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SOWACS (apologies for double posting if you are on TRICKLE-L too) I thought the information below would be of interest to Sowacs members - and should provoke a few comments..? Bruce Metelerkamp >>>>> From: Jed Waddell (trickle-l) To: trickle-l@unl.edu Date: Tuesday, October 8, 1996 7:45 pm Subject: Re: drip management At 03:45 AM 10/8/96 -0500, you wrote: >Hi All, >Has anyone Practical experience (successful or otherwise) of, or ideas on, >the best Economical means of Managing and Monitorinng the daily >two-dimensional flux of water under drippers in a sandy (orchard) soil? >Aim : Water saving through optimum uptake and minimum losses. > For the past two years I have been measuring the matric potential at two depths (50 and 100 cm) under potato in the central sands of Minnesota. Because of the hills created in potato production I placed tensiometers directly under the hill and the furrow positions. With the matric potential I can find the hydraulic gradient and multiply by the hydraulic conductivity to get the flux. I determined the hydraulic conductivity from the average matric potential. As far as economics, tensiometers are cheap compared to the pressure transducers and a data logger. Pressure transducers range in price but I used Soil Moisture's version which cost about $250 for one. In my opinion these are the best transducers because one calibration can be used for years. Other cheaper transducers require annual or monthly calibrations. My collegue used TDR to measure water distribution in a fine grid under the potato hill. This method has high initial cost but is relatively cost free after purchased. We also used neutron probe tubes placed in the hill. These have a sphere of influence about 20 cm or so. Once tubes are in place you can read them as often as you want but is not practical for hourly measurements. We used them for weekly measurements. Because of the radiation saftey procedures, neutron probes are a hassle but you could probably find one fairly cheap. Ours are old and have been around for years I don't know how much they cost. Hope this information helps, Jed **************************************************** * Jed T. Waddell * * Graduate Research Assistant * * University of Minnesota * * Department of Soil, Water, and Climate * * St. Paul, MN 55108 * * office (612) 625-1968 * * fax (612) 625-2208 * ****************************************************