH 12) than from the anaerobic and aerobic sludges. No detectable NH3 was lost from the compost. Volatilization decreased with decreasing temperature. When the sludge contained large sludge particles, NH3 loss increased with vegetative cover. However, cover had no effect when the sludge was well homogenized. For all experiments, 24‐h volatilization losses ranged from 0 to 32% of the NH3‐N applied.

Experimental study on thermal properties of frozen soils

A series of measurements of the effective thermal conductivity, specific heat and unfrozen-water content of various soils exposed to a cold environment have been carried out by a transient probe method and a calorimetric technique. The present experiments were performed at a very slow rate of cooling of the moist-soil and using four kinds of soil samples from fine to coarse grain-size. It was established that the amount of unfrozen-water in the frozen soil was dependent on the initial moisture content, the grain-size of the soil and the temperature (below 0°C). Measured values of the effective thermal conductivity and specific heat show a strong dependence on temperature, initial moisture content and grain-size of soil in the temperature range T = 0°C to −10°C. The anomalous behavior of a decrease in the effective thermal conductivity of frozen soil for the finest grain-size with decreasing temperature (below 0°C) was observed for a large initial moisture content w = 30–40%.

INFILTRATION CHARACTERISTICS IN RELATION TO TILLAGE PRACTICES AND INITIAL MOISTURE IN SANDY LOAM SOIL

Effect of tillage practices and initial soil moisture contents on infiltration rate and cumulative infiltration in sandy loam soil were studied and cumulative infiltration was predicted by using Kostiakov equation. The decrease in density values from 1.42 to 1,37 and 1.30 g cm, at air dry moisture content, resulted in increase in infiltra- tion rate considerably from 18,76 cm hour, to 22.53 and 30 43 cm hour, respec- tively. With increase in initial moisture content both infiltration rate and cumulative infiltration showed decreasing trend. The predicted cumulative infiltration values were in good agreement with the corresponding observed values with deviation of 102 2.23 and 1.61 per cent in zero tillage. normal tillage and light compaction, respecti- vely. The constants in Kostiakov equation relating to cumulative influx and infiltra- tion rate were found out in different surface conditions at air dry moisture content.

A LABORATORY STUDY ON THE EFFECTS OF SOIL MOISTURE CONTENT, TEXTURE, AND TIMING OF LEACHING ON N LOSS FROM TWO SOUTHERN ALBERTA SOILS

A column study was conducted to determine the effects of soil texture, initial soil moisture content and timing of leaching on N removal from two irrigated soils of southern Alberta. Pelleted NH4NO3 fertilizer (0.639 g N per column = 336 kg∙ha−1) was applied to Lethbridge loam (Leth L) and Cavendish fine sandy loam (CV FSL) at three initial levels of soil moisture: air dry (AD), 0.5 field capacity (0.5 FC), and wet (W, 25 cm suction). Leaching began immediately after the fertilizer application or was delayed 1 wk. Water was applied in 1400-mL (7.6 cm depth) increments every 2nd day for a total of 33 600 mL (175 cm depth). The leachate was collected, measured, and analyzed for NH4-N and NO3-N. The soil was analyzed for N content before and after leaching. More N was leached from CV FSL (0.600 g) than from Leth L (0.521 g). Responses to initial soil moisture were similar for both soils; the NO3-N concentration peak followed the advancing wetting front more closely in the AD than in the W systems and leaching losses were greatest from the 0.5 FC treatment. Delayed leaching did not significantly affect the amount of N leached. N losses, other than from leaching, were greatest in the W and AD treatments, in the AD treatment these losses were attributed to volatilization and, in the W soils, to denitrification.

Miscible displacement of reactive solutes in saline-sodic soils under varying flow conditions

SummaryThe paper reports a laboratory study on miscible displacement of reactive solutes during leaching a highly saline-sodic soil rich in soluble sodium carbonate with solutions of calcium chloride. The effect of varying flow velocities, initial soil moisture content and concentration of calcium in the leaching water on the extent of carbonate precipitation and replacement of sodium by calcium from the exchange positions was studied in soil columns. The results showed that precipitation of soluble carbonates in the soil increased with increasing flow velocity, initial soil moisture content and concentration of calcium in the leaching solution. The results further showed that the calcium exchange capacity of the soil was reduced significantly and nearly proportionally with decrease in the degree of water saturation as a consequence of decreased water application rate and initial soil moisture content. In view of the results obtained, a simple model to describe calcium-sodium exchange under unsaturated flow conditions in saline-sodic soils under consideration has been proposed. Possible implications of the results in actual field situations is discussed.

Factors affecting the accumulation of Dimethoate in soil

The effects of frequency of application, initial soil moisture content, rate of water application and soil organic matter content on the accumulation of dimethoate in different soils have been studied in the laboratory. It was found that: residual accumulation of the pesticide increased with frequency of application (even under leaching conditions) increasing the initial soil moisture content resulted in increased loss by leaching and therefore a reduction in the proportion of pesticide retained in the soil increased frequency of water application favours the loss of pesticide from the soil, thereby reducing the amount retained removal of soil organic matter reduces the biological degradation of the pesticide but accelerates the loss by leaching, evaporation or co‐distillation so that retention is reduced. Some measures are suggested for minimizing the accumulation of dimethoate in soils.

The effects of moisture stress on the germination of some Australian native grass seeds

The effects of moisture stress on the germination of the native grasses Themeda australis, Bothriochloa macra, Danthonia spp. and Stipa bigeniculata and the introduced species Lolium perenne (ryegrass) were investigated under laboratory and glasshouse conditions. At osmotic potentials between -3 and -10 bars and soil water potentials between -4.5 and -10 bars, the level of germination of ryegrass was greater than that of the native grasses. Also, at any given soil water potential, the levels of germination of both ryegrass and the native grasses were greater in a clay soil than in a sandy one. When native grass seeds were sown on the surface of the soil in flats in a glasshouse there was no germination in the absence of added water, even though the initial soil moisture content was as high as 40 per cent in some cases and a straw mulch was applied. When flats were watered daily, Stipa had the highest percentage establishment and Themeda the least. Establishment of all species was reduced by a decline in soil moisture content.

Field infiltration indices in the evaluation of tillage practices

Field infiltration rates were determined in order to evaluate different tillage treatments on a sandy loam soil. The following indices were chosen for evaluation: the infiltration rates at 5 min (IR-5), at 30 min (IR-30), and at 90 min (IR-90); the change in infiltration rate during 1 hour from 30 min to 90 min, designated as IR-(30–90); and also the cumulative infiltration at 90 min (CI-90). It was found that the index IR-(30–90) is statistically superior to other indices for the evaluation of tillage practices. It was also found that initial soil moisture content influences infiltration. The regression coefficients between initial moisture and IR-30, and initial moisture and CI-90 may also be used as indices for describing field infiltration differences. However, the index IR-(30–90) has been found to be free from the influence of initial moisture, and can be used directly for the evaluation of tillage treatments. For other soil types, however, the times used for the indices may be different.

Experiments relating to techniques for direct drilling of seeds into untilled dead turf

A method of comparing the design and performance of direct drilling drill coulters in terms of seed response, is described. A triple disc, hoe and an experimental chisel coulter are compared at very low forward speeds using small tillage bins containing undisturbed turf blocks under a maintained moisture stress. Maximum wheat seedling emergence with the chisel coulter assembly was 77% which was significantly greater than hoe and triple disc coulters with 27% and 26% respectively. A repeat experiment confirmed these trends, and a 22·3% comparative decrease in initial soil moisture content was necessary to reduce the performance of the chisel coulter to a similar standard to that of the other two types. Soil moisture measurements, irrigation response and counts of the fate of individual seeds suggested that the nature of the cover over the seed and the moisture retention properties of the groove were the main factors affecting the ability of seeds to germinate and subsequently to emerge. In this respect, the experimental chisel coulter confined most of its ground disturbance to a sub-surface zone, leaving the dead turf mulch substantially intact. This is in contrast to the “V”-shaped grooves created by the triple disc and hoe coulters. All coulters were followed by a special bar covering harrow.

Reactions of Ammonium Ortho‐ and Polyphosphate Fertilizers in Soil: I. Mobility of Phosphorus

AbstractThe mobility of P applied as diammonium orthophosphate (DAP), triammonium pyrophosphate (TPP), or ammonium polyphosphate (APP) was studied in columns of Hartsells fine sandy loam. The fertilizer dissolved in soil moisture that moved towards the application site. This water movement was sometimes against a gradient in soil moisture content, but it was along a gradient in the total potential of soil water.The extent of P movement from all three sources was similar, but the distribution patterns were different. The extent of P movement was influenced more by the initial soil moisture content than by the source of P.A higher fraction of the added P was precipitated when the source was TPP or APP than when it was DAP. The ability of the polyphosphates to sequester soil Fe and Al did not prevent the precipitation of these phosphates nor did it make them more mobile than the orthophosphates. It only delayed the precipitation reaction to a degree that depended on the polyphosphate content of the fertilizer material.

Studies on the Relationship between Liquid Limit and Initial Moisture Content of Volcanic Ash Soil

Studies on the Relationship between Liquid Limit and Initial Moisture Content of Volcanic Ash Soil

Vertical Infiltration into a Layered Soil

AbstractLayered soils are often encountered in nature, and the analysis of water movement in such soils is difficult and relies on detailed numerical computations. We present here an analytical model which describes the soil moisture profiles for vertical infiltration into a layered soil (a fine textured layer over a coarser layer). For the case of constant imposed flux of water at the surface, we consider the effect of an initial soil moisture content that increases with depth which causes a steepening of the moisture profile; and we also consider the effect of the discontinuity in soil texture at the interface which causes an accumulation of water above the interface in the fine textured soil. Our technique is easy to apply and gives results which are in good agreement with experiment and substantially better than those obtained by a recent computer simulation.

Simultaneous Solute and Water Transfer for an Unsaturated Soil

The simultaneous transfer of solute and water during infiltration was studied both in the field and numerically. An apparent diffusion coefficient of about 0.07 cm2/min provided maximum solute concentration values agreeable with field data over a 17‐hour period. The advance of a solute front introduced as irrigation water is shown to be nearly independent of the initial soil moisture content but highly dependent on the moisture content maintained at the soil surface during infiltration.

Application of the principle of calculated risk to scheduling of supplemental irrigation, II. Use on flue-cured tobacco

A simulation model was constructed to test the application of an irrigation-scheduling decision model which incorporated the basic concepts of calculated risk. Inputs for the model included: (1) the official probability precipitation forecasts for the periods “today”, “tonight” and “tomorrow”; (2) initial soil moisture content; (3) daily precipitation; (4) daily mean temperatures; (5) daily potential evapotranspiration and daylength values; (6) functions relating existing soil moisture content and stage of growth to the corresponding damage done to the crop; and (7) cost of irrigation. The loss functions were developed specifically for flue-cured tobacco. Two methods were used for calculating the cost of the irrigation. The decision criterion was applied by means of the simulation model to data from three growing seasons. The results were compared to the results as arrived at by irrigating at a 50% available moisture depletion level. It was found that the new criterion (using either method for calculating the cost of irrigation) yielded less total cost plus loss and achieved a better utilization of the available water than did the 50% criterion. While the state of the art does not allow extremely well-based development of the input variables and parameters, available data have shown the concepts of the model to yield adequate results. Much future development of the approach remains, however.