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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 From: Leonard Ornstein <lenornst@pipeline.com> ===8<==============Original message text=============== The only effect of the polyacrylamide granules is to provide more moisture retention per unit volume of soil than in their absence. Any tensiometer will return the true matric potential in the soil, independent of the presence or absence of the polyacrylamide. For well-aerated, open-textured potting medium, a matric potential of about -0.1 atmospheres (bars) will encourage rapid germination at temperatures above 25 degrees Celsius. Such conditions also encourage mold growth, so an application of an appropriate fungicide is recommended. I don't agree with Bruce; A matric potential readout, which measures water availability to the plant, rather than a volumetric readout, is to be preferred. Len Ornstein [Thanks for correcting me Len. I agree that matric potential will be preferable, especially where there are water retention granules that will increase the volumetric water content but not the matric potetential. This raises the interesting question of the real purpose of retention media. My understanding is that the main benefit seems to be that more water can be held in a given volume of soil, (than would otherwise be possible), which will become available as the soil dries. This means that the intervals between irrigations is increased. My point about the presence of polyacrylamide is whether this could bias any of the sensors that operate by use the measuring the soil's dielectric characteristics. Bruce] At 8:11 AM +0000 2/18/02, owner-sowacs@aqua.ccwr.ac.za wrote: > >I would like some information on the ideal moisture for seedling germination. > >Tomato and peppers. > >Also which probe would you recommend. > >I am a chemist and am interested in experimenting on optimising >growing conditions for seedling germination. > >I am using poly acrylamide water retention granules at about 1% %v/v > >Can you help > >Bernard Irving <bernardirving@hotmail.com> > >[Bruce comments >Assuming these are potted plants, the sensor probe would need to be small >enough to insert into the pot without disturbing the roots too much, >and provide a volumetric readout. >Please provide more information on the application. >I wonder if anyone can comment on the effect of water retention >granules on measured water content?! > >I am sure the various manufacturers will also contact you directly. >Bruce] ===8<===========End of original message text===========