From: Tim Hess ("t.hess") To: sowacs@aqua.ccwr.ac.za Date: Thursday, July 25, 1996 11:40 am Subject: High transpiration rates Jochen Eberhard wrote; > While thinking about my own problems another question came up inmy mind. With > high transpiration rates the soil moisture is not the same aswith low > transpiration rates although the tensiometers show the same soilmoisture > tension. Is this correct? Than there sould be some kind of cropcoefficient to > get some kind of plant moisture status. It depends what you mean by IS NOT THE SAME . If the soil water potential is the same, then the water content will be the same (allowing for hysteresis). However, the availability of water tothe plant will not be the same. At high transpiration rates, a greater hydraulic gradient is required between the soil and the root to maintain the water supply at the same rate as the water use. Inwhich case, for a given root water potential, the soil water potential will have to be higher at high transpiration rates. i.e. the tensiometer reading will have to be lower. --------------------------------------------------------------------- PLEASE NOTE CHANGE TO EMAIL ADDRESS --------------------------------------------------------------------- Tim Hess Department of Water Management Silsoe College Cranfield University Silsoe Tel (0)1525863292 Bedford, MK45 4DT Fax (0)1525863300 UK e-mailt.hess@cranfield.ac.uk ---------------------------------------------------------------------- CC: jochen.eberhard@t-online.de