scholarly journals Modelling of Unsaturated Flow in Heterogeneous Soils

1986 ◽  
Vol 17 (4-5) ◽  
pp. 281-294 ◽  
Author(s):  
K. Høgh Jensen ◽  
M. B. Butts
Keyword(s):  
Soil Moisture ◽  
Hydraulic Conductivity ◽  
Unsaturated Flow ◽  
Soil Surface ◽  
Saturated Hydraulic Conductivity ◽  
Stochastic Methods ◽  
Physical Parameters ◽  
Heterogeneous Soils ◽  
Physically Based ◽  
Moisture Conditions

Modelling of soil moisture conditions in spatially variable fields is treated using stochastic methods. Spatial variability of moisture content in a vegetation covered field is partly caused by field variability in soil physical parameters. In the present study a physically based model is coupled with a statistical description of retention properties and saturated hydraulic conductivity respectively to simulate moisture conditions in heterogeneous soils. Results are compared with measurements obtained from two 0.5 ha field sites. Simulations based on the variation in retention properties are shown to account for much of the observed variation in soil moisture conditions with some deficiencies evident close to the soil surface. Variations in saturated hydraulic conductivity alone give an incomplete description of observed variability in soil moisture conditions.

Modelling leaching and recharge in a bare transitional red-brown earth ponded with low salinity water in summer

1994 ◽  
Vol 34 (7) ◽  
pp. 1085 ◽  
Author(s):  
L Cai ◽  
SA Prathapar ◽  
HG Beecher
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Soil Profile ◽  
Soil Surface ◽  
Saturated Hydraulic Conductivity ◽  
Rate Dependent ◽  
Water And Salt Movement ◽  
Winter Fallow

A modelling study was conducted to evaluate water and salt movement within a transitional red-brown earth with saline B horizon soil when such waters are used for ponding in summer. The model was calibrated using previously published experimental data. The calibrated model was used to evaluate the effect of depth to watertable, saturated hydraulic conductivity, and ponding water salinity on infiltration, water and salt movement within the soil profile, and recharge. The study showed that when initial soil water content and the saturated hydraulic conductivity (Ks) are low, infiltrating water will be stored within the soil profile even in the absence of a shallow watertable. Once the soil water content is high, however, recharge will be significant in winter, even if there is no net infiltration at the soil surface. Infiltration rates depend more on Ks than the depth to watertable if it is at, or below, 1.5 m from the soil surface. When Ks is high, recharge under ponding will be higher than that under winter fallow. Subsequent ponding in summer and fallow in winter tend to leach salts from the soil profile, the leaching rate dependent on Ks. During winter fallow, due to net evaporation, salts tend to move upwards and concentrate near the soil surface. In the presence of shallow watertables, leached salts tend to concentrate at, or near, the watertable.

EVAPOTRANSPIRATION AND LEAF WATER STATUS OF ALFALFA GROWING UNDER ADVECTIVE CONDITIONS

1981 ◽  
Vol 61 (3) ◽  
pp. 601-607 ◽  
Author(s):  
R. J. WILLIAMS ◽  
DARRYL G. STOUT
Keyword(s):  
Soil Moisture ◽  
Potential Evapotranspiration ◽  
Water Status ◽  
Bowen Ratio ◽  
High Rate ◽  
Leaf Water Status ◽  
Leaf Osmotic Potential ◽  
Physically Based ◽  
Environmental Demand ◽  
Moisture Conditions

Actual evapotranspiration (LE) and leaf osmotic potential (ψs) were measured on a Medicago sativa L. (alfalfa, cv. Thor) field in interior British Columbia that is subject to advection. During periods of advection, LE, measured by the Bowen ratio energy balance method, exceeded both the net radiation (Q*) and the potential evapotranspiration (PE) calculated by the physically based formula of Priestley and Taylor (1972). During advection, Q* was a better approximation of LE than was PE. During nonadvection periods, LE was approximately equal to PE. It was found that the Jury and Tanner (1975) modification of PE for advective conditions gave favorable results during periods immediately following irrigation. Diurnal measurements revealed that leaf ψs reached a minimum by about 1200 h and then remained constant even though LE continued at a high rate. Leaf ψs measured at 0800 h reflected soil moisture conditions, and leaf ψs measured at 1400 h reflected both soil moisture conditions and environmental demand.

COMPARISON OF METHODS FOR DETERMINING SATURATED HYDRAULIC CONDUCTIVITY AND DRAINABLE POROSITY OF TWO SOUTHERN ALBERTA SOILS

1986 ◽  
Vol 66 (2) ◽  
pp. 249-259 ◽  
Author(s):  
G. D. BUCKLAND ◽  
D. B. HARKER ◽  
T. G. SOMMERFELDT
Keyword(s):  
Soil Moisture ◽  
Hydraulic Conductivity ◽  
Characteristic Curve ◽  
Subsurface Drainage ◽  
Saturated Hydraulic Conductivity ◽  
Drainage Design ◽  
Moisture Characteristic ◽  
Constant Head ◽  
Subsurface Drains ◽  
Drainable Porosity

Saturated hydraulic conductivity (Ks) and drainable porosity (f) determined by different methods and for different depths were compared with those determined from the performance of drainage systems installed at two locations. These comparisons were made to determine which methods are suitable for use in subsurface drainage design. Auger hole and constant-head well permeameter Ks were 140 and 110%, respectively, of Ks determined from subsurface drains. Agreement of horizontal or vertical Ks, from in situ falling-head permeameters; to other methods was satisfactory providing sample numbers were large. Ks by Tempe cells was only 3–10% of drain Ks and in one instance was significantly lower than Ks determined by all other methods. At one site a profile-averaged value of f determined from the soil moisture characteristic curve (0–5 kPa) of semidisturbed cores agreed with that determined from drainage trials. At the other site, a satisfactory value of f was found only when the zone in which the water table fluctuated was considered. Results indicate that Ks determined by the auger hole and constant-head well permeameter methods, and f determined from the soil moisture characteristic curve of semidisturbed cores, are sufficiently reliable and practical for subsurface drainage design. Key words: Subsurface drainage, hydraulic conductivity, drainable porosity

Measuring saturated hydraulic conductivity and sorptivity using twin rings

Soil Research ◽  
1982 ◽  
Vol 20 (4) ◽  
pp. 295 ◽  
Author(s):  
DR Scotter ◽  
BE Clothier ◽  
ER Harper
Keyword(s):  
Steady State ◽  
Hydraulic Conductivity ◽  
Soil Surface ◽  
Soil Disturbance ◽  
Saturated Hydraulic Conductivity ◽  
Field Soil ◽  
Field Soils

A method of measuring, with minimal soil disturbance, the saturated hydraulic conductivity and sorptivity of field soil is presented and discussed. It involves measuring the steady-state infiltration of ponded water from two rings, of different radii, that have been lightly pressed into the soil surface. The method is based on Wooding's solution for steady infiltration from a shallow, circular pond. Criteria for selecting ring radii are discussed. Results for three field soils are found to give consistent values for the conductivity and sorptivity.

Impact of incorporated hay mulch on selected physical, chemical and microbiological properties of a loam soil in Atlantic Canada after five years of continuous potato production

2005 ◽  
Vol 85 (1) ◽  
pp. 161-172 ◽  
Author(s):  
H. W. Rees ◽  
T. L. Chow
Keyword(s):  
Soil Moisture ◽  
Hydraulic Conductivity ◽  
Organic Carbon ◽  
Soil Quality ◽  
Solanum Tuberosum L ◽  
Total Yield ◽  
Growing Season ◽  
Crop Productivity ◽  
Saturated Hydraulic Conductivity ◽  
Soil Productivity

Maintenance of soil quality and crop productivity is a major concern under intensive potato (Solanum tuberosum L.) production. The effects of four consecutive annual applications of 0.00, 2.25, 4.50 and 9.00 t ha-1 wet hay on growing season soil moisture and thermal regimes, soil quality and yield were evaluated on a loamy Orthic Humo-Ferric Podzol between 1995 and 1999. Hay mulching increased soil moisture at the beginning of the growing season by 6.5 to 12.7%, with increases significant until June 24, September 07 and September 20 for the 2.25, 4.50 and 9.00 t ha-1 treatments, respectively. Growing season soil temperature of the 4.50 and 9.00 t ha-1 treatments were lower than control, but only by −0.2 and −0.8°C, respectively. Hay mulching increased soil organic carbon (SOC) of the plow layer (0–25 cm), which increased biological activity resulting in better soil aggregation with more macropores, faster saturated hydraulic conductivity and reduced bulk density. Soil air CO2 concentration was significantly correlated to SOC content, aggregation, porosity and saturated hydraulic conductivity. Hay mulching at 2.25 and 4.50 t ha-1 increased total potato yield over that of the unmulched control by 11–14%, but was insufficient to maintain soil productivity. Hay mulching at 9.00 t ha-1 may have been excessive in terms of crop yield as it showed no total yield benefits. Key words: Organic carbon, CO2 concentration, aggregates, porosity

scholarly journals Form and function in hillslope hydrology: in situ imaging and characterization of flow-relevant structures

2017 ◽  
Vol 21 (7) ◽  
pp. 3749-3775 ◽  
Author(s):  
Conrad Jackisch ◽  
Lisa Angermann ◽  
Niklas Allroggen ◽  
Matthias Sprenger ◽  
Theresa Blume ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Hydraulic Conductivity ◽  
Soil Water ◽  
Time Lapse ◽  
Saturated Hydraulic Conductivity ◽  
Form And Function ◽  
And Function ◽  
Hillslope Scale

Abstract. The study deals with the identification and characterization of rapid subsurface flow structures through pedo- and geo-physical measurements and irrigation experiments at the point, plot and hillslope scale. Our investigation of flow-relevant structures and hydrological responses refers to the general interplay of form and function, respectively. To obtain a holistic picture of the subsurface, a large set of different laboratory, exploratory and experimental methods was used at the different scales. For exploration these methods included drilled soil core profiles, in situ measurements of infiltration capacity and saturated hydraulic conductivity, and laboratory analyses of soil water retention and saturated hydraulic conductivity. The irrigation experiments at the plot scale were monitored through a combination of dye tracer, salt tracer, soil moisture dynamics, and 3-D time-lapse ground penetrating radar (GPR) methods. At the hillslope scale the subsurface was explored by a 3-D GPR survey. A natural storm event and an irrigation experiment were monitored by a dense network of soil moisture observations and a cascade of 2-D time-lapse GPR trenches. We show that the shift between activated and non-activated state of the flow paths is needed to distinguish structures from overall heterogeneity. Pedo-physical analyses of point-scale samples are the basis for sub-scale structure inference. At the plot and hillslope scale 3-D and 2-D time-lapse GPR applications are successfully employed as non-invasive means to image subsurface response patterns and to identify flow-relevant paths. Tracer recovery and soil water responses from irrigation experiments deliver a consistent estimate of response velocities. The combined observation of form and function under active conditions provides the means to localize and characterize the structures (this study) and the hydrological processes (companion study Angermann et al., 2017, this issue).

Alvar seed bank germination responses to variable soil moisture

2007 ◽  
Vol 85 (10) ◽  
pp. 986-993 ◽  
Author(s):  
Jeremy T. Lundholm ◽  
Kaeli E. Stark
Keyword(s):  
Soil Moisture ◽  
Environmental Heterogeneity ◽  
Seedling Recruitment ◽  
Soil Surface ◽  
Drought Treatment ◽  
Southern Ontario ◽  
Soil Seed Banks ◽  
Niche Differences ◽  
Moisture Conditions ◽  
Rarefaction Effects

Environmental heterogeneity can create differential opportunities for seedling recruitment among plant species. We collected soil seed banks from alvar habitats in southern Ontario and exposed them to three soil moisture treatments. Density and species richness of germinants were greatest in treatments kept moist compared with treatments where soil was either saturated with standing water at the soil surface or where drought was imposed. Contrary to previous studies, the drought treatment did not stimulate the germination of species that remained ungerminated in other treatments, but did increase the germination of five species that also germinated in wetter soils. Although 12 of the 40 species germinated in only one of the three treatments, overall community composition among watering treatments was relatively consistent; few species showed evidence of differential responses to soil moisture conditions. Variability in soil moisture in this system can alter population and community properties by rarefaction effects, as opposed to niche differences among species.

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