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Dear Peter, We did not do any systematic analysis or experiments but in one study we found greatly enhanced root growth around sensors buried in the profile. We were using heat dissipating sensors to monitor soil water potential in clay/clay loam profiles in a forested catchment. After a couple of years in the ground we noticed that some instruments started to give anomalous behaviour - very rapid decreases in soil water pressure after profile wetting. When we pulled the sensors out of the ground we found quite a mat of roots developed on the interface between the sensor and the soil. The tree roots had found the access hole drilled for the sensor to be a convenient conduit for colonising what was otherwise a relatively impenetrable profile. They also liked to grow along interfaces. Regards Colin ------------------------------------------------------------------- Colin Johnston email: colin@per.clw.csiro.au CSIRO Land and Water www: http://www.dwr.csiro.au Floreat Park Laboratory phone: (08) 9333-6328 Private Bag, PO WEMBLEY, W.A. 6014, fax: (08) 9387-8211 AUSTRALIA intern. fax: 61-8-9387-8211 ------------------------------------------------------------------- [Bruce Metelerkamp comments] As my Agrometeorology used to say: "the closer you get to what you want to measure, the more you disturb whats you want to measure" ... (or words to that effect - apologies). The importance of site disturbance is often over-looked, or else it is impractical to take measures sufficient to prevent it completely. Burying larger any sensor is best accomplished with a horizontal access tube. This, however requires a trench from which to work. It could be argued that the effects of the disturbance of such a refilled trench would not affect the point measurement being made IF the point measurement is far enough from the trench. A further consideration is the length of time that sensor is to be in place for, prior to use, and in use. In an ideal world, we would allow the sensor time to "settle" before using the measurements. For long term monitoring plots, the continuity of the soil-sensor contact will, depending on the type and soil type, improve or worsen. For very long term situations, surely the conventional neutron probe access tube must be one of the more stable options. Having said that, once a probe is buried, as long as it does not degrade, and has been carefully placed, there is less chance of interference from the surface. A further advantage is that such probes can have long lead wires emerging remotely to some extent from the site. Just my 2c. Bruce On Mon, 2 Feb 1998 owner-sowacs@aqua.ccwr.ac.za wrote: > NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za > with the body of the message containing the line: > unsubscribe sowacs > > > Dear All, > > Does anybody know of, or had experience in, studying the affect of > compaction near a monitoring site ( eg. Tensiometer, Neutron Probe etc ) on > water use, extraction pattern at that montiroing site. And whether this site > over time, becomes un representative of the field ? > > Regards > > Peter Broomhall > Peter Broomhall > Horticultural Consultant > > Hortech Services Pty Ltd > a.c.n. 060 406 957 > P.O. Box 370 > Kallangur QLD 4503 > Australia > > P: +61 418 878 484 > F: +61 7 3886 0389 > > hortech@ats.com.au > > home page : http://ats.com.au/~hortech/index.html > > >