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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 Demetrios, As to your second case you likely could use watermark sensors with reasonable success. The sensors read in kilopascals (kPa) which are equivalent to centibars. The watermark will only measure in units of one whole unit, so if you suspect to need units of matric potential in fractions of units, the sensor will not do that. The watermarks are far more durable than gypsum blocks, although the results obtained should be similar. The watermark sensors are about $30.00 (U.S)each. They are manufactured by Irrometer Co. http://www.irrometer.com. The watermarks can be used with a Hansen AM 400 soil moisture monitor http://www.mkhansen.com. The AM400 can link with six watermarks and either one or two soil temperature probes. This unit will give you a graphic display of the soil moisture pattern at the push of a button, and can store up to two year's worth of data. The Hansen AM400 retails for $379.00 (U.S). Hope this will be of some use to you. Steve Cheyne -----Original Message----- From: owner-sowacs@aqua.ccwr.ac.za [mailto:owner-sowacs@aqua.ccwr.ac.za] Sent: 28 July, 2000 11:54 PM Subject: Watermark or gypsum blocks? 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 Sowacsers: I am a research plant pathologist working at the present time on the epidemiology of a cucumber disease caused by a fungal parasite. In my study I would like to investigate the effect of osmotic and matric potential of water on fungal growth, survival and disease development. 1st case: To study the effect of osmotic potential on mycelial growth, we could put a mycelial plug of the fungus in a Petri dish containing a substrate and measure the fungal diameter. The osmotic potential of the substrate could be adjusted to various values by using various osmotica like KCl, NaCl, PEG 6000 etc. Question: Could I use any instrument of your company or of any other company (if you could inform me) to measure the osmotic potential of the substrate and how?? 2nd case: To study the effect of matric potential on disease development a first thought of mine is to use potted plants using different soil types and possibly vermiculite with various values of water content from the saturation condition until the permanent wilt point one. Question: In such a case, could I use the Watermark Sensors and Gypsum Block Sensors to measure the matric potential of the soil and how?? If not what do you propose to me?? (Which procedure or instrument??) What is the cost of Watermark and Gypsum sensors? Thanking you very much, in advance, for your kind cooperation I look forward to hearing from you. Demetrios vakalounakis PLANT PROTECTION INSTITUTE P.O. BOX 2228, 711 03 HERAKLIO, CRETE, GREECE TEL.: +3081-240.986, 228.236, FAX: +3081-245.858 E-MAIL: vakalounakis@imbb.forth.gr N.AG.RE.F. National Agricultural Research Foundation -- Bruce Metelerkamp ---------------------------------------------------------------------------- -- +NZ 6 870 6303 Hawke's Bay New Zealand _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/brooz@pobox.com http://pobox.com/~brooz _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/