The use of computer assisted tomography to determine spatial distribution of soil water content

Soil Research ◽  
1983 ◽  
Vol 21 (4) ◽  
pp. 435 ◽  
Author(s):  
JM Hainsworth ◽  
LAG Aylmore
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Plant Root ◽  
Computer Assisted ◽  
X Ray ◽  
Computer Assisted Tomography ◽  
Spatial Changes ◽  
Exciting Possibility ◽  
Non Destructive

To date no experimental technique has been capable of directly and repetitively measuring spatial distributions of soil water content in a non-destructive manner. The potential of computer assisted tomography (CAT) to overcome this problem has been examined in this paper. The results obtained from a commercially-produced X-ray CAT scanner and a conventional gamma scanner suggest that CAT scanning can be used to determine spatial changes in soil water content with adequate resolution for soil-plant studies. The technique can clearly be used to resolve spatial changes in soil water content with time. Application of the technique to water uptake by a single plant root shows that CAT scanning presents an extremely exciting possibility for studies of soil-plant water relations.

Studies of soil water drawdowns by single radish roots at decreasing soil water content using computer-assisted tomography

Soil Research ◽  
2001 ◽  
Vol 39 (6) ◽  
pp. 1387 ◽  
Author(s):  
M. A. Hamza ◽  
S. H. Anderson ◽  
L. A. G. Aylmore
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Transpiration Rate ◽  
Osmotic Adjustment ◽  
Temporary Increase ◽  
Computer Assisted ◽  
X Rays ◽  
Beam Hardening ◽  
Computer Assisted Tomography

Application of computer-assisted tomography to the attenuation of X-rays has been used to compare the drawdowns in soil water content associated with radish roots at starting soil water contents (θv) of 0.3 cm3/cm3 and 0.1 cm3/cm3, respectively. Decreasing soil water content results in an increase in the appearance of ‘beam hardening’. Decreasing soil water content from 0.3 to 0.1 cm3/cm3 caused the transpiration rate to decrease by 6–10 times. This was presumably due to a reduction in the water potential gradient across the root membrane. The transpiration rate decreased less rapidly than did the water content at the soil–root interface, suggesting some osmotic adjustment by the leaves. This osmotic adjustment would allow the plant to maintain transpiration rate even at relatively low soil water content. The drawdown distances associated with roots growing at the lower soil water content were 8 times smaller than those at the high soil water content and the value of θv at the soil–root interface at the end of the transpiration period was 2.5 times lower. The radish roots exhibited a temporary slight decrease in diameter after the transpiration commenced followed by a significant temporary increase. However, root diameter stabilised around its original value when the plant attained an almost steady water uptake rate. Despite the complexity arising from ‘beam hardening’, CAT scanning can provide valuable information on processes at the root–soil interface.

Application of computer assisted tomography (CAT) to gamma attenuation measurement of soil water content

Soil Research ◽  
1988 ◽  
Vol 26 (1) ◽  
pp. 105 ◽  
Author(s):  
JM Hainsworth ◽  
LAG Aylmore
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Computer Assisted ◽  
Scanning System ◽  
Advantages And Disadvantages ◽  
Computer Assisted Tomography ◽  
Scanning Systems ◽  
Gamma System ◽  
Gamma Scanning

This paper demonstrates the successful application of computer assisted tomography (CAT) to �-ray attenuation measurements and the modification of a conventional gamma scanning system to enable changes in the spatial distribution of soil water content to be accurately monitored in soil columns. The relatively inexpensive gamma system has been shown to provide a resolution comparable to that obtainable with commercially available but extremely expensive X-ray CAT scanning systems. However, longer counting times are required with gamma radiation, thus limiting the usefulness of the technique for some soil water studies. A comparison of the efficiency of several source-detection combinations illustrates their relative advantages and disadvantages.

scholarly journals Relationship of Soil Respiration to Crop and Landscape in the Walnut Creek Watershed

2005 ◽  
Vol 6 (6) ◽  
pp. 812-824 ◽  
Author(s):  
T. B. Parkin ◽  
T. C. Kaspar ◽  
Z. Senwo ◽  
J. H. Prueger ◽  
J. L. Hatfield
Keyword(s):  
Microbial Biomass ◽  
Soil Respiration ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Net Primary Production ◽  
Plant Root ◽  
System Effect ◽  
Organic C ◽  
Creek Watershed

Abstract Soil respiration is an important component of the carbon dynamics of terrestrial ecosystems. Many factors exert controls on soil respiration, including temperature, soil water content, organic matter, soil texture, and plant root activity. This study was conducted to quantify soil respiration in the Walnut Creek watershed in central Iowa, and to investigate the factors controlling this process. Six agricultural fields were identified for this investigation: three of the fields were cropped with soybean [Glycine max (L.) Merr.] and three were cropped with corn (Zea mays L.). Within each field, soil respiration was measured at nine locations, with each location corresponding to one of three general landscape positions (summit, side slope, and depression). Soil respiration was measured using a portable vented chamber connected to an infrared gas analyzer. Soil samples were collected at each location for the measurement of soil water content, pH, texture, microbial biomass, and respiration potential. Field respiration rates did not show a significant landscape effect. However, there was a significant crop effect, with respiration from cornfields averaging 37.5 g CO2 m−2 day−1 versus an average respiration of 13.1 g CO2 m−2 day−1 in soybean fields. In contrast, laboratory measurements of soil respiration potential, which did not include plant roots, showed a significant landscape effect and an insignificant cropping system effect. Similar relationships were observed for soil organic C and microbial biomass. Additional analyses indicate that corn roots may be more important than soybean roots in their contribution to surface CO2 flux, and that root respiration masked landscape effects on total soil respiration. Also, the failure to account for soil respiration may lead to biased estimates of net primary production measured by eddy covariance.

Modelling oxygen transport in soil with plant root and microbial oxygen consumption: depth of oxygen penetration

Soil Research ◽  
2013 ◽  
Vol 51 (6) ◽  
pp. 539 ◽  
Author(s):  
F. J. Cook ◽  
J. H. Knight ◽  
F. M. Kelliher
Keyword(s):  
Diffusion Coefficient ◽  
Redox Potential ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Oxygen Concentration ◽  
Oxygen Diffusion ◽  
Plant Root ◽  
Critical Value ◽  
Critical Values

A set of equations governing oxygen diffusion and consumption in soils has been developed to include microbial and plant-root sinks. The dependent variable is the transformed oxygen concentration, which is the difference between the gaseous concentration and a scaled value of the aqueous oxygen concentration at the root–soil interface. The results show how, as the air-filled porosity decreases, the reduced oxygen flux causes the depth of extinction to decrease. The results also show how the depth of extinction at a particular value of soil water content decreases with increasing temperature, due to increased microbial respiration. The critical value of water content at which the oxygen concentration goes to extinction at a finite depth was compared with alternative calculations with only a microbial sink. By ignoring the feedback of oxygen concentration on root uptake, the alternative calculations yielded substantially higher critical values of water content at all temperatures. Two soil oxygen diffusion coefficient functions from the literature were compared and shown to give significantly different critical values of water content for fine-textured soils, one more realistic than the other. A single relationship between the extinction depth and the ratio of the water content to the critical value was shown to apply for all temperatures and soil textures. The oxygen profiles were used along with a function relating redox potential to oxygen concentration to generate redox potential profiles. This application of the model could be useful in explaining soil biochemical processes in soils. For one such process, denitrification, the depth at which a critical oxygen concentration is reached was calculated as a function of the air-filled porosity and temperature of the soil. The implications of the critical value of soil water content in terms of water-filled pore space and matric potential are discussed in relation to the diffusion coefficient functions and recent literature.

Soil moisture heterogeneity during deficit irrigation alters root-to-shoot signalling of abscisic acid

2007 ◽  
Vol 34 (5) ◽  
pp. 439 ◽  
Author(s):  
Ian C. Dodd
Keyword(s):  
Water Content ◽  
Root System ◽  
Soil Water ◽  
Soil Water Content ◽  
Deficit Irrigation ◽  
Plant Root ◽  
Arithmetic Mean ◽  
Similar Amount ◽  
Graft Union ◽  
Plant Root System

The effects of different irrigation techniques on leaf xylem ABA concentration ([X-ABA]leaf) were compared in tomato (Lycopersicon esculentum Mill.). During partial rootzone drying (PRD), water was distributed unevenly to the root system such that part was irrigated while the remainder was allowed to dry the soil. During conventional deficit irrigation (DI), plants received the same volume of water as PRD plants, but water was distributed evenly to the entire root system. When the plant root system was allowed to explore two separate soil compartments, DI plants had a higher [X-ABA]leaf than PRD plants with moderate soil drying, but PRD plants had a higher [X-ABA]leaf than DI plants as the soil dried further. The difference in [X-ABA]leaf between the two sets of plants was not because of differences in either whole pot soil water content (θpot) or leaf water potential (Ψleaf). To investigate the contribution of different parts of the root system to [X-ABA]leaf, individual shoots were grafted onto the root systems of two plants grown in two separate pots, so that the graft union had the appearance of an inverted ‘Y’. After sap collection from detached leaves, removal of the shoot below the graft union allowed sap collection from each root system. Again, DI plants had a higher [X-ABA]leaf than PRD plants when the soil was relatively wet, but the opposite occurred as the soil dried. Root xylem ABA concentration ([X-ABA]root) increased exponentially as soil water content (θ) declined. In DI plants, [X-ABA]root from either pot (or the arithmetic mean of [X-ABA]root) accounted for a similar amount of the variation in [X-ABA]leaf. In PRD plants, [X-ABA]root from the watered side underestimated [X-ABA]leaf, whereas [X-ABA]root from the dry side overestimated [X-ABA]leaf. The arithmetic mean of [X-ABA]root best explained the variation in [X-ABA]leaf, implying continued sap flow from the dry part of the root system (Jdry) at soil water potentials (Ψsoil) at which Jdry had ceased in previous studies of PRD plants (Yao et al. 2001). Evaluating the relationship between Jdry and Ψsoil may assist in maintaining export of ABA (and other growth regulators) from the drying part of the root system, to achieve desirable horticultural outcomes during PRD.

scholarly journals Disentangling temporal and population variability in plant root water uptake from stable isotopic analysis: a labeling study

2019 ◽  
Author(s):  
Valentin Couvreur ◽  
Youri Rothfuss ◽  
Félicien Meunier ◽  
Thierry Bariac ◽  
Philippe Biron ◽  
...  
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Physical Model ◽  
Soil Water Content ◽  
Water Uptake ◽  
Temporal Dynamics ◽  
Plant Root ◽  
Root Water Uptake ◽  
Leaf Water ◽  
Stable Isotopic

Abstract. Isotopic labeling techniques have the potential to minimize the uncertainty of plant root water uptake (RWU) profiles estimated through multi-source (statistical) modeling, by artificially enhancing soil water isotopic gradient. Furthermore, physical models can account for hydrodynamic constraints to RWU if simultaneous soil and plant water status data is available. In this study, a population of tall fescue (Festuca arundinacae cv Soni) was grown in a macro-rhizotron setup under semi-controlled conditions to monitor such variables for a 34-hours long period following the oxygen stable isotopic (18O) labeling of deep soil water. Aboveground variables included tiller and leaf water oxygen isotopic compositions as well as leaf water potential (ψleaf), relative humidity, and transpiration rate. Belowground profiles of root length density (RLD), soil water content and isotopic composition were also sampled. While there were strong correlations between hydraulic variables as well as between isotopic variables, the experimental results underlined the discrepancy between variations of hydraulic and isotopic variables. In order to dissect the problem, we reproduced both types of observations with a one-dimensional physical model of water flow in the soil-plant domain, for 60 different realistic RLD profiles. While simulated ψleaf followed clear temporal variations with little differences across plants as if they were “on board of the same rollercoaster”, simulated δtiller values within the plant population were rather heterogeneous (“swarm-like”) with relatively little temporal variation and a strong sensitivity to rooting depth. The physical model thus suggested that the discrepancy between isotopic and hydraulic observations was logical, as the variability captured by the former was spatial and may not correlate with the temporal dynamics of the latter. For comparison purposes a Bayesian statistical model was also used to simulate RWU. While they predicted relatively similar cumulative RWU profiles, the physical model could differentiate spatial from temporal dynamics of the isotopic signature, and supported that the local increase of soil water content and formation of a peak of labelled water observed overnight were due to hydraulic lift.

scholarly journals Effect of Soil Water on GPR Estimation of Bulked Roots, Methods, and Suggestions

2021 ◽  
Author(s):  
Brody L Teare ◽  
Henry Ruiz ◽  
Afolabi Agbona ◽  
Matthew Wolfe ◽  
Iliyanna Dobreva ◽  
...  
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Pearson Correlation ◽  
Good Practice ◽  
Estimation Methods ◽  
Root Mass ◽  
Early Maturity ◽  
Root Phenotyping ◽  
Non Destructive

Abstract Background: Root phenotyping methods are of increasing importance as researchers seek to understand belowground productivity and breeders work to select for root traits. Effective non-destructive root phenotyping methods do not exist for bulked-root and tuber crops such as potato and cassava. Cassava is a tropical crop widely grown by subsistence farmers throughout the tropics and is the fourth most important staple food crop in the world, yet lags in research. It has an extensive growth period sometimes exceeding 12 months. Early maturity is a major goal for breeders, but the ability to select for it is hampered by the lack of non-destructive yield estimation methods. GPR is a tool with potential to aid in bulked root selection, but standard methods have yet to be developed. In this study, we demonstrate good practice in GPR estimation of root mass, which was used as a proxy for cassava root mass, and investigate the effect of soil water content on measurement.Results: Significant correlation between GPR data and daikon root mass was found for three of the five irrigation treatments. Correlation strength improved with increased soil water content and decreased variation of soil water content between plots. Pearson correlation coefficient varied from 0.53 – 0.79.Conclusions: GPR can be used to estimate bulked root mass. Wet soil can improve the predictive quality of GPR data, but water content needs to be homogeneous throughout the study site and period. Determining the optimal soil water content will require further research.

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