Field Soil Water Content Research Articles

Effects of coarse fragment content on soil physical properties, soil erosion and potato production

Most potato (Solanum tuberosum L.) production in northeastern America is on till soils with an abundance of stones. Stone picking has removed many coarse fragments to a point that it might be detrimental to soil quality. This study was to assess the impacts of coarse fragment content (10–19 mm in diameter) on selected soil physical properties, field soil thermal and water regimes, runoff and soil loss and potato yield and tuber quality on a sandy loam soil in New Brunswick. The objectives were to evaluate both beneficial and adverse effects of coarse fragment content (0, 10, 20 and 30% by volume) on soil quality in relation to potato production over a 4-yr period. Soil bulk density increased significantly by incorporating 10 to 30% coarse fragments into the plow layer. Porosity and available soil water-holding capacity were reduced in response to this increase in bulk density. In spite of the reduction in total porosity, pore size greater than 148 µm diameter of the 30% coarse fragment treatment was significantly greater than the 0, 10 and 20% treatments during 2001, 1 yr after the treatments were applied. This increase in macropores may have been responsible for the significantly higher saturated hydraulic conductivity of the soil treated with 30% coarse fragments. The results from 2002 and 2003 show that these beneficial effects on soil physical properties were short lived in this study; however, this may not be the case under field conditions because experimental plot problems of relocation of coarse fragments beyond plot boundaries and/or dilution with incorporation of stone-free subsoil material is not an issue in the field. Volumetric water content at field capacity of −33.3 kPa matric potential declined from 20.9% for the control to 7.7% for the 30% coarse fragment treatment. Cumulative soil heat greater than 10°C of the 30% treatment showed significant increases of 11.2, 8.8, and 3.7% during the growing season of 2001, 2002, and 2003, respectively, as compared with the control. Although field soil water tension regimes revealed that soil water in different treatments was held at a somewhat similar energy status, field soil water content was reduced considerably with increasing amount of coarse fragments. No significant differences in runoff and soil loss were found between treatments, but average reductions in soil loss over the 3-yr period were 9, 36, and 47% lower than the control for the 10, 20, and 30% treatments, respectively. Although no significant difference in yield and tuber quality between treatments was found in 2001–2003, both total and marketable yield decreased with increasing time. The yield reduction over time may be directly attributed to the mono-culture of potatoes practiced during the course of this experiment. Key words: Soil temperature, soil moisture, conductivity, bulk density, tillage erosion, potato cropping

Slurry-application implement tine modification of soil hydraulic properties under different soil water content conditions for silt–clay loam soils

Tillage action associated with liquid slurry application systems/management practices can modify soil infiltration properties. The degree or nature of such modification will depend largely on the type of tillage implement used, and the soil conditions at time of tillage activity. The specific objective of this study is to evaluate differences in soil infiltration properties, as measured using pressure infiltrometers and Guelph permeameters, resulting from the immediate tine action of two commonly used slurry application tillage implements (Kongskilde Vibro-Flex (S-tine) and the AerWay SSD (rolling aerator-type tine)) over a variety of silt–clay loam soil water content conditions. The results indicated that there were consistent negative correlations between field saturated hydraulic conductivity and soil water content for all tine-disturbed and undisturbed soil treatments. For Kongskilde, field-saturated hydraulic conductivity was, on average, lower in tine-influenced furrow bottoms, relative to those measured in undisturbed conditions at similar depths for most water content conditions. Generally, the Kongskilde tine-action reduced macropore-based infiltration in the bottom of the furrow for most soil conditions, albeit, this effect was most pronounced at the higher soil water contents. For AerWay, the tine-disturbed soils had generally higher field saturated hydraulic conductivities than undisturbed soil treatments over the observed water content range. This effect was manifested to a greater degree at higher, relative to lower observed water contents.

Changes in physical properties of a loess soil in China following two long-term fertilization regimes

A 13-year long-term experiment on the Loess Plateau of China was used to evaluate the effect of two different fertilizer regimes on the soil's physical/hydraulic properties. The fertilizer regimes included (i) control without any fertilizer (C), (ii) applications of chemical fertilizer (NPK), and (iii) applications of chemical fertilizer plus dairy manure (MNPK). Undisturbed soil cores were collected from the field to determine soil water retention curves and hydraulic conductivity (saturated and unsaturated). In addition, gravimetric water content, soil bulk density, porosity and saturated hydraulic conductivity were measured several times during the crop growing season to check seasonal variations. Annual application of manure increased soil water retention at the two soil depths tested (0–5 and 10–15 cm) relative to the control treatment ( P ≤ 0.1), by 13 to 32% at tension ranges from 0 to 300 kPa for the 0–5 cm layer, and by 5 to 19% from 0 to 2 kPa for the 10–15 cm layer. The field soil water content was also significantly increased at 0–10 cm depth ( P ≤ 0.05). Saturated hydraulic conductivity did not show any significant differences among treatments on the sampling dates due to large variations in the data. In contrast, the MNPK and NPK treatments decreased unsaturated hydraulic conductivity compared with C at 0–5 cm depth. No significant differences between treatments in this variable were observed at 10–15 cm depth. Generally, NPK showed similar effects to C. Soil physical properties (bulk density and porosity) showed significant seasonal variations.

Estimating actual evapotranspiration using water budget and soil water reduction methods

Studies on estimation of actual evapotranspiration on disturbed lands are scarce and yet such data are essential in hydrologic modeling. Our study compared the variability of estimates of actual evapotranspiration (AET) from a reclaimed site in northern Alberta using the simplified water budget (WB) and soil water reduction (SWR) methods. The AET estimates from the simplified water budget equation (AET1) required field soil water content, precipitation and runoff. The AET estimates from the soil water reduction method (AET2) required daily potential evapotranspiration (PET), field capacity (FC) water content, minimum field-measured water content, and field water content. Soil water was measured using neutron moisture gauge every 2 wk during the growing season for a 2-yr period. The average AET1 and AET2 estimates for 2001 were 1.9 and 1.4 mm per day, respectively, where as those for 2002 were 2.1 and 1.2 mm per day, respectively. The paired t-tests to compare AET1 against AET2 indicated significance differences (P ≤ 0.05) in 5 out of 11 measurement dates, especially during high rainfall periods. Overall AET2 estimates were more variable than AET1 estimates. Therefore, the larger variability of AET2 estimates imply less reliability of spatially averaged AET2 estimates for use in regional and global circulation models. Key words: Extractable water, reclaimed land, water budget, soil water reduction, potential evapotranspiration

Numerical Analysis of Coupled Water, Vapor, and Heat Transport in the Vadose Zone

Vapor movement is often an important part in the total water flux in the vadose zone of arid or semiarid regions because the soil moisture is relatively low. The two major objectives of this study were to develop a numerical model in the HYDRUS‐1D code that (i) solves the coupled equations governing liquid water, water vapor, and heat transport, together with the surface water and energy balance, and (ii) provides flexibility in accommodating various types of meteorological information to solve the surface energy balance. The code considers the movement of liquid water and water vapor in the subsurface to be driven by both pressure head and temperature gradients. The heat transport module considers movement of soil heat by conduction, convection of sensible heat by liquid water flow, transfer of latent heat by diffusion of water vapor, and transfer of sensible heat by diffusion of water vapor. The modifications allow a very flexible way of using various types of meteorological information at the soil–atmosphere interface for evaluating the surface water and energy balance. The coupled model was evaluated using field soil temperature and water content data collected at a field site. We demonstrate the use of standard daily meteorological variables in generating diurnal changes in these variables and their subsequent use for calculating continuous changes in water contents and temperatures in the soil profile. Simulated temperatures and water contents were in good agreement with measured values. Analyses of the distributions of the liquid and vapor fluxes vs. depth showed that soil water dynamics are strongly associated with the soil temperature regime.

Long-term effect of ploughing, and organic matter input on soil moisture characteristics of a Ferric Lixisol in Burkina Faso

Soil moisture characteristic curves were determined in long-term trials at the agronomic research center of Saria (latitude 12°16′ N, longitude 2°09′ W) in West-central Burkina Faso. The agronomic treatments combined soil tillage with organic and chemical fertilizers. The twin values for soil moisture and water potential showed that on ploughed plots, moisture content was higher at low suction and lower at high suction than the hand hoed plots. Moisture contents were higher for extreme suctions (pF < 1.5 and >3) on plots that received high dose of animal manure. The bush fallow plots behaved as a ploughed plot at low suction and like a hand hoed plot at the high suction. Field capacities were around 9.50% (g/g) and 8% (g/g), respectively, for hand hoed and ploughed plots, while the wilting points for both were of 5–6% (g/g). Organic matter input improved field capacity and soil water content at wilting point but not the useful available water (UAW). The UAW ≥10 mm on the fallow and the control, while it was <9 mm on the other treatments in 0–20 cm soil layer. Soil structural modifications induced by tillage and organic matter input explained these differences in soil hydrologic regime.

Soil moisture monitoring in the Toce valley (Italy)

Abstract. In the framework of the Mesoscale Alpine Programme (MAP), soil water content profiles were collected at a point station in the Toce Valley (Lago Maggiore MAP Target Area). The data are for the first 70 cm depth of soil for the period April–November, 1999. All measurements were made by a Time Domain Reflectometry device. The time variation of the water stored in a column of soil was estimated by a mass balance method. Evaporation was estimated from the data collected in the summer period. Likewise, by applying the mass balance method to the data collected during and after heavy precipitation events, the water infiltrated into the soil was also estimated. A qualitative evaluation of ponding and/or runoff as the difference between the precipitated and the drained water was obtained under suitable assumptions. Furthermore, the time evolution of the soil water content profile was studied by solving the Richards equation both analytically and numerically for two particular cases: the driest period and a period following a heavy precipitation event. Finally, during the MAP Special Observing Period, two intensive campaigns were performed, together with measurements using an airborne passive microwave radiometer, to assess the spatial distribution of the surface (0–30 cm depth) soil water content in fields with different physical and agricultural characteristics. Keywords: soil water content, Time Domain Reflectometry, TDR temperature-dependence, evaporation, infiltration, runoff, linearised Richards equation.

Errors in Heat Flux Measurement by Flux Plates of Contrasting Design and Thermal Conductivity

The thermal conductivity (λ) of soils may vary by a factor of about 4 for a range of field soil water contents. Measurement of soil heat flux (G) using a heat flux plate with a fixed λ distorts heat flow through the plates and in the adjacent soil. The objectives of this research were to quantify heat flow distortion errors for soil heat flux plates of widely contrasting designs and to evaluate the accuracy of a previously reported correction. Six types of commercially available heat flux plates with varying thickness, face area, and thermal conductivity (λm) were evaluated. Steady‐state laboratory experiments at flux densities from 20 to 175 W m−2 were completed in a large box filled with dry or saturated sand having λ of 0.36 and 2.25 W m−1 K−1 A field experiment compared G measured with pairs of four plate types buried at 6 cm in a clay soil with G determined using the gradient technique. The flux plates underestimated G in the dry sand by 2.4 to 38.5% and by 13.1 to 73.2% in saturated sand while in moist clay plate performance ranged from a 6.2% overestimate to a 71.4% underestimate. Application of the correction generally improved agreement between plate estimates and independent G measurements, especially when λ &gt; λm, although most plate estimates were still significantly lower than the actual G Limitations of the correction procedure indicate that renewed effort should be placed on innovative sensor designs that avoid or minimize heat flow distortion and/or provide direct, in situ calibration capability.

Spatial and Temporal Distribution of Soil Water Content in Fields under Different Vegetation Conditions Based on TDR Measurements

TDR (Time-domain reflectometry) is an advanced method for monitoring the water content in fields. TDR measurements can provide accurate information about vegetation effects on both spatial and temporal soil water distribution. The objective of this study was to examine the effects of vegetation conditions on the distribution of the soil water content. Soil water content was measured to express the spatial distribution in the surface layer (0-0.2 m) in grass, corn, and non-planted fields. Additionally, using the TDR method with multiple probes with different lengths, the measurements were conducted on a temporal basis at 4 depths (0--0.1, 0.1-0.2, 0.2-0.3 and 0.3-0.5 m) to determine the soil-water content profiles in the 3 fields. A significantly higher water content in both the grass and cornfields was found, compared to the non-planted field. Moreover, in the cornfield, we observed that microtopographic features significantly affected the spatial water distribution. The lower the soil water content, the higher the coefficient of variation of the soil moisture content. These results indicated that the effects of the vegetation conditions on the soil water distribution in the fields were significant. From the observation of the temporal soil water profiles in the 3 fields, it was found that soil management, i.e. tillage or no-tillage, was a major factor affecting the profiles.

Hydrological properties of a clay loam soil after long-term cattle manure application.

Limited information exists on the effect of long-term application of beef cattle (Bos taurus) manure on soil hydrological properties in the Great Plains region of North America. A site on a clay loam soil (Typic Haploboroll) was used to examine the effect of manure addition on selected soil hydrological properties in 1997 and 1998. The manure was annually applied in the fall for 24 yr at one, two, and three times the recommended rates (in 1973) under dryland (0, 30, 60, and 90 Mg ha(-1) wet basis) and irrigation (0, 60, 120, and 180 Mg ha(-1)). Manure significantly (P < or = 0.05) increased soil water retention (0-5 and 10-15 cm) by 5 to 48% compared with the control at most potentials between 0 and -1500 kPa. Field soil water content (0-5 and 10-15 cm) was increased by 10 to 22% in the summers of 1997 and 1998. Manure increased ponded infiltration by more than 200% at 90 Mg ha(-1) under dryland (1998) and at rates > or = 120 Mg ha(-1) under irrigation (1997). Field-saturated hydraulic conductivity (Kfs) of surface soil (1-cm depth) was significantly increased by 76 to 128% under dryland (1998) and irrigation (1997), as were number of pores > 1120 microm in diameter (37-128% increase). In contrast, manure rate had little or no effect on unsaturated hydraulic conductivity [K(psi)] values (-0.3, -0.5, -0.7, and -1.0 kPa) in 1997 and 1998. Overall, soil hydrological parameters generally had a neutral or positive response to 24 yr of annual manure addition.

Variability of soil water content and bulk density in a sugarcane field

The change in management practices of the sugarcane crop in Brazil, from the traditional trash burning before harvest to the new practice that leaves harvest residues on the field after harvest, can lead to alterations in the water regime and also in soil compaction levels. In this study a neutron-gamma surface gauge was used to monitor spatial and temporal variabilities of soil moisture and density in a experimental sugarcane area submitted to 3 harvest management practices: (i) mulched crop with harvest residues, (ii) crop with bare inter-row, and (iii) crop with ash residues from trash burning before harvest. Variability of soil water content and bulk density was studied using geostatistical tools and analysis of variance was used to compare averages. Autocorrelations and semivariograms indicate a spatial dependence of soil water contents, which were higher in the presence of trash residues left on the soil surface after harvest. The average difference between treatments (i) and (ii) was about of 15%, indicating the beneficial mulching effect with respect to soil water retention. Differences between (ii) and (iii) were much smaller.

A one-dimensional model for simulating soil water movement

Two simulation models have been used to predict water movement in soil and soil water content in a wheat field at Guan Yun (China). A backward finite difference approach was used to solve for the upward water flux and the water movement under a water table control system. It was found that the upward water flux decreased non-linearly as the water table depth (depth below root zone) increased, and a regression analysis revealed the relati-onship to be exponential. The values of calculated and measured soil water content and total evapotranspiration decreased with number of days after rain or irrigation. The nodal soil water content also decreased with the soil depth. (Journal of Applied Science and Technology: 2001 6(1-2): 56-64)

An exponential root-water-uptake model

Macroscopic root-water-extraction models often do not adequately account for the non-uniform distribution of roots in the soil profile. We developed an exponential root-water-uptake model, which was derived from a measured root density distribution function. The model, incorporated in the Soil-Water-Atmosphere-Plant (SWAP) simulation model, was tested on a clay loam soil cropped to soybeans and on a sandy loam soil cropped to corn, near Ottawa. Comparisons of measured and simulated soil water contents with the exponential model, a linear depth-dependent model and a constant-extraction-rate model were also made. The exponential model performed satisfactorily (average relative errors &lt;20%) when used to simulate measured field soil water contents at various depths. The constant-extraction-rate model overestimated the soil water contents in the upper part of the soil profile (maximum error 0.24 cm3 cm−3) and underestimated them (maximum error −0.09 cm3 cm−3) in the lower part. The exponential model and the linear model performed fairly similarly at the lower depths, but the exponential model gave better results in the near-surface horizons. The exponential model was sensitive to the root distribution coefficient and to the rooting depth, when the latter was approximately less than 40 cm. The results of this study suggest that the exponential root-water-uptake model as incorporated in SWAP is an improvement over those models, which do not account for the root distribution in the soil. Key words: SWAP, soil water simulation, root distribution, corn, soybeans, sensitivity analysis

Evaluation of the Root Zone Water Quality Model Using Field‐Measured Data from a Sandy Soil

AbstractTesting of simulation models against field‐measured data is an important step that must be taken before a model can be used as a management tool. Field soil water contents, intensively measured by time‐domain reflectometry (TDR) on a Zimmerman fine sand soil (Argic Udipsamments) in the Minnesota Management System Evaluation Area (MSEA), were used to evaluate the Root Zone Water Quality Model (RZWQM) over two rotated crop growing seasons in 1992 (corn, Zea mays L.) and 1993 [soybean, Glycine max (L.) Merr.]. The model was evaluated based on laboratory‐measured soil hydraulic properties. Reasonable agreement exists between the daily TDR‐measured and RZWQM‐predicted water contents for the upper soil depths. However, the model overestimated the lower soil profile, leading to a consistent overestimation of the total water depth (TWO) in the entire root zone (0 to 150 cm) during both the 1992 and 1993 growing seasons. The maximum errors in TWD for the entire root zone were 2.47 and 2.77 cm, respectively, in 1992 and 1993. Predictions of solute transport by RZWQM were examined for three herbicides: atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine], alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl) acetamide], and metribuzin [4‐amino‐6‐(1,1‐dimethylethyl)‐3‐(methylthio)‐1,2,4‐triazin‐5(4H)‐one]. Comparison between measured and predicted soil herbicide concentrations averaged over the top 15‐cm layer showed that the model matched the temporal changes of the field measurements reasonably well, although the measurements showed that all pesticides were somewhat more persistent over time than the model predicted.

State–space prediction of field–scale soil water content time series in a sandy loam

The description of field soil water content time series can be affected by uncertainty due to measurement errors of the respective state variables, errors due to assumptions underlying the model, and errors in the determination of boundary conditions. In this study, a simple state-equation was applied for predicting field soil water contents at three different soil depths. The simple state-model yielded large deviations of predictions from the measured soil water content, especially for the upper soil depth. Apparently, the magnitude of the estimated evaporation rate was too high. The prediction result could significantly be improved when the calculated evaporation was reduced by a factor of 0.7. In order to account for uncertainty sources associated with this simple approach, the state-equation was combined with a stochastic technique, the so-called Kalman–Filter. Applying the Kalman–Filter, the prediction quality significantly increased, even when the erroneously high evaporation was assumed to be true. However, prediction uncertainty increased for the same time periods, for which it was shown earlier that spatial correlation of soil water status was either random or very short. When the Kalman–Filter was applied in a scenario to the surface layer only, simulated soil water content in layers 2 and 3 agreed to measurements and were highly improved compared to simulations when layer 1 was not filtered. Hence, application of lab determined soil hydraulic property functions in combination with state observations of upper soil horizon water content and with the Kalman–Filter provides a promising opportunity to describe and predict soil water contents for entire soil profiles even under the presence of uncertainty sources.

Improvement of Planosol Solum: Part 7, Mechanical Properties of Soils

Abstract The planosol solum in China is a binary mixture of soil particles where silt forms the frame structure and clay fills the pore spaces. It is extremely hard and impermeable and has particular mechanical properties. This paper deals with the mechanical properties of the three horizons (Ap, Aw and B) of the planosol solum as an aid to understanding the draught requirement of a three-stage subsoil mixing plough for improvement of the planosol solum. Pseudogley soil which is a typical heavy clay soil in Japan was also tested for comparison. Tensile strength, compressive strength, shearing strength, soil-metal friction as static properties and soil brittleness as a dynamic property were determined. The results show that the cohesive strengths of all soils, except the B horizon, had maximums at particular soil water contents. These values were nearly the same as the plastic limits. The B horizon did not have a maximum value in the range of soil water content studied. The cohesion of the pseudogley soil was the smallest and that of the Aw horizon was the largest. The Ap and Aw horizons had the same trend in brittleness; the impact energy required to fracture both soils increased with decreasing soil water content. The required impact energy of the B horizon showed a quite different trend from that of the other soils and was a maximum at 30% d.b. soil water content. When the B horizon was dry, the required impact energy decreased and it became brittle. The commonly occurring soil water content in the actual planosol fields was more than 20% d.b. In this range, the tensile strength of the Aw horizon was the largest, followed by the B horizon, Ap horizon and pseudogley soil. Comparing the cohesion at soil water contents in excess of 20% d.b., the tensile strength of the pseudogley soil was about one-seventh of its cohesion but the tensile strengths of all planosols was about one-half of their cohesive values.

Field scale variability of solute transport parameters and related soil properties

Abstract. The spatial variability of transport parameters has to be taken into account for a reliable assessment of solute behaviour in natural field soils. Two field sites were studied by collecting 24 and 36 small undisturbed soil columns at an uniform grid of 15 m spacing. Displacement experiments were conducted in these columns with bromide traced water under unsaturated steady state transport conditions. Measured breakthrough curves (BTCs) were evaluated with the simple convective-dispersive equation (CDE). The solute mobility index (MI) calculated as the ratio of measured to fitted pore water velocity and the dispersion coefficient (D) were used to classify bromide breakthrough behaviour. Experimental BTCs were classified into two groups: type I curves expressed classical solute behaviour while type II curves were characterised by the occurrence of a bromide concentration maximum before 0.35 pore volumes of effluent (MI&lt;0.35) resulting from preferential flow conditions. Six columns from site A and 8 from site B were identified as preferential. Frequency distributions of the transport parameters (MI and D) of both sites were either extremely skewed or bimodal. Log-transformation did not lead to a normal distribution in any case. Contour maps of bromide mass flux at certain time steps indicated the clustering of preferential flow regions at both sites. Differences in the extent of preferential flow between sites seemed to be governed by soil structure. Linear cross correlations among transport parameters and independently measured soil properties revealed relations between solute mobility and volumetric soil water content at time of sampling, texture and organic carbon content. The volumetric field soil water content, a simple measure characterising the soil hydraulic behaviour at the sampling location, was found to be a highly sensitive parameter with respect to solute mobility and preferential flow situations. Almost no relation was found between solute transport parameters and independently determined soil properties when non-preferential and preferential samples were considered separately in regression analyses. Future work should concentrate to relate integrated parameters such as the infiltration rate or the soil hydraulic functions to solute mobility under different flow situations.

Parameter selection and testing the soil water model SOIL

The soil water and heat simulation model SOIL was tested for its suitability to study the processes of transport of water in soil. Required parameters, particularly soil hydraulic parameters, were determined by field and laboratory tests for some common soil types and for soils subjected to contrasting treatments of long-term grassland and tilled land under cereal crops. Outputs from simulations were shown to be in reasonable agreement with independently measured field drain outflows and soil water content histories.

Iterative solution of a stochastic differential equation: an efficient method for simulating soil variability

A simple and efficient method was developed to simulate one-, two- and three-dimensional random fields with one particular kind of variogram for each dimension. The proposed method used an iterative numerical scheme to solve a stochastic differential equation. Since the procedure required minimal computer memory and computation time, it was especially attractive for simulating a large number of points in studying spatial distributions of soil properties. Furthermore, the procedure produced accurate realizations of random fields, in terms of simulation mean and covariance. The mean values and the covariances or variogram structures calculated from the simulated data by the proposed procedure matched closely to the theoretical values and functions. The procedure was app!ied to simulate spatial variability of soil water content, soil chemicals, and soil reflectance in the real field. Based on available measured data of these soil properties, conditional simulations using the proposed technique were compared with kriged results. Both methods produced very similar spatial distributions of the soil properties.

Determination of Field Soil Water Content by Frequency Domain Reflectometry (FDR) Technique

Determination of Field Soil Water Content by Frequency Domain Reflectometry (FDR) Technique