AUTOMATIC PLANT EXTENSION MEASUREMENT IN SUGARCANE IN RELATION TO TEMPERATURE AND SOIL-MOISTURE

Plant extension is one of the first components of plant growth to be affected by water stress. Its importance led to the development of an inexpensive semi-automatic growth transducer of sufficient accuracy for hourly recording. The instrument, based on a 10-turn potentiometer, could detect 0.25 mm extension growth. Thirty transducers were installed in a rainfed experiment conducted on sugarcane during a drought near Durban, South Africa. Mean daily plant extension rate (PER) was linearly related (r(2) = 0.61***) to mean daily air temperature when the upper 30 cm soil contained 30 mm or more available water. Five diurnal growth patterns were identified as plants succumbed to water stress. With adequate moisture PER increased from morning to evening and then decreased overnight as temperature declined. As soil water became more limiting, day-time growth was reduced. The use of these measurements for modelling and irrigation research are discussed.