A computer‐controlled multi‐titration system to study transpiration, OH− efflux and nitrate uptake by intact lettuce plants (Lactuca sativa L.) under different environmental conditions

An apparatus is described in which water and nutrient uptake (NO−3) and pH were measured and controlled by a microcomputer. Measurements were made twice hourly using appropriate electrodes, both in the nutrient solutions in which the plants were grown and in standard reference solutions. The signals from the electrodes were amplified to a range of 0–10 V and were fed to an A/D converter activated by the computer. The needs for water, NO−3, H+ and OH− were then calculated and the necessary adjustments were made to the solutions by automatic injection of the correct amounts to each container in turn. These amounts were records of water and nitrate uptake and pH shift and were saved on disc. The plants were arranged on a turntable which gave additional benefit by smoothing out variations in light intensity. The system allowed a different solution to be maintained for each plant if required.