Thermal Neutron Computed Tomography of Soil Water and Plant Roots

Tumlinson, Leanne G.; Liu, Hungyuan; Silk, Wendy Kuhn; Hopmans, Jan W.

doi:10.2136/sssaj2007.0302

Cited by 70 publications

(49 citation statements)

References 30 publications

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“…Nakanishi et al (2005) showed an accumulation of water in the vicinity of soybean root by using neutron tomography. A similar result was obtained by Tumlinson et al (2008) for a corn seed in sand. The authors concluded that water content gradients in the rhizosphere need further investigation.…”

Section: Introductionsupporting

confidence: 87%

Dynamics of soil water content in the rhizosphere

et al. 2010

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Water flow from soil to plants depends on the properties of the soil next to roots, the rhizosphere. Although several studies showed that the rhizosphere has different properties than the bulk soil, effects of the rhizosphere on root water uptake are commonly neglected. To investigate the rhizosphere's properties we used neutron radiography to image water content distributions in soil samples planted with lupins during drying and subsequent rewetting. During drying, the water content in the rhizosphere was 0.05 larger than in the bulk soil. Immediately after rewetting, the picture reversed and the rhizosphere remained markedly dry. During the following days the water content of the rhizosphere increased and after 60 h it exceeded that of the bulk soil. The rhizosphere's thickness was approximately 1.5 mm. Based on the observed dynamics, we derived the distinct, hysteretic and time-dependent water retention curve of the rhizosphere. Our hypothesis is that the rhizosphere's water retention curve was determined by mucilage exuded by roots. The rhizosphere properties reduce water depletion around roots and weaken the drop of water potential towards roots, therefore favoring water uptake under dry conditions, as demonstrated by means of analytical calculation of water flow to a single root.

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Section: Introductionsupporting

confidence: 87%

Dynamics of soil water content in the rhizosphere

et al. 2010

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“…In recent years some imaging techniques have been introduced and tested for plant-soil studies, providing the possibility of measuring specific properties of the plantsoil-water system. Among the few available nondestructive methods, Neutron Radiography (NR) has increasingly allowed researchers to simultaneously image living roots and quantify soil water distribution in soil in situ (e.g., Furukawa et al 1999;Menon et al 2007;Oswald et al 2008;Tumlinson et al 2008;Moradi et al 2011;Zarebanadkouki et al 2012;Moradi et al 2013). Roots can be distinguished in neutron radiographs from soil, and soil water changes can be quantified with high spatial and temporal resolution (Moradi et al 2009;Esser et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Mapping compensating root water uptake in heterogeneous soil conditions via neutron radiography

et al. 2015

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Background and aims Water is often heterogeneously distributed in soils. Understanding roots' responses to this soil-water heterogeneity is a key parameter defining plant survival in dry climates. To determine local root water uptake for partly dry conditions in a plant's root system, we prepared soil patches with different water contents, then used neutron radiography to monitor daily changes in root structure and water uptake. Methods Lupin plants were grown in 30×25×1 cm 3 aluminum containers filled with sandy soil. In two partitioning set-ups, the soil-root zone was divided into either two or nine hydraulically-isolated soil compartments. This was done by packing layers of coarse sand as capillary barriers, by which vertical and/or horizontal soil water heterogeneity as well as homogeneous wellwatered treatments were applied for control. Daily changes in soil water content in each compartment, water uptake and root growth were monitored noninvasively and quantified by neutron radiography during a period of 15 consecutive days. Results In optimal homogeneously-wet soil, lateral roots in the top 10 cm of the root system showed the highest water uptake rate, up to around 10 mg/(mm. root. day), which on average was twice as much as that for younger lateral roots in lower position and taproot. In heterogeneous treatments, root water uptake declined strongly in compartments with the soil water content below 0.13-0.10 cm 3 /cm 3 while in parallel an enhanced uptake rate, rising by up to 100 %, was observed for the roots in wet compartments, presumably to compensate for roots in dry compartments and, therefore, sustain the total transpiration. Also, our observations showed that in the drying compartment a reduction of soil water content to 0.10-0.15 triggered local cluster root formation. Conclusions With the experimental set-up presented the pattern of water uptake across a lupin root system can be quantified and normalized to root length. Water uptake was shown to be highly variable in different parts of the root system. A threshold for water stress to cause cessation of local water uptake was identified, and the considerable amount of compensation by water uptake in other parts identified. The dynamic trade-off among different parts of the root system seems to regulate total root uptake also during water stress to sustain the daily transpirational demand. Plant Soil

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“…These are usually the basis for calculation of water storage and its changes at the field scale (up to 1 km 2 ). Point measurements are scaled up to large areas applying geostatistical techniques (Western et al, 2002;Bogena et al, 2010). However, inherent small-scale soil heterogeneities and nonlinearity of processes dominate spatial and temporal variability of soil moisture and introduce sources of error that can produce significant misinterpretation of hydrological scenarios and unrealistic predictions.…”

Section: Introductionmentioning

confidence: 99%

“…At the laboratory scale, Oswald et al (2008) and Tumlinson et al (2008) presented an imaging technique (2-D and 3-D) based on a beam of low energy neutrons to investigate water redistribution and plant water uptake of a single plant in detail. Recently, using neutron transport simulations and field measurements, Zreda et al (2008) and Desilets et al (2010) introduced a new methodology of soil moisture measurements via counting natural aboveground fast neutrons, generated primarily by interactions of secondary cosmic-ray neutrons with terrestrial and atmospheric nuclei.…”

Section: Introductionmentioning

confidence: 99%

Integral quantification of seasonal soil moisture changes in farmland by cosmic-ray neutrons

Villarreyes

Baroni

Oswald

2011

Hydrol. Earth Syst. Sci.

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Abstract. Soil moisture at the plot or hill-slope scale is an important link between local vadose zone hydrology and catchment hydrology. However, so far only a few methods are on the way to close this gap between point measurements and remote sensing. One new measurement methodology that could determine integral soil moisture at this scale is the aboveground sensing of cosmic-ray neutrons, more precisely of ground albedo neutrons. The present study performed ground albedo neutron sensing (GANS) at an agricultural field in northern Germany. To test the method it was accompanied by other soil moisture measurements for a summer period with corn crops growing on the field and a later autumn-winter period without crops and a longer period of snow cover. Additionally, meteorological data and aboveground crop biomass were included in the evaluation. Hourly values of ground albedo neutron sensing showed a high statistical variability. Six-hourly values corresponded well with classical soil moisture measurements, after calibration based on one reference dry period and three wet periods of a few days each. Crop biomass seemed to influence the measurements only to minor degree, opposed to snow cover which has a more substantial impact on the measurements. The latter could be quantitatively related to a newly introduced field neutron ratio estimated from neutron counting rates of two energy ranges. Overall, our study outlines a procedure to apply the ground albedo neutron sensing method based on devices now commercially available, without the need for accompanying numerical simulations and suited for longer monitoring periods after initial calibration.

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Thermal Neutron Computed Tomography of Soil Water and Plant Roots

Cited by 70 publications

References 30 publications

Dynamics of soil water content in the rhizosphere

Dynamics of soil water content in the rhizosphere

Mapping compensating root water uptake in heterogeneous soil conditions via neutron radiography

Integral quantification of seasonal soil moisture changes in farmland by cosmic-ray neutrons

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