54 research outputs found
Short, Multineedle Frequency Domain Reflectometry Sensor Suitable for Measuring Soil Water Content
No full textTime domain reflectometry (TDR) is a well-established electromagnetic technique used to measure soil water content. Time domain reflectometry sensors have been combined with heat pulse sensors to produce thermo-TDR sensors. Thermo-TDR sensors are restricted to having relatively short needles to accurately measure soil thermal properties. Short needle lengths, however, can limit the accuracy of the TDR measurement of soil water content. Frequency domain reflectometry (FDR) sensors are an alternative to TDR sensors that can provide an inexpensive measurement of soil water content. The objective of this study was to determine whether short FDR sensors can accurately measure soil water content. We designed and constructed a short FDR sensor. For four soil types across a range of water contents, temperatures, and salt contents, we measured soil dielectric spectra with the short FDR sensor. A vector network analyzer was used to obtain soil dielectric spectra in the 1-MHz to 3-GHz frequency range. The ideal frequency of a short FDR sensor is the frequency at which the permittivity is not altered by changing temperature or salt content. The 47- to 200-MHz range was an ideal frequency range for measuring soil water content, and 70 MHz was the frequency least influenced by temperature and salt content. The short FDR sensor provided quick, continuous, stable, and cheap measurements of soil water content. Because of the promising performance of the short thermo-FDR sensor in laboratory studies, sensors should be evaluated in future field studies.This article is published as Xu, Jinghui, Xiaoyi Ma, Sally D. Logsdon, and Robert Horton. "Short, multineedle frequency domain reflectometry sensor suitable for measuring soil water content." Soil Science Society of America Journal 76, no. 6 (2012): 1929-1937. doi: 10.2136/sssaj2011.0361. Posted with permission.</p
Determining solute transport parameters in field soil
No full textDetermining the preferential flow characteristics of a soil is important because agrichemicals can contaminate groundwater via preferential flow pathways. One model that predicts solute transport due to preferential flow is the mobile/immobile solute transport model, which partitions the total water content (θ) into a mobile fraction (θₘ) and an immobile fraction (θᵢₘ). Recently, an in situ method was proposed for determining the mobile/immobile model parameters of θᵢₘ and mass exchange coefficient (α). The in situ method uses a tension infiltrometer to apply a series of four fluorobenzoate tracers to determine α and θᵢₘ. This new method was field tested at 47 sites along a transect in a ridge-till com field of Nicollet soil, a fine-loamy, mixed, mesic Aquic Hapludoll. The immobile fraction (θᵢₘ/θ) ranged from 0.40 to 0.95 with a mean of 0.65 and standard deviation of 0.14. The mass exchange coefficient ranged from 0.0002 min⁻¹ to 0.006 min⁻¹ with a mean of 0.002 min⁻¹ and standard deviation of 0.002 min⁻¹. These values are similar in magnitude and range to values reported by other investigators. The values of θᵢₘ/θ and α along the transect indicated no spatial trends, and significant correlations existed between α and soil water flux, α and θᵢₘ² and θ and θᵢₘ.
Concerns with the presence of agricultural chemicals in groundwater have drawn attention towards the processes of chemical transport in field soil. The hydraulic and preferential flow properties of a field soil play an active role in the transport of chemicals to groundwater. In this study the hydraulic conductivity (K) and the preferential flow parameters (immobile water content (θᵢₘ) and mass exchange coefficient (α)) of the mobile/immobile domain model are investigated. Forty field measurements were made within a no-till com field consisting of a Harps series soil, a fine-loamy, mixed, mesic Typic Calciaquoll. Hydraulic conductivity, θᵢₘ, and α values were determined at four pressure heads of 10, -30, -60, and -150 mm using ponded and tension infiltrometers. Immobile water content and α values were determined by using a recently described in situ technique. The immobile water content decreased with lower water contents associated with the lower pressure heads. However, the immobile water fraction (θᵢₘ/θ) did not show a clear trend with pressure head or hydraulic conductivity. The mean θᵢₘ/θ values were 0.40, 0.27, 0.22, and 0.35 for the respective pressure heads of 10, -30, -60, and -150 mm. The mass exchange coefficient showed an obvious association with the different flow regimes. As the pressure head decreased so did α. The mean α values were 1.34⁻¹, 0.036 h⁻¹, 0.0044 h⁻¹, and 0.0033 h⁻¹ for pressure heads of 10, -30, -60, and -150 mm respectively. The preferential flow parameters determined by the recent technique compare well with previously found values from other field studies
Fitting performance of particle-size distribution models on data derived by conventional and laser diffraction techniques
No full textMathematical description of most classical particle size distribution (PSD) data is often used for estimating soil hydraulic properties. Fast laser diffraction (LD) techniques now provide more detailed PSDs, but deriving a function to characterize the entire range of sizes is a major challenge. The aim of this study was to compare the fitting performance of seven PSD functions with one to four parameters on sieve-pipette and LD data sets of fine-textured soils. The fits were evaluated by the adjusted R 2, MSE, and Akaike's information criterion. The fractal and exponential functions performed poorly while the performance of the Gompertz model increased with clay content for the LD data sets. The Fredlund function provided very good fits with sieve-pipette PSDs but not the corresponding LD data sets, probably due to underestimation of the clay fraction in the latter. The two-parameter lognormal function showed better overall performance and provided very good fits with both sieve-pipette and LD data sets.Abdul R. Bah, Olena Kravchuk and Gunnar Kirchho
Measurement of Field Soil Hydraulic and Solute Transport Parameters
No full textAgricultural chemical presence in groundwater has drawn attention toward transport processes occurring in soil. Hydraulic conductivity (K) and water-holding capacity of a soil have great influence on water flow and solute transport. However, much of the chemical transport to groundwater can occur through preferential flow pathways. The simplified, preferential flow, mobile-immobile model partitions the water content (θ) into mobile (θm) and immobile (θim) domains, with solute exchange between the domains characterized by the mass-exchange coefficient (α). In this study a sequential tracer application technique was used and K, θ, θim, and α were estimated for a series of pressure heads (H = 10, −30, −60, and −150 mm). This method uses a tension infiltrometer to measure both hydraulic and solute transport parameters in situ. The study took place in a no-till corn (Zea mays L.) field mapped as a Harps series soil (fine-loamy, mixed, mesic Typic Calciaquoll). Unsaturated values of θ and K were distinct from the saturated values. Similarly, though less clear cut, distinctions between saturated and unsaturated values of θim, immobile water fraction (θim/θ), and α were observed. The medians of θ for the sequence of decreasing H values were 0.40, 0.34, 0.34, and 0.33 m3 m-3. The median K values for the same sequence of H were 108, 1.69, 1.51, and 0.72 µm s-1. The median θim/θ values for the H sequence were 0.40, 0.28, 0.25, and 0.39. The median values of α for the H sequence were 0.59, 0.015, 0.0028, and 0.0029 h-1. A strong correlation between α and H suggests a velocity dependence of α.This article is published as Casey, Francis XM, Robert Horton, Sally D. Logsdon, and Dan B. Jaynes. "Measurement of field soil hydraulic and solute transport parameters." Soil Science Society of America Journal 62, no. 5 (1998): 1172-1178. doi: 10.2136/sssaj1998.03615995006200050003x. Posted with permission.</p
Measurement of Soil Water Content with Dielectric Dispersion Frequency
No full textFrequency domain reflectometry (FDR) is an inexpensive and attractive methodology for repeated measurements of soil water content (θ). Although there are some known measurement limitations for dry soil and sand, a fixed-frequency method is commonly used with commercially available FDR probes. The purpose of our study was to determine if the soil dielectric spectrum could be used to measure changes in θ. A multifrequency FDR probe was constructed with a 6-mm diameter, and a soil dielectric spectrum was obtained. Using the dielectric spectrum, the dielectric dispersion frequency (fd) was determined. It was discovered that changes in fd were highly correlated with changes in θ, and a third-order polynomial equation (R2 = 0.96) was developed describing the relationship. The effectiveness of fd for θ measurement was evaluated for three soils and a sand across a range of θ. The effects of soil temperature and soil salinity were also evaluated. Accurate measurements of θ were obtained even in dry soil and sand. The root mean square error of the θ estimated by the fdmeasurement was 0.021. The soil temperature and soil salinity had no measureable effects on θ determination. The use of fd for θ determination should be an effective and accurate methodology, especially when dry soils, soil temperature, and/or soil salinity could potentially cause problems with the θ measurements.This article is published as Xu, Jinghui, Sally D. Logsdon, Xiaoyi Ma, Robert Horton, Wenting Han, and Ying Zhao. "Measurement of Soil Water Content with Dielectric Dispersion Frequency." Soil Science Society of America Journal 78, no. 5 (2014): 1500-1506. doi: 10.2136/sssaj2013.10.0429. Posted with permission.</p
Thirteen-year stover harvest and tillage effects on soil compaction in Iowa
No full textCorn (Zea mays L.) stover is an abundant biomass source with multiple end-uses including cellulosic biofuel production. However, stover removal may increase soil compaction by reducing organic matter inputs and increasing vehicle loads during harvest. While numerous studies have reported stover removal impacts on soil physical quality, few have assessed the role played by traffic compaction. Our objective was to quantify subsurface soil compaction after 13 years of chisel plow versus no-till management and no, moderate (3.5 ± 1.1 Mg ha−1 year−1), or high (5.0 ± 1.7 Mg ha−1 year−1) stover harvest rates. Penetration resistance was measured in most- and least-trafficked interrow spaces. Chisel plowed plots with moderate and high levels of stover removal had higher penetration resistance in trafficked areas relative to least-trafficked areas, whereas there was no evidence of traffic compaction when stover was retained. Traffic compaction did not negatively impact yields, which were greater with high levels of stover removal compared to no removal. The no-till practice led to very small increases in penetration resistance with wheel traffic and had no evidence of increased compaction with residue removal. This lack of traffic compaction indicated soils under no-till practice have a higher load-bearing capacity than soils under chisel plow practice. Overall, there were no yield-limiting effects of tillage practice or stover removal, and no evidence of soil compaction below the plow layer, suggesting stover removal with both tillage practices can be effectively employed without detrimental effects on plant or soil health.This is the published version of the following article: Phillips, Claire L., Mehari Z. Tekeste, Elnaz Ebrahimi, Sally D. Logsdon, Robert W. Malone, Peter L. O'Brien, Bryan D. Emmett, and Douglas Karlen. "Thirteen‐year stover harvest and tillage effects on soil compaction in Iowa." Agrosystems, Geosciences & Environment 6, no. 2 (2023): e20361.
DOI: 10.1002/agg2.20361.
Copyright 2023 The Authors.
Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0).
Posted with permission
Corn root growth and distribution as influenced by soil physical properties
No full textMechanisms of root growth under variable field conditions were investigated by observing corn ( Zea mays L.) root growth and distribution in the field and by observing the influence of soil physical stresses on corn seedling root growth in controlled environments. The field soil was Groseclose silt loam (clayey, mixed, mesic Typic Hapludult). Groseclose A horizon material was used for the growth chamber experiments where corn was grown in a range of aggregate sizes, bulk densities, low and high soil moisture levels, and temperatures. Rooting patterns in the field were altered by drought. Root length density decreased in the dry surface soil and proliferated in the moist subsurface soil. Distribution of roots length densities was skewed. A few samples contained many roots and many samples contained few roots because roots were restricted to interpedal voids. In the growth chamber experiments, roots were not able to penetrate large aggregates and were restricted to interaggregate zones. This tortuous path of root growth led to transitory impedances as roots were deflected around aggregates. Corn roots were able to push small aggregates out of their path. An equation was developed to describe this impedance as a function of aggregate size, root diameter, and deflection angle. Mechanical impedance, oxygen stress, lower temperatures, and moisture stress reduced seedling root elongation to some extent, but the influence of reduced temperature was the most dramatic. At 6 days corn root length at 21°C was 20% of that at 25°C while root length at 17°C was only 5% of that at 25°C. Mechanical impedance and reduced temperatures also increased root diameter. In wet soil, oxygen stress was the most immediate factor affecting root growth, but after 4 days root elongation was stimulated suggesting other unknown factors. Two semi-empirical models were developed. One was based on the exponential growth rate of the root system and the other based on the linear growth rate of each root member. These models accounted for the reduction in root growth rate due to the soil physical stresses.Ph. D
- …
