Determining the Optimum Plant Temperature of Cotton Physiology and Yield to Improve Plant‐Based Irrigation Scheduling

Abstract

ABSTRACT A plant‐based thermal optimum approach to irrigation scheduling provides potential benefits in that water applications are scheduled on the basis of plant response to water status. Such irrigation systems require a defined thermal optimum for the crop and while such optimum values have been identified for cotton ( Gossypium hirsutum L.) cultivars in the United States, there is no information of this type for cultivars common in Australian production. This paper outlines a threefold approach to determining the optimum temperature (T opt ) of the commercial Australian cotton cultivar Sicot 70BRF in an Australian production system. It combines the use of a laboratory‐based fluorescence assay, field‐based net C assimilation rate (A) and stomatal conductance to water vapor (g s ), and canopy temperature (T c )–yield relations. The fluorescence assay showed a T opt between 28 and 30°C while leaf gas exchange rates peaked at a leaf temperature (T l ) of 29°C. The T c –yield relations peaked at 26°C, with yield reductions observed when T c > 28°C. We conclude the T opt of the Australian upland cotton cultivar Sicot 70BRF to be 28 ± 2°C. This T opt will provide valuable information for use in thermal optimum irrigation scheduling systems.