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

Soil Research ◽  
2001 ◽  
Vol 39 (6) ◽  
pp. 1387 ◽  
Author(s):  
M. A. Hamza ◽  
S. H. Anderson ◽  
L. A. G. Aylmore

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.


Soil Research ◽  
1983 ◽  
Vol 21 (4) ◽  
pp. 435 ◽  
Author(s):  
JM Hainsworth ◽  
LAG Aylmore

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.


Soil Research ◽  
1988 ◽  
Vol 26 (1) ◽  
pp. 105 ◽  
Author(s):  
JM Hainsworth ◽  
LAG Aylmore

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.


Author(s):  
M.C.H.Mouat Pieter Nes

Reduction in water content of a soil increased the concentration of ammonium and nitrate in solution, but had no effect on the concentration of phosphate. The corresponding reduction in the quantity of phosphate in solution caused an equivalent reduction in the response of ryegrass to applied phosphate. Keywords: soil solution, soil water content, phosphate, ryegrass, nutrition.


2010 ◽  
Vol 59 (1) ◽  
pp. 157-164 ◽  
Author(s):  
E. Tóth ◽  
Cs. Farkas

Soil biological properties and CO2emission were compared in undisturbed grass and regularly disked rows of a peach plantation. Higher nutrient content and biological activity were found in the undisturbed, grass-covered rows. Significantly higher CO2fluxes were measured in this treatment at almost all the measurement times, in all the soil water content ranges, except the one in which the volumetric soil water content was higher than 45%. The obtained results indicated that in addition to the favourable effect of soil tillage on soil aeration, regular soil disturbance reduces soil microbial activity and soil CO2emission.


Author(s):  
Justyna Szerement ◽  
Aleksandra Woszczyk ◽  
Agnieszka Szyplowska ◽  
Marcin Kafarski ◽  
Arkadiusz Lewandowski ◽  
...  

2014 ◽  
Vol 22 (3) ◽  
pp. 300-307
Author(s):  
Meijun ZHANG ◽  
Wude YANG ◽  
Meichen FENG ◽  
Yun DUAN ◽  
Mingming TANG ◽  
...  

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 549f-550
Author(s):  
Mongi Zekri ◽  
Bruce Schaffer ◽  
Stephen K. O'Hair ◽  
Roberto Nunez-Elisea ◽  
Jonathan H. Crane

In southern Florida, most tropical fruit crops between Biscayne and Everglades National Parks are irrigated at rates and frequencies based on experience and observations of tree growth and fruit yield rather than on reliable quantitative information of actual water use. This approach suggests that irrigation rates may be excessive and could lead to leaching of agricultural chemicals into the groundwater in this environmentally sensitive area. Therefore, a study is being conducted to increase water use efficiency and optimize irrigation by accurately scheduling irrigation using a very effective management tool (EnviroScan, Sentek Environmental Innovations, Pty., Kent, Australia) that continuously monitors soil water content with highly accurate capacitance multi-sensor probes installed at several depths within the soil profile. The system measures crop water use by monitoring soil water depletion rates and allows the maintenance of soil water content within the optimum range (below field capacity and well above the onset of plant water stress). The study is being conducted in growers' orchards with three tropical fruit crops (avocado, carambola, and `Tahiti' lime) to facilitate rapid adoption and utilization of research results.


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