Comparison of Water Stress of Cotton from Measurements with the Hydraulic Press and the Pressure Chamber1

Abstract

AbstractThe Hydraulic Press (HP) is gaining some acceptance as a tool for estimating plant water status and some large cotton growers in the Central California area are already using this instrument for irrigation scheduling. Since no published data validating the use of the HP with cotton have been found, the objective of this research was to develop a data set to support or reject the use of the HP for estimating cotton water status, as compared to the widely accepted Pressure Chamber (PC).Measurements of water status of cotton (Gossypium hirsutum L., Acala SJ2 Var.) obtained with the HP and the PC were compared and correlated hi replicated experiments under greenhouse and field conditions. Results indicate that 1) the HP does not measure low water potential accurately below −940 kPa as determined by the PC, and 2) the most representative endpoint to use with the HP is the pressure at which water exudes from the cut edge of a tip of an uppermost fully expanded leaf.The HP can be used advantageously for irrigation scheduling of cotton if the threshold value is −940 kPa or higher, as determined when the highest water potential values for a day are found (i.e., predawn). However, this inability of the HP to estimate low water potentials of cotton leaves, under the conditions herein described, seems to be a serious limitation of the instrument.